Novel chemistry of rhodium induced by a new type of ligand, a phosphino-N-benzoylhydrazone: crystal structure of [Rh(Co){C(CO2Me)=CHCO2Me} {PPh2CH[C(CO2Me)=C(CO2Me)]C(Bu-t)=N-N=C(Ph)O}]

Treatment of the phosphino-N,N-dimethylhydrazone Z-PPh2CH2C(Bu-t)=NNMe2 with benzohydrazide in the presence of acetic acid gave the phosphino-N-benzoylhydrazone PPh2CH2C(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){PPh2CH2C-(Bu-t)=N-N=C(Ph)O}] 1 containing two fused five-membered chelate rings. Complex 1 readily reacted with Br-2 to give the dibromorhodium(III) complex [RhBr2(CO){PPh2CH2C(Bu-t)=N-N=C(Ph)O}] 2. Similarly, it underwent oxidative-addition reactions with Mel or HC=CCH2Cl to give rhodium(III) complexes of type [RhX(R)(CO){PPh2CH2C(Bu-t)=N-N=C(Ph)O}] (R = Me, X = I 3; R = CH-C=CH2, X = Cl 4). In contrast, treatment of 1 with allyl bromide caused loss of the carbon monoxide ligand to give the eta(3)-allylrhodium(III) complex [RhBr(eta-3-C3H5){PPh2CH2C(Bu-t)=N-N=C(Ph)O}] 5. Treatment of 1 with MeO2CC=CCO2Me gave the cyclometallated alkenylrhodium(III) complex [Rh(CO){C(CO2Me)=CHCO2Me}{PPh2CH[C(CO2Me)=C(CO2Me)]C(Bu-t)=N-N=C(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(CO2Me)=CH(CO2Me). On the prolonged heating 6 isomerised to give the rhodium(III) complex 7; in this isomer the C(CO2Me)=CH(CO2Me) ligand is trans to phosphorus whereas in 6 it is cis. The crystal structure of 6 has been determined.