Diphosphine-bridged, heterobimetallic complexes containing iridium and osmium. Reversible ortho metalation of a bridging bis(diphenylphosphino)methane group at the Iridium Center promoted by the Adjacent Osmium Center

Article abstract of DOI:10.1021/om00051a018

The compound (PPN)[HOs(CO)₄] reacts readily with [IrCl(η²-dppm)₂] (PPN⁺ = (Ph₃P)₂N⁺, dppm = Ph₂PCH₂PPh₂) at ambient temperature, yielding the heterobinuclear complex [IrOs(H)₂(CO)₃(μ₂-η ³-(o-C₆H₄)PhPCH₂PPh ₂)(dppm)] (1), in which one phenyl group is ortho-metalated at the Ir center. Treatment of 1 with the electrophile sources HBF₄-Et₂O or [AuPPh₃]BF₄ reverses the ortho metalation to give the hydrido-bridged species, [IrOs(CO)₃(μ-H)(μ-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(μ-H)(μ-I)(dppm)₂] [BF₄] (4). Under a CO atmosphere, compound 2 yields [IrOs(CO)₅(dppm)₂] [BF₄] (5), and reaction of 5 with Me₃NO·2H₂O 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 CH₂Cl₂, in the monoclinic space group P2₁/c, with cell parameters a = 12.063 (2) A?, b = 22.725 (3) A?, c = 22.050 (3) A?, β = 101.66 (1)°, V = 5920 A?³, and Z = 4. The structure has refined to R = 0.043 and R_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.