Selective Transformation of Nickel-Bound Formate to CO or C-C Coupling Products Triggered by Deprotonation and Steered by Alkali-Metal Ions

摘要

The complexes [(LNi)-Ni-tBu(OCO-kappa O-2,C)]M-3[N(SiMe3)(2)](2) (M=Li, Na, K), synthesized by deprotonation of a nickel formate complex [(LNiOOCH)-Ni-tBu] with the corresponding amides M[N(SiMe3)(2)], feature a Ni-II-CO22- core surrounded by Lewis-acidic cations (M+) and the influence of the latter on the behavior and reactivity was studied. The results point to a decrease of CO2 activation within the series Li, Na, and K, which is also reflected in the reactivity with Me3SiOTf leading to the liberation of CO and formation of a Ni-OSiMe3 complex. Furthermore, in case of K+, the {[K-3[N(SiMe3)(2)](2)}(+) shell around the Ni-CO22- entity was shown to have a large impact on its stabilization and behavior. If the number of K[N(SiMe3)(2)] equivalents used in the reaction with [(LNiOOCH)-Ni-tBu] is decreased from 3 to 0.5, the deprotonated part of the precursor enters a complex reaction sequence with formation of [(LNiI)-Ni-tBu(mu-OOCH)(NiLtBu)-L-I]K and [(LNi)-Ni-tBu(C2O4)NiLtBu]. The same reaction at higher concentrations additionally led to the formation of a unique hexanuclear Ni-II complex containing both oxalate and mesoxalate ([O2C-CO2-CO2](4-)) ligands.