Rhodium Complexes Bearing 1,10-Phenanthroline Analogue Bis-NHC Ligands Are Active Catalysts for Transfer Hydrogenation of Ketones

Synthesis of a new example of the pyridazine annelated bis­(N-heterocyclic carbene) ligand <b>3b</b> (vegi) bearing benzyl substituents is reported, as well as the synthesis of its cationic Rh­(cod) complex <b>5b</b>. The mechanism of formation of the [Rh­(cod)­(vegi)]⁺ complexes was investigated, showing a stepwise deprotonation of the imidazolium moieties via the mono-carbene imidazolium Rh­(cod)Cl species <b>4</b>. The [Rh­(cod)­(vegi)]⁺ complexes <b>5a</b>,<b>b</b> show catalytic activity in the transfer hydrogenation of even sterically hindered ketones

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

The in situ generated CNC pincer lithium complex [Li­(bimca)] (<b>2</b>) (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 <b>3</b>. 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 <b>4</b> have been prepared from the hydrido complexes <b>3</b> 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 [Pd₂(bimca)₂]­K₂ (<b>6</b>) 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)]⁻ (<b>5b</b>). 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

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

The in situ generated CNC pincer lithium complex [Li­(bimca)] (<b>2</b>) (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 <b>3</b>. 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 <b>4</b> have been prepared from the hydrido complexes <b>3</b> 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 [Pd₂(bimca)₂]­K₂ (<b>6</b>) 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)]⁻ (<b>5b</b>). 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

Dinuclear Coinage-Metal Complexes of Bis(NHC) Ligands: Structural Features and Dynamic Behavior of a Cu–Cu Complex

Binuclear complexes of copper, silver, and gold bearing a 2,2′-bipyridine analogue, the pyridazine annelated bis­(N-heterocyclic carbene) ligand (vegi) <b>1</b>, were prepared and structurally characterized. They all feature the shortest metal–metal distances that have been measured so far in complexes with this structural motif bearing neutral bidentate ligands, indicative of d¹⁰–d¹⁰ interactions. While in the silver complex the linear coordination of each silver atom with two carbene ligands results in a planar complex, the ligand planes are twisted by 70° in the Cu complex <b>4</b> and by 31° in the gold complex <b>3</b>. The copper complex shows a solvent-dependent equilibrium between the [Cu₂L₂]²⁺ complex and a [Cu₂L₃]²⁺ complex along with solvated CuPF₆

Dinuclear Coinage-Metal Complexes of Bis(NHC) Ligands: Structural Features and Dynamic Behavior of a Cu–Cu Complex

Binuclear complexes of copper, silver, and gold bearing a 2,2′-bipyridine analogue, the pyridazine annelated bis­(N-heterocyclic carbene) ligand (vegi) <b>1</b>, were prepared and structurally characterized. They all feature the shortest metal–metal distances that have been measured so far in complexes with this structural motif bearing neutral bidentate ligands, indicative of d¹⁰–d¹⁰ interactions. While in the silver complex the linear coordination of each silver atom with two carbene ligands results in a planar complex, the ligand planes are twisted by 70° in the Cu complex <b>4</b> and by 31° in the gold complex <b>3</b>. The copper complex shows a solvent-dependent equilibrium between the [Cu₂L₂]²⁺ complex and a [Cu₂L₃]²⁺ complex along with solvated CuPF₆