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

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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.

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