Crystal Structures Of 1a Research Articles

Functionalized Pyrazoles as Agents in C–C Cross-Coupling Reactions

The 1-tetrahydropyranyl-(THP-)protected pyrazoles 4-R-pz(THP) (R=pinacolatoboryl=Bpin (3a(THP)), Me3Si (4a(THP)), Me3Sn (5a(THP)), and 4-R-3,5-Ph2pz (R=Bpin (3b(THP)), Me3Si (4b(THP)), Me3Sn (5b(THP)) were obtained by the following syntheses: i) In a first step, 4-X-pz (X=Br (1a), I (2a)) and 4-X-3,5-Ph2pz (X=Br (1b), I (2b)) were reacted with 3,4-dihydro-2Hpyran (DHP) to give the related THP-protected bromo- or iodopyrazole derivatives. ii) In a second step these THP derivatives were metalated by treatment with nBuLi or iPrMgCl. Subsequent reactions of the THP-protected metallopyrazoles 4-M-pz(THP) and 4-M-3,5-Ph2pz(THP) (M=Li, MgBr) with Bpin(OiPr), Me3SiCl, and Me3SnCl yielded the pyrazole derivatives 3a(THP), 3b(THP), 4a(THP), 4b(THP), 5a(THP), and 5b(THP). In contrast to the stannylated pyrazoles 5a(THP) and 5b(THP), the corresponding borylated and silylated derivatives could be easily deprotected: treatment of 3a(THP), 3b(THP), and 4a(THP) with HCl yielded the parent pyrazoles 3a, 3b and 4a. The microwave-assisted C-C cross-coupling reactions of these pyrazoles with aryl halides were examined, e. g. Suzuki reactions of 3a with p-pentylphenylbromide, p-hexylphenylbromide, and p- (2-ethylhexyl)phenylbromide. Similar reactions were also performed with 1a, 1b, 2a, and 2b and aryl-substituted pinacolatoboranes or boronic acids. Crystals of 5b(THP) suitable for X-ray diffraction were grown (monoclinic P21/c) and their structure determined. The crystal structures of 1a·HBr (monoclinic P21/n), 1b (triclinic P̄1̄), (1c)2·HBr (monoclinic P2/c), 1c·HBr·(Br2)0.5 (triclinic P̄1̄), (2a)3·H2SO4 (triclinic P̄1̄), 3a (orthorhombic P212121), (3a)3·H2O (trigonal R3c), 3b (orthorhombic Pna21), and 4a (monoclinic Pc) reveal interesting hydrogen bonding networks.

Deep Red Phosphorescence of Cyclometalated Iridium Complexes by o-Carborane Substitution

Heteroleptic (C(∧)N)2Ir(acac) (C(∧)N = 5-MeCBbtp (5a); 4-BuCBbtp (5b); 5-BuCBbtp (5c); 5-(R)CBbtp = 2-(2'-benzothienyl)-5-(2-R-ortho-carboran-1-yl)-pyridinato-C(2),N, R = Me and n-Bu; 4-BuCBbtp = 2-(2'-benzothienyl)-4-(2-n-Bu-ortho-carboran-1-yl)-pyridinato-C(2),N, acac = acetylacetonate) complexes supported by o-carborane substituted C(∧)N-chelating ligand were prepared, and the crystal structures of 5a and 5b were determined by X-ray diffraction. While 5a and 5c exhibit a deep red phosphorescence band centered at 644 nm, which is substantially red-shifted compared to that of unsubstituted (btp)2Ir(acac) (6) (λem = 612 nm), 5b is nonemissive in THF solution at room temperature. In contrast, all complexes are emissive at 77 K and in the solid state. Electrochemical and theoretical studies suggest that the carborane substitution leads to the lowering of both the HOMO and LUMO levels, but has higher impact on the LUMO stabilization than the HOMO, resulting in the reduction of the triplet excited state energy. In particular, the LUMO stabilization in the 4-substituted 5b is more contributed by carborane than that in the 5-substituted 5a. The solution-processed electroluminescent device incorporating 5a as an emitter displayed deep red phosphorescence (CIE coordinate: 0.693, 0.290) with moderate performance (max ηEQE = 3.8%) whereas the device incorporating 5b showed poor performance, as well as weak luminance.

Preparation and characterization of palladium(II) complexes with N-arylalkyliminodiacetic acids. Catalytic activity of complexes in methoxycarbonylation of iodobenzene

The reactions of N-arylalkyl derivatives of iminodiacetic acid (H2Bnida, H2Peida, H2Ppida, o-H2Cbida; Bn = benzyl, Pe = 2-phenylethyl; Pp = 3-phenylprop-1-yl; o-Cb = o-chlorobenzyl) with sodium tetrachloropalladate(II) in aqueous solutions were investigated. Five new palladium(II) complexes [Pd(HBnida)2]·2H2O (1a), [Pd(HBnida)2] (1b), [Pd(HPeida)2] (2), [Pd(HPpida)2] (3) and [Pd(o-HCbida)2] (4) were prepared and characterized by infrared spectroscopy, 1H, 13C and 15N NMR spectroscopy and thermal analysis (TGA/DTA). The crystal structure of 1a was determined by single-crystal X-ray structural analysis. The palladium(II) ion in the molecule of 1a adopts a square planar coordination with two N,O-bidentate N-benzyl-hydrogeniminodiacetate ions. Complex 1a is a trans-isomer. Antitumor properties of the complexes were tested on three human cell lines. The compounds did not significantly inhibit the growth of colon (HCT 116), breast (MCF-7) and lung (H 460) tumor cell lines. All prepared palladium(II) complexes exhibit the acceptable activities towards the methoxycarbonylation of iodobenzene.

Copper(II) thiocyanate complexes of 2-(2-pyridinyl)-benzthiazole: synthesis, structure, redox behavior, thermal aspects, and DFT calculations

Reaction of 2-(2-pyridinyl)-benzthiazole (Pbt), KSCN, and copper(II)perchlorate hexahydrate in 1 : 2 : 1 molar proportion in dimethyl sulfoxide gives monomeric [Cu(Pbt)(SCN)2DMSO] (1a). In another run, identical proportions of the same reactants in methanol generates a symmetric thiocyanate bridged dimeric copper(II) compound, [Cu2(Pbt)2(SCN)2] (2a), in 72% yield. Both 1a and 2a have been characterized by C, H, and N microanalyses, copper estimation, FTIR, UV–vis spectra, and room temperature magnetic susceptibility measurements. The X-ray crystal structures of 1a and 2a have been determined. Electrochemical studies of 1a and 2a show Cu(II) to Cu(III) oxidation in solution. The thermal behaviors of 1a and 2a have been studied. Bond valence sum method of analysis was performed to assign the oxidation state for each copper center in 1a and 2a. Geometry optimization of 1a, 2a, and their linkage isomers has also been performed at the level of the density functional theory to show that 1a and 2a are the most stable congeners. These results corroborate our experimental findings.

Extended TTF-type donors fused with pyrazine units; synthesis and characterization

Pyrazinedicyanoethylthiotetrathiafulvalene, (pzdc-TTF) (1a), an extended TTF fused with a pyrazine moiety and also a dithiolene ligand precursor, was synthesized through a cross-coupling with triethyl phosphite between pyrazine-1,3-dithiole-2-thione (I) and 4,5-bis(2-cyanoethylthio)-1,3-dithiole-2-one (III). This reaction also yields to dipyrazine TTF derivative (1b) and 2,3,6,7-Tetrakis(2-cyanoethylthio)TTF (1c), resulting from the self-coupling reactions of the thione (I) and ketone (III). The crystal structure of 1a is composed by pairs of head to head donor stacks of pzdc-TTF molecules along b in opposite orientations. Single crystals of 1b revealed a new polymorph with a face-to-face π-stacking motif. The electrochemical properties of 1a studied by cyclic voltammetry (CV) in DMF, shows two single electron oxidation processes typical of TTF-based donors; one pair of asymmetric redox waves centered at 627mV versus Ag/Ag+ is ascribed to the couple [pzdc-TTF]+/[pzdc-TTF]2+, and one pair of quasi-reversible redox waves centered at 430mV is ascribed to the couple [pzdc-TTF]0/[pzdc-TTF]+.

Exploring the Variable Hapticity of the Arylamide Ligand: Access to σ-Amidophenyl and π-Cyclohexadienylimine Structures

A study of the preference for σ vs π coordination of the arylamido ligand to a late transition metal shows that LiNPh2 reacts with RuHCl(PPh3)3 (1) to yield the bent-seat piano-stool complex RuH[(η5-C6H5)NPh](PPh3)2 (2a) but with RuHCl(CO)(PPh3)3 (3) to yield the σ-amide RuH(η1-NPh2)(CO)(PPh3)2 (4). The stability of the σ-bound NPh2 ligand in 4 reflects the π acidity of the CO ligand, which inhibits PPh3 loss. Carbonylation of 2a at 50 °C affords Ru(CO)3(PPh3)2 (8) and HNPh2, suggesting sequential π → σ isomerization and reductive elimination. The phenoxide ligand behaves similarly: RuH(η5-C6H5O)(PPh3)2 (2b) is formed from 1 but RuH(η1-OPh)(CO)(PPh3)3 (5) is formed from 3, and carbonylation of 2b gives 8 and phenol, although more forcing conditions are required (90 °C). The crystal structure of 2a is reported.

The synthesis and characterization of 4-isopropylanilino derivatives of cyclotriphosphazene

Hexachlorocyclotriphosphazene N3P3Cl6 and gem-disubstituted cyclotriphosphazene derivatives N3P3Cl4X2 (X=Ph, PhS, PhNH) were reacted with 4-isopropylaniline to give geminal tetra and hexa substituted compounds (1a–4a, 1b–4b). The compounds (1a–4a, 1b–4b) were separated by column chromatography on silica gel and analyzed by elemental analysis, mass spectrometry, and 31P and 1H NMR spectroscopies, and also crystal structures of 2a and 3b were determined by X-ray crystallography. Compounds were prepared to cover the normal ranges of C-, S- and N-substituents in cyclophosphazene (X=Cl, Ph, SPh, NHPh). Compounds (1a–4a, 1b–4b) were reported for the first time. We additionally investigated the effect of substituent (Cl, Ph, SPh, NHPh) on 31P NMR chemical shifts of neighboring phosphorus atoms.

8-Amino-BODIPYs: Structural Variation, Solvent-Dependent Emission, and VT NMR Spectroscopic Properties of 8-R2N-BODIPY

New 8-NR2-BODIPYs, R2 = H(i)Pr (3a), H(i)Bu (3b), and Et2 (4), are reported. Restricted rotation about the C8-N bond in such molecules has been observed for the first time (3a and 3b) and evaluated using VT NMR. The fluorophores 3a and 3b are blue emitters, and the efficiency of the emission is closely related to the polarity of the solvent, e.g., hexane > toluene > DCM > THF > MeOH > H2O, an effect also noted by emission variation in alcohol solvents H(CH2)nOH, n = 1-6. In mixed-solvent systems, addition of 10-15% of the more polar solvent results in transformation of the emission properties to those of the bulk polar solvent. Compound 4 has zero emission in all solvents. The crystal structures of 3a, 3b, and 4 are reported, along with that of the parent 8-NH2-BODIPY (2). Compounds 2, 3a, and 3b exhibit trigonal planar N atoms which are coplanar with the BODIPY core; 4 exhibits a very significant distortion that breaks the planarity of the extended BODIPY π system due to the steric impact of the two ethyl groups, an observation that explains the lack of emission for 4.

Zig-zag [MnIII4] clusters from polydentate Schiff base ligands

Reactions of Schiff base ligands, OH–C6H4–CHNC(R)(CH2OH)2 (R=CH3, H3L1; R=C2H5, H3L2; R=CH2OH, H3L3) with Mn(ClO4)2·6H2O in MeOH solutions afforded MnIII4 complexes, i.e. compounds [Mn4(L1)2(HL1)2(H2O)2(MeOH)2](ClO4)2·yH2O (y=1, 1a·H2O; y=2, 1b·2H2O), [Mn4(L2)2(HL2)2(MeOH)4](ClO4)2 (2a), [Mn4(L2)2(HL2)2(H2O)2(MeOH)2] (ClO4)2·MeOH (2b·MeOH) and [Mn4(L3)2(HL3)2(H2O)4](ClO4)2 (3). The crystal structures of 1a, 1b, 2a and 2b revealed the first examples of MnIII4 complexes consisting of three corner sharing [MnIII2(μ-OR)2] units in trans orientation. The Schiff bases behave as chelating through their phenolato oxygen and imino nitrogen atoms as well as bridging ligands through their deprotonated alkoxo oxygen atoms. In each tetranuclear entity, there are two doubly deprotonated and two triply deprotonated Schiff base ligands which connect two and three metal ions, respectively. Magnetic susceptibility measurements for 2b indicate the interplay of ferromagnetic and antiferromagnetic interactions resulting in a diamagnetic ground state.

Phosphorus–nitrogen compounds: Part 26. Syntheses, spectroscopic and structural investigations, biological and cytotoxic activities, and DNA interactions of mono and bisferrocenylspirocyclotriphosphazenes

The condensation reactions of the tetrachloro mono (1 and 2) and bisferrocenylspirocyclotriphosphazenes (3–5) with 1,4-dioxa-8-azaspiro[4,5]decane (DASD) resulted in the formation of the partly and fully DASD-substituted phosphazenes. The reactions of equal amounts of 1–5 and DASD produced the mono-DASD-substituted ferrocenylphosphazenes (1a–5a), as the major product. When the reactions were carried out with 1equiv of 1–5 and 2equiv of DASD, corresponding geminal-phosphazenes (1b–5b) were isolated. Moreover, the reactions of 1equiv of 1–5 and 3equiv of DASD gave the tri- (1c–4c) and tetra-substituted (1d–5d) phosphazenes. When the excess DASD was used, the fully-substituted phosphazenes (1d–5d) were obtained. The chirality of 3a was evaluated using chiral HPLC column. The structures of all the phosphazenes were verified by FTIR, MS, 1H, 13C and 31P NMR, and HSQC spectral data. The crystal structures of 4a, 2b, 5b, and 1d were determined by X-ray diffraction techniques. The 10 phosphazene derivatives were screened for antimicrobial activity. Meanwhile, interactions between the compounds and pBR322 plasmid DNA were presented by agarose gel electrophoresis. The compounds 2b, 1d, 2d, and 4d were tested against HeLa cancer cell lines. Among these compounds, 4d had cytotoxic effect on HeLa cell after 24h treatment.

Synthesis and characterization of a series of chiral NHC–Pd complexes derived from l-phenylalanine

The synthesis of a series of chiral Pd(L)PyBr2 (3a–3e) and Pd(L)PyCl2 (4d and 4e) complexes from l-phenylalanine is presented (L = (S)-3-allyl-4-benzyl-1-(2,6-diisopropylphenyl)-imidazolin-2-ylidene (a), (S)-4-benzyl-1-(2,6-diisopropylphenyl)-3-(naphthalen-2-ylmethyl)imidazolin-2-ylidene (b), (S)-4-benzyl-3-(biphenyl-4-ylmethyl)-1-(2,6-diisopropylphenyl)imidazolin-2-ylidene (c), (S)-4-benzyl-1-(2,6-diisopropylphenyl)-3-(naphthalen-1-ylmethyl)imidazolin-2-ylidene (d) or (S)-4-benzyl-1-(2,6-diisopropylphenyl)-3-(2,4,6-trimethylbenzyl)imidazolin-2-ylidene (e). The complexes were characterized by physicochemical and spectroscopic methods, and the X-ray crystal structures of 3a–3c and 4d are reported. In each case, there is a slightly distorted square-planar geometry around palladium, which is surrounded by imidazolylidene, two trans halide ligands and a pyridine ligand. There are π–π stacking interactions in the crystal structures of these complexes. Complex 3a showed good catalytic activity in the Cu-free Sonogashira coupling reaction under aerobic conditions.

New emissive organic molecule based on pyrido[3,4-g]isoquinoline framework: synthesis and fluorescence tuning as well as optical waveguide behavior

In this paper we report the synthesis and crystal structures of emissive organic molecule (1a) based on pyrido[3,4-g]isoquinoline framework as well as its isomers 1b and 1c. The emission quantum yields decrease after transformation of pyridine moieties in 1a into the cyclic-amides in 1b and 1c. The fluorescent spectral results reveal that 1a, 1b, and 1c exhibit no AIE behavior. This is tentatively attributed to intramolecular weak C⋯H interactions, which may impede the intramolecular rotations based on the crystal structures of 1a and 1c. Interestingly, 1a, 1b, and 1c are emissive in the solid state, and among them 1a possesses the highest emission quantum yield (0.22). Moreover, the fluorescence of 1a in solution and solid state can be reversibly tuned by reactions with trifluoroacetic acid and triethylamine. Microarea PL studies reveal that microrods of 1a and these after exposure to HCl gas show typical waveguide behavior.

Bisdithiazolyl Radical Spin Ladders

A series of four bisdithiazolyl radicals 1a-d (R(1) = Pr, Bu, Pn, Hx; R(2) = F) has been prepared and characterized by X-ray crystallography. The crystal structure of 1a (R(1) = Pr) belongs to the tetragonal space group P42(1)m and consists of slipped π-stack arrays of undimerized radicals packed about 4 centers running along the z-direction, an arrangement identical to that found for 1 (R(1) = Et; R(2) = F). With increasing chain length of the R(1) substituent, an isomorphous set 1b-d is generated. All three compounds crystallize in the P2(1)/c space group and consist of pairs of radical π-stacks locked together by strong intermolecular F···S' bridges to create spin ladder arrays. The slipped π-stack alignment of radicals produces close S···S' interactions which serve as the "rungs" of a spin ladder, and the long chain alkyl substituents (R(1)) serve as buffers which separate the ladders from each other laterally. Variable temperature magnetic susceptibility measurements indicate that 1a behaves as an antiferromagnetically coupled Curie-Weiss paramagnet, the behavior of which may be modeled as a weakly coupled AFM chain. Stronger antiferromagnetic coupling is observed in 1b-d, such that the Curie-Weiss fit is no longer applicable. Analysis of the full data range (T = 2-300 K) is consistent with the Johnston strong-leg spin ladder model. The origin of the magnetic behavior across the series has been explored with broken-symmetry Density Functional Theory (DFT) calculations of individual pairwise exchange energies. These confirm that strong antiferromagnetic interactions are present within the ladder "legs" and "rungs", with only very weak magnetic exchange between the ladders.

Synthesis, characterization, and cytotoxic activity of tricyclohexyltin(IV) carboxylates derived from cyclic dicarboxylic anhydrides

Some tricyclohexyltin(IV) carboxylates, HOOC–R–COOSn(c-C6H11)3 (1) and (c-C6H11)3SnOOC–R–COOSn(c-C6H11)3 (2) [R = 1,2-C6H4 (a), 1,2-C6F4 (b), (Z)-CH=CH (c), CH2CH2 (d)], have been synthesized from reaction of tricyclohexyltin hydroxide with cyclic dicarboxylic anhydrides under microwave irradiation in 1 : 1 and 2 : 1 M ratio, respectively, and characterized by elemental analysis, IR and NMR (1H, 13C, and 119Sn) spectra. Crystal structures of 1a–1c and 2d are determined by X-ray single crystal diffraction. The carboxylate in each compound is monodentate to tin. Compounds 1a and 1c possess a trans-C3SnO2 trigonal bipyramidal geometry with axial positions occupied by carboxylate and carbonyl oxygen of carboxylate of an adjacent molecule forming a one-dimensional chain. Compound 1b is tetrahedral and forms R 2 2(8) hydrogen-bonded dimers by pairs of intermolecular O–HO hydrogen bonds between two carboxylic acid groups. Compound 2d is dinuclear with tin possessing distorted tetrahedral geometry; a trimer supramolecular structure is formed by weak intermolecular SnO interactions. The compounds have potent in vitro cytotoxic activity against two human tumor cell lines, A549 and HeLa.

Low-Spin Hexacoordinate Mn(III): Synthesis and Spectroscopic Investigation of Homoleptic Tris(pyrazolyl)borate and Tris(carbene)borate Complexes

Three complexes of Mn(III) with "scorpionate" type ligands have been investigated by a variety of physical techniques. The complexes are [Tp(2)Mn]SbF(6) (1), [Tp(2)*Mn]SbF(6) (2), and [{PhB(MeIm)(3)}(2)Mn](CF(3)SO(3)) (3a), where Tp(-) = hydrotris(pyrazolyl)borate anion, Tp*(-) = hydrotris(3,5-dimethylpyrazolyl)borate anion, and PhB(MeIm)(3)(-) = phenyltris(3-methylimidazol-2-yl)borate anion. The crystal structure of 3a is reported; the structures of 1 and 2 have been previously reported, but were reconfirmed in this work. The synthesis and characterization of [{PhB(MeIm)(3)}(2)Mn]Cl (3b) are also described. These complexes are of interest in that, in contrast to many hexacoordinate (pseudo-octahedral) complexes of Mn(III), they exhibit a low-spin (triplet) ground state, rather than the high-spin (quintet) ground state. Solid-state electronic absorption spectroscopy, SQUID magnetometry, and high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy were applied. HFEPR, in particular, was useful in characterizing the S = 1 spin Hamiltonian parameters for complex 1, D = +19.97(1), E = 0.42(2) cm(-1), and for 2, D = +15.89(2), E = 0.04(1) cm(-1). In addition, frequency domain Fourier-transform THz-EPR spectroscopy, using coherent synchrotron radiation, was applied to 1 only and gave results in good agreement with HFEPR. Variable-temperature dc magnetic susceptibility measurements of 1 and 2 were also in good agreement with the HFEPR results. This magnitude of zero-field splitting (zfs) is over 4 times larger than that in comparable hexacoordinate Mn(III) systems with S = 2 ground states. Complexes 3a and 3b (i.e., regardless of counteranion) have a yet much larger magnitude zfs, which may be the result of unquenched orbital angular momentum so that the spin Hamiltonian model is not appropriate. The triplet ground state is rationalized in each complex by ligand-field theory (LFT) and by quantum chemistry theory, both density functional theory and unrestricted Hartree-Fock methods. This analysis also shows that spin-crossover behavior is not thermally accessible for these complexes as solids. The donor properties of the three different scorpionate ligands were further characterized using the LFT model that suggests that the tris(carbene)borate is a strong σ-donor with little or no π-bonding.

Crystal Structure of the 5-Chloro Salicylamides: Three Different Types of the H-bonding Influenced Linear Chain Formation in the Solid State

Three N-substituted 5-chlorosalicylamides (4-chlorophenyl, 2a; benzyl, 2b; phenethyl 2c) differing in the length of the 'linker' between the benzene ring and the amide moiety were prepared in order to compare their supramolecular architecture. The intramolecular NH···O(H) hydrogen bond and the intermolecular C=O···H–O hydrogen bond were found in the crystal structure of 2a and 2c thus forming an infinite linear chain. Compound 2b had a different arrangement with the intramolecular C=O···H–O hydrogen bond and another intermolecular NH···O(H) hydrogen forming a linear infinite chain.

Design, synthesis of some new (2-aminothiazol-4-yl)methylester derivatives as possible antimicrobial and antitubercular agents

A series of (2-aminothiazol-4-yl)methylester (5a–t) derivatives were synthesized in good yields and characterized by 1H NMR, 13C NMR, mass spectral and elemental analyses. The crystal structure of 5a was evidenced by X-ray diffraction study. The compounds were evaluated for their preliminary in vitro antibacterial, antifungal activity and were screened for antitubercular activity against Mycobacterium tuberculosis H37Rv strain. The synthesized compounds displayed interesting antimicrobial activity.

Palladium, iridium and ruthenium complexes with acyclic imino-N-heterocyclic carbenes and their application in aqua-phase Suzuki–Miyaura cross-coupling reaction and transfer hydrogenation

Palladium (4a–4c), iridium (5a–5c) and ruthenium (6a–6c) complexes have been prepared by in situ transmetalation from the corresponding silver complexes of acyclic imino-functionalized imidazolium chlorides [1-(Me)-imidazolium-3-{C(p-CH(3)-Ph)=N(Ar)}]Cl (3) (Ar = 2,4,6-trimethylphenyl (3a), 2,6-diisopropylphenyl (3b) and phenyl (3c)) with [Pd(COD)Cl(2)], [Cp*IrCl(2)](2) or [Ru(p-cymene)Cl(2)](2), respectively. Iridium and ruthenium complexes, 5a[PF(6)]–5c[PF(6)], 6a[PF(6)]–6c[PF(6)], 6c[BF(4)], 6c[BPh(4)] and 6c[NTf(2)], were obtained directly from 5a–5c and 6a–6c through an anion-exchange process with KPF(6), NaBF(4), NaBPh(4) and LiNTf(2) (bis(trifluoromethylsulfonyl)imide lithium), respectively. All complexes were characterized by FT-IR, (1)H and (13)C NMR spectroscopy and elemental analysis. Crystal structures of 4a, 5a and 6c[NTf(2)], and show that five-membered chelate ring is formed in these complexes by the coordination of the carbene carbon and the imino nitrogen atom, and the latter two are cationic compounds with Cl(-) and NTf(2)(-) as counteranion respectively. The catalytic performance of Pd complexes for Suzuki-Miyaura cross-coupling reactions in pure water and Ir and Ru complexes for transfer hydrogenation of ketones and imines was tested in a wide scope of substrates. Pd complex 4b with the largest steric hinder exhibited the best performance to gain moderate to excellent yields on catalyzing Suzuki-Miyaura cross-coupling of aryl chlorides and arylboronic acids in water. While in transfer hydrogenation of various ketones, all the Ir and Ru complexes were effective with good to excellent yields. Among all these complexes, 6c[PF(6)] was found most effective, and moderate yields could be obtained even in the transfer hydrogenation of imines. Moreover, different counteranions of Ru complexes are influential on catalyzing the transfer hydrogenation, with the sequence of PF(6)(-) ≈ BF(4)(-) > BPh(4)(-) > Cl(-) > NTf(2)(-).

Mononuclear palladium and heterodinuclear palladium–ruthenium complexes of semicarbazone ligands. Synthesis, characterization, and application in C–C cross-coupling reactions

Reaction of salicylaldehyde semicarbazone (L1), 2-hydroxyacetophenone semicarbazone (L2), and 2-hydroxynaphthaldehyde semicarbazone (L3) with [Pd(PPh3)2Cl2] in ethanol in the presence of a base (NEt3) affords a family of yellow complexes (1a, 1b and 1c, respectively). In these complexes the semicarbazone ligands are coordinated to palladium in a rather unusual tridentate ONN-mode, and a PPh3 also remains coordinated to the metal center. Crystal structures of the 1b and 1c complexes have been determined, and structure of 1a has been optimized by a DFT method. In these complexes two potential donor sites of the coordinated semicarbazone, viz. the hydrazinic nitrogen and carbonylic oxygen, remain unutilized. Further reaction of these palladium complexes (1a, 1b and 1c) with [Ru(PPh3)2(CO)2Cl2] yields a family of orange complexes (2a, 2b and 2c, respectively). In these heterodinuclear (Pd–Ru) complexes, the hydrazinic nitrogen (via dissociation of the N–H proton) and the carbonylic oxygen from the palladium-containing fragment bind to the ruthenium center by displacing a chloride and a carbonyl. Crystal structures of 2a and 2c have been determined, and the structure of 2b has been optimized by a DFT method. All the complexes show characteristic 1H NMR spectra and, intense absorptions in the visible and ultraviolet region. Cyclic voltammetry on all the complexes shows an irreversible oxidation of the coordinated semicarbazone within 0.86–0.93 V vs. SCE, and an irreversible reduction of the same ligand within −0.96 to −1.14 V vs. SCE. Both the mononuclear (1a, 1b and 1c) and heterodinuclear (2a, 2b and 2c) complexes are found to efficiently catalyze Suzuki, Heck and Sonogashira type C–C coupling reactions utilizing a variety of aryl bromides and aryl chlorides. The Pd–Ru complexes (2a, 2b and 2c) are found to be better catalysts than the Pd complexes (1a, 1b and 1c) for Suzuki and Heck coupling reactions.

Ni(ii), Pd(ii) and Pt(ii) complexes of PNP and PSP tridentate amino–phosphine ligands

The ligands D((CH(2))(2)NHPiPr(2))(2) (D = NH 1, S 2) react with (dme)NiCl(2) or (PhCN)(2)MCl(2) (M = Pd, Pt) to give complexes of the form [D((CH(2))(2)NHPiPr(2))(2)MX]X (X = Cl, I; M = Ni, Pd, Pt) which were converted to corresponding iodide derivatives by reaction with Me(3)SiI. Reaction of 1 or 2 with (COD)PdMeCl affords facile routes to [κ(3)P,N,P-NH((CH(2))(2)NHPiPr(2))(2)PdMe]Cl (8a) and [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)PdMe]Cl (9a) in high yields. An alternative synthetic approach involves oxidative addition of MeI to a M(0) precursor yielding [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)NiMe]I (10), [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MMe]I (M = Pd 8b Pt 11) and [κ(3)P,S,P-S(CH(2)CH(2)NHPiPr(2))(2)MMe]I (M = Pd 9b, Pt 12). Alternatively, use of NEt(3)HCl in place of MeI produces the species [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MH]X (X = Cl, M = Ni 13a, Pd 14a, Pt 16a). The analogs containing 2; [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)MH]X (M = Pd, X = PF(6)15: M = Pt, X = Br, 17a, PF(6)17b) were also prepared in yields ranging from 74-93%. In addition, aryl halide oxidative addition was also employed to prepare [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MC(6)H(4)F]Cl (M = Ni 18, Pd 19) and [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)Pd(C(6)H(4)F)]Cl (20). Crystal structures of 3a, 4a, 5a, 6a, 8a, 9a, 14b and 16b are reported.