Organoiridium Pyridonates and Their Role in the Dehydrogenation of Alcohols

New derivatives of 2 hydroxypyridine (2 hpH) and Cp*Ir(III) are described Under conditions for catalytic dehydrogenation of 1 phenylethanol catalyzed by Cp*IrCl(kappa(2) 2 hp) (1) the main species observed are [Cp*(2)Ir(2)H(2)(2 hp)]Cl ([2]Cl) and Cp*IrHCl(kappa(1) 2 hpH) (3) Crystallographic analysis confirms that the cation in [2]PF(6) consists of a Cp*(2)Ir(2)(mu H)(lambda)(2+) core complemented by a pyridonate ligand that bridges via O and N centers Although [2]Cl is catalytically highly active the related salt [2]PF(6) is not Addition of chloride sources reactivates [2]PF(6) Collectively our experiments indicate that [2]Cl is a resting state that reverts to a more active species which we propose is 1 itself In situ NMR observations and PPh(3) trapping experiments show that under catalytically relevant conditions 1 rapidly converts to 3 which can be observed spectroscopically Compound 3 was independently generated by transfer hydrogenation of 1 In other experiments 1 was found to ring open upon treatment with PPh(3) to give Cp*IrCl(kappa(1) 2 hp)(PPh(3)) which in turn was found to react with AgPF(6) to give [Cp*Ir(kappa(2) 2 hp)(PPh(3))]PF(6) Both PPh(3) derivatives proved catalytically inactive for dehydrogenation Cp*IrCl(kappa(2) 2 hp 6 Me) was also prepared but could not be converted to kappa(1) 2 hpH 6 Me derivatives The complex Cp*IrCl(C(5)H(3)O(2)NH) nominally derived from the conjugate base of 2 6 dihydroxypyridine features the novel ligand eta(3) C(3)H(3)(CO)(2)NH