Interactions of Rh(III)-dihydrido-bis(phosphine) complexes with semicarbazones

Interaction of cis, trans, cis-[Rh(H)(2)(PR3)(2)(acetone)(2)] PF6 complexes (R = aryl or R-3 = Ph2Me, Ph2Et) under H-2 with E-semicarbazones gives the Rh(III)-dihydrido-bis(phosphine)-semicarbazone species cis, trans-[Rh(H)(2)(PR3)(2)-{R’(R")C=N-N(H)CONH2}]PF6, where R’ and R" are Ph, Et, or Me. The complexes are generally characterized by elemental analysis, P-31{H-1} NMR, H-1 NMR, and IR spectroscopies, and MS. X-ray analysis of three PPh3 complexes reveals chelation of E-semicarbazones by the imine-N atom and the carbonyl-O atom. In contrast, the corresponding reaction of [Rh(H)(2)(PPhMe2)(2)(acetone)(2)]PF6 with acelophenone semicarbazone gives the orthometalated-semicarbazone species cis-[RhH(PPhMe2)(2){o-C6H4(Me)C=N-N(H)CONH2}]PF6. The X-ray structure of E-propophenone semicarbazone is also reported. Rhodium-catalyzed, homogeneous hydrogenation of semicarbazones was not observed even at 40 atm H-2.