Planar Pd Research Articles

Chirality in Distorted Square Planar Pd(O,N)2 Compounds

Salicylidenimine palladium(II) complexes trans-Pd(O,N)2 adopt step and bowl arrangements. A stereochemical analysis subdivides 52 compounds into 41 step and 11 bowl types. Step complexes with chiral N-substituents and all the bowl complexes induce chiral distortions in the square planar system, resulting in Δ/Λ configuration of the Pd(O,N)2 unit. In complexes with enantiomerically pure N-substituents ligand chirality entails a specific square chirality and only one diastereomer assembles in the lattice. Dimeric Pd(O,N)2 complexes with bridging N-substituents in trans-arrangement are inherently chiral. For dimers different chirality patterns for the Pd(O,N)2 square are observed. The crystals contain racemates of enantiomers. In complex two independent molecules form a tight pair. The (RC) configuration of the ligand induces the same Δ chirality in the Pd(O,N)2 units of both molecules with varying square chirality due to the different crystallographic location of the independent molecules. In complexes and atrop isomerism induces specific configurations in the Pd(O,N)2 bowl systems. The square chirality is largest for complex [(Diop)Rh(PPh3 )Cl)], a catalyst for enantioselective hydrogenation. In the lattice of two diastereomers with the same (RC ,RC) configuration in the ligand Diop but opposite Δ and Λ square configurations co-crystallize, a rare phenomenon in stereochemistry.

Axially chiral monomeric and dimeric square planar Pd(ii) complexes and their application to chiral tectonics

Mononuclear and dinuclear square planar palladium(II) complexes (denoted by [(hfac)Pd(II)(L-LH)] and [(hfac)Pd(II)(L-L)Pd(II)(hfac)], respectively) were synthesized. Here hfac(-), HL-L(-) and L-L(2-) denote hexafluoroacetylacetonato, monoprotonated and non-protonated bis-β-diketonato ligands, respectively. Three bis-β-diketones were used as HL-LH: 1,2-diacetyl-1,2-dibenzoylethane (denoted by dabeH2), 1,2-diacetyl-1,2-bis(3-methylbutanoyl)ethane (baetH2) and 1,2-diacetyl-1,2-propanoylethane (dpeH2). Both the monomeric and dimeric Pd(II) complexes were chiral due to the orthogonal twisting of the two non-symmetric diketonato moieties in HL-L(-) and L-L(2-), respectively. Optical resolution of [(hfac)Pd(II)(dabe)Pd(II)(hfac)] was achieved chromatographically on a chiral column to obtain a pair of optical antipodes which were stable against racemization. As for the other complexes, resolution was possible only after replacing hfac(-) with a bulky ligand such as dibenzoylmethanato (dbm(-)). Although a dinuclear complex with a symmetric bis-β-diketonato ligand, [(hfac)Pd(II)(taet)Pd(II)(hfac)] (taet(2-) = 1,1,2,2-tetraacetylethanato), was achiral, the replacement of the terminal ligands with non-symmetric β-diketonates yielded an axially chiral complex such as [(phacac)Pd(II)(taet)Pd(II)(phacac)], wherein phacac(-) denotes 1-phenyl-1,3-butanedionato. The UV and CD spectra of the Pd(II) complexes were analyzed with the help of the TDDFT calculations. The chiral monomeric species, [(dbm)Pd(II)(R- or S-baetH)], formed a heterometallic tetranuclear complex, [Fe(III){(dbm)Pd(II)(R- or S-baet)}3], in methanol solution.

Binuclear cyclopalladated benzo[h]quinoline and 2-tolylpyridine complexes with the bridging 2-mercaptopyridine ligand

The planar binuclear cyclometalated Pt(II) and Pd(II) complexes with the metal–metal bonding are of wide interest due to the important role of such complexes in the metal catalysis [1], their anti-carcinogenic properties [2], and the possibility of their use as the components in light-emitting diodes [3, 4]. This work presents the results of a study of spectroscopic and electrochemical characteristics of the [Pd(C^N)(μ-S^N)]2 complexes, where (C^N) denotes the deprotonated forms of benzo[h]quinolone and 2-tolylpyridine, and (S^N) corresponds to that of 2-mercaptopyridine. DOI: 10.1134/S1070363213010222

Antimicrobial and antitumor activity of platinum and palladium complexes of novel spherical aramides nanoparticles containing flexibilizing linkages: Structure–property relationship

Square planar Pd (II) and octahedral Pt (IV) complexes with novel spherical aramides nanoparticles containing flexible linkages ligands have been synthesized and characterized using analytical and spectral techniques. The synthesized complexes have been tested for their antimicrobial activity using Kirby-Bauer disc diffusion method. The antitumor activity has been performed using liver carcinoma (HEPG2), breast carcinoma (MCF7) and colon carcinoma (HCT 116) cell lines. Palladium complexes of polyamides containing sulfones showed the highest potency as antibacterial and antifungal agents. Platinum complexes containing sulfone and ether flexible linkages and chloro groups exhibited high potency as antitumor and antimicrobial agents. The uniform sizes of these nanomaterials could find biological uses such as immune assay and other medical purposes.

Preparation, Characterization, Biological Activity and 3D Molecular Modeling of Mn(II), Co(II), Ni(II), Cu(II), Pd(II) and Ru(III) Complexes of Some Sulfadrug Schiff Bases

AbstractMn(II), Co(II), Ni(II), Cu(II), Pd(II) and Ru(III) complexes of Schiff bases derived from the condensation of sulfaguanidine with 2,4‐dihydroxy benzaldehyde (HL1), 2‐hydroxy‐1‐naphthaldehyde (HL2) and salicylaldehyde (HL3) have been synthesized. The structures of the prepared metal complexes were proposed based on elemental analysis, molar conductance, thermal analysis (TGA, DSC and DTG), magnetic susceptibility measurements and spectroscopic techniques (IR, UV‐Vis, and ESR). In all complexes, the ligand bonds to the metal ion through the azomethine nitrogen and α‐hydroxy oxygen atoms. The structures of Pd(II) complex 8 and Ru(III) complex 9 were found to be polynuclear. Two kinds of stereochemical geometries; distorted tetrahedral and distorted square pyramidal, have been realized for the Cu(II) complexes based on the results of UV‐Vis, magnetic susceptibility and ESR spectra whereas octahedral geometry was predicted for Co(II), Mn(II) and Ru(III) complexes. Ni(II) complexes were predicted to be square planar and tetrahedral and Pd(II) complexes were found to be square planar. The antimicrobial activity of the ligands and their metal complexes was also investigated against the gram‐positive bacteria Staphylococcus aures and Bacillus subtilis and gram‐negative bacteria, Escherichia coli and Pesudomonas aeruginosa, by using the agar dilution method. Chloramphenicol was used as standard compound. The obtained data revealed that the metal complexes are more or less, active than the parent ligand and standard. The X‐ray crystal structure of HL3 has been also reported.

Origin for Fluxional Structure of Tetracoordinate PdIIComplexes

In the Pd-catalyzed cross-coupling reactions, the PdL2 complexes with the bulky and electron-rich L ligands (phosphines, NHCs, etc) are important compounds as a Pd(L)nprecusor. The catalytic activity of Pd(L)n-precusors was influenced by the electronic property of the strong σ-donor and the steric effect of the bulky L ligands. Due to the electron-transfer from the strong σ-donor L ligand to Pd, the oxidation state of Pd in the neutral [PdLnX] catalysts is zerovalent. In some X-ray crystallography results, the Pd([9]aneB2A)L2 complexes with mixed hard/soft tridentate ligand have been observed as a five-coordinate geometry with an apical (soft A...Pd) interaction. In Pd(η,η,ηC10H16N2Me2) complexes with an aza-macrocyclic ligand, the six coordination bonds of the three olefin units with Pd were symmetrically formed via three (olefin...Pd) interactions. Meanwhile, in hydration reactions on square planar [PdCl4] complexes, two vertical (H2O...Pd) and (HOH... Pd) interactions for the ligand exchange processes were investigated theoretically and experimentally. With increasing the strength of the fifth (solvent...Pd) interaction, the replacement of the equatorial (Pd-Cl) bond with (solvent...Pd) takes place via a five-coordinate transition states. Is there any relationship between the relative stability and fluxional configuration of the Pd isomers (exoand endotypes) and the apical (soft P...Pd) interaction in the Pd complexes? The unusual stereochemistry of square planar Pd complexes might be influenced by the fifth special (soft P...Pd) interaction, and the conformational rearrangement for the relative stability. The vacant bond on the zaxis allows the occupied dz2-orbital of Pd to interact with the Lewis acid ligand (σ-acceptor), but it is difficult for electron-rich substrates and Pd to interact apically (σ-donor ...filled dz2-orbital). Therefore, for Pd([9]aneB2A)L2, the apical (σ-donor...filled 4dz2-orbital) repulsion shown in Scheme 1 is suggested. In the present work, we have investigated the relative stabilities and extraordinary structures of the macrocyclic Pd([9]aneB2A)L2 complexes within the frameworks of the orbital interactions. The equilibrium geometric structures of tetracoordinate palladium [Pd([9]aneB2A)L2, Pd([9]aneBAB)L2 (A: P; B=N; L=Cl−, PH3)] complexes were fully optimized with the B3P86/6-311+G** (LanL2DZ for Pd) level using Gaussian 03. Optimized geometric structures of tetracoordinate Pd([9]aneN2P)L2 {Pd([9]aneN2P)L2} isomers including HOMO were represented in Figure 1 and their parameters were listed in Table 1. In the Pd complexes, Pd locates at the center of the tetracoordinate Pd complexes with a ([9]aneN2P) ligand and two L monodentates. In endo-Pd([9]aneN2P)Cl2

Helicity inversion from left- to right-handed square planar Pd(ii) complexes: synthesis of a diastereomer pair from a single chiral ligand and their structure dynamism

A diastereomer pair of left- and right-handed square planar Pd(II) complexes was synthesized from a single chiral ligand as kinetic and thermodynamic products. Helicity inversion between the diastereomers occurred rapidly under thermal and microwave irradiation conditions.

Directed secondary interactions in transition metal complexes of tripodal pyrrole imine and amide ligands

Tripodal pyrrole imine and amide ligands provide platforms for combined primary and secondary coordination sphere interactions in square planar Pd and Cu, and octahedral Ti complexes.

Tetrapalladium Complex with Bridging Germylene Ligands. Structural Change of the Planar Pd4Ge3 Core

A complex with a planar hexagonal Pd(4)Ge(3) core, [Pd{Pd(dmpe)}(3)(μ(3)-GePh(2))(3)], was synthesized and characterized by X-ray and NMR measurements as well as by DFT calculations. 4-tert-Butylbenzenethiol converted the Pd(4) complex into a hexapalladium complex, [{Pd(3)(μ-GePh(2))(2)(μ-H)(μ(3)-GePh(2)(SC(6)H(4)(t)Bu-4))}(2)(μ-dmpe)], composed of two Pd(3)Ge(3) units bridged by a dmpe ligand. The addition of CuI or AgI to the Pd(4) complex yielded [Pd(μ-MI){Pd(dmpe)}(3)(μ(3)-GePh(2))(3) ] (M = Cu, Ag), in which Cu or Ag bridges a Pd-Pd bond of the Pd(4)Ge(3) core. The CuI adducts in solution undergo a pivot motion of the CuI on the surface of the Pd(4)Ge(3) plane on the NMR time scale.

Mechanisms of Reductive Eliminations in Square Planar Pd(II) Complexes: Nature of Eliminated Bonds and Role oftransInfluence

The trans influence of various phosphine ligands (L) in direct as well as dissociative reductive elimination pathways yielding CH(3)CH(3) from Pd(CH(3))(2)L(2) and CH(3)Cl from Pd(CH(3))(Cl)L(2) has been quantified in terms of isodesmic reaction energy, E(trans), using the MPWB1K level of density functional theory. In the absence of a large steric effect, E(trans) correlated linearly with the activation barrier (E(act)) of both direct and dissociation pathways. The minimum of molecular electrostatic potential (V(min)) at the lone pair region of phosphine ligands has been used to assess their electron donating power. E(trans) increased linearly with an increase in the negative V(min) values. Further, the nature of bonds that are eliminated during reductive elimination have been analyzed in terms of AIM parameters, viz. electron density (ρ(r)), Laplacian of the electron density (∇(2)ρ(r)), total electron energy density (H(r)), and ratio of potential and kinetic electron energy densities (k(r)). Interestingly, E(act) correlated inversely with the strength of the eliminated metal-ligand bonds measured in terms of the bond length or the ρ(r). Analysis of H(r) showed that elimination of the C-C/C-Cl bond becomes more facile when the covalent character of the Pd-C/Pd-Cl bond increases. Thus, AIM details clearly showed that the strength of the eliminated bond is not the deciding factor for the reductive elimination but the nature of the bond, covalent or ionic. Further, a unified picture showing the relationship between the nature of the eliminated chemical bond and the tendency of reductive elimination is obtained from the k(r) values: the E(act) of both direct and dissociative mechanisms for the elimination of CH(3)CH(3) and CH(3)Cl decreased linearly when the sum of k(r) at the cleaved bonds showed a more negative character. It means that the potential electron energy density dominates over the kinetic electron energy density when the bonds (Pd-C/Pd-Cl) become more covalent and the eliminated fragments attain more radical character leading to the easy formation of C-C/C-Cl bond.

Binding Studies of a Novel Antitumor Palladium(II) Complex to Calf Thymus DNA

The interaction of new 1, 10-phenanthrolineoctyldithiocarbamatopalladium (II) nitrate with DNA from calf thymus was investigated at 300 and 310 K in a Tris-HCl buffer of pH 7.0 medium containing 20 mM sodium chloride. This water soluble, square planar Pd(II) complex has been synthesized and spectroscopic (electronic, infrared, and nuclear magnetic resonance) and elemental analysis of the complex are discussed. This complex shows greater growth inhibitory activity against human tumor cell line K562 than cisplatin. Results of UV-visible studies show that the complex exhibits cooperative binding with DNA and denatures the DNA at an extremely low concentration (∼11.98 μM). Fluorescence studies reveal that the mode of binding of this complex with DNA seems to be intercalation. The results of sephadex G-25 column show that the binding of metal complex with DNA is so strong that it does not readily break. Several binding and thermodynamic parameters are also described. They may shed light on the mechanisms of interaction of this agent with DNA, which should be quite different from that of cisplatin.

The electrochemical reduction of PdCl 42− and PdCl 62− in polyaniline: Influence of Pd deposit morphology on methanol oxidation in alkaline solution

The controlled uptake and electrochemical reduction of metal precursors PdCl 4 2− and PdCl 6 2− in polyaniline (PANI) is demonstrated. The formation of PANI/Pd composites is achieved with a reduction in proton doping and an increase in the oxidation of the polymer with Pd deposits physically blocking the nitrogen groups. High surface area filaments (PdCl 4 2−) or a rough encapsulation (PdCl 6 2−) of Pd metal on PANI are obtained. The structural differences highlight the influence of the metal precursor oxidation state on the morphology of the Pd deposits in PANI. Thermal gravimetric analysis provides an estimate of the Pd content for each composite of ∼40%. X-ray Photoelectron Spectroscopy and X-ray-excited Auger Electron Spectroscopy analyses confirm the deposition of Pd metal. The catalytic oxidation of methanol was demonstrated for both PANI/Pd composites in alkaline solutions that prohibit proton doping of the polymer. The data indicates that Pd metal acts as a solid-state dopant that may delocalize the charge on the polymer backbone to maintain conductivity. Methanol oxidation at PANI/Pd composites produced using PdCl 4 2− was enhanced relative to the composite produced using PdCl 6 2− and a planar Pd electrode. Comparison of PANI/Pd composite produced using PdCl 4 2− with other Pd catalysts from the literature indicates surface poisoning is reduced when Pd is coupled with the polymer. The composite is robust and stable in alkaline solution with the charge density decreasing by 5% on the positive scan and 13% on the negative scan after 200 voltammetric cycles. The data also indicates that the reductive desorption of surface contaminants is possible, minimizing the catalytic loss due to surface poisoning.

Liaisons between photoconductivity and molecular frame in organometallic Pd(ii) and Pt(ii) complexes

The synthesis and a comprehensive experimental study of molecular structure, electrochemical properties, photoconductivity, absorption and emission properties of two homologous series of square planar cyclometallated Pd(II) and Pt(II) complexes are described. In these complexes, a five member (C,N) metallacycle is formed by either azobenzene, 2-phenylpyridine or benzo[h]quinoline, while the ancillary (O,N) ligand required to complete the metal coordination sphere is the Schiff base resulting from the condensation of 4-n-hexylaniline with 2-hydroxy-4-n-hexyloxybenzaldehyde. The study is complemented by Density Functional Theory calculations of molecular structure in the ground state, frontier orbitals distribution and energies. Absorption energies, intensities for the transitions and composition of the excited states are characterized by Time Dependent Density Functional Theory computations. Results show that for these complexes the HOMO is located on the Schiff base and the LUMO on the cyclometalated ligand. As also indicated by spectroscopic and photoconductivity results, the photogeneration of charge carriers might be associated with the spatial separation of HOMO and LUMO, while an additional contribution could derive from a conformational variation in the excited state. The separation of the frontier orbitals on different ligands provides simple synthetic routes towards band-gap tuning and energy matching with other molecular species and electrodes, both important features for several applications of molecular semiconductors. The results of the present investigation suggest that these square planar cyclometalated Pd(II) and Pt(II) complexes actually form a new class of photoconductors.

The effect of cluster thickness on the adsorption of CH 4 on Pd n

Adsorptions of methane on Pd n clusters were studied using PW91 functional with a plane wave basis set to understand the role of Pd n clusters in detecting trace amounts of CH 4 in air and the observations made in the temperature-programmed desorption experiment on the CH 4 physisorption on Pd clusters supported by Al 2O 3. Fifteen Pd n clusters consisting of up to 13 atoms were chosen to form various CH 4 · · · Pd n adducts. Dispersion correction to the adsorption energy was also calculated. Our results show that the interaction between CH 4 and Pd n cluster depends strongly on the adsorption site and CH 4 orientation. The most preferred adsorption occurs (1) along the C ∞ axis of the linear Pd n clusters, (2) perpendicular to the main C n axis of the planar Pd n clusters, and (3) at the atop site of the three-dimensional Pd n clusters. All four coordination modes of σ−bonds, η 1, η 2–C,H, η 2–H,H, and η 3, are found in these adducts. Additionally, the η 3–C,H,H, η 3-Pd,Pd,Pd, and η 1-Pd,Pd modes are identified. The η 1 σ−bond is found to be dominant in the CH 4 · · · Pd n adducts with Pd n clusters larger than trimer. Our results show that the CH 4 does not adsorb on top of the monolayer Pd clusters. Furthermore, the adsorption strength is more dependent on the thickness of the Pd clusters than the cluster size.

Bond dissociation energies of ligands in square planar Pd(II) and Pt(II) complexes: An assessment using trans influence

DFT calculations using MPWB1K method with COSMO continuum solvation model have been carried out to quantify the trans influence of various X ligands ( E X) in [Pt IICl 3X] n− complexes as well as the mutual trans influence of two X and Y ligands ( E XY) in [Pt IICl 2XY] n− complexes. A quantitative structure energy relationship (QSER) is derived for predicting the E XY using E X and E Y and this relationship showed a strong similarity to a QSER derived for predicting E XY of [Pd IICl 2XY] n− complexes. Quantification of the contributions of E X and E XY to the bond dissociation energy of the ligand X ( BDE X) in complexes of the type [M IIX(Y)X′(Y′)] (M = Pd, Pt) is also achieved. The BDE X of any ligand X in these complexes can be predicted using the equations, viz. BDE X(Pd) = 1.196 E X − 0.603 E XY − 0.118 E X’Y’ + 0.442 D X + 15.169 for Pd(II) complexes and BDE X(Pt) = 1.420 E X − 0.741 E XY − 0.125 E X’Y’ + 0.498 D X + 13.852 for Pt(II) complexes, where D X corresponds to the bond dissociation energy of X in [M IICl 3X] n− complexes. These expressions suggest that the mutual trans influence from X and Y is more dominant than the mutual trans influence from X′ and Y′ and both factors contribute significantly to the weakening of M–X bond. We also obtained a strong linear relationship between E X and the electron density ρ( r) at the bond critical point of M–Cl bond trans to the X in [M IICl 3X] n− and this allows us to express the BDE X(Pd) and BDE X(Pt) in terms of only the ρ( r) and D X. We have demonstrated that using a database comprising of D X and the ρ( r), the bond dissociation energy of X in complexes of the type [M IIX(Y)X′(Y′)] can be predicted.

Synthesis of complexes with the polydentate ligand N,N′-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide

The pentadentate ligand N,N′-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide (POPYH4) has been used to prepare a variety of new complexes [HNEt3]2[Zn4Cl(POPYH)3] (2), [HNEt3][PdCl(POPYH2)] (3), [HNEt3][Ni(POPYH)] (4) and K[Ni(POPYH)] (5) which show the versatility of this multidentate ligand. The complexes have been characterised spectroscopically and their molecular and crystal structures have been determined by single crystal X-ray diffraction techniques. In these complexes the ligand exhibits different modes of coordination towards different transition metal ions. The structure of triethylammonium salt of the Zn(II) dianion 2 consists of an unusual tetra-zinc core supported by three POPYH ligands each one of which links two adjacent zinc centres through two oxygen and two nitrogen donor atoms. The salt of the square planar Pd(II) anion 3 contains one POPYH2 ligand which coordinates in a tridentate fashion through the two deprotonated amido groups and by the central pyridine nitrogen donor. The two Ni(II) salts 4 and 5 contain the same [Ni(POPYH)]− anion in which the square planar Ni(II) centre is chelated by a POPYH ligand through the two deprotonated amido nitrogen atoms, the pyridine nitrogen and a deprotonated hydroxyl group.

N-Aryl Pyrrolo-tetrathiafulvalene Based Ligands: Synthesis and Metal Coordination

A straightforward general synthetic access to N-aryl-1,3-dithiolo[4,5-c]pyrrole-2-thione derivatives 6 from acetylenedicarbaldehyde monoacetal is depicted. In addition to their potentiality as precursors to dithioalkyl-pyrrole derivatives, thiones 6 are key building blocks to N-aryl monopyrrolo-tetrathiafulvalene (MPTTF) derivatives 10. X-ray structures of four of these thiones intermediates, reminiscent of the corresponding MPTTF derivatives, are provided. When the aryl group is a binding pyridyl unit, the MPTTF derivative 10a can coordinate M(II) salts (M = Pt, Pd). The first examples of metal-directed orthogonal MPTTF-based dimers 11-14, obtained through coordination of 10a to cis-blocked square planar Pt or Pd complexes are described. Studies on the parameters influencing the dimer construction are presented, as well as first recognition properties of the resulting electron-rich clip for C(60).

Pd(ii)-promoted direct cross-coupling reaction of arenes via highly regioselective aromatic C–H activation: a theoretical study

The direct cross-coupling reaction of arenes promoted by Pd(OAc)(2) is synthetically very useful because the preparation of a haloarene as a substrate is not necessary. This reaction interestingly only occurs in the presence of benzoquinone (BQ). DFT, MP2 to MP4(SDQ), and CCSD(T) computations elucidated the whole mechanism of this cross-coupling reaction and the key roles of BQ. The first step is the heterolytic C-H activation of benzo[h]quinoline (HBzq) by Pd(OAc)(2) to afford Pd(Bzq)(OAc). The Pd center is more electron-rich in Pd(Bzq)(OAc) than in Pd(OAc)(2). Hence, BQ easily coordinates to Pd(Bzq)(OAc) with a low activation barrier to afford a distorted square planar complex Pd(Bzq)(OAc)(BQ) which is as stable as Pd(Bzq)(OAc). Then, the second C-H activation of benzene occurs with a moderate activation barrier and small endothermicity. The final step is the reductive elimination which occurs with little barrier. The rate-determining step of the overall reaction is the second C-H activation whose activation barrier is considerably higher than that of the first C-H activation. BQ plays a key role in accelerating this reaction; (i) the phenyl group must change its position a lot to reach the transition state in the reductive elimination from the square planar intermediate Pd(Ph)(Bzq)(OAc) but only moderately in the reaction from the trigonal bipyramidal intermediate Pd(Ph)(Bzq)(OAc)(BQ). This is because BQ suppresses the phenyl group to take a position at a distance from the Bzq. (ii) BQ stabilizes the transition state and the product complex by the back-donation interaction. In the absence of BQ, the reductive elimination step has a much higher activation barrier. Though it was expected that the BQ coordination accelerates the second C-H activation of benzene by decreasing the electron density of Pd in Pd(Bzq)(OAc), the activation barrier of this second C-H activation is little influenced by BQ.

Homo- and heterodinuclear complexes of the tetrakis(pyrazolyl)borate ligand

Monometallic complexes of the tetrakis(pyrazolyl)borate ligand [ML(2){B(pz)(4)}] {M = Rh, Ir; L(2) = eta-cod, eta-nbd, (CO)(2), (CO)(PPh(3))} have two free pyrazolyl rings which can be coordinated to a second ML(2) unit to give the dimeric compounds [L(2)M{mu-B(pz)(4)}ML(2)](+), and to a metal halide to give heterobimetallic species [L(2)M{mu-B(pz)(4)}M'Cl(2)]. (1)H NMR spectroscopy shows that [(eta-cod)Rh{mu-B(pz)(4)}Rh(eta-cod)](+) 1(+), [(eta-nbd)Rh{mu-B(pz)(4)}Rh(eta-nbd)](+) 2(+), [(eta-cod)Ir{mu-B(pz)(4)}Ir(eta-cod)](+) 3(+) and [(CO)(2)Rh{mu-B(pz)(4)}Rh(CO)(2)](+) 4(+) are fluxional at room temperature. Cooling a solution of [(eta-cod)Rh{mu-B(pz)(4)}Rh(eta-cod)](+) 1(+) to -90 degrees C slows the fluxional process, which involves inversion of the two B-(N-N)(2)-M six-membered rings. Attempts to synthesise the asymmetric complexes [(eta-cod)Rh{mu-B(pz)(4)}Rh(eta-nbd)](+) 7(+), [(eta-cod)Rh{mu-B(pz)(4)}Ir(eta-cod)](+) 8(+) and [(eta-cod)Rh{mu-B(pz)(4)}Rh(CO)(2)](+) 9(+) produced a mixture of [L(2)M{mu-B(pz)(4)}ML(2)](+), [L'(2)M'{mu-B(pz)(4)}M'L'(2)](+) and the desired species. The heterobimetallic complexes [L(2)Rh{mu-B(pz)(4)}M'Cl(2)] (M' = Co, L(2) = eta-cod 10; M' = Co, L(2) = eta-nbd 11; M' = Co, L = CO 12; M' = Co, L(2) = (CO)(PPh(3)) 13; M' = Zn, L(2) = eta-cod 14; M' = Zn, L(2) = eta-nbd 15; M' = Pd, L(2) = eta-cod 16) possess square planar Rh(I) linked to square planar Pd(II) or tetrahedral Zn(II) and Co(II) centres. The paramagnetic Co(II) complexes give (1)H NMR spectra with signals shifted over a range of 75 ppm. The UV-Vis spectra of 10-13 show four bands, one MLCT at Rh and three d-d transitions arising from the splitting of the (4)T(1)(P) excited state due to approximate C(2v) symmetry at Co.

Synthesis and structural investigations of Ni(II)- and Pd(II)-coordinated α-diimines with chlorinated backbones

Novel square planar Pd(II) α-diimines [PdX 2{ArN C(Cl)} 2], where Ar = C 6H 5, (2,6-Me 2C 6H 3), (2,6- i Pr 2C 6H 3) and X = Cl or Br, and the octahedral Ni(II) complex [NiBr 2{(C 6H 5)N C(Cl)} 2(THF) 2] have been prepared and characterised by spectroscopic methods. For two of the Pd(II) complexes and the Ni(II) complex the crystal structures were determined by X-ray crystallography. A further insight into the geometry and electronic structure of [PdBr 2{(2,6-Me 2C 6H 3)N C(Cl)} 2] was gained using density functional theoretical calculations (DFT). This compound resembles structurally and electronically typical olefin polymerisation pre-catalysts supported by α-diimines incorporating methyl- and 1,8-naphtalenyl substituents at the ligand backbone. The chlorine-substituted backbone of the free ligand [2,6-Me 2C 6H 3N C(Cl)] 2 can be employed in further alkylation reactions to generate new multifunctional ligand prototypes with potential uses as ansa-metallocene/diimines building blocks for catalytic applications of heterobimetallic complexes.