Spin-Crossing in the (Z)-Selective Alkyne Semihydrogenation Mechanism Catalyzed by Mo₃S₄ Clusters: A Density Functional Theory Exploration

Abstract

Semihydrogenation of internal alkynes catalyzed by the air-stable imidazolyl amino [Mo 3 S 4 Cl 3 (ImNH 2 ) 3 ] + cluster selectively affords the (Z)-alkene under soft conditions in excellent yields. Experimental results suggest a sulfur-based mechanism with the formation of a dithiolene adduct through interaction of the alkyne with the bridging sulfur atoms. However, computational studies indicate that this mechanism is unable to explain the experimental outcome: mild reaction conditions, excellent selectivity toward the (Z)-isomer, and complete deuteration of the vinylic positions in the presence of CD 3 OD and CH 3 OD. An alternative mechanism that explains the experimental results is proposed. The reaction begins with the hydrogenation of two of the Mo 3 (μ 3 -S)(μ-S) 3 bridging sulfurs to yield a bis(hydrosulfide) intermediate that performs two sequential hydrogen atom transfers (HAT) from the S−H groups to the alkyne. The first HAT occurs with a spin change from singlet to triplet. After the second HAT, the singlet state is recovered. Although the dithiolene adduct is more stable than the hydrosulfide species, the large energy required for the subsequent H 2 addition makes the system evolve via the second alternative pathway to selectively render the (Z)-alkene with a lower overall activation barrier.

Unprecedented Mo3S4 cluster-catalyzed radical C–C cross-coupling reactions of aryl alkynes and acrylates

“…3b. 30 Hydrogen activation in pathway A takes place after alkyne insertion into two of the Mo 3 (μ 3 -S)(μ-S 3 ) bridging atoms to form I1 . Then, H 2 activation occurs at the third bridging sulfur atom and one of the dithiolene carbon atoms ( I2 ).…”

Revisiting the quasi-aromaticity in polynuclear metal chalcogenide clusters and their derivative “cluster-assembly” crystalline structures

“…This robust core, coordinated by various ligands, offers significant reactivity due to multiple adsorption sites. 30–32 However, a comprehensive and quantitative understanding of the aromaticity and electronic structure of this type of cluster is still lacking and ambiguous. In this research, we explore the chemical bonding mechanism of a series of metal chalcogenide clusters [M 3 X 4 (H 2 O) 9 ] 4+ (M = Cr, Mo, W, and Sg; X = O, S, Se, and Te), by using different methods including localized orbital partitions, and nucleus-independent chemical shift (NICS) index values on the specific planes.…”