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

The dihydrido-1-butene complex OsH 2 (η 2 -CH 2 CHEt)(CO)(P i Pr 3 ) 2 ( 1 ) reacts with PHPh 2 to give OsH 2 (CO)(PHPh 2 )(P i Pr 3 ) 2 ( 2 ), which can also be prepared from the reaction of OsH(η 2 -H 2 BH 2 )(CO)(P i Pr 3 ) 2 ( 3 ) with PHPh 2 . Similarly, treatment of RuH(η 2 -H 2 BH 2 )(CO)(P i Pr 3 ) 2 ( 4 ) with PHPh 2 affords RuH 2 (CO)(PHPh 2 )(P i Pr 3 ) 2 ( 5 ). Complex 2 reacts with HBF 4 in dichloromethane- d 2 as the solvent to give the cis -hydrido−dihydrogen derivative [OsH(η 2 -H 2 )(CO)(PHPh 2 )(P i Pr 3 ) 2 ]BF 4 ( 6 ), which in solution exchanges the relative positions of the hydrido and dihydrogen ligands. The protonation of 2 with HBF 4 in acetone affords the solvate complex [OsH{η 1 -OC(CH 3 ) 2 }(CO)(PHPh 2 )(P i Pr 3 ) 2 ]BF 4 ( 7 ). The reaction of 7 with carbon monoxide leads to a mixture of the cis -dicarbonyl-[OsH(CO) 2 (PHPh 2 )(P i Pr 3 ) 2 ]BF 4 ( 8 ) and trans -dicarbonyl-[OsH(CO) 2 (PHPh 2 )(P i Pr 3 ) 2 ]BF 4 ( 9 ). The reactions of 7 with CH 3 CN, LiC⋮CPh, and KBr give [OsH(CH 3 CN)(CO)(PHPh 2 )(P i Pr 3 ) 2 ]BF 4 ( 10 ), OsH(C 2 Ph)(CO) (PHPh 2 )(P i Pr 3 ) 2 ( 11 ), and OsHBr(CO)(PHPh 2 )(P i Pr 3 ) 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.