Synthesis and reactivity of five- and six-coordinate hydrido(vinyl) iridium(III) complexes

The reaction of the dihydrido iridium(III) precursor [IrH2(Cl)(PiPr3)2] (5) with internal alkynes RCtriple bond; length of mdashC(CO2Me) (R = Me, CO2Me) afforded the five-coordinate hydrido(vinyl) complexes [IrH(Cl){(E)-C(R)double bond; length as m-dashCH(CO2Me)}(PiPr3)2] (6, 7), via insertion of the alkyne into one of the Irsingle bondH bonds. Compounds 6 and 7 are also accessible by careful hydrogenation of the alkyne iridium(I) derivatives trans-[IrCl{RCtriple bond; length of mdashC(CO2Me)}(PiPr3)2] (9, 10), the latter being prepared from in situ generated trans-[IrCl(C8H14)(PiPr3)2] and RCtriple bond; length of mdashC(CO2Me). UV irradiation of 6 (R = CO2Me) led to the formation of the isomer [IrH(Cl){κ2(C,O)-C(CO2Me)double bond; length as m-dashCHC(OMe)double bond; length as m-dashO}(PiPr3)2] (3) having the vinyl ligand coordinated in a bidentate fashion. While 6 reacted with acetonitrile and CO to afford the six-coordinate iridium(III) compounds [IrH(Cl){(E)-C(CO2Me)double bond; length as m-dashCH(CO2Me)}(L′)(PiPr3)2] (11, 12), treatment of 6 with LiC5H5 gave the half-sandwich-type complex [(η5-C5H5)IrH{(E)-C(CO2Me)double bond; length as m-dashCH(CO2Me)}(PiPr3)] (13) by, the loss of one PiPr3. The reaction of 3 with CO under pressure resulted in the formation of [IrH(Cl){(Z)-C(CO2Me)double bond; length as m-dashCH(CO2Me)}(CO)(PiPr3)2] (14) in which, in contrast to the stereoisomer 12, the two CO2Me substituents are trans disposed.