Alkyne Hydrofunctionalization Mechanism Including an Off-Cycle Alkoxycarbene Deactivation Complex

Abstract

The cooperative [Ru(Cp)(P 2 Cy N 2 Ph )(MeCN)][PF 6 ] (Ru2) complex was utilized for additive-free hydroalkoxylation of 2-ethynylbenzyl alcohol (1a) to generate isochromene. The phenyl-substituted pendent amine of the supporting ligand effectively mediated proton-transfer steps and mitigated a vinyl ammonium deactivation pathway that was previously favored with a more nucleophilic N-benzyl substituent. A select set of substrates were cyclized to uncover mechanistic opportunities and limitations of Ru2 and related catalysts. Isotopic labeling and kinetic studies, using the variable time normalization analysis (VTNA) method, were utilized to identify vinylidene formation as the most likely rate-limiting step of catalysis. Attempted cyclization of 3-butyn-1-ol afforded an isolable alkoxycarbene complex, the stability of which was investigated both computationally and through stoichiometric reactions. This compound is identified as an off-cycle catalytic species, and it reveals a critical competing proton-transfer pathway for this family of cooperative catalysts.

Chemoselective Ru-Catalyzed Oxidative Lactamization vs Hydroamination of Alkynylamines: Insights from Experimental and Density Functional Theory Studies

“…Thus, the 1,5-alkynylamide 9a underwent an oxidative lactamization to afford the imide 10 (benzazepine-2,4(3H)-dione) in a quite good yield, and the lower homolog 1,4-alkynylamide 9b gave the hydroamination product 11 (isoquinolin-1-one) in a moderate 48% yield under the same oxidative conditions or a 83% yield in the absence of 4-Pic- N -oxide (Scheme ). By contrast, the reaction of 1,5-alkynylamide 9a in the absence of 4-Pic- N -oxide gave a complex mixture.…”

The Backbone of Success of P,N-Hybrid Ligands: Some Recent Developments

“…As seen in previous sections within this review, the interaction of the pendant amine in complexes of cyclic diphosphines of 9c (and related analogues) has previously been studied towards protonation reactions [171], heterolytic splitting of H 2 [172], electrocatalytic alcohol oxidation [173], and hydroalkoxylation [174].…”

Metal-Catalyzed Cascade Reactions between Alkynoic Acids and Dinucleophiles: A Review

“…In fact, terms such as atom-economy and green chemistry are often associated with metal-catalyzed cascade reactions [5,6]. The last decades have witnessed significant advances in the fields of metal-catalyzed hydrofunctionalization of alkynes [7][8][9][10][11][12][13], and, more specifically, of cascade reactions involving alkyne hydrofunctionalization steps [14][15][16][17][18][19]. The intramolecular version of such cascade reactions, often based on the presence of suitably located carbo-and heteronucleophiles in the starting materials, has been also described [16,18,19].…”