| Two efficient transition metal catalyst systems for alkane functionalization have been developed and investigated. Rh(PMe3) 2(CO)Cl catalyzes photocarbonylation of n-alkane and the pincer-ligated iridium complexes, (Y-RPCP)IrH4 (Y = H or MeO, R = tBu or iPr, Y-RPCP = η3-1,3,5-C 6H2-(CH2-PR2)2Y) catalyze alkane transfer- and acceptorless-dehydrogenation.; Mechanistic studies of photochemical carbonylation of n-hexane catalyzed by Rh(PMe3)2(CO)Cl suggested the reaction proceeds via at least two different mechanisms. One requires a secondary photochemical reaction and gives primarily linear aldehyde, while the other is radical-based, much less regioselective, and apparently involves only one photochemical step. In accord with this mechanistic understanding, linear aldehyde can be photochemically synthesized from linear alkane and CO for the first time with both high regioselectivity (98%) and high photoefficiency.; Two new PCP ligated catalysts, (MeO-t BuPCP)IrH4 (2c), and (MeO- iPrPCP)IrH4 (3c), have been synthesized and their catalytic dehydrogenation activities, along with previously reported (H-t BuPCP)IrH4(1c), have been investigated. 3c exhibits exceptionally high activity for linear alkane transfer-dehydrogenation with norbornene (NBE) as the acceptor at 150°C. Conversions as high as 40% have been achieved. 3c also shows the highest activity in the cyclodecane (CDA) acceptorless dehydrogenation with unprecedented turnover numbers about 3,000, while 2c gives the highest turnovers for cyclooctane (COA) and n-undecane acceptorless dehydrogenation (430 and 107 turnovers, respectively). All these results, to our knowledge, represent the best achievements so far in the field of alkane dehydrogenation catalyzed by homogeneous transition metal complexes. |
