Short-Chained Platinum Complex Catalyzed Hydrosilylation under Thermomorphic Conditions: Heterogeneous Phase Separation at Ice Temperature

Abstract

Homogeneous catalysts PtCl2[5,5′-bis-(n-ClCF2(CF2)3CH2OCH2)-2,2′-bpy] (2A) and PtCl2[5,5′-bis-(n-HCF2(CF2)3CH2OCH2)-2,2′-bpy] (2B), which contained short fluorous chains, were synthesized and used in catalysis of hydrosilylation of alkynes. In these reactions the thermomorphic mode was effectively used to recover these catalysts from the reaction mixture up to eight cycles by taking advantage of heterogeneous phase separation at ice temperature. This kind of catalysis had previously been observed in fluorous catalysts of platinum containing about 50% F-content, but in this work the percentage of F-content is decreased to only about 30%, by which we termed them as “very light fluorous”. Our new type of catalyst with limited number of F-content is considered as the important discovery in the fluorous technology field as the reduced number of fluorine atoms will help to be able to comply the EPA 8-carbon rule. The metal leaching after the reaction has been examined by ICP-MS, and the testing results show the leaching of residual metal to be minimal. Additionally, comparing these results to our previous work, fluorous chain assisted selectivity has been observed when different fluorous chain lengths of the catalysts are used. It has been found that there exists fluorous chain assisted better selectivity towards β-(E) form in the Pt-catalyzed hydrosilylation of non-symmetric terminal alkyne when the Pt catalyst contains short fluorous chain (i.e., 4 Cs). Phenyl acetylenes showed the opposite regioselectivity due to pi-pi interaction while using the same catalyst via Markovnikov’s addition to form terminal vinyl silane, which is then a major product for Pt-catalyzed hydrosilylation of terminal aryl acetylene with triethylsilane. Finally, the kinetic studies indicate that the insertion of alkyne into the Pt-H bond is the rate-determining step.

Evidence for the “cocktail” nature of platinum-catalyzed alkyne and alkene hydrosilylation reactions

“…43,44 It should be noted that some aspects of the dynamic nature have been noticed for Pt-catalysed hydrosilylation. Discussions on the catalyst changes during the reaction, [45][46][47][48] the existence of leaching, 49 and the formation of colloidal particles [50][51][52][53][54][55] and nanoparticles [56][57][58][59] have been reported. The catalytic activity of platinum clusters 60,61 and platinum nanoparticles [62][63][64][65] in the hydrosilylation reaction of alkynes has also been studied.…”

Recoverable Phospha-Michael Additions Catalyzed by a 4-N,N-Dimethylaminopyridinium Saccharinate Salt or a Fluorous Long-Chained Pyridine: Two Types of Reusable Base Catalysts

“…The B-catalyzed phospha-Michael addition of diisopropyl phosphite (1a) with 2-benzylidenemalononitrile-type substrates [3 (X = H), or 4 (X = CH3)]. In Scheme 6, the B-catalyzed phospha-Michael addition of diisopropyl phosphite (1a) with 2-benzylidenemalononitrile (3) was selected to demonstrate the feasibility of recycling usage with B as a catalyst using a solvent free method, at 80 • C for 1 h. At the end of each cycle, the product mixtures were cooled to room temperature, resulting in catalyst precipitation due to their thermomorphic behavior where the solubility of the catalyst increased dramatically with the increasing temperature [36,38]. Finally, after centrifugation, the catalyst was recovered by decantation.…”

“…The thermomorphic method is an alternative way to use the different solubility of fluorous long-chained compounds between high and low temperature in the common organic compounds [29][30][31][32][33][34][35]. In this method, a fluorous chain-containing pyridine-based catalyst could be soluble at high temperatures during the catalytic reactions, but insoluble at room temperature for the recovery of catalysts via a simple liquid-solid separation [36][37][38].…”