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In tris(tert-butyl)­phosphine selenide, C12H27PSe, all the methyl ligands are disordered over two sites in the ratio 70/30. The mol­ecule displays crystallographic C3 symmetry. The bond angles at the P atom are distorted tetrahedral [C-P-C 110.02 (5)° and Se=P-C 108.91 (5)°]. The P-C and P=Se bond lengths are 1.908 (1) and 2.1326 (6) Å, respectively. A comparison of the structural data of the complete series of tris(tert-butyl)­phosphine chalcogenides (tBu3PO, tBu3PS, tBu3PSe and tBu3PTe) with the corresponding data of other phosphine chalcogenides substituted by smaller organic groups shows the great influence of the bulky tert-butyl ligands.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010002000X/jz1439sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010002000X/jz1439Isup2.hkl
Contains datablock I

CCDC reference: 162585

Comment top

Phosphine chalcogenides are well known compounds and have been fully studied (Patai & Hartley, 1992). Here we report the structure of tris(tert-butyl)phosphine selenide, (I). Together with the recently published molecular structure of tBu3PS (Steinberger et al., 2001), the series of X-ray structures of tris(tert-butyl)phosphine chalcogenides has now been completed. The previously reported data are summarized in a review by Gilheany (1992). \sch

Compound (I) was first prepared from tris(tert-butyl)phosphine and Se in the late seventies (DuMont et al., 1976; Philip & Polenski, 1980), but the molecular structure was not determined. In order to compare the structural differences, the characteristic data for (I), together with the corresponding values for tBu3PO (Rankin et al., 1985), tBu3PS (Steinberger et al., 2001), tBu3PTe (Kuhn et al., 1987) and the starting material, tBu3P (Krüger & Bruckmann, 1995), are listed in Table 1.

The crystal structure of (I) is disordered. However, this disorder only involves the methyl groups, and in the structure refinement a 'split model' for these atoms appeared to handle the problem adequately. Similar disorder was observed for the isomorphous sulfur derivative. We assume that this disorder has not significantly affected the geometry determined for the inner part of the molecule.

In (I), the geometry at the P atom is distorted tetrahedral [C—P—C 110.02 (5) and SeP—C 108.91 (5)°] and the P—C and PSe bond lengths are 1.9079 (14) and 2.1326 (6) Å, respectively. The PSe bond in (I), together with the value in tris(2,4-dimethoxyphenyl)phosphine selenide [2.135 (3) Å; Allen et al., 1990] represents an upper limit for phosphorus selenides.

From the data in Table 1 it can be seen that there is a marked steric influence of the tert-butyl group. In comparison with phosphine chalcogenides substituted by less bulky groups at the phosphorus, such as Me3PO [1.772 (6) and 1.770 (10) Å; Engelhardt et al., 1986], Me3PS [1.798 (2) Å; Eller & Corfield, 1971] or Me3PSe [1.786 (14) Å; Cogne et al., 1980], a distinct lengthening of the P—C bonds [1.888 (6)–1.9079 (14) Å] is observed. Furthermore, Gilheany (1992) concluded that bulky substituents lengthen the PX bond distance (X is O, S, Se or Te) by ca 0.002–0.004 Å. In (I), the increase of the PSe distance is about 0.002 Å, compared with Me3PSe [2.111 (3) Å (X-ray data; Cogne et al., 1980) and 2.091 (3) Å (electron diffraction; Jacob & Samdal, 1977)] and Ph3PSe [2.106 (2) Å (Codding & Kerr, 1979)]. However, in the case of the phosphine sulfides, such as tBu3PS [1.962 (3) Å; Steinberger et al., 2001] and Me3PS [1.959 (2) Å; Eller & Corfield, 1971], the difference in the P—S bond length is only small.

The P—X distances in phosphine chalcogenides obtained by X-ray structure determination (XR) are about 0.0015–0.002 Å longer than those obtained by electron diffraction in the gas phase (ED), as can be seen from the examples of Me3PO [1.489 (6) Å (XR; Engelhardt et al., 1986) and 1.476 (2) Å (ED; Wilkins et al., 1975)], Me3PS [1.959 (2) Å (XR; Eller & Corfield, 1971) and 1.940 (2) Å (ED; Wilkins et al., 1975)] and Me3PSe [2.111 (3) Å (XR; Cogne et al., 1980) and 2.091 (3) (ED; Jacob & Samdal, 1977)]. To the best of our knowledge, no corresponding data for phosphine tellurides are available.

Related literature top

For related literature, see: Allen et al. (1990); Codding & Kerr (1979); Cogne et al. (1980); DuMont, Kroth & Schumann (1976); Eller & Corfield (1971); Engelhardt et al. (1986); Gilheany (1992); Jacob & Samdal (1977); Krüger & Bruckmann (1995); Kuhn et al. (1987); Patai & Hartley (1992); Rankin et al. (1985); Sheldrick (1997); Steinberger et al. (2001); Wilkins et al. (1975).

Experimental top

To a solution of tris(tert-butyl)phosphine (0.97 g, 4.82 mmol) in toluene (10 ml), grey selenium granules (0.39 g, 4.92 mmol; 2% excess) were added and the mixture heated for 16 h at 338 K. After removal of excess Se by filtration, the solvent was completely evaporated in high vacuum, yielding tBu3PSe, (I) (yield 1.31 g, 97%). The title compound was characterized by 31P NMR [121.472 MHz, toluene, 298 K: d = 92.92 p.p.m. (3JP—H = 13.6 Hz; 1JP—Se = 691 Hz)] and mass spectroscopy. Recrystallization from toluene at 238 K afforded single crystals of (I).

Refinement top

At the end of the conventional refinement all methyl C atoms revealed very anisotropic displacement parameters. Split sites for these atoms and their associated H atoms were introduced. The major methyl component was refined as a rigid group and allowed to rotate but not tip; the minor component was refined with a riding model assuming ideally staggered torsion angles. Moreover, nine restraints were used [DFIX = 1.54 for the six C1—Cmethyl distances and SADI for the three Cmethyl—Cmethyl,split disorder pairs; SHELXL97 (Sheldrick, 1997)?]. The site occupancy converged to about 70/30. Hereby, R1 and wR2 decreased from 0.040 and 0.100 to 0.019 and 0.047, respectively. Additionally, the deviations from the zero level in the corresponding final difference maps changed from -0.53 and 0.62 to -0.19 and 0.62 e/Å3, respectively, and the displacement ellipsoids became normal. The P—C1 distance discussed in this work changed insignificantly, from 1.907 (3) to 1.908 (2) Å.

Computing details top

Data collection: IPDS (Stoe & Cie, 1997); cell refinement: IPDS; data reduction: IPDS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XSTEP32 (Stoe & Cie, 1997); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) showing 50% probability displacement ellipsoids. Only the main disorder component is shown. H atoms have been omitted for clarity.
Tris(tert-butyl)phosphine selenide top
Crystal data top
C12H27PSeDx = 1.231 Mg m3
Mr = 281.27Mo Kα radiation, λ = 0.71073 Å
Cubic, Pa3Cell parameters from 5000 reflections
Hall symbol: -P 2ac 2ab 3θ = 5–20°
a = 14.4773 (18) ŵ = 2.55 mm1
V = 3034.3 (7) Å3T = 180 K
Z = 8Cube, colourless
F(000) = 11840.60 × 0.56 × 0.52 mm
Data collection top
Stoe IPDS
diffractometer
993 independent reflections
Radiation source: fine-focus sealed X-ray tube867 reflections with I > 2σ(I)
Planar graphite monochromatorRint = 0.049
Detector resolution: 6.667 pixels mm-1θmax = 26.0°, θmin = 3.5°
ϕ–rotation, steps of 1.2°, 177 exposures scansh = 1717
Absorption correction: numerical
(X-RED; Stoe & Cie, 1997)
k = 1717
Tmin = 0.310, Tmax = 0.351l = 1717
20131 measured 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)] = 0.018Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.046H-atom parameters not refined
S = 1.03 w = 1/[σ2(Fo2) + (0.0301P)2 + 0.3113P]
where P = (Fo2 + 2Fc2)/3
993 reflections(Δ/σ)max = 0.011
74 parametersΔρmax = 0.62 e Å3
9 restraintsΔρmin = 0.19 e Å3
Crystal data top
C12H27PSeZ = 8
Mr = 281.27Mo Kα radiation
Cubic, Pa3µ = 2.55 mm1
a = 14.4773 (18) ÅT = 180 K
V = 3034.3 (7) Å30.60 × 0.56 × 0.52 mm
Data collection top
Stoe IPDS
diffractometer
993 independent reflections
Absorption correction: numerical
(X-RED; Stoe & Cie, 1997)
867 reflections with I > 2σ(I)
Tmin = 0.310, Tmax = 0.351Rint = 0.049
20131 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0189 restraints
wR(F2) = 0.046H-atom parameters not refined
S = 1.03Δρmax = 0.62 e Å3
993 reflectionsΔρmin = 0.19 e Å3
74 parameters
Special details top

Experimental. Recrystallized from toluene. During data collection the crystal was in cold N2 gas from a cryostream cooler (Oxford Cryosystems, 1992).

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

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

All crystal faces were indexed by microscope on the diffractometer and thereafter a Gaussian integration for absorption correction was carried out, as implemented in X-RED (Stoe & Cie, 1997).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
C10.31865 (11)0.68057 (10)0.02827 (10)0.0321 (3)
C20.3603 (3)0.7760 (2)0.0040 (2)0.0448 (9)0.698 (9)
H2A0.33970.82190.04940.054*0.698 (9)
H2B0.33980.79460.05780.054*0.698 (9)
H2C0.42790.77210.00510.054*0.698 (9)
C2S0.3102 (9)0.7853 (5)0.0135 (5)0.046 (2)0.302 (9)
H2S10.26400.81050.05610.055*0.302 (9)
H2S20.29120.79770.05030.055*0.302 (9)
H2S30.37010.81470.02520.055*0.302 (9)
C30.3561 (3)0.6083 (3)0.0398 (2)0.0422 (8)0.698 (9)
H3A0.42260.60030.03000.051*0.698 (9)
H3B0.34500.62920.10330.051*0.698 (9)
H3C0.32450.54930.02970.051*0.698 (9)
C3S0.3922 (7)0.6412 (8)0.0403 (5)0.046 (2)0.302 (9)
H3SA0.40020.57490.02920.055*0.302 (9)
H3SB0.45130.67290.03070.055*0.302 (9)
H3SC0.37140.65110.10390.055*0.302 (9)
C40.2124 (2)0.6899 (3)0.0141 (2)0.0423 (9)0.698 (9)
H4A0.18790.73630.05680.051*0.698 (9)
H4B0.18270.63030.02600.051*0.698 (9)
H4C0.19980.70910.04960.051*0.698 (9)
C4S0.2246 (5)0.6397 (8)0.0025 (4)0.044 (2)0.302 (9)
H4SA0.22630.57250.01010.053*0.302 (9)
H4SB0.21040.65470.06200.053*0.302 (9)
H4SC0.17680.66580.04280.053*0.302 (9)
P0.34528 (2)0.65472 (2)0.15472 (2)0.02013 (14)
Se0.260232 (9)0.739768 (9)0.239768 (9)0.02804 (10)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0382 (8)0.0351 (8)0.0230 (7)0.0052 (6)0.0013 (6)0.0008 (6)
C20.063 (3)0.0385 (16)0.0333 (14)0.0033 (15)0.0060 (15)0.0119 (11)
C2S0.074 (7)0.038 (3)0.025 (3)0.012 (4)0.002 (3)0.007 (2)
C30.050 (2)0.053 (2)0.0242 (12)0.0093 (14)0.0022 (14)0.0099 (14)
C3S0.058 (6)0.055 (6)0.025 (3)0.016 (4)0.003 (3)0.005 (3)
C40.0406 (15)0.051 (2)0.0348 (14)0.0116 (14)0.0121 (10)0.0015 (13)
C4S0.045 (4)0.057 (5)0.029 (3)0.007 (3)0.004 (2)0.004 (3)
P0.02013 (14)0.02013 (14)0.02013 (14)0.00120 (12)0.00120 (12)0.00120 (12)
Se0.02804 (10)0.02804 (10)0.02804 (10)0.00518 (5)0.00518 (5)0.00518 (5)
Geometric parameters (Å, º) top
C1—C4S1.531 (7)C1—C3S1.564 (8)
C1—C31.537 (4)C1—P1.9079 (14)
C1—C2S1.537 (7)P—C1i1.9079 (14)
C1—C21.548 (3)P—C1ii1.9079 (14)
C1—C41.558 (3)P—Se2.1326 (6)
C4S—C1—C383.9 (3)C4—C1—C3S128.4 (4)
C4S—C1—C2S106.1 (4)C4S—C1—P109.8 (3)
C3—C1—C2S127.7 (3)C3—C1—P114.26 (16)
C4S—C1—C2129.5 (3)C2S—C1—P110.1 (3)
C3—C1—C2109.0 (2)C2—C1—P108.29 (14)
C2S—C1—C228.2 (4)C4—C1—P110.08 (13)
C4S—C1—C428.7 (3)C3S—C1—P113.6 (3)
C3—C1—C4108.8 (2)C1i—P—C1110.02 (5)
C2S—C1—C479.5 (4)C1i—P—C1ii110.02 (5)
C2—C1—C4106.1 (2)C1—P—C1ii110.02 (5)
C4S—C1—C3S108.1 (4)C1i—P—Se108.91 (5)
C3—C1—C3S26.4 (3)C1—P—Se108.91 (5)
C2S—C1—C3S109.0 (4)C1ii—P—Se108.91 (5)
C2—C1—C3S85.2 (4)
C4S—C1—P—C1i167.6 (5)C2—C1—P—C1ii167.6 (2)
C3—C1—P—C1i75.4 (2)C4—C1—P—C1ii76.8 (2)
C2S—C1—P—C1i76.0 (5)C3S—C1—P—C1ii74.9 (5)
C2—C1—P—C1i46.2 (2)C4S—C1—P—Se73.1 (5)
C4—C1—P—C1i161.8 (2)C3—C1—P—Se165.3 (2)
C3S—C1—P—C1i46.5 (5)C2S—C1—P—Se43.3 (5)
C4S—C1—P—C1ii46.3 (5)C2—C1—P—Se73.1 (2)
C3—C1—P—C1ii46.0 (2)C4—C1—P—Se42.5 (2)
C2S—C1—P—C1ii162.6 (5)C3S—C1—P—Se165.8 (5)
Symmetry codes: (i) z+1/2, x+1, y1/2; (ii) y+1, z+1/2, x+1/2.

Experimental details

Crystal data
Chemical formulaC12H27PSe
Mr281.27
Crystal system, space groupCubic, Pa3
Temperature (K)180
a (Å)14.4773 (18)
V3)3034.3 (7)
Z8
Radiation typeMo Kα
µ (mm1)2.55
Crystal size (mm)0.60 × 0.56 × 0.52
Data collection
DiffractometerStoe IPDS
diffractometer
Absorption correctionNumerical
(X-RED; Stoe & Cie, 1997)
Tmin, Tmax0.310, 0.351
No. of measured, independent and
observed [I > 2σ(I)] reflections
20131, 993, 867
Rint0.049
(sin θ/λ)max1)0.616
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.018, 0.046, 1.03
No. of reflections993
No. of parameters74
No. of restraints9
H-atom treatmentH-atom parameters not refined
Δρmax, Δρmin (e Å3)0.62, 0.19

Computer programs: IPDS (Stoe & Cie, 1997), IPDS, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), XSTEP32 (Stoe & Cie, 1997), SHELXL97.

Structural data (Å, °, p.p.m.) for tris(tert-butyl)phosphine chalcogenides tBu3PX (X = O, S, Se, Te) top
tBu3POatBu3PStBu3PSetBu3PTetBu3P
PX1.590 (12)1.962 (3)2.1326 (6)2.368 (4)
P-C1.888 (6)1.899 (4)1.9079 (14)1.896 (14)1.911 (2)
C-P-C112.9 (5)109.63 (12)110.02 (5)110.2 (6)107.4 (1)
XP-C106.1 (5)109.31 (12)108.91 (5)108.7 (5)
31P NMR41b89.792.9275.2c62.9
a determined by electron diffraction; b, c 31P NMR chemical shifts were measured in toluene or benzene solution (external standard H3PO4 85%); b Rosenberg & Drenth (1971); c DuMont et al. (1976).
 

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