Solution and solid state behavior of Co2+, Ni2+ and Zn2+ tosylaminoacidate systems: Crystal and molecular structure of bis(N-tosylglycinato)tetraaquocobalt(II) and bis(N-tosyl-β-alaninato)tetraaquozinc(II) complexes

The interactions between N-tosylamino acids and cobalt(II), nickel(II) and zinc(II) ions in aqueous solution and in the solid state have been investigated. From concentrated aqueous solutions, compounds of general formula [M(II)(N-tosylaminoacidato)₂(H₂O)₄](M = Co(II), Ni(II) and N-tosylaminoacidato = N-tosylglycinate (Tsgly^?), N-tosyl-α- and -β-alaninate (Ts-α- and Ts-β-ala^?); M = Zn(II) and N-tosylaminoacidate = Tsgly^?, Ts-β-ala^?) and [Zn(II)(N- tosylaminoacidato)₂(H₂O)₂] were isolated and characterized by means of thermogravimetric, electronic and infrared spectra. For two of them: [Co(Tsgly)₂(H₂O)₄](I) and [Zn(Ts-β-ala)₂(H₂O)₄](II) the crystal and molecular structures were also determined. Both compounds crystallize in the monoclinic space group P2₁/c, with two formula units in a cell of dimensions: a = 13.007(6), b = 5.036(2), c = 18.925(7) Å, β = 102.33(3)° for (I) and a = 14.173(6), b = 5.469(2), c = 17.701(7) Å, β = 106.63(3)° for (II). The structures were solved by the heavy-atom method and refined by least-squares calculations to R = 0.031 and 0.064 for (I) and (II) respectively. The cobalt and zinc atoms lie in the centers of symmetry, each bonded to two amino- acid molecules through a carboxylic oxygen atom and four water molecules in a slightly tetragonally distorted octahedral geometry. The second carboxylic oxygen atom is not involved in metal coordination. Electronic and X ray-powder spectra suggest that the tetrahydrate complexes of Co²⁺, Ni²⁺ and Zn²⁺ ions of the same amino acids are isomorphous and isostructural. No coordinative interactions between ligand and metal ions were found in aqueous solution on varying the pH values before hydroxide precipitation.     

Synthesis of palladium(II) 3d-metal(II) paddlewheel acetate-bridged heterodimetallic complexes: Unexpected catalysis by water molecules

A study of the reaction kinetics between the trinuclear palladium(II) acetate Pd₃(μ-OOCMe)₆ (1) and the mononuclear 3d-metal (Ni^II, Co^II, Cu^II) acetates in acetic acid under water-specified conditions revealed a fairly complicated reaction mechanism triggered by the primary hydrolytic cleavage of an acetate bridge in molecule 1. The isolated reaction products, as established by X-ray diffraction study, are 1D polymeric complexes {Pd(μ-OOCMe)₄M(OH₂)(HOOCMe)₂}_n (M = Ni^II, Co^II, Cu^II, Mn^II, Zn^II) built of the Pd^II-based paddlewheel units [Pd(μ-OOCMe)₄M] and linked trough the H-bonded H₂O and MeCOOH molecules.     

The kinetics of ligand substitution in bis(N-alkylsalicylaldiminato)nickel(II) Complexes: a study on the reactivity of square-planar versus octahedral coordination

The bis(N-alkylsalicylaldiminato)nickel(II) complexes Ni(R-sal)₂ with R = CH(CH₂OH)CH(OH)Ph (I), R = CH(CH₃)CH(OH)Ph (II) and R = CH₂CH₂Ph (III; Ph = phenyl) were prepared and characterized. In the solid state I and II are paramagnetic (μ = 3.2 and 3.3 BM at 20 °C, respectively), whereas III is diamagnetic. It follows from the UV-Vis spectra that in acetone solution I is six-coordinate octahedral and III is four-coordinate planar, the spectrum of II showing characteristics of both modes of coordination. Vis spectrophotometry and stopped-flow spectrophotometry were applied to study the kinetics of ligand substitution in I–III by H₂salen (= N,N′-disalicylidene-ethylenediamine) in the solvent acetone at different temperatures. The kinetics follow a second-order rate law, rate = k[H₂-salen] [complex]. At 20 °C the sequence of rate constants is k(III):k(II):k(I) = 11 850:40.6:1. The activation parameters are ΔH^≠(I) = 112, ΔH^≠(II) = 40.7, ΔH^≠(III) = 35.7 kJ mol⁻¹ and ΔS^≠(I) = 92, ΔS^≠(II) = −103, ΔS^≠(III) = −89 J K⁻¹ mol⁻¹. The enormous difference in rate between complexes I, II and III, which is less pronounced in methanol, is attributed to the existence of a fast equilibrium planar ⇌ octahedral, which is established in the case of I and II by intramolecular octahedral coordination through the hydroxyl groups present in the organic group R. An A-mechanism is suggested to control the substitution in the sense that the entering ligand attacks the four-coordinate planar complex, the octahedral complex being kinetically inert.     

Preparation,structure and properties of dicyano silver complexes of the M(en)3Ag2(CN)4 and M(en)2Ag2(CN)4 type

Complexes of the M(en)₃Ag₂(CN)₄ (M = Ni, Zn, Cd) and M(en)₂Ag₂(CN)₄ (M = Ni, Cu, Zn, Cd) type were prepared and identified by elemental analysis, infrared spectroscopy, measurement of magnetic susceptibility, and X-ray powder diffractometry. The crystal structures of Ni(en)₃Ag₂(CN)₄ (I) and Zn(en)₂Ag₂(CN)₄ (II) were determined by the method of monocrystal structure analysis. Complex I crystallizes in the space group C2/c, a = 1.2639(5), b = 1.3739(4), c = 1.2494(4) nm, β = 113.25(4)°, D_m = 1.86(1), D_c = 1.86 gcm⁻³ Z = 4, R = 0.0429. The crystal structure of I consists of complex cations [Ni(en)₃]²⁺ and complex anions [Ag(CN)₂]⁻. Complex II crystallizes in the space group I2/m, a = 0.9150(3), b = 1.3308(4), c = 0.6442(2) nm, β = 95.80(3)°, D_m = 2.14(1), D_c = 2.15 gcm⁻³, Z = 2, R = 0.0334. Its crystal structure consists of infinite, positively charged chains of the [-NCAgCNZn- (en)₂]_nⁿ⁺ type and isolated [Ag(CN)₂]⁻ anions. The atoms of Ag are positioned parallely to the z axis and the AgAg distance is equal to 0.3221(2) nm.     

Structure and electrochemistry of the bridging-ligand mono-substituted diruthenium compound, [Ru2(II,III)(O2CCH3)3(admpym)(Cl)(MeOH)] (Hadmpym=2-amino-4,6-dimethylpyrimidine)

The ligand substitution reaction of Ru₂(O₂CCH₃)₄Cl with 2-amino-4,6-dimethylpyrimidine (Hadmpym) under gentle refluxing conditions in methanol led to the formation of a bridging-ligand mono-substituted compound, [Ru₂(O₂CCH₃)₃(admpym)(Cl)(MeOH)] (1). Compound 1 crystallized in monoclinic space group P2₁/n (no. 14) with a=8.3074(8) Å, b=12.3722(8) Å, c=18.913(1) Å, β=95.559(3)°, V=1934.8(3) ų, and Z=4. Temperature dependence of the magnetic susceptibility of 1 revealed it to be in a spin ground state S=3/2 arising from the electronic configuration of σ²π⁴δ²(δ*π*)³. Compound 1 undergoes three metal-centered redox reactions in electrochemistry: E_1/2 ^(ox)=+0.72 V (I_a/I_c<1, ΔE_p=0.17 V); E_1/2 ^(1,red)=−0.65 V (I_a/I_c≈1, ΔE_p=0.10 V); and E_1/2 ^(2,red)=−1.80 V (I_a/I_c?1, ΔE_p=0.16 V). Then, the redox species produced by electrolysis were characterized by spectroscopic studies.     

The tungsten-tungsten triple bond. XV. Synthesis,structure and reactivity of 1,2-W2[CH(SiMe3)2]2(NMe2)4: the remarkable inertness of a sterically-encumbered tungsten-amido complex

Addition of 1,2-W₂Cl₂(NMe₂)₄(W≡W) to a toluene slurry of LiCH(SiMe₃)₂(2 equiv) results in the formation of 1,2-W₂[CH(SiMe₃)₂]₂(NMe₂)₄(W≡W) (I) in 79% isolated yield. Compound I has been characterized by ¹H and ¹³C NMR, IR, elemental analysis and single-crystal X-ray diffraction. The molecule exists exclusively in the gauche conformation in solution and in the solid state with WW = 2.320(1) Å. Compound I is very sterically encumbered as evidenced by: (1) large WWC angles, 110°, at the disyl ligand; (2) skewing of the NC₂ planes of the NMe₂ ligands off the WW vector; (3) anomalously large barriers to WNM₂ bond rotation in solution; (4) the inertness of I towards CO₂ and alcohols. However, compound I reacts with acetic anhydride to form 1,2-W₂[CH(SiMe₃)₂]₂(O₂CMe)₄(W≡W) (II) in 31% isolated yield. Compound II has been characterized by ¹H and ¹³C NMR, IR, and elemental analysis. The mechanistic implications of these studies with regard to alcoholysis and CO₂ insertion reactions of other 1,2-W₂R₂(NMe₂)₄ compounds are discussed. Crystal data for 1,2-W₂[CH(SiMe₃)₂]₂(NMe₂)₄ at −140°C: space group P2₁/n, a = 12.555(3), b = 18.699(5), c = 15.214(4) Å, β = 95.24(1)° and Z = 4.     

The crystal and molecular structures of dioxo mo(VI) complexes of tripodal,tetradentate N,S-donor ligands

The crystal and molecular structures of the complexes MoO₂((SCH₂CH₂)₂NCH₂CH₂SCH₃), I and MoO₂((SCH₂CH₂)₂NCH₂CH₂N(CH₃)₂), II, have been determined from X-ray intensity data collected by counter methods. Compound I crystallizes in two forms, Ia and Ib. In form Ia the space group is P2₁/n with cell parameters a = 7.235(2), b = 7.717(2), c = 24.527(6) Å, β = 119.86(2)°, V = 1188(1) ų, Z = 4. In form Ib the space group is P2₁/c with cell parameters a = 14.945(5), b = 11.925(5), c = 14.878(4) Å, β = 114.51(2)°, V = 2413(3) ų, Z = 8. The molecules of I in Ia and Ib are very similar having an octahedral structure with cis oxo groups, trans thiolates (cis to both oxo groups) and N and thioether sulfur atoms trans to oxo groups. Average ditances are MoO = 1.70, MoS (thiolate) = 2.40, MoN = 2.40 and MoS (thioether) = 2.79 Å. Molecule II crystallizes in space group P2₁2₁2₁ with a = 7.188(1), b = 22.708(8), c = 7.746(2) Å, V = 1246(1) ų and Z = 4. The coordination about Mo is octahedral with cis oxo groups, trans thiolates and N atoms trans to oxo. Distances in the first coordination sphere are MoO = 1.705(2), 1.699(2), MoS = 2.420(1), 2.409(1) and MoN = 2.372(2), 2.510(2) Å. The conformational features of the complexes are discussed. Complex I displays MoO and MoS distances which are very similar to those found by EXAFS in sulfite oxidase. This similarity is discussed.     

Chiral metal complexes. 29. A crystallographic study of the stereoselective hydrogenation of 1,2-dehydroproline coordinated to cobalt(III)

The crystal structure of the complex Λ-β₂-[Co(R,R-picchxn)(pro-2H)]Cl·ClO₄·H₂O (I) where R,R-picchxn is N,N′-bis(2-picolyl)-1R,2R-diaminocyclohexane and pro-2H is the 1,2-dehydroprolinate anion) has been determined. The complex crystallises in the orthorhombic space group P2₁2₁2₁, with a = 8.063(5),b = 15.320(9),c = 21.043(11)Å and Z and 4. The structure was refined by full-matrix least-squares methods to R = 0.049 for 2501 non-zero reflexions. The coordinated dehydroproline iminoacid is closely planar, and the structure suggest that the CN double bond would be equally accessible to a reacting species approaching from either side of the ring.The crystal structure of the two products obtained after hydrogenation of I,i.e. Λ-β₂-[Co(R,R-picchxn)(R-pro)](ClO₄)₂ (II) and Λ-β₂-[CoR,R-picchxn)(S-pro)](ClO₄)₂·H₂O (III), have also been determined by similar means. ComplexII is monoclinic, space group P2₁ with a = 9.385(3),b = 15.066(5),c = 1.4925(7)Å, β = 110.79°,Z = 2, and was refined to R = 0.029 for 2650 non-zero reflexions. Crystals of III are trigonal, space group P3₂21 with a = 11.417(2),c = 38.586(7)Å,Z = 6, and was refine to R = 0.039 for 2686 non-zero reflexions.The molecular geometry of the Co^III(R,R-picchxn) fragment is essentially the same in each structure. However, upon hydrogenation of I the iminoacid CN bond increases by 0.22Åin conjunction with the expected lack of planarity of the aminoacid pyrolidine and chelate rings. Short non-bonded H⋯H contacts that are produced in the hydrogenation productsII and III suggest thatIII would be the more sterically hindered. Comparisons are made between these structures and those of models computed for Λ-β₁-pro analogues.     

Studies on dithio-o-toluate copper(I) complexes with bis(diphenylphosphino)methane. Crystal structures of {di-μ3-dithio-o-toluato-S,S′,S′-bis[μ-bis(diphenylphosphino)methane-μ-dithio-o-toluato-S,S′]} tetracopper(I) and {di[μ-bis(diphenylphosphino)methane]bis(dithio-o-toluato-S,S′)} dicopper(I)

The structures of [(CuS₂CT)₂dppm]₂ (I) (T = o-tolyl; dppm = bis(diphenylphosphino)methane) and [CuS₂CTdppm]₂ (II) have been determined by X-ray methods. Crystals of I are monoclinic, space group P2₁/n, with a = 15.163(4), b = 18.691(5), c = 13.478(4) Å, β = 96.81(3)°, Z = 2; crystals of II are orthorhombic. space group Pccn, with a = 23.267(4), b = 13.016(3), c = 20.731(5) Å, Z = 4. The structures of I and II have been solved by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.082 for I and 0.092 for II. The structure of I consists of centrosymmetric tetranuclear complexes in which two pairs of Cu atoms are triply bridged by a dppm ligand and two dithiocarboxylate groups from the dithio-o-toluate ligands. These last behave differently: one of them through a sulphur atom is also bonded to a Cu atom of the other pair so forming a tetranuclear complex. The Cu atoms of each pair show different coordination: Cu(1) displays a distorted trigonal and Cu(2) a distorted trigonal pyramidal geometry. The structure of II consists of dimers, in which each copper atom, doubly bridged by two dppm ligands, completes a distorted trigonal pyramidal coordination through two sulphur atoms from dithio-o-toluate anions acting as chelating ligands. In both compounds the phenyl group of the dithio-o-toluate anions is orthogonal to the corresponding CS₂ group. Both complexes give methyldithio-o-toluate in high yields by reaction with methyl iodide.     

Metal—phenoxyalkanoic acid interactions. Part 14. The crystal and molecular structures of diaquabis(4-fluorophenoxyacetato)copper(II) bis(4-fluorophenoxyacetic acid)dihydrate and tetra-μ-(4-fluorophenoxyacetato-0,0′)-bis[(2-aminopyrimidine)copper(II)]

The crystal structures of two copper(II) complexes of 4-fluorophenoxyacetic acid (4-FPAH) have been determined by X-ray diffraction. [Cu(4-FPA)₂(H₂O)₂]·2(4-FPAH)·2H₂O (1) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 14.808(2), b = 9.832(2), c = 6.847(2) Å, α = 87.77(2), β = 98.41(2), γ = 112.33(2)° and was refined to a residual of 0.038 for 1697 ‘observed’ reflections. The coordination sphere in this complex is tetragonally distorted octahedral comprising two waters [CuO, 1.940(3) Å], two unidentate carboxylate oxygens [CuO, 1.942(2) Å] and two ether oxygens [CuO, 2.471(2) Å]. Two adducted [4-FPAH] acid molecules are linked to the un-coordinated oxygens of the acid ligands by hydrogen bonds [2.547(4) Å]. [Cu₂(4-FPA)₄(2-aminopyrimidine)₂] (2) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 12.688(2), b = 11.422(2), c = 7.951(1) Å, α = 78.74(1), β = 107.51(1), γ = 75.78(1)°, and was refined to a residual of 0.042 for 2683 ‘observed’ reflections. (2) is a centrosymmetric tetracarboxylate bridged dimer with four similar CuO (equatorial) distances [1.967–1.987 Å; 1.977(3) Å mean] and the axial position occupied by the hetero nitrogen of the 2-aminopyrimidine ligand [CuN, 2.176(3) Å]. The Cu---Cu separation is 2.710(1) Å. Crystal data are also presented which confirm the isostructurality of complex (2) with [Cu₂(phenoxyacetate)₄(2-aminopyrimidine)₂], the Co^II, Mg^II and Mn^II4-fluorophenoxyacetate complexes with their phenoxyacetic and 4-chlorophenoxyacetic acid analogues, and of Cd^II4-fluorophenoxyacetate with Cd^II and Zn^II phenoxyacetates.     

Three coordination modes of the pentadentate ligand 2,6-diacetylpyridinedisemicarbazone

The pentadentate ligand 2,6-diacetylpyridinedisemicarbazone, DAPSC, reacts with Cr(NO₃)₃·9H₂O and forms two kinds of complexes. At pH=3, the ligand is singly-deprotonated and crystals of [Cr- (DAPSCH)(H₂O)₂](NO₃)₂·H₂O (Ia) are obtained. Evaporation of a solution at pH=0, yields crystals of [Cr(DAPSC)(H₂O)₂](NO₃)₃·2H₂O (II) in which the ligand is fully protonated. The reaction of DAPSC with UO₂(O₂CCH₃)₂ in methanol, followed by crystallization of the product from DMSO yields crystals of [UO₂(DAPSC2H)(H₂O)]·2DMSO (III) in which the ligand is fully deprotonated. Compound Ia is monoclinic, space group P2₁/n with a=11.746(1), b=14.752(2), c=11.866(1) Å,β=105.53(2)°, V= 1981(1) ų and Z=4. Compound II is monoclinic, space group, P2₁/n with a=38.000(3), b= 14.939(2), c=8.233(1) Å, β=96.12(2)°, V= 4647(1) Å and Z=8. Compound III is monoclinic, space group P2₁/n with a=18.048(2), b=15.207(2), c=8.842(1) Å,β=97.72(2)°, V=2405(1) ų and Z=4. The structures were refined using 2084, 4169 and 2516 reflections to R values of 4.4%, 7.8% and 4.8% respectively.     

Interaction of metal ions with humic-like models. Part 6. Molecular structure,spectral and thermal properties of diaquabis(2,6-dimethoxybenzoato)dioxouranium(VI) monohydrate

The crystal and molecular structure of [UO₂(DMB)₂(H₂O)₂]·H₂O (DMB = 2,6-dimethoxybenzoate), complex I, has been detcrmined by X-ray diffraction and refined to a final R value of 0.0411. The compound belongs to the space group P2₁/a with cell constants a = 12.649(4), b = 14.418(5), c = 13.460(4) Å and Z = 4. As in the analogous complex [UO₂(DHB)₂(H₂O)₂]·8H₂O (DHB = 2,6- dihydroxybenzoate), compound II, the uranyl ion is bound to two bidentate carboxylate groups and two water molecules, but the point-symmetry is lower because the carboxylates, and the water molecules, are in vicinal positions. The lack of hydrogen- bonds between carboxylate groups and ortho-methoxy substituents and, possibly, steric factors account for the rotation of the phenyl rings with respect to the equatorial plane of the metal, the dihedral angle between the ‘best planes’ being about 77°. Detectable changes in the bond distances and angles within the carboxylate groups are produced by the non-planarity of the ligand. Spectroscopic and thermal properties of complexes I and II are also compared.     

Interaction of Pt(II) and Pd(II) complexes of terpyridine with 1-methylazoles: A combined experimental and density functional study

The synthesis and characterization of several complexes of the composition [{M(terpy)}_n(L)](ClO₄)_m (M = Pt, Pd; L = 1-methylimidazole, 1-methyltetrazole, 1-methyltetrazolate; terpy = 2,2′:6′,2″-terpyridine; n = 1, 2; m = 1, 2, 3) is reported and their applicability in terms of a metal-mediated base pair investigated. Reaction of [M(terpy)(H₂O)]²⁺ with 1-methylimidazole leads to [M(terpy)(1-methylimidazole)](ClO₄)₂ (1: M = Pt; 2: M = Pd). The analogous reaction of [Pt(terpy)(H₂O)]²⁺ with 1-methyltetrazole leads to the organometallic compound [Pt(terpy)(1-methyltetrazolate)]ClO₄ (3) in which the aromatic tetrazole proton has been substituted by the platinum moiety. For both platinum(II) and palladium(II), doubly metalated complexes [{M(terpy)}₂(1-methyltetrazolate)](ClO₄)₃ (4: M = Pt; 5: M = Pd) can also be obtained depending on the reaction conditions. In the latter two compounds, the [M(terpy)]²⁺ moieties are coordinated via C5 and N4. X-ray crystal structures of 1, 2, and 3 are reported. In addition, DFT calculations have been carried out to determine the energy difference between fully planar [Pd(mterpy)(L)]²⁺ complexes Ip-IVp (mterpy = 4′-methyl-2,2′:6′,2″-terpyridine; L = 1-methylimidazole-N3 (I), 1-methyl-1,2,4-triazole-N4 (II), 1-methyltetrazole-N3 (III), or 3-methylpyridine-N1 (IV)) and the respective geometry-optimized structures Io-IVo. Whereas this energy difference is larger than 70 kJ mol⁻¹ for compounds I, II, and IV, it amounts to only 0.8 kJ mol⁻¹ for the tetrazole-containing complex III, which is stabilized by two intramolecular C-H?N hydrogen bonds. Of all complexes under investigation, only the terpyridine-metal ion-tetrazole system with N3-coordinated tetrazole appears to be suited for an application in terms of a metal-mediated base pair in a metal-modified oligonucleotide.     

Synthesis, crystal structure, magnetic properties and electrochemical behaviour of the mixed valence compound [Cu(CN)3Cu(C3H10N2)2]

The binuclear mixed valence copper(I/II) compound [Cu^I(CN)₃Cu^II(tn)₂] (1) (tn = propane-1,3-diamine) and its acetonitrile adduct [Cu^I(CN)₃Cu^II(tn)₂] · 2MeCN (2) have been synthesized. Complex 1 crystallizes triclinic, space group , a = 8.117(2) Å, b = 8.389(2) Å, c = 11.920(2) Å, α = 108.728(3)°, β = 100.024(3)°, γ = 104.888(4)°, Z = 2, and compound 2 monoclinic, space group P2₁/m, a = 8.752(2) Å, b = 13.243(3) Å, c = 9.549(2) Å, β = 114.678(4)°, Z = 2. In both crystal structures, the binuclear [Cu^I(CN)₃Cu^II(tn)₂] complex with slightly different bonding geometries is formed. One of the three nitrogen atoms of a Cu^I(CN)₃ moiety is coordinated to Cu(II) at the apex of a square-pyramid with two chelating ligands tn on its base. The shortest intramolecular Cu^II?Cu^II distance in 1 is 5.640(7) Å. The EPR behaviour of 1 has been investigated at room temperature and at 77 K. The magnetic properties were measured in the temperature range 1.8-300 K.     

Synthesis,structure, reactivity and electrochemistry of a new molybdenum(0) dithiocarbamato complex, [Et4N][Mo(CO)4(S2CNEt2)]

A new molybdenum(0) dithiocarbamato complex [Et₄N] [Mo(CO)₄(S₂CNEt₂)] (1) has been synthesized by the reaction of Mo(CO)₆, NaS₂CNEt₂ and Et₄NCl in MeCN and characterized by routine elemental analysis, spectroscopy methods. The crystal and molecular structure of 1 was determined from X-ray three dimension data. 1 crystallizes in the orthorhombic, space group Pbc2₁ with a= 8.148(2), b=19.618(2), c=14.354(2) Å; V=2294 ų; Z=4; R₁=0.052, R₂=0.058 for 1308 independent reflections with I ⩾ 3σ(I). The geometry around Mo(0) atom in the anion [Mo(CO)₄(S₂CNEt₂)]^- of 1 is distorted octahedral with a small SMoS of 67.70° and a small angle of 3.6° between plane MoSS and MoC(1)C(2). Two groups of MoCO bond distances and the longer MoS bond distance observed in 1 are similar to that in the dinuclear Mo(0) complexes containing SR bridges but very different from those observed in the dithiocarbamato complexes of Mo in higher oxidation states. Different oxidizing products containing Mo in II-V oxidation states Mo(CO)₂(S₂CNEt₂)₂, MoO(S₂CNEt₂)₂, Mo₂O₃(S₂CNEt₂)₄ and Mo₂O₄(S₂CNEt₂)₂ were isolated from the oxidation of 1 with I₂ (or in the presence of traces of air). The electrochemical behavior of 1 in MeCN was investigated by cyclic voltammetry at Pt and C electrodes. The anodic peaks observed at 0.04, 0.14, 0.26 and 0.44 V versus SCE implied that 1 probably underwent oxidation in company with dissociation of dithiocarbamate and substitution of carbonyls resulting in several complexes of Mo in different oxidation states. The relationship between reactivity and structure is also discussed.     

3(5)-Pyrazolyl substituted triphenylphosphines as ligands for the palladium catalyzed Heck reaction

3(5)-Pyrazolyl substituted triphenylphosphines have been investigated as ligands for the palladium catalyzed Heck reaction of aryl halides with styrene. Catalysts formed in situ from those phosphines and Pd^II(OAc)₂ are comparable in activity and selectivity with the corresponding pre-synthesized Pd(II) complexes, while Pd₂(dba)₃ has turned out to be a less suitable palladium source. Among the ligands investigated, the bidentate P,N-ligand 2-[3(5)-pyrazolylphenyl]diphenylphosphine has shown the highest activities for the coupling of bromobenzene with styrene in the presence of Pd^II(OAc)₂. In the presence of 1 equiv. of nBu₄NI as the additive, unreactive 4-chloroacetophenone also undergoes Heck coupling with styrene.     

The phenomenon of conglomerate crystallization. XV. Spontaneous resolution in coordination compounds. XIII. The crystallization behaviour and the crystal and molecular structure of Δ(λδ)-cis-Rh(en)2(NO2)2]Cl

The title compound, I, crystallizes in the monoclinic space group P2₁ with cell constants: a = 6.599(3), b = 11.121(2), c = 8.375(1) Å and β = 106.35(2)°; V = 589.74 ų and D(calc; Z = 2) = 1.974 g cm⁻³. The compound is isomorphous and isostructural with its Co analogue. A total of 2982 data were collected over the range of 4°  20  70°; of these, 2537 (independent and with I ⩾ 3σ(I)) were used in the structural analysis. Data were corrected for absorption (μ = 16.6 cm⁻¹) and the relative transmission coefficients ranged from 1.000 to 0.9504. Refinement was carried out for both enantiomeric configurations and the crystal used was found to contain cations with Δ(λδ) absolute configuration. The final R(F) and R_w(F) residuals were, respectively 0.0220 and 0.0239 for (−−−; i.e.Δ(λδ)) and 0.0231 AND 0.0317 FOR (+++; i.e.Λ(δλ)). Thus, the former was selected as correct for our specimen.In the case of I, as well as in the Co derivative [cis-Co(en)₂(NO₂)₂]Cl (II), the conformation of one of the rings is opposite that expected for the lowest energy conformation, which in the current case should be Δ(λλ)).The RhN(NO)₂ distances are 2.020(2) and 2.010(2) Å, while the RhN(amine) distances, trans to the NO₂ ligands are 2.085(2) and 2.093(1) Å, values distinctly longer than the other two RhN distances (2.064(1) and 2.068(1) Å). The latter are the RhN distances to the terminalNH₂ ligands located trans to each other. Thus, we observe a trans effect, which is more pronounced in I than in II, and which is of comparable magnitude to that observed in the case of the trien derivative, [cis-α-Rh(trien)(NO₂)₂]Cl(III).Parallel with an increase in metalN distances in going from [cis-α-Co(trien)NO₂)₂]Cl·H₂) (IV) to (III) is an increase in the torsional angles of the outer rings (NCCN) of about 10°. Comparison of these parameters in I and II reveal that this change is not so marked for this pair since in I they are −54.9° and 52.8° while in II they are 50.2° and −48.1°; i.e. a change of only 4°. This important difference between trien and en derivatives is caused by the presence of the central five-membered ring, which for compounds III and IV remains largely unchanged, except for the metalN distances.The NO bond lengths are 1.244(3), 1.220)(2), 1.237(2) and 1.211(2) Å, which are similar to those found for the analogous Co isomer. The CN bond lengths are 1.492(3), 1.474(2), 1.486(2) and 1.475(2) Å, while the CC bonds are 1.509(3) and 1.524(3) Å. These values are also comparable with those obtained for the Co isomer and, in fact, the pattern of the bonds is nearly identical in both, including the common feature of having a longer CC bond for the en ring with the conformation opposite that expected.As was the case with the Co analogue, the Cl⁻ anion is associated with the hydrogens of the secondary nitrogen (trans to the −NO₂) ligands, the Cl…H7 distance being 2.18(3) Å and the <Cl…H7N2 = 163°.     

Influence of Pt and Pd coordination on the equilibrium of 2,2′-dipyridylketone (dpk) with its hydrated gem-diol form (dpk·H2O)

2,2′-Dipyridylketone (dpk), when acting as a chelating ligand for Pd^II or Pt^II, is in slow equilibrium with its corresponding gem-diol form (dpk·H₂O). In D₂O, equilibrium constants K = (dpk·H₂O)/(dpk) change from ca. 0.04 for the free ligand to ca. 3 in the corresponding complexes with cis-[Pt(H₂O)₂]²⁺. In solution, species of both ligands can be identified and differentiated by ¹H NMR spectroscopy, and in the trinuclear μ-OH bridged Pt^II complex [Pt₃(μ-OH)₃(dpk·H₂O)₂(dpk)](NO₃)₃·4.5H₂O (4), both types of ligands are present simultaneously in a ratio of (dpk·H₂O):(dpk) = 2. As demonstrated with a series of Pd^II complexes containing dpk·H₂O and dpk ligands, a straightforward differentiation is possible when DMSO-d₆ is used as solvent, because then also the OH protons of dpk·H₂O are observable. It is also shown that monocrystalline [PdCl₂(dpk·H₂O)] (1), when dissolved in DMSO-d₆, partially converts, with loss of H₂O, to [PdCl₂(dpk)].