Silylene‐Bridged Tetranuclear Palladium Cluster as a Catalyst for Hydrogenation of Alkenes and Alkynes

Abstract

A planar tetranuclear palladium cluster was obtained from the reaction of a cyclotetrasilane with [Pd(CNtBu)2]3. Single‐crystal X‐ray diffraction analysis and DFT calculations revealed that the tetranuclear framework of the cluster was supported effectively by the bridging organosilylene ligand. Although [Pd(CNtBu)2]3 as well as mononuclear palladium bis(silyl) complex, cis‐Pd(SiMePh2)2(CNtBu)2, do not act as the effective catalyst, the planar tetranuclear palladium cluster acts as an efficient catalyst for the hydrogenation of alkenes and alkynes including sterically hindered tri‐ and tetra‐substituted alkenes.

Parts-Per-Million of Soluble Pd0 Catalyze the Semi-Hydrogenation Reaction of Alkynes to Alkenes

“…At lower loadings (<0.04 mol %), although the grids were extensively loaded, no Pd species could be found. Therefore, given the high catalytic activity displayed by PdCl 2 at parts-per-million concentrations and the inability to detect them under the microscope, it seemed clear that the species had to be sub-nanometrical. − Simultaneously to the TEM analysis, the solutions were analyzed by emission spectrophotometry to detect Pd clusters, which are known to show different fluorescence behavior depending on their size. , Indeed, the solutions with the lowest loadings (0.004 and 0.0004 mol % Pd) displayed a broad band from 320 to 410 nm when excited at a wavelength of 300 nm, while the other samples displayed some scattering, especially at 0.04 mol % concentration (Figure S25). Therefore, one can conclude that extremely low PdCl 2 loadings in ethanolic solutions have been identified as very efficient and selective catalysts for the hydrogenation of 1 to 2 , a terminal aliphatic alkynol, and Pd 0 species have been found to act as the actual catalyst of the reaction, after being formed in situ .…”

“…Therefore, given the high catalytic activity displayed by PdCl 2 at parts-per-million concentrations and the inability to detect them under the microscope, it seemed clear that the species had to be sub-nanometrical. 46 − 48 Simultaneously to the TEM analysis, the solutions were analyzed by emission spectrophotometry to detect Pd clusters, which are known to show different fluorescence behavior depending on their size. 49 , 50 Indeed, the solutions with the lowest loadings (0.004 and 0.0004 mol % Pd) displayed a broad band from 320 to 410 nm when excited at a wavelength of 300 nm, 51 while the other samples displayed some scattering, especially at 0.04 mol % concentration ( Figure S25 ).…”

Well-Defined Pdn Clusters for Cross-Coupling and Hydrogenation Catalysis: New Opportunities for Catalyst Design

“…Sunada et al also synthesized a Pd 4 cluster by reactions between [Pd 0 (CN t -Bu) 2 ] and substituted cyclotetrasilanes, forming a hexagonal planar core structure with a central Pd atom surrounded by alternating Pd and Si atoms ( XI ; Scheme , top). Each edge Pd was additionally stabilized by a CN- t -Bu ligand. , The Pd 4 cluster demonstrated good activity as a catalyst for the hydrogenation of alkenes and alkynes.…”

Di- and Trinuclear Complexes of Pd(0) and Pt(0) with Bridging Silylene Ligands: Structures with a Coordinatively Unsaturated Metal Center and Their Reactions with Alkynes

“…Multinuclear Pd(0) and Pt(0) complexes bearing bridging silylene ligands have been reported to catalyze several synthetic organic reactions . A dinuclear Pd(0) complex with bridging silylene ligands, [{Pd­(μ-SiN­( t Bu)–CHCHN t Bu)­(PPh 3 )} 2 ], has been used as a catalyst for Suzuki–Miyaura coupling reaction.…”