Abstract
The synthesis of a novel pyridine diphosphite ligand 1 has been described. From this ligand, rhodium– and iridium–chlorido complexes of formula [MCl(1)] (M = Rh, Ir) have been prepared. Chloride abstraction by treatment with NaBPh~4~ and a phosphane produced the corresponding cationic phosphane derivatives [M(1)L][BPh~4~] [L = PPh~3~ (Rh, Ir), PPh~2~Me (Ir)]. The analogous reaction of [RhCl(1)] with CNXy (Xy = 2,6‐Me~2~‐C~6~H~3~) and NaBPh~4~ yielded the monosubstituted complex [Rh(1)(CNXy)][BPh~4~], whereas the reaction between [IrCl(1)] and isonitriles led to the disubstituted complexes [Ir(1)(L)~2~][BPh~4~] (L = CNBn, CNCy). Ethylene compound [Rh(1)(C~2~H~4~)][BPh~4~] was obtained from the reaction of [RhCl(1)] with NaBPh~4~ under ethylene, whereas [Ir(1)(C~2~H~4~)][BPh~4~] was synthesized by a treatment of [{IrCl(COE)~2~}~2~] with ethylene followed by addition of 1 and NaBPh~4~. An IR analysis of the isocyanide complexes indicates a very poor π‐donor ability of the [M(1)]^+^ fragment, therefore the isocyanide metal bond is mostly due to σ donation from the isocyanide. Characterization by X‐ray crystallography of [Rh(1)(PPh~3~)][BPh~4~], [Rh(1)(MeCN)][BPh~4~] and [Ir(1)(PPh~2~Me)][BPh~4~] displays a square‐planar structure with ligand 1 coordinated in a pincer fashion for these complexes. In addition, the ethylene derivative [Rh(1)(C~2~H~4~)][BPh~4~] shows a near in‐plane conformation of the ethylene ligand, with a short C–C distance (1.319 Å). Moreover, in all the structures, the diphosphite ligand exhibits a meso conformation irrespective of the size of the neutral ancillary ligand. An examination of the behaviour of some of these complexes in catalytic hydrogenation has shown that [IrCl(1)] is an active catalyst in the reduction of 2‐methylquinoline and 2‐methylquinoxaline.