Formation of Osmium Alkylidene, Alkylidyne, and Dinitrogen Complexes from Reactions of OsCl2(PPh3)3 with Diazoalkanes

The reactions of OsCl2(PPh3)(3) with a series of diazoalkanes were investigated. The reactions with monosubstituted diazoalkanes N2CHR gave the desired osmium alkylidene complexes OsCl2(= CHR)(PPh3)(2), the stability of which is dependent on the substituent on the alkylidene carbons. The five- coordinate osmium alkylidene complex OsCl2(= CHCOOMe)(PPh3)(2) is thermally stable, whereas the analogous complex OsCl2(=CH-p-tol)( PPh3)(2) readily rearranges to its hydrido-alkylidyne form OsHCl2( C-p-tol)(PPh3)(2). A substitution reaction of OsCl2(= CHCOOMe)(PPh3)(2) with PCy3 produced the hydrido-alkylidyne complex OsHCl2( CCOOMe)(PCy3)(2), revealing the effect of the phosphine on the relative stability of OsCl2(= CHCOOMe)(PR3)(2) and OsHCl2( CCOOMe)(PR3)(2). The reaction of OsCl2(PPh3)(3) with the acceptoracceptor disubstituted diazoalkane dibenzoyl diazomethane, bearing COPh substituents, led to the formation of the metallacyclic complex OsCl2{kappa(2)-N,O-[N2C(COPh)C(Ph)O]}(PPh3)(2) due to the chelating effect of dibenzoyl diazomethane. The complex OsCl2(PPh3)(3) catalyzed the homocoupling of the diazoalkane N2CPh2 to give the azine Ph2C = N-N = CPh2. The eta(1)-N-2 coordinated binuclear complex (Ph3P)(2)ClOs(mu-Cl)(3)Os(PPh3)(2)(N-2) was isolated as a minor product, which was considered to be an off-cycle product in the catalytic reaction.

Automated summary

The reactions of OsCl2(PPh3)(3) with various diazoalkanes led to the formation of osmium alkylidene complexes with different stabilities. The substituents on the alkylidene carbons and the presence of phosphines affect the stability of the complexes.