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.