Methyl­zinc tert-butoxide tetra­hydro­furan solvate

The crystal structure of tetra-μ₃-tert-butoxo-tetrakis­(methyl­zinc) tetra­hydro­furan (THF) solvate, [Zn₄(CH₃)₄(C₄H₉O)₄]·C₄H₈O, has been determined at 230 (1) K. The structure is based on a (^tBuOZnMe)₄ pseudo-cube and contains one lattice mol­ecule of tetra­hydro­furan per (^tBuOZnMe)₄ unit. Comparison with a previously reported unsolvated structure of methyl­zinc tert-butoxide suggests that this also contains lattice THF.

Key indicators

• Single-crystal X-ray study
• T = 230 K
• Mean [sigma](C-C) = 0.005 Å
• Disorder in solvent or counterion
• R factor = 0.039
• wR factor = 0.110
• Data-to-parameter ratio = 22.1

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR') is < 0.90
          Tmin and Tmax reported:      0.425     0.515
          Tmin' and Tmax expected:      0.503     0.515
          RR' =      0.844
          Please check that your absorption correction is appropriate.

PLAT_302  Alert C Anion/Solvent Disorder .......................      25.00 Perc.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 2 Alert Level C = Please check

---

S1. Comment

Lithiated derivatives of zinc compounds have been shown to exhibit unique and useful properties in organic synthesis (e.g. Harada et al., 1992; Kondo et al., 1996; Uchiyama et al., 1998). Intermediate species in processes of this type are often highly oxophilic; this observation has led to recent investigations into the methods and selectivities with which they scavenge oxygen from the environment (Wheatley et al., 2001). Accordingly, treatment with molecular oxygen of the presumed lithium zincate product resulting from sequential treatment of N-methylbenzamide with ZnMe₂ and ^tBuLi affords colourless blocks of the title compound, (I)·THF, as the sole crystalline product.

Complex (I)·THF crystallizes in the high-symmetry tetragonal space group I4₁/acd. The solid-state structure reveals tetrameric molecules of methylzinc tert-butoxide (Fig. 1). Such pseudo-cubic tetramers are a common structure type in alkoxide structural chemistry, not only of Group 12 elements (Boersma, 1982; Nöth & Thömann, 1995), but also of many main group elements (Lindsell, 1982; Rothfuss et al., 1993; Wright & Beswick, 1995) and transition metals (Geerts et al., 1983; McNeese et al., 1984; Darensbourg et al., 1998). In (I)·THF, the tetrameric aggregates form an approximate face-centred-cubic lattice, with the octahedral sites occupied by positionally disordered THF molecules (Fig. 2).

A previous crystallographic study of methylzinc tert-butoxide has been reported (Herrmann et al., 1992) in which the unit-cell parameters are comparable with those reported here: I4₁/acd, a = b = 14.935 (1) Å, c = 30.220 (2) Å at T = 295 (1) K; the observed unit-cell expansion relative to the present study can be attributed to the difference in temperature between the two investigations. This structure was refined to give an apparently acceptable R factor (R1 = 0.077), with residual electron density reported as 0.49 and -0.27 e Å^-3. Inspection of the structure, however, reveals that the tetramers form an approximate face-centred-cubic lattice identical to that reported here, but with the octahedral sites left vacant. Inclusion at these sites of the disordered solvent molecules affords an R1 value of 0.039 for our refinement (for reflections with I > 4σ(I), directly comparable with that reported by Herrmann et al. (1992), and a goodness-of-fit value (S) of 1.076, compared with 3.157 for the previously reported refinement. Omission of the THF molecules in our structure increases R1 by only a very small amount to 0.053 [I > 4σ(I)], but the solvent molecules are readily apparent in a difference Fourier map (maximum residual electron density 1.05 e Å^-3). Given that the work of Herrmann et al. (1992) employed dimethylzinc in THF as a metallating agent, it is highly likely that the previously reported structure also incorporates lattice THF molecules but that these could not be resolved in the original study. It is probable that the decreased temperature of our study facilitates their location and subsequent refinement.

S2. Experimental

A solution of N-methylbenzamide (0.14 g, 1 mmol) in toluene (1 ml) was treated with ZnMe₂ (0.5 ml, 1 mmol, 2 M in toluene) at ambient temperature. The mixture was stirred for 10 min whereupon it was cooled to 195 K and ^tBuLi (0.6 ml, 1 mmol, 1.7 M in pentane) was added. The resultant suspension was allowed to warm to room temperature before being treated with dry O₂ (ca 15 s). Dissolution was effected by the addition of THF (1.25 ml). Filtration, reduction to half-volume and storage at 243 K for 2 d gave (I)·THF.

S3. Refinement

All H atoms were placed geometrically and allowed to ride during subsequent refinement with an isotropic displacement parameter fixed at 1.5 times U_iso for the C atom to which the H atom was attached. The solvent molecule is disordered extensively around the special position at (0,3/4,7/8) (point symmetry 222). The C—C and C—O bond distances in the THF solvent molecule were restrained to a common value with an s.u. of 0.02 Å and 1,3-distances were also restrained to ensure a reasonable molecular geometry. The C and O atoms in this solvent molecule were refined with a single common isotropic displacement parameter.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick 1997); program(s) used to refine structure: SHELXL97 (Sheldrick 1997); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Pseudo-cubic molecular unit in (I)·THF showing displacement ellipsoids at the 50% probability probability level. H atoms have been omitted for clarity (XP; Sheldrick, 1993).
	Fig. 2. Projection on to (110) showing the approximate face-centred-cubic arrangement of (^tBuOZnMe)4 units (H atoms omitted) with THF molecules in all octahedral sites. For clarity, only one orientation of the THF molecules is shown (Cerius^2; Molecular Simulations Inc., 1999).

tetra-µ₃-tert-butoxo-tetrakis(methylzinc) tetrahydrofuran solvate

Crystal data

[Zn4(CH3)4(C4H9O)4]·C4H8O	Dx = 1.377 Mg m^−3
Mr = 686.17	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I41/acd	Cell parameters from 6316 reflections
a = 14.8323 (7) Å	θ = 1.0–27.5°
c = 30.0976 (10) Å	µ = 2.89 mm^−1
V = 6621.4 (5) Å^3	T = 230 K
Z = 8	Block, colourless
F(000) = 2880	0.23 × 0.23 × 0.23 mm

Data collection

Nonius KappaCCD diffractometer	1876 independent reflections
Radiation source: fine-focus sealed tube	1421 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.055
thin–slice ω and ϕ scans	θmax = 27.5°, θmin = 3.7°
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	h = 0→19
Tmin = 0.425, Tmax = 0.515	k = −19→19
10143 measured reflections	l = −38→39

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.110	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0531P)^2 + 5.782P] where P = (Fo^2 + 2Fc^2)/3
1876 reflections	(Δ/σ)max = 0.016
85 parameters	Δρmax = 0.40 e Å^−3
10 restraints	Δρmin = −0.53 e Å^−3

Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Zn1	0.92092 (2)	0.31641 (2)	0.411143 (11)	0.04359 (17)
O1	0.92858 (12)	0.30983 (13)	0.34258 (6)	0.0379 (5)
C1	0.8386 (3)	0.3859 (3)	0.44904 (14)	0.0948 (14)
H1A	0.8558	0.3785	0.4799	0.142*
H1B	0.7774	0.3644	0.4449	0.142*
H1C	0.8418	0.4492	0.4411	0.142*
C2	0.8667 (2)	0.3620 (2)	0.31474 (11)	0.0674 (10)
C3	0.7720 (3)	0.3322 (3)	0.32614 (16)	0.0916 (14)
H3A	0.7606	0.3429	0.3574	0.137*
H3B	0.7655	0.2684	0.3198	0.137*
H3C	0.7290	0.3661	0.3085	0.137*
C4	0.8815 (3)	0.4603 (3)	0.32558 (16)	0.0970 (15)
H4A	0.8683	0.4708	0.3567	0.146*
H4B	0.8420	0.4971	0.3074	0.146*
H4C	0.9438	0.4762	0.3196	0.146*
C5	0.8898 (4)	0.3403 (3)	0.26667 (13)	0.1000 (16)
H5A	0.8813	0.2764	0.2614	0.150*
H5B	0.9521	0.3563	0.2609	0.150*
H5C	0.8507	0.3744	0.2471	0.150*
O2	0.5473 (14)	0.1892 (11)	0.3922 (8)	0.123 (4)*	0.25
C6	0.542 (2)	0.2796 (17)	0.4086 (7)	0.123 (4)*	0.25
H6A	0.5095	0.2806	0.4369	0.148*	0.25
H6B	0.6026	0.3036	0.4134	0.148*	0.25
C7	0.496 (3)	0.3331 (14)	0.3768 (9)	0.123 (4)*	0.25
H7A	0.5349	0.3814	0.3659	0.148*	0.25
H7B	0.4420	0.3604	0.3902	0.148*	0.25
C8	0.470 (2)	0.2738 (16)	0.3406 (7)	0.123 (4)*	0.25
H8A	0.4068	0.2832	0.3327	0.148*	0.25
H8B	0.5074	0.2859	0.3144	0.148*	0.25
C9	0.4839 (19)	0.1837 (13)	0.3556 (11)	0.123 (4)*	0.25
H9A	0.5085	0.1464	0.3316	0.148*	0.25
H9B	0.4268	0.1572	0.3656	0.148*	0.25

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0424 (2)	0.0425 (2)	0.0458 (3)	0.00873 (13)	0.00716 (14)	−0.00553 (13)
O1	0.0359 (10)	0.0374 (10)	0.0403 (10)	0.0039 (7)	−0.0077 (7)	0.0077 (8)
C1	0.091 (3)	0.098 (3)	0.095 (3)	0.034 (3)	0.029 (2)	−0.030 (2)
C2	0.061 (2)	0.069 (2)	0.073 (2)	0.0131 (18)	−0.0218 (17)	0.0262 (18)
C3	0.050 (2)	0.106 (3)	0.118 (3)	0.018 (2)	−0.030 (2)	0.023 (3)
C4	0.100 (3)	0.058 (2)	0.133 (4)	0.025 (2)	−0.018 (3)	0.039 (2)
C5	0.110 (4)	0.132 (4)	0.058 (2)	0.009 (3)	−0.033 (2)	0.036 (2)

Geometric parameters (Å, º)

Zn1—C1	1.963 (3)	C4—H4A	0.9700
Zn1—O1^i	2.0647 (19)	C4—H4B	0.9700
Zn1—O1^ii	2.0673 (18)	C4—H4C	0.9700
Zn1—O1	2.0690 (19)	C5—H5A	0.9700
Zn1—Zn1^iii	3.0633 (7)	C5—H5B	0.9700
Zn1—Zn1^i	3.0701 (6)	C5—H5C	0.9700
Zn1—Zn1^ii	3.0701 (6)	O2—C6	1.429 (17)
O1—C2	1.465 (3)	O2—C9	1.451 (17)
O1—Zn1^ii	2.0647 (19)	C6—C7	1.419 (18)
O1—Zn1^i	2.0673 (18)	C6—H6A	0.9800
C1—H1A	0.9700	C6—H6B	0.9800
C1—H1B	0.9700	C7—C8	1.450 (17)
C1—H1C	0.9700	C7—H7A	0.9800
C2—C4	1.510 (6)	C7—H7B	0.9800
C2—C3	1.512 (5)	C8—C9	1.424 (18)
C2—C5	1.522 (6)	C8—H8A	0.9800
C3—H3A	0.9700	C8—H8B	0.9800
C3—H3B	0.9700	C9—H9A	0.9800
C3—H3C	0.9700	C9—H9B	0.9800
C1—Zn1—O1^i	129.30 (15)	H3A—C3—H3B	109.5
C1—Zn1—O1^ii	129.54 (15)	C2—C3—H3C	109.5
O1^i—Zn1—O1^ii	83.97 (8)	H3A—C3—H3C	109.5
C1—Zn1—O1	129.66 (15)	H3B—C3—H3C	109.5
O1^i—Zn1—O1	83.85 (7)	C2—C4—H4A	109.5
O1^ii—Zn1—O1	83.78 (8)	C2—C4—H4B	109.5
C1—Zn1—Zn1^iii	144.49 (14)	H4A—C4—H4B	109.5
O1^i—Zn1—Zn1^iii	42.19 (5)	C2—C4—H4C	109.5
O1^ii—Zn1—Zn1^iii	42.12 (5)	H4A—C4—H4C	109.5
O1—Zn1—Zn1^iii	85.85 (5)	H4B—C4—H4C	109.5
C1—Zn1—Zn1^i	144.76 (14)	C2—C5—H5A	109.5
O1^i—Zn1—Zn1^i	42.09 (5)	C2—C5—H5B	109.5
O1^ii—Zn1—Zn1^i	85.70 (5)	H5A—C5—H5B	109.5
O1—Zn1—Zn1^i	42.06 (5)	C2—C5—H5C	109.5
Zn1^iii—Zn1—Zn1^i	60.073 (7)	H5A—C5—H5C	109.5
C1—Zn1—Zn1^ii	144.96 (14)	H5B—C5—H5C	109.5
O1^i—Zn1—Zn1^ii	85.74 (5)	C6—O2—C9	106.2 (10)
O1^ii—Zn1—Zn1^ii	42.10 (5)	C7—C6—O2	108.6 (10)
O1—Zn1—Zn1^ii	41.98 (5)	C7—C6—H6A	110.0
Zn1^iii—Zn1—Zn1^ii	60.073 (7)	O2—C6—H6A	110.0
Zn1^i—Zn1—Zn1^ii	59.855 (13)	C7—C6—H6B	110.0
C2—O1—Zn1^ii	121.28 (19)	O2—C6—H6B	110.0
C2—O1—Zn1^i	121.07 (19)	H6A—C6—H6B	108.3
Zn1^ii—O1—Zn1^i	95.70 (8)	C6—C7—C8	107.0 (10)
C2—O1—Zn1	120.74 (19)	C6—C7—H7A	110.3
Zn1^ii—O1—Zn1	95.92 (8)	C8—C7—H7A	110.3
Zn1^i—O1—Zn1	95.84 (7)	C6—C7—H7B	110.3
Zn1—C1—H1A	109.5	C8—C7—H7B	110.3
Zn1—C1—H1B	109.5	H7A—C7—H7B	108.6
H1A—C1—H1B	109.5	C9—C8—C7	107.1 (12)
Zn1—C1—H1C	109.5	C9—C8—H8A	110.3
H1A—C1—H1C	109.5	C7—C8—H8A	110.3
H1B—C1—H1C	109.5	C9—C8—H8B	110.3
O1—C2—C4	107.2 (3)	C7—C8—H8B	110.3
O1—C2—C3	107.3 (3)	H8A—C8—H8B	108.5
C4—C2—C3	111.7 (4)	C8—C9—O2	106.2 (12)
O1—C2—C5	106.9 (3)	C8—C9—H9A	110.5
C4—C2—C5	112.1 (3)	O2—C9—H9A	110.5
C3—C2—C5	111.3 (4)	C8—C9—H9B	110.5
C2—C3—H3A	109.5	O2—C9—H9B	110.5
C2—C3—H3B	109.5	H9A—C9—H9B	108.7
C1—Zn1—O1—C2	0.0 (3)	Zn1^ii—Zn1—O1—Zn1^i	−96.37 (8)
O1^i—Zn1—O1—C2	−137.5 (2)	Zn1^ii—O1—C2—C4	−179.3 (2)
O1^ii—Zn1—O1—C2	137.9 (2)	Zn1^i—O1—C2—C4	−59.2 (4)
Zn1^iii—Zn1—O1—C2	−179.9 (2)	Zn1—O1—C2—C4	60.5 (3)
Zn1^i—Zn1—O1—C2	−131.6 (2)	Zn1^ii—O1—C2—C3	60.5 (3)
Zn1^ii—Zn1—O1—C2	132.0 (2)	Zn1^i—O1—C2—C3	−179.3 (2)
C1—Zn1—O1—Zn1^ii	−131.96 (19)	Zn1—O1—C2—C3	−59.6 (3)
O1^i—Zn1—O1—Zn1^ii	90.47 (9)	Zn1^ii—O1—C2—C5	−58.9 (3)
O1^ii—Zn1—O1—Zn1^ii	5.90 (8)	Zn1^i—O1—C2—C5	61.2 (3)
Zn1^iii—Zn1—O1—Zn1^ii	48.15 (5)	Zn1—O1—C2—C5	−179.1 (2)
Zn1^i—Zn1—O1—Zn1^ii	96.37 (8)	C9—O2—C6—C7	−14 (4)
C1—Zn1—O1—Zn1^i	131.67 (19)	O2—C6—C7—C8	1 (6)
O1^i—Zn1—O1—Zn1^i	−5.90 (8)	C6—C7—C8—C9	12 (6)
O1^ii—Zn1—O1—Zn1^i	−90.47 (9)	C7—C8—C9—O2	−21 (5)
Zn1^iii—Zn1—O1—Zn1^i	−48.22 (6)	C6—O2—C9—C8	22 (3)

Symmetry codes: (i) y+3/4, −x+5/4, −z+3/4; (ii) −y+5/4, x−3/4, −z+3/4; (iii) −x+2, −y+1/2, z.