Alkoxy-substituted group 6 allenylidene complexes - Synthesis and properties

Bis(alkoxy)allenylidene complexes, [(CO)₅MCCC(OR′)OR], as well as mono(alkoxy)allenylidene complexes, [(CO)₅MCCC(OR′)Ph], of chromium and tungsten are accessible from propynones [HCCC(O)Ph] or propynoic acid esters [HCCC(O)OR; R = Et, (−)-menthyl, endo-bornyl] by the following reaction sequence: (a) deprotonation of the alkynes, (b) reaction with [(CO)₅M-THF] (M = Cr, W), and (c) alkylation of the resulting alkynyl metallate, [(CO)₅MCCC(O)R], with Meerwein salts. Vinylidene complexes, [(CO)₅MCC(R′)C(O)OR], are formed as a by-product by C_β-alkylation of the alkynyl metallate. Dimethylamine displaces one alkoxy substituent of the bis(alkoxy)allenylidene complexes to give dimethylamino(alkoxy)allenylidene complexes, [(CO)₅MCCC(OR)NMe₂]. The analogous reaction of dimethylamine with a mono(alkoxy)-substituted allenylidene complex affords the aminoallenylidene complex [(CO)₅CrCCC(NMe₂)Ph]. When the amine is used in large excess, the α,β-unsaturated aminocarbene complex [(CO)₅CrC(NMe₂)C(H)C(NMe₂)Ph] is additionally formed by addition of the amine across the C_αC_β-bond of the allenylidene ligand. The reaction of [(CO)₅MCCC(OEt)₂] with dimethyl ethylenediamine offers access to bis(amino)allenylidene complexes, in which C_γ is part of a five-membered heterocycle. Photolysis of bis(alkoxy)allenylidene complexes in the presence of triphenylphosphine yields tetracarbonyl- and tricarbonyl{bis(phosphine)}allenylidene complexes. Diethylaminopropyne inserts into the C_βC_γ bond of [(CO)₅MCCC(OEt)OMethyl] to give alkenylallenylidene complexes. Subsequent acid-catalyzed intramolecular cyclization affords a pyranylidene complex.     

Synthesis, structures and luminescent properties of novel coordination polymers constructed by lanthanide salts and benzimidazole-5,6-dicarboxylic acid

Two three-dimensional (3D) novel lanthanide complexes with the H₂Lbenzimidazole-5,6-dicarboxylate [Ln₂L₃(H₂O)] [Ln = Eu (1), Tb (2)] and one two-dimensional (2D) novel lanthanide complex [Pr(L)(HL)H₂O]·H₂O (3) were synthesized by hydrothermal reaction at 180 °C and characterized by elemental analysis, infrared spectra and single-crystal X-ray diffraction. The result showed that complexes 1 and 2 are isostructural and build porous 3D networks by L²⁻ groups linking Ln(III) atoms via tetradentate (bridging and bridging) and pentadentate (bridging/chelating and bridging) coordination modes. Complex 3 is a eight-coordinated Pr(III) chain complex, exhibiting a 2D polymeric network with parallel Pr-carboxylate chains along the crystallographic c-axis. In addition, it is found that in these structures, coordination modes of L²⁻ and HL⁻ are versatile and can adopt different conformations according to distinct dimensions of polymeric structures. The photoluminescent properties of 1, 2 and thermogravimetric analyses of the three complexes were discussed in detail.     

Orthomercurated and cycloaurated derivatives of the iminophosphorane Ph3PNPh

Ortho-lithiation of Ph₃PNPh followed by reaction with HgCl₂ gave good yields of [Hg{C₆H₄(PPh₂NPh)-2}Cl], 3, which was characterised spectroscopically and by an X-ray crystal structure determination. This is an isomer of the product of direct mercuration of Ph₃PNPh which occurs on the N-bonded phenyl ring [J. Vicente, J.A. Abad, R. Clemente, J. Lopez-Serrano, M.C. Ramirez de Arellano, P.G. Jones, D. Bautista, Organometallics, 22 (2003) 4248]. Transmetallation of 3 with [AuCl₄]⁻ gave the corresponding cycloaurated complex [Au{κ²-C,N-C₆H₄(PPh₂NPh)-2}Cl₂], with a five-membered metallocyclic ring incorporating four different elements.     

Regioselective addition of bifunctional oximehydroxamic acid by the hydroxamic group to Pt(IV)-coordinated nitriles

The metal-mediated coupling between the nitriles RCN in the platinum(IV) complexes trans-[PtCl₄(RCN)₂] (RMe, Et, CH₂Ph, Ph), cis/trans-[PtCl₄(MeCN)(Me₂SO)] and the newly synthesized bifunctional oximehydroxamic acid, viz. N,2-dihydroxy-5-(1-hydroxyiminoethyl)benzamide, proceeds smoothly in CH₂Cl₂ at 40-45 °C to accomplish the new metallaligands HNC(R)ONHC(O)C₆H₃(2-OH)(5-C(Me)NOH) with pendant oxime functionalities due to the regioselective addition of the reagent via its hydroxamic groups. The obtained iminoligands exist in hydroxamic/hydroximic tautomeric equilibrium in solution. The structures of the isolated compounds are based on elemental analyses (C, H, N), IR, 1D ¹H, ¹³C{¹H}, and 2D NMR correlation experiments, i.e. ¹H,¹³C-COSY, ¹H,¹³C long range COSY, ¹H,¹⁵N-COSY, and ¹H,¹⁵N long range COSY.     

A study on the reaction of copper complex of dioxotetraamine with superoxide ion by spectrophotometry and pulse radiolysis

The reactions of a dioxotetraamine Cu(II) complex [Cu(H₋₂L)] (L is 6-(9-fluorenyl)-1,4,8,11-tetraazaandencane-5,7-dione)with O₂ ⁻ were investigated by electrochemistry, UV-Vis spectrophotometry and pulse radiolysis, respectively. In DMSO solution, [Cu^II(H₋₂L)] was oxidized into [Cu^III(H₋₂L)]⁺ by O₂ ⁻, a consecutive reaction was observed with [Cu^III(H₋₂L)(O₂ ²⁻)] ⁻ as intermediates (k₁=1.71×10³ M⁻¹ s⁻¹, k₂=1.2×10⁻² s⁻¹). The mechanism of O₂ ⁻ dismutation catalyzed by the complex involved alternate oxidation and reduction of Cu(II) by O₂ ⁻ and the k_cat is 6.07 × 10⁷ M⁻¹ s⁻¹ (pH 7.4).     

Kinetic studies of the reduction of hexaaquacobalt(III) perchlorate by a cobaloxime, [Co(dmgBF2)2(H2O)2]

The reaction of with Co(dmgBF₂)₂(H₂O)₂ in 1.0 M HClO₄/LiClO₄ was found to be first-order in both reactants and the [H⁺] dependence of the second-order rate constant is given by k_2obs = b/[H⁺], b at 25 °C is 9.23 ± 0.14 × 10² s⁻¹. The [H⁺] dependence at lower temperatures shows some saturation effect that allowed an estimate of the hydrolysis constant for as K_a = 9.5 × 10⁻³ M at 10 and 15 °C. Marcus theory and the known self-exchange rate constant for Co(OH₂)₅OH^2+/+ were used to estimate an electron self-exchange rate constant of k₂₂ = 1.7 × 10⁻⁴ M⁻¹ s⁻¹ for .     

Atmospheric pressure photoionization mass spectrometry of per-O-methylated oligosaccharides related to D-xylans

Three d-xylan type per-O-methylated trisaccharides with various types of linkages between the d-xylopyranose units were examined by atmospheric pressure photoionization (APPI) mass spectrometry in the positive ion mode. The most interesting feature of a thermospray mass spectrum using the APPI source with UV lamp switched off, is the exclusive production of [M+Na]⁺ adduct ions. [M+Na]⁺ cationized ions are the most abundant species in the case of APPI mass spectrometry. The second ionization process has no analogy in the case of substances studied using APPI to date. This aspect involves the addition of a water molecule to the molecular ion of a per-O-methylated saccharide, giving rise to [M+H₂O]⁺ adduct ions. The [M+H₂O]⁺ species are readily detected at m/z 544, and are clearly visible for all three isomers studied. The MS/MS spectrum of [M+Na]⁺ ions contains a base peak at m/z 375, produced by a Y-type cleavage of the trisaccharide, along with a hydrogen rearrangement on the terminal interglycosidically linkage glycosidic oxygen atom. The [M+H₂O]⁺ species fragment largely give rise to ions at m/z 175, 143 and, as a result, the m/z 111 ion is unique to nonreducing terminal units.     

Oxidovanadium(IV) complexes containing ligands derived from dithiocarbazates - Models for the interaction of VO with thiofunctional ligands

The tetragonal-pyramidal VO²⁺ complexes [VO{(RSC-S)N-NX}₂] (1-6) were synthesised by the reactions of VO(OCHMe₂)₃ with the dithiocarbazate ligands RSC(S)-NH-NX, where X = cyclo-pentyl, cyclo-hexyl or 4-Me₂N-C₆H₄-CH, and R = CH₃ or CH₂C₆H₅. The compounds were characterised by elemental analysis, IR- and mass spectrometries, and in cases of compounds 1, 3, 4 and 5, by X-ray diffraction. The chiral compound 4 (X = cyclo-hexyl, R = CH₂C₆H₅) crystallises in the C configuration. In compound 5, the VO moiety is disordered (83.3:16.7%) with respect to the plane spanned by the four equatorial ligand functions.     

A heterotrinuclear and a polynuclear complex constructed from a ferrocenyl carboxylate and an N-containing ligand: Synthesis, crystal structures and electrochemical properties

Treatment of NaO₂CCHC(Me)Fc with cadmium acetate and iron(II) sulfate in the presence of 2,2′-bipy yielded [Cd₂Fe(μ-O₂CCHC(Me)Fc)₂(μ₂-O₂CCHC(Me)Fc)₂(μ₂-η²-O₂CCHC(Me)Fc)₂(2,2′-bipy)₂] · 2H₂O (1); while from NaO₂CC₆H₄{C(O)Fc-o}, cadmium acetate, and pbbm the product was {[Cd(η²-O₂CC₆H₄{C(O)Fc-o})₂(pbbm)] · 0.5H₂O}_n (2) [Fc = (η⁵-C₅H₅)Fe(C₅H₄-η⁵); 2,2′-bipy = 2,2′-bipyridyl; pbbm = 1,1′-(1,5-pentamethylene)bis-1H-benzimidazole]. Compounds 1 and 2 have been characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. In centro-symmetric crystalline 1, the Fe and the two flanking atoms are six-coordinate; the three carboxylato ligands between the Fe and a Cd atom have different coordination modes. Crystalline 2 consists of an infinite polymeric chain, in which adjacent [Cd(η²-O₂CC₆H₄{C(O)Fc-o})₂] units are linked by pbbm ligands; thus each Cd atom is six-coordinate. Some electrochemical properties of the two complexes are reported.     

Solution structure of molybdic acid from Raman spectroscopy and DFT analysis

Protonation of produces the well-characterized polymolybdates, but at concentrations below 10⁻³ M the dominant species is monomeric molybdic acid, H₂MoO₄. It is likely to be the species adsorbed on manganese oxide, a process thought to control levels in the ocean, because of the strong proton dependence of adsorption. The molecular structure of H₂MoO₄ is elusive, since it occurs only in dilute solutions. Using 244 nm laser excitation, near resonance with O → Mo charge-transfer electronic transitions of H₂MoO₄, we have detected a 919 cm⁻¹ Raman band assignable to ν_sMoO. Using DFT, we have computed geometries and vibrational modes for the various structures consistent with the H₂MoO₄ formula. We tested the computations on a series of Mo(VI) oxo complexes with known vibrational frequencies, at several levels of theory. Best agreement with experimental values, at reasonable computational cost, was obtained with the B3LYP functional, employing a LANL2DZ ECP basis set for Mo and the 6-311+G(2df,p) basis set for O and H. Among the possible H₂MoO₄ structures only those based on the MoO₃ unit, with one, two or three coordinated water molecules, gave a scaled frequency for ν_sMoO that was within two standard deviations of 919 cm⁻¹. Best agreement was obtained for MoO₃(H₂O)₃. The MoO₂ and MoO structures gave frequencies that were too high. The Mo(OH)₆ structure could be excluded, because its vibrational frequencies shift down strongly upon H/D exchange, whereas the 919 cm⁻¹H₂MoO₄ band shifts up 1 cm⁻¹ in D₂O.     

Redox reactions of [VO(salen)] couple in acetonitrile: Volume analyses in relation to large chiral recognitions observed for electron self-exchange reactions of [VO(Schiff-Base)]

Kinetic measurements were carried out for the outer-sphere electron transfer reactions involving [VO(Schiff-Base)]^+/0 couples. Electron self-exchange rate constant for [VO(3-MeOsal-(RR)-chxn)]^+/0 couple was determined as k_ex = (5.2 ± 0.8) × 10⁶ kg mol⁻¹s⁻¹ at 25 °C. It was found that added water in acetonitrile solvent retarded the electron transfer reactions between [VO(salen)]⁺ and [Co(o-phen)₃]²⁺: the six-coordinate V(V) species, [VO(salen)(OH₂)]⁺ was found to be ca. 3.5 times less reactive compared with the five-coordinate species, [VO(salen)]⁺. This small difference between the reactivity of five- and six-coordinate species indicates that the reaction through the direct OV(V)-OV(IV) interaction is outer-sphere in nature, contrary to the previously proposed inner-sphere mechanism. Activation volumes corresponding to the electron self-exchange reactions for [VO(salen)]⁺/[VO(salen)]⁰ and [VO(salen)OH₂]⁺/[VO(salen)]⁰ couples were estimated from the volume profiles of the reduction reactions of [VO(salen)]⁺ by [Co(o-phen)₃]²⁺, with and without added water in acetonitrile: ΔV* = −3.4 ± 3.7 and −8.0 ± 4.0 cm³ mol⁻¹ for [VO(salen)]⁺/[VO(salen)]⁰ and [VO(salen)OH₂]⁺/[VO(salen)]⁰ couples, respectively. It was suggested that previously reported chiral recognitions in the redox reactions involving [VO(Schiff-Base)]^+/0 redox couples take place within the encounter complex through the outer-sphere mechanism by maximizing the direct coupling between the dπ orbitals of V(IV) and V(V) species (Scheme 2).     

Platinum allenylidene complexes and formation of platinum and palladium acetonitrile alkynyl complexes

The platinum(0) complex [Pt(PPh₃)₄] reacts with brominated propargylic amides and esters in benzene by oxidative addition to give trans-[Br(PPh₃)₂Pt-CC-C(O)R] complexes whereas no reaction occurs when halogenated solvents (CH₂Cl₂, CHCl₃) are used. The cis-ligands PPh₃ can be replaced by P(ⁱPr)₃ and the bromide by trifluoroacetate. O-Alkylation of those trans-[X(PR′₃)₂Pt-CC-C(O)R] complexes (X = Br, CF₃COO; R′ = Ph, ⁱPr) derived from propargylic amides with MeOTf or [Me₃O]BF₄ in CH₂Cl₂ gives the first cationic monoallenylidene complexes of platinum, trans-[X(PR′₃)₂PtCCC(OMe)NR₂]⁺Y⁻ (Y = OTf, BF₄). In contrast, trans-[Br(PPh₃)₂Pt-CC-C(O)OMenthyl] derived from a propargylic ester does not react with MeOTf in CH₂Cl₂. However, in acetonitrile instead of O-methylation the substitution of acetonitrile for the bromide ligand to yield the cationic acetonitrile alkynyl platinum complex trans-[MeCN(PPh₃)₂Pt-CC-C(O)OMenthyl]⁺OTf⁻ is observed. The related palladium complexes trans-[X(PR′₃)₂Pd-CC-C(O)OR] (X = Br, CF₃COO; R′ = Ph, ⁱPr, R = menthyl, Et) react with MeOTf or [Et₃O]BF₄ analogously affording trans-[MeCN(PR′₃)₂Pd-CC-C(O)OR]⁺Y⁻ (Y = OTf, BF₄).     

H2O2 and (.)NO scavenging by Mycobacterium leprae truncated hemoglobin O

Kinetics of ferric Mycobacterium leprae truncated hemoglobin O (trHbOFe(III)) oxidation by H₂O₂ and of trHbOFe(IV)O reduction by NO and NO₂⁻ are reported. The value of the second-order rate constant for H₂O₂-mediated oxidation of trHbOFe(III) is 2.4 × 10³ M⁻¹ s⁻¹. The value of the second-order rate constant for NO-mediated reduction of trHbOFe(IV)O is 7.8 × 10⁶ M⁻¹ s⁻¹. The value of the first-order rate constant for trHbOFe(III)ONO decay to the resting form trHbOFe(III) is 2.1 × 10¹ s⁻¹. The value of the second-order rate constant for NO₂⁻-mediated reduction of trHbOFe(IV)O is 3.1 × 10³ M⁻¹ s⁻¹. As a whole, trHbOFe(IV)O, generated upon reaction with H₂O₂, catalyzes NO reduction to NO₂⁻. In turn, NO and NO₂⁻ act as antioxidants of trHbOFe(IV)O, which could be responsible for the oxidative damage of the mycobacterium. Therefore, Mycobacterium leprae trHbO could be involved in both H₂O₂ and NO scavenging, protecting from nitrosative and oxidative stress, and sustaining mycobacterial respiration.     

Reaction of hydrogen peroxide with hexaaquacobalt(III) perchlorate

The reaction of with H₂O₂ in 1.0 M HClO₄/LiClO₄ was found to be first-order in both reactants and the [H⁺] dependence of the second-order rate constant is given by k_2obs = b/[H⁺], b at 25 °C is 26.4 ± 0.5 s⁻¹. The rate law shows a simple inverse dependence on [H⁺] that is consistent with a rapidly maintained equilibrium between and its hydrolyzed form Co(H₂O)₅(OH)²⁺, followed by the rate controlling step, i.e. oxidation of H₂O₂ by Co(H₂O)₅(OH)²⁺.     

Diffusion NMR studies on neutral and cationic square planar palladium(II) complexes

Diffusion NMR investigations were carried out in CD₂Cl₂ for a series of neutral (1-7) and cationic (8-10) square planar palladium complexes. Diffusion data were elaborated through a modified Stokes-Einstein equation that takes into account the size and shape of molecules. The hydrodynamic volume at infinite dilution of all complexes was found to be similar to the crystallographic volume and always much larger than the van der Waals volume. The self-aggregation tendency of [Pd(N,C⁻)(N,N)][PF₆] ionic complexes [(N,C⁻) = (C₆H₄-(Ph)C(O)-CN-Et); 8, (N,N) = 2,2′-bipirydine; 9, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(Me)-C(Me)N(2,6-(iPr)₂-C₆H₃); 10, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(R′)-C(R′)N(2,6-(iPr)₂-C₆H₃), R′₂ = naphthalene-1,8-diyl] was investigated by performing ¹H and ¹⁹F diffusion experiments as a function of the concentration. Clear evidence for the formation of ion triples containing two cationic units was obtained for 8, most likely due to the establishment of a weak Pd?O interaction. The tendency to form ion triples was much reduced in 9 and 10, having an increased steric hindrance in the apical positions. While 9 showed the usual tendency to afford a mixture of free ions and ion pairs, solvated ions were the predominant species in the case of 10 even at high concentration values (approaching 100 mM).     

Reactivity of alkynyl Pd(II) azido complexes toward organic isocyanides, isothiocyanates, and nitriles

Alkynyl Pd(II) azido complexes of the type [Pd(N₃)(CCR)L₂] (1-3) were obtained by reactions of aqueous NaN₃ with [Pd(Cl)(CCR)L₂] (R = Ph or C(O)OMe). Treating compounds 1-3 with organic isocyanides (R-NC) afforded novel complexes, trans-[Pd(CCPh)(NCNR)(PMe₃)₂] (R = 2,6-Me₂C₆H₃ (4) or 2,6-Et₂C₆H₃ (5)) and trans-[Pd(CCR)(CN₄-t-Bu)L₂] (6: L = PMe₃, R = Ph; 7: L = PEt₃, R = C(O)OMe; 8: L = PMe₃, R = C(O)OMe), which contain either a carbodiimido or a C-coordinated tetrazolato group. Reactions of compounds 1 and 2 with R-NCS (R = 2,6-Me₂C₆H₃ or CH₂CH₃) and 1,4-phenylene diisothiocyanate (C₆H₄(NCS)₂) smoothly proceeded to give tetrazole-thiolato complexes, trans-[Pd(CCPh)(SCN₄-R)L₂] (L = PMe₃, R = Et (9) or 2,6-Me₂C₆H₃ (10); L = PEt₃, R = 2,6-Me₂C₆H₃ (11)), and a phenylene-bridged dinuclear Pd(II) tetrazole-thiolato complex, [(PEt₃)₂(CCPh)Pd(SCN₄-(μ-C₆H₄)-SCN₄)Pd(CCPh)(PEt₃)₂] (12), respectively. Complexes 9-12 contain the Pd-S bond that is formed by the dipolar cycloaddition of the organic isothiocyanate to the Pd-azido bond. In contrast, the corresponding reactions of compounds 1and 2 with C₆F₅CN and Me₃SiCN (organic nitriles, R-CN) gave an N-coordinated Pd(II)-tetrazolato compound {trans-[Pd(CCPh)(N₄C-C₆F₅)(PMe₃)₂] (13)} and a mixture of Pd(II)-cyano complexes {trans-[Pd(CCPh)(CN)(PEt₃)₂] (14) and [Pd(CN)₂(PEt₃)₂] (15)}, respectively. Bis(phosphine) bis(cyano) complexes of Pd and Ni, [M(CN)₂L₂] (L = PEt₃, PMe₃; L₂ = DEPE), could be obtained independently by the reactions of [M(N₃)₂L₂] with excess Me₃SiCN in organic solvents.     

NO, NO, NO! Nitrosyl siblings from [IrCl5(NO)]

Pentachloronitrosyliridate(III) ([IrCl₅(NO)]⁻), the most electrophilic NO⁺ known to date, can be reduced chemically and/or electrochemically by one or two electrons to produce the NO and HNO/NO⁻ forms. The nitroxyl complex can be formed either by hydride attack to the NO⁺ in organic solvent, or by decomposition of iridium-coordinated nitrosothiols in aqueous solutions, while NO is produced electrochemically or by reduction of [IrCl₅(NO)]⁻ with H₂O₂. Both NO and HNO/NO⁻ complexes are stable under certain conditions but tend to labilize the trans chloride and even the cis ones after long periods of time. As expected, the NO⁺ is practically linear, although the IrNO moiety is affected by the counterions due to dramatic changes in the solid state arrangement. The other two nitrosyl redox states comprise bent structures.     

Syn-anti and anti-anti conformations of a diimine derived from p-xylylenediamine and its neutral Co and Zn dinuclear complexes

A symmetric diimine ligand containing a CH₂PhCH₂ bridging group (H₂XyTs: N,N′-bis(2-tosylaminobenzylidene)-1,4-xylylenediamine) and its neutral Co^II and Zn^II dinuclear complexes have been prepared. Two different crystal structures of the free ligand, H₂XyTs, and that corresponding to [Co₂(XyTs)₂], have been solved by X-ray diffraction methods. These revealed two different conformations (syn-anti and anti-anti) for H₂XyTs and an infrequent rotational isomerism on the xylylene rings of its Co^II dinuclear complex, where both ligands are syn-anti conformed. Characterisation of the compounds is completed with FT-IR, ESI-MS and ¹H NMR spectroscopic techniques, when possible.     

Complexes of [Re(CO)3Cl] with different oxidation states of the polyfunctional bmtz/H2bmtz ligand system (bmtz=3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine)

Combining fac-[Re(CO)₃Cl] with components of the ligand redox system bmtz/bmtz⁻/H₂bmtz/H₂bmtz⁻ (bmtz=3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine) has led to the isolation of the complexes (H₂bmtz)Re(CO)₃Cl, (μ-H₂bmtz)[Re(CO)₃Cl]₂ and (μ-bmtz)[Re(CO)₃Cl]₂. Other species characterized were (bmtz)Re(CO)₃Cl (UV/Vis, IR), [(H₂bmtz)Re(CO)₃Cl]⁻ (UV/Vis, IR, EPR), {(μ-H₂bmtz)[Re(CO)₃Cl]₂}⁻ (UV/Vis, IR, EPR) and {(μ-bmtz)[Re(CO)₃Cl]₂}⁻ (UV/Vis, IR, X band and high-field EPR). The results confirm bmtz as very strong and H₂bmtz as moderate π acceptor ligand versus one or two chelate-bonded low-valent metal centers. Reactivity is observed in terms of oxidative proton and reductive chloride dissociation.     

Rigid-rod structured palladium complexes

Mononuclear and homobimetallic palladium complexes of structural type [trans-(Me(O)CS-4-C₆H₄)(Ph₃P)₂Pd(N^∩N)]OTf (8a, N^∩NC₄H₄N₂; 8b, N^∩NC₅H₄N-4-CN) and {[trans-(Me(O)CS-4-C₆H₄)(Ph₃P)₂Pd]₂N^∩N}(OTf)₂ (9a, N^∩N = 4,4′-bipyridine (=bipy); 9b, N^∩N = C₆H₄-1,4-(CN)₂; 9c, N^∩N = (C₆H₄-4-CN)₂) are accessible by the reaction of trans-(Ph₃P)₂Pd(C₆H₄-4-SC(O)Me)(OTf) (6) with 1 or 0.5 equivalents of the Lewis-bases N^∩N (7a, N^∩N = C₄H₄N₂; 7b, N^∩N = C₅H₄N-4-CN; 7c, N^∩N = bipy; 7d, N^∩N = C₆H₄-1,4-(CN)₂; 7e, N^∩N = (C₆H₄-4-CN)₂) in high yield. Complex 6 can be prepared in a two-step synthesis procedure. Oxidative addition of I-1-C₆H₄-4-SC(O)Me (2) to Pd(PPh₃)₄ (3) gives trans-(Ph₃P)₂Pd(C₆H₄-4-SC(O)Me)(I) (4), which further reacts with [AgOTf] (5) to afford 6.The formation of 8 and 9 strongly depends on the size of the Lewis-bases N^∩N. It is obvious that the co-ordination of the second N-ligated site of 8a or 8b to a further bulky[(PPh₃)₂Pd(C₆H₄-4-SC(O)Me)]⁺ unit is not possible. In contrast, more extended N^∩N species such as 7c-7e will result in the formation of linear structured homobimetallic 9a-9c.The solid-state structures of 4 and 4 · CH₂Cl₂ are reported. Complex 4 is packed in the orthorhombic space group Pbca. The assembly of dichloromethane into the crystal lattice breaks the symmetry, whereby 4 · CH₂Cl₂ crystallises in the triclinic space group . In both modifications a square-planar palladium(II) ion is present, with the iodo atom and the Me(O)CS-C₆H₄ unit trans-positioned. The different crystal packing has no significant influence onto the geometry around the d⁸-configurated palladium atoms.