Reactivity of Amido-Digermynes, LGeGeL (L = Bulky Amide), toward Olefins and Related Molecules: Facile Reduction, C-H Activation, and Reversible Cycloaddition of Unsaturated Substrates

Reactions of two sterically hindered amido-digermynes, L*GeGeL* (1; L* = -N(Ar*)(SiMe3); Ar* = C6H2Me{C(H)Ph-2}(2)-4,2,6) and (LGeGeL dagger)-Ge-dagger (2; L-dagger = -N(Ar-dagger)-(SiPr3i); Ar-dagger = C6H2Pri{C(H)Ph-2}-4,2,6), with a variety of olefins and related molecules are investigated. These lead to the facile reduction, C H activation, dehydrogenation, and/or cycloaddition of the unsaturated substrate. Specifically, reaction of LtGeGeLt with ethylene proceeds via a formal [2 + 2 + 2] cycloaddition to give the digermabicydo[2.2.0]hexane (LGe)-Ge-dagger(mu-C2H4)(2)GeL dagger (3). In contrast, treating (LGeGeL dagger)-Ge-dagger with norbornaliene proceeds via reductive insertion of one olefin moiety of the organic substrate into the Ge Ge bond of 1, yielding the norbomenediyl-bridged bis(germylene) (LGe)-Ge-dagger(mu-C7H8)GeL dagger(4). Similarly, L*GeGeL* doubly reduces cyclooctatetraene (COT) to give the planar cydooctateraenediyl inverse sandwich complex L*Ge(mu-eta(2),eta(2)-COT)GeL* (5). An indication that this reaction occurs via an initial formal [2 + 2] cydoaddition intermediate comes from the reaction of (LGeGe dagger)-Ge-dagger with 1,5-cydooctadiene (COD). This affords the [2 + 2] cydoaddition product (LGe)-Ge-dagger(COD)GeL dagger (6), which exists in solution in equilibrium with 2 and free COD. A computational study indicates that 6 readily dissociates, as the reaction that gave it is close to thermoneutral. Reaction of 1,3-cydohexadiene (1,3-CHD) with (LGeGeL dagger)-Ge-dagger yields the 1,4-bis(germylene) substituted cydohex-2-enediyl (LGe)-Ge-dagger(mu-C6H8)GeL dagger. (7), which is an isolated intermediate in the transfer hydrogenation, or C-H activation, reaction between (LGeGeL dagger)-Ge-dagger and 1,3-CHD. Heating 7 gives benzene and the known digermene L-dagger(H)GeGe(H)L-dagger. Reactions of 1 or 2 with propyne, bis(trimethylsily0butadiyne, and azobenzene all lead to reductive insertion of the unsaturated substrate into the Ge Ge bond of the digermyne and formation of (LGe)-Ge-dagger{mu-HC=C(Me)}GeL dagger. (8), L*Ge{mu-(Me3Si)C=C(CCSiMe3)}GeL* (9), and L*Ge{mu-(Ph)NN(Ph)}GeL* (10), respectively. The reaction of 4-dimethylaminopyridine (DMAP) with L*GeGeL* gives the adduct complex L*(DMAP)GeGe(DMAP)L* (11). Taken as a whole, this study highlights both similarities and significant differences between the reactivities of the amido-digermynes 1 and 2 and those of their previously described terphenyl-substituted counterparts.