H-H INTERACTION IN 4-MEMBERED P-H-H-M (M=OSMIUM, RUTHENIUM) RINGS

The dihydrido-1-butene complex OsH2(eta(2)-CH2=CHEt)(CO)((PPr3)-Pr-i)( 2) (1) reacts with PHPh2 to give OsH2(CO)(PHPh2)((PPr3)-Pr-i)(2) (2), which can also be prepared from the reaction of OsH(eta(2)-H2BH2)(CO)( (PPr3)-Pr-i)(2) (3) with PHPh2. Similarly, treatment of RuH(eta(2)-H2B H2)(CO)((PPr3)-Pr-i)(2) (4) with PHPh2 affords RuH2(CO)(PHPh2)((PPr3)- Pr-i)(2) (5). Complex 2 reacts with HBF4 in dichloromethane-d(2) as th e solvent to give the cis-hydrido-dihydrogen derivative [OsH(eta(2)H(2 ))(CO)(PHPh2)((PPr3)-Pr-i)(2)]BF4 (6), which in solution exchanges the relative positions of the hydride and dihydrogen ligands. The protona tion of 2 with HBF4 in acetone affords the solvate complex (eta(1)-OC( CH3)(2))(CO)(PHPh2)((PPr3)-Pr-i)(2)]BF4 (7). The reaction of 7 with ca rbon monoxide leads to a mixture of the -dicarbonyl-[OsH(CO)(2)(PHPh2) ((PPr3)-Pr-i)(2)]BF4 (8) land -dicarbonyl-[OsH(CO)(2)(PHPh2)((PPr3)-Pr -i)(2)]BF4 (9). The reactions of 7 with CH3CN, LiC=CPh, and KBr give [ OsH(CH3CN)(CO)(PHPh2)((PPr3)-Pr-i)(2)]BF4 (10), OsH(C2Ph)(CO) (PHPh2)( (PPr3)-Pr-i)(2) (11), and OsHBr(CO)(PHPh2)((PPr3)-Pr-i)(2) (12), respe ctively. The structures of 5 and 8 have been determined by X-ray diffr action analysis. In both cases, the coordination geometry around the m etal 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 hydride ligand, suggesting that there is a H ... H interaction between the hydride and the HP hyd rogen atom. For 5 the II-II separation is about 2.6 Angstrom, while fo r 8 the H-H separation is about 2.9 Angstrom. Spectroscopic studies al so suggest that one of the hydride ligands of 2 and the HP hydrogen at om of the diphenylphosphine interact. In this case, the estimated H-H separation is 2.5 Angstrom. 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.