Synthesis, characterization, and reactivity toward MeI of carbonyl Rh(I) complexes containing a PNO hydrazonic ligand

The reaction of the potentially tridentate hydrazonic ligand 2-(diphenylpho sphino)-benzaldehyde benzoylhydrazone (HL, 1) with Rh-2(CO)(4)Cl-2 in dieth yl ether led to the isolation of Rh(HL)(CO)Cl (2), where the neutral ligand was PN bidentate. Addition of Et3N or NaOMe caused the deprotonation of th e ligand, with the consequent formation of the three-coordinated carbonyl R h(I) complex Rh(L)(CO) (3), which was X-ray characterized. The 2 3 conversi on was reversible, as it was found that 2 could be regenerated by bubbling a stoichiometric amount of HCl into an ethereal solution of 3. On treating a solution of 2 with Silver triflate, the cationic carbonyl complex [Rh(HL) (CO)](CF3SO3) (4) was obtained, where the neutral ligand showed a tridentat e PNO behavior. All the complexes were allowed to react with MeI at room te mperature. Complex 2 led to two different acetyl stereoisomers Rh(HL)(MeCO) ClI. (5), where the neutral ligand coordinated in a PNO fashion. Complex 3 led to different products depending on the reaction solvent; thus the penta coordinated acetyl complex Rh(L)(MeCO)I(8) and the solvated octahedral acet yl complex [Rh(L)(MeCO)(THF)I]-(THF) (9) were isolated in CH2Cl2 and in THF , respectively; the X-ray structure of 9 is reported. On carrying out the r eaction in Et2O, the immediate precipitation of the hexacoordinated methylc arbonyl complex Rh(L)(CO)(Me)I (7) was observed, which rapidly rearranged i nto 8 after dissolution in CH2Cl2 or CHCl3. Finally, the reaction between 4 and Mel formed the cationic PNO coordinated acetyl complex [Rh(HL)(MeCO)I] (CF3SO3) (10) All the oxidative addition reactions were monitored by liquid IR spectroscopy.