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 R3 = Ph2Me, Ph2Et) under H2 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, 31P{1H} NMR, 1H 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 acetophenone semicarbazone gives the ortho-metalated-semicarbazone species cis-[RhH(PPhMe2)2{o-C6H4(Me)CN−N(H)CONH2}]PF6. The X-ray structure of
E-propiophenone semicarbazone is also reported. Rhodium-catalyzed, homogeneous hydrogenation of semicarbazones was not observed even at 40 atm H2.