Molybdenum and Tungsten Germylyne Complexes of the General Formula <i>trans</i>-[X(dppe)<sub>2</sub>M⋮Ge-(η<sup>1</sup>-Cp*)] (X = Cl, Br, I; dppe = Ph<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>PPh<sub>2</sub>; Cp* = C<sub>5</sub>Me<sub>5</sub>): Syntheses, Molecular Structures, and Bonding Features of the Germylyne Ligand
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The halogermylenes (Cp*GeX)n (1a, X = Cl, n = 1; 1b, X = Br, n = 2; Cp* = pentamethylcyclopentadienyl) were prepared in high yield by a redistribution reaction of GeCp*2 with GeX2(1,4-dioxane). The ionic compounds [Cp*Ge][GeX3] (2a, X = Cl; 2b, X = Br) were also formed to a small extent in this reaction. Treatment of trans-[Mo(dppe)2(N2)2] (3) (dppe = Ph2PCH2CH2PPh2) with 1 equiv of 1a,b affords in refluxing toluene the germylyne complexes trans-[X(dppe)2Mo⋮Ge−(η1-Cp*)] (4a, X = Cl; 4b, X = Br). Concomitant formation of GeCp*2 and the dihalo complexes trans-[Mo(dppe)2(X)2] (5a, X = Cl; 5b, X = Br) is observed in this reaction. In comparison, the reactions of trans-[W(dppe)2(N2)2] (6) with 1a,b and (Cp*GeI)∞ (1c) afford selectively the germylyne complexes trans-[X(dppe)2W⋮Ge−(η1-Cp*)] (7a−c). The molecular structures of 4a·0.5pentane and 4b·0.5pentane reveal very short Mo−Ge bonds, almost linear Mo−Ge−C(Cp*) sequences, and an η1-bonded Cp* substituent indicating the presence of a molybdenum−germanium triple bond. The structural features of the germylyne ligand in 4a and 4b are compared with those in the corresponding tungsten complexes trans-[X(dppe)2W⋮Ge−(η1-Cp*)] (7a−c), and the bonding parameters of the Cp* substituent are shown to be similar to those in the germanes (η1-Cp*)GeI3 (8) and (η1-Cp*)2GeCl2 (9).
