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)=NNMe 2 with benzohydrazide in the presence of acetic acid gave the phosphin o-N-benzoylhydrazone PPh2CH2C(Bu-t)=NNHC(=O)Ph I. Treatment of the pho sphine 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 f ive-membered chelate rings. Complex 1 readily reacted with Br-2 to giv e 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 cont rast, treatment of 1 with allyl bromide caused loss of the carbon mono xide ligand to give the eta(3)-allylrhodium(III) complex [RhBr(eta-3-C 3H5){PPh2CH2C(Bu-t)=N-N=C(Ph)O}] 5. Treatment of 1 with MeO2CC=CCO2Me gave the cyclometallated alkenylrhodium(III) complex 2Me}{PPh2CH[C(CO2 Me)=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 h as attacked the methylene carbon of the phosphine ligand and the secon d has added to Rh-H to give RhC(CO2Me)=CH(CO2Me). On the prolonged hea ting 6 isomerised to give the rhodium(III) complex 7; in this isomer t he C(CO2Me)=CH(CO2Me) ligand is trans to phosphorus whereas in 6 it is cis. The crystal structure of 6 has been determined.