Synthesis of bimetallic complexes bridged by 2,6-bis(benzimidazol-2-yl) pyridine derivatives and their catalytic properties in transfer hydrogenation.

A series of binuclear rhodium(i) and iridium(i) complexes with 2,6-bis(benzimidazol-2-yl) pyridine (bzimpy) derivatives were synthesized and characterized by elemental analysis and spectroscopic methods. The molecular and crystal structures of complex 3d were determined by the single crystal X-ray diffraction technique. Their monometallic analogues were prepared to compare the catalytic properties of the bimetallic complexes. To determine the catalyst properties that result in a cooperative, bimetallic enhancement of the reaction rate, the systematic variation of the intermetallic distance and the ligand donor properties of the bimetallic complexes were explored based on the transfer hydrogenation reactions of ketones.

N-benzyl substituted N-heterocyclic carbene complexes of iridium(I): assessment in transfer hydrogenation catalyst.

Iridium(I) complexes of N-heterocyclic carbenes (NHCs) (1a-3a) were obtained by transmetalation reactions from the corresponding Ag(I)-NHC complexes. These complexes have been fully characterized by (1)H, (13)C, heteronuclear multiple-bond correlation NMR spectroscopies, and elemental analysis. X-ray diffraction studies on single crystals of 1a and 2a confirm the square planar geometry at the metal center. [IrCl(CO)2(NHC)] complexes 1b-3b were also synthesized to compare σ-donor/π-acceptor strength of NHC ligands. Transfer hydrogenation (TH) reactions of various ketones and imines have been studied using complexes 1a-3a as precatalysts. N-Benzyl substituted NHC complexes of Ir(I) proved to be highly efficient precatalysts in the reduction of aromatic and aliphatic ketones to afford the corresponding alcohol products with turnover frequencies values up to 24,000 h(-1).

Iridium(I) N-heterocyclic carbene complexes of benzimidazol-2-ylidene: effect of electron donating groups on the catalytic transfer hydrogenation reaction.

Two new [Ir(NHC)(COD)Cl] (NHC = N-heterocyclic carbene; COD = 1,5-cyclooctadiene) iridium complexes (2a,b) have been prepared by the reaction of [Ir(COD)Cl]2 with in situ prepared NHC-Ag carbene transfer agents in dichloromethane at ambient temperature. They have been fully characterized by (1)H, (13)C NMR, and elemental analysis. X-ray diffraction studies on single crystals of 2a and 2b confirm the square planar geometry. Complexes of type [Ir(NHC)(CO)2Cl] [NHC = 1,3-diisopropyl(5,6-dimethyl)benzimidazol-2-ylidene] 3 were also synthesized to compare σ-donor/π-acceptor strength of NHC ligands. Transfer hydrogenation (TH) reactions of various aldehydes and ketones have been studied using complexes 2a and 2b as catalysts. The 5,6-dimethyl substituted iridium complex (2b) showed the highest catalytic activity for the TH reaction.

Supramolecular structure of racemic 5-hydroxy-4-(4-methoxyphenyl)-10-oxa-4-azatricyclo[5.2.1.0(2,6)]dec-8-en-3-one.

The structure of the title compound, C(15)H(15)NO(4), comprises a racemic mixture of chiral molecules containing five stereogenic centres. The cyclohexane ring tends towards a boat conformation and the two tetrahydrofuran rings adopt envelope conformations. Molecules are linked into sheets parallel to (100) by a combination of O-H...O, C-H...O and C-H...pi hydrogen bonds, leading to a two-dimensional supramolecular structure.

trans-Bis[1-benzyl-3-(2,3,4,5,6-pentafluorobenzyl)benzimidazol-2-ylidene]dibromopalladium(II).

The title compound, [PdBr2(C21H13F5N2)2], crystallizes with two independent centrosymmetric conformational isomers having a square-planar coordination at the Pd atom. The conformational isomers differ by the ligands having a cis or trans orientation of their benzyl and pentafluorobenzyl rings with respect to the benzimidazole ring plane. The benzimidazole rings are rotated with respect to the coordination plane of the metal by 79.1 (2) and 75.2 (1) degrees for molecules A and B, respectively. The Pd-Br bond lengths are 2.4218 (8) and 2.4407 (10) A for molecules A and B, respectively, and the Pd-C bond lengths are 2.030 (8) and 2.018 (9) A. The crystal structure contains two types of C-H...F and one type of C-H...Br intramolecular contact, as well as C-H...pi interactions.

The two-dimensional coordination polymer poly[[bis(3-methylpyridine)cadmium(II)]-tetra-mu-cyano-nickel(II)].

The title complex, [CdNi(CN)4(C6H7N)2]n, adopts a slightly distorted octahedral geometry around the Cd centre. Four cyanide N atoms occupy the equatorial coordination sites around the Cd centre. The structure consists of corrugated and cyanide-bridged polymeric networks made up of tetracyanonickelate ions coordinated to cadmium, with the Ni ion coordinated by four cyanide ligands in a square-planar arrangement. The Cd and Ni atoms occupy special positions of 2/m site symmetry. The 3-methylpyridine group, except for two methyl H atoms, lies on a crystallographic mirror plane. The 3-methylpyridine molecules, bound to cadmium in trans positions, are located on both sides of the network. The bonding in the networks occurs because of a departure of the Ni-C-N-Cd sequence of atoms from linearity at the C and N atoms.

trans-[1,3-Bis(2,4-dimethylphenyl)imidazolidin-2-ylidene]dichloro(triphenylphosphine-kappaP)palladium(II).

The title complex, [PdCl(2)(C(19)H(22)N(2))(C(18)H(15)P)], shows slightly distorted square-planar coordination of the palladium(II) metal center. The Pd-C bond distance between the N-heterocyclic ligand and the metal atom is 2.008 (3) A. The dihedral angle between the two dimethylphenyl ring planes is 33.17 (13) degrees.