Bekir Çetinkaya

Direct Arylation of Arene C−H Bonds by Cooperative Action of NHCarbene−Ruthenium(II) Catalyst and Carbonate via Proton Abstraction Mechanism

Direct functionalization of sp2 C−H bonds via ortho diarylation of 2-pyridyl benzene with arylbromides was achieved using ruthenium(II) catalysts containing a RuCl2(NHC) unit and generated from [RuCl2(arene)]2 and two types of NHC precursors, pyrimidinium and benzimidazolium salts, in the presence of Cs2CO3. DFT calculations from RuCl2(NHC)(2-pyridylbenzene) show that a proton abstraction mechanism, on cooperative actions of both the coordinated base and the Ru(II) center, is favored via a 13.7 kcal·mol-1 exothermic process affording an orthometalated intermediate with a 2.009 A Ru−C bond.

Synthesis and catalytic properties of N-functionalized carbene complexes of rhodium(I) and ruthenium(II)

Abstract Imidazolidin-2-ylidene derivatives of rhodium(I) and ruthenium(II), having 2-methoxyethyl substituent on the N-atom, [Rh(L)Cl(PPh3)2], [Rh(L)CI(COD)] or [Ru(L)Cl2(arene)] ( L 1 = CN ( Me ) CH 2 CH 2 N ︹ CH 2 CH 2 OMe and L 2 = CN ( CH 2 CH 2 OMe ) CH 2 CH 2 N ︹ CH 2 CH 2 OMe ) have been prepared by treatment of [RhCl(PPh3)3], [RhCI(COD)]2 or [RuCl2(arene)]2 with the N-functionalized electron-rich olefins L1 = L1 or L2 = L2. All of the new carbene rhodium(I) or ruthenium(II) complexes have proved to be effective catalysts for the cyclopropanation reactions of diazoalkane derivatives with styrene and the rhodium(I) precursors lead to the highest catalytic activity.

First ruthenium complexes with a chelating arene carbene ligand as catalytic precursors for alkene metathesis and cycloisomerisation

Electron-rich carbene precursors 2 and 3, containing the imidazolidin-2-ylidene moiety with one (2) and two (3) pendent N-(2,4,6-trimethylbenzyl) groups, on reaction with [RuCl2(arene)]2 lead to ruthenium(II) complexes 5 and 6 containing the chelating 8-electron mixed arene–carbene ligand; the X-ray diffraction crystal structure of RuCl2{η1-CN[CH2( η6-2,4,6-Me3C6H2)]CH2CH2N(CH2CH2OMe)} 6, was established. These complexes are precursors of the unstable ruthenium-allenylidene intermediates 7 and 8, but are active catalysts either for selective catalytic alkene metathesis or cycloisomerization, depending on the nature of the 1,6-diene.

Synthesis of a water-soluble carbene complex and its use as catalyst for the synthesis of 2,3-dimethylfuran

Abstract 1,1′,3,3′-Tetrakis(p-dimethylaminobenzyl)-2,2′-biimidazolidinylidene, L2R (R=CH2C6H4NMe2-p) which contains four peripheral NMe2 substituents, was obtained from 4-dimethylaminobenzaldehyde by a three-step reaction sequence, and was used for the preparation of imidazolidin-2-ylidene Ru(II) and Rh(I) complexes 1 and 2. Etherial HCl readily protonates the NMe2 functionality on the carbene ligand of 1 to give the corresponding salt, 1′; whereas the reaction of 2 with HCl gave a hygroscopic and ill-defined rhodium species. In aqueous solution the salt 1′ is an efficient and active catalyst for intramolecular cyclisation of (Z)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran. The catalyst 1′ could be recovered by simple phase separation and the catalytic reaction was maintained for five different runs. All of the new compounds were characterised by elemental analyses, IR and NMR spectroscopy and the molecular structure of 1 was determined by X-ray crystallography.

Ruthenium(II) complexes with 2,6-pyridyl-diimine ligands : synthesis, characterization and catalytic activity in epoxidation reactions

Abstract Reaction of [RuCl 2 ( p -cymene)] 2 with the tridentate N - N ′- N ligands, 2,6-pyridyl-diimines, led to substitution of p -cymene. The resulting complexes, believed to be coordinatively unsaturated, exhibit efficient activity for the epoxidation of cyclohexene in the presence of iodosobenzene (PhIO): the complexes formed initially take up donor molecules such as acetonitrile to achieve hexacoordination. The molecular structure for one of these, (acetonitrile){2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine}dichlororuthenium(II), 2 , has been determined by X-ray diffraction. The immediate coordination sphere is a distorted octahedron with trans chloride atoms and a short Ru–N(py) (1.906 A) bond.

Ruthenium-carbene catalysts for the synthesis of 2,3-dimethylfuran

Abstract A variety of neutral arene-ruthenium-carbenes of type (arene)RuCl 2 (= C(NR)CH 2 CH 2 N R) have been used for the catalytic transformation of ( Z )-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran. The catalytic reaction takes place at 80°C with mononuclear complexes III–V to afford the furan in ∼ 90% yield. The binuclear catalysts VIa and VIIa having a linked bis-carbene bridge operate at room temperature to initiate an exothermic reaction offering 90–97% of furan.

Synthesis and immobilization of N-heterocyclic carbene complexes of Ru(II): catalytic activity and recyclability for the furan formation

Abstract Synthesis, characterization and immobilization of ruthenium(II) complexes of the type [RuCl 2 L(η 6 -arene)] (L= , arene= p -cymene, 3 and arene=C 6 Me 6 , 4 ) and [RuCl 2 L] (L=η 1 -carbene-η 6 -arene bidentate ligand, ), 5 , morphologically different silicas by sol–gel method are described and their reactivity and recyclability in the furan formation were also reported.

Aqueous-phase Suzuki-Miyaura cross-coupling reactions catalyzed by Pd-NHC complexes.

Cleavage reactions of [PdBr(2)(NHC)](2) with two equiv. of pyridine derivatives (L), having one or two carboxylic acid groups [L = NC(5)H(4)-2-COOH, NC(5)H(4)-3-COOH, NC(5)H(4)-4-COOH, or NC(5)H(3)-2,6-(COOH)(2) in chloroform or DMSO, respectively, afforded the monomeric mixed ligand complexes trans-[PdBr(2)(NHC)L] (1-4) which, due to deprotonation of the carboxylic acid functionality, are water soluble in KOH. The catalytic activity of complexes 1-4 in aqueous Suzuki-Miyaura cross-coupling reactions were evaluated and compared. The dicarboxylic functionality enhances the catalyst reactivity and stability and the carboxylate derived from 4 could be easily recovered and reused for several cycles under the mild reaction conditions.

An electron-rich olefin as a source of co-ordinated carbene; synthesis of trans-PtCl2[C(NPhCH2)2]PEt3

Interaction of the appropriate electron-rich olefin and chloride bridged PtII dimer has yielded the unreactive trans-PtII carbene complex (I) which is belived to isomerise thermally to the cis-isomer; the structure of the trans-complex is established inter alia by a single crystal X-ray analysis.

Chitosan-ferrocene film as a platform for flow injection analysis applications of glucose oxidase and Gluconobacter oxydans biosensors

Chitosan-ferrocene (CHIT-Fc) hybrid was synthesized through covalent modification and its electrochemical properties in immobilized form were studied by using cyclic voltammetry. The hybrid film exhibited reversible electrochemistry with a formal potential of +0.35 V (vs. Ag/AgCl) at pH 5.5. The Fc in CHIT matrix retained its electrocatalytic activity and did not diffuse from the matrix. This redox-active hybrid was further employed as a support for immobilization of glucose oxidase (GOx) and whole cells of Gluconobacter oxydans using glutaraldehyde on a glassy carbon electrode (GCE). The experimental conditions were optimized and the analytical characteristics of enzyme and microbial biosensors were evaluated for glucose in flow injection analysis (FIA) system. Under optimized conditions, both enzyme and microbial biosensors exhibited wide linear ranges for glucose from 2.0 to 16.0 mM and from 1.5 to 25.0 mM, respectively. Moreover, the biosensors have the advantages of relatively fast response times, good reproducibility and stability in FI mode. It was demonstrated that CHIT-Fc provides a biocompatible microenvironment for both bioctalysts and an electron transfer pathway. Additionally, integration of the enzyme and microbial biosensors into the FIA system has several advantages including capability of automation and high throughput at low cost. This promising redox hybrid can be utilized as an immobilization matrix for biomolecules in biosensor systems.