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Crystallographic characterization of (C5H4SiMe3)3U(BH4)

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aLos Alamos National Laboratory, Los Alamos, New Mexico 87544, USA, and bDepartment of Chemistry, University of California, Irvine, California 92697, USA
*Correspondence e-mail: stosh@lanl.gov, wevans@uci.edu

Edited by M. Zeller, Purdue University, USA (Received 6 January 2021; accepted 3 March 2021; online 12 March 2021)

New syntheses have been developed for the synthesis of (borohydrido-κ3H)tris­[η5-(tri­methyl­sil­yl)cyclo­penta­dien­yl]uranium(IV), [U(BH4)(C8H13Si)3] or Cp′3U(BH4) (Cp′ = C5H4SiMe3) and its structure has been determined by single-crystal X-ray crystallography. This compound crystallized in the space group P[\overline{1}] and the structure features three η5-coordinated Cp′ rings and a κ3-coordinated (BH4) ligand.

1. Chemical context

Actinide borohydrides have been of inter­est since the 1940s, owing to their potential volatility and applied use in vapor deposition technologies for the production of thin films (Hoekstra & Katz, 1949[Hoekstra, H. R. & Katz, J. J. (1949). J. Am. Chem. Soc. 71, 2488-2492.]; Daly & Girolami, 2010[Daly, S. R. & Girolami, G. S. (2010). Chem. Commun. 46, 407-408.]). Uranium borohydride compounds are structurally inter­esting because the (BH4) ligand can coordinate large electropositive cations (such as uranium) in several modes. For example, κ1, κ2, and κ3 U–(BH4) binding has previously been reported (Ephritikhine, 1997[Ephritikhine, M. (1997). Chem. Rev. 97, 2193-2242.]). Borohydrides can also achieve high coordination numbers with uranium, e.g. the oligomeric 14-coordinate U(BH4)4 (Bernstein et al., 1972[Bernstein, E. R., Hamilton, W. C., Keiderling, T. A., La Placa, S. J., Lippard, S. J. & Mayerle, J. J. (1972). Inorg. Chem. 11, 3009-3016.]). Although several cyclo­penta­dienyl uranium borohydrides have been crystallographically characterized (Ephritikhine, 1997[Ephritikhine, M. (1997). Chem. Rev. 97, 2193-2242.]), the structure of Cp′3U(BH4) (Cp′ = C5H4SiMe3), made in 1992 (Berthet & Ephritikhine, 1992[Berthet, J.-C. & Ephritikhine, M. (1992). New J. Chem. 16, 767-768.]), has not been reported. Our inter­est in Cp′ uranium chemistry (MacDonald et al., 2013[MacDonald, M. R., Fieser, M. E., Bates, J. E., Ziller, J. W., Furche, F. & Evans, W. J. (2013). J. Am. Chem. Soc. 135, 13310-13313.]; Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]) prompted us to determine the coordination mode of (BH4) within the tris-cyclo­penta­dienyl uranium platform using single-crystal X-ray diffraction. Toward this end, we developed new synthetic routes to the Cp′3U(BH4) compound.

[Scheme 1]

The Cp′3U(BH4) compound was originally synthesized by reacting Cp′3UH with H3B-PPh3 (Berthet & Ephritikhine, 1992[Berthet, J.-C. & Ephritikhine, M. (1992). New J. Chem. 16, 767-768.]). Our attempts to repeat this procedure in toluene and diethyl ether solvents were unsuccessful, potentially because we were uncertain about the details of the reaction. However, we were successful in synthesizing Cp′3U(BH4) from Cp′3UH with H3B-PPh3 in hot THF solvent. We also observed Cp′3U(BH4) could be prepared in high yield (96%) by reacting Cp′3UI with NaBH4 in the presence of 15-crown-5. When this reaction was carried out in toluene at room temperature, the I ligand was substituted by the (BH4) anion. Another method we developed for synthesizing Cp′3U(BH4) involved reacting U(BH4)4 with KCp′ (3 equiv.) in diethyl ether. This reaction, where (BH4) was substituted by (Cp′), also proceeded in high yield (89%). X-ray quality crystals of Cp′3U(BH4) formed at 253 K overnight from diethyl ether solutions.

Of our two synthetic routes, we preferred making Cp′3U(BH4) from Cp′3UI over U(BH4)4 because the U(BH4)4 starting material was more challenging to isolate in a chem­ic­ally pure form. Another inter­esting comparison between the two synthetic methods involved the substitution chemistry. The (Cp′) anion displaced (BH4) from U(BH4)4 and (BH4) displaced I in Cp′3UI. Hence, we qualitatively concluded that the stability of the U—X bond for mol­ecular compounds dissolved in organic solvents was largest for (Cp′), inter­mediate for (BH4), and lowest for I. The generality of this conclusion is limited, and we acknowledge the solubility of the other reaction products (such as NaI) might significantly influence the substitution chemistry on uranium.

2. Structural commentary

Single crystal X-ray data from Cp′3U(BH4) were refined in the triclinic P[\overline{1}] space group with one crystallographically unique mol­ecule in the unit cell, see Fig. 1[link]. The data are of high quality, and electron-density difference peaks consistent with the location and geometry of bridging hydrides were located from a difference-Fourier map with U—H distances of 2.35 (5), 2.35 (5), and 2.36 (5) Å. Although the uncertainty associated with the U—H bonds is relatively high, they are consistent with previously reported bond lengths for actin­ide(IV) hydride inter­actions (Ephritikhine, 1997[Ephritikhine, M. (1997). Chem. Rev. 97, 2193-2242.]; Daly et al., 2010[Daly, S. R., Piccoli, P. M., Schultz, A. J., Todorova, T. K., Gagliardi, L. & Girolami, G. S. (2010). Angew. Chem. Int. Ed. 49, 3379-3381.]). Significantly lower uncertainty is associated with the U—B distance at 2.568 (4) Å, which is similar to two of the three U—B distances in [U(BH4)3(DME)]2(μ-O) (DME = 1,2-di­meth­oxy­ethane), 2.574 (6), 2.584 (6), and 2.635 (7) Å (Daly et al., 2012[Daly, S. R., Ephritikhine, M. & Girolami, G. S. (2012). Polyhedron, 33, 41-44.]). The U—B distance in (C5H5)3U(BH4) was reported to be 2.48 Å (Zanella et al., 1988[Zanella, P., Brianese, N., Casellato, U., Ossola, F., Porchia, M., Rossetto, G. & Graziani, R. (1988). Inorg. Chim. Acta, 144, 129-134.]), although disorder in that structure prevented a full solution from being obtained. Theoretical calculations on (C5H5)3U(BH4) in the gas phase and in solution predicted U—B distances of 2.533 and 2.557 Å (Elkechai et al., 2009[Elkechai, A., Boucekkine, A., Belkhiri, L., Amarouche, M., Clappe, C., Hauchard, D. & Ephritikhine, M. (2009). Dalton Trans. pp. 2843-2849.]), which are also consistent with our data. Other (C5R5)2U(BH4)2 structures showed similar U—B distances of 2.56 (1) Å for [C5H3(SiMe3)2]2U(BH4)2 (Blake et al., 1995[Blake, P. C., Lappert, M. F., Taylor, R. G., Atwood, J. L., Hunter, W. E. & Zhang, H. (1995). J. Chem. Soc. Dalton Trans. pp. 3335-3341.]), 2.58 (3) Å in (C5Me5)2U(BH4)2 (Gradoz et al., 1994[Gradoz, P., Baudry, D., Ephritikhine, M., Lance, M., Nierlich, M. & Vigner, J. (1994). J. Organomet. Chem. 466, 107-118.], Marsh et al., 2002[Marsh, R. E., Kapon, M., Hu, S. & Herbstein, F. H. (2002). Acta Cryst. B58, 62-77.]), and 2.553 (1) Å in (PC4Me4)2U(BH4)2 (Baudry et al., 1990[Baudry, D., Ephritikhine, M., Nief, F., Ricard, L. & Mathey, F. (1990). Angew. Chem. Int. Ed. Engl. 29, 1485-1486.]).

[Figure 1]
Figure 1
Structure of Cp′3U(BH4) with atomic displacement parameters drawn at the 50% probability level. Boron-bound hydrogen atoms are represented as isotropic circles. All carbon-bound hydrogen atoms are omitted. Selected structural metrics, U—(Cp′ centroid) average 2.48 (2) Å, U—H average 2.35 (1) Å, (Cp′ centroid)—U—(Cp′ centroid) average 113.9 (6)°, (Cp′ centroid)—U—B average 104.4 (4)°, and terminal B—H distance of 1.11 (5) Å.

The uranium–(Cp′ centroid) distances in Cp′3U(BH4) range from 2.458–2.500 Å and average 2.48 (2) Å (uncertainty reported as the standard deviation from the mean at 1σ). These uranium–(Cp′ centroid) distances compare well with the 2.473 Å analogous metric in Cp′3UCl (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]) and other Cp′3UX structures (see Table 1[link]) with average U–(Cp′ centroid) distances of 2.478 (3) Å in Cp′3UI (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]), 2.484 (4) Å in Cp′3U(η1-CH=CH2) (Schock et al., 1988[Schock, L. E., Seyam, A. M., Sabat, M. & Marks, T. J. (1988). Polyhedron, 7, 1517-1529.]) and 2.478 (7) Å in Cp′3U[Si(SiMe3)3] (Réant et al., 2020[Réant, B. L. L., Berryman, V. E. J., Seed, J. A., Basford, A. R., Formanuik, A., Wooles, A. J., Kaltsoyannis, N., Liddle, S. T. & Mills, D. P. (2020). Chem. Commun. 56, 12620-12623.]). The 113.9 (6)° average of (Cp′ centroid)—U—(Cp′ centroid) angles in Cp′3U(BH4) is more acute than the 117.0° angle in Cp′3UCl and other Cp′3UX structures, where the average (Cp′ centroid)—U—(Cp′ centroid) angles were reported as 117 (1)° in Cp′3UI, 112 (2)° in Cp′3U(η1-CH=CH2), and 118.7 (4)° in Cp′3U[Si(SiMe3)3]. The more acute (Cp′ centroid)—U—(Cp′ centroid) angles are complemented by a more obtuse average (Cp′ centroid)—U—B angle of 104.4 (4)° in Cp′3U(BH4), likely due to the close proximity of the (BH4)1− ligand compared with (Cp′ centroid)—U—X angles of 100.0° in Cp′3UCl, 100 (2)° in Cp′3UI, 98 (3)° in Cp′3U(η1-CH=CH2), and 96.7 (9)° in Cp′3U[Si(SiMe3)3], see Table 1[link].

Table 1
A comparison of structural parameters (Å, °) in Cp′3U(BH4) and other Cp′3UX {X = Cl, I, [Si(SiMe3)3]} complexes

cent = C5H4SiMe3 centroid.

  Cp′3U(BH4) Cp′3UCla (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]) Cp′3UI (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]) Cp′3U(η1-CH=CH2) (Schock et al., 1988[Schock, L. E., Seyam, A. M., Sabat, M. & Marks, T. J. (1988). Polyhedron, 7, 1517-1529.]) Cp′3U[Si(SiMe3)3] (Réant et al., 2020[Réant, B. L. L., Berryman, V. E. J., Seed, J. A., Basford, A. R., Formanuik, A., Wooles, A. J., Kaltsoyannis, N., Liddle, S. T. & Mills, D. P. (2020). Chem. Commun. 56, 12620-12623.])
U—(cent) 2.458, 2.490, 2.500 2.473 2.475, 2.478, 2.480 2.481, 2.483, 2.489 2.472, 2.478, 2.485
(cent)—U—X 104.13, 104.14, 104.83 100.00 97.9, 101.2, 101.6 95.1 100.0 100.2 96.04, 96.30, 97.65
(cent)—U—(cent) 113.28, 114.26, 114.26 117.00 116.1, 116.4, 118.3 116.4, 117.2, 120.0 118.28, 118.88, 119.08
Note: (a) The asymmetric unit contains one Cp′ ring, one-third of a chloride atom, and one-third of a uranium atom.

An unusual feature of the Cp′3U(BH4) structure is that all three of the tri­methyl­silyl groups are oriented in a single direction towards the (BH4) unit. This orientation has not been observed in other Cp′3U(anion) and Cp′3U(μ-dianion)UCp′3 structures, which are shown in Figs. 2[link]–12[link][link][link][link][link][link][link][link][link][link]. The closest comparison is with the Cp′3UCl structure (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]), where all three tri­methyl­silyl groups are oriented towards the Cl unit, but twisted down and away from the chloride towards the meridian. The Cp′3UI (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]) and Cp′3U(η1-CH=CH2) (Schock et al., 1988[Schock, L. E., Seyam, A. M., Sabat, M. & Marks, T. J. (1988). Polyhedron, 7, 1517-1529.]) complexes have one tri­methyl­silyl group pointed away from the anionic ligand. The Cp′3U[Si(SiMe3)3] complex (Réant et al., 2020[Réant, B. L. L., Berryman, V. E. J., Seed, J. A., Basford, A. R., Formanuik, A., Wooles, A. J., Kaltsoyannis, N., Liddle, S. T. & Mills, D. P. (2020). Chem. Commun. 56, 12620-12623.]) represents the opposite extreme where all of the tri­methyl­silyl groups are oriented away from the [Si(SiMe3)3]1− unit. Since Cp′3U(BH4) has the smallest mono-anion of the Cp′3U(anion) complexes and the correspondingly smallest (Cp′ centroid)—U—(Cp′ centroid), and the largest (Cp′ centroid)—U—X angles, the orientation of the silyl groups could occur due to steric factors. However, it is also possible that some dispersion forces between the (BH4) and the tri­methyl­silyl groups could contribute to the orientation (Liptrot et al., 2016[Liptrot, D. J., Guo, J.-D., Nagase, S. & Power, P. P. (2016). Angew. Chem. Int. Ed. 55, 14766-14769.]). It is inter­esting to note that in the Cp′3ThX series where X = Cl (Réant et al., 2020[Réant, B. L. L., Berryman, V. E. J., Seed, J. A., Basford, A. R., Formanuik, A., Wooles, A. J., Kaltsoyannis, N., Liddle, S. T. & Mills, D. P. (2020). Chem. Commun. 56, 12620-12623.]), Br (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]), and CH3 (Wedal et al., 2019[Wedal, J. C., Bekoe, S., Ziller, J. W., Furche, F. & Evans, W. J. (2019). Dalton Trans. 48, 16633-16640.]), all three tri­methyl­silyl groups are oriented towards the anion, but twisted down and away from the anion towards the meridian as in Cp′3UCl.

[Figure 2]
Figure 2
Structure of Cp′3UCl with atomic displacement parameters drawn at the 50% probability level, as reproduced from the published CIF (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]); the isomorphous thorium complex, Cp′3ThCl, is also known (Réant et al., 2020[Réant, B. L. L., Berryman, V. E. J., Seed, J. A., Basford, A. R., Formanuik, A., Wooles, A. J., Kaltsoyannis, N., Liddle, S. T. & Mills, D. P. (2020). Chem. Commun. 56, 12620-12623.]). Hydrogen atoms are omitted for clarity.
[Figure 3]
Figure 3
Structure of Cp′3UCH3/Cl with only the (CH3) ligand shown, with atomic displacement parameters drawn at the 50% probability level, except the –CH3 unit, which has been plotted as an isotropic sphere, as reproduced from the published CIF (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]), see the manuscript for further details. Hydrogen atoms are omitted for clarity.
[Figure 4]
Figure 4
Structure of Cp′3UI with atomic displacement parameters drawn at the 50% probability level, as reproduced from the published CIF (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]). Hydrogen atoms are omitted for clarity.
[Figure 5]
Figure 5
Structure of Cp′3U(η1-CH=CH2) with atomic displacement parameters drawn as isotropic spheres, as reproduced from the CIF (Schock et al., 1988[Schock, L. E., Seyam, A. M., Sabat, M. & Marks, T. J. (1988). Polyhedron, 7, 1517-1529.]). Hydrogen atoms are omitted for clarity.
[Figure 6]
Figure 6
Structure of Cp′3U[Si(SiMe3)3] with atomic displacement parameters drawn at the 50% probability level, as reproduced from the published CIF (Réant et al., 2020[Réant, B. L. L., Berryman, V. E. J., Seed, J. A., Basford, A. R., Formanuik, A., Wooles, A. J., Kaltsoyannis, N., Liddle, S. T. & Mills, D. P. (2020). Chem. Commun. 56, 12620-12623.]); the isomorphous thorium complex, Cp′3Th[Si(SiMe3)3], is also known (Réant et al., 2020[Réant, B. L. L., Berryman, V. E. J., Seed, J. A., Basford, A. R., Formanuik, A., Wooles, A. J., Kaltsoyannis, N., Liddle, S. T. & Mills, D. P. (2020). Chem. Commun. 56, 12620-12623.]). Hydrogen atoms are omitted for clarity.
[Figure 7]
Figure 7
Structure of Cp′3ThCH3 with atomic displacement parameters drawn at the 50% probability level, as reproduced from the published CIF (Wedal et al., 2019[Wedal, J. C., Bekoe, S., Ziller, J. W., Furche, F. & Evans, W. J. (2019). Dalton Trans. 48, 16633-16640.]). Hydrogen atoms are omitted for clarity.
[Figure 8]
Figure 8
Structure of Cp′3ThBr with atomic displacement parameters drawn at the 50% probability level, as reproduced from the published CIF in the P[\overline{3}] space group (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]); there is a second report of the same mol­ecule in the P21/c space group, featuring the same ligand orientation (Wedal et al., 2019[Wedal, J. C., Bekoe, S., Ziller, J. W., Furche, F. & Evans, W. J. (2019). Dalton Trans. 48, 16633-16640.]). Hydrogen atoms are omitted for clarity.
[Figure 9]
Figure 9
Structure of (Cp′3U)2(μ-O) with atomic displacement parameters drawn as isotropic spheres, as reproduced from the CIF (Berthet et al., 1991[Berthet, J.-C., Le Maréchal, J.-F., Nierlich, M., Lance, M., Vigner, J. & Ephritikhine, M. (1991). J. Organomet. Chem. 408, 335-341.]); the isomorphous thorium complex, (Cp′3Th)2(μ-O), is also known (Wedal et al., 2019[Wedal, J. C., Bekoe, S., Ziller, J. W., Furche, F. & Evans, W. J. (2019). Dalton Trans. 48, 16633-16640.]). Hydrogen atoms are omitted for clarity.
[Figure 10]
Figure 10
Structure of (Cp′3U)2[μ-(N2C4H4)] with atomic displacement parameters drawn at the 50% probability level, as reproduced from the published CIF (Mehdoui et al., 2004[Mehdoui, T., Berthet, J.-C., Thuéry, P. & Ephritikhine, M. (2004). Eur. J. Inorg. Chem. pp. 1996-2000.]). Hydrogen atoms are omitted for clarity.
[Figure 11]
Figure 11
Structure of (Cp′3U)2(μ-CCO) with atomic displacement parameters drawn at the 50% probability level and disorder in the (μ-CCO)2− unit displayed in one configuration, as reproduced from the published CIF (Tsoureas & Cloke, 2018[Tsoureas, N. & Cloke, F. G. N. (2018). Chem. Commun. 54, 8830-8833.]). The mol­ecule contains a plane of symmetry, and the unit cell contains two half mol­ecules with the same orientation. For clarity, only one full mol­ecular unit is depicted and hydrogen atoms are omitted for clarity.
[Figure 12]
Figure 12
Structure of (Cp′3U)4(μ-L) where L = a complex organic structure containing a central cyclo­butene-1,3-dione ring, with atomic displacement parameters drawn at the 50% probability level, as reproduced from the published CIF (Tsoureas & Cloke, 2018[Tsoureas, N. & Cloke, F. G. N. (2018). Chem. Commun. 54, 8830-8833.]). Hydrogen atoms and disorder in the –SiMe3 groups are omitted for clarity.

3. Supra­molecular features

There are no major supra­molecular features to report. The mol­ecules pack in an alternating 180° rotation from one another within the unit cell and stack `head to tail' between the unit cells.

4. Database survey

A search using the Cambridge Structural Database (Version 5.41, March 2020; Groom et al., 2016[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]) for borohydride structures containing η5-aromatic five-membered rings bound to uranium showed two classes of complexes. There were the uranium(IV) piano-stool complexes: (C5H5)U(BH4)3 (DEKVEU and DEKVEU10; Baudry et al., 1985[Baudry, D., Charpin, P., Ephritikhine, M., Folcher, G., Lambard, J., Lance, M., Nierlich, M. & Vigner, J. (1985). J. Chem. Soc. Chem. Commun. pp. 1553-1554.], 1989[Baudry, D., Bulot, E., Charpin, P., Ephritikhine, M., Lance, M., Nierlich, M. & Vigner, J. (1989). J. Organomet. Chem. 371, 163-174.]); (C5Me5)U(BH4)(SPSMe) (JOJTIM; Arliguie et al., 2008[Arliguie, T., Blug, M., Le Floch, P., Mézailles, N., Thuéry, P. & Ephritikhine, M. (2008). Organometallics, 27, 4158-4165.]), where SPSMe = PC5H-3,5-Ph,-2,6-(P(S)Ph2)-1-Me, a λ4-phosphinine with two lateral phosphino­sulfide groups, and the tetra­methyl­phosphol (PC4Me4) compound (PC4Me4)(C8H8)U(BH4)(THF) (MOBVEE; Cendrowski-Guillaume et al., 2002[Cendrowski-Guillaume, S. M., Nierlich, M. & Ephritikhine, M. (2002). J. Organomet. Chem. 643-644, 209-213.]). There were also uranium(IV) metallocene structures, (Ring)2U(BH4)2, where Ring = C5H5 (CPURBH; Zanella et al., 1977[Zanella, P., De Paoli, G., Bombieri, G., Zanotti, G. & Rossi, R. (1977). J. Organomet. Chem. 142, C21-C24.]), C5H3(SiMe3)2 (ZEYZOS; Blake et al., 1995[Blake, P. C., Lappert, M. F., Taylor, R. G., Atwood, J. L., Hunter, W. E. & Zhang, H. (1995). J. Chem. Soc. Dalton Trans. pp. 3335-3341.]), C5Me5 (WIFFOG and WIFFOG01; Gradoz et al., 1994[Gradoz, P., Baudry, D., Ephritikhine, M., Lance, M., Nierlich, M. & Vigner, J. (1994). J. Organomet. Chem. 466, 107-118.]; Marsh et al., 2002[Marsh, R. E., Kapon, M., Hu, S. & Herbstein, F. H. (2002). Acta Cryst. B58, 62-77.]), C9H7 (VASVUG, C9H7 = indenide; Rebizant et al., 1989[Rebizant, J., Spirlet, M. R., Bettonville, S. & Goffart, J. (1989). Acta Cryst. C45, 1509-1511.]) and PC4Me4 (KIJBEK, PC4Me4 = tetra­methyl­phosphol; Baudry et al., 1990[Baudry, D., Ephritikhine, M., Nief, F., Ricard, L. & Mathey, F. (1990). Angew. Chem. Int. Ed. Engl. 29, 1485-1486.]). The macrocyclic trans-calix[2]benzene­[2]pyrrolide (L) complex [LU(BH4)][B(C6F5)4] was also in the database (CUJMEB; Arnold et al., 2015[Arnold, P. L., Farnaby, J. H., Gardiner, M. G. & Love, J. B. (2015). Organometallics, 34, 2114-2117.]). This last compound features two η5-bound NC4H2R2 ligands. Also in the database were a few examples of uran­ium(III) borohydrides, such as the mono borohydride [(PC4Me4)2U(BH4)]2 (YEZJES; Gradoz et al., 1994[Gradoz, P., Baudry, D., Ephritikhine, M., Lance, M., Nierlich, M. & Vigner, J. (1994). J. Organomet. Chem. 466, 107-118.]) and the mixed oxidation state piano stool [Na(THF)6][(C5Me5)U(BH4)3]2 (VAXMUC; Ryan et al., 1989[Ryan, R. R., Salazar, K. V., Sauer, N. N. & Ritchey, J. M. (1989). Inorg. Chim. Acta, 162, 221-225.])] complexes.

There are also three dimeric uranium(IV) complexes with Cp′ ligands, all of the form (Cp′3U)2(μ-X) where X = O2− (SOSXON; Berthet et al., 1991[Berthet, J.-C., Le Maréchal, J.-F., Nierlich, M., Lance, M., Vigner, J. & Ephritikhine, M. (1991). J. Organomet. Chem. 408, 335-341.]), (pyrazine)2−, (N2C4H4)2− (EYERIJ; Mehdoui et al., 2004[Mehdoui, T., Berthet, J.-C., Thuéry, P. & Ephritikhine, M. (2004). Eur. J. Inorg. Chem. pp. 1996-2000.]), and CCO2− (PIKFAT; Tsoureas & Cloke, 2018[Tsoureas, N. & Cloke, F. G. N. (2018). Chem. Commun. 54, 8830-8833.]). There is also the tetra­metallic (Cp′3U)4(μ-L) (PIKDUL; Tsoureas & Cloke, 2018[Tsoureas, N. & Cloke, F. G. N. (2018). Chem. Commun. 54, 8830-8833.]) where L is a complex organic structure containing a central cyclo­butene-1,3-dione ring.

5. Spectroscopic Features

The fully defined Cp′3U(BH4) compound was also characterized by 1H, 11B{1H}, 13C{1H}, and 29Si{1H} multi-nuclear NMR spectroscopy. It was of particular inter­est to examine the 29Si{1H} spectrum for comparison with previous studies of silicon-containing paramagnetic uranium complexes (Windorff & Evans, 2014[Windorff, C. J. & Evans, W. J. (2014). Organometallics, 33, 3786-3791.]). The 1H NMR spectrum in C7D8 was in good agreement with the literature (Berthet & Ephritikhine, 1992[Berthet, J.-C. & Ephritikhine, M. (1992). New J. Chem. 16, 767-768.]). 11B{1H}, 13C{1H}, and 29Si{1H} spectra were also obtained in both C7D8 and C6D6, as well as different field strengths, 500 vs 600 MHz for 1H, to see if any significant solvent or field effects were present. Since the spectra were not dependent on solvent or field strength, only the spectra obtained in C6D6 in a 600 MHz field will be discussed here. See Section 6 for full details.

In general, the resonances attributable to the Cp′ ligands are sharp (ν1/2 < 50 Hz) and paramagnetically shifted over a range of δ 9.6 to −22.6 ppm, in the 1H NMR spectrum, and a 29Si{1H} resonance at δ −57.4 ppm was observed, typical of other tetra­valent uranium complexes (Windorff & Evans, 2014[Windorff, C. J. & Evans, W. J. (2014). Organometallics, 33, 3786-3791.]). The resonances attributable to the (BH4) unit showed considerably more shifting and broadening, resonating at δ −59.5 (ν1/2 = 300 Hz) and 79.6 (ν1/2 = 240 Hz) in the 1H and 11B{1H} spectra, respectively. Since the (BH4) ligand exhibited a single 1H NMR resonance whereas two distinct hydride environments are present in the solid state, it appears that the complex is fluxional in solution. This is in line with previous studies (Ephritikhine, 1997[Ephritikhine, M. (1997). Chem. Rev. 97, 2193-2242.]).

6. Synthesis and crystallization

6.1. General considerations

All manipulations and syntheses described below were conducted with the rigorous exclusion of air and water using glovebox techniques under an argon atmosphere. Solvents (THF, Et2O, toluene, hexane, and penta­ne) were sparged with UHP argon (Praxair) and dried by passage through columns containing a copper(II) oxide oxygen scavenger (Q-5) and mol­ecular sieves prior to use or stirred over sodium benzo­phenone ketyl, briefly exposed to vacuum several times to degas and distilled under vacuum. All ethereal solvents were stored over activated 4 Å mol­ecular sieves. Deuterated solvents (Cambridge Isotopes) used for nuclear magnetic resonance (NMR) spectroscopy were dried over sodium benzo­phenone ketyl, degassed by three freeze-pump-thaw cycles, and distilled under vacuum before use. The 1H, 11B{1H}, 13C{1H} and 29Si{1H} NMR spectra were recorded on a GN 500, Cryo 500 or Bruker Avance 600 spectrometer operating at 500.2 MHz, 160.1 MHz, 125.8 MHz, and 99.1 MHz for the 500 MHz spectrometers, respectively, and 600.1 MHz, 192.6 MHz, 150.9 MHz and 119.2 MHz for the 600 MHz spectrometer, respectively, at 298 K unless otherwise stated. The 1H and 13C{1H} NMR spectra were referenced inter­nally to solvent resonances, 11B and 29Si{1H} NMR spectra were referenced externally to BF3(Et2O) and SiMe4, respectively, the 29Si{1H} spectra were acquired using the INEPT pulse sequence. The 15-crown-5 (Aldrich) reagent was dried over activated mol­ecular sieves and degassed by three freeze–pump–thaw cycles before use. The NaBH4 (Aldrich) reagent was placed under vacuum (10 −3 Torr) for 12 h before use. The following compounds were prepared following literature procedures: KCp′ (Peterson et al., 2013[Peterson, J. K., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2013). Organometallics, 32, 2625-2631.]), U(BH4)4 (Schles­inger & Brown, 1953[Schlesinger, H. I. & Brown, H. C. (1953). J. Am. Chem. Soc. 75, 219-221.]), Cp′3UI (Windorff et al., 2017[Windorff, C. J., MacDonald, M. R., Ziller, J. W. & Evans, W. J. (2017). Z. Anorg. Allg. Chem. 643, 2011-2018.]).

6.2. Cp′3U(BH4) from Cp′3UI, NaBH4 and 15-crown-5

Solid NaBH4 (15 mg, 0.40 mmol) was added to a C7D8 (toluene-d8, 0.6 mL) solution of Cp′3UI (37 mg, 0.048 mmol) in a J-Young NMR tube, an excess of 15-crown-5 (1 drop) was added and the tube was sealed and removed from the glovebox and vortexed (30 s). The NaBH4 was not fully soluble in C7D8 even in the presence of 15-crown-5. After 18 h, NMR spectroscopy showed complete conversion to Cp′3U(BH4). The sample was brought back into the glovebox and the volatiles were removed under reduced pressure. The product was then extracted into Et2O, filtered away from white insoluble solids [presumably Na(15-crown-5)I and excess NaBH4] and the volatiles were removed under reduced pressure to give Cp′3U(BH4) (30 mg, 96%) as a wine-red solid. 1H NMR (C7D8, 500.2 MHz): δ 9.7 (s, C5H4SiMe3, 6H), −2.1 (s, C5H4SiMe3, 27H), −23.1 (s, C5H4SiMe3, 6H), −59.8 (s, br, ν1/2 = 325 Hz, U—(BH4), 4H); 11B{1H} NMR (C7D8, 160.1 MHz): δ 79.1 [s, br, ν1/2 = 230 Hz, U—(BH4)]; 13C{1H} NMR (C7D8, 125.8 MHz): δ 233.1 (C5H4SiMe3), 214.0 (C5H4SiMe3), 185.6 (C5H4SiMe3), 0.4 (C5H4SiMe3); 29Si{1H} NMR (C7D8, 99.1 MHz, INEPT): δ −57.7 (s, C5H4SiMe3); 1H NMR (C6D6, 600.1 MHz): δ 9.6 (s, C5H4SiMe3, 6H), −2.0 (s, C5H4SiMe3, 27H), −22.6 (s, C5H4SiMe3, 6H), −59.3 (s, br, ν1/2 = 300 Hz, U—(BH4), 4H); 11B{1H} NMR (C6D6, 192.6 MHz): δ 79.6 [s, br, ν1/2 = 240 Hz, U-(BH4)]; 13C{1H} NMR (C6D6, 150.9 MHz): δ 232.0 (C5H4SiMe3), 214.2 (C5H4SiMe3), 186.5 (C5H4SiMe3), 0.6 (C5H4SiMe3); 29Si{1H} NMR (C6D6, 119.2 MHz, INEPT): δ −57.4 (s, C5H4SiMe3).

6.3. Cp′3U(BH4) from U(BH4)4 and KCp′

An Et2O (5 mL) solution of KCp′ (460 mg, 2.61 mmol) was added to a pale-green solution of U(BH4)4 (250 mg, 0.841 mmol), also dissolved in Et2O (5 mL). White solids precipitated (presumably KBH4) as the solution quickly turned orange and then slowly changed to dark red (30 min). After stirring the mixture for an additional 12 h, volatiles were removed under reduced pressure, and the product was extracted into hexane leaving white solids behind (presumably KBH4). Removal of the volatiles under reduced pressure gave Cp′3U(BH4) (496 mg, 89%) as a dark wine-red solid. X-ray quality crystals were grown from a concentrated ether solution at 253 K.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. Analytical scattering factors neutral atoms were used throughout the analysis. A 3-D rendering of the mol­ecule can be found at the following web address: https://submission.iucr.org/jtkt/serve/z/Utgd9EjfTrqJVoXA/zz0000/0/.

Table 2
Experimental details

Crystal data
Chemical formula [U(BH4)(C8H13Si)3]
Mr 664.69
Crystal system, space group Triclinic, P[\overline{1}]
Temperature (K) 112
a, b, c (Å) 8.7530 (15), 12.217 (2), 13.657 (2)
α, β, γ (°) 94.159 (3), 96.016 (3), 103.256 (3)
V3) 1406.6 (4)
Z 2
Radiation type Mo Kα
μ (mm−1) 5.91
Crystal size (mm) 0.88 × 0.62 × 0.17
 
Data collection
Diffractometer Bruker D8 Quest with Photon II detector
Absorption correction Multi-scan (SADABS; Krause et al., 2015[Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3-10.])
Tmin, Tmax 0.413, 0.747
No. of measured, independent and observed [I > 2σ(I)] reflections 30231, 10686, 9355
Rint 0.055
(sin θ/λ)max−1) 0.769
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.037, 0.102, 1.07
No. of reflections 10686
No. of parameters 274
H-atom treatment H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3) 3.87, −2.72
Computer programs: APEX3 and SAINT (Bruker, 2018[Bruker (2018). APEX3, and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]), SHELXL2018/3 (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. C71, 3-8.]), and SHELXTL2018/3 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]).

C—H bond distances were constrained to 0.95 Å for cyclo­penta­dienyl C—H moieties, and to 0.98 Å for aliphatic CH3 moieties, respectively. Methyl torsion angles were not refined but constrained to be staggered. The borohydride H atoms were located from a difference-Fourier map and their positions were freely refined. Uiso(H) values were set to a multiple of Ueq(C/B) with 1.5 for CH3 and BH4 and 1.2 for C—H units, respectively.

Supporting information


Computing details top

Data collection: APEX3 (Bruker, 2018); cell refinement: APEX3 (Bruker, 2018); data reduction: SAINT (Bruker, 2018); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015); molecular graphics: SHELXTL2018/3 (Sheldrick, 2008); software used to prepare material for publication: SHELXTL2018/3 (Sheldrick, 2008).

(Borohydrido-κ3H)tris[η5-(trimethylsilyl)cyclopentadienyl]uranium(IV) top
Crystal data top
[U(BH4)(C8H13Si)3]Z = 2
Mr = 664.69F(000) = 652
Triclinic, P1Dx = 1.569 Mg m3
a = 8.7530 (15) ÅMo Kα radiation, λ = 0.71073 Å
b = 12.217 (2) ÅCell parameters from 30231 reflections
c = 13.657 (2) Åθ = 2.4–33.1°
α = 94.159 (3)°µ = 5.91 mm1
β = 96.016 (3)°T = 112 K
γ = 103.256 (3)°Plate, red
V = 1406.6 (4) Å30.88 × 0.62 × 0.17 mm
Data collection top
Bruker D8 Quest with Photon II detector
diffractometer
9355 reflections with I > 2σ(I)
Radiation source: IµS 3.0 microfocusRint = 0.055
ω scansθmax = 33.1°, θmin = 2.4°
Absorption correction: multi-scan
(SADABS; Krause et al., 2015)
h = 1313
Tmin = 0.413, Tmax = 0.747k = 1818
30231 measured reflectionsl = 2020
10686 independent reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.037Hydrogen site location: mixed
wR(F2) = 0.102H atoms treated by a mixture of independent and constrained refinement
S = 1.07 w = 1/[σ2(Fo2) + (0.0549P)2]
where P = (Fo2 + 2Fc2)/3
10686 reflections(Δ/σ)max = 0.002
274 parametersΔρmax = 3.87 e Å3
0 restraintsΔρmin = 2.72 e Å3
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
U10.51249 (2)0.16808 (2)0.26353 (2)0.00963 (4)
B10.8150 (5)0.2329 (4)0.3009 (4)0.0177 (8)
H1A0.761 (6)0.294 (5)0.308 (4)0.027*
H1B0.771 (6)0.205 (5)0.219 (4)0.027*
H1C0.762 (6)0.166 (5)0.348 (4)0.027*
H1D0.944 (6)0.271 (5)0.317 (4)0.027*
Si10.76504 (13)0.39347 (9)0.07862 (8)0.0156 (2)
Si20.71528 (13)0.35432 (9)0.54090 (9)0.0161 (2)
Si30.79753 (13)0.07373 (10)0.23562 (8)0.0161 (2)
C10.5747 (4)0.3269 (3)0.1255 (3)0.0134 (6)
C20.4548 (4)0.2353 (3)0.0762 (3)0.0142 (7)
H20.4676640.1856420.0224850.017*
C30.3126 (4)0.2291 (3)0.1192 (3)0.0168 (7)
H3A0.2056860.1827520.0902350.020*
C40.3423 (5)0.3169 (3)0.1952 (3)0.0194 (8)
H4A0.2598200.3431090.2295490.023*
C50.5036 (5)0.3754 (3)0.2021 (3)0.0170 (7)
H5A0.5515540.4493340.2423240.020*
C60.8516 (6)0.2832 (4)0.0182 (4)0.0258 (9)
H6A0.7738940.2377130.0347550.039*
H6B0.9467500.3200070.0096980.039*
H6C0.8794930.2343150.0674810.039*
C70.9080 (5)0.4833 (4)0.1805 (4)0.0259 (9)
H7A0.9358610.4357040.2310090.039*
H7B1.0036590.5210950.1537410.039*
H7C0.8593310.5401470.2103420.039*
C80.7126 (6)0.4851 (4)0.0173 (4)0.0284 (10)
H8A0.6376270.4384420.0709500.043*
H8B0.6642180.5419880.0127680.043*
H8C0.8085450.5229370.0438330.043*
C90.5445 (4)0.2558 (3)0.4617 (3)0.0139 (6)
C100.5031 (4)0.1358 (3)0.4589 (3)0.0129 (6)
H10A0.5669600.0905860.4962410.016*
C110.3457 (4)0.0938 (3)0.4159 (3)0.0148 (7)
H11A0.2804900.0154680.4182430.018*
C120.2877 (4)0.1864 (3)0.3859 (3)0.0159 (7)
H12A0.1744870.1842440.3635460.019*
C130.4089 (5)0.2856 (3)0.4155 (3)0.0156 (7)
H130.4006500.3603710.4060080.019*
C140.7834 (5)0.4881 (3)0.4818 (4)0.0236 (9)
H14A0.6942520.5230950.4679300.035*
H14B0.8674330.5404880.5267810.035*
H14C0.8239950.4706690.4197940.035*
C150.6386 (6)0.3890 (4)0.6594 (3)0.0269 (9)
H15A0.5536510.4280130.6459440.040*
H15B0.5975290.3191420.6889040.040*
H15C0.7246650.4381540.7054070.040*
C160.8764 (5)0.2804 (4)0.5706 (3)0.0226 (8)
H16A0.9653810.3325560.6120590.034*
H16B0.8365220.2150570.6061930.034*
H16C0.9119470.2549110.5090970.034*
C170.6012 (4)0.0360 (3)0.2171 (3)0.0128 (6)
C180.4764 (5)0.0648 (3)0.2755 (3)0.0140 (6)
H180.4859990.0882230.3402260.017*
C190.3343 (4)0.0530 (3)0.2215 (3)0.0153 (7)
H190.2326170.0687130.2432790.018*
C200.3699 (4)0.0141 (3)0.1306 (3)0.0145 (7)
H20A0.2908110.0137750.0722510.017*
C210.5350 (4)0.0017 (3)0.1283 (3)0.0130 (6)
H21A0.5893240.0099390.0676620.016*
C220.8854 (5)0.0487 (4)0.3683 (3)0.0238 (9)
H22A0.9047910.0319030.3907610.036*
H22B0.8119130.0926480.4083880.036*
H22C0.9854860.0720760.3752880.036*
C230.7622 (7)0.2283 (4)0.1955 (4)0.0334 (11)
H23A0.7160590.2432680.1259280.050*
H23B0.8628890.2509330.2032650.050*
H23C0.6893160.2715050.2363650.050*
C240.9339 (5)0.0070 (4)0.1537 (4)0.0277 (10)
H24A0.8839750.0081590.0848910.042*
H24B0.9549020.0881420.1743930.042*
H24C1.0336650.0168780.1592880.042*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
U10.00980 (6)0.01025 (6)0.00983 (7)0.00336 (4)0.00194 (4)0.00341 (4)
B10.0131 (18)0.019 (2)0.021 (2)0.0041 (15)0.0016 (16)0.0059 (16)
Si10.0167 (5)0.0131 (4)0.0176 (5)0.0025 (4)0.0052 (4)0.0052 (4)
Si20.0188 (5)0.0123 (4)0.0163 (5)0.0030 (4)0.0004 (4)0.0002 (4)
Si30.0160 (5)0.0195 (5)0.0161 (5)0.0099 (4)0.0025 (4)0.0049 (4)
C10.0143 (15)0.0126 (15)0.0135 (16)0.0032 (12)0.0010 (12)0.0050 (12)
C20.0163 (16)0.0158 (16)0.0109 (16)0.0038 (13)0.0015 (13)0.0037 (12)
C30.0140 (16)0.0207 (18)0.0172 (18)0.0051 (13)0.0010 (13)0.0098 (14)
C40.0163 (17)0.0192 (18)0.028 (2)0.0106 (14)0.0061 (15)0.0141 (16)
C50.0186 (17)0.0148 (16)0.0210 (19)0.0079 (13)0.0051 (14)0.0091 (14)
C60.030 (2)0.020 (2)0.029 (2)0.0048 (17)0.0154 (19)0.0026 (17)
C70.024 (2)0.021 (2)0.030 (2)0.0006 (16)0.0056 (18)0.0030 (17)
C80.028 (2)0.029 (2)0.032 (3)0.0063 (18)0.0100 (19)0.021 (2)
C90.0145 (15)0.0117 (15)0.0165 (17)0.0045 (12)0.0024 (13)0.0022 (12)
C100.0168 (16)0.0122 (15)0.0102 (15)0.0033 (12)0.0028 (12)0.0028 (12)
C110.0148 (15)0.0169 (16)0.0132 (16)0.0016 (13)0.0061 (13)0.0057 (13)
C120.0119 (15)0.0236 (18)0.0143 (17)0.0067 (13)0.0046 (13)0.0026 (14)
C130.0167 (16)0.0175 (17)0.0145 (17)0.0076 (13)0.0025 (13)0.0023 (13)
C140.026 (2)0.0122 (17)0.032 (2)0.0031 (15)0.0054 (18)0.0032 (16)
C150.037 (2)0.023 (2)0.018 (2)0.0031 (18)0.0037 (18)0.0048 (16)
C160.0228 (19)0.0204 (19)0.025 (2)0.0080 (15)0.0036 (16)0.0027 (16)
C170.0141 (15)0.0125 (15)0.0126 (16)0.0041 (12)0.0025 (12)0.0029 (12)
C180.0190 (17)0.0126 (15)0.0104 (16)0.0033 (13)0.0025 (13)0.0024 (12)
C190.0137 (15)0.0127 (15)0.0182 (18)0.0003 (12)0.0032 (13)0.0031 (13)
C200.0140 (15)0.0176 (16)0.0097 (16)0.0018 (13)0.0030 (12)0.0001 (12)
C210.0149 (16)0.0140 (15)0.0111 (16)0.0063 (12)0.0007 (12)0.0007 (12)
C220.0220 (19)0.033 (2)0.020 (2)0.0142 (17)0.0007 (16)0.0059 (17)
C230.040 (3)0.025 (2)0.041 (3)0.022 (2)0.001 (2)0.001 (2)
C240.023 (2)0.038 (3)0.030 (2)0.0164 (19)0.0102 (18)0.014 (2)
Geometric parameters (Å, º) top
U1—B12.568 (4)C7—H7B0.9800
U1—C212.731 (4)C7—H7C0.9800
U1—C102.732 (4)C8—H8A0.9800
U1—C202.733 (4)C8—H8B0.9800
U1—C52.740 (4)C8—H8C0.9800
U1—C122.748 (4)C9—C131.419 (5)
U1—C112.754 (3)C9—C101.424 (5)
U1—C42.755 (4)C10—C111.403 (5)
U1—C32.755 (4)C10—H10A1.0000
U1—H1A2.35 (5)C11—C121.411 (5)
U1—H1B2.35 (5)C11—H11A1.0000
U1—H1C2.36 (5)C12—C131.417 (5)
B1—H1A0.98 (6)C12—H12A1.0000
B1—H1B1.15 (6)C13—H130.9500
B1—H1C1.12 (5)C14—H14A0.9800
B1—H1D1.11 (5)C14—H14B0.9800
Si1—C71.868 (5)C14—H14C0.9800
Si1—C81.871 (4)C15—H15A0.9800
Si1—C61.872 (5)C15—H15B0.9800
Si1—C11.877 (4)C15—H15C0.9800
Si2—C161.867 (4)C16—H16A0.9800
Si2—C91.871 (4)C16—H16B0.9800
Si2—C151.873 (5)C16—H16C0.9800
Si2—C141.877 (4)C17—C181.415 (5)
Si3—C221.867 (5)C17—C211.421 (5)
Si3—C231.873 (5)C18—C191.420 (5)
Si3—C171.876 (4)C18—H180.9500
Si3—C241.884 (5)C19—C201.402 (5)
C1—C21.418 (5)C19—H190.9500
C1—C51.432 (6)C20—C211.421 (5)
C2—C31.420 (5)C20—H20A1.0000
C2—H20.9500C21—H21A1.0000
C3—C41.396 (6)C22—H22A0.9800
C3—H3A1.0000C22—H22B0.9800
C4—C51.418 (5)C22—H22C0.9800
C4—H4A1.0000C23—H23A0.9800
C5—H5A1.0000C23—H23B0.9800
C6—H6A0.9800C23—H23C0.9800
C6—H6B0.9800C24—H24A0.9800
C6—H6C0.9800C24—H24B0.9800
C7—H7A0.9800C24—H24C0.9800
B1—U1—C2191.29 (14)C3—C4—H4A125.3
B1—U1—C1088.27 (13)C5—C4—H4A125.3
C21—U1—C10121.25 (11)U1—C4—H4A125.3
B1—U1—C20121.42 (14)C4—C5—C1108.8 (4)
C21—U1—C2030.15 (11)C4—C5—U175.7 (2)
C10—U1—C20116.28 (11)C1—C5—U177.6 (2)
B1—U1—C589.68 (13)C4—C5—H5A124.8
C21—U1—C5119.23 (12)C1—C5—H5A124.8
C10—U1—C5119.52 (12)U1—C5—H5A124.8
C20—U1—C5115.78 (12)Si1—C6—H6A109.5
B1—U1—C12128.78 (14)Si1—C6—H6B109.5
C21—U1—C12131.96 (12)H6A—C6—H6B109.5
C10—U1—C1248.97 (11)Si1—C6—H6C109.5
C20—U1—C12104.45 (12)H6A—C6—H6C109.5
C5—U1—C1289.90 (12)H6B—C6—H6C109.5
B1—U1—C11117.73 (13)Si1—C7—H7A109.5
C21—U1—C11113.80 (11)Si1—C7—H7B109.5
C10—U1—C1129.63 (11)H7A—C7—H7B109.5
C20—U1—C1195.57 (11)Si1—C7—H7C109.5
C5—U1—C11118.89 (12)H7A—C7—H7C109.5
C12—U1—C1129.73 (11)H7B—C7—H7C109.5
B1—U1—C4119.54 (13)Si1—C8—H8A109.5
C21—U1—C4115.96 (13)Si1—C8—H8B109.5
C10—U1—C4114.79 (12)H8A—C8—H8B109.5
C20—U1—C498.00 (13)Si1—C8—H8C109.5
C5—U1—C429.91 (11)H8A—C8—H8C109.5
C12—U1—C470.43 (12)H8B—C8—H8C109.5
C11—U1—C499.66 (12)C13—C9—C10105.6 (3)
B1—U1—C3129.05 (13)C13—C9—Si2125.9 (3)
C21—U1—C387.02 (12)C10—C9—Si2126.4 (3)
C10—U1—C3134.56 (12)C11—C10—C9109.8 (3)
C20—U1—C369.70 (12)C11—C10—U176.0 (2)
C5—U1—C349.08 (12)C9—C10—U177.7 (2)
C12—U1—C385.59 (12)C11—C10—H10A124.4
C11—U1—C3109.24 (11)C9—C10—H10A124.4
C4—U1—C329.34 (13)U1—C10—H10A124.4
B1—U1—H1A22.4 (14)C10—C11—C12107.6 (3)
C21—U1—H1A110.3 (14)C10—C11—U174.3 (2)
C10—U1—H1A88.4 (14)C12—C11—U174.9 (2)
C20—U1—H1A139.8 (14)C10—C11—H11A125.7
C5—U1—H1A70.3 (13)C12—C11—H11A125.7
C12—U1—H1A115.5 (14)U1—C11—H11A125.7
C11—U1—H1A116.7 (14)C11—C12—C13107.6 (3)
C4—U1—H1A99.3 (13)C11—C12—U175.4 (2)
C3—U1—H1A116.2 (13)C13—C12—U176.6 (2)
B1—U1—H1B26.5 (14)C11—C12—H12A125.4
C21—U1—H1B70.8 (14)C13—C12—H12A125.4
C10—U1—H1B113.0 (14)U1—C12—H12A125.4
C20—U1—H1B100.0 (14)C12—C13—C9109.4 (3)
C5—U1—H1B85.6 (13)C12—C13—H13125.3
C12—U1—H1B154.6 (14)C9—C13—H13125.3
C11—U1—H1B141.1 (13)Si2—C14—H14A109.5
C4—U1—H1B113.1 (13)Si2—C14—H14B109.5
C3—U1—H1B109.6 (13)H14A—C14—H14B109.5
H1A—U1—H1B39.9 (19)Si2—C14—H14C109.5
B1—U1—H1C25.8 (13)H14A—C14—H14C109.5
C21—U1—H1C90.4 (14)H14B—C14—H14C109.5
C10—U1—H1C66.9 (14)Si2—C15—H15A109.5
C20—U1—H1C116.7 (13)Si2—C15—H15B109.5
C5—U1—H1C112.4 (13)H15A—C15—H15B109.5
C12—U1—H1C114.2 (14)Si2—C15—H15C109.5
C11—U1—H1C94.8 (13)H15A—C15—H15C109.5
C4—U1—H1C140.7 (13)H15B—C15—H15C109.5
C3—U1—H1C154.7 (13)Si2—C16—H16A109.5
H1A—U1—H1C42.1 (18)Si2—C16—H16B109.5
H1B—U1—H1C46.4 (18)H16A—C16—H16B109.5
U1—B1—H1A66 (3)Si2—C16—H16C109.5
U1—B1—H1B66 (3)H16A—C16—H16C109.5
H1A—B1—H1B97 (4)H16B—C16—H16C109.5
U1—B1—H1C67 (3)C18—C17—C21106.5 (3)
H1A—B1—H1C107 (4)C18—C17—Si3126.3 (3)
H1B—B1—H1C110 (4)C21—C17—Si3125.2 (3)
U1—B1—H1D174 (3)C17—C18—C19108.8 (3)
H1A—B1—H1D108 (4)C17—C18—H18125.6
H1B—B1—H1D115 (4)C19—C18—H18125.6
H1C—B1—H1D118 (4)C20—C19—C18108.2 (3)
C7—Si1—C8109.1 (2)C20—C19—H19125.9
C7—Si1—C6111.5 (2)C18—C19—H19125.9
C8—Si1—C6108.4 (2)C19—C20—C21107.5 (3)
C7—Si1—C1110.74 (19)C19—C20—U177.0 (2)
C8—Si1—C1106.02 (19)C21—C20—U174.8 (2)
C6—Si1—C1110.83 (18)C19—C20—H20A125.5
C16—Si2—C9109.96 (19)C21—C20—H20A125.5
C16—Si2—C15107.7 (2)U1—C20—H20A125.5
C9—Si2—C15105.7 (2)C20—C21—C17109.0 (3)
C16—Si2—C14113.1 (2)C20—C21—U175.0 (2)
C9—Si2—C14111.05 (19)C17—C21—U178.9 (2)
C15—Si2—C14109.0 (2)C20—C21—H21A124.6
C22—Si3—C23108.2 (2)C17—C21—H21A124.6
C22—Si3—C17111.93 (19)U1—C21—H21A124.6
C23—Si3—C17107.1 (2)Si3—C22—H22A109.5
C22—Si3—C24111.8 (2)Si3—C22—H22B109.5
C23—Si3—C24108.4 (3)H22A—C22—H22B109.5
C17—Si3—C24109.23 (18)Si3—C22—H22C109.5
C2—C1—C5105.6 (3)H22A—C22—H22C109.5
C2—C1—Si1126.1 (3)H22B—C22—H22C109.5
C5—C1—Si1126.4 (3)Si3—C23—H23A109.5
C1—C2—C3109.7 (4)Si3—C23—H23B109.5
C1—C2—H2125.2H23A—C23—H23B109.5
C3—C2—H2125.2Si3—C23—H23C109.5
C4—C3—C2107.5 (3)H23A—C23—H23C109.5
C4—C3—U175.3 (2)H23B—C23—H23C109.5
C2—C3—U175.9 (2)Si3—C24—H24A109.5
C4—C3—H3A125.5Si3—C24—H24B109.5
C2—C3—H3A125.5H24A—C24—H24B109.5
U1—C3—H3A125.5Si3—C24—H24C109.5
C3—C4—C5108.4 (4)H24A—C24—H24C109.5
C3—C4—U175.3 (2)H24B—C24—H24C109.5
C5—C4—U174.4 (2)
C7—Si1—C1—C2164.8 (3)Si2—C9—C10—U1128.1 (3)
C8—Si1—C1—C276.9 (4)C9—C10—C11—C123.1 (4)
C6—Si1—C1—C240.5 (4)U1—C10—C11—C1268.1 (3)
C7—Si1—C1—C533.1 (4)C9—C10—C11—U171.2 (3)
C8—Si1—C1—C585.2 (4)C10—C11—C12—C132.8 (4)
C6—Si1—C1—C5157.4 (3)U1—C11—C12—C1370.5 (3)
C5—C1—C2—C31.5 (4)C10—C11—C12—U167.7 (3)
Si1—C1—C2—C3163.6 (3)C11—C12—C13—C91.6 (4)
C1—C2—C3—C40.3 (4)U1—C12—C13—C968.1 (3)
C1—C2—C3—U169.1 (3)C10—C9—C13—C120.3 (4)
C2—C3—C4—C52.0 (4)Si2—C9—C13—C12163.7 (3)
U1—C3—C4—C567.7 (3)C22—Si3—C17—C1845.2 (4)
C2—C3—C4—U169.7 (3)C23—Si3—C17—C1873.3 (4)
C3—C4—C5—C13.0 (4)C24—Si3—C17—C18169.5 (4)
U1—C4—C5—C171.3 (3)C22—Si3—C17—C21153.2 (3)
C3—C4—C5—U168.3 (3)C23—Si3—C17—C2188.3 (4)
C2—C1—C5—C42.8 (4)C24—Si3—C17—C2128.9 (4)
Si1—C1—C5—C4162.3 (3)C21—C17—C18—C192.5 (4)
C2—C1—C5—U167.2 (2)Si3—C17—C18—C19161.9 (3)
Si1—C1—C5—U1127.7 (3)C17—C18—C19—C201.5 (4)
C16—Si2—C9—C13172.4 (3)C18—C19—C20—C210.0 (4)
C15—Si2—C9—C1371.6 (4)C18—C19—C20—U169.3 (3)
C14—Si2—C9—C1346.5 (4)C19—C20—C21—C171.6 (4)
C16—Si2—C9—C1026.8 (4)U1—C20—C21—C1772.3 (3)
C15—Si2—C9—C1089.2 (4)C19—C20—C21—U170.8 (3)
C14—Si2—C9—C10152.7 (3)C18—C17—C21—C202.5 (4)
C13—C9—C10—C112.1 (4)Si3—C17—C21—C20162.1 (3)
Si2—C9—C10—C11161.8 (3)C18—C17—C21—U167.2 (3)
C13—C9—C10—U168.0 (3)Si3—C17—C21—U1128.1 (3)
A comparison of structural parameters (Å, °) in Cp'3U(BH4) and other Cp'3UX {X = Cl-, I-, [Si(SiMe3)3]-} complexes top
cent = C5H4SiMe3 centroid.
Cp'3U(BH4)Cp'3UCla (Windorff et al., 2017)Cp'3UI (Windorff et al., 2017)Cp'3U(η1-CHCH2) (Schock et al., 1988)Cp'3U[Si(SiMe3)3] (Réant et al., 2020)
U—(cent)2.458, 2.490, 2.5002.4732.475, 2.478, 2.4802.481, 2.483, 2.4892.472, 2.478, 2.485
(cent)—U—X104.13, 104.14, 104.83100.0097.9, 101.2, 101.695.1 100.0 100.296.04, 96.30, 97.65
(cent)—U—(cent)113.28, 114.26, 114.26117.00116.1, 116.4, 118.3116.4, 117.2, 120.0118.28, 118.88, 119.08
Note: (a) The asymmetric unit contains one Cp' ring, one-third of a chloride atom, and one-third of a uranium atom.
 

Footnotes

Present address: New Mexico State University, Department of Chemistry and Biochemistry, Las Cruces, NM 88003, USA.

Acknowledgements

We wish to thank Robert T. Pain (University of New Mexico) for the gift of U(BH4)4. We also wish to thank Dr Joseph W. Ziller (UC-Irvine) for helpful discussions.

Funding information

Funding for this research was provided by: U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Heavy Element Chemistry program (grant No. 2020LANLE372 to SAK, BLS; grant No. DE-SC0004739 to WJE); U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Oak Ridge Institute for Science and Education (ORISE), Office of Science Graduate Student Research (SCGSR) program. (contract No. DE-AC05-06OR23100 to CJW); Los Alamos, Director's Postdoctoral Fellowship (award to JNC); U.S. Department of Energy, NNSA, Triad National Security, LLC (contract No. 89233218CNA000001).

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