The effect of ultrasound and of phosphine and phosphine-oxides on the Khand reaction

New promoters for the molybdenum hexacarbonyl- mediated Pauson–Khand reaction

“…22,27 This assumption was confirmed by 31 P-NMR, where either no free (Figure 1 The peaks at 77.37 and 65.43 ppm should correspond to tributylphosphine oxide coordinated to molybdenum. However, to the best of our knowledge the only pure phosphine oxide molybdenum carbonyl complexes (with no other group attached to the metal) that are reported in literature are complexes of triphenylphosphine oxide.…”

The Pauson–Khand Reaction: the Catalytic Age Is Here!

“…Evidence that [Co 4 (CO) 12 ] cannot be considered inactive towards the CPKR, even under atmospheric pressures of carbon monoxide, has recently been provided by Krafft and Boaeaga. [29] In early experiments from this group, the observed activity of [Co 4 (CO) 12 ] was associated with the use of [29]…”

“…[28,31] Advantages of this technique, as reported by the author, include high solubility of gaseous reactants, rapid diffusion of solutes, and weakening of the solvation around the reacting species. In a recent communication, they described the intermolecular versions of the CPKR in supercritical ethene, employing [Co 2 (CO) 8 ] and the two cobalt clusters [Co 4 (CO) 12 ] and [Co 4 (CO) 11 {P(OPh) 3 }] as catalysts under 5 atm of carbon monoxide (Scheme 7). [28] Although the TONs were generally not impressive, it noteworthy that the phosphite-substituted cobalt species was remarkably easier to handle than the unsubstituted complexes.…”

“…[11] In an attempt to overcome the formation of inactive clusters, Pauson, Billington, and co-workers studied the influence of phosphanes and phosphites as coligands for the stoichiometric variants of the PKR. [12] Subsequently, a catalytic conversion of enynes into cyclopentenones employing phosphites as coligands was reported by Jeong, Chung, and co-workers (Table 1, entry 3). [10] Remarkably, under 1 atm of CO the use of phosphites as coligands did not show any positive effect on the PKR conversions (they were either ineffective or detrimental); the advantages of this procedure were only apparent at pressures of 3 atm.…”

“…At 50 8C, [Co 2 (CO) 8 ] is converted into [Co 4 (CO) 12 ], which was believed to be inert towards alkyne substrates. [11] In an attempt to overcome the formation of inactive clusters, Pauson, Billington, and co-workers studied the influence of phosphanes and phosphites as coligands for the stoichiometric variants of the PKR.…”