Providing support in favor of the existence of a Pd(II)/Pd(IV) catalytic cycle in a Heck-type reaction

The complex [Pd(O,N,C-L)(OAc)], in which L is a monoanionic pincer ligand derived from 2,6-diacetylpyridine, reacts with 2-iodobenzoic acid at room temperature to afford the very stable pair of Pd(IV) complexes (OC-6-54)- and (OC-6-26)-[Pd(O,N,C-L)(O,C-C(6)H(4)CO(2)-2)I] (1.5:1 molar ratio, at -55?°C). These complexes and the Pd(II) species [Pd(O,N,C-L)(OX)] and [Pd(O,N,C-L')(NCMe)]ClO(4), (X = MeC(O) or ClO(3), L' = another monoanionic pincer ligand derived from 2,6-diacetylpyridine), are precatalysts for the arylation of CH(2)=CHR (R = CO(2)Me, CO(2)Et, Ph) using IC(6)H(4)CO(2)H-2 and AgClO(4). These catalytic reactions have been studied and a tentative mechanism is proposed. The presence of two Pd(IV) complexes was detected by ESI(+)-MS during the catalytic process. All the data obtained strongly support a Pd(II)/Pd(IV) catalytic cycle.     

Reactivity of ammonia ligands of the antitumor agent cisplatin: a unique dodecanuclear Pt4,Pd4,Ag4 platform for four cytosine model nucleobases

The reaction of a potential mono(nucleobase) model adduct of cisplatin, cis-[Pt(NH(3))(2)(1-MeC-N3)(H(2)O)](2+) (6; 1-MeC: 1-methylcytosine), with the electrophile [Pd(en)(H(2)O)(2)](2+) (en: ethylenediamine) at pH approximately 6 yields a kinetic product X which is likely to be a dinuclear Pt,Pd complex containing 1-MeC(-)-N3,N4 and OH bridges, namely cis-[Pt(NH(3))(2)(1-MeC(-)-N3,N4)(OH)Pd(en)](2+). Upon addition of excess Ag(+) ions, conversion takes place to form a thermodynamic product, which, according to (1)H NMR spectroscopy and X-ray crystallography, is dominated by a mu-NH(2) bridge between the Pt(II) and Pd(II) centers. X-ray crystallography reveals that the compound crystallizes out of solution as a dodecanuclear complex containing four Pt(II), four Pd(II), and four Ag(+) entities: [{Pt(2)(1-MeC(-)-N3,N4)(2)(NH(3))(2)(NH(2))(2)(OH)Pd(2)(en)(2)Ag}(2){Ag(H(2)O)}(2)](NO(3))(10) 6 H(2)O (10) is composed of a roughly planar array of the 12 metal ions, in which the metal ions are interconnected by mu-NH(2) groups (between Pt and Pd centers), mu-OH groups (between pairs of Pt atoms), and metal-metal donor bonds (Pt-->Ag, Pd-->Ag). The four 1-methylcytosinato ligands, which are stacked pairwise, as well as the four NH(3) ligands and parts of the en rings, are approximately perpendicular to the metal plane. Two of the four Ag ions (Ag2, Ag2') of 10 are labile in solution and show the expected behavior of Ag(+) ions in water, that is, they are readily precipitated as AgCl by Cl(-) ions. The resulting pentanuclear complex [Pt(2)Pd(2)Ag(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(4)7 H(2)O (11) largely maintains the structural features of one half of 10. The other two Ag(+) ions (Ag1, Ag1') of 10 are remarkably unreactive toward excess NaCl. In fact, the pentanuclear complex [Pt(2)Pd(2)AgCl(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(3)4.5 H(2)O (12), obtained from 10 with excess NaCl, displays a Cl(-) anion bound to the Ag center (2.459(3) A) and is thus a rare case of a crystallized "AgCl molecule".     

Stepwise synthesis, structures, and reactivity of mono-, di-, and trimetallic metal complexes with a 6pi + 6pi quinonoid zwitterion

The benzoquinonemonoimine N,N'-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C(6)H(2)(NHCH(2)t-Bu)(2)(O)(2)] 6, which is a rare example of an organic zwitterion being more stable than its canonical form, is best described as constituted of two chemically connected but electronically not conjugated 6pi electron subunits. The two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of the pi-system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one N-H function, and the isolated sodium salt 9, which is stable under N(2), reacts with chloride-bridged Pd(II) homodimetallic complexes, [AuCl(PPh(3))] or trans-[NiCl(Ph)(PPh(3))(2)], to afford the monometallic complexes 10-15 in which the pi-system is localized. A second in situ deprotonation of the remaining N-H amino function of 10 with NaH followed by reaction with [Pd(8-mq)(mu-Cl)](2) (8-mq = orthometalated 8-methylquinoline) affords the homodimetallic complex 17 in which the pi-system of the quinonoid ligand is delocalized between the two metal centers. Deprotonation of both N-H amino functions of the square-planar complex trans-[Ni(N,O)(2)] 15 with NaH and reaction with [Pd(8-mq)(mu-Cl)](2) affords the heterotrimetallic (Pd, Ni, Pd) complex 18 in which the pi-system of the two quinonoid ligands is delocalized between the three metal centers. The crystal structures of the monometallic complexes 10 and 13 and of the dipalladium complex 17 are reported and consequences of metal coordination discussed. Complex 15 was tested in catalytic ethylene oligomerization with AlEtCl(2) as cocatalyst.     

Assembly of a heterobinuclear 2-D network: a rare example of endo- and exocyclic coordination of Pd(II)/Ag(I) in a single macrocycle

The S3O2 macrocycle L1 was synthesized by a dithiol-dihalide coupling reaction under high-dilution conditions. The reaction of L1 with K2PdCl4 afforded an exocoordinated complex 1, [cis-Cl2Pd(L1)], which can then be manipulated to provide a heterobinuclear complex 3, {[Pd(L1)Ag(NO3)(2.5)](NO3)(0.5)}n, utilizing endocyclic Pd(II) and exocyclic Ag(I) in a single macrocycle through a successive reaction with AgNO3. The network of 3 contains a unique honeycomb-like 2-D sheet made up of the repeating unit [Ag6(NO3)6].     

ELECTRON SPIN RESONANCE OR Pd(I). III: The Nature of the Metal-ligand Bonds in Square Planar Complexes of Palladium(I)

Abstract

ESR spectra for a variety of palladium(I) complexes produced in the powders and the frozen solutions of palladium(II) complexes by γ -ray irradiation have been interpreted in terms of the nature of the metal-ligand bonds. It has been found that the covalency for the palladium-ligand σ-bond increases in the order of Pd[sbnd]O, Pd[sbnd]Cl < Pd[sbnd]N < Pd[sbnd]S, Pd[sbnd]C, and that the nature of the metal-ligand bond in palladium(I) complexes is very similar to that in copper(II) complexes. The ratio of the magnitude of the ligand field splitting for palladium(I) complex to that for the copper(II) complex with the same ligand has been estimated from the comparison of their g values.     

Variable coordination behaviour of pyrazole-containing N,P and N,P(O) ligands towards palladium(II)

Three bidentate, mixed-donor ligands based on a triphenylphosphine unit bearing a pyrazole group in the ortho-position of one phenyl ring have been synthesised; the N,P ligand [2-(3-pyrazolyl)phenyl]diphenylphosphine pzphos has been synthesised and transformed into new N,P(O) and N,P(S) derivatives, [2-(3-pyrazolyl)phenyl]diphenylphosphine oxide pzphos(O) and [2-(3-pyrazolyl)phenyl]diphenylphosphine sulfide pzphos(S), respectively. The coordination chemistry of pzphos and pzphos(O) towards palladium(II) has been investigated. Depending on the ligand to metal molar ratio employed in the reactions of palladium(II) with pzphos, either the 1 : 1 chelate [Pd(pzphos)Cl2] 1a or the 2 : 1 N,P chelate [Pd(pzphos)2]Cl2 1b was obtained. 1b contains two six-membered chelate rings in which the chlorides have been displaced from the inner coordination sphere of palladium. Exchange of the chloride anions in 1b for perchlorate anions was achieved using AgClO4 to give [Pd(pzphos)2][ClO4]2 1c. Reaction of pzphos(O) under the same conditions forms the 2 : 1 adduct [Pd(pzphos(O))2Cl2] 2b regardless of the metal to ligand ratio or the order of addition of reactants. Unlike the N,P chelate 1b, the N,P(O) ligands in complex 2b bind in a monodentate fashion through the N-donor atoms of the pyrazole rings. Abstraction of the chloro ligands in compound 2b using AgClO4 gave the 2 : 1 N,P(O) chelate [Pd{pzphos(O)}2][ClO4]2 2c, in which entropically unfavourable 7-membered chelate rings are formed. X-Ray diffraction has been used to confirm the solid-state structures of the pzphos(O) ligand and the complexes 1b, 1c, 2b and 2c.     

Synthesis,Structure and Noncovalent Interactions Palladium（Ⅱ）Complexes with N—Benzoyl—β—phenylalaniate Dianion and Aromatic Diimine

Two palladium(II) complexes, [Pd(bipy)(BzPhe‐N,O)] and [Pd(phen)(BzPhe‐N,O)]·4H₂O were synthesized by reactions between Pd(bipy)Cl₂ and BzPheH₂ (N‐benzoyl‐β‐phenylalanine), Pd(phen) Cl₂ and BzPheH₂ in water at pH‐9, with their structures determined by X‐ray diffraction analysis. The Pd atom is coordinated by two nitrogen atoms of bipy (or phen), the deprotonated amido type nitrogen atom and one of the carboxylic oxygens of BzPhe (BzPhe = N‐benzoyl‐β‐phenylalaninate dianion). In the complex [Pd(phen) (BzFne‐N,O)] · 4H₂O, the side chain of phenylalanine is located above and approximately parallels to the coordination plane. Both the aromatic‐aromatic stacking interaction between the phenyl ring of phenylalanine and phen, and the metal ion‐aromatic interaction between the phenyl ring of phenylalanine and Pd(II) were observed. [Pd(bipy)(BzPhe‐N,O)] has the phenylalanyl side chain oriented outwards from the coordination plane, which is mainly due to the interaction between the carbonyl oxygen atom of the amido group and the phenyl ring of phenylalanine. The reason for the different orientation of phenylalanyl side chain in the complexes was suggested.     

Pd2Ag triangle supported by two micro3-amidopyridine ligands

[Pd(tmeda)(Hampy-N1)(H2O)]2+ (tmeda=N,N,N',N'-tetramethylethylenediamine; Hampy=2-aminopyridine) forms in the presence of Ag+ at pH 8-9 a triangular Pd2Ag complex containing two deprotonated ampy- ligands. It has been crystallized and structurally characterized with nitrate anions and a second co-crystallized AgNO3, [{Pd(ampy)(tmeda)}2Ag(micro-NO3)2Ag(NO3)2]. The two amidopyridine ligands are triply bridging, binding to Ag+ in a monodentate fashion viaN1, and to two PdII centres in a micro2-bridging fashion via the monodeprotonated N2 position. The resulting four-membered Pd(ampy)2Pd metallacycle is syn-planar with Pd[dot dot dot]Pd separations of 3.0878(13) A. The Pd...Ag distances are 3.0879(14) A in (isosceles triangle). In solution (D2O), the two ampy- ligand in are non-equivalent as concluded from a detailed 1H NMR spectroscopic study and confirmed by a 13C NMR spectrum. Removal of Ag+ from, as achieved by addition of Cl-, causes cluster degradation and linkage isomerization of PdII(tmeda) from the exocyclic N2 to the endocyclic N1 position.     

Theoretical investigation into the mechanism of reductive elimination from bimetallic palladium complexes

Reductive elimination of C-Cl and C-C bonds from binuclear organopalladium complexes containing Pd-Pd bonds with overall formal oxidation state +III are explored by density functional theory for dichloromethane and acetonitrile solvent environments. An X-ray crystallographically authenticated neutral complex, [(L-C,N)ClPd(μ-O(2)CMe)](2) (L = benzo[h]quinolinyl) (I), is examined for C-Cl coupling, and the proposed cation, [(L-C,N)PhPd(1)(μ-O(2)CMe)(2)Pd(2)(L-C,N)](+) (II), examined for C-C coupling together with (L-C,N)PhPd(1)(μ-O(2)CMe)(2)Pd(2)Cl(L-C,N) (III) as a neutral analogue of II. In both polar and nonpolar solvents, reaction from III via chloride dissociation from Pd(2) to form II is predicted to be favored. Cation II undergoes Ph-C coupling at Pd(1) with concomitant Pd(1)-Pd(2) lengthening and shortening of the Pd(1)-O bond trans to the carbon atom of L; natural bond orbital analysis indicates that reductive coupling from II involves depopulation of the d(x(2)-y(2)) orbital of Pd(1) and population of the d(z(2)) orbitals of Pd(1) and Pd(2) as the Pd-Pd bond lengthens. Calculations for the symmetrical dichloro complex I indicate that a similar dissociative pathway for C-Cl coupling is competitive with a direct (nondissociative) pathway in acetonitrile, but the direct pathway is favored in dichloromethane. In contrast to the dissociative mechanism, direct coupling for I involves population of the d(x(2)-y(2)) orbital of Pd(1) with Pd(1)-O(1) lengthening, significantly less population occurs for the d(z(2)) orbital of Pd(1) than for the dissociative pathway, and d(z(2)) at Pd(2) is only marginally populated resulting in an intermediate that is formally a Pd(1)(I)-Pd(2)(III) species, (L-Cl-N,Cl)Pd(1)(μ-O(2)CMe)Pd(2)Cl(O(2)CMe)(L-C,N) that releases chloride from Pd(2) with loss of Pd(I)-Pd(III) bonding to form a Pd(II) species. A similar process is formulated for the less competitive direct pathway for C-C coupling from III, in this case involving decreased population of the d(z(2)) orbital of Pd(2) and strengthening of the Pd(I)-Pd(III) interaction in the analogous intermediate with η(2)-coordination at Pd(1) by L-Ph-N, C(1)-C(2).     

X-ray structure characterization of palladium(II) ternary complexes of pyridinedicarboxylic and phthalic acid with phenanthroline and bipyridine

The crystal structures of the series of four ternary complexes, [Pd(phen)(2,6-PDCA)].4H(2)O (1) (phen=1,10-phenanthroline; 2,6-PDCA=2,6-pyridinedicarboxylic acid), [Pd(bpy)(2,3-PDCA)].3H(2)O (2) (bpy=2,2'-bipyridineand; 2,3-PDCA=2,3-pyridinedicarboxylic acid) and [Pd(phen)(PHT)].2.5H(2)O (3) (PHT=o-phthalic acid ) and [Pd(bpy)(PHT)].1.5H(2)O (4), are determined and the coordination modes of palladium(II) ternary complexes are characterized. All complexes take the mononuclear Pd(II) complexes, in which central Pd(II) atom of each complex has a similar distorted square-planar four coordination geometry. In all complexes, the aromatic heterocyclic compounds, phen and bpy, behave as a bidentate N, N' ligand. In the complex 1 and 2, 2,6-PDCA and 2,3-PDCA behave as a bidentate N, O ligand, and in complex 3 and 4, PHT behaves as a bidentate O, O' ligand.     

Photoinduced isomerisation of cis-[M(L-S,O)2](M = Pt(II) and Pd(II)) complexes of N,N-diethyl-N'-3,4,5-trimethoxybenzoylthiourea: key to preparation of the trans isomer

In acetonitrile solutions at room temperature, cis-[M(L-S,O)2] Pt(II) and Pd(II) complexes of N,N-diethyl-N'-3,4,5-trimethoxybenzoylthiourea undergo reversible photoinduced isomerisation to the corresponding trans isomer upon irradiation with visible light in the 320-570 nm range, the rate and extent of isomerisation being significantly higher for the cis-[Pd(L-S,O)2] complex compared to the Pt(II) analogue; in the dark trans-[M(L-S,O)2] cleanly reverts back to the cis complex at a rate dependent on the solution temperature, indicating a thermally controlled reverse process.     

Synthesis, characterization of Ag(I), Pd(II) and Pt(II) complexes of a triazine-3-thione and their interactions with bovine serum albumin

Ag(I), Pd(II) and Pt(II) complexes of 5-methoxy-5,6-diphenyl-4,5-dihydro-2H-[1,2,4]triazine-3-thione (LH(2)OCH(3)) have been synthesized and characterized by elemental analysis, molar conductance, (1)H NMR, IR spectra, UV spectra and thermal analysis (TG-DTA). The components of the three complexes are [Ag(C(15)H(10)N(3)S)](6), Pd(C(15)H(10)N(3)S)(2) and Pt(C(15)H(10)N(3)S)(2).C(3)H(6)O.2H(2)O, respectively. All the complexes are nonelectrolyte and have high thermodynamic stability. The ligand may act as bidentate NS donor for Pd(II) and Pt(II) complexes, while it seems to be bidentate NS bridging via sulphur atom for Ag(I) complex. A planar quadrangular structure is proposed for Pd(II) and Pt(II) complexes and Ag(I) complex may be a hexanuclear cluster. Their interactions with bovine serum albumin (BSA) are investigated using steady state fluorescence technology. It is observed that all of them can quench the intrinsic fluorescence of BSA through static quenching procedure. The binding constants (K(A)) at different temperatures, thermodynamic parameters enthalpy changes (DeltaH) and entropy changes (DeltaS) between BSA and the compounds are calculated. Based on the values of DeltaH and DeltaS, it is judged that the main acting force of PtL(2).C(3)H(6)O.2H(2)O with BSA may be electrostatic interaction, and for the LH(2)OCH(3), Ag(6)L(6) and PdL(2), hydrophobic and electrostatic interactions may be involved in their binding processes.     

Orthopalladation of iminophosphoranes: synthesis, structure and study of stability

The reaction of Pd(OAc)(2) with polyfunctional iminophosphoranes Ph(3)P=NCH(2)CO(2)Me (1a), Ph(3)P=NCH(2)C(O)NMe(2) (1b), Ph(3)P=NCH(2)CH(2)SMe (1c) and Ph(3)P=NCH(2)-2-NC(5)H(4) (1d), gives the orthopalladated dinuclear complex [Pd(mu-Cl){C(6)H(4)(PPh(2)=NCH(2)CO(2)Me-kappa-C,N)-2}](2) (2a) and the mononuclear derivatives [PdCl{C(6)H(4)(PPh(2)=NCH(2)CONMe(2)-kappa-C,N,O)-2}] (2b), [PdCl{C(6)H(4)(PPh(2)=NCH(2)CH(2)SMe-kappa-C,N,S)-2}] (2c) and [PdCl{C(6)H(4)(PPh(2)=NCH(2)-2-NC(5)H(4)-kappa-C,N,N)-2}] (2d). The reaction implies the activation of a C-H bond in a phenyl ring of the phosphonium group, this fact being worthy of note due to the strongly deactivating nature of the phosphonium unit. The palladacycle containing the metallated carbon atom is remarkably stable toward the coordination of incoming ligands, while that formed by the iminic N atom and another heteroatom (O, 2a and 2b; S, 2c; N, 2d) is less stable and the resulting complexes can be considered as hemilabile. The X-ray crystal structures of the cyclopalladated [Pd(mu-Cl){C(6)H(4)(PPh(2)=NCH(2)CO(2)Me-kappa-C,N)-2}](2) (2a), [PdCl{C(6)H(4)(PPh(2)=NCH(2)-2-NC(5)H(4)-kappa-C,N,N)-2}] (2d), [Pd{C(6)H(4)(PPh(2)=NCH(2)CONMe(2)-kappa-C,N,O)-2}(NCMe)](ClO(4)) (7b) and [Pd{C(6)H(4)(PPh(2)NCH(2)CONMe(2)-kappa-C,N,O)-2}(py)](ClO(4)) (3b), and the coordination compound cis-[Pd(Cl)(2)(Ph(3)P=NCH(2)CH(2)SMe-kappa-N,S)] (8) are also reported.     

Mixed-metal (platinum, palladium), mixed-pyrimidine (uracil, cytosine) self-assembling metallacalix[n]arenes: dynamic combinatorial chemistry with nucleobases and metal species

Reactions between the mononuclear mixed-nucleobase complex [Pt(en)(UH-N1)(CH2-N3)]+ (1; en: ethylenediamine; UH-N1: uracil monoanion bonded through the N1 atom; CH2-N3: neutral cytosine bonded through the N3 atom) and [Pd(II)(en)] or [Pd(II)(2,2'-bpy)] (2,2'-bpy: 2,2'-bipyridine) lead to libraries of compounds of different stoichiometries and different connectivities. In these compounds, the palladium entity binds to or cross-links either the N3 sites of uracil and/or the N1 sites of cytosine, following deprotonation of these positions to give uracil dianions (U) and cytosine monoanions (CH). Cyclic species, which can be considered as metallacalix[n]arenes, have been detected in several cases, with n being 4 and 8. The complexity of the compounds formed not only results from the possibility of the two different nucleobases in building block 1 engaging in different connectivities with the Pd entities, but also from the potential for the formation of oligomers of different sizes and different conformations; in the case of cyclic tetranuclear Pt(2)Pd(2) species, this can, in principle, lead to the various arrangements (cone, partial cone, 1,2-alternate, 1,3-alternate) known from calix[4]arene chemistry. A further complication arises from the fact that, depending on the mutual orientation of the exocyclic groups of the two nucleobases (O2 and O4 of uracil, O2 and N4 of cytosine), these sites can be engaged in additional chelation of [Pd(II)(en)] and [Pd(II)(2,2'-bpy)]. Thus, penta-, hexa-, and octanuclear complexes, Pt(2)Pd(3), Pt(2)Pd(4), and Pt(2)Pd(6), derived from cyclic Pt(2)Pd(2) tetramers have been isolated and characterized.     

Molecular and electronic structure of square planar complexes [PdII(tbpy)(L N,O IP)]0, [PdII(tbpy)(LN,O ISQ)](PF6), and [PdII(tbpy)(L N,O IBQ)](PF6)(BF4).2CH2Cl2: an o-iminophenolato based ligand centered, three-membered redox series

Three Pd(II) complexes which are members of the same electron-transfer series have been synthesized. Refluxing of the reaction mixture containing equimolar amounts of PdCl(2), 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol (H(2)L(N,O)), 4,4'-di-tert-butyl-2,2'-dipyridyl ((t)bpy), and 3 equiv of triethylamine in MeOH under an argon atmosphere followed by exposure to air and addition of KPF(6) after cooling to room temperature yields reddish brown crystals of paramagnetic (S = 1/2) [Pd(L(N,O)(ISQ))((t)bpy)](PF6) (2). Reaction of 2 with one equiv of [CoCp2] in dry and degassed CH(2)Cl(2) using anaerobic conditions gives diamagnetic [Pd(L(N,O)(IP))((t)bpy)] (1), which is the one-electron reduced form of 2. One-electron oxidation of 2 in CH(2)Cl(2) under argon with one equiv of NOBF4 affords diamagnetic [Pd(L(N,O)(IBQ))((t)bpy)](PF6)(BF4).2CH(2)Cl(2) (3). Complexes 1, 2, and 3 constitute three members of the same electron-transfer series. They are ideally suited to distinctly distinguish the geometrical and spectroscopic features of the N,O-coordinated, closed-shell, diamagnetic o-iminophenolate (L(N,O)(IP))2-, the corresponding open-shell pi-radical o-iminobenzosemiquinonate (L(N,O)(ISQ))1-.(S(rad) = 1/2), and the closed-shell o-iminobenzoquinone (L(N,O)(IBQ))0 forms. All complexes were characterized by X-ray crystallography (100 K), cyclic voltammetry, EPR, and UV-vis spectroscopy. Complex 2 exhibits three reversible electron transfer waves in the cyclic voltammogram. Structural characterization of complex 3 reveals an interesting strong ion pairing between the BF4 anion and the complex dication with a short C-F distance of 2.7 A.     

A Coordination Polymer of Nickel(II) Based on a Pentadentate N, S, and O Donor Ligand

The synthesis, structural characterization, and electrochemical properties of a Ni(II) complex derived from the template reaction of N,N'-bis(2-mercaptoethyl)-1,5-diazacyclooctane nickel(II), Ni-1, with ICH(2)CO(2)Na are described. Blue N-(3-thiabutyl)-N'-(3-thiapentanoate)-1,5-diazacyclooctanenickel(II)iodide, [(tbtp-daco)Ni][I], [5]I, contains Ni(II) in an octahedral environment with N(2)S(2)O(2) donor atoms; one oxygen is from an adjacent [(tbtp-daco)Ni] ion and has the same distance to Ni(II) as the intramolecular oxygen, resulting in a coordination polymer. Complex [5]I.H(2)O, C(13)H(27)N(2)O(3)S(2)NiI, crystallizes in the orthorhombic space group Pbca with a = 10.898(3), b = 18.103(5), c = 19.020(5), and Z = 8. The extent to which the polymer is retained in solution is counterion dependent, which influences redox properties (accessibility of Ni(I) and Ni(III)).     

The pressure tunning Raman and IR spectral studies on the multinuclear metal carbyne complexes

The Raman and infrared (IR) spectra of four tungsten metal carbyne complexes I, II, IV and V [Cl(CO)2(L)W[triple bond]CC6H4[triple bond](C[triple bond]CC6H4)n[triple bond]N[triple bond]C[triple bond]]2M (L = TMEDA, n = 0, M = PdI2 or ReCl(CO)3; L = DPPE, n = 1, M = PdI2 or ReCl(CO)3) were studied at high external pressure. Their pressure-induced phase transitions were observed near 20kbar (complexes I), 15 kbar (complexes II), 25 kbar (complex IV) and 30 kbar (complex V). The pressure-induced phase transition likely is first order in complex I and the pressure-induced phase transitions of complexes II, IV and V are mostly second order. The pressure sensitivities d nu/dp of nu(W[triple bond]C) are high in the low-pressure phase area and very low in the high-pressure phase area due to the pressure strengthening pi back-bonding from metal W to pi* orbital of C[triple bond]O in fragment Cl(CO)2(L)W[triple bond]C. The pressure strengthening metal pi back-bonding from metal Re or Pd to pi* orbital of C[triple bond]O or C[triple bond]N also happened to both of central metal centers of NCPd(I2)CN in complex I and NCReCl(CO)3CN in complex II.     

Different rotamer states of cytosine nucleobases in heteronuclear PtPd-, PtPd2, and Pt2Pd2Ag complexes derived from [Pt(2,2'-bpy)(1-MeC-N3)2]2+ (1-MeC = 1-methylcytosine): first examples of species with head-head oriented 1-MeC(-) ligands

[Pt(2,2'-bpy)(1-MeC-N3)(2)](NO(3))(2) (1) (2,2'-bpy = 2,2'-bipyridine; 1-MeC = 1-methylcytosine) exists in water in an equilibrium of head-tail and head-head rotamers, with the former exceeding the latter by a factor of ca. 20 at room temperature. Nevertheless, 1 reacts with (en)Pd(II) (en = ethylenediamine) to give preferentially the dinuclear complex [Pt(2,2'-bpy)(1-MeC(-)-N3,N4)(2)Pd(en)](NO(3))(2)·5H(2)O (2) with head-head arranged 1-methylctosinato (1-MeC(-)) ligands and Pd being coordinated to two exocyclic N4H(-) positions. Addition of AgNO(3) to a solution of 2 leads to formation of a pentanuclear chain compound [{Pt(2,2'-bpy)(1-MeC(-))(2)Pd(en)}(2)Ag](NO(3))(5)·14H(2)O (5) in which Ag(+) cross-links two cations of 2 via the four available O2 sites of the 1-MeC(-) ligands. 2 and 5 appear to be the first X-ray structurally characterized examples of di- and multinuclear complexes derived from a Pt(II) species with two cis-positioned cytosinato ligands adopting a head-head arrangement. (tmeda)Pd(II) (tmeda = N,N,N',N'-tetramethylethylenediamine) and (2,2'-bpy)Pd(II) behave differently toward 1 in that in their derivatives the head-tail orientation of the 1-MeC(-) nucleobases is retained. In [Pt(2,2'-bpy)(1-MeC(-))(2){Pd(2,2'-bpy)}(2)](NO(3))(4)·10H(2)O (4), both (2,2'-bpy)Pd(II) entities are pairwise bonded to N4H(-) and O2 sites of the two 1-MeC(-) rings, whereas in [Pt(2,2'-bpy)(1-MeC(-))(2){Pd(tmeda)}(2)(NO(3))](NO(3))(3)·5H(2)O (3) only one of the two (tmeda)Pd(II) units is chelated to N4H(-) and O2. The second (tmeda)Pd(II) is monofunctionally attached to a single N4H(-) site. On the basis of these established binding patterns, ways to the formation of mixed Pt/Pd complexes and possible intermediates are proposed. The methylene protons of the en ligand in 2 are special in that they display two multiplets separated by 0.64 ppm in the (1)H NMR spectrum.     

Cyclic trimer versus head-tail dimer in metal-nucleobase complexes: importance of relative orientation (syn, anti) of the metal entities and relevance as a metallaazacrown compound

The formation and crystal structure analysis of a cyclic trinuclear Pd complex with bridging 1-methylcytosinato model nucleobases is reported: [[(tmeda)Pd(1-MeC(-)-N3,N4)]3] (ClO4)3.5.5H2O (tmeda = N,N,N',N'-tetramethylethylenediamine; 1-MeC- = 1-methylcytosine deprotonated at exocyclic amino group) is obtained, among others, from the hydroxo-bridged dinuclear species [[(tmeda)Pd(OH)]2](ClO4)2, which likewise has been characterized by X-ray crystallography, and 1-MeC (1-MeC = neutral 1-methylcytosine) in aqueous solution. The usual head-tail dimer (HT1) appears not to be formed presumably because of the steric bulk of the tmeda ligand, which prevents a close approach of two tmeda ligands. There is also no evidence for formation of an alternative head-tail dimer structure (HT2) which, in principle, would not lead to any steric clash of ligands, but would require an orientation of the metal at N4 that is almost perpendicular to the nucleobase plane. In the Pd3 compound, the bridging metals are approximately in an anti arrangement, thereby leading to Pd...Pd separations within the Pd3 triangle close to 5.2 angstroms. This arrangement is reflected in the 1H NMR spectrum by a strongly deshielded H5 resonance of the nucleobase, occurring at 6.56 ppm (D2O). The overall structure of the Pd3 is that of a double cone, with ClO4- counterions approaching the cavities from either side. The trinuclear structure is also maintained in Me2SO-d6. In this solvent, Pd3 acts as a fluoride anion receptor, with F- binding to the N4H protons, as evident from large downfield shifts of these protons. The compound is compared with cyclic adeninato complexes of hexacoordinated metal ions, and a conceptional analogy with [12]metallacrown-3 species is outlined.     

Insertion reactions into Pd[bond]O and Pd[bond]N bonds: preparation of alkoxycarbonyl,carbonato, carbamato,thiocarbamate, and thioureide complexes of palladium(II)

Mononuclear palladium hydroxo complexes of the type [Pd(N[bond]N)(C(6)F(5))(OH)] [(N[bond]N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me(2)bipy), 1,10-phenanthroline (phen), or N,N,N',N'-tetramethylethylenediamine (tmeda)] have been prepared by reaction of [Pd(N[bond]N)(C(6)F(5))(acetone)]ClO(4) with KOH in methanol. These hydroxo complexes react, in methanol, with CO (1 atm, room temperature) to yield the corresponding methoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)Me)]. Similar alkoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)R)] (N[bond]N = bis(3,5-dimethylpyrazol-1-yl)methane); R = Me, Et, or (i)Pr) are obtained when [Pd(N[bond]N)(C(6)F(5))Cl] is treated with KOH in the corresponding alcohol ROH and CO is bubbled through the solution. The reactions of [Pd(N[bond]N)(C(6)F(5))(OH)] (N[bond]N = bipy or Me(2)bipy) with CO(2), in tetrahydrofuran, lead to the formation of the binuclear carbonate complexes [(N[bond]N)(C(6)F(5))Pd(mu-eta(2)-CO(3))Pd(C(6)F(5))(N[bond]N)]. Complexes [Pd(N[bond]N)(C(6)F(5))(OH)] react in alcohol with PhNCS to yield the corresponding N-phenyl-O-alkylthiocarbamate complexes [Pd(N[bond]N)(C(6)F(5))[SC(OR)NPh]]. Similarly, the reaction of [Pd(bipy)(C(6)F(5))(OH)] with PhNCO in methanol gives the N-phenyl-O-methylcarbamate complex [Pd(bipy)(C(6)F(5))[NPhC(O)OR]]. The reactions of [(N[bond]N)Pd(C(6)F(5))(OH)] with PhNCS in the presence of Et(2)NH yield the corresponding thioureidometal complexes [Pd(N[bond]N)(C(6)F(5))[NPhCSNR(2)]]. The crystal structures of [Pd(tmeda)(C(6)F(5))(CO(2)Me)], [Pd(2)(Me(2)bipy)(2)(C(6)F(5))(2)(mu-eta(2)-CO(3))].2CH(2)Cl(2), and [Pd(tmeda)(C(6)F(5))[SC(OMe)NPh]] have been determined.