Imidazole phosphine ligands

Ligand screening experiments were conducted on the alkenes 1-pentene and pent-4-en-l-ol, because such substrates were inert to 3a-3c (15). Pentene lacks any polar or protic group and pentenol contains the alkene and OH separated by 3 carbons. The preliminary studies involved phosphines with both imidazol-2-yl and pyrid-2-yl substituents on P as well as t-Bu, i-Pr, Ph, and Me groups (16). From the screening, complex 1 derived from the phosphine ligand 4 (17) was identified as the most capable (in terms of both reaction rate and final yield) of promoting isomerization of both 1-pentene and pent-4-en-l-ol. 

Thermolysis of (LH)2[RuCl5(NO)] (L = benzimidazole, imidazole, 5-nitrobenzimidazole, benzo-triazole, py) leads to the initial formation of [RuC NOJL]- with subsequent reaction to afford [RuCl3(NO)L2].M6 When solutions of RuCl with NaNCS in pyridine are refluxed for three days, a product formulated as [Ru(NCS)2py4] can be isolated.667 Nitrosyl and thionitrosyl complexes containing heterocycles with arsine or phosphine ligands have been reported.668... 

Cleavage of imidazoles dehydroamino acids,3 2,4-Disubstituted imidazoles4 undergo a Diels-Alder-like reaction with singlet oxygen in the presence of DBU (1-2 equiv.) to provide imine diamides, which isomerize to dehydroamino acid derivatives in the presence of base. Hydrogenation in the presence of catalysts with chiral phosphine ligands results in optically active amino acid diamides. The overall process is illustrated for the synthesis of the N-benzylamide of N-acetylleucine (equation I). 

Other catalytically active species for C02 hydration include [(CR)Zn-OH] + (CR = Me2pyo[14]trieneN4, / at = 225 +23 M-1 s 1, Fig. 6a), which exhibits a pK value of 8.69 at 25 °C.40 Zinc complexes supported by tris(imidazole)phosphine-type (Fig. 6b-d) or tris(imidazole)phosphineoxide-type ligands also exhibit catalytic C02 hydration reactivity.41-44 All of these complexes exhibit maximum rate constants for C02 hydration below 2500 M-1 s 1 in the pH = 6-7 range. Above or below this pH... 

Seller Adamantyl-, Arylpyrrole- and Arylindol-Based Phosphine Ligands The adamantly-, arylpyrrole-/imidazole- and indole-derived ligands [105] (Figure 3.8) presented by Beller are related to P(t-Bu)3 and Singer s heterocyclic ligands, respectively. They were applied to aminations of aryl chlorides under mild reaction conditions [105]. 

This concept was applied to the intramolecular alkylation of imidazole and benzimidazole derivatives (Scheme 19.86) [121]. Preliminary results showed that while the Wilkinson catalyst was effective for this transformation, standard ruthenium catalysts were unreactive. Further screening using [RhCl(coe)2]2 as the rhodium source with various phosphine ligands revealed that electron-rich ligands such as PCyj yielded the best results. As the reaction was found to be more efficient in the presence of the Lewis or Bronsted acid, an optimized protocol was devised through the use of [HPCyjKQ] imder microwave irradiation [122]. Mechanistic studies showed that the reaction is zero order in substrate and first order in catalyst. 

To further expand the scope of Ru-arene catalyst precursors in olefin metathesis, we have investigated the replacement of phosphine ligands by NHC species, either preformed or generated in situ, in monometallic dichlororuthenium complexes of the [RuCl2(p-cymene)(L)] type/ In this contribution, we summarize the main results that were obtained with both imidazole- or triazole-based ancillary ligands for the ROMP of cyclooctene. 

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