Mechanistic investigation on hydrogenation and hydrosilylation of ethylene catalyzed by rhenium nitrosyl complex

Hydrosilylation Reactions Catalyzed by Rhenium

Hydrosilylation is an important process, not only in the silicon industry to produce silicon polymers, but also in fine chemistry. In this review, the development of rhenium-based catalysts for the hydrosilylation of unsaturated bonds in carbonyl-, cyano-, nitro-, carboxylic acid derivatives and alkenes is summarized. Mechanisms of rhenium-catalyzed hydrosilylation are discussed.

Hexene hydrogenation catalysed by the complex monohydrid complexes: A DFT study of associated vs dissociated pathways

A DFT study was conducted to elucidate the mechanism of hexene hydrogenation catalysed by a series of ruthenium (II) monohydride catalysts: RuH(CO)(Cl)(LL') where L and L' represent C(cyclohexyl), Me (methyl) and IMe (N, N '-bis (mesityl) imidazole-2-ylidene). This investigation explores the feasibility of two different proposed mechanisms: the first describes the dissociated pathway and exploits a single phosphine complex. The second is the associative one and uses a two phosphines complex. The detailed pathways have been explored for the catalyst model with L = L' = Me. Three possibilities have been supported for the dissociative route. Pathway (A) begins with a phosphine release. The initial addition of hexane or a dihydrogen molecule on the ruthenium catalyst generates the pathways (B) and (C), respectively. Pathways (B) and (C) merge with the pathway (A) before and after the first proton transfer, respectively. Activation energies in the first hydrogen migration (the key-step of the mechanism) are close. Therefore, both mechanisms (A) and (B) are possible but the former is more probable. The substitution of the catalyst model RuHCl(CO)(PMe₃)₂ by the real catalysts RuHCl(CO)(PCy₃)₂ or RuHCl(CO)(IMes)(PMe₃) shows no significant influence on the energetic barriers of hexene hydrogenation mechanism. The energy profile of the first hydrogen migration for the catalyst RuHCl(CO)(PCy₃)₂ is characteristic of a concerted asynchronous mechanism while our calculation led to two separated synchronous steps when the model catalyst is used. The associative pathway (D) integrates the two experimentally detected intermediates and generates activation energies close to those of dissociative pathways (A) and (B). The rationale to explain the experimentally detected species is achieved by considering the four proposed mechanisms where they occur simultaneously and with different rates (ie. The dissociative mechanism has the highest rate).

Nitrosylruthenium Complexes as Polymerization Catalysts for Acrylonitrile in DMF

Nitrosylruthenium complexes bearing two 2,2'-bipyridine (bpy) or 2-pyridinecarboxylate (pyc) ligands, [Ru(NO)X(bpy)₂ ]³⁺ (X=CH₃ CN, CH₂ =CHCN, H₂ O, Cl, ONO₂ ) and [Ru(NO)(OH₂ )(pyc)₂ ]⁺ , were used as catalysts for the polymerization of acrylonitrile in N,N-dimethylformamide (DMF) under air without initiators to obtain polyacrylonitrile (PAN) with a high molecular weight and a narrow molecular weight distribution.