Organometallic chemistry of methylene-bridged rhodium/osmium and iridium/ruthenium complexes

The binuclear complex [RhOs(CO)4(dppm)2][BF 4] (1) (dppm = Ph2PCH2PPh2) reacts with diazomethane to give three products depending on temperature. At -80°C the methylene-bridged product [RhOs(CO)3(mu-CH 2)(mu-CO)(dppm)2][BF4] (2) is obtained. Warming this complex to -40°C in the presence of diazomethane yields the butanediyl species [RhOs(C4H8)(CO)3(dppm) 2][BF4] (3). If either 1 or 2 is treated with diazomethane at ambient temperature, the sole product obtained is [RhOs(CH2CH=CH2)(CH3)(CO) 3(dppm)2][BF4] (4) in which the allyl group is bound to Rh and the methyl group is bound to Os. Attempts to model the above processes by reaction of a number of substrates with 2 support our assumption of substrate coordination at Rh and insertion into the Rh-CH2 bond.;The heterobinuclear complexes [IrRu(CO)3(mu-H)(dppm) 2] and [IrRuH(CO)3(mu-CO)(dppm)2] are prepared from the reactions of [PPN][HRu(CO)4] with [IrCl(dppm)2] and [Ir(CO)(dppm)2][Cl], respectively (PPN = (Ph3P) 2N; dppm = Ph2PCH2PPh2). Protonation of each monohydride species yields [IrRu(CO)3(mu-H)2(dppm) 2][BF4], which under an atmosphere of carbon monoxide gives [IrRu(CO)4(dppm)2][BF4] (5). The complex [IrRu(CO)3(mu-CH2)-(mu-CO)(dppm) 2][BF4] (6) is obtained by the reaction of compound [IrRu(CO)4(dppm)2][BF4] with diazomethane. Although [IrRu(CO)3(mu-CH2)(mu-CO)(dppm)2][BF 4] does not react further with diazomethane under these conditions, carbonyl abstraction using trimethylamine oxide in the presence of CH 2N2 yields the methylene-bridged, ethylene adduct, [IrRu(C 2H4)(CO)3(mu-CH2)-(dppm)2][BF 4] (7). The compounds [IrRuL(CO)3(mu-CH 2)-(dppm)2][BF4] (L = NCMe, PMe3, CH 2CHCN) can also be prepared from 6 in the presence of Me 3NO or by ethylene displacement from 7.;Protonation of [RhOs(CO)3(mu-CH2)(mu-CO)(dppm) 2][CF3SO3] (2) with triflic acid at -80°C yields the methyl complex [RhOs(CO)4(mu-CH 3)(dppm)2]-[CF3SO3]2 in which the methyl group is primarily bound to Os while involved in an agostic interaction with Rh. Warming this species to -20°C results in methyl migration to a terminal site on Rh yielding [RhOs(CH3)(CO) 2(mu-CO)2(dppm)2]-[CF3SO3] 2 and subsequent warming to ambient temperature results in migratory insertion to yield the acetyl-bridged [RhOs(CF3SO3)(CO) 2(mu-C(CH3)O)(mu-CO)(dppm)2][CF3SO 3]. The coordinated triflate anion can be replaced at low temperature by CO and PMe3 to give [RhOs(L)(CO)2(mu-C(CH 3)O)(mu-CO)(dppm)2][CF3SO3] 2 (L = CO, PMe3). Spectroscopic and structural evidence suggests an oxycarbene formulation for the acetyl group. Warming the PMe3 adduct results in isomerization involving the acetyl bridging group, which is C-bound to Rh, to a group which is C-bound to Os. Similar acetyl complexes have been obtained with the analogous Ir/Ru system.