CARBONYLATION OF HYDROCARBONS VIA C-H ACTIVATION CATALYZED BY RHCL(CO)(PME3)2 UNDER IRRADIATION

C-H bonds in hydrocarbons are carbonylated into aldehydes by reaction with carbon monoxide in the presence of RhCl(CO)(PR3)2 under irradiation. The reaction proceeds at an ambient temperature under an atmospheric pressure of CO. The catalytic activity of RhCl(CO)(PR3)2 decreases in the order PMe3 = 1,3,4-trimethylphospholane = 1,3,4-trimethylphospholene > P(CH2O)3CMe > PEt3 = PBu3 ≈ P(i-Pr)3 = PPh3 ≈ P(OMe)3 > dppe. The thiocyanate complex exhibits a similar catalytic activity to the chloro complex. The use of other complexes of Co, Ir, and Ru resulted in much lower catalytic activities. In the carbonylation of benzene, benzophenone and benzyl alcohol are formed as byproducts. The yield of benzaldehyde reached 3.3% on the basis of benzene. Monosubstituted benzenes are converted mainly to meta-substituted benzaldehydes. In the reaction of ≪-alkanes, a terminal methyl group is selectively carbonylated to give a linear aldehyde. These regioselectivities are explainable in terms of thermodynamic stability of hydridoalkyl (or alkyl) intermediates. The linear aldehyde obtained from n-alkane undergoes a secondary photoreaction (Norrish Type II) to afford a terminal olefin and acetaldehyde. The catalytic activity, regioselectivity of the carbonylation, and the occurrence of Norrish Type II reaction are markedly affected by irradiation wavelength. RhCl(PMe3)2 formed via CO dissociation is proposed as a possible active species for the C-H activation. © 1990, American Chemical Society. All rights reserved.