SIMULTANEOUS PHOTODISSOCIATION OF H2 AND PME2PH FROM OSH4(PME2PH)3 - PRODUCTION OF DIMERIC AND PARAMAGNETIC OSMIUM POLYHYDRIDES

Chemical trapping with PMe2Ph (“P”), PEt3, and H2 (to 60 atm) has been used to prove the concurrent photodissociation of both H2 and PMe2Ph from OsH4P3 in benzene, THE, and ethanol; the ratio of the former to the latter processes is 1:1.7. The final products observed on photolysis of OsH4P3 under vacuum is an equilibrium mixture of Os2H4P6 and Os2H4P6. The crystal structure of the former shows it to be comprised of two octahedra sharing an edge, the edge being composed of two bridging hydrides; the Os-Os distance is 2.818 (1) Å. The structure of an analogue of the latter has been determined: Os2H4(PMePh2)5has a face-shared octahedral structure with a distance between chemically inequivalent osmiums of 2.551 (1) Å. By a study of the photolysis of OsH4(PEt3)3, which shows PEt3 dissociation but no H2 dissociation, it was concluded that a transient dihydride is the crucial intermediate in leading to dimeric products. Dimeric Os2H4P6 is itself photosensitive, leading to products of P-CH3 cleavage (Os2H4(PMe2Ph)4(µ-PMePh)2), as well as to a product of Os-H heterolysis, [Os2H3P6+][trans-OsH4P2-], the latter containing a unique paramagnetic polyhydride anion. © 1990, American Chemical Society. All rights reserved.