Molybdenum and Tungsten Germylyne Complexes of the General Formulatrans-[X(dppe)2M⋮Ge-(η1-Cp*)] (X = Cl, Br, I; dppe = Ph2PCH2CH2PPh2; Cp* = C5Me5): Syntheses, Molecular Structures, and Bonding Features of the Germylyne Ligand

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 GeX 2 (1,4-dioxane). The ionic compounds [Cp*Ge][GeX 3 ] ( 2a, X = Cl; 2b, X = Br) were also formed to a small extent in this reaction. Treatment of trans -[Mo(dppe) 2 (N 2 ) 2 ] ( 3 ) (dppe = Ph 2 PCH 2 CH 2 PPh 2 ) with 1 equiv of 1a, b affords in refluxing toluene the germylyne complexes trans -[X(dppe) 2 Mo⋮Ge−( η 1 -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 (N 2 ) 2 ] ( 6 ) with 1a, b and (Cp*GeI) ∞ ( 1c ) afford selectively the germylyne complexes trans -[X(dppe) 2 W⋮Ge−( η 1 -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 η 1 -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) 2 W⋮Ge−( η 1 -Cp*)] ( 7a − c ), and the bonding parameters of the Cp* substituent are shown to be similar to those in the germanes ( η 1 -Cp*)GeI 3 ( 8 ) and ( η 1 -Cp*) 2 GeCl 2 ( 9 ).