Rhodium and Iridium Phosphine Olefin Complexes. Phosphorus-31 Nuclear Magnetic Resonance Assignment of Trigonal-Bipyramidal Structures

The structures of the five-coordinate compounds RhCl(mbp)z (mbp = Ph2PCH2CH2CH=CH2), RhBr(mbp)z, RhCl(map)z (map = PhzPOCH2CH=CH2), and RhCl(tpb) (tbp = P(CH~CH~CH=CHZ)~) were investigated in solution by infrared and 31P NMR spectroscopy. On the basis of 31P NMR temperature studies, several isomers are observed which, depending on the compound and the temperature, undergo differing degrees of exchange with each other. Four-coordinate isomers of RhCl(mpb)2 and RhBr(mbp)2 are present at 32 "C by infrared analysis although absent at -75 O C by 31P NMR analysis. Comparisons are made between Rh and Ir, C1 and Br, and mbp and map as to their control upon the isomers present in solution