Reactions of cationic dirhodium and diiridium complexes [Cp*M(μ-Cl)(μ-SPri)2MCp*][OTf] (M=Rh, Ir) with terminal alkynes. Comparison with the diruthenium system

Reactions of the cationic dirhodium and diiridium complexes [Cp*M(μ-Cl)(μ-SPri)2MCp*][OTf] (2, M=Rh; 3, M=Ir; Cp*=η5-C5Me5, OTf=OSO2CF3) with terminal alkynes were investigated. Treatment of 2 and 3 with methyl propiolate afforded the cationic complexes [Cp*MCl(μ-SPri){μ-S(Pri)CCHCOOMe}MCp*][OTf] (4, M=Rh; 5, M=Ir), in which the substituted vinyl ligand forms an M(1)CSM(2) bridge and is further coordinated to the M(1) center at the carbonyl oxygen. On the other hand, [Cp*IrCl(μ-SPri){μ-C(SPri)CH2} IrCp*][OTf] (8), in which the olefinic CC bond of the α-(isopropylthio)vinyl ligand also works as an η2 ligand, was obtained by the reaction of 3 with acetylene gas. Complex 3 reacted with 1,1-diphenyl- or 1,1-ditolyl-2-propyn-1-ol to give the hydroxycarbene complexes [Cp*IrCl(μ-SPri)2Ir{C(OH)CHCAr2}Cp*][OTf](11) Ar=Ph; 12, Ar=Tol), while the reactions of complexes 2 and 3 with 3-butyn-1-ol and 4-pentyn-1-ol produced cyclic alkoxycarbene complexes [Cp*MCl(μ-SPri)2M{}Cp*][OTf] (15, M=Rh, n=1; 16, M=Ir, n=1; 17, M=Ir, n=2). All of the products are considered to be formed via the initial formation of a dinuclear vinylidene or allenylidene complex followed by the nucleophilic attack of an SPri ligand, H2O molecule, or the ω-OH group at the Cα atom of the vinylidene-type ligand. The intermediate vinylidene and allenylidene species are regarded to have higher reactivity in the nucleophilic addition reactions than the corresponding diruthenium complexes, and the difference in the reactivities is interpreted in terms of the extended Hückel molecular orbital calculations of model complexes. The molecular structures of complexes 3, 4, 5, [Cp*IrCl(μ-SPri){μ-C(SPri)CH2}IrCp*][PF6]·THF (8′·THF), 12, and 16 were determined by X-ray diffraction studies.