Stabilized Terphenyl-Substituted Digermene Derivatives of Simple Organic Groups and Their Halide Precursors:  Preference for Symmetrically Bonded Structures

The reaction of 1 equiv of MeMgBr, EtMgBr, or LiPh with Ge(Cl)C 6 H 3 -2,6-Trip 2 ( 1; Trip = C 6 H 2 -2,4,6- i -Pr 3 ) in diethyl ether solution afforded the dimers {Ge(R)C 6 H 3 -2,6-Trip 2 } 2 (R = Me ( 2 ), Et ( 3 ), Ph ( 4 )), which have trans-bent Ge−Ge-bonded structures that are maintained in solution. The compounds 2 and 3 are rare examples of “digermene” species having alkyl substituents. The previously described halide precursor 1 was found to crystallize simultaneously as both a V-shaped monomer and weakly Ge−Ge-bonded dimer {Ge(Cl)C 6 H 3 -2,6-Trip 2 } 2 ( 5 ), which dissociated readily to monomers in hydrocarbon solution. This species reacted readily with pyridine (py) to form the monomeric 1:1 adduct py·Ge(Cl)C 6 H 3 -2,6-Trip 2 ( 7 ), which has pyramidal coordination at germanium. The dimeric structures found for 2 − 4 were in sharp contrast with recently published results for their tin and lead analogues, which displayed either unsymmetric dimeric structures as in 2,6-Trip 2 H 3 C 6 (Me) 2 SnS̈nC 6 H 3 -2,6-Trip 2 or monomeric structures as in Pb(Me)C 6 H 3 -2,6-Trip 2 . The chloro derivatives {Ge(Cl)C 6 H 3 -2,6-Trip 2 } n ( n = 1, 2; i.e. 1 and 5 ) also differed from their tin congeners in that the corresponding tin dimer is associated through chloride bridging, whereas 5, and the related dimer {Ge(Cl)C 6 H 3 -2,6-Mes 2 } 2 ( 6 ), are associated through weak element−element bonding. The experimental results are in general agreement with earlier theoretical data on the hypothetical M 2 H 4 (M = Ge, Sn, Pb) model compounds which predicted a stable, symmetric, dimeric, Ge−Ge-bonded structure for germanium but an unsymmetric methylmethylene analogue structure for tin.