Iridium PCP pincer complexes: highly active and robust catalysts for novelhomogeneous aliphatic dehydrogenations

The PCP pincer complexes, IrH2{C6H3(CH2PR2)(2)-2,6} (R = Bu-t, Pr-i) are ex traordinarily active and robust catalysts for aliphatic dehydrogenation rea ctions. Their application to alkane dehydrogenation has resulted in the fir st efficient catalytic systems for homogeneous thermochemical alkane dehydr ogenation without the use of a sacrificial hydrogen acceptor and for dehydr ogenation of n-alkanes to alpha-olefins. The pincer catalysts also effect o ther aliphatic dehydrogenations which had not previously been accomplished via homogeneous catalysis including the conversion of cycloalkanes to arene s, ethylbenzene to styrene and tetrahydrofuran to furan. All of these catal ytic reactions are inhibited by even traces of nitrogen. This is apparently due to the formation of the remarkably stable dinitrogen complexes: [Ir{C6 H3(CH2PR2)(2)-2,6}](2)(mu-N-2). Mechanistic studies have indicated that the high activity of the pincer catalysts may be in part due to 'agostic promo tion' by phosphino aliphatic groups.