Comments on the catalytic alkoxycarbonylation of alkynes

Structures, Mechanisms, and Results in Bifunctional Catalysis and Related Species Involving Proton Transfer

“…In pioneering work at Shell in the 1990s [23,24], a pyrid-2-yl or 6-methyl-2-pyrid-yl phosphine led to very significant enhancements in rate and selectivity for Pd-catalyzed methoxycarbonylation of propyne. A strong acid with weakly coordinating conjugate base (toluenesulfonic acid) was a co-catalyst in this transformation, suggesting that a pyridinium species may be important in the catalytic cycle, though there is more than one possibility for its precise role [25,26]. Despite the benefits of the novel use of pyridylphosphines noted above, until our work on imidazolyl-and pyridylphosphines there appeared to be no other reports of catalysis using these species.…”

Synthesis, characterization, reactivity and theoretical studies of ruthenium carbonyl complexes containing ortho-substituted triphenyl phosphanes

“…The tendency to produce strongly chelated complexes is typical of this particular (np) ligand [33,34] and examples of non-chelated metal complexes of this ligand are, to the best of our knowledge, not reported. In contrast, other (np) ligands such as the 2-(diphenylphosphino)-pyridine (PPh 2 py) [35][36][37] and the 2-(diphenylphosphino)-1-methyl-imidazole (dpim) [38] show slightly better hemilabile properties and the non-chelated metal complexes containing these phosphanes have been identified. In the latter two cases chelation has to be promoted in contrast to our complex in which the chelated product is the only one observed.…”

Bifunctional Organometallic Catalysts Involving Proton Transfer or Hydrogen Bonding

“…The 2-pyridyl group on a phosphine moiety, as shown in 8, enables a highly selective alkoxycarbonylation of terminal alkynes, increasing reaction rates by factors of over 1000 times those obtained with only phenyl groups on the ligand. [54][55][56] Although several roles of the pyridine nitrogen atom and added acid have been discussed, the most recent evidence suggests [55] that a pyridinium moiety may help protonate a p-bound alkyne (in 8) to form a cationic vinyl complex (9).…”