G.K.N. Reddy

Cyclometallation of bis-benzimidazole derivatives with rhodium(III) halides

Abstract Treatment of rhodium(III) halides with the N-heterocycles (LH), 1,3-bis(benzimidazolyl)benzene (bBzlH 2 bzH; Ia ) and its N-methyl derivative (bBzlMe 2 bzH; Ib ) in methanol gave halobridged binuclear cyclometallated products of the composition [RhX 2 L] 2 (X=Cl, Br or I). The chloro complex undergoes halobridge cleavage reactions to yield several new mononuclear complexes of the types RhCl 2 (bBzlH 2 bz)(AsPh 3 ), RhCl(bBzlH 2 bz)(OClO 3 )(L′/N-N) (L′=AsPh 3 ; N-N=2,2′-bipyridine or 1,10-phenanthroline) and the heterocycle bridged binuclear complexes of the composition [RhCl 2 (bBzlH 2 bz)] 2 ( μ -N-N) (N-N=pyrazine or 4,4′-bipyridine). Passage of CO through [RhCl 2 (bBzlH 2 bz)] 2 in DMF yielded mononuclear carbonyl complex RhCl 2 (CO)(bBzlH 2 bz)·2H 2 O. Treatment of carbonylated solution of rhodium trichloride with Ia produced non-cyclometallated mononuclear complex of the type [Rh(CO) 2 (bBzlH 2 bzH)]Cl. The complexes are characterised by 1 H, 13 C NMR, IR, Far-IR, electronic and FAB-mass spectral studies.

Reactions of rhodium and iridium salts with multidentate N-heterocycles

Abstract Complexes of rhodium and iridium of the types MX 3 L, MX(CO) 2 L and MX 3 (CO)L (X = halide) containing multidentate N -heterocycles (L),2,6-bis(benzimidazolyl)pyridine(bBzlH 2 py) and 2,6-bis( N -methyl-benzimidazolyl)pyridine (bBzlMe 2 py) have been prepared and characterized by IR, electronic and 1 H and 13 C NMR spectral data. RhX(CO) 2 L, on treatment with alcoholic solvents or DMF undergoes reversible decarbonylation to produce RhXL·2H 2 O. Passage of NO or O 2 through the carbonyl suspended in hot 2-methoxyethanol releases CO 2 .

Synthesis and reactions of binuclear diolefin rhodium(I) compounds bridged by nitrogen heterocycles. Crystal structure of dichloro-di-1,5-cyclooctadiene(μ-pyrazine)-dirhodium(I) [{Rh(1,5-C8H12)Cl}2(μ-C4H4N2)]

Binuclear complexes of rhodium(I) of the type [(dien)(X)Rh(μ-N-N)Rh(X)(dien)] (dien = 1,5-cyclooctadiene or norbornadiene; N-N = pyrazine, 4,4′-bipyridine or Phenazine and X = Cl or Br) with bridging heterocycles have been isolated and their reactions with carbon monoxide, 2,2′-bipyridine and 1,10-phenanthroline investigated. The crystal structure of [(COD)(Cl)Rh(μ-pyrazine)Rh(Cl)(COD)] has been determined.

Carbonyl complexes of rhodium(I) and rhodium(III) with 2,2′-biquinoline

Abstract Novel carbonyl complexes of rhodium(I) and rhodium(III) containing the bidenate nitrogen donor ligand 2,2′-biquinoline (biq) have been prepared; they are of the types RhX(CO) 2 biq and RhX(CO)biq (X = Cl, Br, I). Cationic carbonyl and substituted carbonyl complexes of the types [Rh(CO) 2 biq]ClO 4 and [Rh(CO)biqL 2 ]ClO 4 , where L is tertiary phosphine or arsine have also been isolated. In spite of considerable steric crowding around the nitrogen atoms, 2,2′-biquinoline behaves much like 2,2′-bipyridine in forming carbonyl complexes of rhodium.

Complexes of ruthenium(II) and ruthenium(III) with tertiary arsines

Abstract Ruthenium trichloride reacts with stoichiometric amounts of tertiary arsines in boiling ethanol to give paramagnetic complexes, RuCl 3 (Ph 2 RAs) 3 (R = Me, Et, Pr, Bu), which react further with 2,2′-bipyridyl(bipy) and o -phenanthroline(phen) to yield brick red crystalline products, RuCl 3 (N-N)(Ph 2 RAs) (N-N = bipy, phen). In the presence of excess arsine Ru(III) is reduced to Ru(II), and trichloro-bridged complexes of the formula [Ru 2 Cl 3 (Ph 2 RAs) 6 ]Cl are formed. These on treatment with carbonylated solutions of rhodium chloride produce yellow crystals of [Ru 2 Cl 3 (Ph 2 RAs) 6 ][RhCl 2 (CO) 2 ] containing Ru(II) and Rh(I). Several dicarbonyl complexes cis -RuX 2 (CO) 2 (Ph 2 RAs) 2 (X = Cl, Br; R = Pr, Bu) have also been isolated.

Carbonyl, hydridocarbonyl and dioxygen complexes of iridium with tertiary arsines

Two isomeric series (α and β) of hydrido carbonyls of iridium of the type IrHX2(CO)L2 (X is Cl or Br and L is AsMePh2 or AsEtPh2) have been prepared. The infrared spectra of the α compounds show a vCO band ca. 2040 cm−1 and a vIrH band ca. 2190 cm−1 whereas the spectra of the β compounds show a vCO band ca. 2110 cm−1 and a vIrH band ca. 2005 cm−1. Similarly the NMR spectra of the α compounds have a hydridic proton resonance peak ca. 26τ while those of the β compounds have the corresponding peak ca. 19τ. The α compounds get converted to compounds of the type trans-IrX(CO)L2 on treatment with sodium methoxide. These latter compounds add on the corresponding halogen as well as molecular oxygen to give compounds of the type IrX3(CO)L2 and IrX(O2)(CO)L2 respectively. Configurations have been assigned to the α and β type of hydrido carbonyls. A comparison of the vCOP4 frequencies suggests that the effective oxidation state of the metal in these carbonyl complexes increases in the order IrX(CO)L2 < IrX(O2)(CO)L2 < IrHX2(α) < IrX3(CO)L2 < IrHX2(CO)L2(β).

Hydride and related complexes of rhodium(III) with nitrogen donor ligands

Abstract The reactions of the two isomeric series (α and β) of complex hydrides of rhodium of the type RhH X 2 L 3 ( X is a halogen and L is a tertiary arsine or phosphine) with the nitrogen donor ligands 2,2′-dipyridyl ( N - N ) and 1,10-phenanthroline ( N - N ) have been investigated. In presence of perchloric acid the α hydrides give new hydrido compounds of the type [RhH X ( N - N ) L 2 ]ClO 4 , while the β hydrides give complexes of the type [Rh X 2 ( N - N ) L 2 ]ClO 4 . Under similar conditions trihalo compounds of rhodium of the type Rh X 3 L 3 also give compounds similar to those obtained from the corresponding β hydrides. Configurations for the cationic species have been assigned on the basis of results of i.r. and NMR measurements.

Cationic complexes of platinum and palladium with p-tolyl isocyanide

Cationic complexes of platinum and palladium of the type [MCl(p-CH3C6H4NC)L2]ClO4 (M = Pt, Pd; L = p-tolyl3P, o-tolyl3P, Cy3P, Ph2MeAs, Ph2EtAs, Ph2PrAs, Cy3As; Cy = cyclohexyl) have been isolated. These show a v(CN) band at ca. 2200 cm-1 compared with 2130 cm-1 for the free isocyanide ligand, suggesting weak π-character in the metal-carbon bond. The PMR spectra of the cationic complexes indicate trans configurations for the complexes.

Complexes of osmium with tertiary arsines and carbonmonoxide

Osmium halides (Cl and Br) react with monotertiary arsines Ph2RAs (R=Me, Et, Pr and Bu) in alcoholic medium to give paramagnetic octahedral complexes of the type OsX3L3 (X=Cl, Br; L=Ph2RAs) which further react with carbonmonoxide to give dihalo dicarbonyl complexes of osmium(II) of the type OsX2 (CO)2 L2. Similarly, osmium halides react with tertiary arsines in the presence of formaldehyde to give monocarbonyl complexes of osmium(II) of the type OsX2 (CO)L3. Structures have been assigned to all these compounds on the basis of IR and NMR studies.

Binuclear and polynuclear complexes of rhodium with nitrogen heterocycles as bridging ligands

A number of binuclear and polynuclear complexes of rhodium(I) with bridging nitrogen heterocycles are known. X-ray crystal structure analysis of some of the complexes has established the bridging nature of the heterocycles. The proximity of the metal atoms is found to considerably influence the electronic spectra of the complexes. Oxidative addition reactions of these compounds are yet to be properly investigated. Some of these compounds are efficient hydrogenation and hydroformylation catalysts.