Evidence for the Formation of Anionic Zerovalent Group 10 Complexes as Highly Reactive Intermediates

The in situ generated CNC pincer lithium complex [Li(bimca)] (2) (bimca = bis(3-methylimidazolin-2-ylidene)carbazolide) reacts with M = Pt(0), Pd(0), and Ni(0) precursors under formal oxidative addition to (bimca)hydrido M(II) complexes 3. This unusual reaction involves proton abstraction that can derive from various sources including the ligand itself. Mechanistic considerations are given. The respective [M(bmica)Cl] complexes 4 have been prepared from the hydrido complexes 3 and subjected to reduction in order to identify a proposed zerovalent anionic [M(bimca)](-) complex. In the case of M = Pt, only the (bimca)hydrido Pt(II) complex is observed, whereas, for [Pd(bimca)Cl], a dimeric Pd(0) complex [Pd-2(bimca)(2)]K-2 (6) bearing an anionic carbazole moiety is formed in the solid state. NMR DOSY experiments show that, in solution, this dimer dissociates to the monomeric anionic complex [Pd(bimca)](-) (5b). We conclude that such anionic zerovalent complexes are plausible intermediates in the synthesis of group 10 metal(II) complexes from the respective metal(0) species with anionic CNC ligands.