Substituent Effects in the Hydrosilylation of Coordinated Dinitrogen in a Ditantalum Complex: Cleavage and Functionalization of N₂

The dinitrogen complex ([NPN]Ta)2(μ-η1:η2-N2)(μ-H)2, 1, (where [NPN] = (PhNSiMe2CH2)2PPh) undergoes hydrosilylation with primary and secondary alkyl- and arylsilanes, giving a new N−Si bond and a new terminal tantalum hydride derived from one Si−H unit. Various primary silanes can be employed to give isolable complexes of the general formula ([NPN]TaH)(μ-N−N−SiHnR3-n)(μ-H)2(Ta[NPN]) (5, RBu, n = 2; 9, RPh, n = 2). Analogous complexes featuring secondary silanes are not isolable, because these products, and 5 and 9, are uniformly unstable toward reductive elimination of bridging hydrides as H2, followed by cleavage of the N−N bond to give ([NPN]TaH)(μ-N)(μ-N−SiHnR3-n)(Ta[NPN]) (6, RBu, n = 2; 10, RPh, n = 2; 15, RPh, n = 1; 16, RPh and Me, n = 1). The bridging nitrido ligand in these complexes is itself a substrate for a second hydrosilylation when n = 2, and schemes leading to Ta(IV) complexes of the general formula ([NPN]Ta)2(μ-N−SiH2R)(μ-N−SiH2R') via elimination of H2 are reported (4, RR‘ = Bu; 12, RBu, R‘ = Ph; 13, RBu, R‘ = CH2CH2SiH3). At this point, the general reaction manifold for these compounds ramifies, with distinct outcomes occurring for different R groups[NPN] ligand amide migration from Ta to RSi affords 11, whereas stable complex 6 rearranges to give 7, in the presence of excess silane. Ethanediylbissilane reacts with 1 to give 14, isostructural to 7.