Reversible Modulation of the Electronic and Spatial Environment around Ni(0) Centers Bearing Multifunctional Carbene Ligands with Triarylaluminum.

Designing and modulating the electronic and spatial environments surrounding metal centers is a crucial issue in a wide range of chemistry fields that use organometallic compounds. Herein, we demonstrate a Lewis-acid-mediated reversible expansion, contraction, and transformation of the spatial environment surrounding nickel(0) centers that bear -phosphine oxide-substituted -heterocyclic carbenes (henceforth referred to as (S)PoxIms). Reaction between tetrahedral (-κ-,-(S)PoxIm)Ni(CO) and Al(CF) smoothly afforded heterobimetallic Ni/Al species such as trigonal-planar {κ--Ni(CO)}(μ--(S)PoxIm){κ--Al(CF)} via a complexation-induced rotation of the -phosphine oxide moieties, while the addition of 4-dimethylaminopyridine resulted in the quantitative regeneration of the former Ni complexes. The corresponding interconversion also occurred between (SPoxIm)Ni(η:η-diphenyldivinylsilane) and {κ--Ni(η:η-diene)}(μ--SPoxIm){κ--Al(CF)} via the coordination and dissociation of Al(CF). The shape and size of the space around the Ni(0) center was drastically changed through this Lewis-acid-mediated interconversion. Moreover, the multinuclear NMR, IR, and XAS analyses of the aforementioned carbonyl complexes clarified the details of the changes in the electronic states on the Ni centers; i.e., the electron delocalization was effectively enhanced among the Ni atom and CO ligands in the heterobimetallic Ni/Al species. The results presented in this work thus provide a strategy for reversibly modulating both the electronic and spatial environment of organometallic complexes, in addition to the well-accepted Lewis-base-mediated ligand-substitution methods.