H···H Interaction in Four-Membered P−H···H−M (M = Osmium, Ruthenium) Rings

Abstract

The dihydrido-1-butene complex OsH2(η2-CH2CHEt)(CO)(PiPr3)2 (1) reacts with PHPh2 to give OsH2(CO)(PHPh2)(PiPr3)2 (2), which can also be prepared from the reaction of OsH(η2-H2BH2)(CO)(PiPr3)2 (3) with PHPh2. Similarly, treatment of RuH(η2-H2BH2)(CO)(PiPr3)2 (4) with PHPh2 affords RuH2(CO)(PHPh2)(PiPr3)2 (5). Complex 2 reacts with HBF4 in dichloromethane-d2 as the solvent to give the cis-hydrido−dihydrogen derivative [OsH(η2-H2)(CO)(PHPh2)(PiPr3)2]BF4 (6), which in solution exchanges the relative positions of the hydrido and dihydrogen ligands. The protonation of 2 with HBF4 in acetone affords the solvate complex [OsH{η1-OC(CH3)2}(CO)(PHPh2)(PiPr3)2]BF4 (7). The reaction of 7 with carbon monoxide leads to a mixture of the cis-dicarbonyl-[OsH(CO)2(PHPh2)(PiPr3)2]BF4 (8) and trans-dicarbonyl-[OsH(CO)2(PHPh2)(PiPr3)2]BF4 (9). The reactions of 7 with CH3CN, LiC⋮CPh, and KBr give [OsH(CH3CN)(CO)(PHPh2)(PiPr3)2]BF4 (10), OsH(C2Ph)(CO) (PHPh2)(PiPr3)2 (11), and OsHBr(CO)(PHPh2)(PiPr3)2 (12), respectively. The structures of 5 and 8 have been determined by X-ray diffraction analysis. In both cases, the coordination geometry around the metal center is octahedral, with the two triisopropylphosphine ligands in a trans position. Also in both cases, the H−P hydrogen atom of the diphenylphosphine ligand points toward one hydrido ligand, suggesting that there is a H···H interaction between the hydrido and the HP hydrogen atom. For 5 the H−H separation is about 2.6 Å, while for 8 the H−H separation is about 2.9 Å. Spectroscopic studies also suggest that one of the hydrido ligands of 2 and the HP hydrogen atom of the diphenylphosphine interact. In this case, the estimated H−H separation is 2.5 Å. In 2 and 5, the H···H interaction blocks the free rotation of the diphenylphosphine group around the Os−P axis, while in 8 it only permits a light oscillation.