Fluxional behaviour of phosphole and phosphine ligands on triosmium clusters

Abstract:

The unsaturated cluster [Os<inf>3</inf>(μ-H)<inf>2</inf>(CO)<inf>10</inf>] reacts with a variety of π-conjugated phosphole ligands: 2,5-bis(2-thienyl)-1-phenylphosphole, 2,5-bis(2-pyridyl)-1-phenylphosphole, and 1,2,5-triphenylphosphole, to give the monosubstituted [Os<inf>3</inf>(μ-H)(H)(CO)<inf>10</inf>(P)] and [Os<inf>3</inf>(μ-H)<inf>2</inf>(CO)<inf>9</inf>(P)] derivatives. Variable-temperature ¹H NMR studies for the decacarbonyltriosmium complexes show that the hydride ligands undergo fluxional behavior and its decarbonylation gave the nonacarbonyl unsaturated species with equivalent hydrides. An X-ray crystallographic analysis of [Os<inf>3</inf>(μ-H)<inf>2</inf>(CO)<inf>9</inf>(P)] (2b) (P = 1,2,5-triphenylphosphole) is reported. From 2,5-bis(2-pyridyl)-1-phenylphosphole four isomers are obtained, the ¹H NMR spectrum at low temperature indicates that the phosphole ligand may occupy pseudoaxial and equatorial sites at one of the osmium atoms bearing the bridging hydride. The reaction of [Os<inf>3</inf>(CO)<inf>10</inf>(CH<inf>3</inf>CN)<inf>2</inf>] with cyanoethyldiphenylphosphine affords mono- and bis(phosphine)-substituted clusters. The X-ray crystal structure of the monosubstituted [Os<inf>3</inf>(CO)<inf>11</inf>(η¹-PC<inf>15</inf>H<inf>14</inf>N)] (3) derivative is discussed. The dynamic behavior observed for [Os<inf>3</inf>(CO)<inf>10</inf>(η¹-PC<inf>15</inf>H<inf>14</inf>N)<inf>2</inf>] (4) is studied by variable-temperature ¹H and ³¹P{¹H} NMR spectroscopy. The latter studies show a mixture of two geometric isomers, which are in dynamic equilibrium at room temperature where the 1,2-trans-trans isomer (4a) is favored, whose molecular structure has been determined by X-ray crystallography.

Año de publicación:

2015

Keywords:

• Mono- and disubstituted triosmium
• Unsaturated osmium cluster
• Phosphine
• Fluxional behavior
• Phosphole

Fuente:

scopus