Bis(amido)ruthenium(IV) Complexes with 2,3-Diamino-2,3-dimethylbutane. Crystal Structure and Reversible Ru(IV)-Amide/Ru(III)-Amine and Ru(IV)-Amide/Ru(II)- Amine Redox Couples in Aqueous Solution

Two bis(amido)ruthenium(IV) complexes, [Ru(IV)(bpy)(L-H)(2)](2+) and [Ru(IV)(L)(L-H)(2)](2+) (bpy = 2,2'-bipyridine, L = 2,3-diamino-2,3-dimethylbutane, L-H = (H(2)NCMe(2)CMe(2)NH)(-)), were prepared by chemical oxidation of [Ru(II)(bpy)(L)(2)](2+) and the reaction of [(n-Bu)(4)N][Ru(VI)NCl(4)] with L, respectively. The structures of [Ru(bpy)(L-H)(2)][ZnBr(4)].CH(3)CN and [Ru(L)(L-H)(2)]Cl(2).2H(2)O were determined by X-ray crystal analysis. [Ru(bpy)(L-H)(2)][ZnBr(4)].CH(3)CN crystallizes in the monoclinic space group P2(1)/n with a = 12.597(2) ?, b = 15.909(2) ?, c = 16.785(2) ?, beta = 91.74(1) degrees, and Z = 4. [Ru(L)(L-H)(2)]Cl(2).2H(2)O crystallizes in the tetragonal space group I4(1)/a with a = 31.892(6) ?, c = 10.819(3) ?, and Z = 16. In both complexes, the two Ru-N(amide) bonds are cis to each other with bond distances ranging from 1.835(7) to 1.856(7) ?. The N(amide)-Ru-N(amide) angles are about 110 degrees. The two Ru(IV) complexes are diamagnetic, and the chemical shifts of the amide protons occur at around 13 ppm. Both complexes display reversible metal-amide/metal-amine redox couples in aqueous solution with a pyrolytic graphite electrode. Depending on the pH of the media, reversible/quasireversible 1e(-)-2H(+) Ru(IV)-amide/Ru(III)-amine and 2e(-)-2H(+) Ru(IV)-amide/Ru(II)-amine redox couples have been observed. At pH = 1.0, the E degrees is 0.46 V for [Ru(IV)(bpy)(L-H)(2)](2+)/[Ru(III)(bpy)(L)(2)](3+) and 0.29 V vs SCE for [Ru(IV)(L)(L-H)(2)](2+)/[Ru(III)(L)(3)](3+). The difference in the E degrees values for the two Ru(IV)-amide complexes has been attributed to the fact that the chelating saturated diamine ligand is a better sigma-donor than 2,2'-bipyridine.     

From one-dimensional chain to pentanuclear molecule. Magnetism of cyano-bridged Fe(III)-Ni(II) complexes

Two cyano-bridged Ni(II)-Fe(III) complexes [(H(3)O)[Ni(H(2)L)](2)[Fe(CN)(6)](2).[Fe(CN)(6)].6H(2)O](n) (1) and [K(18-C-6)(H(2)O)(2)][Ni(H(2)L)](2)[Fe(CN)(6)](3).4(18-C-6).20H(2)O (2) (L = 3,10-bis(2-aminoethyl)-1,3,6,8,10,12-hexaazacyclotetradecane, 18-C-6 = 18-crown-6-ether) have been synthesized and characterized structurally and magnetically. Complex 1 has a zigzag one-dimensional structure, in which two trans-CN(-) ligands of each [Fe(CN)(6)](3)(-) link two trans-[Ni(H(2)L)](4+) groups, and in turn, each trans-[Ni(H(2)L)](4+) links two [Fe(CN)(6)](3)(-) in a trans fashion. Complex 2 is composed of cyano-bridged pentanuclear molecules with moieties connected by the trans-CN(-) ligands of [Fe(CN)(6)](3)(-). Magnetic studies show the existence of ferromagnetic Ni(II)-Fe(III) interactions in both complexes. The intermetallic magnetic coupling constant of both complexes was analyzed by using an approximate model on the basis of the structural features.     

Synthesis, structures, and magnetic properties of the copper(II), cobalt(II), and manganese(II) complexes with 9-acridinecarboxylate and 4-quinolinecarboxylate ligands

To explore the relationships between the structures of ligands and their complexes, we have synthesized and characterized a series of metal complexes with two structurally related ligands, 9-acridinecarboxylic acid (HL(1)) and 4-quinolinecarboxylate acid (HL(2)), [Cu(2)(mu(2)-OMe)(2)(L(1))(2)(H(2)O)(0.69)](n) 1, [Cu(2)(L(1))(4)(CH(3)OH)(2)] 2, [Cu(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 3, [Mn(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 4, [Co(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 5, [Cu(L(2))(2)](n) 6, [Mn(L(2))(2)(H(2)O)](n) 7, and [Co(L(2))(2)(H(2)O)](n) 8. 1 is a three-dimensional (3D) polymer with an interpenetrating NbO type network showing one-dimensional (1D) channels, whereas 2 and 3 take bi- and trinuclear structures, respectively, because of the differences in basicity of the reaction systems in preparing the three complexes. 4 and 5 have trinuclear structures similar to that of 3. In 1-5, ligand L(1) performs different coordination modes with N,O-bridging in 1 and O,O'-bridging in 2-5, and the metal ions also show different coordination geometries: square planar in 1, square pyramidal in 2, and octahedral in 3-5. 6 has a two-dimensional structure containing (4,4) grids in which L(2) adopts the N,O-bridging mode and the Cu(II) center takes square planar geometry. 7 and 8 are isostructural complexes showing 1D chain structures, with L(2) adopting the O,O-bridging mode. In addition, the intermolecular O-H...N hydrogen bonds and pi-pi stacking interactions further extend the complexes (except 1 and 6), forming 3D structures. The magnetic properties of 2-7 have been investigated and discussed in detail.     

New structural forms in molecular metal phosphonates: novel tri- and hexanuclear zinc(II) cages containing phosphonate and pyrazole ligands

The reaction of ZnCl(2) with tert-butylphosphonic acid and 3,5-dimethylpyrazole in the presence of triethylamine as a hydrogen chloride scavenger affords a trinuclear molecular zinc phosphonate [Zn(3)Cl(2)(3,5-Me(2)Pz)(4)(t-BuPO(3))(2)]. The structure of this compound contains a planar trizinc assembly containing two bicapping mu(3) [t-BuPO(3)](2-) ligands and terminal pyrazole and chloride ligands. In contrast an analogous reaction of ZnCl(2) with phenylphosphonic acid and 3,5-dimethylpyrazole affords a hexanuclear zinc phosphonate [Zn(6)Cl(4)(3,5-Me(2)PzH)(8)(PhPO(3))(4)]. The six zinc centers are arranged in a chairlike conformation. The four phosphonates in this complex also act as bridging tripodal mu(3) [RPO(3)](2-) ligands.     

Cyclodiphosphazanes with hemilabile ponytails: synthesis, transition metal chemistry (Ru(II), Rh(I), Pd(II), Pt(II)), and crystal and molecular structures of mononuclear (Pd(II), Rh(I)) and bi- and tetranuclear rhodium(I) complexes

Cyclodiphosphazanes having hemilabile ponytails such as cis-[(t)()BuNP(OC(6)H(4)OMe-o)](2) (2), cis-[(t)()BuNP(OCH(2)CH(2)OMe)](2) (3), cis-[(t)BuNP(OCH(2)CH(2)SMe)](2) (4), and cis-[(t)BuNP(OCH(2)CH(2)NMe(2))](2) (5) were synthesized by reacting cis-[(t)()BuNPCl](2) (1) with corresponding nucleophiles. The reaction of 2 with [M(COD)Cl(2)] afforded cis-[MCl(2)(2)(2)] derivatives (M = Pd (6), Pt (7)), whereas, with [Pd(NCPh)(2)Cl(2)], trans-[MCl(2)(2)(2)] (8) was obtained. The reaction of 2 with [Pd(PEt(3))Cl(2)](2), [{Ru(eta(6)-p-cymene)Cl(2)](2), and [M(COD)Cl](2) (M = Rh, Ir) afforded mononuclear complexes of Pd(II) (9), Ru(II) (11), Rh(I) (12), and Ir(I) (13) irrespective of the stoichiometry of the reactants and the reaction condition. In the above complexes the cyclodiphosphazane acts as a monodentate ligand. The reaction of 2 with [PdCl(eta(3)-C(3)H(5))](2) afforded binuclear complex [(PdCl(eta(3)-C(3)H(5)))(2){((t)BuNP(OC(6)H(4)OMe-o))(2)-kappaP}] (10). The reaction of ligand 3 with [Rh(CO)(2)Cl](2) in 1:1 ratio in CH(3)CN under reflux condition afforded tetranuclear rhodium(I) metallamacrocycle (14), whereas the ligands 4 and 5 afforded bischelated binuclear complexes 15 and 16, respectively. The crystal structures of 8, 9, 12, 14, and 16 are reported.     

Syntheses, emission properties and intramolecular ligand exchange of zinc complexes with ligands belonging to the tmpa family

The zinc complexes [(L1)(2)Zn(MeOH)(2)](OTf)(2), [(L1)ZnCl(2)], [(L2)ZnCl(2)], [(L2)Zn(OTf)(H(2)O)]OTf and [(Me-bispic)ZnCl(2)] of the ligands N-[(2-pyridyl)methyl]-2,2'-dipyridylamine (L1), N-[bis(2-pyridyl)methyl]-2-pyridylamine (L2) and N-methyl-[bis(2-pyridyl)methyl]amine (Me-bispic) were synthesised and characterised. The first copper(I) complexes of the ligands L1 and L2 were also synthesised and structurally characterised. [(L1)ZnCl(2)] showed unexpected fluxional behaviour in solution and revealed an interesting intramolecular ligand exchange mechanism in the coordination sphere of the zinc ion. Furthermore, strong blue emission was observed under UV-light excitation.     

Nickel(II) and iron(II) triple helicates assembled from expanded quaterpyridines incorporating flexible linkages

In the present study the interaction of Fe(II) and Ni(II) with the related expanded quaterpyridines, 1,2-, 1,3- and 1,4-bis-(5'-methyl-[2,2']bipyridinyl-5-ylmethoxy)benzene ligands (4-6 respectively), incorporating flexible, bis-aryl/methylene ether linkages in the bridges between the dipyridyl domains, was shown to predominantly result in the assembly of [M(2)L(3)](4+) complexes; although with 4 and 6 there was also evidence for the (minor) formation of the corresponding [M(4)L(6)](8+) species. Overall, this result contrasts with the behaviour of the essentially rigid 'parent' quaterpyridine 1 for which only tetrahedral [M(4)L(6)](8+) cage species were observed when reacted with various Fe(II) salts. It also contrasts with that observed for 2 and 3 incorporating essentially rigid substituted phenylene and biphenylene bridges between the dipyridyl domains where reaction with Fe(II) and Ni(II) yielded both [M(2)L(3)](4+) and [M(4)L(6)](8+) complex types, but in this case it was the latter species that was assigned as the thermodynamically favoured product type. The X-ray structures of the triple helicate complexes [H(2)O?Ni(2)(4)(3)](PF(6))(4)·THF·2.2H(2)O, [Ni(2)(6)(3)](PF(6))(4)·1.95MeCN·1.2THF·1.8H(2)O, and the very unusual triple helicate PF(6)(-) inclusion complex, [(PF(6))?Ni(2)(5)(3)](PF(6))(3)·1.75MeCN·5.25THF·0.25H(2)O are reported.     

Reversible anion exchanges between the layered organic-inorganic hybridized architectures: syntheses and structures of manganese(II) and copper(II) complexes containing novel tripodal ligands

Six noninterpenetrating organic-inorganic hybridized coordination complexes, [Mn(3)(2)(H(2)O)(2)](ClO(4))(2).2 H(2)O (5), [Mn(3)(2)(H(2)O)(2)](NO(3))(2) (6), [Mn(3)(2)(N(3))(2)].2 H(2)O (7), [Cu(3)(2)(H(2)O)(2)](ClO(4))(2) (8), [Mn(4)(2)(H(2)O)(SO(4))].CH(3)OH.5 H(2)O (9) and [Mn(4)(2)](ClO(4))(2) (10) were obtained through self-assembly of novel tripodal ligands, 1,3,5-tris(1-imidazolyl)benzene (3) and 1,3-bis(1-imidazolyl)-5-(imidazol-1-ylmethyl)benzene (4) with the corresponding metal salts, respectively. Their structures were determined by X-ray crystallography. The results of structural analysis of complexes 5, 6, 7, and 8 with rigid ligand 3 indicate that their structures are mainly dependant on the nature of the organic ligand and geometric need of the metal ions, but not influenced greatly by the anions and metal ions. While in complexes 9 and 10, which contain the flexible ligand 4, the counteranion plays an important role in the formation of the frameworks. Entirely different structures of complexes 5 and 10 indicate that the organic ligands greatly affect the structures of assemblies. Furthermore, in complexes 5 and 6, the counteranions located between the cationic layers can be exchanged by other anions. Reversible anion exchanges between complexes 5 and 6 without destruction of the frameworks demonstrate that 5 and 6 can act as cationic layered materials for anion exchange, as determined by IR spectroscopy, elemental analyses, and X-ray powder diffraction.     

Di- and trinuclear complexes derived from hexakis(2-pyridyloxy)cyclotriphosphazene. Unusual P-O bond cleavage in the formation of [{(L'CuCl)2(Co(NO3)}Cl] (L' = N3P3(OC5H4N)5(O))

Hexakis(2-pyridyloxy)cyclotriphosphazene (L) is an efficient multisite coordination ligand which binds with transition metal ions to produce dinuclear (homo- and heterometallic) complexes [L(CuCl)(CoCl3)], [L(CuCl)(ZnCl3)], [L(CoCl)(ZnCl3)], and [L(ZnCl2)2]. In these dinuclear derivatives the cyclophosphazene ligand utilizes from five to six nitrogen coordination sites out of the maximum of nine available sites. Further, the spacer oxygen that separates the pyridyl moiety from the cyclophosphazene ring ensures minimum steric strain to the cyclophosphazene ring upon coordination. This is reflected in the near planarity of the cyclophosphazene ring in all the dinuclear derivatives. In the dinuclear heterobimetallic derivatives one of the metal ions [Cu(II) or Co(II)] is hexacoordinate and is bound by the cyclophosphazene in a eta5-gem-N5 mode. The other metal ion in these heterobimetallic derivatives [Co(II) or Zn(II)] is tetracoordinate and is bound in an eta(1)-N(1) fashion. In the homobimetallic derivative, [L(ZnCl2)2], one of the zinc ions is five-coordinate (eta3-nongem-N3), while the other zinc ion is tetracoordinate(eta2-gem-N2). The reaction of L with CuCl2 followed by Co(NO3)2.6H2O yields a trinuclear heterobimetallic complex [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)]. In the formation of this compound an unusual P-O bond cleavage involving one of the phosphorus-pyridyloxy bonds is observed. The molecular structure of [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)] reveals that each of the two the P-O-cleaved L' ligands is involved in binding to Cu(II) to generate the motif L'CuCl. Two such units are bridged by a Co(II) ion. The coordination environment around the bridging Co(II) ion contains four oxygen (two P-O units, one chelating nitrate) and two nitrogen atoms (pyridyloxy nitrogens).     

Diastereospecific and diastereoselective syntheses of Ruthenium(II) complexes using N,N' bidentate ligands aryl-pyridin-2-ylmethyl-amine ArNH-CH2-2-C5H4N and their oxidation to imine ligands

Coordination of N,N' bidentate ligands aryl-pyridin-2-ylmethyl-amine ArNH-CH2-2-C5H4N 1 (Ar = 4-CH3-C6H4, 1a; 4-CH3O-C6H4, 1b; 2,6-(CH3)2-C6H3, 1c; 4-CF3-C6H4, 1d) to the moieties [Ru(bipy)2]2+, [Ru(eta5-C5H5)L]+ (L = CH3CN, CO), or [Ru(eta6-arene)Cl]2+ (arene = benzene, p-cymene) occurs under diastereoselective or diastereospecific conditions. Detailed stereochemical analysis of the new complexes is included. The coordination of these secondary amine ligands activates their oxidation to imines by molecular oxygen in a base-catalyzed reaction and hydrogen peroxide was detected as byproduct. The amine-to-imine oxidation was also observed under the experimental conditions of cyclic voltammetry measurements. Deprotonation of the coordinated amine ligands afforded isolatable amido complexes only for the ligand (1-methyl-1-pyridin-2-yl-ethyl)-p-tolyl-amine, 1e, which doesn't contain hydrogen atoms in a beta position relative to the N-H bond. The structures of [Ru(2,2'-bipyridine)2(1b)](PF6)2, 2b; [Ru(2,2'-bipyridine)(2)(1c)](PF6)2, 2c; trans-[RuCl2(COD)(1a)], 3; and [RuCl2(eta6-C6H6)(1a)]PF6, 4a, have been confirmed by X-ray diffraction studies.     

Structural Chemistry of Poly(ethylene glycol) Complexes of Lead(II) Nitrate and Lead(II) Bromide

The reaction of 1:1 stoichiometries (1:1.5 for the nitrate/tetraethylene glycol (EO4) and pentaethylene glycol (EO5) complexes) of PbX(2) (X = NO(3), Br) with five- to eight-donor poly(ethylene glycols) (PEGs) in 3:1 CH(3)CN/CH(3)OH (CH(3)CN only for the nitrate/EO5 complex) followed by solvent evaporation resulted in six crystalline materials upon which X-ray structural analyses were carried out: [Pb(NO(3))(2)(EO4)](n)(), [Pb(NO(3))(2)(EO5)], [Pb(NO(3))(2)(EO6)], [PbBr(EO5)(&mgr;-Br)PbBr(2)].H(2)O, [PbBr(NCMe)(EO6)](2)[PbBr(2)(EO6)][PbBr(3)](2), and [PbBr(EO7)][PbBr(3)]. The nitrates crystallize as tight ion pairs with the PEG ligands coordinating in an equatorial plane around the Pb(2+) ions. Because EO4 has only five oxygen donors, this complex exhibits steric unsaturation which is overcome by a monodentate interaction with a third nitrate anion that is also coordinated to a neighboring Pb(2+) ion. The six donors of EO5 coordinate in an equatorial plane resulting in a 10-coordinate complex with trans, twisted, bidentate nitrate anions. The seven-donor hexaethylene glycol (EO6) only uses six of its oxygen donors to coordinate Pb(2+). [Pb(NO(3))(2)(EO4)](n)() is monoclinic, P2(1)/c, with a = 7.902(3) ?, b = 22.136(6) ?, c = 8.910(2) ?, beta = 90.96(3) degrees, and Z = 4. [Pb(NO(3))(2)(EO5)] is triclinic P&onemacr;, with a = 9.332(3) ?, b = 10.025(3) ?, c = 11.688(4) ?, alpha = 68.41(3) degrees, beta = 68.39(3) degrees, gamma = 68.58(3) degrees, and Z = 2. [Pb(NO(3))(2)(EO6)] is monoclinic P2(1)/c, with a = 16.289(4) ?, b = 10.773(4) ?, c = 12.329(4) ?, beta = 106.77(2) degrees, and Z = 4. Lead(II) bromide complexes with PEGs tend to crystallize as PEG complexed cations with polymeric lead(II) bromide anions. In the EO5 complex, bromide anions in the polymer also coordinate to the PEG-wrapped Pb(2+) cations. The hexa- and heptaethylene glycol (EO6 and EO7, respectively) complexes contain discreet ions. In these halide complexes, EO7 is the only PEG to expand the Pb(2+) coordination number from eight to nine. [PbBr(EO5)(&mgr;-Br)PbBr(2)].H(2)O is triclinic P&onemacr;, with a = 7.922(6) ?,b = 15.802(9) ?, c = 19.001(9) ?, alpha = 73.19(8) degrees, beta = 88.91(9) degrees, gamma = 87.22(9) degrees, and Z = 4. [PbBr(NCMe)(EO6)](2)[PbBr(2)(EO6)][PbBr(3)](2) is monoclinic P2(1)/c, with a = 14.389(4) ?, b = 31.931(9) ?, c = 8.029(2) ?, beta = 97.76(3) degrees, and Z = 2. [PbBr(EO7)][PbBr(3)] is monoclinic Cc, with a = 13.165(3) ?, b = 24.732(5) ?, c = 8.007(1) ?, beta = 94.58(2) degrees, and Z = 4.     

Monoanionic {Mn(NO)}5 and dianionic {Mn(NO)}6 thiolatonitrosylmanganese complexes: [(NO)Mn(L)2]- and [(NO)Mn(L)2]2- (LH2 = 1,2-benzenedithiol and toluene-3,4-dithiol)

The reaction of MnBr(2) and [PPN](2)[S,S-C(6)H(3)-R] (1:2 molar ratio) in THF yielded [(THF)Mn(S,S-C(6)H(3)-R)(2)](-) [R = H (1a), Me (1b); THF = tetrahydrofuran]. Formation of the dimeric [Mn(S,S-C(6)H(3)-R)(2)](2)(2-) [R = H (2a), Me (2b)] was presumed to compensate for the electron-deficient Mn(III) core via two thiolate bridges upon dissolution of complexes 1a and 1b in CH(2)Cl(2). Complex 2a displays antiferromagnetic coupling interaction between two Mn(III) centers (J = -52 cm(-1)), with the effective magnetic moment (mu(eff)) increasing from 0.85 mu(B) at 2.0 K to 4.86 mu(B) at 300 K. The dianionic manganese(II) thiolate complexes [Mn(S,S-C(6)H(3)-R)(2)](2-) [R = H (3a), Me (3b)] were isolated upon the addition of [BH(4)](-) into complexes 1a and 1b or complexes 2a and 2b, respectively. The anionic mononuclear {Mn(NO)}(5) thiolatonitrosylmanganese complexes [(NO)Mn(S,S-C(6)H(3)-R)(2)](-) [R = H (4a), Me (4b)] were obtained from the reaction of NO(g) with the anionic complexes 1a and 1b, respectively, and the subsequent reduction of complexes 4a and 4b yielded the mononuclear {Mn(NO)}(6) [(NO)Mn(S,S-C(6)H(3)-R)(2)](2-) [R = H (5a), Me (5b)]. X-ray structural data, magnetic susceptibility measurement, and magnetic fitting results imply that the electronic structure of complex 4a is best described as a resonance hybrid of [(L)(L)Mn(III)(NO(*))](-) and [(L)(L(*))Mn(III)(NO(-))](-) (L = 1,2-benzenedithiolate) electronic arrangements in a square-pyramidal ligand field. The lower IR v(NO) stretching frequency of complex 5a, compared to that of complex 4a (shifting from 1729 cm(-1) in 4a to 1651 cm(-1) in 5a), supports that one-electron reduction occurs in the {(L)(L(*))Mn(III)} core upon reduction of complex 4a.     

Tuning redox potentials of bis(imino)pyridine cobalt complexes: an experimental and theoretical study involving solvent and ligand effects

The structure and electrochemical properties of a series of bis(imino)pyridine Co(II) complexes (NNN)CoX(2) and [(NNN)(2)Co][PF(6)](2) (NNN = 2,6-bis[1-(4-R-phenylimino)ethyl]pyridine, with R = CN, CF(3), H, CH(3), OCH(3), N(CH(3))(2); NNN = 2,6-bis[1-(2,6-(iPr)(2)-phenylimino)ethyl]pyridine and X = Cl, Br) were studied using a combination of electrochemical and theoretical methods. Cyclic voltammetry measurements and DFT/B3LYP calculations suggest that in solution (NNN)CoCl(2) complexes exist in equilibrium with disproportionation products [(NNN)(2)Co](2+) [CoCl(4)](2-) with the position of the equilibrium heavily influenced by both the solvent polarity and the steric and electronic properties of the bis(imino)pyridine ligands. In strong polar solvents (e.g., CH(3)CN or H(2)O) or with electron donating substituents (R = OCH(3) or N(CH(3))(2)) the equilibrium is shifted and only oxidation of the charged products [(NNN)(2)Co](2+) and [CoCl(4)](2-) is observed. Conversely, in nonpolar organic solvents such as CH(2)Cl(2) or with electron withdrawing substituents (R = CN or CF(3)), disproportionation is suppressed and oxidation of the (NNN)CoCl(2) complexes leads to 18e(-) Co(III) complexes stabilized by coordination of a solvent moiety. In addition, the [(NNN)(2)Co][PF(6)](2) complexes exhibit reversible Co(II/III) oxidation potentials that are strongly dependent on the electron withdrawing/donating nature of the N-aryl substituents, spanning nearly 750 mV in acetonitrile. The resulting insight on the regulation of redox properties of a series of bis(imino)pyridine cobalt(II) complexes should be particularly valuable to tune suitable conditions for reactivity.     

Variation of heterometallic structural motifs based on [W(CN)8]3- anions and Mn(II) ions as a function of synthetic conditions

Reactions of [W(CN)(8)](3-/4-) anions with complexes of Mn(2+) ion with tridentate organic ligand 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) lead to a series of heterobimetallic complexes. The crystal structures of these compounds are derived from the same basic structural fragment, namely a W(2)Mn(2) square constructed of alternating cyanide-bridged W and Mn ions. In [Mn(II)(tptz)(OAc)(H(2)O)(2)](2){[Mn(II)(tptz)(MeOH)(1.58)(H(2)O)(0.42)](2)[W(V)(CN)(8)](2)}.5 MeOH.9.85 H(2)O (3), isolated molecular squares are co-crystallized with mononuclear cationic Mn(II) complexes. The structure of {[Mn(II)(tptz)(MeOH)](2)[W(IV)(CN)(8)].2 MeOH}(infinity) (4) is based on an infinite chain of vertex-sharing squares, while {[Mn(II) (2)(tptz)(2)(MeOH)(3)(OAc)][W(V)(CN)(8)].3.5 MeOH0.25 H(2)O}(infinity) (5) and {[Mn(II) (2)(tptz)(2)(MeOH)(3)W(V)(CN)(8)][Mn(II)(tptz)(MeOH)W(V)(CN)(8)].2 H(2).OMeOH}(8) (7) are derived from such an infinite chain by removing one of the W-C[triple bond]N-Mn linkages in each of the squares. The decanuclear cluster [Mn(II) (6)(tptz)(6)(MeOH)(4)(DMF)(2)W(V) (4)(CN)(32)].8.2 H(2)O.2.3 MeOH (6) is a truncated version of structure 4 and consists of three vertex-sharing W(2)Mn(2) squares. The structure of [Mn(II)(tptz)(MeOH)(NO(3))](2)[Mn(II)(tptz)(MeOH) (DMF)](2)[W(V)(CN)(8)](2).6 MeOH (8) consists of a hexanuclear cluster, in which the central W(2)Mn(2) square is extended by two Mn side-arms attached via CN(-) ligands to the W corners of the square. The magnetic behavior of these heterobimetallic complexes (except for 4) is dominated by antiferromagnetic coupling between Mn(II) and W(V) ions mediated by cyanide bridges. Compounds 3, 6, and 8 exhibit high spin ground states of S=4, 13, and 9, respectively, while 5 and 7 exhibit behavior typical of a ferrimagnetic chain with alternating spin centers. Complex 4 contains diamagnetic W(IV) centers but holds promise as a potential photomagnetic solid.     

Self-assembly of polymer and sheet structures in palladium(II) complexes containing carboxylic acid substituents

A series of complexes trans-[PdCl(2)L(2)] has been prepared by the reaction of [PdCl(2)(PhCN)(2)] and/or Na(2)[PdCl(4)] with L = pyridine or quinoline ligands having one or two carboxylic acid groups. These complexes can form 1-D polymers through O-H.O hydrogen bonding between the carboxylic acid groups, as demonstrated by structure determinations of [PdCl(2)(NC(5)H(4)-4-COOH)(2)], [PdCl(2)(NC(5)H(4)-3-COOH)(2)], and [PdCl(2)(2-Ph-NC(9)H(5)-4-COOH)(2)]. In some cases, solvation breaks down the O-H.O hydrogen-bonded structures, as in the structures of [PdCl(2)(NC(5)H(4)-3-COOH)(2)].2DMSO and [PdCl(2)(2-Ph-NC(9)H(5)-4-COOH)(2)].4DMF, while pyridine-2-carboxylic acid underwent deprotonation to give the chelate complex [Pd(NC(5)H(4)-2-C(O)O)(2)]. The complexes trans-[PdCl(2)L(2)], L = pyridine-3,5-dicarboxylic acid or 2,6-dimethyl pyridine-3,5-dicarboxylic acid, self-assembled to give 2-D sheet structures, with hydrogen bonding between the carboxylic acid groups mediated by solvate methanol or water molecules. In the cationic complexes [PdL'(2)L(2)](2+) (L'(2) = Ph(2)PCH(2)PPh(2), Ph(2)P(CH(2))(3)PPh(2); L = pyridine carboxylic acid; anions X(-) = CF(3)SO(3)(-)), hydrogen bonding between the carboxylic acid groups and anions or solvate acetone molecules occurred, and only in one case was a polymeric complex formed by self-assembly.     

Metal complexes from 1,1'-di(pyrazinyl)ferrocene: coordination polymers and bridged diferrocenes

Ferrocene-based ligands 1,1'-di(pyrazinyl)ferrocene (L1) and 1,1'-di(2-pyrimidinyl)ferrocene (L2) were synthesized and copper and silver complexes were obtained from L1. Coordination polymers [{Cu(2)(PhCOO)(4)}(L1)](n) (1), [{Cu(2)(C(5)H(11)COO)(4)}(L1)](n) (2), and [{Cu(2)(OAc)(4)}(L1)](n).0.5n[Cu(2)(OAc)(4)(H(2)O)(2)].1.5nCH(3)CN (3) resulted from the reaction with the corresponding copper carboxylates. In all three complexes, L1 links the dinuclear copper carboxylate units to form one-dimensional step-like chains. In 2, these chains are further linked by [Cu(2)(OAc)(4)(H(2)O)(2)] dinuclear units via hydrogen bonding to form sheet structures. The reaction of L1 with copper(I) iodide resulted in a multinuclear complex [(CuI)(4)(L1)(2)].(L1) (4), which contains a [(CuI)(4)(L1)(2)] diferrocene unit with a step-like (CuI)(4) core. Reactions of L1 with silver(I) salts resulted in silver-bridged diferrocenes [Ag(2)(L1)(2)]X(2) (X = ClO(4) (5a, b), NO(3) (6a-c) and PF(6) (7)), some of which incorporate aromatic solvents into their crystal lattices. The intramolecular Ag...Ag separations in these metallamacrocycles (3.211-3.430 A) depended upon the counter-anions and on the coordination mode of the silver ions. In all of these coordination complexes, L1adopts a synperiplanar eclipsed conformation and acts as a bidentate ligand, with only the 5-nitrogen of each pyrazine ring involved in coordination.     

Synthesis, structure and reactivity of palladium(II) complexes of chiral N-heterocyclic carbene-imine and -amine hybrid ligands

The synthesis and structures of chiral N-heterocyclic carbene (NHC)-N-donor complexes of silver(I) and palladium(II) are reported. The X-ray structure of an NHC-imine silver(I) complex [((nPr)CN(CHPh))AgBr](2) exhibits an Ag(2)Br(2) dimer motif where the imine group is not coordinated to the silver atom. Reaction between 2 and [PdCl(2)(MeCN)(2)] gives the palladium(II) complex [(kappa(2)-(nPr)CN(CHPh))PdCl(2)](3) that contains a chelating NHC-imine ligand as shown by single-crystal X-ray diffraction. Slow hydrolysis of related complexes [(kappa(2)-(nPr)CN(CHPh))PdCl(2)](3) and [(kappa(2)-((Ph)(2)CH)CN(CHPh))PdCl(2)](4) using triethylammonium chloride and water lead to the precipitation of single crystals of insoluble NHC-amino palladium(II) complexes [(kappa(2)-(nPr)CN(H(2)))PdCl(2)](6) and [(kappa(2)-((Ph)(2)CH)CN(H(2)))PdCl(2)](7), respectively. In the solid state, complexes 6 and 7 both exhibit intermolecular hydrogen bonding between chlorine and an amino-hydrogen atom resulting in an infinite chain structure. Substitution of an amino hydrogen for an ethyl group gives the soluble complex [(kappa(2)-(iPr)CN((H)Et))PdCl(2)](12). Reaction between two equivalents of 2 and [PdCl(2)(MeCN)(2)] gives the di-NHC complex [(kappa(1)-(nPr)CN(CHPh))(2)PdCl(2)](5) that does not contain a coordinated imine as shown by single crystal X-ray diffraction. Conproportionation between 5 and an equivalent of [PdCl(2)(MeCN)(2)] to does not occur at temperatures up to 100 degrees C in CD(3)CN.     

Phenylphosphatrioxa-adamantanes: bulky, robust, electron-poor ligands that give very efficient rhodium(I) hydroformylation catalysts

The cage phosphines 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane (1a) and 1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6-phosphaadamantane (1b) have been made by the acid catalysed addition of PhPH(2) to the appropriate beta-diketones; the acid used (HCl, H(3)PO(4) or H(2)SO(4)) and its concentration affect the rate and selectivity of these condensation reactions. Phosphines 1a and 1b react with [PdCl(2)(NCPh)(2)] to form complexes trans-[PdCl(2)(1a)(2)](2a) and trans-[PdCl(2)(1b)(2)](2b) as mixtures of rac and meso diastereoisomers. The platinum(II) chemistry is more complicated and when 1a or 1b is added to [PtCl(2)(cod)], equilibrium mixtures of trans-[PtCl(2)L(2)] and [Pt(2)Cl(4)L(2)](L = or ) are formed in CH(2)Cl(2) solution. Meso/rac mixtures of trans-[MCl(CO)(1a)(2)] M = Ir (6a) or Rh (7a) are formed upon treatment of MCl(3).nH(2)O with an excess of 1a and the anionic cobalt complex [NHEt(3)][CoCl(3)(1a)](9) was isolated from the product formed by CoCl(2).6H(2)O and 1a. The nu(CO) values from the IR spectra of 6a and 7a suggest that 1a resembles a phosphonite in its bonding to Rh and Ir. Crystal structures of meso-2a, meso-2b, rac-6a and 9 are reported and in each case a small intracage C-P-C angle of ca. 94 degrees is observed; this may partly explain the bonding characteristics of ligands 1a and 1b. The cone angles for 1a and 1b are similar and large (ca. 200 degrees). Rhodium complexes of ligands 1a and 1b are hydroformylation catalysts with similarly high activity to catalysts derived from phosphites. The catalysts derived from 1a and 1b gave unusually low linear selectivity in the hydroformylation of hexenes. This feature has been further exploited in quaternary-selective hydroformylations of unsaturated esters; catalysts derived from 1a give better yields and regioselectivities than any previously reported catalyst.     

The synthesis and structure of heteroleptic tris(diimine)ruthenium(II) complexes

The reactions of bidentate diimine ligands (L2) with cationic bis(diimine)[Ru(L)(L1)(CO)Cl]+ complexes (L, L1, L2 are dissimilar diimine ligands), in the presence of trimethylamine-N-oxide (Me3NO) as a decarbonylation reagent, lead to the formation of heteroleptic tris(diimine) ruthenium(II) complexes, [Ru(L)(L1)(L2)]2+. Typically isolated as hexafluorophosphate or perchlorate salts, these complexes were characterised by UV-visible, infrared and mass spectroscopy, cyclic voltammetry, microanalyses and NMR spectroscopy. Single crystal X-ray studies have elucidated the structures of K[Ru(bpy)(phen)(4,4'-Me(2)bpy)](PF(6))(3).1/2H(2)O, [Ru(bpy)(5,6-Me(2)phen)(Hdpa)](ClO(4))(2), [Ru(bpy)(phen)(5,6-Me(2)phen)](ClO(4))(2), [Ru(bpy)(5,6'-Me(2)phen)(4,4'-Me(2)bpy)](PF(6))(2).EtOH, [Ru(4,4'-Me(2)bpy)(phen)(Hdpa)](PF(6))(2).MeOH and [Ru(bpy)(4,4'-Me(2)bpy)(Hdpa)](ClO(4))(2).1/2Hdpa (where Hdpa is di(2-pyridyl)amine). A novel feature of the first complex is the presence of a dinuclear anionic adduct, [K(2)(PF(6))(6)](4-), in which the two potassium centres are bridged by two fluorides from different hexafluorophosphate ions forming a K(2)F(2) bridging unit and by two KFPFK bridging moieties.     

Variable coordination of amine functionalised N-heterocyclic carbene ligands to Ru, Rh and Ir: C-H and N-H activation and catalytic transfer hydrogenation

Chelating amine and amido complexes of late transition metals are highly valuable bifunctional catalysts in organic synthesis, but complexes of bidentate amine-NHC and amido-NHC ligands are scarce. Hence, we report the reactions of a secondary-amine functionalised imidazolium salt 2a and a primary-amine functionalised imidazolium salt 2b with [(p-cymene)RuCl(2)](2) and [Cp*MCl(2)](2) (M = Rh, Ir). Treating 2a with [Cp*MCl(2)](2) and NaOAc gave the cyclometallated compounds Cp*M(C,C)I (M = Rh, 3; M = Ir, 4), resulting from aromatic C-H activation. In contrast, treating 2b with [(p-cymene)RuCl(2)](2), Ag(2)O and KI gave the amine-NHC complex [(p-cymene)Ru(C,NH(2))I]I (5). The reaction of 2b with [Cp*MCl(2)](2) (M = Rh, Ir), NaO(t)Bu and KI gave the amine-NHC complex [Cp*Rh(NH(2))I]I (6) or the amido-NHC complex Cp*Ir(C,NH)I (7); both protonation states of the Ir complex could be accessed: treating 7 with trifluoroacetic acid gave the amine-NHC complex [Cp*Ir(C,NH(2))I][CF(3)CO(2)] (8). These are the first primary amine- or amido-NHC complexes of Rh and Ir. Solid-state structures of the complexes 3-8 have been determined by single crystal X-ray diffraction. Complexes 5, 6 and 7 are pre-catalysts for the catalytic transfer hydrogenation of acetophenone to 1-phenylethanol, with ruthenium complex 5 demonstrating especially high reactivity.