Relative stability of half-sandwich η6-benzene Ru(II) complexes of tridentate (2-pyridyl)alkylamine ligands of varying chelate ring-size: Nucleophilic addition of hydride ion onto the benzene ring

Crystal structure of cis,fac-{N,N-bis-[(pyridin-2-yl)meth-yl]methyl-amine-κ(3) N,N',N''}di-chlorido-(dimethyl sulfoxide-κS)ruthenium(II)

The reaction of di-chlorido-tetra-kis-(dimethyl sulfoxide)-ruthen-ium(II) with N,N-bis[(pyridin-2-yl)meth-yl]methyl-amine aff-ords the title complex, [RuCl2(C13H15N3)(C2H6OS)]. The asymmetric unit contains a well-ordered complex mol-ecule. The N,N-bis-[(pyridin-2-yl)meth-yl]methyl-amine (bpma) ligand binds the cation through its two pyridyl N atoms and one aliphatic N atom in a facial manner. The coordination sphere of the low-spin d (6) Ru(II) is distorted octahedral. The dimethyl sulfoxide (dmso) ligand coordinates to the cation through its S atom and is cis to the aliphatic N atom. The two chloride ligands occupy the remaining sites. The bpma ligand is folded with the dihedral angle between the mean planes passing through its two pyridine rings being 64.55 (8)°. The two N-Ru-N bite angles of the ligand at 81.70 (7) and 82.34 (8)° illustrate the distorted octa-hedral coordination geometry of the Ru(II) cation. Two neighboring molecules are weakly associated through mutual intermolecular hydrogen bonding involving the O atom and one of the methyl groups of the dmso ligand. One of the chloride ligands is also weakly hydrogen bonded to a pyridyl H atom of another molecule.

The coordination chemistry of organo-hydride donors: new prospects for efficient multi-electron reduction

In biological reduction processes the dihydronicotinamides NAD(P)H often transfer hydride to an unsaturated substrate bound within an enzyme active site. In many cases, metal ions in the active site bind, polarize and thereby activate the substrate to direct attack by hydride from NAD(P)H cofactor. This review looks more widely at the metal coordination chemistry of organic donors of hydride ion--organo-hydrides--such as dihydronicotinamides, other dihydropyridines including Hantzsch's ester and dihydroacridine derivatives, those derived from five-membered heterocycles including the benzimidazolines and benzoxazolines, and all-aliphatic hydride donors such as hexadiene and hexadienyl anion derivatives. The hydride donor properties--hydricities--of organo-hydrides and how these are affected by metal ions are discussed. The coordination chemistry of organo-hydrides is critically surveyed and the use of metal-organo-hydride systems in electrochemically-, photochemically- and chemically-driven reductions of unsaturated organic and inorganic (e.g. carbon dioxide) substrates is highlighted. The sustainable electrocatalytic, photochemical or chemical regeneration of organo-hydrides such as NAD(P)H, including for driving enzyme-catalysed reactions, is summarised and opportunities for development are indicated. Finally, new prospects are identified for metal-organo-hydride systems as catalysts for organic transformations involving 'hydride-borrowing' and for sustainable multi-electron reductions of unsaturated organic and inorganic substrates directly driven by electricity or light or by renewable reductants such as formate/formic acid.