Diphosphine-bridged, heterobimetallic complexes containing iridium and osmium. Reversible orthometalation of a bridging bis(diphenylphosphino)methane group at the iridium center promoted by the adjacent osmium center
The compound (PPN)[HOs(CO)4] reacts readily with [IrCl(i)1 2-dppm)2] (PPN+ = (Ph3P)2N+, dppm = Ph2PCH2PPh2) at ambient temperature, yielding the heterobinuclear complex [IrOs(H)2(CO)3(#t2-’?3-(oCeH^PhPCI^PPh^(dppm)] (1), in which one phenyl group is ortho-metalated at the Ir center. Treatment of 1 with the electrophile sources HBF4-Et¡>0 or [AuPPh3]BF4 reverses the ortho metalation to give the hydrido-bridged species, [IrOs(CO)3Gt-H)(M-X)(dppm)2][BF4] (X = H (2), AuPPh3 (3)). Deprotonation of 2 with use of NaH regenerates compound 1. The AuPPh3 group in 3 is readily replaced by an iodo group in the reaction with I2 to give [IrOs(CO)3^-H)(/¿-I)(dppm)2] [BF4] (4). Under a CO atmosphere, compound 2 yields [IrOs(CO)6(dppm)2] [BF4] (5), and reaction of 5 with Me3N0-2H20 results in loss of one carbonyl group from the Ir center to yield [IrOs(CO)4(dppm)2] [BF4] (6). The structure of 5 has been determined by X-ray techniques. This compound crystallizes, together with 1.5 equiv of CH2C12, in the monoclinic space group P2,/c, with cell parameters o = 12.063 (2) Á, b = 22.725 (3) Á, c = 22.050 (3) Á, ß = 101.66 (1)°, V = 5920 A3, and Z = 4. The structure has refined to R = 0.043 and f?w = 0.063 on the basis of 5515 unique observations with 444 parameters varied. Compound 5 has a trans-bridging arrangement of diphosphine ligands and has two carbonyls bound to Ir and three on Os. The carbonyl and phosphine arrangement on Os suggests a trigonal bipyramidal (TBP) arrangement characteristic of Os(0), which then forms a dative Os Ir bond to the Ir(+I) center, giving it a TBP geometry also. The Os-Ir separation of 2.9652 (4) A is at the long end of the range expected for a normal single bond.
Robert W. Hilts, Roberta A. Franchuk, and Martin Cowie. Diphosphine-bridged, heterobimetallic complexes containing iridium and osmium. Reversible orthometalation of a bridging bis(diphenylphosphino)methane group at the iridium center promoted by the adjacent osmium center. Organometallics 1991 10 (5), 1297-1304. DOI: 10.1021/om00051a018
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