Interactions of hydridocarbonyltriphenylphosphine complexes of rhodium and iridium with conjugated dienes and allene

Abstract

The hydrides IrH(CO)₂(PPh₃)₂ and RhH(CO)(PPh₃)₃ react with allene and with certain conjugated dienes to give π-ally complexes M(allyl)(CO)(PPh₃)₂. The allyl and 2-methylallyl complexes have also been prepared by reaction of the appropriate Grignard reagent with trans-MCl(CO)(PPh₃)₂. N.m.r. studies show that the allyl groups are dynamic at normal temperatures. The compound Ir(π-2-methylallyl)(CO)(AsPh₃)₂ was also prepared by the Grignard reaction.

The reactions of these species with carbon, monoxide, hydrogen, and hydrogen chloride have been studied by i.r. and n.m.r. techniques. The solids IrR(CO)₂(PPh₃)₂[R = C₃H₅(allyl) or C₄H₇(2-methylallyl)] and Ir(COR)(CO)₂(PPh₃)₂[R = C₃H₅(allyl), C₄H₇(2-methylallyl and but-2-enyl), C₅H₉(1,2-dimethylallyl), or C₇H₁₃(1-isopropyl-2-methylallyl)] have been isolated. The IrR(CO)₂(PPh₃)₂ complexes have σ-allyl groups in the solid state but exist in solution largely as dynamic π-allyl systems. The acyl complexes Ir(COR)(CO)₂(PPh₃)₂[R = C₄H₇(but-2-enyl), C₅H₉, or C₇H₁₃] are formed as mixtures of cis- and trans-isomers about the double bond; CO insertion occurs at the unsubstituted end of the allylic system. There is spectroscopic evidence for the existence of Ir(σ-allyl)(CO)₃(PPh₃) species in solution.