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Single crystal X-ray diffraction reveals that 4,4'-bis(tetrahydrothiopyranyl) crystallizes in an equatorial-equatorial geometry with a gauche conformation along the central carbon-carbon bond. B3LYP/6-311G** and MP2/6-311G** calculations show that the antiperiplanar conformation is higher in energy than the gauche one because of sulfur induced stretching and widening of the cyclohexane-like rings. Calculations at various levels of theory suggest that in the antiperiplanar region the twisting coordinate of 4,4'-bis(tetrahydrothiopyranyl) exhibits a very shallow double-well potential. The gauche molecular structure of 4,4'-bis(tetrahydrothiopyranyl) thwarts efficient packing of its molecules in the solid state. Crown Copyright 2012 Published by Elsevier B.V. All rights reserved.

The coordination chemistry in aqueous media was studied for the platinum center of low-molecular-weight cationic NCN-pincer platinum complexes [RC6H2(CH2NMe2)2-3,5-Pt(H2O)-4]+ (R = −(CH2)3P(═O)(OEt)(OC6H4NO2-4) (1(OH2)), H (2(OH2))) as well as of the platinum center of the NCN-pincer platinum cation embedded in the lipase cutinase (cut-1; molecular weight 20 619.3) with various anionic, neutral, and cationic triarylphosphines. A 31P NMR study of the coordination of triarylphosphines to the cationic NCN-pincer platinum center in low-molecular-weight [2(OH2)][OTf] in both D2O and Tris buffer (Tris = tris(hydroxylmethyl)aminomethane) showed that the phosphine–platinum coordination is strongly affected by Tris buffer molecules. Two crystal structures of a NCN-pincer platinum–phosphine and a NCN-pincer platinum–ethanolamine coordination complex with ethanolamine as a functional model of Tris with hydrogen bridges, provoking a dimeric supramolecular structure, confirmed that the coordination observed in solution occurred in the solid state as well. A 31P NMR and ESI-MS study of the lipase cut-1 showed that the coordination of various triarylphosphines to the enzyme-embedded platinum center is affected by the surrounding protein backbone, discriminating between phosphines on the basis of their size and charge. By using 31P NMR spectroscopy and ESI-MS spectrometry, study of the coordination of triarylphosphines to cut-1 was possible, thereby avoiding the need for the application of laborious biochemical procedures. To the best of our knowledge, this is the first example of a study involving the selective binding of organic ligands to the metal center of a semisynthetic metalloprotein, unequivocally demonstrating that the well-established coordination chemistry for small-molecule complexes can be transferred to biological molecules. This initial study allows future explorations in the field of selective protein targeting and identification, as in protein profiling or screening studies

P-chirogenic, supramolecular hydrogen-bonding C1-symmetrical sulfonamido–phosphinamides (METAMORPhos) have been successfully prepared. They were all found to possess a characteristic prototropic equilibrium between the PIII and the PV tautomers that is slow on the NMR spectroscopic timescale. Despite the dynamic and reversible protonation of the P centre, the P-chirogenic information was found to be retained in the tautomerization process, even in a protic solvent environment. Several strategies to access the corresponding enantiopure compounds were investigated, such as diastereoselective crystallization, or enantioselective synthesis. It was possible to resolve such a class of chiral ligands with up to 99 % ee, and apply them in the Rh-catalyzed asymmetric hydrogenation of alkenes. These ligands are interesting new building blocks in the area of acid/base-type noninnocent ligand catalysis.

The preparation and comprehensive characterization of a series of homoleptic sandwich complexes containing diphosphacyclobutadiene ligands are reported. Compounds [K([18]crown-6)(thf)(2)][Fe(η(4)-P(2)C(2)tBu(2))(2)] (K1), [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)tBu(2))(2)] (K2), and [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)Ad(2))(2)] (K3, Ad = adamantyl) were obtained from reactions of [K([18]crown-6)(thf)(2)][M(η(4)-C(14)H(10))(2)] (M = Fe, Co) with tBuC[triple bond]P (1, 2), or with AdC[triple bond]P (3). Neutral sandwiches [M(η(4)-P(2)C(2)tBu(2))(2)] (4: M = Fe 5: M = Co) were obtained by oxidizing 1 and 2 with [Cp(2)Fe]PF(6). Cyclic voltammetry and spectro-electrochemistry indicate that the two [M(η(4)-P(2)C(2)tBu(2))(2)](-)/[M(η(4)-P(2)C(2)tBu(2))(2)] moieties can be reversibly interconverted by one electron oxidation and reduction, respectively. Complexes 1-5 were characterized by multinuclear NMR, EPR (1 and 5), UV/Vis, and Mossbauer spectroscopies (1 and 4), mass spectrometry (4 and 5), and microanalysis (1-3). The molecular structures of 1-5 were determined by using X-ray crystallography. Essentially D(2d)-symmetric structures were found for all five complexes, which show the two 1,3-diphosphacyclobutadiene rings in a staggered orientation. Density functional theory calculations revealed the importance of covalent metal-ligand π bonding in 1-5. Possible oxidation state assignments for the metal ions are discussed.

A series of η6,η1-heterobimetallic complexes have been prepared in which a [Ru(η6-arene)(C5R5)]+ fragment (R = H or Me) and an η1-NCN-pincer platinum fragment are combined within the same molecule. In complexes [2]+ and [3]+, the ruthenium and platinum centers are η6 and η1 coordinated, respectively, to the same arene ring, whereas in [4A]+ and [5A]+ they are coordinated to two different arene rings that are linked with a covalent bond ([4A]+) or an ethyl bridge ([5A]+). Upon changing the organic manifold between both metal centers, very strong ([2]+) to very weak ([5A]+) ruthenium- to-platinum interactions are obtained. Experimentally, X-ray crystal structures show an increaing steric hindrance when the Ru–Pt distance diminishes, and electrochemical and 195Pt NMR spectroscopic studies show a decreasing electron density on platinum from [5A]+ to [2]+. Theoretical DFT calculations were undertaken, which show an increasing charge on platinum from [5A]+ to [2]+. Our theoretical analysis shows that the particularly strong ruthenium-to-platinum electronic interactions in [2]+ and [3]+ do not come from binding of ruthenium to platinum, but from the pincer Cipso sharing its electron density between both metal centers, which decreases the σ donation to platinum, and from increased backdonation of the platinum d electrons into the π system of the arene ring.

The high-yielding synthesis and detailed characterization of two well-defined, linkage isomeric tripodal, tetradentate all-phosphorus ligands 1-3 is described. Coordination to Cu(I) resulted in formation of complexes 4-6, for which the molecular structures indicate overall tridentate coordination to the copper atom in the solid state, with one dangling peripheral phosphine. The solution studies suggest fast exchange between the three phosphine side-arms. For these new Cu(I) complexes, preliminary catalytic activity in the cyclopropanation of styrene with ethyldiazoacetate (EDA) is disclosed. The anticipated well-defined tetradentate coordination in a C(3)-symmetric fashion was achieved with Rh(I) and Ir(I), leading to the overall five-coordinated complexes 7-12. Complex 11 has the norbornadiene (nbd) ligand coordinated in an unprecedented monodentate 2,3-eta(2) mode to Rh. Furthermore, unexpected but very interesting redox-chemistry and reactivity was displayed by the Rh(Cl)-complexes 7 and 8. Oxidation resulted in the formation of stable Rh(II) metalloradicals [7]PF(6) and [8]PF(6) that were characterized by X-ray crystallography, magnetic susceptibility measurements, cyclic voltammetry, and electron paramagnetic resonance (EPR) spectroscopy. Subsequent redox-reactivity of these metalloradicals toward molecular hydrogen is described, resulting in the formation of Rh(III) hydride compounds.

We report the synthesis of a novel type of phosphinourea ligand, its coordination chemistry with rhodium, its use in the asymmetric hydroformylation of styrene, and investigations on the hydroformylation reaction mechanism. Complex studies on the 2:1 complex of phosphinourea to [Rh(acac)(CO)2] showed that a neutral trans-coordinating complex [Rh(HL-κP)(L-κ2O,P)(CO)] was formed. An anionic O,P-chelating ligand has displaced the anionic acac− ligand via an acid−base reaction involving the deprotonation of an acidic urea proton, giving Hacac. A second phosphinourea is coordinated as a neutral monodentate ligand and is linked to the chelating anionic ligand via an intramolecular hydrogen bond. The behavior of these supramolecular complexes in the hydroformylation reaction and the possible cooperative role of the ligands in the catalytic cycle were studied both experimentally and by computational methods. High-pressure NMR spectroscopy revealed that the catalytically active rhodium hydride species further consists of two neutral phosphinourea ligands and is in equilibrium with the neutral species [Rh(HL-κP)(L-κ2O,P)(CO)]. This equilibrium is likely an integrated part of a productive hydroformylation cycle involving a ligand-assisted reductive elimination of the aldehyde. DFT calculations revealed that the ligand-assisted mechanism could well be the preferred lower energetic pathway; however, the orientation of the anionic oxygen donor atom in [Rh(HL-κP)(L-κ2O,P)(CO)] prevented us from finding a direct (nonsolvent assisted) transition state to connect the intermediates. We therefore cannot exclude a mechanism where [Rh(HL-κP)(L-κ2O,P)(CO)] is a dormant species outside the productive hydroformylation cycle, although the intermediate associated with this mechanism is higher in energy. Finally, the synthesis of heteroligated complexes was investigated, consisting of two electronically different phosphinoureas, which sets the stage for combinatorial supramolecular ligand approaches in catalysis. Simply mixing two electronically different phosphinoureas with metal precursor [Rh(acac)(CO)2] resulted in the formation of a heterobidentate ligand. A set of six new phosphinoureas was used to prepare such rhodium complexes in a combinatorial fashion for the asymmetric hydroformylation of styrene, resulting in high conversions and selectivities for the branched product and moderate enantioselectivities.

We report the coordination behavior of ureaphosphane ligand 1[2-(diphenylphosphanyl)ethyl]-3-phenylurea (L1) towards different rhodium precursor complexes. Depending on the nature of the anion and the ligand/metal ratio, L1 acts either as a hybrid P, O-coordinating chelate, as an anionic P,N-coordinating chelate or as a supramolecular (hydrogen-bonded) bidentate ligand. The different types of complexes were investigated in the asymmetric hydrogenation of three olefinic substrates using ureaphosphanes L2 and L3, which are chiral analogues of L1. For methyl 2-acetamidoacrylate (Si) and dimethyl itaconate (S2) the neutral complex [Rh(L2-kappa P-2,N)(cod)], containing an anionic RN-coordinating ureaphosphane ligand, provided the best enantioselectivity (69.2 and 24.3 %, respectively). For N-(3,4-dihydro-2-naphth-alenyl)acetamide (S3) the best enantioselectivity was obtained with the cationic complex [Rh(L3-kappa P-2,O)(nbd)]BF4, containing a hybrid PO-coordinating ureaphosphane ligand (86.1 %).

The synthesis of a new series of diphosphine ligands based on 2,7-di-tert-butyl-9,9-dimethylxanthene (1), p-tolyl ether (2), ferrocene (3), and benzene (4) backbones, containing one or two 2,8-dimethylphenoxaphosphine moieties, is reported. The ligands were employed in the rhodium-catalyzed hydroformylation of 1-octene. For all four ligand backbones, introduction of phenoxaphosphine moieties led to an increase in catalytic activity and a decrease in regioselectivity toward the linear aldehyde product. Xanthene-based ligands 1a-1c yielded highly active and regioselective hydroformylation catalysts; ligands containing p-tolyl ether and ferrocene backbones 2a-2c and 3a-3c provided less active and less regioselective catalysts. Catalysts containing benzene-derived ligands 4a and 4b showed a remarkable preference for the formation of the branched aldehyde product. The coordination behavior of ligands 1-4 under hydroformylation conditions was investigated using high-pressure NMR and IR spectroscopy, revealing the distinct steric and electronic properties of the diphenylphosphine and 2,8-dimethylphenoxaphosphine moieties in ligands 1-4. The phosphacyclic moieties proved to be less basic and less sterically demanding toward other ligands in metal complexes than the acyclic diphenylphosphine moieties. For ligands that contain rigid backbones, the lack of conformational freedom in these phosphacyclic moieties does lead to repulsive interactions between the substituents of the two phosphorus donor atoms, resulting in an increase in the bite angle of the ligand. The low catalytic activity of rhodium catalysts modified by benzene-based ligands 4a-4c was attributed to the quantitative formation of HRh(L)(2) under hydroformylation conditions.

A palladium-catalyzed Stille coupling reaction was employed as a versatile method for the synthesis of a novel terpyridine-pincer (3, TPBr) bridging ligand, 4'-{4-BrC6H2(CH2NMe2)2-3,5}-2,2':6',2' '-terpyridine. Mononuclear species [PdX(TP)] (X = Br, Cl), [Ru(TPBr)(tpy)](PF6)2, and [Ru(TPBr)2](PF6)2, synthesized by selective metalation of the NCNBr-pincer moiety or complexation of the terpyridine of the bifunctional ligand TPBr, were used as building blocks for the preparation of heterodi- and trimetallic complexes [Ru(TPPdCl)(tpy)](PF6)2 (7) and [Ru(TPPdCl)2](PF6)2 (8). The molecular structures in the solid state of [PdBr(TP)] (4a) and [Ru(TPBr)2](PF6)2 (6) have been determined by single-crystal X-ray analysis. Electrochemical behavior and photophysical properties of the mono- and heterometallic complexes are described. All the above di- and trimetallic Ru complexes exhibit absorption bands attributable to (1)MLCT (Ru --tpy) transitions. For the heteroleptic complexes, the transitions involving the unsubstituted tpy ligand are at a lower energy than the tpy moiety of the TPBr ligand. The absorption bands observed in the electronic spectra for TPBr and [PdCl(TP)] have been assigned with the aid of TD-DFT calculations. All complexes display weak emission both at room temperature and in a butyronitrile glass at 77 K. The considerable red shift of the emission maxima relative to the signal of the reference compound [Ru(tpy)2]2+ indicates stabilization of the luminescent 3MLCT state. For the mono- and heterometallic complexes, electrochemical and spectroscopic studies (electronic absorption and emission spectra and luminescence lifetimes recorded at room temperature and 77 K in nitrile solvents), together with the information gained from IR spectroelectrochemical studies of the dimetallic complex [Ru(TPPdSCN)(tpy)](PF6)2, are indicative of charge redistribution through the bridging ligand TPBr. The results are in line with a weak coupling between the {Ru(tpy)2} chromophoric unit and the (non)metalated NCN-pincer moiety.

The formation of a dimeric structure of a nonsymmetric Zn(II)salphen complex is reported. The X-ray molecular structure show the formation of an oxygen-bridged species (2). In addition to this structure, a pyridine-ligated complex and an 1:2 dabco/Zn(II)salphen supramolecular assembly (dabco = diazabicyclo[2.2.2]octane) are presented. Their coordination behavior has been studied and can be correlated with the substitution pattern of the salphen ligand and the donor-strength of the involved axial ligands. The Zn(II)salphen building blocks bind in a cooperative fashion to the dabco template, the second unit being bound 4 times more strongly.

The synthesis of the first series of 4-mono and 3,5-bis(dimethylamino)methyl-functionalized triarylphosphanes of the general formula PPh 3 − n Ar n (Ar = 1-C 6 H 3 (CH 2 NMe 2 ) 2 -3,5 (NC(H)N), n = 1 (ligand 2 ) or n = 3 (ligand 4 ); Ar = 1-C 6 H 4 (CH 2 NMe 2 )-4 (NC(H)), n = 3 (ligand 7 )) is described. These phosphanes were used for the construction of complexes of the form [AuCl(P)] and [PtCl 2 (P) 2 ]. In these complexes selective coordination of phosphorus to the metal ion is observed. The 31 P NMR data show the formation of cis -Pt complexes, even in the case of triarylphosphane 4 , which features a tris{3,5-bis(dimethylamino)methyl} substitution pattern. The structure of the gold complex of mono-3,5-functionalized triarylphosphane 2 in the solid state shows a striking resemblance to the structure of the corresponding complex [AuCl(PPh 3 )]. The solid-state structure of the AuCl complex of tris-4-functionalized ligand 7 differs from that of [AuCl(PPh 3 )] in the sign of the torsion angles. The amine functionalities in this class of gold compounds could be reacted selectively with either acid (HCl, H 3 PO 4 ) to generate ammonium salts or with an alkylating agent (benzyl bromide) to afford benzyl ammonium salts, without the violation of the Au–P bond.

A series of mononuclear Fe(II) triflate complexes based on the 3,3-bis(1-alkylimidazole-2-yl)propionate ester (BAIP) ligand scaffold are reported. I, these complexes, the tripodal N,N,O-BAIP ester ligand is varied by (i) changing the ester moiety (i.e., n-Pr, tert-Bu esters, n-Pr amide), (ii) changing the methylimidazole moieties to methylbenzimidazole moieties, and (iii) changing the methylimidazole moieties to 1-ethyl-4-isopropylimidazole moieties. The general structure of the resulting complexes comprises two facially capping BAIP ligands around a coordinatively saturated octahedral Fe(II) center, with either a transoid or cisoid orientation of the N,N,O-donor manifold that depends on the combined steric and electronic demand of the ligands, In the ligands. In the case of the sterically most encumbered ligand, a four-coordinate all N-coordinate complex is formed as well, which cocrystallizes with the six-coordinate complex. In combination with the catalytic properties of the new complexes in the epoxidation/cis-dihydroxylation of cyclooctene with H2O2, in terms of turnover number and cis-diol formation, these studies provide a number of insights for further ligand design and catalyst development aimed at Fe-mediated cis-dihydroxylation.

In this paper we report the application of bis-(thiosemicarbazonato) Zn(II) complexes as building blocks in the construction of supramolecular transition metal assemblies. We investigated their coordination behaviour towards pyridylphosphine molecules and found these systems comparable to those based on Zn(porphyrin) and Zn(salphen) complexes. Additionally, catalytic experiments and an in situ high-pressure FTIR study of the supramolecular rhodium hydroformylation catalysts, assembled using the bis-(thiosemicarbazonato) Zn(II) complexes, demonstrate their applicability in supramolecular catalysis and their potential for application in other areas of supramolecular chemistry.

Liquid-chromatography electrospray-ionisation mass spectrometry (LC-ESI-MS) studies on reaction mixtures of the telomerization of 1,3-butadiene with biomass-based polyols revealed that the TOMPP (TOMPP = tris(2-methoxyphenyl)phosphine) ligand is converted towards the corresponding (2,7-octadienyl) phosphonium species during catalysis. The extent of ligand alkylation is substrate dependent and was identified as the primary cause of deactivation for carbohydrate substrates with anomeric hydroxyl groups. Coordination studies of the phosphonium cation with [Pd(dba)(2)] (dba=dibenzylideneacetone) gave insight into the alkylation mechanism and showed that the formation of the phosphonium cation is fully reversible. The reaction yields the key cationic intermediate [Pd(1,2,3,7,8-eta(5)-octa-2,7- dien-1-yl)(TOMPP)](+), which, in the presence of the iodide anion, results in the formation of [Pd(1,2,3-eta(3)-octa-2,7-dien-1-yl)(I)(TOMPP)]. Both complexes were fully characterized by various techniques including single crystal X-ray crystallography. Based on these results, an extension to the Pd/TOMPP-catalyzed telomerization mechanism was formulated to include the 2,7-octadienylphosphonium cation as a ligand reservoir. Catalytic tests show that the use of [Pd(dba)(2)] as precatalyst improves the telomerization of glucose and xylose.

[EN] The newly synthesized dinuclear complex [Fe-2(III)(mu-OH)(2)(bik)(4)](NO3)(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe center dot center dot center dot Fe (3.0723(6) angstrom) and Fe-O distances (1.941(2)/1.949(2) angstrom) compared to other unsupported Fe-2(III)(mu-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The Fe-57 isomer shift (delta = 0.45 mm s(-1)) and quadrupole splitting (Delta E-Q = 0.26 mm s(-1)) obtained from Mossbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1).S-2) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe center dot center dot center dot Fe and Fe-OH distances are overestimated (3.281 and 2.034 angstrom, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 angstrom) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J. by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe-II(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe-II(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe-II(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3 degrees/2 degrees value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O-2, and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under both limiting oxidant and substrate conditions., This work was financially supported by the National Research School Combination-Catalysis (P.C.A.B.), the Council for Chemical Sciences of The Netherlands Organization for Scientific Research (CW-NWO) (M.L. and A.L.S.), and the National Institutes of Health Grant EB-001475 (E.M.). Dr. Stefania Tanase-Grecea is kindly acknowledged for her help with the collection of the magnetic measurements. Part of the work was financially supported the EC-RTN "QuEMolNa" (No. MRTN-CT-2003-504880) and the EC Network of Excellence "MAG-MANet" (No. 515767-2).

Reaction of (S,S)-2,6-bis(4′-isopropyl-2′-oxazolinyl)phenyllithium (i-Pr-Phebox-Li) (2a) with 4,4′-bis[P-(chlorogold(I))diphenylphosphino]biphenyl [(dppbp)(AuCl)2] (5) afforded the new, bimetallic gold complex 4,4′-bis[P-(η1-C-i-Pr-Phebox-gold)diphenylphosphino]biphenyl [(P-Au(η1-C-i-Pr-Phebox))2(dppbp)] (6). Transmetalation of 6 with 2 equiv of Cl3MX (MX = TiOi-Pr, VCl, CrPy, ZrCl, HfCl, NbO) afforded the corresponding monopincer compounds [MCl2X(i-Pr-Phebox)] (M = Ti, V, Cr) (7) and [MCl2X(i-Pr-Phebox)]2 (M = Zr, Hf, Nb) (8) in high yields and the gold starting material 5, which could be quantitatively recovered and reused. The structures in the solid state of the digold compound 6, the monopincer compounds R-PheboxAu(PPh3) (R = i-Pr, t-Bu), and a number of Phebox-ETM complexes (7a, 7b, 7c, 8a, 8b, and 8c) were obtained. In each of these structures the i-Pr-Phebox monoanion is mer-N,C,N-tridentate bonded. The monopincer Phebox-Zr and -Hf compounds are dimeric because of two bridging chlorides, while the corresponding Nb compound has bridging oxygen atoms. Reaction of 6 with iron(III) chloride resulted in the formation of a N4(FeCl2)2 complex, characterized by X-ray crystal structure determination, comprising a bridging, tetradentate N4 ligand formed by C–C coupling of two Phebox anions to a biphenyl species. The new Phebox complexes 7 and 8 have been tested as olefin polymerization precatalysts. Rapid catalyst deactivation was observed in ethene polymerization under homogeneous conditions, whereas stable activity was obtained after immobilization on MgCl2-based supports. From preliminary investigations on the reaction of 8a with either methylmagnesium chloride or methyllithium we assume that the low reactivity in homogeneous polymerization is due to the alkylation of the Phebox ligand.

Transmetallation of 4,4'-bis{(2,6-bis[(dimethylamino)methyl]phenylgold)diphenyl-phosphino}biphenyl (3) with MCl(4) (M = Ti, NbCl, V) in benzene gave the corresponding transition metal pincer complexes (4) and insoluble 4,4'-bis[P-(chloro gold(I))diphenylphosphino]biphenyl (2), which can be quantitatively recovered and recycled. Interestingly, 3 did not react with TiCl(3). However, reaction of 2,6-bis[(dimethylamino)methyl]phenyllithium (1) with TiCl(3) resulted in formation of the novel diaryltitanium(IV) compound 5 (16% yield), comprising one N,C,N-mer bound NCN-pincer ligand and a second NCN-pincer ligand that is rearranged from a 1,2,6-isomer to a 1,2,4 one. The latter NCN-ligand is dianionic and is bidentate bonded; one of the CH(2)NMe(2) substituents (para to C'(ipso)) is non-coordinated, while the second CH(2)NMe(2) group, after C-H activation of one of the Me groups, is η(2)-C,N-bonded to the titanium centre trans to C(ipso) of the mer-NCN ligand. The new NCN-pincer metal complexes 2,6-bis[(dimethylamino)methyl]phenylTiCl(3) (4a) and 2,6-bis[(dimethylamino)methyl]-phenylVCl(2) (4d) gave, after immobilization on MgCl(2)-based supports, very high activity in ethene polymerisation.

A square-planar compound [Cu(pyrimol)Cl] (pyrimol = 4-methyl-2-N-(2-pyridylmethylene)aminophenolate) abbreviated as CuL–Cl) is described as a biomimetic model of the enzyme galactose oxidase (GOase). This copper(II) compound is capable of stoichiometric aerobic oxidation of activated primary alcohols in acetonitrile/water to the corresponding aldehydes. It can be obtained either from Hpyrimol (HL) or its reduced/hydrogenated form Hpyramol (4-methyl-2-N-(2-pyridylmethyl)aminophenol; H2L) readily converting to pyrimol (L ) on coordination to the copper(II) ion. Crystalline CuL–Cl and its bromide derivative exhibit a perfect square-planar geometry with Cu–O(phenolate) bond lengths of 1.944(2) and 1.938(2) A. The cyclic voltammogram of CuL–Cl exhibits an irreversible anodic wave at +0.50 and +0.57 V versus ferrocene/ferrocenium (Fc/Fc+) in dry dichloromethane and acetonitrile, respectively, corresponding to oxidation of the phenolate ligand to the corresponding phenoxyl radical. In the strongly donating acetonitrile the oxidation path involves reversible solvent coordination at the Cu(II) centre. The presence of the dominant CuII–L chromophore in the electrochemically and chemically oxidised species is evident from a new fairly intense electronic absorption at 400–480 nm ascribed to a several electronic transitions having a mixed p?p⁄(L ) intraligand and Cu–Cl ?L charge transfer character. The EPR signal of CuL–Cl disappears on oxidation due to strong intramolecular antiferromagnetic exchange coupling between the phenoxyl radical ligand (L ) and the copper(II) centre, giving rise to a singlet ground state (S = 0). The key step in the mechanism of the primary alcohol oxidation by CuL–Cl is probably the a-hydrogen abstraction from the equatorially bound alcoholate by the phenoxyl moiety in the oxidised pyrimol ligand, Cu–L , through a five-membered cyclic transition state.

Herein, we wish to describe the efficient three-step synthesis of a novel highly hindered, but flexible, N-heterocyclic carbene and its coordination chemistry to Ag(I) and Rh(I).

Oxalate from Air In light of increasing concerns about the consequences of excessive atmospheric carbon dioxide, there is demand for methods to use carbon dioxide in the preparation of more elaborate compounds. Though reactions with hydroxide salts to form carbonates tend to proceed fairly cleanly, reductive processes to form carboxylic acids, esters, and alcohols are often rather unselective. Angamuthu et al. (p. 313 ; see the news story by Service ) discovered that a copper complex exhibited remarkable selectivity in reductively coupling carbon dioxide to form oxalate through coordinative electron transfer, even in the presence of excess oxygen, normally a much more potent electron acceptor. Precipitation of the oxalate as a lithium salt and electrochemical re-reduction of the copper produced a preliminary catalytic cycle, demonstrated through six turnovers.

The synthesis and catalytic properties of ditopic mono-pincer-mono-porphyrin complexes were investigated. The statistical Adler condensation reaction of 3,5-bis(methoxymethyl)-4-bromo-benzaldehyde, p-tolylaldehyde, and pyrrole, furnished an AB(3)-type tetraphenylporphyrin, containing three meso-p-tolyl groups and one meso-3,5-bis(methoxymethyl)-4-bromophenyl group. This material was converted into the ditopic ligand [2H(Br)], which comprises one porphyrin site and an NCN-pincer type ligand moiety. In order to metalate this compound in a stepwise, site-selective manner, two distinct synthetic routes were followed. Route A relies on the introduction of a metal in the porphyrin cavity followed by pincer metalation and a reversal of this order is employed for route B. For the hetero-bimetallic pincer-porphyrin target compounds, route A invariably proved to be the highest yielding alternative, giving pincer-porphyrin hybrids of general formula [M(1)(M(2)X)] (M(1) = 2H, Mg, Co, Ni, Zn; M(2) = Pd, Br; X = Cl, Br). (195)Pt NMR spectroscopy revealed that the porphyrin metal has a modest influence on the electron density on the NCN-pincer Pt site. When the analogous cationic Pd complexes were used as Lewis acid catalysts for the double Michael addition between methyl vinyl ketone and ethyl alpha-cyanoacetate, it was noted that the catalytic activity did not depend on the central metal for M(1) = 2H, Ni, and Zn. However, when Mg occupied the porphyrin cavity, the rate of the reaction increased by a factor of six. Although a rate enhancement was observed when catalysis was conducted with a mixture of the two constituents of [Mg(PdOH(2))]BF(4) (i.e. MgTTP and [PdOH(2)(NCN)]BF(4)) this could not fully account for the rate enhancement. We believe that the rationale for this behaviour is dual, consisting of "cooperative dual catalysis" and supramolecular aggregation of two or more catalyst-substrate complexes.

The search for platinum compounds structurally different from cisplatin has led to two new platinum(II) compounds containing quinoxaline-2-carboxamide as a carrier ligand, i.e. cis-[Pt(qnxca)(MeCN)Cl2] (1) and the [Pt(qnxca-H)(dmso)Cl] (2). Both compounds have been synthesized and characterized using different spectroscopic methods. In addition, single-crystal structures have been determined by X-Ray diffraction for both compounds. In each case a square planar Pt(II) is present; in (1) the qnxca is monodentate and neutral, whereas in (2) the ligand has lost a hydrogen, to form the anionic chelating ligand abbreviated as qnxca-H. The biological activity of both compounds has been investigated in a panel of seven human tumour cells, displaying poor cytotoxic activity, compared to cisplatin. The interaction of the new compounds with 1 or 2 equiv. of 9-ethylguanine has been studied using (1)H NMR, (195)Pt NMR and ESI-MS spectroscopy, finding poor reactivity of 1 towards the model base, forming only the monosubstituted adduct. Surprisingly, compound 2, which is more sterically crowded, interacts more efficiently with the 9-EtG, forming a bifunctional adduct with two 9-EtG with substitution of the dmso and the chloride ligand. Unwinding studies of pUC19 plasmid DNA by compound 1 show similar unwinding properties to cisplatin.

New coordination polymers based on different combinations of silver atoms and pyridyl-substituted N-heterocyclic carbene moieties are described. The addition of Zn(II) templates leads to Ag-Zn supramolecular assemblies via selective Zn⋯N interactions; a process that can be reverted.

Two new, potentially cyclometalating terdentate ligands bearing phosphonate substituents, Et2O3PN^ C(H)^N (5) and Et2O3P-C(H)^N^N (7), have been prepared. The corresponding ruthenium complexes, [1]+ and [2]+, respectively, were obtained by reaction with [RuCl3(tpy)]. Complexes [1]+ and [2]+ display electronic properties characteristic for cyclometalated ruthenium complexes. The platinum complex [3], of N^C(H)^N ligand 5, was also prepared and is highly phosphorescent in solution. In general, the phosphonate group electronically behaves equivalent to a carboxylate moiety.

Novel P-stereogenic bis-phosphoramidite pincer palladium complexes 1 and 2 derived from (S)-(-)-R,R-diphenyl-2-pyrrolidinemethanol and (S)-(þ)-indolinemethanol, respectively, were synthesized in reasonable yields (i.e., 55-62%) by using a flexible, modular synthetic approach and were characterized by X-ray crystal structure determination. Reacting (S)-(þ)-indolinemethanol with PCl3 leads to the formation of a novel P-chiral building block, which exhibits good thermal stability of its stereochemical features. This enabled the design and development of new P-chiral bisphosphoramidite pincer arene ligands and their corresponding metal complexes. The molecular structure of the new indolinemethanol-derived phosphoramidite pincer metal complex screens quadrants I and III, which is in contrast to the previously reported L-proline-derived P-chiral ligands that screen quadrants II and IV. The bis-phosphoramidite pincer palladium complexes 1 and 2 are active catalysts for asymmetric homoallylation of sulfonimines, where low (ee 33%) or no enantioselectivity was observed for reactions catalyzed by 2 and 1, respectively. Preliminary catalytic results revealed that enantiomeric excess values varied by using differently functionalized sulfonimines, suggesting that both electronic properties and steric congestion of sulfonimines affect the transition state of the electrophilic attack of the 1η-allyl Pd intermediate in the allylation.

The synthesis of η6,η1 SCS- and PCP-pincer ruthenium palladium complexes [3] þ-[6] þ by direct η6-coordination of [Ru(C5R5)] þ (R = H or Me) to the arene ring of η1-palladated ECE-pincer ligands (E = S or P) is described. In the resulting hetero bis-organometallic complexes, the π- and σ-electrons of the ECE-pincer phenyl anion are involved in η6- and η1-coordination to ruthenium(II) and palladium(II), respectively. In addition to electrochemical data, which show that both metal centers are electron poor, steric effects are clearly observed by X-ray crystallography and solution NMR spectroscopy. With SCS-pincer derivatives [3] þ and [4] þ , replacement of the cyclopentadienyl ligand (complex [3] þ ) by the more hindered pentamethylcyclopentadienyl ligand (complex [4] þ ) induces an inversion of the configuration of one sulfur atom in the solid state. In parallel, the dynamic inversion of configuration of the sulfur ligand observed for [3] þ in solution is frozen for the more hindered complex [4] þ . Finally, preliminary catalytic studies in the cross-coupling reaction between trans-phenylvinylboronic acid and vinylepoxide show that, for SCS-pincer palladium complexes, η6-coordination of [Ru(C5R5)] þ has a positive influence on the catalytic activity of the palladium center.

International audience; The synthesis of an S,NH,S-pincer ligand possessing a pyrrole core and two O,O-diethylthiophosphonyl groups to design P[double bond, length as m-dash]S lateral coordination sites is reported. The synthetic procedure to produce this ligand makes use of the nitrogen atom of the pyrrole heterocycle to successively functionalize the ortho-positions with the two O,O-diethylthiophosphonyl moieties. The ortho-functionalization arises from a repetition of a [1,2] base-induced rearrangement allowing the transformation of O,O-diethyl-N-pyrollylthiophosphoramidate to ortho-thiophosphonate. The coordination properties of this tridentate S,NH,S-ligand have been investigated with silver and palladium metals. Reaction of the monoanionic S,N,S-pincer ligand 4 (O,O,O,O-tetraethylpyrrol-2,5-yl-dithiophosphonate) with PdCl2(MeCN)2 at room temperature in the presence of triethylamine gives rise to the formation of the η3-complex [Pd(η3-4′)Cl] 5. Ligand 4 also reacts with silver oxide in dichloromethane to produce complex 6 which, in the solid state, exists as a tetramer involving an almost linear arrangement of four silver atoms.

The reaction of tin dichloride with catalytically-relevant group 10 metal precursors [M(Cl)(X)(2-PyPPh(2))(2)] (M = Ni, Pd, Pt; 2-PyPPh(2) = 2-pyridyldiphenylphosphine; X = Cl, Me) provides easy access to unprecedented cationic dichlorostannylene complexes [M(X)(2-PyPPh(2))(2)(SnCl(2))](+) where the M-Sn bond is bridged by two head-to-head coordinated 2-PyPPh(2) ligands. The formation of such species instead of the classical neutral trichlorostannyl derivatives [M(X)(SnCl(3))(2-PyPPh(2))(2)] offers a new insight on the specific effect of the SnCl(2) cocatalyst in group 10 metal catalyzed transformations.

A silver-free route has been employed for the synthesis of a number of Pd and Pt complexes supported by an NCN "pincer" ligand (NCN = [2,6-(Me2NCH2)2C6H3]-) via halide abstraction. This was achieved by the use of o-, m-, and p-hydroxypyridines or o- and p-mercaptopyridines in basic ethanol solutions. The acidic OH or SH protons are removed to generate the formally anionic ligands. X-ray crystal structure determination of these complexes shows that the bonding of the substituted pyridine ligands occurs exclusively through the pyridine N for hydroxypyridines and exclusively through the thiol S in mercaptopyridines. In the hydroxypyridine case, the ortho and para isomers tautomerize to generate pyridone structures with a covalent M-N bond, whereas the m-hydroxypyridine complex, which is unable to tautomerize, is found to still be bound through the pyridine N but in a zwitterionic structure. The mercaptopyridine complexes are the first reported examples of pincer-ligated Pd and Pt thiolate species. The pyridine ligands can be quantitatively exchanged for chloride by reaction with excess NH4Cl, a potentially useful chemical switch for ligation/decomplexation of this ligand type.

Reaction of RuH2CO(PPh3)3 with tetrafluorosuccinic acid at 100 °C gave rise to the formation of the dinuclear bis(tetrafluorosuccinate)-bridged Ru(II) complex 2, containing two water ligands. Exchange of the PPh3 in complex 2 with various diphosphine ligands afforded a series of analogous complexes 3. Reaction of the latter with 1-phenylethanol at 130 °C or with 2-propanol/Et3N at room temperature furnished the dinuclear dihydrido-bridged Ru(II) complexes 4. Complexes 2 and 4 were characterized by X-ray diffraction analysis. Both bis(tetrafluorosuccinate)-bridged complexes 3 and dihydrido-bridged complexes 4 catalyze the acceptorless dehydrogenation of 1-phenylethanol to acetophenone and dihydrogen with good yields and excellent selectivity under relatively mild conditions in the absence of acid or base. A tentative catalytic cycle for the dehydrogenation of secondary alcohols by Ru(II) complexes of type 3 is presented.

The Sn(IV) butyl complexes [Bu n SnCl 3 − n (NCN)] (NCN = [C 6 H 3 (CH 2 NMe 2 ) 2 -2,6] − , n = 1 ( 1 ), 2 ( 2 ), 3 ( 3 )) were prepared. Spectroscopic analysis of 1 – 3 by 1 H and 119 Sn NMR gave evidence for the presence of intramolecular N → Sn interactions in solution. The molecular structure of 1 , as determined by a single-crystal X-ray diffraction study, revealed that it contained a six-coordinate Sn(IV) center with intramolecular N → Sn coordination of both ortho -amine substituents. Addition of SnCl 4 to 1 resulted in the isolation of the HCl adduct [BuSnCl 3 (NCN + H)] ( 6 ). Reactions of 2 and 3 with SnCl 4 each resulted in the HCl salt [SnCl 4 (NCN + H)] ( 8 ) and the corresponding butyltin chloride, Bu 2 SnCl 2 and Bu 3 SnCl, respectively. The formation of HCl adducts 6 and 8 was ascribed to transfer of the NCN ligand to SnCl 4 and the presence of HCl (from partial hydrolysis of the product or SnCl 4 during the work up procedure). The molecular structures of 6 and 8 have been determined through single-crystal X-ray diffraction and revealed the presence of a [BuSnCl 3 (aryl)] − or [SnCl 4 (aryl)] − stannate anion, respectively, with in each case one coordinated ortho -amine function and one protonated amine moiety involved in N–H⋯Cl–Sn hydrogen bonding in both compounds (2.14 A for 6 and 2.18 A for 8 ).

New asymmetric trans-platinum(II) complexes, composed of an isopropylamine, an azole and two carboxylate leaving groups, are presented. The crystal and molecular structures of one of the complexes has been determined and the cytotoxicity and reactivity with 5′-guanosine monophosphate is reported. The complexes show a reduced reactivity, but no decrease in cytotoxic activity compared to their chloro-counterparts. Furthermore the complexes largely overcome cisplatin resistance, they therefore present an interesting class of antitumour active trans-platinum complexes.

Three ruthenium polypyridyl compounds of structural formula [Ru(apy)(tpy)Ln−](ClO4)(2−n) (apy = 2,2′-azobispyridine; tpy = 2,2′:6′,2″-terpyridine; L = Cl, H2O, CH3CN) (1a–c) were synthesized and crystallized. These complexes were fully characterized by means of 1D and 2D 1H NMR spectroscopy, as well as mass spectrometry and elemental analysis. Although in theory two isomers are possible, i.e. the one in which the central N atom in tpy is trans to the azo N in apy and the one in which the former is trans to the pyridine N in apy, in all cases only the latter was observed. The molecular structures of the compounds were elucidated by single-crystal X-ray diffraction.

Cationic rhodium and iridium complexes with dibenzo[a,e]cyclooctatetraene (dbcot) and bislutidylamine (bla) were synthesized from the respective [M(μ-Cl)(dbcot)]2 dimers and the bla ligand and were characterized by NMR, X-ray diffraction, and cyclic voltammetry. Both [MI(dbcot)(bla)]+ complexes are easily oxidized by one electron to form paramagnetic dicationic analogues [MII(dbcot)(bla)]2+ (M = Rh, Ir). In the solid state, the geometry changes from a distorted trigonal bipyramid to square pyramidal upon oxidation of the metal from MI to MII, as evidenced by X-ray diffraction studies of the iridium complexes. The paramagnetic complexes undergo facile one-electron reduction in the presence of base, most likely involving oxidation of the solvent or hydroxide anions. A control experiment using the corresponding [RhII(dbcot)(Bn-bla)]2+ complex, wherein Bn-bla is the N-benzyl-protected bla ligand, gives similar results, which strongly suggests that deprotonation of the N−H moiety of the [MII(dbcot)(bla)]2+ plays a minor role (if any at all) in the observed base-mediated reduction processes. Reaction of bla with [Ir(μ-Cl)(coe)]2 (coe = cis-cyclooctene) results in oxidative addition of the vinylic C−H bond of coe to the metal center, as evidenced by X-ray diffraction.

The reaction of the complexes [FeCpX(CO)2] (X = Cl, Br, I) into either [FeCp(CO)(PP)]X or [FeCpX(PP)] (PP = a bidentate diphosphine ligand) is shown to be highly dependent of the phosphine ligand used. Diphosphine ligands that form stable chelates favor formation of the neutral complex, whereas diphosphine ligands that form less stable chelates favor formation of the cationic complex. Thus, with the use of dppdmp (= 1,3-bis(diphenylphosphino)-2,2-dimethylpropane) the [FeCpX(PP)] complexes (X = Cl, Br, I) are selectively formed, induced by a gem-dialkyl effect. Apart from the bidentate phosphine ligand, the halide ion present in the iron complex has a significant influence on the course of the substitution reaction.

The Pt(II) coordination chemistry of oligocationic ammoniomethyl- and neutral aminomethyl-substituted triarylphosphines (L) is described. Complexes of the type PtX(2)(L)(2) (X = Cl, I) have been isolated and characterized. For the hexa-meta-ammoniomethyl-substituted ligands [1](6+) and [2](6+), two ligands always occupy a trans-configuration with respect to each other in complexes of the type PtX(2)(L)(2), while for the tri-para-ammoniomethyl-substituted ligand [7](3+), the trans/cis ratio is dependent on the ionic strength of the solution. This behaviour was not observed for the neutral aminomethyl-substituted ligands. In the crystal structure of trans-[PtI(2)(1)(2)]I(12), the geometrical parameters of the phosphine ligand [1](6+) are very similar to those found in the analogous complex of the benchmark ligand PPh(3), i.e. trans-PtI(2)(PPh(3))(2), indicating that no significant increase in the steric congestion is present in the complex. Instead, the coordination chemistry of this class of phosphine ligands is dominated by repulsive Coulombic inter-ligand interactions.

A new class of cyclic double bridged diphosphine ligands was developed and the coordination properties are described. The reaction of 4,5-dilithioxanthene with dichlorophenylphosphine gave a cyclic double bridged diphosphine ligand based on two xanthene backbones (4) as a single stereoisomer. X-ray crystal structure determination revealed that the groups bridging the two phosphorus atoms are arranged in a syn-disposition. This new cyclic bisxantphos structure was modified with bulky residues at the third substituent of the phosphorus atoms, thus forming cavity-shaped ligands.

Complexes of the type [Pd(ligand)(2)](anion)(2) were prepared with a series of bidentate di(o-methoxyphenyl)phosphine ligands with increasing steric bulk on the meta position of the phenyl groups: m-H (L1); m-MeO (L2); and m-Me (L3). The solid-state structure of [Pd(L2)(2)](OTs)(2) revealed that the two ligands are symmetrically coordinated to Pd(2+). In the solid state structure of [Pd(L3)(2)](OTs)(2) however, the two ligands are unsymmetrically coordinated to Pd(2+), yielding an unprecedented conformation of this bis-chelate P(4)Pd(2+) complex. (1)H-(1)H-COSY and NOESY analysis and a (31)P-NMR simulation showed that the asymmetric structure of [Pd(L3)(2)](OTs)(2) is retained in solution.

A mono- and a 1,3-bis-phosphite arene ligand based on 2,20-biphenol have been synthesized in order to study the synthesis of the corresponding palladium(II) complexes starting from different Pd precursors. Novel bis-phosphite palladium complex 1 [PdCl2(L)2] (L¼ dibenzo[d,f][1,3,2]dioxaphosphepin, 6-phenoxy), C,P-chelate bonded monophosphite palladium complex 2 [Pd(k2-L)(m-Cl)]2, and PCP-pincer palladium complex 3 have been prepared from these ligands in promising to excellent yields (50e95%). Additionally, complexes 1 and 3 have been characterized by X-ray crystal structure determinations. The application of 2,6-bis-phosphite pincer palladium(II) complex 3 in CeP cross-coupling between diphenylphosphine- borane and a wide range of various aryl iodides under very mild conditions is reported. Kinetic investigations indicate that 3 merely acts as a pre-catalyst and that Pd nanoparticles are the actual catalytically active species.

New heterobidentate N-heterocyclic carbene-triazolyl ligands and several of their palladium(II) complexes have been synthesized in a modular fashion using click chemistry. These complexes are the first examples where triazolyl-substituted NHCs exhibit bidentate behavior, which was confirmed by NMR and X-ray diffraction studies. The synthesis of the complexes could be achieved in relatively few steps by introducing the diversity at a late stage in the synthesis. The complexes are active precatalysts in the transfer semihydrogenation of alkynes to Z-alkenes, with activity and selectivity depending on the triazolyl substituent and the NHC nitrogen substituent. Selectivities as high as 99% were observed.

The new phenoxo-bridged uranyl [(UO2)2L2(thf)2] [H2L = N(2-oxyphenyl)-3-methoxy salicylaldiminato (C14H11NO3)] compound has been synthesized and characterized. The 3D structure of the free ligand is also reported. The complex crystallizes in the monoclinic space group P21/c with lattice parameters a = 19.5915(15) A, b = 10.4096(9) A, c = 17.5216(14) A and β = 99.9960(7)° with z = 4. The compound consists of a dinuclear unit composed of two dioxouranium(VI) ions, bridged by two phenoxide oxygens. The coordination around each uranium atom can be regarded as approximately pentagonal bipyramidal. The two uranyl groups are separated by 3.9192(5) A. The title complex is one of the few examples for bis-uranyl groups bridged by phenoxo ligands. These types of ligands are candidates for the sequestration of the uranium from nuclear waste and provide a good selectivity over competing lanthanide cations in solution. The ligand has been found to selectively bind to a representative actinide ( UO 2 2 + ) rather than to lanthanum (Ln3+), which is probably related to the larger ionic radii of Ln(III). So, the ligand is not suitable to clutch two lanthanide metals via the phenolate bridge (Ln–O(phenol)–Ln). The spherical shape and the larger size of the Ln(III) ions apparently do not allow a fit within the byte angle of phenolate bridge.