Density Functional Study of Mo-Carbonyl-Catalyzed Alkynol Cycloisomerization:  Comparison with W-Catalyzed Reaction

Abstract

Mo-catalyzed endo-cycloisomerizations of alkynes tethered to alcohols have been studied using density functional theory, and comparisons were made with the W-catalyzed reaction. The cycloisomerization is initiated with the formation of metal alkyne π complex and is followed by the rate-determining step, which transforms the π complex to a vinylidene carbene complex, considered to be critical for endo-mode cyclization. Several different alkynols have been selected to investigate five-and six-membered ring endo-cycloisomerizations in the presence of Mo(CO) 5 catalyst. The energy barriers calculated for five-and six-membered ring cycloisomerizations are within a range of 25-30 kcal/mol for most cases studied, showing no significant energy difference between the two metals. The stabilization effect of THF and Et 3 N solvents and the substitution reaction of THF by alkynol substrates in the reaction process with Mo and W complexes are studied as well. The principal difference between Mo-and W-catalyzed cycloisomerization processes appears to be the initial formation of a π complex, which is more stabilizing for formation of the W-alkyne vs Mo-alkyne complexes.

The fate of branched and linear isomers in the rhodium-catalyzed hydroformylation of 3,4,4-trimethylpent-1-ene

“…From the superimposition of the profiles Opposite, yet limited, effects are found on the CO addition TS (whose barrier increases) and on the tetracarbonyl intermediate. Similar negligible effects have been obtained with PCM on metal catalyzed reactions by other authors as well using gas phase-optimized geometries either in benzene [64] or in diethyl ether solution [65] with the B3LYP hybrid functionals.…”

Metal Vinylidenes and Allenylidenes in Catalysis: Applications in Anti‐Markovnikov Additions to Terminal Alkynes and Alkene Metathesis

“…[93] The catalytic version, illustrated by the endo cyclization of 3-and 4-alkyn-1-ols to give cyclic five-and six-membered enol ethers has been extensively studied, especially with molybdenum [94] and tungsten [95,96] carbonyl promoters (Scheme 12). [97,98] [Mo(CO) 6 ], [W(CO) 6 ], [W(CO) 5 (thf)], and [W(CO) 5 (Et 3 N)] are the most commonly used catalyst precursors, and photochemical activation is often used to generate the active promoters. These catalytic systems usually do not exhibit high turnover numbers, but are compatible with a variety of functional groups such as ethers, esters, amides, and carbamates, and thus have been used in sugar, aminosugar, and polyol chemistry.…”

Pentynol to furan conversion – Search for the best trans-[MX2(YNC10H14O)2] catalyst

“…In fact, the poorest catalyst (Y = Ph) is that with less basic Y group. In addition, the Y group also stabilizes the alcohol group of 4-pentyn-1-ol inhibiting ready cyclization to a vinylidene type species observed in the cycloisomerization of 4-pentyn-1-ol promoted by Mo or W carbonyl catalysts [4,[11][12][13][14][15]. No such vinylidene type species was detected in processes catalysed by camphorimine catalysts.…”

“…The presence of a base (Et 3 N [11]) or THF, [12] was previously mentioned to enable the catalytic cycloisomerization of 4-pentyn-1ol. Using trans-[PdCl 2 (YNC 10 H 14 O) 2 ] as catalysts neither a base nor a basic solvent is necessary since the camphor ligands play that role through the Y group.…”