Polymer-bound iridium catalysis. Hydrogen transfer from formic acid to unsaturated carbon-carbon bonds

Abstract

Polystyrene-bound IrCl(CO)(PPh3)2 promotes hydrogen transfer from formic acid to a variety of olefinic substances. The activity of the catalyst increases after the first few uses during which time a substrate-iridium complex is formed. Detailed kinetic studies were carried out with benzylideneacetophenone as the hydrogen acceptor. The catalysis is assumed to proceed by the following steps: (a) cleavage (dissociation) of an Ir-P bond in the supported complex ®-(PPh2) 2IrCl(CO); (b) coordination of the acceptor at the vacated site; (c) oxidative addition of formic acid followed by olefin insertion leading to the formation of an iridium oxopropenyl formate complex; (d) hydrogen transfer from the formate to the iridium accompanied by loss of carbon dioxide; (e) reductive elimination to give the final product. Step d is considered rate detemining on the basis of kinetic isotope effect measurements with HCOOD, DCOOH, and DCOOD. The catalytic activity of the system is decreased by swelling solvents and increased by nonswelling ones. The fully activated, supported catalyst is air stable, essentially leach proof, and capable of being used for an unlimited number of catalytic cycles.

Kinetic study of hydrogen transfer from benzyl alcohol to aliphatic aldehydes catalysed by heterogenised ruthenium(II) catalysts

“…The results listed in Table 4 were plotted in Figure 6. The figure indicated a rate increase up to 0.52 M of the aldehyde concentration and a rate decrease above 0.52 M. Such rate dependence has also been reported in some other related hydrogen transfer process (Beaupere et al, 1983;Azran et al, 1984;Bar et al, 1985). It suggested a first-order dependence at lower aldehyde concentration, but a nonlinear relationship at higher aldehyde concentration.…”

Applications of ammonium formate‐catalytic transfer hydrogenation.

“…When Boc-D-p-CIPhe was subjected to AF-CTH in CH,OH using NH: HCOO-, the reaction rate was 2.5 times faster than when the donor was NH: DCOO-. A similar conclusion was reached by Blum et al (13) for the formic acidtransfer hydrogenation of benzylideneacetophenone using a polymer bound iridium-based homogeneous catalyst.…”

“…For example, the mechanism of hydrogen transfer from formic acid to unsaturated C-C bonds utilizing a polystyrene anchored iridium complex catalyst has been shown by Blum er al. (13) to involve hydrogen transfer from the formate to iridium accompanied by loss of COz as the .h I . rate determining step.…”

Isomerization of Allylbenzenes

“…Blum and co-workers also developed a polymer-bound iridium hydrogen transfer catalyst, this time based on the IrCl­(CO)­(PPh 3 ) 2 complex. These researchers found that when they tested their polymer-bound iridium catalyst, ●-[(PPh 2 ) 2 Ir­(CO)­Cl] n , with formic acid as donor, the substrate allylbenzene was not hydrogenated efficiently (only 32% propylbenzene obtained).…”