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

Reactions of the cationic dirhodium and diiridium complexes [Cp*M(mu-Cl)(mu -SPri)(2)MCp*][OTf] (2, M = Rh; 3, M = Ir; Cp* = eta(5)-C5Me5, OTf = OSO2CF 3) with terminal alkynes were investigated. Treatment of 2 and 3 with methy l propiolate afforded the cationic complexes [Cp*MCl(mu-SPri){mu-S(Pr-i)C=C HCOOMe}MCp*][OTf], (4, M = Rh; 5, M = Ir), in which the substituted vinyl l igand 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(mu-SPri){mu-C(SP ri)=CH2} IrCp*][OTf] (8), in which the olefinic C=C bond of the alpha-(isop ropylthio)vinyl ligand also works as an eta(2) 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(mu-S Pri)(2)Ir{=C(OH)CH=CAr2}Cp*][OTf](11) Ar = Ph; 12, Ar = Tol), while the rea ctions of complexes 2 and 3 with 3-butyn-1-ol and 4-pentyn-1-ol produced cy clic alkoxycarbene complexes [Cp*MCl(mu-SPri)(2)M {=(CH2)(n) + 2O}Cp*][OTf] (15, M = Rh, n = 1; 16, M = Ir, n = 1; 17, M = Ir, n = 2). All of the prod ucts are considered to be formed via the initial formation of a dinuclear v inylidene or allenylidene complex followed by the nucleophilic attack of an SPri ligand, H2O molecule, or the omega-OH group at the C-alpha atom of th e vinylidene-type ligand. The intermediate vinylidene and allenylidene spec ies are regarded to have higher reactivity in the nucleophilic addition rea ctions than the corresponding diruthenium complexes, and the difference in the reactivities is interpreted in terms of the extended Huckel molecular o rbital calculations of model complexes. The molecular structures of complex es 3, 4, 5, [Cp*IrCl(mu-SPri){mu-C(SPri)=CH2}IrCp*][PF6].THF (8'.THF), 12, and 16 were determined by X-ray diffraction studies. (C) 2000 Elsevier Scie nce S.G. All rights reserved.