835890-03-4Relevant academic research and scientific papers
Electronic and steric effects in the insertion of alkynes into an iridium(III) hydride
Li, Xingwei,Vogel, Tiffany,Incarvito, Christopher D.,Crabtree, Robert H.
, p. 62 - 76 (2008/10/09)
Insertion of a variety of alkynes into the Ir-H bond of trans-[IrH(PPh 3)2(C(Ph.)=CHC-(O)Me)(acetone)]+ (1) follows three different routes depending on the alkyne structures. For relatively electron-rich alkynes (PhC≡CH, PhCH2C≡CH, and p-OMeC 6H4C≡CH), double insertion occurs stepwise, each alkyne undergoing rearrangement to a vinylidene intermediate independently to afford an iridium(III) η2-butadienyl. In the first alkyne insertion, deuterium labeling and crossover experiments confirm that the alkyne to vinylidene rearrangement is intraligand. Both a vinyl and a vinylidene intermediate were trapped and isolated during this first insertion. In the second alkyne insertion, a C - H agostic intermediate was isolated. Electron-poor alkynes (p-CF3C6H4C≡CH and p-NO2C6H4C≡CH) also undergo double insertion into 1, but deuterium labeling experiments using p-CF 3C6H4C≡CD indicate reversible C(sp)-H oxidative addition. Insertion of highly polarized alkynes (R 1C≡CC(O)R2] to 1 occurs only once and involves no vinylidene intermediates even when R1 = H. The regio- and stereochemistry in this case are mainly controlled by the steric effects of R1. In this series, rare cis-(PPh3)2 intermediates were isolated for HC≡CC(O)R (R = Me or OMe). X-ray crystal structures of representative products are reported.
