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By taking advantage of a sequence of oxidative addition/reductive elimination reactions, Pt(II) cyclometalated derivatives are able to promote a rare C(sp2)-C(sp3) bond coupling, resulting in the production of novel methyl-substituted pyridines and bipyridines. Starting from 6-phenyl-2,2′-bipyridine, the step-by-step full sequence of reactions has been followed, leading to the unprecedented 3-methyl-6-phenyl-2,2′-bipyridine, which was isolated and fully characterized. The synthesis involves the following steps: (1) rollover cyclometalation to give the starting complex [Pt(N^C)(DMSO)Me]; (2) the synthesis of a more electron-rich complex [Pt(N^C)(PPh3)Me] by the substitution of DMSO with triphenylphosphine; (3) oxidative addition with methyl iodide to give the Pt(IV) complex [Pt(N^C)(PPh3)(Me)2(I)]; (4) iodide abstraction with silver tetrafluoborate to give an unstable pentacoordinate intermediate, which rapidly evolves through a carbon–carbon reductive coupling, forming a new C(sp3)-C(sp2) bond; (5) finally, the extrusion and characterization of the newly formed 3-methyl-6-phenyl-2,2′-bipyridine. The reaction has been therefore extended to a well-known classical cyclometalating ligand, 2-phenylpyridine, demonstrating that the method is not restricted to rollover derivatives. Following the same step-by-step procedure, 2-phenylpyridine was converted to 2-o-tolyl-pyridine, displaying the potential application of the method to the larger family of classical cyclometalated complexes. The application of this protocol may be useful to convert an array of heterocyclic compounds to their methyl- or alkyl-substituted analogs. [ABSTRACT FROM AUTHOR]

Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)2](ClO4)2∙4H2O (1) and [Ni(terpyepy)2](ClO4)2 MeOH (2) [terpyCOOH = 4′-carboxyl-2,2′:6′,2″-terpyridine and terpyepy = 4′-[(2-pyridin-4-yl)ethynyl]-2,2′:6′,2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel–nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9–200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χMT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to −6.0 (1) and −4.7 cm−1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0–5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • The first regioselective palladium(II)-catalyzed alkoxy-aryloxycarbonylation of olefins is described. • Various olefins, alcohols and phenols have been converted into the corresponding mixed alkyl-aryl succinates in one-step, with yields up to 90%, under mild reaction conditions (4 bar of CO and 20 °C). • The selectivity of the process has been explained by means of DFT calculations. • The unexpected role of the oxidant benzoquinone, in promoting the final elimination step leading to the succinic product, has been identified. The direct alkoxy-aryloxycarbonylation reaction of olefins has been realized for the first time. Under palladium(II) catalysis and with p -benzoquinone as oxidant, various olefins (aromatic, aliphatic and 1,2-disubstituted), alcohols (primary, secondary and tertiary) and phenols (with different para , meta and ortho substituents) have been converted in one-step into mixed alkyl aryl succinates in moderate to excellent yields (up to 90%). The reaction is completely regioselective, as the aryl ester moiety was consistently observed on the more substituted carbon of the starting alkene double bond. Based on experimental results and detailed DFT calculations, a plausible catalytic cycle has been proposed, accounting for the observed regioselectivity. Interestingly, from our computation studies, benzoquinone was found to be crucial not only to regenerate the catalytic active species, but also for promoting the final elimination step, leading to the desired succinate. Finally, some reactions were performed to prove the different chemical behavior of the two installed ester groups. [ABSTRACT FROM AUTHOR]

By taking advantage of a sequence of oxidative addition/reductive elimination reactions, Pt(II) cyclometalated derivatives are able to promote a rare C(sp2)-C(sp3) bond coupling, resulting in the production of novel methyl-substituted pyridines and bipyridines. Starting from 6-phenyl-2,2′-bipyridine, the step-by-step full sequence of reactions has been followed, leading to the unprecedented 3-methyl-6-phenyl-2,2′-bipyridine, which was isolated and fully characterized. The synthesis involves the following steps: (1) rollover cyclometalation to give the starting complex [Pt(N^C)(DMSO)Me]; (2) the synthesis of a more electron-rich complex [Pt(N^C)(PPh3)Me] by the substitution of DMSO with triphenylphosphine; (3) oxidative addition with methyl iodide to give the Pt(IV) complex [Pt(N^C)(PPh3)(Me)2(I)]; (4) iodide abstraction with silver tetrafluoborate to give an unstable pentacoordinate intermediate, which rapidly evolves through a carbon–carbon reductive coupling, forming a new C(sp3)-C(sp2) bond; (5) finally, the extrusion and characterization of the newly formed 3-methyl-6-phenyl-2,2′-bipyridine. The reaction has been therefore extended to a well-known classical cyclometalating ligand, 2-phenylpyridine, demonstrating that the method is not restricted to rollover derivatives. Following the same step-by-step procedure, 2-phenylpyridine was converted to 2-o-tolyl-pyridine, displaying the potential application of the method to the larger family of classical cyclometalated complexes. The application of this protocol may be useful to convert an array of heterocyclic compounds to their methyl- or alkyl-substituted analogs.

The equilibrium of copper-catalyzed atom transfer radical polymerization was investigated in silico with the aim of finding an explanation for the experimentally observed solvent effect. Various combinations of alkyl halide initiators and copper complexes in acetonitrile (MeCN) and dimethyl sulfoxide (DMSO) were taken into consideration. A continuum model for solvation, which does not account for the explicit interactions between the solvent and metal complex, is not adequate and does not allow the reproduction of the experimental trend. However, when the solvent molecules are included in the coordination sphere of the copper(I,II) species and the continuum description of the medium is still used, a solvent dependence of process thermodynamics emerges, in fair agreement with experimental trends. [ABSTRACT FROM AUTHOR]

Rollover cyclometalated complexes constitute a family of derivatives which differ from classical cyclometalated species in certain aspects. Various potential application fields have been developed for both classes of compounds, which have both similarities and differences. In order to uncover the relationships and distinctions between these two families of compounds, four Pt(II) cyclometalated complexes derived from 2-phenylpyridine (ppy) and 2,2′-bipyridine (bpy), assumed as prototypical ligands, were compared. For this study, an electron rich isostructural and isoelectronic pair of compounds, [Pt(N^C)Me(PPh3)], and an electron-poorer compound, [Pt(N^C)Cl(PPh3)] were chosen (N^C = ppy or bpy). DFT calculations, cyclic voltammetry, and UV-Vis spectra also helped to shed light into these species. Due to the presence of the more electronegative nitrogen in place of a C-H group, the rollover bpy-H ligand becomes a slightly weaker donor than the classical ppy-H ligand, and hence, generates (slightly) more stable cyclometalated complexes, lower energy frontier molecular orbitals, and electron-poorer platinum centers. On the whole, it was revealed that classical and rollover complexes have overall structural similarity, which contrasts to their somewhat different chemical behavior. [ABSTRACT FROM AUTHOR]

Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)2](ClO4)2∙4H2O (1) and [Ni(terpyepy)2](ClO4)2 MeOH (2) [terpyCOOH = 4′-carboxyl-2,2′:6′,2″-terpyridine and terpyepy = 4′-[(2-pyridin-4-yl)ethynyl]-2,2′:6′,2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel–nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9–200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χMT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to −6.0 (1) and −4.7 cm−1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0–5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2.

Three 2,1,3-benzothiadiazole-based ligands decorated with two pyridyl groups, 4,7-di(2-pyridyl)-2,1,3-benzothiadiazol (2-PyBTD), 4,7-di(3-pyridyl)-2,1,3-benzothiadiazol (3-PyBTD) and 4,7-di(4-pyridyl)-2,1,3 benzothiadiazol (4-PyBTD), generate ZnII and AgI complexes with a rich structural variety: [Zn(hfac)2(2-PyBTD)] 1, [Zn2(hfac)4(2-PyBTD)] 2, [Ag(CF3SO3)(2-PyBTD)]23, [Ag(2-PyBTD)]2(SbF6)24, [Ag2(NO3)2(2-PyBTD)(CH3CN)] 5, [Zn(hfac)2(3-PyBTD)] 6, [Zn(hfac)2(4-PyBTD)] 7, [ZnCl2(4-PyBTD)2] 8 and [ZnCl2(4-PyBTD)] 9 (hfac = hexafluoroacetylacetonato). The nature of the resulting complexes (discrete species or coordination polymers) is influenced by the relative position of the pyridyl nitrogen atoms, the nature of the starting metal precursors, as well as by the synthetic conditions. Compounds 1 and 8 are mononuclear and 2, 3 and 4 are binuclear species. Compounds 6, 7 and 9 are 1D coordination polymers, while compound 5 is a 2D coordination polymer, the metal ions being bridged by 2-PyBTD and nitrato ligands. The solid-state architectures are sustained by intermolecular π–π stacking interactions established between the pyridyl group and the benzene ring from the benzothiadiazol moiety. Compounds 1, 2, 7–9 show luminescence in the visible range. Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) calculations have been performed on the ZnII complexes 1 and 2 in order to disclose the nature of the electronic transitions and to have an insight on the modulation of the photophysical properties upon complexation.

Copper(I) halide complexes are well sought-after materials due to their rich structural diversities and photophysical properties. Profoundly, there is a direct relationship between each structural variation and luminescence of these complexes, for a purported use. In this review, recent publications within the last 2 years about copper(I) halide complexes, centering on their structural dimensionalities with derivatives of nitrogen, phosphorus, and sulfur ligands, have been considered alongside their effects on luminescence.

Rollover cyclometalated complexes constitute a family of derivatives which differ from classical cyclometalated species in certain aspects. Various potential application fields have been developed for both classes of compounds, which have both similarities and differences. In order to uncover the relationships and distinctions between these two families of compounds, four Pt(II) cyclometalated complexes derived from 2-phenylpyridine (ppy) and 2,2′-bipyridine (bpy), assumed as prototypical ligands, were compared. For this study, an electron rich isostructural and isoelectronic pair of compounds, [Pt(N^C)Me(PPh3)], and an electron-poorer compound, [Pt(N^C)Cl(PPh3)] were chosen (N^C = ppy or bpy). DFT calculations, cyclic voltammetry, and UV-Vis spectra also helped to shed light into these species. Due to the presence of the more electronegative nitrogen in place of a C-H group, the rollover bpy-H ligand becomes a slightly weaker donor than the classical ppy-H ligand, and hence, generates (slightly) more stable cyclometalated complexes, lower energy frontier molecular orbitals, and electron-poorer platinum centers. On the whole, it was revealed that classical and rollover complexes have overall structural similarity, which contrasts to their somewhat different chemical behavior.

The iron(II) complexes [Fe(bpy)3](OTf)2 (bpy = 2,2'-bipyridine; OTf = CF3SO3) (1) and [Fe(bpydeg)3](OTf)2 (bpydeg = N4,N4-bis(2-(2-methoxyethoxy)ethyl) [2,2'-bipyridine]-4,4'-dicarboxamide) (2), the latter being a newly synthesized ligand, were employed as catalyst precursors for the oxidation of 1-phenylethanol with hydrogen peroxide in water, using either microwave or conventional heating. With the same oxidant and medium the oxidation of glycerol was also explored in the presence of 1 and 2, as well as of two similar iron(II) complexes bearing tridentate ligands, i.e., [Fe(terpy)2](OTf)2 (terpy = 2, 6-di(2-pyridyl)pyridine) (3) and [Fe(bpa)2](OTf)2 (bpa = bis(2-pyridinylmethyl)amine) (4): in most reactions the major product formed was formic acid, although with careful tuning of the experimental conditions significant amounts of dihydroxyacetone were obtained. Addition of heterocyclic amino acids (e.g., picolinic acid) increased the reaction yields of most catalytic reactions. The effect of such additives on the evolution of the catalyst precursors was studied by spectroscopic (NMR, UV-visible) and ESI-MS techniques.

Dianionic N,N-chelating ligands play a crucial role in coordination chemistry, but reports on related complexes remain limited to certain types of ligands. In here, the reactions of two diprotic ligands, i.e., a biguanide and a carbothiamide, with trimethylaluminium, are reported, which give rise to mono- and dinuclear aluminium(III) complexes. In addition, single deprotonation of the diprotic biguanide using potassium bis(trimethylsilyl)amide gives rise to a one-dimensional coordination polymer. All complexes have been fully characterized, and their solid-state structures were determined by single crystal X-ray diffraction analysis.

Four new compounds of formulas [Cu(hfac)2(L)] (1), [Ni(hfac)2(L)] (2), [{Cu(hfac)2}2(µ-L)]·2CH3OH (3) and [{Ni(hfac)2}2(µ-L)]·2CH3CN (4) [Hhfac = hexafluoroacetylacetone and L = 3,6-bis(picolylamino)-1,2,4,5-tetrazine] have been prepared and their structures determined by X-ray diffraction on single crystals. Compounds 1 and 2 are isostructural mononuclear complexes where the metal ions [copper(II) (1) and nickel(II) (2)] are six-coordinated in distorted octahedral MN2O4 surroundings which are built by two bidentate hfac ligands plus another bidentate L molecule. This last ligand coordinates to the metal ions through the nitrogen atoms of the picolylamine fragment. Compounds 3 and 4 are centrosymmetric homodinuclear compounds where two bidentate hfac units are the bidentate capping ligands at each metal center and a bis-bidentate L molecule acts as a bridge. The values of the intramolecular metal···metal separation are 7.97 (3) and 7.82 Å (4). Static (dc) magnetic susceptibility measurements were carried out for polycrystalline samples 1–4 in the temperature range 1.9–300 K. Curie law behaviors were observed for 1 and 2, the downturn of χMT in the low temperature region for 2 being due to the zero-field splitting of the nickel(II) ion. Very weak [J = −0.247(2) cm−1] and relatively weak intramolecular antiferromagnetic interactions [J = −4.86(2) cm−1] occurred in 3 and 4, respectively (the spin Hamiltonian being defined as H = −JS1·S2). Simple symmetry considerations about the overlap between the magnetic orbitals across the extended bis-bidentate L bridge in 3 and 4 account for their magnetic properties.

Abstract In recent years, considerable effort has been focused in Pd catalyzed cross-coupling reactions, especially the use of less reactive and economically viable substrates like aryl chlorides. Unfortunately, Pd complexes containing the ligands having only N as a donor atom has some limitations, as it couples, mostly aryl iodides and bromides with different nucleophiles, and shows less activity towards aryl chlorides. This restriction can overwhelm by the use of Pd complexes containing N in combination with the C as a donor atom such as palladacycles, pincers, PEPPSI and carbene ligands. The advantages of these ligands include high activity with enhanced selectivity, less toxicity, moisture, air as well as thermal stability. Most importantly, such complexes have broad applications in catalysis under ambient conditions. This part of compressive review highlights the results of the highly active C N based Pd complexes and their applications in cross-coupling reactions. In the next part, we will cover all ligands and complexes containing N in combination with P, O and S as a donor atoms (Pd catalysts based on C P, C O and C S ligands). Though, the number of C N based Pd complexes containing Ferrocene and Buchwald ligands were reported for Pd catalyzed cross-coupling reaction, these complexes will be covered in the next part of the article. Graphical abstract Image 1 Highlights • Pd catalyzed cross coupling reaction of compounds containing C N bonds. • Update of the recent efforts made in the coupling reactions by Pd complexes based on the C N ligands. • The present part focused on the applications of the ligands containing C N as donor atoms. • Next part covers all ligands and catalysts containing N in combination with O, P and S as a donor atoms. [ABSTRACT FROM AUTHOR]

Abstract Oxidation of primary and secondary alcohols, including two diols and glycerol, with H 2 O 2 was catalyzed by the iron(II) complexes [FeL 3 ](OTf) 2 (L = 2,2′-bipyridine, 2,2′-bipyrimidine, 1,10-phenanthroline and substituted derivatives) and [FeL 2 ](OTf) 2 (L = bis(2-pyridinylmethyl)amine, 2,6-di(2-pyridyl)pyridine). The reactions were performed in acetonitrile, water or mixed solvent (typically water/acetonitrile 4:1) in a microwawe reactor at low power. Effect of addition of a cocatalyst, which in some cases improved the yields of the catalytic reaction, was investigated by means of NMR and UV–Visible techniques. Graphical abstract The iron(II) complexes [FeL 3 ](OTf) 2 (L = 2,2′-bipyridine, 2,2′-bipyrimidine, 1,10-phenanthroline and substituted derivatives) and [FeL 2 ](OTf) 2 (L = bis(2-pyridinylmethyl)amine, 2,6-di(2-pyridyl)pyridine) are competent catalysts for microwave-assisted oxidation of alcohols. Addition of some heterocyclic aminoacids as cocatalysts improved the reaction yields; the effect of such additives was studied by NMR and UV–Visible spectroscopies. Image 1 Highlights • Highly sustainable oxidation due to choice of oxidant, solvents and MW heating. • Iron-based catalysts with simple, commercial nitrogen ligands. • Water or water/organic solvent as green reaction medium. • Improved reaction yields by addition of some aminoacids as cocatalysts. • Spectroscopic (NMR, UV–Visible) studies on the effect of cocatalyst. [ABSTRACT FROM AUTHOR]

The Pd catalyzed cross coupling reactions of compounds containing C-X bonds (C-I, C-Br, C-Cl, C-N, C-O and C-H) with a variety of nucleophiles is one of the most efficient and reliable approachs for the construction of new C-C and C-heteroatom bonds. In recent years, great achievements have been made in this field, and many powerful catalytic systems based on ligand design have been developed. This comprehensive review covers recent effort made in the constructions of C-C and C-heteroatom bonds through Pd complexes based on the N ligands. We divided this topic into two parts. In present part we have focused on the applications of the ligands containing only N as a donor atom. In the next part we will cover all ligands and complexes containing N in combination with C, P, O and S as a donor atom. [ABSTRACT FROM AUTHOR]

Twelve new imidazole-based potential bi- and tridentate ligands were synthesized and characterized. Whereas in the first series the α-amino acid and imidazole moieties were linked by an amino bond, in the second series the tridentate ligands, containing two imidazole groups, were separated by an amide bond. The first series was obtained by the reductive amination of 2-phenylimidazole-4-carboxaldehyde with α-amino acid esters. The tridentate ligands were prepared from 2-phenylimidazole-4-carboxylic acid and chiral amines. In the Henry reaction, the amines were revealed as a more reactive species than the less nucleophilic amides, however the enantiomeric excesses were generally poor.

Tris(pyrazolyl)borate (scorpionate) ligands can be considered as the most prolific ligands in contemporary coordination chemistry due to the availability of various steric and electronic substituents at the pyrazolyl rings that allow fine-tuning of the open-coordination site for metal centres. The thallium(I) complexes of anionic tridentate-chelating scorpionate ligands, namely [tris(3-mesityl-5-methyl-1 H-pyrazol-1-yl-κ N2)hydroborato]thallium(I) monohydrate, [Tl(C39H46BN6)]·H2O, (I), and [bis(3-mesityl-5-methyl-1 H-pyrazol-1-yl-κ N2)(5-mesityl-3-methyl-1 H-pyrazol-1-yl-κ N2)hydroborato]thallium(I), [Tl(C39H46BN6)], (II), show a {TlIN3} coordination, with average TlI-N bond lengths of 2.53 and 2.55 Å in (I) and (II), respectively. The overall TlI coordination geometry is distorted trigonal pyramidal, with the average N-TlI-N angle being approximately 73° for both. The dihedral angle between the planes of the pyrazolyl and benzene rings of the mesityl group is 82° in (I), while the corresponding angles in (II) are in the range 64-104°. The structural differences between the two ligands are expected to contribute to the different reactivities of the transition metal coordination complexes towards activation of small molecules such as dioxygen and ethylene. [ABSTRACT FROM AUTHOR]

The iron(II) complexes [Fe(N-N) 3 ](OTf) 2 (N-N = 2,2′- bipyridine, 1,10-phenanthroline and substituted derivatives) were employed as catalyst precursors for the oxidation of primary and secondary alcohols, including glycerol. The single-crystal structure of [Fe(bipy) 3 ](OTf) 2 was determined by X-ray crystallography.The catalytic reactions were performed using either H 2 O 2 or tert -butilhydroperoxide (TBHP) as oxidating agent, in mild experimental conditions: with all catalysts employed, secondary alcohols were oxidized to the corresponding ketones with up to 100% yields, whereas other substrates gave lower conversions. Indications on the nature of the catalytically active species, which is probably formed via dissociation of a nitrogen ligand from the iron center, were obtained from NMR and ESI–MS spectra. [ABSTRACT FROM AUTHOR]

Highlights: [•] High activities of palladium nanoparticle catalysts stabilized by nitrogen ligands in micellar nanoreactors (TOF=110,000h−1). [•] Superior activity over water-soluble Pd/TPPTS benchmark catalyst. [•] Hydrogenation of renewable polyunsaturated methyl esters of soybean oil. [•] Upgraded biodiesel of improved oxidative stability, energy and environmental performance. [•] Environmentally friendly aqueous medium. [ABSTRACT FROM AUTHOR]

Highlights: [•] We use calorimetry to study bidentate ligand binding to a solvated Pd(II) salt. [•] Favorable enthalpic contributions dictate the stability of the chelated complexes. [•] Ligands with P donor atoms contribute more favorably to enthalpy than N atoms. [•] Solvent reorganization contributes to the observed enthalpy of binding. [ABSTRACT FROM AUTHOR]

Abstract: The coordination chemistry of the ferrocene ligands [(4-pyridylamino)carbonyl]ferrocene (L1) and 1,1′-bis[(4-pyridylamino)carbonyl]ferrocene (L2) with group 11 metals and thallium has been studied, and several complexes with coordination of the metal to the pyridine nitrogen atom or to the pyridine and carbonyl group have been prepared. For the ligand L1 complexes such as [AuX(L1)] (X = Cl, C6F5), [M(PPh3)(L1)]OTf (M = Au, Ag) (OTf = trifluoromethylsulfonate), [Ag(OTf)(L1)] or [M(L1)2]+ (M = Au, Ag, Cu) have been obtained. The thallium compound [Tl2(L1)4]2+ has also been prepared by reaction of Tl(PF6) with L1 and show an interesting structural framework with formation of a metalacycle resembling a macrocyclic compound. For the disubstituted ligand L2 dinuclear complexes such as [Au2(C6F5)2(μ-L2)] or [M2(PPh3)2(μ-L2)](OTf)2 (M = Au, Ag) or the polymeric species [Ag(μ-L2)]OTf have been isolated. The crystal structures of some of these derivatives show supramolecular assemblies through hydrogen bonding. [Copyright &y& Elsevier]

Abstract: Methyldihalobismuthines, BiMeX2 (X = Cl or Br) prepared from MeLi and a stoichiometric amount of BiX3 in thf, react with 1,10-phenanthroline, 2,2′-bipyridyl or Me2NCH2CH2NMe2 (L−L) in thf or MeCN to give [BiMeX2(L−L)], which are poorly soluble in non-polar solvents. X-Ray structures of [BiMeBr2(L−L)] and of [BiMeCl2(Me2NCH2CH2NMe2)] show discrete square pyramidal molecules with apical methyl groups, and no intermolecular contacts within the sum of the appropriate Van der Waals radii. The structure of BiMe2Br is a 1-D polymer chain with bromine bridges containing a pseudo-trigonal bipyramidal geometry at bismuth. The reactions of BiMe2X with the bidentate N-donor ligands result in disproportionation to also form [BiMeX2(L–L)]. An unusual [BiMeBr4]2− anion in the salt [Li(H2O)(1,10-phen)2][Li(1,10-phen)2(μ-Br)BiMeBr3]·thf, was isolated as a by-product and shows a Li−Br−Bi bridge to one of the Li cations. BiMe2Br disproportionates on reaction with [M(CO)5(thf)] (M = Cr or W) to form [M(CO)5(BiMe3)]. [Copyright &y& Elsevier]

Abstract: The reactions of 1,3-diisopropyl-4,5-dimethylimidazolin-2-imine (Im i PrNH) with the trimethylsilylmethyl (neosilyl) complexes [M(CH2SiMe3)3(THF)2] (M=Sc, Y, Lu) in a 3:1 ratio afforded tetramethylsilane (TMS) and the dinuclear imidazolin-2-iminato complexes [M2(Im i PrN)6(THF)n] (1a, M=Sc, n=0; 1b, M=Y, n=1; 1c, M=Lu, n=1), in which the metal atoms are bridged by two μ2-Im i PrN ligands. 1a crystallized from THF/pentane solution to afford a solvent-free, centrosymmetric, dimeric complex, in which both scandium atoms attain a coordination number of four; three uncoordinated THF per dimer are observed. In contrast, the X-ray crystal structures of 1b·2THF and 1c·2THF reveal the formation of unsymmetric THF solvate complexes that contain one THF ligand and therefore both four- and five-coordinated rare earth metal atoms; other THF molecules are non-coordinating. The reaction of [Y(CH2SiMe3)3(THF)2] with three equivalents of the sterically more demanding 1,3-di-tert-butylimidazolin-2-imine (Im t BuNH) afforded the mononuclear complex [Y(Im t BuN)3(THF)2] (2) with a five-coordinated yttrium atom, as indicated by X-ray diffraction analysis of 2·2THF. [ABSTRACT FROM AUTHOR]

Abstract: Taking advantage of palladium peculiar “rollover” C,N cyclometallation, it is possible to promote C(3) functionalization of 6-alkyl-substituted-2,2′-bipyridines. The carbonylation reaction of rollover species [Pd(L n )Cl]2, (HL1 =6-isopropyl-2,2′-bipy, 1; HL2 =6-neopentyl-2,2′-bipy, 2; HL3 =6-ethyl-2,2′-bipy, 3; HL4 =6-methyl-2,2′-bipy, 4) allowed the synthesis of 2-(pyridin-2-yl)-6-alkyl-nicotinic acids or esters. These nicotinic derivatives are extremely rare and, as far as we know, quite unreported in the case of the 6-substituted molecules. [Copyright &y& Elsevier]

Abstract: Reaction of K2[PtCl4] or Na2[PdCl4] with 6,6′-diphenyl-2,2′-bipyridine, L, gives the cyclometallated species [Pt(L–H)Cl], 1, and [Pd(L–H)Cl], 2, respectively, where L–H is a terdentate N^N^C anionic ligand originated by direct activation of a C(sp2)–H bond. The crystal structure of 2 has been solved by X-ray diffraction and compared to that of the analogous complex [Pd(L′–H)Cl] L′=6-phenyl-2,2′-bipyridine. The second phenyl ring in 2 entails a considerable distortion of the coordination around the metal. A similar distortion is also to be expected in the analogous compound 1, due to the almost equal covalent radii of palladium(II) and platinum(II). From the complexes 1 and 2 the chloride can be displaced with AgBF4 and substituted by CO or PPh3 to give the corresponding cationic species. By reaction of 1 with Na[BH4] substitution of H− for Cl− can be achieved: the rare hydrido complex [Pt(L–H)H], stabilized only by nitrogen ligands, was isolated in the solid state and fully characterized in solution. It is noteworthy that in the case of the 6-phenyl-2,2′-bipyridine the analogous terminal hydride [Pd(L′–H)H] is unstable. In platinum chemistry the reaction of 6-substituted 2,2′-bipyridines is known to give either N^N^C or N′^C(3) rollover cyclometallation, depending on the nature of the metal precursor. In the case of 6,6′-Ph2-2,2′-bipy cyclometallation was also shown to undergo multiple C–H activation giving the C^N^C pincer complex [Pt(L-2H)(DMSO)]. The latter species can be related to complex 1: indeed its reaction with HCl produces complex 1 and [Pt(L–H)(DMSO)Cl], a rollover species with a pendant phenyl substituent. [Copyright &y& Elsevier]

Abstract: Reaction of Na[AuCl4] with 2-vinylpyridine (vinpy) and 2-ethylpyridine (etpy) affords the N-bonded adducts Au(Rpy)Cl3 (R=CH2 ; CH3CH2, etpy). Cationic adducts, [Au(vinpy)2Cl][X]2 (X=BF4, PF6) and [Au(etpy)2Cl2][BF4], were also obtained by reaction of Au(Rpy)Cl3 with Rpy (1:1) and excess NaBF4 or KPF6. Thermal activation of Au(vinpy)Cl3 in water gives the five-membered cycloaurated derivative [Au(k 2-C,N–CH2CH(Cl)–C5H4N)Cl2] formally resulting through a trans nucleophilic addition of a chloride onto the Co cyclometallated derivatives are obtained by reactions of Au(etpy)Cl3. An X-ray crystal structure determination on the PPh3 derivative [Au(k 2-C,N–CH2CH(Cl)–C5H4N)(PPh3)Cl][PF6] was carried out. [Copyright &y& Elsevier]

Abstract: The synthesis and characterization of novel benzisothiazole-tetrazolyl derivatives differing on the spacer-group used for the linkage of two heterocycles are described. The application of these compounds as nitrogen ligands for coordination with transition metals was also explored, leading to the preparation of 3-[1-(2-1H-tetrazol-5-yl)ethoxy]-1,2-benzisothiazole 1,1-dioxide-Mn(II) and N-(1,1-dioxo-1,2-benzisothiazol-3-yl)-amine-1H-tetrazole-Mn(II) complexes. [Copyright &y& Elsevier]

• Pd catalyzed C-C and C-X cross coupling reactions. • Update of the recent efforts made in the coupling reactions by Pd complexes based on the N-O ligands. • The present part focused on the applications of the ligands containing N and O as a donor atoms. • Next part covers all ligands and catalysts containing N in combination with P as a donor atoms. The Pd catalyzed cross-coupling reactions have played a crucial role in accomplishing different valuable organic transformations. These transformations involve the use of homogeneous as well as heterogeneous Pd catalysts. A large variety of ligands have been used in Pd catalyzed coupling reactions. Traditionally, these transformations have been carried out by various phosphine-based ligands. The phosphine ligands are suffering from poor air, moisture, and thermal stability. Hence, in recent years phosphine-free ligands such as N-heterocyclic carbenes and amines have been attracted great attention in the field of catalysis. Though the N-containing ligands have showed comparatively low activity as compared to phosphine and carbene-based ligands, most importantly, these complexes have broad scope in catalysis, as they represent a low cost, less toxic, good moisture, thermal and air stability as well as environmentally friendly. In this review, we present the developments made in the field of Pd complexes of N and O donor ligands in various cross-coupling reactions. [Display omitted] [ABSTRACT FROM AUTHOR]

The reductive cyclization of suitably substituted organic nitro compounds by carbon monoxide is a very appealing technique for the synthesis of heterocycles because of its atom efficiency and easiness of separation of the only stoichiometric byproduct CO2, but the need for pressurized CO has hampered its diffusion. We have recently reported on the synthesis of indoles by reductive cyclization of o-nitrostyrenes using phenyl formate as a CO surrogate, using a palladium/1,10-phenanthroline complex as catalyst. However, depending on the desired substituents on the structure, the use of β-nitrostyrenes as alternative reagents may be advantageous. We report here the results of our study on the possibility to use phenyl formate as a CO surrogate in the synthesis of indoles by reductive cyclization of β-nitrostyrenes, using PdCl2(CH3CN)2 + phenanthroline as the catalyst. It turned out that good results can be obtained when the starting nitrostyrene bears an aryl substituent in the alpha position. However, when no such substituent is present, only fair yield of indole can be obtained because the base required to decompose the formate also catalyzes an oligo-polymerization of the starting styrene. The reaction can be performed in a single glass pressure tube, a cheap and easily available piece of equipment. [ABSTRACT FROM AUTHOR]

Abstract: A series of nickel(II) halide complexes [NiCl2(L)] (1a–12a) and [NiBr2(L)] (1b–12b) bearing 2-pyrazolyl substituted 1,10-phenanthroline derivatives (L 1 –L 12 ) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray diffraction analysis (for 1a′, 10b and 12b). Upon activation with methylaluminoxane (MAO), these complexes display good catalytic activities in ethylene oligomerization (up to 3.01×105 gmol(Ni)−1 h−1 at 10atm of ethylene for 12a with L 12 = 2-(3,5-diphenylpyrazol-1-yl)-9-mesityl-1,10-phenanthroline). Complexes with bulkier aryl groups in the 9-position of the phenanthroline ring and the 3- and 5-position of the pyrazolyl ring give higher activities. This is explained with the formation of a more directional environment, a reaction channel around the nickel center which enhances the probability of insertion over dissociation after ethylene coordination to Ni. Also, bulkier aryl substituents can suppress chain-transfer reactions (typically β-H elimination) and therefore increase the activity. [Copyright &y& Elsevier]

Abstract: Cationic palladium(II) complexes of the type containing bisnitrogen ligands with a pyrazole moiety were synthesized from the corresponding neutral derivatives [PdClMe(N–N′)]. Their characterization by 1H and 13C NMR spectroscopy in solution evidences the presence of the Pd–Me group cis to the pyrazole ring. The catalytic behaviour of the cationic complexes in CO/4-tert-butylstyrene copolymerization and CO/ethylene/4-tert-butylstyrene terpolymerization was investigated. Productivity was greatly enhanced when the reaction was carried out in 2,2,2-trifluoroethanol (TFE). Molecular weights and polydispersity (M w/M n) of the obtained polyketones resulted among the best reported for C s -bisnitrogen planar ligands. [Copyright &y& Elsevier]

Abstract: A series of dinuclear platinum complexes where the metal ions are linked by a twofold deprotonated 2,2′:6′,2″-terpyridine (terpy) has been synthesized. Reaction of cis-[Pt(Me)2(DMSO)2] with terpy in toluene at 90°C (molar ratio Pt:terpy 2:1) results in activation of the C(3)- and C(5)–H bonds of the inner pyridinic ring to give the cyclometalated dinuclear derivative [Pt2(terpy-2H)(Me)2(DMSO)2] (1a), (trans Me–Pt–N). From complex 1a, substitution of DMSO with neutral two-electron donors, L, allows isolation of a number of new species [Pt2(terpy-2H)(Me)2(L)2] with the same N,C∧C,N bridging ligand. The “Pt2(terpy-2H)” fragment is very robust: it is not affected by alkylating reagents such as MeI or acids such as HPF6 or even HCl. Nevertheless the latter acid cleaves the Pt–Me bond affording another series of complexes having a chloride in place of a methyl, [Pt2(terpy-2H)(Cl)2(L)2], (trans-Cl–Pt–C). The structure of complex 7, [Pt2(terpy-2H)(Cl)2(PPh3)2], has been solved by X-ray analysis: the platinum atoms are in a tetrahedrally distorted square planar coordination. The inner framework of the molecule is not flat: the dihedral angle between the best planes of the metal ions is 37.2(1)°. The coordinated chlorides can be abstracted to give cationic solvento derivatives or exchanged with other anions such as iodides. Exchange with [BH4]− allows to obtain the corresponding hydrides, examples of very rare C,N cyclometalated platinum(II) hydrides. Finally a two step approach allows the synthesis of unsymmetric derivatives, [Pt2(terpy-2H)(Cl)2(L)(L′)], with different ligands around each platinum atom. The surprising deprotonation of terpy, typically a neutral ligand, points to the potential of the “Pt(Me)2” fragment in the intramolecular C–H bond activation. [Copyright &y& Elsevier]

Abstract: A series of ionic dioxomolybdenum(VI) complexes of general formula [MoO2Cl(L)]Y containing tridentate nitrogen ligands [L=1,4,7-triazacyclononane (tacn), 1,1,1-tris(methylaminomethyl)ethane (Me3-tame) and N,N′,N″-tribenzyl-1,1,1-tris(methylaminomethyl)ethane (Bn3Me3-tame); Y=Cl, BF4 −] were prepared by replacement of the solvent molecules and one of the chloride ligands in the adducts MoO2Cl2(solv)2 (solv=THF, DMF). The complexes were examined as catalysts for the epoxidation of cyclooctene at 55°C, using tert-butyl hydroperoxide (t-BuOOH) as the oxidant. The kinetic profiles and initial activities (60–100molmolMo −1 h−1) were comparable with those usually exhibited by MoO2Cl2L complexes bearing bidentate heterocyclic amines. The tricarbonyl complexes (Me3-tame)M(CO)3 (M=Mo, Cr) were also prepared and used directly as catalyst precursors for the epoxidation of cyclooctene using t-BuOOH. Induction periods were observed due to relatively slow oxidative decarbonylation and formation of the active oxidising species. When the Mo tricarbonyl complex was used, 1,2-epoxycyclooctane was the only product, while with the Cr complex a significant amount of 1,2-cyclooctanediol was formed due to the enhanced Lewis acidity of the active catalyst. The Mo complexes containing the tame ligands were further studied as catalysts or catalyst precursors for the epoxidation of cyclododecene, 1-octene, trans-2-octene, (R)-(+)-limonene and α-pinene. [Copyright &y& Elsevier]

Abstract: The reaction of compound cis-[PtCl2(dmso)2] with ligands RCHN(CH2)3NMe2 (1a–1h) in which R is a phenyl group containing substituents such as Cl, F, Me, NO2 and MeO produced compounds [PtCl2{(CH3)2N(CH2)3NCHR}] (2), as mixtures of Z and E isomers. When treated with an equimolar amount of sodium acetate in refluxing methanol compounds 2 gave cyclometallated platinum compounds 3 containing a terdentate [C,N,N′] ligand. The obtained compounds were fully characterized including structure determinations for compounds 3a, 3b and 3e. The effects of the substituents in the regioselectivity of the cyclometallation reaction and the reactivity of 3a and 3b with mono and bidentate phosphines were also studied. [Copyright &y& Elsevier]

A new family of tetracarbonyl molybdenum(0) and tungsten(0) complexes based on new 6,6′-disubstituted-4,4′-bipyrimidine ligands was synthesized and characterized. The visible region of the absorption spectrum of each complex is dominated by a metal-to-ligand charge transfer band significantly lower in energy than the corresponding transition in 2,2′-bipyridine tetracarbonyl metal complexes. The 6,6′-substituents create a larger π-electronic system in the substituted bipyrimidines and are consequently better π acceptors than even the parent 4,4′-bipyrimidine. The absorption bands are shifted bathochromically with a decrease in solvent polarity. [ABSTRACT FROM AUTHOR]

Abstract: MALDI and ESI-MS have been applied to the characterization of the reaction products between the labile cis-[Pt(DMSO)2Cl2] (1) and trans-[Pt(DMSO)2Cl(CH3)] (2) complexes with the simplest poly(amidoamine) ligand (PAMAM, G=0, 1,2-diaminoethane as core). The comparison of the mass spectra of the starting G0 and those of the metallo-dendrimers formed upon mixing of the reagents in an equimolecular ratio, and the analysis of the isotopic distribution in the ESI spectra, have revealed the formation of cationic and neutral mononuclear complexes with PAMAM as ligand, e.g., cis-[Pt(DMSO)(PAMAM)Cl]Cl or trans-(C,N)[Pt(DMSO)(PAMAM)Cl(CH3)], together with various minor components, which have been identified as derivatives from defective structures of PAMAM. The geometry of the main products has been deduced from the values of the protons coupling constants with the isotopically abundant 195Pt. The metal-to-ligand bond is restricted to the peripheral amino groups of PAMAM which shows sufficient flexibility to involve either one or two branches in the coordination bonding. [Copyright &y& Elsevier]