Novel chemistry of rhodium induced by a new type of ligand, a phosphino-N-benzoylhydrazone: crystal structure of [Rh (CO){C(CO2Me)CHCO2 Me}{P PPh2CH[C(CO 2Me)C (CO2 Me)]C -(But)N –N C(Ph)O }

Abstract

Treatment of the phosphino-N,N-dimethylhydrazone Z-PPh 2 CH 2 C(Bu t )NNMe 2 with benzohydrazide in the presence of acetic acid gave the phosphino-N-benzoylhydrazone PPh 2 CH 2 C(Bu t )NNHC(O)Ph I. Treatment of the phosphine I with 0.5 equivalent of [{RhCl(CO) 2 } 2 ] gave the rhodium(I) complex [Rh(CO){PPh 2 CH 2 C(Bu t )N–NC(Ph)O}] 1 containing two fused five-membered chelate rings. Complex 1 readily reacted with Br 2 to give the dibromorhodium(III) complex [RhBr 2 (CO){PPh 2 CH 2 C(Bu t )N–NC(Ph) O }] 2. Similarly, it underwent oxidative-addition reactions with MeI or HCCCH 2 Cl to give rhodium(III) complexes of type [RhX(R)(CO){ PPh 2 CH 2 C(Bu t ) N–NC(Ph) O }] (R = Me, X = I 3; R = CHCCH 2 , X = Cl 4). In contrast, treatment of 1 with allyl bromide caused loss of the carbon monoxide ligand to give the η 3 -allylrhodium(III) complex [RhBr(η-3-C 3 H 5 ){ PPh 2 CH 2 C(Bu t ) N–NC(Ph)O }] 5. Treatment of 1 with MeO 2 CCCCO 2 Me gave the cyclometallated alkenylrhodium(III) complex [Rh(CO){C(CO 2 Me)CHCO 2 Me }{ PPh 2 CH[C(CO 2 Me) C(CO 2 Me)]C(Bu t ) N–NC(Ph)O }] 6, in which the phosphine ligand is tetradentate through P, N, O and C; in the formation of 6 one alkyne has attacked the methylene carbon of the phosphine ligand and the second has added to Rh–H to give RhC(CO 2 Me)CH(CO 2 Me). On the prolonged heating 6 isomerised to give the rhodium(III) complex 7; in this isomer the C(CO 2 Me)CH(CO 2 Me) ligand is trans to phosphorus whereas in 6 it is cis. The crystal structure of 6 has been determined.