Phosphine-free Complexes Research Articles

Phosphine-free Ru(ii)–CNC pincer complexes with mixed protic- and classical-NHCs in the same molecule for hydrogen production via oxidant-free benzyl alcohol dehydrogenation to benzoic acids

New phosphine-free complexes with mixed protic- and classical-NHCs in the same molecule are reported. These complexes are shown to be effective catalysts for hydrogen production via oxidant-free benzyl alcohol dehydrogenation to benzoic acids.

Palladium nanoparticles supported on cysteine-functionalized MNPs as robust recyclable catalysts for fast O- and N-arylation reactions in green media

A magnetically robust recyclable nanocatalyst was fabricated by immobilizing of Pd onto the surface of cysteine-functionalized magnetic nanoparticles (MNPs@Cys-Pd). This nanocatalyst was characterized using various techniques such as FT-IR, XRD, TEM, SEM, EDX, VSM, and ICP. The application of catalyst (MNPs@Cys-Pd) was investigated for O-arylation and N-arylation reactions. This phosphine-free complex was found as highly efficient heterogeneous catalyst in green media and mild reaction conditions. In addition, it gave excellent recyclability without significant deactivation after ten cycles.

A computational study on possible active species in nickel(II)-catalyzed 1-butene dimerization in [BMIM]+[AlCl4]− ionic liquid solution

The butene insertion step of nickel complex-catalyzed butene dimerization in the presence of a [BMIM]+[AlCl4]− ionic liquid has been studied using density functional theory. The possibility of anion coordination from the ionic liquid to the catalyst complex has explicitly been taken into account. The calculated relative energies of various possible active catalyst complexes suggest that anion coordination to the nickel center may be thermodynamically favorable. Phosphine-free complexes which are only coordinated by one or two anions are higher in energy and show higher activation barriers for butene insertion. The lowest activation barrier has been found for a mono-phosphine nickel complex. Explanations for the calculated barriers based on structural data are offered.

Highly active phosphine-free bifunctional iron complex for hydrogenation of bicarbonate and reductive amination.

Based on a "transition metal frustrated Lewis pair" approach, a cyclopentadienone iron tricarbonyl complex has been designed and applied in the reductive amination and hydrogenation of bicarbonate. This well-defined phosphine-free complex displays the best activities reported to date for an iron complex in the reduction of bicarbonate into formate and in reductive amination.

Preparation, Structure, and Reactions of Trifluoroacetimidoyl Palladium(II) Complexes

Trifluoroacetimidoyl metal complexes are useful intermediates for the selective synthesis of organofluorine compounds. Herein, we report preparations, structures, and reactions of fluorinated imidoyl palladium complexes. Oxidative addition of trifluoroacetimidoyl halides to Pd(PPh3)4 afforded quantitatively the imidoyl palladium(II) complexes with phosphine ligands. The reaction of trifluoroacetimidoyl iodides with Pd2(dba)3 provided the phosphine-free imidoyl palladium complex in high yields. The X-ray crystal structure analysis of the phosphine-free complex [Pd(μ-I){μ-C(CF3)═N(PMP)}]4 revealed a cyclic tetranuclear structure containing the imidoyl and iodo bridges. The generation of aminotrifluoromethylcarbene equivalents by protonation or electrophilic alkylation of imidoyl palladium(II) complexes is discussed.

Pincer-type Pyridine-Based N-Heterocyclic Carbene Amine Ru(II) Complexes as Efficient Catalysts for Hydrogen Transfer Reactions

Stable well-defined pincer-type N-heterocyclic carbene−ruthenium complexes were developed as an alternative to phosphine complexes. These highly stable phosphine-free complexes were found to be efficient catalysts for transfer hydrogen reactions: the conversion of primary alcohols to esters and the reduction of carbonyl compounds. We also describe one approach toward immobilization through covalent bonding to silica via a pendant alkoxysilane group.

Probing the catalytic potential of chloro nitrosyl rhenium(i) complexes

The reduction of the mononitrosyl Re(II) salt [NMe(4)](2)[ReCl(5)(NO)] (1) with zinc in acetonitrile afforded the Re(i) dichloride complex [ReCl(2)(NO)(CH(3)CN)(3)] (2). Subsequent ligand substitution reactions with PCy(3), PiPr(3) and P(p-tolyl)(3) afforded the bisphosphine Re(i) complexes [ReCl(2)(NO)(PR(3))(2)(CH(3)CN)] (3, R = Cy a, iPr b, p-tolyl c) in good yields. The acetonitrile ligand in 3 is labile, permitting its replacement with H(2) (1 bar) to afford the dihydrogen Re(I) complexes [ReCl(2)(NO)(PR(3))(2)(η(2)-H(2))] (4, R = Cy a, iPr b). The catalytic activity of 2, 3 and 4 in hydrogen-related catalyses including dehydrocoupling of Me(2)NH·BH(3), dehydrogenative silylation of styrenes, and hydrosilylation of ketones and aryl aldehydes were investigated, with the main focus on phosphine and halide effects. In the dehydrocoupling of Me(2)NH·BH(3), the phosphine-free complex 2 exhibits the same activity as the bisphosphine-substituted systems. In the dehydrogenative silylation of styrenes, 3a and 4a bearing PCy(3) ligands exhibit high catalytic activities. Monochloro Re(I) hydrides [Re(Cl)(H)(NO)(PR(3))(2)(CH(3)CN)] (5, R = Cy a, iPr b) were proven to be formed in the initiation pathway. The phosphine-free complex 2 showed in dehydrogenative silylations even higher activity than the bisphosphine derivatives, which further emphasizes the importance of a facile phosphine dissociation in the catalytic process. In the hydrosilylation of ketones and aryl aldehydes, at least one rhenium-bound phosphine is required to ensure high catalytic activity.

Deactivation of Ruthenium Olefin Metathesis Catalysts through Intramolecular Carbene–Arene Bond Formation

for olefin metathesis have been reported, for which strikingly different influences of the ligands on the efficiency of C C bond formation have been observed. For example, notable effects have been found in the class of alkoxy benzylidene ligands first introduced by Hoveyda and coworkers. Phosphine-free complexes such as the secondgeneration Hoveyda–Grubbs catalyst (4 ; IMesH2= 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) are especially wellsuited for cross metathesis with electron-deficient olefins such as a,b-unsaturated nitriles. The stability and the initiation rate of the precatalyst could be tuned by steric and electronic effects of the substituents. Additional intramolecular interactions of functional groups or atoms with the metal center have been reported for some ligands. 6] Grubbs and co-workers recently found an accelerating effect in olefin metathesis through fluorine– ruthenium interaction. Besides knowledge of such ligand and substituent effects, an understanding of catalyst decomposition and transformation to catalytically inactive ruthenium species is of major importance for the rational design and improvement of metathesis catalysts. Fundamental studies have been presented by Grubbs and co-workers and by Dinger and Mol. Herein, we report a novel deactivation reaction pathway transforming active ruthenium catalysts with alkoxy benzylidene ligands into catalytically inactive carbene complexes. During our study of diastereoselective ring rearrangement metathesis reactions (dRRM), we found that the neutral ligand that remains on the metal center has a pronounced effect on conversion and diastereoselectivity. While only moderate diastereoselectivities could be seen for the firstgeneration catalysts (1, 3), the sterically more demanding and more active second-generation catalysts (2, 4) led to significantly higher selectivities. Thus, we focused on the development of a bulky ruthenium carbene complex to increase the diastereoselective interaction between the olefine moiety and the catalytically active ruthenium species. To do this, we connected the N-aryl substituent with the N-heterocyclic carbene (NHC) through a C2 unit. Unlike in 2 or 4, the aromatic moiety in this new ruthenium complex (5, Scheme 1) should exert a much stronger steric influence on the ruthenium alkylidene moiety through torsion of approximately 458 and hindered rotation. The synthesis of the NHC ligand started from commercially available 2,2’-biquinoline (6). The first step was hydration to octahydrobiquinoline; the result of the hydration was strongly dependent on the catalyst system. PtO2 and H2 under ambient pressure led to the formation of a 3:1 mixture of the meso and racemic forms. Simple chromatography on silica gel

Synthesis, characterization, and catalytic activity of a ruthenium carbene complex coordinated with bidentate 2-pyridine-carboxylato ligands

The halide and phosphine free complex [(sIMes)(C 5H 4N-2-CO 2) 2Ru CHPh] ( 7) (sIMes = 1,3-dimesitylimidazolidin-2-ylidene) bearing two bidentate 2-pyridinecarboxylato ligands was synthesized from the carbene complex [(sIMes)(PCy 3)(Cl) 2Ru CHPh] ( 4) and the silver 2-pyridine-carboxylate ( 8). The molecular structure of the octahedral complex 7 reveals that the two carboxylato functions are coordinated in cis geometry to the ruthenium center. Catalyst 7 exhibits activity in ring-closing metathesis (RCM) reactions after addition of a cocatalyst (HCl) in dichloromethane as well as in methanol solution.