Lewis base mediated β-elimination and Lewis acid mediated insertion reactions of disilazido zirconium compounds.

The reactivity of a series of disilazido zirconocene complexes is dominated by the migration of anionic groups (hydrogen, alkyl, halide, OTf) between the zirconium and silicon centers. The direction of these migrations is controlled by the addition of two-electron donors (Lewis bases) or two-electron acceptors (Lewis acids). The cationic nonclassical Cp2ZrN(SiHMe2)2 (2) is prepared from Cp2Zr{N(SiHMe2)2}H (1) and B(C6F5)3 or [Ph3C][B(C6F5)4], while reactions of B(C6F5)3 and Cp2Zr{N(SiHMe2)2}R (R = Me (3), Et (5), n-C3H7 (7), CH═CHSiMe3 (9)) provide a mixture of 2 and Cp2ZrN(SiHMe2)(SiRMe2). The latter products are formed through B(C6F5)3 abstraction of a β-H and R group migration from Zr to the β-Si center. Related β-hydrogen abstraction and X group migration reactions are observed for Cp2Zr{N(SiHMe2)2}X (X = OTf (11), Cl (13), OMe (15), O-i-C3H7 (16)). Alternatively, addition of DMAP (DMAP = 4-(dimethylamino)pyridine) to 2 results in coordination to a Si center and hydrogen migration to zirconium, giving the cationic complex Cp2Zr{N(SiHMe2)(SiMe2DMAP)}H (19). Related hydrogen migration occurs from Cp2ZrN(SiHMe2)(SiMe2OCHMe2) (18) to give Cp2Zr{N(SiMe2DMAP)(SiMe2OCHMe2)}H (22), whereas X group migration is observed upon addition of DMAP to Cp2ZrN(SiHMe2)(SiMe2X) (X = OTf (12), Cl (14)) to give Cp2Zr{N(SiHMe2)(SiMe2DMAP)}X (X = OTf (26), Cl (20)). The species involved in these transformations are described by resonance structures that suggest β-elimination. Notably, such pathways are previously unknown in early metal amide chemistry. Finally, these migrations facilitate direct Si-H addition to carbonyls, which is proposed to occur through a pathway that previously had been reserved for later transition metal compounds.