Carbene iridium(I) and iridium(III) complexes containing the metal center in different stereochemical environments

The mixed-ligand complex [IrCl(C2H4)(SbiPr(3))(PiPr(3))] (2), prepared from [IrCl(C2H4)-(PiPr(3))](2) (1) and SbiPr3, reacts not only with CO, diphenylacetylene, and H-2 by ligand substitution or oxidative addition but also with diaryldiazomethanes R2CN2 to give the four-coordinate iridium(I) carbenes [IrCl(=CR2)(SbiPr(3))(PiPr(3))] (8-10) in 60-70% isolated yield. In contrast, treatment of 2 and of the related cyclooctene derivative trans-[IrCl(C8H14)-(SbiPr(3))(2)] (12) with C5Cl4N2 affords the diazoalkane complexes trans-[IrCl(N2C5C14)(SbiPr(3))-(EiPr(3))] (11, E = P; 13, E = Sb) without elimination of N-2. Displacement of the stibine ligand in 8-10 by PiPr3 leads to the corresponding bis(phosphine) compounds trans-[IrCl(=CR2)(PiPr(3))(2)] (14-16), while the reaction of 8 (R = C6H5) with NaC5H5 yields the half-sandwich-type complex [(eta(5)-C5H5)Ir(=CPh2)(PiPr(3))] (17). Protonation of 17 with HCl occurs stepwise to give via the iridium(III) alkyl [(eta(5)-C5H5)IrCl(CHPh2)(PiPr(3))] (20) the ring-substituted isomer [(eta(5)-C5H4CHPh2)IrHCl(PiPr(3))] (21); however, if 17 is treated with HBF4, a cationic complex is formed which probably contains a eta(3)-coordinated benzylic ligand. The square-planar iridium(I) carbenes 8 and 14 react with HBX4 (X = F, Ar-F) to afford the ionic products [IrHCl(=CPh2)(PiPr(3))(EiPr(3))]BX4 (23, 24, E = P; 25, E = Sb) and with HCl to give the relatively labile octahedral species [IrHCl2(=CPh2)(PiPr(3))(EiPr(3))] (26, E = P; 27, E = Sb). Treatment of 8 and 14 with ethene yields, besides [IrCl(C2H4)(2)(SbiPr(3))(2)] (18) and/or trans-[IrCl(C2H4)(PiPr(3))(2)] (28), a mixture of two isomeric olefinic products CH2=CHCHPh2 (29) and CH3CH=CPh2 (30), the ratio of which is independent of the ligand sphere of the iridium precursor. The molecular structures of 13, 14, 17, and 24 have been determined by X-ray crystallography.