7-6-7 Ring-based transition-metal catalysts for the transfer dehydrogenation of isopropanol

Abstract

A family of 7-6-7 ring-based PCP pincer iridium/rhodium complexes has been applied to the transfer dehydrogenation of isopropanol to give acetone using tert-butylethylene (TBE) as the hydrogen acceptor. For the iridium complexes, high initial activity was achieved with the turnover number (TON) being as high as 6000 after 2 h at 200 °C, even when TBE was present in high concentration (6000 equivalents). The inhibition effect of TBE was found to be somewhat weaker than in the case of alkane dehydrogenation using the same catalysts. Whereas the corresponding rhodium complex was inactive in alkane dehydrogenation, it was unexpectedly found to have a catalytic activity of 2000 TONs (3000/1 TBE/catalyst ratio) after 2 h at 200 °C in the same transfer dehydrogenation. The bonding properties of the reactive complexes were investigated through natural bond orbital (NBO) analysis and compared.