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A series of organometallic 4,4'-substituted benzylidene aniline complexes 4-ClPt-3,5-(CH2NMe2)2C6H2CH=NC6H4R'-4', abbreviated as PtCl[NCN(CH=NC6H4R'-4')-4], with R' = NMe2, Me, H, Cl, CN (1-5, respectively), was synthesized via a Schiff-base condensation reaction involving reaction of PtCl[NCN(CH=O)-4] (7) with the appropriate 4-R'-substituted aniline derivative (6a-e) in toluene. The resulting arylplatinum(II) products were obtained in 75-88% yield. Notably, product 2 was also obtained in 68% yield from a reaction in the solid state by grinding solid 7 with aniline 6b. The structures of 2, 4, and 5 in the solid state (single crystal X-ray diffraction) showed a non-planar geometry, in particular for compound 5. The electronic interaction between the donor benzylidene fragment PtCl(NCN-CH) and the para-R' aniline substituent through the azomethine bridge was studied with NMR and UV/Vis spectroscopy. Linear correlations were found between the azomethine ¹H, the 195Pt NMR and various 13C NMR chemical shifts, and the substituent parameters sF and sR of R' at the aniline site. In common with organic benzylidene anilines, the azomethine ¹H NMR chemical shift showed anomalous substituent behavior. The 195Pt NMR chemical shift of the platinum center can be used as a probe for the electronic properties of the delocalized p-system of the benzylidene aniline framework, to which it is connected. The dual substituent parameter treatment of the azomethine 13C NMR shift gave important insight into the unique behaviour of the Pt-pincer group as a substituent. Inductively, it is a very strong electron-withdrawing group, whereas mesomerically it behaves like a very strong electron donating group. [ABSTRACT FROM AUTHOR]

A series of new chiral pyridinyl prolinate (RPyProR) ligands and their corresponding Fe(II) triflate and chloride complexes are reported. The ligands possess an NN'O coordination motif, as found in the active site of non-heme iron enzymes with the so-called 2-His-1-carboxylate facial triad. The coordination behaviour of these ligands towards iron turned out to be dependent on the counter ion (chloride or triflate), the crystallization conditions (coordinating or non-coordinating solvents) and the presence of substituents on the ligand. In combination with Fe(II)(OTf)2, coordinatively saturated complexes of the type [Fe(L)2](OTf)2 are formed, in which the ligands adopt a meridional coordination mode. The use of FeCl2 in a non-coordinating solvent leads to 5-coordinated complexes [Fe(L)(Cl)2] with a meridional N,N',O ligand. Crystallization of these complexes from a coordinating solvent leads to 6-coordinated [Fe(L)(solv)(Cl)2] complexes (solv = methanol or acetonitrile), in which the N,N',O ligand is coordinated in a facial manner. For RPyProR ligands bearing a 6-Me substituent on the pyridine ring, solvent coordination and, accordingly, ligand rearrangement are prevented by steric constraints. The complexes were tested as oxidation catalysts in the epoxidation of alkene substrates in acetonitrile with hydrogen peroxide as the oxidant under oxidant limiting conditions. The complexes were shown to be especially active in the epoxidation of styrene type substrates (styrene and trans-beta-methylstyrene). In the best case, complex [Fe(6-Me- PyProNH2)Cl2] (15) allowed for 65% productive consumption of hydrogen peroxide toward epoxide and benzaldehyde products. [ABSTRACT FROM AUTHOR]

Starting from the Ru(iii) complex, [RuCl3(L1)](H2O) (L1: 2,6-bis(2,4,6-trimethylphenyliminomethyl)pyridine), the chemical reactivity and cytotoxic activity of a new family of Ru(ii) complexes with a number of bidentate co-ligands have been studied. The synthesis of the Ru(ii)-bis(arylimino)pyridine complexes with the co-ligands 1,10-phenanthroline (phen), 2,2′dipyridyl-(bpy), 2-(phenylazo)pyridine (azpy), 2-(phenylazo)-3-methylpyridine (3mazpy), 2-(tolylazo)pyridine (tazpy), and 2-picolinate (pic) is reported. These new six complexes, with L1 and different bidentate N donor co-ligands, have been designed to allow the binding of a monodentate chloride ligand, which would be easily hydrolysed in vitro. Elemental analysis and several spectroscopic techniques (IR, UV-Vis, 1D and 2D 1H NMR and ESI-MS) have been used for the characterization of the new Ru(ii) compounds. In addition, the crystal structure of the chlorido(2-picolinato)(2,6-bis(2,4,6-trimethylphenyliminomethyl)pyridine)ruthenium(ii) was solved and shows a slightly distorted octahedral geometry for the Ru(ii) centre with the tridentate L1 ligand coordinated in a planar mer fashion, with the bidentate ligand in a perpendicular orientation and a monodentate chloride, trans to the coordinating oxygen of the picolinate ion. The in vitro cytotoxic properties of these new Ru(ii) complexes in comparison with the parent, starting Ru(iii)-compound (IC50 values = 11–17 μM) appear to be encouraging for a broad range of cancer cell-lines tested (IC50 values = 0.4–10 μM). Some of them show better cytotoxic effects than cisplatin on a straight comparison with the same cancer cell lines. The cytotoxicity data are discussed in the light of structure–activity relationships and these ruthenium(ii) compounds could well be promising next generation candidates worth further investigation. [ABSTRACT FROM AUTHOR]

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 AB3-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 [M1(M2X)](M1= 2H, Mg, Co, Ni, Zn; M2= Pd, Br; X = Cl, Br). 195Pt 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 α-cyanoacetate, it was noted that the catalytic activity did not depend on the central metal for M1= 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(PdOH2)]BF4(i.e.MgTTP and [PdOH2(NCN)]BF4) 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. [ABSTRACT FROM AUTHOR]

ECE-pincer sulfato palladium complexes (pincer = [C6H3(CH2E)2-2,6]-; E = SPh (1), SMe (2), StBu (3), NMe2 (4)) were synthesized and characterized. In the solid-state (X-ray determinations) 3 and 4 exist as neutral ECE-pincer palladium sulfato complexes with a μ2-O,O' bridging sulfato ligand. IR and Raman spectroscopic studies revealed that in the solid-state the complexes can be present as either solely neutral or as a mixture of neutral and ionic species, depending on the preparation and morphology of the solids. In water, ionic complexes with non-coordinating sulfate ions prevail. Preliminary studies of the catalytic activity of 2-4 in the Suzuki-Miyaura C-C cross-coupling reaction of 3-iodobenzoic acid and sodium tetraphenylborate in water reveal that the C-C cross-coupling product is efficiently formed in good yields at room temperature. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a series of cationic and neutral Ni-complexes with the non-innocent PNPtBu pincer ligand is discussed. Starting with the dicationic complex 1, [Ni(PNPtBu)(NCMe)](BF4)2, a small series of dicationic and monocationic NiII complexes has been prepared. Substitution with tert-butyl isocyanide and azide occurs readily in MeCN solution. IR spectroscopy provided a practical handle to access the formal valence state of the ligand. For the monoand dicationic tert-butyl isocyanide species 3 and 6 the main vibrational bands in the IR spectra were reproduced quantitatively by DFT theoretical calculations, showing good agreement with the experimentally observed Δv upon dearomatization of the PNPtBu backbone. Using a selective dearomatization-reprotonation methodology the mononuclear Ni-thiolate species 7 and 8 are cleanly generated and their structures have been determined by X-ray crystal structure determination. Alternatively, starting from the monocationic species [Ni(PNPtBu)Cl]BF4, neutral alkyl derivatives are easily available in a two-step procedure, and these species have been spectroscopically characterized. [ABSTRACT FROM AUTHOR]

Reaction of Cp*Ti{NC(ArF2)NiPr2}Me2(1, ArF2= 2,6-C6H3F2) with [Ph3C][B(C6F5)4] gave the base-free structurally authenticated dication [Cp*2Ti2{NC(ArF2)NiPr2}2(μ-Me)2][B(C6F5)4]2(3-[BF20]2) containing two doubly α-agostic bridging methyl groups. 3-[BF20]2is a highly effective ethylene–propylene polymerization catalyst at 90 °C, and its performance is identical to the catalyst generated in situfrom 1and [Ph3C][B(C6F5)4]. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

8-Hydroxy-6-methyl-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine was formed selectively in high yields from N-(β-methallyl)imidazole by a tandem hydroformylation-cyclization sequence, representing a novel one-pot catalytic synthesis of bicyclic imidazole derivatives. [ABSTRACT FROM AUTHOR]

8-Hydroxy-6-methyl-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine was formed selectively in high yields from N-(β-methallyl)imidazole by a tandem hydroformylation–cyclization sequence, representing a novel one-pot catalytic synthesis of bicyclic imidazole derivatives. [ABSTRACT FROM AUTHOR]

A new mononuclear low-spin nickel(II) dithiolato complex, [NiL2] (1), reacts with copper iodide to form the heterooctanuclear cluster [{Ni(L)2}2(CuI)6] (2) with four trigonal-planar CuI2S and two tetrahedral CuI2S2 sites; anagostic interactions between the nickel(II) ions and aromatic protons have been demonstrated by variable-temperature NMR studies to pertain in solution. [ABSTRACT FROM AUTHOR]

A new mononuclear low-spin nickel(ii) dithiolato complex, [NiL2] (1), reacts with copper iodide to form the hetero-octanuclear cluster [{Ni(L)2}2(CuI)6] (2) with four trigonal-planar CuI2S and two tetrahedral CuI2S2sites; anagostic interactions between the nickel(ii) ions and aromatic protons have been demonstrated by variable-temperature NMR studies to pertain in solution. [ABSTRACT FROM AUTHOR]