Bis(1,2-dimethoxyethane)-1κ2 O,O′;3κ2 O,O′-tetra­kis­(μ-1,1,1,3,3,3-hexa­fluoro-2-methyl­propan-2-olato)-1:2κ4 O:O;2:3κ4 O:O-1,3-dilithium-2-magnesium

Klaus Wurst; Michael R Buchmeiser

doi:10.1107/S1600536812032679

. 2012 Jul 25;68(Pt 8):m1106. doi: 10.1107/S1600536812032679

Bis(1,2-dimethoxyethane)-1κ² O,O′;3κ² O,O′-tetrakis(μ-1,1,1,3,3,3-hexafluoro-2-methylpropan-2-olato)-1:2κ⁴ O:O;2:3κ⁴ O:O-1,3-dilithium-2-magnesium

Klaus Wurst ^a, Michael R Buchmeiser ^b,^*

PMCID: PMC3414154 PMID: 22904761

Abstract

The title compound, [Li₂Mg(C₄H₃F₆O)₄(C₄H₁₀O₂)₂], forms as a white crystalline powder by-product of the reaction of lithium 1,1,1,3,3,3-hexafluoro-2-methyl-2-propoxide with Mo(N-2,6-Me₂—C₆H₃)(CHCMe₂Ph)(O₃SCF₃)₂·2DME (DME is 1,2-dimethoxyethane) contaminated with MgCl₂. The crystal structure of this compound contains half a molecule in the asymmetric unit, with a twofold rotation axis through the central Mg²⁺ cation. The four 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-olate ligands serve as bridging ligands connecting the Li⁺ and Mg²⁺ cations. The Li⁺ cation is additionally stabilized by a DME ligand. This results in a distorted tetrahedral ligand field around both the Mg²⁺ and Li⁺ cations.

Related literature

For general background on the properties and synthesis of Schrock-type catalysts, see: Oskam et al. (1993 ▶).

Experimental

Crystal data

[Li₂Mg(C₄H₃F₆O)₄(C₄H₁₀O₂)₂]
M _r = 942.69
Monoclinic,
a = 23.8629 (4) Å
b = 9.5396 (6) Å
c = 18.3700 (7) Å
β = 109.041 (2)°
V = 3953.0 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.20 mm⁻¹
T = 233 K
0.41 × 0.25 × 0.07 mm

Data collection

Nonius KappaCCD diffractometer
10600 measured reflections
3490 independent reflections
2603 reflections with I > 2σ(I)
R _int = 0.031

Refinement

R[F ² > 2σ(F ²)] = 0.048
wR(F ²) = 0.127
S = 1.06
3490 reflections
271 parameters
H-atom parameters constrained
Δρ_max = 0.25 e Å⁻³
Δρ_min = −0.32 e Å⁻³

Data collection: COLLECT (Nonius, 1998 ▶); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997 ▶); data reduction: DENZO/SCALEPACK (Otwinowski & Minor, 1997 ▶); program(s) used to solve structure: SHELXS86 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL (Sheldrick, 2008 ▶); software used to prepare material for publication: SHELXTL and publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812032679/zl2496sup1.cif

e-68-m1106-sup1.cif^{(30.3KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812032679/zl2496Isup2.hkl

e-68-m1106-Isup2.hkl^{(171.2KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected geometric parameters (Å, °).

Mg1—O1	1.9526 (14)
Mg1—O2	1.9551 (14)
Li1—O1	1.961 (4)
Li1—O2	1.942 (4)
Li1—O3	1.988 (4)
Li1—O4	2.019 (5)
Mg1⋯Li1	2.818 (4)

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O1—Mg1—O1ⁱ	126.14 (10)
O1—Mg1—O2	87.54 (6)
O1—Mg1—O2ⁱ	119.89 (6)
O2—Mg1—O2ⁱ	119.61 (10)
O1—Li1—O2	87.69 (16)
O1—Li1—O3	125.3 (2)
O1—Li1—O4	122.7 (2)
O2—Li1—O3	120.0 (2)
O2—Li1—O4	125.3 (2)
O3—Li1—O4	80.86 (17)
Li1⋯Mg1⋯Li1ⁱ	174.14 (18)

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Symmetry code: (i) Inline graphic .

Acknowledgments

Financial support provided by the DFG (BU 2174/8-1) is gratefully acknowledged. The authors thank S. P. Westrip and the IUCr for the development of publCIF.

supplementary crystallographic information

Comment

The synthesis of molybdenum-based Schrock-type catalysts involves the reaction of the catalyst progenitor, a Mo–trifluoromethanesulfonate compound such as Mo(N-2,6-Me₂—C₆H₃)(CHCMe₂Ph)(OTf)₂.2DME (OTf = CF₃SO₃^-), with a lithium alkoxide (Oskam et al., 1993), e.g. LiOC(CF₃)₂CH₃, to yield the corresponding Schrock catalyst Mo(N-2,6-Me₂2-C₆H₃)(CHCMe₂Ph)(OC(CF₃)₂CH₃)₂. This reaction step requires high-purity educts in which case the target compounds can be prepared in high yields. However, occasionally, lower yields are observed and could not be explained so far. Here we report on the X-ray structure of a trinuclear Li–Mg compound that forms virtually quantitatively in case the progenitor compound Mo(N-2,6-Me₂—C₆H₃)(CHCMe₂Ph)(OTf)₂.2DME is contaminated with MgCl₂, which is a by-product of the synthesis of this progenitor.

The structure is shown to be a trinuclear complex containing two Li cations and one central Mg cation. Selected geometry parameters are given in Table 1. The two halves of the title compound are related by a twofold axis, which passes through the central magnesium. The Mg atom is coordinated by four η²-bridging Li–1,1,1,3,3,3-hexafluoro-2-methylpropionate ligands that are themselves coordinated to the two Li ions. The latter have each with one 1,2-dimethoxyethane (DME) ligand a distorted tetrahedral ligand sphere. The same distorted tetrahedral ligand sphere exists for the central Mg cation.

In the crystal structure no strong intermolecular hydrogen bonds are present, only F—H distances over 2.47 Å could be observed. Therefore the displacement parameters of the CF₃ groups and the DME ligands are comparatively large, showing a higher mobility of these atoms. An attempt to refine all non-hydrogen atoms of DME with a disordering model by splitting of the positions leads to a better R value, but was rejected because of too short C—O bond lengths. The distances between these split positions were only in the range of 0.28 to 0.46 Å.

Experimental

All reactions were carried out in an MBraun glove box system (Garching, Germany) using carefully dried and deoxygenated solvents. Mo(N-2,6-Me₂—C₆H₃)(CHCMe₂Ph)(OTf)₂.2DME (1) was prepared according to the literature (Oskam et al., 1993). Briefly, ethereal solutions of 1 (1.21 g, contaminated with MgCl₂) and LiOC(CF₃)₂CH₃ (0.62 g, 3.3 mmol) were combined at -36°C and the reaction mixture was allowed to warm to room temperature. Filtration through a pad of Celite and crystallization at -36°C yielded the title complex in 10% yield.