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

Designing and modulatingthe electronic and spatial environmentssurrounding metal centers is a crucial issue in a wide range of chemistryfields that use organometallic compounds. Herein, we demonstrate aLewis-acid-mediated reversible expansion, contraction, and transformationof the spatial environment surrounding nickel(0) centers that bear N-phosphine oxide-substituted N-heterocycliccarbenes (henceforth referred to as (S)PoxIms). Reaction between tetrahedral(syn-& kappa;-C,O-(S)PoxIm)Ni(CO)(2) and Al(C6F5)(3) smoothly afforded heterobimetallic Ni/Al species such astrigonal-planar {& kappa;-C-Ni(CO)(2)}(& mu;-anti-(S)PoxIm){& kappa;-O-Al(C6F5)(3)} via a complexation-induced rotation ofthe N-phosphine oxide moieties, while the additionof 4-dimethylaminopyridine resulted in the quantitative regenerationof the former Ni complexes. The corresponding interconversion alsooccurred between (SPoxIm)Ni(& eta;(2):& eta;(2)-diphenyldivinylsilane) and {& kappa;-C-Ni(& eta;(2):& eta;(2)-diene)}(& mu;-anti-SPoxIm){& kappa;-O-Al(C6F5)(3)} via the coordination and dissociation of Al(C6F5)(3). The shape and size of the spacearound the Ni(0) center was drastically changed through this Lewis-acid-mediatedinterconversion. Moreover, the multinuclear NMR, IR, and XAS analysesof the aforementioned carbonyl complexes clarified the details ofthe changes in the electronic states on the Ni centers; i.e., theelectron delocalization was effectively enhanced among the Ni atomand CO ligands in the heterobimetallic Ni/Al species. The resultspresented in this work thus provide a strategy for reversibly modulatingboth the electronic and spatial environment of organometallic complexes,in addition to the well-accepted Lewis-base-mediated ligand-substitutionmethods.