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Pincer Complexes (pincer + complex)
Selected AbstractsRuthenium ONO-Type Pincer Complex: Synthesis, Structural Characterization, and CatalysisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Yao Zhang Abstract A novel nitrone-based pincer ligand was developed by a single-step synthesis from N -(tert -butyl)hydroxylamine acetate and 2,6-pyridinedicarboxaldehyde. The developed ligand allowed us to synthesize a cationic ruthenium pincer complex. A distorted octahedral coordination environment around the ruthenium center was observed. The complex showed excellent catalytic activity in transfer hydrogenation reactions with turnover numbers up to 590,000. [source] The 1,3-Diaminobenzene-Derived Aminophosphine Palladium Pincer Complex {C6H3[NHP(piperidinyl)2]2Pd(Cl)} , A Highly Active Suzuki,Miyaura Catalyst with Excellent Functional Group ToleranceADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Jeanne Abstract The rapidly prepared 1,3-diaminobenzene-derived aminophosphine pincer complex {C6H3[NHP(piperidinyl)2]2Pd(Cl)} (1) is an effective Suzuki catalyst with excellent functional group tolerance. Side-product formations, such as homocoupling, debromation or protodeboration have only rarely been detected and if so, were in all cases below the 5% level. The presented reaction protocol is universally applicable. Experimental observations indicate that palladium nanoparticles are the catalytically active form of 1. [source] Amido Pincer Complex of Nickel-Catalyzed Kumada Cross-Coupling Reactions.CHEMINFORM, Issue 44 2007Zhong-Xia Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] A SeCSe,Pd(II) Pincer Complex as a Highly Efficient Catalyst for Allylation of Aldehydes with Allyltributyltin.CHEMINFORM, Issue 48 2006Qingwei Yao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Insights into the Role of New Palladium Pincer Complexes as Robust and Recyclable Precatalysts for Suzuki,Miyaura Couplings in Neat WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Blanca Inés Abstract Suzuki,Miyaura biaryl and diarylmethane syntheses via the coupling of arylboronic acids with aryl and arylmethyl bromides are performed in water by means of two new CNC-type palladium pincer complexes. Good to excellent results (including high TON values and extended recycling procedures) are obtained in most cases for a range of electronically dissimilar halides and boronic acids. On the basis of a series of kinetics studies, transmission electron microscopy (TEM), mercury drop tests, and quantitative poisoning experiments, the real role of the latter palladacycles, closely linked to the formation and active participation of palladium nanoparticles, is discussed. [source] Highly Convenient, Clean, Fast, and Reliable Sonogashira Coupling Reactions Promoted by Aminophosphine-Based Pincer Complexes of Palladium Performed under Additive- and Amine-Free Reaction ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Jeanne No abstract is available for this article. [source] Highly Convenient, Clean, Fast, and Reliable Sonogashira Coupling Reactions Promoted by Aminophosphine-Based Pincer Complexes of Palladium Performed under Additive- and Amine-Free Reaction ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009Jeanne Abstract Sequential addition of 1,1,,1,,-phosphinetriyltripiperidine and 1,3-diaminobenzene or resorcinol to toluene solutions of (cyclooctadiene)palladium dichloride [Pd(cod)(Cl)2] under nitrogen in "one pot" almost quantitatively yielded the aminophosphine-based pincer complexes {[C6H3 -2,6-(XP{piperidinyl}2)2]Pd(Cl)} (X=NH 1; X=O 2). Complex 1 (and to a minor extent 2) proved to be efficient Sonogashira catalysts, which allow the quantitative coupling of various electronically deactivated and/or sterically hindered and functionalized aryl iodides and aryl bromides with several alkynes as coupling partners within very short reaction times and low catalyst loadings. Importantly, in contrast to most of the Sonogashira catalysts, which either are both air- and moisture-sensitive and/or require the addition of co-catalysts, such as copper(I) iodide [CuI], for example, or a large excess of an amine, the coupling reactions were carried out without the use of amines, co-catalysts or other aditives and without exclusion of air and moisture. Moreover, the desired products were exclusively formed (no side-products were detected) without employing an excess of one of the substrates. Ethylene glycol and potassium phosphate (K3PO4) were found to be the ideal solvent and base for this transformation. Experimental observations strongly indicate that palladium nanoparticles are not the catalytically active form of 1 and 2. On the other hand, their transformation into another homogeneous catalytically active species cannot be excluded. [source] Alkyl- and Arylthiolation of Aryl Halides Catalyzed by Fluorinated Bis-Imino-Nickel NNN Pincer Complexes [NiCl2{C5H3N-2,6-(CHNArf)2}]ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2006Oscar Baldovino-Pantaleón Abstract The synthesis of bis-imino nickel(II) NNN pincer complexes of the type [NiCl2{C5H3N-2,6-(CHNArf)2}]; Arf=C6H3 -2,3-F2 (1), C6H3 -2,5-F2 (2), C6H3 -3,4-F2 (3), C6H3 -3,5-F2 (4), C6H2 -2,3,4-F3 (5), C6H2 -2,3,6-F3 (6), C6H2 -2,4,5-F3 (7), C6H2 -2,4,6-F3 (8), has been achieved and their reactivity in alkyl- and arylthiolation reactions of halobenzenes examined. The use of fluorinated substituents Arf on the imines has allowed the tuning of the electronics in these complexes and the influence of these substituents and those of the disulfides in the thiolation reactions have been analyzed. [source] ChemInform Abstract: Synthesis, Structure and Catalytic Activity of Macrocyclic NHC Pd Pincer Complexes.CHEMINFORM, Issue 41 2009Noriaki Watarai Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: N-Heterocyclic Carbene Derived Nickel,Pincer Complexes: Efficient and Applicable Catalysts for Suzuki,Miyaura Coupling Reactions of Aryl/Alkenyl Tosylates and Mesylates.CHEMINFORM, Issue 40 2009Jun-ichi Kuroda Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Phosphido Pincer Complexes of Palladium as New Efficient Catalysts for Allylation of Aldehydes.CHEMINFORM, Issue 14 2009Mina Mazzeo Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Alkyl- and Arylthiolation of Aryl Halides Catalyzed by Fluorinated Bis-Imino-Nickel NNN Pincer Complexes [NiCl2{C5H3N-2,6- (CHNArf)2}].CHEMINFORM, Issue 23 2006Oscar Baldovino-Pantaleon Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] ChemInform Abstract: Palladium(II) Pincer Complexes of ,-Amino Acids: Towards the Synthesis of Catalytically Active Artificial Peptides.CHEMINFORM, Issue 36 2002Gabriela Guillena Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Can [M(H)2(H2)(PXP)] Pincer Complexes (M=Fe, Ru, Os; X=N, O, S) Serve as Catalyst Lead Structures for NH3 Synthesis from N2 and H2?CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2007Markus Hölscher Dr. Abstract The potential of pincer complexes [M(H)2(H2)(PXP)] (M=Fe, Ru, Os; X=N, O, S) to coordinate, activate, and thus catalyze the reaction of N2 with classical or nonclassical hydrogen centers present at the metal center, with the aim of forming NH3 with H2 as the only other reagent, was explored by means of DF (density functional) calculations. Screening of various complexes for their ability to perform initial hydrogen transfer to coordinated N2 showed ruthenium pincer complexes to be more promising than the corresponding iron and osmium analogues. The ligand backbone influences the reaction dramatically: the presence of pyridine and thioether groups as backbones in the ligand result in inactive catalysts, whereas ether groups such as ,-pyran and furan enable the reaction and result in unprecedented low activation barriers (23.7 and 22.1,kcal,mol,1, respectively), low enough to be interesting for practical application. Catalytic cycles were calculated for [Ru(H)2(H2)(POP)] catalysts (POP=2,5-bis(dimethylphosphanylmethyl)furan and 2,6-bis(dimethylphosphanylmethyl)-,-pyran). The height of activation barriers for the furan system is somewhat more advantageous. Formation of inactive metal nitrides has not been observed. SCRF calculations were used to introduce solvent (toluene) effects. The Gibbs free energies of activation of the numerous single reaction steps do not change significantly when solvent is included. The reaction steps associated with the formation of the active catalyst from precursors [M(H)2(H2)(PXP)] were also calculated. The otherwise inactive pyridine ligand system allows for the generation of the active catalyst species, whereas the ether ligand systems show activation barriers that could prohibit practical application. Consequently the generation of the active catalyst species needs to be addressed in further studies. [source] Non-Tethered Organometallic Phosphonate Inhibitors for Lipase Inhibition: Positioning of the Metal Center in the Active Site of Cutinase,,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2008Cornelis A. Kruithof Abstract Organometallic NCN-pincer complexes, bearing either a p -nitrophenyl phosphonate ester or a phosphonic acid group directly attached to the aromatic ring of the pincer complex, were synthesized. These compounds were tested as covalent inhibitors for the lipase cutinase. In a stoichiometric reaction of the NCN-pincer platinum phosphonate p -nitrophenyl ester 2 with cutinase, a 94,% conversion to the protein,pincer metal complex hybrid was obtained in 48 h. The NCN-pincer metal phosphonic acid derivatives (3, 4) appeared to be inactive as cutinase inhibitors. In contrast to our previous work which entails propyl tethered phosphonate esters connected to pincer metal complexes, the presented strategy allows positioning of metal complexes inside the active site of lipases. This opens up the possibility for fine-tuning the chemical environment (second coordination sphere) around a synthetic metal center inside the pocket of an enzyme for diagnostic and catalytic purposes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Ruthenium ONO-Type Pincer Complex: Synthesis, Structural Characterization, and CatalysisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Yao Zhang Abstract A novel nitrone-based pincer ligand was developed by a single-step synthesis from N -(tert -butyl)hydroxylamine acetate and 2,6-pyridinedicarboxaldehyde. The developed ligand allowed us to synthesize a cationic ruthenium pincer complex. A distorted octahedral coordination environment around the ruthenium center was observed. The complex showed excellent catalytic activity in transfer hydrogenation reactions with turnover numbers up to 590,000. [source] The 1,3-Diaminobenzene-Derived Aminophosphine Palladium Pincer Complex {C6H3[NHP(piperidinyl)2]2Pd(Cl)} , A Highly Active Suzuki,Miyaura Catalyst with Excellent Functional Group ToleranceADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Jeanne Abstract The rapidly prepared 1,3-diaminobenzene-derived aminophosphine pincer complex {C6H3[NHP(piperidinyl)2]2Pd(Cl)} (1) is an effective Suzuki catalyst with excellent functional group tolerance. Side-product formations, such as homocoupling, debromation or protodeboration have only rarely been detected and if so, were in all cases below the 5% level. The presented reaction protocol is universally applicable. Experimental observations indicate that palladium nanoparticles are the catalytically active form of 1. [source] Palladium Pincer Complex Catalyzed Cross-Coupling of Vinyl Epoxides and Aziridines with Organoboronic AcidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2005Johan Kjellgren Abstract Palladium-catalyzed cross-coupling of vinyl epoxides and aziridines with organoboronic acids was performed by using 0.5,2.5 mol,% pincer-complex catalyst. The reactions proceed under mild conditions affording allyl alcohols and amines with high regioselectivity and in good to excellent yields. Under the applied reaction conditions aromatic chloro-, bromo- and iodo substituents are tolerated. Our results indicate that the mechanism of the pincer complex catalyzed and the corresponding palladium(0) catalyzed process is substantially different. It was concluded that the transformations proceed via transmetalation of the organoboronic acids to the pincer-complex catalyst followed by an SN2,-type opening of the vinyl epoxide or aziridine substrate. In this process the palladium atom is kept in oxidation state +2 under the entire catalytic process, and therefore oxidative side reactions can be avoided. [source] Insights into the Role of New Palladium Pincer Complexes as Robust and Recyclable Precatalysts for Suzuki,Miyaura Couplings in Neat WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Blanca Inés Abstract Suzuki,Miyaura biaryl and diarylmethane syntheses via the coupling of arylboronic acids with aryl and arylmethyl bromides are performed in water by means of two new CNC-type palladium pincer complexes. Good to excellent results (including high TON values and extended recycling procedures) are obtained in most cases for a range of electronically dissimilar halides and boronic acids. On the basis of a series of kinetics studies, transmission electron microscopy (TEM), mercury drop tests, and quantitative poisoning experiments, the real role of the latter palladacycles, closely linked to the formation and active participation of palladium nanoparticles, is discussed. [source] Highly Convenient, Clean, Fast, and Reliable Sonogashira Coupling Reactions Promoted by Aminophosphine-Based Pincer Complexes of Palladium Performed under Additive- and Amine-Free Reaction ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009Jeanne Abstract Sequential addition of 1,1,,1,,-phosphinetriyltripiperidine and 1,3-diaminobenzene or resorcinol to toluene solutions of (cyclooctadiene)palladium dichloride [Pd(cod)(Cl)2] under nitrogen in "one pot" almost quantitatively yielded the aminophosphine-based pincer complexes {[C6H3 -2,6-(XP{piperidinyl}2)2]Pd(Cl)} (X=NH 1; X=O 2). Complex 1 (and to a minor extent 2) proved to be efficient Sonogashira catalysts, which allow the quantitative coupling of various electronically deactivated and/or sterically hindered and functionalized aryl iodides and aryl bromides with several alkynes as coupling partners within very short reaction times and low catalyst loadings. Importantly, in contrast to most of the Sonogashira catalysts, which either are both air- and moisture-sensitive and/or require the addition of co-catalysts, such as copper(I) iodide [CuI], for example, or a large excess of an amine, the coupling reactions were carried out without the use of amines, co-catalysts or other aditives and without exclusion of air and moisture. Moreover, the desired products were exclusively formed (no side-products were detected) without employing an excess of one of the substrates. Ethylene glycol and potassium phosphate (K3PO4) were found to be the ideal solvent and base for this transformation. Experimental observations strongly indicate that palladium nanoparticles are not the catalytically active form of 1 and 2. On the other hand, their transformation into another homogeneous catalytically active species cannot be excluded. [source] Alkyl- and Arylthiolation of Aryl Halides Catalyzed by Fluorinated Bis-Imino-Nickel NNN Pincer Complexes [NiCl2{C5H3N-2,6-(CHNArf)2}]ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2006Oscar Baldovino-Pantaleón Abstract The synthesis of bis-imino nickel(II) NNN pincer complexes of the type [NiCl2{C5H3N-2,6-(CHNArf)2}]; Arf=C6H3 -2,3-F2 (1), C6H3 -2,5-F2 (2), C6H3 -3,4-F2 (3), C6H3 -3,5-F2 (4), C6H2 -2,3,4-F3 (5), C6H2 -2,3,6-F3 (6), C6H2 -2,4,5-F3 (7), C6H2 -2,4,6-F3 (8), has been achieved and their reactivity in alkyl- and arylthiolation reactions of halobenzenes examined. The use of fluorinated substituents Arf on the imines has allowed the tuning of the electronics in these complexes and the influence of these substituents and those of the disulfides in the thiolation reactions have been analyzed. [source] Pincer-Type Heck Catalysts and Mechanisms Based on PdIV Intermediates: A Computational StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2010Olivier Blacque Dr. Abstract Pincer-type palladium complexes are among the most active Heck catalysts. Due to their exceptionally high thermal stability and the fact that they contain PdII centers, controversial PdII/PdIV cycles have been often proposed as potential catalytic mechanisms. However, pincer-type PdIV intermediates have never been experimentally observed, and computational studies to support the proposed PdII/PdIV mechanisms with pincer-type catalysts have never been carried out. In this computational study the feasibility of potential catalytic cycles involving PdIV intermediates was explored. Density functional calculations were performed on experimentally applied aminophosphine-, phosphine-, and phosphite-based pincer-type Heck catalysts with styrene and phenyl bromide as substrates and (E)-stilbene as coupling product. The potential-energy surfaces were calculated in dimethylformamide (DMF) as solvent and demonstrate that PdII/PdIV mechanisms are thermally accessible and thus a true alternative to formation of palladium nanoparticles. Initial reaction steps of the lowest energy path of the catalytic cycle of the Heck reaction include dissociation of the chloride ligands from the neutral pincer complexes [{2,6-C6H3(XPR2)2}Pd(Cl)] [X=NH, R=piperidinyl (1,a); X=O, R=piperidinyl (1,b); X=O, R=iPr (1,c); X=CH2, R=iPr (1,d)] to yield cationic, three-coordinate, T-shaped 14e, palladium intermediates of type [{2,6-C6H3(XPR2)2}Pd]+ (2). An alternative reaction path to generate complexes of type 2 (relevant for electron-poor pincer complexes) includes initial coordination of styrene to 1 to yield styrene adducts [{2,6-C6H3(XPR2)2}Pd(Cl)(CH2CHPh)] (4) and consecutive dissociation of the chloride ligand to yield cationic square-planar styrene complexes [{2,6-C6H3(XPR2)2}Pd(CH2CHPh)]+ (6) and styrene. Cationic styrene adducts of type 6 were additionally found to be the resting states of the catalytic reaction. However, oxidative addition of phenyl bromide to 2 result in pentacoordinate PdIV complexes of type [{2,6-C6H3(XPR2)2}Pd(Br)(C6H5)]+ (11), which subsequently coordinate styrene (in trans position relative to the phenyl unit of the pincer cores) to yield hexacoordinate phenyl styrene complexes [{2,6-C6H3(XPR2)2}Pd(Br)(C6H5)(CH2CHPh)]+ (12). Migration of the phenyl ligand to the olefinic bond gives cationic, pentacoordinate phenylethenyl complexes [{2,6-C6H3(XPR2)2}Pd(Br)(CHPhCH2Ph)]+ (13). Subsequent ,-hydride elimination induces direct HBr liberation to yield cationic, square-planar (E)-stilbene complexes with general formula [{2,6-C6H3(XPR2)2}Pd(CHPhCHPh)]+ (14). Subsequent liberation of (E)-stilbene closes the catalytic cycle. [source] Can [M(H)2(H2)(PXP)] Pincer Complexes (M=Fe, Ru, Os; X=N, O, S) Serve as Catalyst Lead Structures for NH3 Synthesis from N2 and H2?CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2007Markus Hölscher Dr. Abstract The potential of pincer complexes [M(H)2(H2)(PXP)] (M=Fe, Ru, Os; X=N, O, S) to coordinate, activate, and thus catalyze the reaction of N2 with classical or nonclassical hydrogen centers present at the metal center, with the aim of forming NH3 with H2 as the only other reagent, was explored by means of DF (density functional) calculations. Screening of various complexes for their ability to perform initial hydrogen transfer to coordinated N2 showed ruthenium pincer complexes to be more promising than the corresponding iron and osmium analogues. The ligand backbone influences the reaction dramatically: the presence of pyridine and thioether groups as backbones in the ligand result in inactive catalysts, whereas ether groups such as ,-pyran and furan enable the reaction and result in unprecedented low activation barriers (23.7 and 22.1,kcal,mol,1, respectively), low enough to be interesting for practical application. Catalytic cycles were calculated for [Ru(H)2(H2)(POP)] catalysts (POP=2,5-bis(dimethylphosphanylmethyl)furan and 2,6-bis(dimethylphosphanylmethyl)-,-pyran). The height of activation barriers for the furan system is somewhat more advantageous. Formation of inactive metal nitrides has not been observed. SCRF calculations were used to introduce solvent (toluene) effects. The Gibbs free energies of activation of the numerous single reaction steps do not change significantly when solvent is included. The reaction steps associated with the formation of the active catalyst from precursors [M(H)2(H2)(PXP)] were also calculated. The otherwise inactive pyridine ligand system allows for the generation of the active catalyst species, whereas the ether ligand systems show activation barriers that could prohibit practical application. Consequently the generation of the active catalyst species needs to be addressed in further studies. [source] Synthesis and Properties of para -Substituted NCN-Pincer Palladium and Platinum ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2004Martijn Q. Slagt Dr. Abstract A variety of para -substituted NCN-pincer palladium(II) and platinum(II) complexes [MX(NCN-Z)] (M=PdII, PtII; X=Cl, Br, I; NCN-Z=[2,6-(CH2NMe2)2C6H2 -4-Z],; Z=NO2, COOH, SO3H, PO(OEt)2, PO(OH)(OEt), PO(OH)2, CH2OH, SMe, NH2) were synthesised by routes involving substitution reactions, either prior to or, notably, after metalation of the ligand. The solubility of the pincer complexes is dominated by the nature of the para substituent Z, which renders several complexes water-soluble. The influence of the para substituent on the electronic properties of the metal centre was studied by 195Pt NMR spectroscopy and DFT calculations. Both the 195Pt chemical shift and the calculated natural population charge on platinum correlate linearly with the ,p Hammett substituent constants, and thus the electronic properties of predesigned pincer complexes can be predicted. The ,p value for the para -PtI group itself was determined to be ,1.18 in methanol and ,0.72 in water/methanol (1/1). Complexes substituted with protic functional groups (CH2OH, COOH) exist as dimers in the solid state due to intermolecular hydrogen-bonding interactions. Een verscheidenheid aan para-gesubstitueerde NCN-pincer-palladium(II) en -platina(II) complexen [MX(NCN-Z)] (M=PdII, PtII; X=Cl, Br, I; NCN-Z=[2,6-(CH2NMe2)C6H2 -4-Z],; Z=NO2, COOH, SO3H, PO(OEt)2, PO(OH)(OEt), PO(OH)2, CH2OH, SMe, NH2) is gesynthetiseerd via substitutiereacties zowel voor, en hoogst opmerkelijk, ook na de metallering van het ligand. De oplosbaarheid van de pincer-complexen wordt gedomineerd door de aard van de para -substituent Z, waardoor enkele van de complexen wateroplosbaar zijn. De invloed van de para -substituent op de elektronische eigenschappen van het metaalcentrum is bestudeerd met behulp van195Pt-NMR en DFT-berekeningen. Zowel de chemische verschuiving van de195Pt-kern, als de berekende ,natural population, lading op platina vertonen een lineaire correlatie met de ,pHammett-substituentconstante, hetgeen het voorspellen van de elektronische eigenschappen van nieuwe pincercomplexen mogelijk maakt. De ,p -waarde van de para-PtI eenheid blijkt respectievelijk ,1.18 in methanol en ,0.72 in waterige methanol (1/1, v/v) te zijn. Door de aanwezigheid van intermoleculaire waterstofbruggen komen de complexen met protische functionele groepen (CH2OH, COOH) in de vaste stof voor als dimeren. [source] | ||||||||||