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.

一系列二硅氮化锆钼化合物的反应活性主要由阴离子基团（氢、烷基、卤素、OTf）在锆和硅中心之间的迁移所主导。这些迁移的方向受两电子供体（路易斯碱）或两电子受体（路易斯酸）的添加所控制。阳离子非经典[Cp2ZrN(SiHMe2)2]+ ([2]+)由Cp2Zr{N(SiHMe2)2}H (1)与B(C6F5)3或[Ph3C][B(C6F5)4]反应制备，而B(C6F5)3与Cp2Zr{N(SiHMe2)2}R (R = Me (3), Et (5), n-C3H7 (7), CH2CHSiMe3 (9))的反应则提供[2]+和[Cp2ZrN(SiHMe2)(SiRMe2)]+的混合物。后者通过B(C6F5)3对β-H和R基团从锆迁移至β-Si中心的抽提作用形成。对于Cp2Zr{N(SiHMe2)2}X (X = OTf (11), Cl (13), OMe (15), O-i-C3H7 (16))，观察到相关的β-氢抽提和X基团迁移反应。另一方面，将DMAP (DMAP = 4-(二甲基氨基)吡啶)添加到[2]+中，导致与硅中心的配位以及氢向锆的迁移，从而得到阳离子复合物[Cp2Zr{N(SiHMe2)(SiMe2DMAP)}H]+ ([19]+)。相关的氢迁移发生在[Cp2ZrN(SiHMe2)(SiMe2OCHMe2)]+ ([18]+)向[Cp2Zr{N(SiMe2DMAP)(SiMe2OCHMe2)}H]+ ([22]+)的转变中，而X基团迁移则是在向[Cp2ZrN(SiHMe2)(SiMe2X)]+ (X = OTf ([12]+), Cl ([14]+))添加DMAP时观察到的，从而得到[Cp2Zr{N(SiHMe2)(SiMe2DMAP)}X]+ (X = OTf ([26]+), Cl ([20]+))。参与这些转变的物种可通过共振结构描述，这些结构暗示了β-消除过程。值得注意的是，此类途径在早期金属酰胺化学中尚属未知。最终，这些迁移促进了直接向羰基的Si-H加成，这被认为是通过之前仅限于后期过渡金属化合物的途径发生的。