Ruthenium precatalyst

Ruthenium Precatalysts with N-Heterocyclic Carbene Ligands.238... 

Phosphine-Free Ruthenium Precatalysts with One NHC Ligand. 245... 

The mechanistic investigations presented in this section have stimulated research directed to the development of advanced ruthenium precatalysts for olefin metathesis. It was pointed out by Grubbs et al. that the utility of a catalyst is determined by the ratio of catalysis to the rate of decomposition [31]. The decomposition of ruthenium methylidene complexes, which attribute to approximately 95% of the turnover, proceeds monomolecularly, which explains the commonly observed problem that slowly reacting substrates require high catalyst loadings [31]. This problem has been addressed by the development of a novel class of ruthenium precatalysts, the so-called second-generation catalysts. 

Ruthenium Precatalysts with JV-Heterocydic Carbene Ligands... 

An alternative approach to phosphine-free ruthenium precatalysts is based on pyridine complex 70 [48], which has been established by Grubbs et al. as a valuable precursor for other mixed NHC-phosphine complexes (cf. Scheme 15). Complex 70 is only moderately active in the cross metathesis of allylbenzene... 

Kim and Park subsequently reported that ruthenium precatalyst (2) racemizes alcohols svithin 30 minutes at room temperature [23]. However, when combined... 

Manufacture of ruthenium precatalysts for asymmetric hydrogenation. The technology in-licensed from the JST for the asymmetric reduction of ketones originally employed BINAP as the diphosphine and an expensive diamine, DAIPEN." Owing to the presence of several patents surrounding ruthenium complexes of BINAP and Xylyl-BINAP, [HexaPHEMP-RuCl2-diamine] and [PhanePHOS-RuCl2-diamine] were introduced as alternative catalyst systems in which a cheaper diamine is used. Compared to the BINAP-based systems both of these can offer superior performance in terms of activity and selectivity and have been used in commercial manufacture of chiral alcohols on multi-100 Kg scales. 

Fig. 3.2 Synthetic routes to ruthenium precatalysts starting from RuCI2(PPh3)3.

Close to polymer boimd-BINAP/diamine ruthenium precatalyst [11], complexes of BINAP or their derivatives in the presence of polymer bound diamine have been employed. These catalytic systems have been mainly studied by Itsuno with immobilized diphenylethylenediamine (DPEN). As the use of A-substituted 1,2-diamine ligands decreased the catalytic activity of hydrogenation of simple ketones contrary to free diamine ligands, they have been less employed. However, A-substitnted 1,2-diamine ligands are rather effective in the hydrogenation of a-snbstitnted ketone, snch as a-amido ketones. Thus, two types of immobilized DPEN have been performed. Fnnctionalized DPEN for subsequent grafting onto polymer or eopolymerization are presented (Scheme 3). 

Amino and Iminophosphine Chloro Ruthenium Precatalysts Synthesis. 54... 

In 2013, Tang and coworkers [55] reported the use of other chiral ligands to catalyze the arylation of aldehydes with ruthenium precatalysts. The same group developed a series of chiral biaryl monophosphorous ligands (Scheme 7.37) that were found to catalyze the addition of arylboronic acids to aryl aldehydes. A series of chiral diarylmethanols were obtained in excellent yields (up to... 

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