Synthesis, characterization and X-ray structure of [Pd(SO4)(dppp)] · H2O, a catalyst for the CO-ethene copolymerization [dppp = 1,3-bis(diphenylphosphino)propane]

The title complex has been synthesized by first reacting dppp with Pd(AcO)₂ in acetone and then with NaHSO₄ in water. It has been characterized by IR, NMR and X-ray diffraction studies. The ³¹P NMR spectrum in DMSO shows a singlet at 16.62 ppm indicating that the two P atoms are equivalent and that the sulfate anion is weakly coordinating. The X-ray structure shows that the Pd atom is surrounded in an almost regular square planar environment by the two P atoms and by two O atoms of the sulfate anion and that the neutral complex is accompanied by a water molecule of crystallization. The Pd-P distances (2.217(1) and 2.233(1)) and the P-Pd-P angle (90.78(3)°) are close to those found in other complexes where the chelating diphosphine is the same. Also the Pd-O distances and the O-Pd-O bond angle are comparable to those of other relevant chelating ligands.In MeOH, the title complex, in combination with H₂SO₄, catalyses the CO-ethene copolymerization. The productivity reaches a maximum upon increasing the H₂SO₄/Pd ratio up to ca. 470 (7650 g of polyketone/g Pd h at 90 °C and 45 atm, CO/ethene 1/1). The viscosity of the polyketone passes through a maximum of 0.95 dL/g in m-cresol when the above ratio is ca. 100. It has been proposed that acid promotes the copolymerization process by destabilizing the β- and γ-chelates intermediates involved in chain growing process, thus favoring the insertion of the monomers. At relatively high acid concentration the lowering of productivity and viscosity suggests that the sulfate anion competes with the monomers for the coordination to the metal center.In H₂O-CH₃COOH as a solvent the productivity strongly depends on the H₂O/CH₃COOH ratio, as it passes through a maximum of 12 000 g polymer/g Pd h in the presence of ca. 60% of H₂O. The productivity is significantly lower than that found when the acetate and chloride analogues are used (27 000 g polyketone/g Pd · h). Thus, it is likely that the sulfate anion assists significantly the copolymerization process even though the concentration of CH₃COOH/CH₃COO⁻ is much preponderant.     

Synthesis and characterisation of palladium(II) and platinum(II) compounds containing pyrazole-derived ligands: crystal structure of [PdCl2(HL)] (HL = 3-phenyl-5-(2-pyridyl)pyrazole)

Reaction of the ligands 3-phenyl-5-(2-pyridyl)pyrazole (HL¹), 3,5-bis(2-pyridyl)pyrazole (HL²), 3-methyl-5-(2-pyridyl)pyrazole (HL³) and 3-methyl-5-phenylpyrazole (HL⁴) with [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) or [PdCl₂(cod)] gives complexes with stoichiometry [PdCl₂(HL)₂] (HL = HL¹, HL², HL³), [Pt(L)₂] (L = L¹, L², L³) and [MCl₂(HL⁴)₂] (M = Pd(II), Pt(II)). The new complexes were characterised by elemental analyses, conductivity measurements, infrared and ¹H NMR spectroscopies. The crystal and molecular structure of [PdCl₂(HL¹)] was resolved by X-ray diffraction, and consists of monomeric cis-[PdCl₂(HL¹)] molecules. The palladium centre has a typical square planar geometry, with a slight tetrahedral distortion. The tetra-coordinated metal atom is bonded to one pyridine nitrogen, one pyrazolic nitrogen and two chloro ligands in a cis disposition. The ligand HL¹ is not completely planar.     

The first pincer-aryl [M-(NCN)] complexes {M = Pd(II); Pt(II)} with chiral pyridine donors: Synthesis and catalytic activity in C-C bond formation

The first chiral bis(pyridine) N-C(H)-N pincer ligand, (5S,7S)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanquinolin-2-yl)benzene (HL) has been synthesized and characterized by a thorough ¹H NMR analysis. Reaction of HL with K₂[PtCl₄] in acetic acid gives [Pt(L)Cl] (1), where L acts as a tridentate N-C-N pincer ligand. The analogous palladium(II) derivatives [Pd(L)Cl] (2), and [Pd(L)(OAc)] (3), were first prepared through a transmetalation reaction between Pd(OAc)₂ and the organomercury compound [Hg(L)Cl] (4). The structures of compounds 1 (Pt) and 2 (Pd), as determined by X-ray diffraction, are reported and compared. Compound 2 can also be obtained from Na₂[PdCl₄] and HL in refluxing acetic acid, i.e., under the same conditions used for compound 1. Apparently, this is the first palladium pincer derivative of a 1,3-bis(pyridyl)benzene ligand synthesized by direct C-H activation.The neutral complexes 1-3 are catalysts of modest activity, but devoid of enantioselectivity in the Heck reaction between iodobenzene and methyl acrylate and in the aldol condensation of benzaldehyde with methyl isocyanoacetate.     

Coordination chemistry of the heterotopic 1,2-phenylenebis(thio)diacetic acid ligand: Rhodium(I), palladium(II) and nickel(II) complexes

Starting from the heterotopic multidentate ligand 1,2-phenylenebis(thio)diacetic acid (1), cis-rac-[PdCl₂{1,2-(HOOCCH₂S)₂C₆H₄-κ²S,S′}] (2), cis-rac-[Rh{1,2-(HOOCCH₂S)₂C₆H₄-κ²S,S′}(cod)]BF₄ (3) and cis-rac-[Ni{1,2-(OOCCH₂S)₂C₆H₄-κ⁴O,O′S,S′}{cis-(C₃H₄N₂)}₂] (4) were prepared and characterised by X-ray diffraction and conventional spectroscopic techniques. Compounds 1-4 show extensive hydrogen-bonded networks (XH?O, X = O, N) in the solid state.     

Reaction of [MCl2(CH3CN)2] (M = Pd(II), Pt(II)) compounds with N1-alkylpyridylpyrazole-derived ligands

Palladium(II) and platinum(II) complexes with N-alkylpyridylpyrazole-derived ligands, 2-(1-ethyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L¹) and 2-(1-octyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L²), cis-[MCl₂(L)] (M = Pd(II), Pt(II)), have been synthesised. Treatment of [PdCl₂(L)] (L = L¹, L²) with excess of ligand (L¹, L²), pyridine (py) or triphenylphosphine (PPh₃) in the presence of AgBF₄ and NaBPh₄ produced the following complexes: [Pd(L)₂](BPh₄)₂, [Pd(L)(py)₂](BPh₄)₂ and [Pd(L)(PPh₃)₂](BPh₄)₂. All complexes have been characterised by elemental analyses, conductivity, IR and NMR spectroscopies. The crystal structures of cis-[PdCl₂(L²)] (2) and cis-[PtCl₂(L¹)] (3) were determined by a single crystal X-ray diffraction method. In both complexes, the metal atom is coordinated by one pyrazole nitrogen, one pyridine nitrogen and two chlorine atoms in a distorted square-planar geometry. In complex 3, π-π stacking between pairs of molecules is observed.     

Concomitant polymorphism and conformational polymorphism in diiodobis[1,2-bis(diphenylphosphino)ethane]platinum(II)

The title organometallic compound crystallizes in two different polymorphic modifications. The conformational differences between the two crystalline modifications lead to differences in crystal packing and thus result in the formation of the two polymorphic forms. Both structures are stabilized by weak non-covalent interactions. The change in the phenyl ring rotation from one structure to the other results in the formation of two distinct network structures in the dimorphs.     

First microwave-assisted synthesis of an electron-rich phosphane and its coordination chemistry with platinum(II) and palladium(II)

The P-O ligand 3-(di(2-methoxyphenyl)phosphanyl)propionic acid (HL) was synthesized by a microwave-assisted reaction of a secondary phosphane. The coordination of HL to Pt^II yielded the neutral mononuclear complex trans-[PtCl(κ²-P,O-L)(κ-P-HL)] (1), while the reaction of PdClMe(η⁴-COD) (COD = 1,4-cyclooctadiene) with HL in the presence of NEt₃ gave the anionic Pd^II compound of the formula (HNEt₃)[PdClMe(κ²-P,O-L)] (2). Upon crystallization of the latter compound the neutral chloride-bridged dimetallic compound cis-[Pd(μ-Cl)Me(HL)]₂ (3) was obtained. HL, 1 and 3·CH₂Cl₂ have been characterized by single crystal X-ray structure analyses.     

Synthesis and crystal structures of trans-dichlorobis{tri(2-methylphenyl)stibine}palladium(II) and trans-dibromobis{tri(2-methylphenyl)stibine}palladium(II)

Tri(2-methylphenyl)stibine reacts with [PdX₂(cod)] or PdX₂ (X = Cl or Br) to give the trans-[PdX₂{Sb(2-Me- C₆H₄)₃}₂]. The single crystal X-ray structures of trans-[PdX₂{Sb(2-Me-C₆H₄)₃}₂] (X = Cl or Br) revealed that the palladium atom is a square planar environment with mutually trans-Sb(2-methylphenyl)₃ ligands. Iodine analogous of complex can also be prepared from trans metallation reaction with sodium iodine.     

Formation of structurally different solvated and non-solvated [Ni(PTSC)(PPh3)] (PTSC = salicylaldehyde-N-phenylthiosemicarbazide anion) crystals from single pot

New thiosemicarbazone nickel(II) complex, derived from salicylaldehyde-N-phenylthiosemicarbazone, was synthesized and characterized by means of IR, electronic, and mass spectral techniques. Its two different types of crystal structures were also characterized by single crystal X-ray diffraction technique and reported here. In type A, the complex crystallizes in the monoclinic space group P2₁/c with four molecules per cell and has the dimensions of a = 9.2066(7), b = 19.1090(13), c = 18.589(2) Å, β = 92.87 (1)°. In type B, the complex crystallizes in the triclinic space group with two molecules per cell and has the dimensions of a = 10.406(4), b = 10.876(4), c = 14.614(5) Å, α = 64.81(1), β = 74.07(2), γ = 70.85(2)°.     

Synthesis and structural characterization of adducts of silver(I) carboxylate salts AgX (X = CF3COO, CH3COO) with ER3 (E = P, As; R = Ph, cy, o-tolyl) and oligodentate aromatic bases derivative of 2,2′-bipyridyl, L, AgX:PR3:L (1:1:1)

Twenty-one adducts of the form AgX:ER₃:L (1:1:1) (X = CF₃COO (‘tfa’), CH₃COO (‘ac’), E = P, As; R = Ph, cy, o-tolyl; L = 2,2′-bipyridyl (‘bpy’)-based ligand) have been synthesized and characterized by analytical, spectroscopic (IR, far-IR, ¹H, ¹⁹F and ³¹P NMR) and single crystal X-ray diffraction studies. The resulting complexes are predominantly of the form [(R₃E)AgL]⁺X⁻, with a trigonal EAgN₂ coordination environment, the planarity of which may be perturbed by the approach of anion or solvent. The carboxylate anions have been found to be uni-, or semi-bidentate, or also completely ionic, as in the complexes [Ag(PPh₃)(bpy)(H₂O)](tfa) and [Ag(PPh₃)(dpk · H₂O)](tfa) (‘dpk · H₂O’ = bis(2-pyridyl)ketone (hydrated)). The complexes Agac:PPh₃:dpa (1:1:1) and Agac:P(o-tol)₃:dpa:MeCN (1:1:1:1) are dinuclear, with bridging unidentate acetate and terminal unidentate dpa (‘dpa’ = bis(2-pyridyl)amine).     

Preparation, crystal structures and spectroscopic properties of novel [MCl3 − n(P)3 + n] (M = Co, Rh; n = 0, 1, 2 or 3) series of complexes containing tripodal tridentate phosphine, 1,1,1-tris(dimethylphosphinomethyl)ethane

Cobalt(III) and rhodium(III) complexes of the series of [M^IIICl_3 − n(P)_3 + n]ⁿ⁺ (M = Co or Rh; n = 0, 1, 2 or 3) have been prepared with the use of 1,1,1-tris(dimethylphosphinomethyl)ethane (tdmme) and mono- or didentate phosphines. The single-crystal X-ray analyses of both series of complexes revealed that the M-P and M-Cl bond lengths were dependent primarily on the strong trans influence of the phosphines, and secondarily on the steric congestion around the metal center resulting from the coordination of several phosphine groups. In fact, the M-P(tdmme) bonds became longer in the order of [MCl₃(tdmme)] < [MCl₂(tdmme)(PMe₃)]⁺ < [MCl(tdmme)(dmpe)]²⁺ (dmpe = 1,2-bis(dimethylphosphino)ethane) < [M(tdmme)₂]³⁺ for both Co^III and Rh^III series of complexes, while the M-Cl bond lengths were shortened in this order (except for [M(tdmme)₂]³⁺). Such a steric congestion around the metal center can also account for the structural and spectroscopic characteristics of the series of complexes, [MCl(tdmme)(dmpm, dmpe or dmpp)]²⁺ (dmpm = bis(dimethylphosphino)methane, dmpp = 1,3-bis(dimethylphosphino)propane). The X-ray analysis for [CoCl(tdmme)(dmpm or dmpe)](BF₄)₂ showed that all Co-P bonds in the dmpm complex were shorter by 0.03-0.04 Å than those in the dmpe complex. Furthermore, the first d-d transition energy of the Co^III complexes and the ¹J_Rh-P(tdmme) coupling constants observed for the Rh^III complexes indicated an unusual order in the coordination bond strengths of the didentate diphosphines, i.e., dmpm > dmpe > dmpp.     

Preparation of an unusual fluoroalkyl phosphinoyl chelate complex, {k-P,C,P,k-O-(CF3)2PCH2C6H3CH2P(CF3)O}2Pt2

Electron poor cationic complexes [(^CF₃PCP)Pt(L)]⁺ (where L = CO, NC₅F₅, or acetone) react with H₂O in polar solvents via selective hydrolysis of a single P-CF₃ substituent to afford the spectroscopically-characterized phosphinoyl-bridged complex {k³-P,C,P,k¹-O-(CF₃)₂PCH₂C₆H₃CH₂P(CF₃)O}₂Pt₂ (1) in good yield. X-ray diffraction confirms the presence of a six-member Pt-P-O-Pt-P-O ring in a chair conformation. The presumed intermediate aqua complex, (^CF₃PCP)Pt(H₂O)⁺, is stable in dichloromethane, but when dissolved in more polar solvents readily converts to 1.     

Iron and cobalt complexes of 2,6-diacetylpyridine-bis(R-thiosemicarbazone) (R = H, phenyl) showing unprecedented ligand deviation from planarity

The syntheses, characterization, and single-crystal X-ray crystal structures are reported for four complexes of iron and cobalt with the pentadentate ligands, 2,6-diacetylpyridinebis(thiosemicarbazone) (H₂L¹) and 2,6-diacetylpyridinebis(phenylthiosemicarbazone) (H₂L²), including a cobalt dimer displaying a deviation from planarity which is unprecedented for this class of ligands and allows the ligand to occupy five positions of a pseudo-octahedral coordination sphere. This dimer reacts with KCN to produce a mononuclear complex of relevance to the active site of cobalt nitrile hydratase.     

Heterodimetallic Pd-based carboxylate-bridged complexes: Synthesis and structure of single-crystalline Pd-M (M = Mn, Co, Ni, Cu, Zn, Nd, Eu, Ce) acetates

A series of crystalline Pd^II-based heterodimetallic acetate-bridged complexes containing the transition (Mn^II, Co^II, Ni^II, Cu^II), post-transition (Zn^II) and rare-earth (Ce^IV, Nd^III, Eu^III) metals were synthesized starting from Pd₃(OOCMe)₆ and the complementary metal(II, III) acetates. The crystal and molecular structures of the binuclear Pd^IIM^II(μ-OOCMe)₄L (M = Mn, Co, Ni, Zn; L = H₂O, MeCN), trinuclear and tetranuclear (M = Nd, Eu) and complexes were established by X-ray diffraction.     

Synthesis, structures, and magnetic properties of one-dimensional Fe-M (M = Ni, Cu) coordination polymers bridged by nitroprusside

Self-assembling [Fe(CN)₅(NO)]²⁻ and [M(L)]²⁺ (M = Ni, Cu; L = macrocycles) led to one-dimensional coordination polymers, [Ni(L1)][Fe(CN)₅(NO)] · 2H₂O (1) with parallel chains and [Cu(L2)][Fe(CN)₅(NO)] · 3H₂O (2) exhibiting a slanted chain structure. Compound 1 contains a planar macrocycle L1 coordinated to a slightly distorted octahedral Ni(II) ion in which the planarity of L1 gives rise to piling up chains in parallel. In contrast, a more flexible macrocyclic ligand L2 in 2 that surrounds a Cu center with a tetragonal elongation has bulky cyclohexyl groups together with pendant methyl side groups. The presence of the methyl groups on L2 in a chain makes the cyclohexyl groups in an adjacent chain tilted against the CuN₄ basal plane with the methyl groups, eventually resulting in the slanted chain structure. Magnetic data demonstrate that antiferromagnetic interactions (J ≈ −0.13 cm⁻¹) are operating although the paramagnetic centers are linked by the long diamagnetic [Fe(CN)₅(NO)]²⁻ anion.     

Synthesis, structures and DNA binding of ternary transition metal complexes M(II)L with the 2,2-bipyridylamine (L = p-HB, M = Co, Ni, Cu and Zn)

New ternary transition metal complexes of formulations [Co(bpa)(p-HB)₂](bpa = 2,2′-bipyridylamine, p-HB = p-hydroxybenzenecarboxylic acid) (1), [Ni(bpa)(p-HB)(H₂O)₂]⁺(NO₃)⁻ · H₂O (2), , [Cu(bpa)(p-HB)Cl] (4) and [Zn(bpa)(p-HB)₂]₂ · 0.5H₂O (5) are prepared, their structural features are characterized by crystal structural studies, and their DNA binding propensity has been evaluated by fluorescence method. The molecular structure of complex 1 shows the six coordinate octahedral geometry with one bpa and two p-HB ligands, complex 2 is the cationic complex and has the six coordinate octahedral structure with one bpa, one p-HB and two aqua ligands, complex 3 is also the cationic complex of octahedral coordination with two bpa and one p-HB ligands, complex 4 is five coordinate distorted square pyramidal with one bpa, one p-HB and chloride ligands and complex 5 has the distorted octahedral coordination with two p-HB and one bpa ligands. In all of the complexes, both bpa and p-HB act as the bidentate N and O-donor ligands, respectively. The intermolecular H-bond networks, together with π-π interaction in their solid state are also described. The complexes show the competitive inhibition of ethidium binding to DNA, and the DNA binding propensity can be reflected as the relative order: 3 > 2 > 1 > 5 > 4, in which the cationic charged Ni(II) complexes 2 and 3 show the most effective inhibition ability.     

Presence of edge-to-face aromatic interaction in bis[1,2-bis(4-alkylphenyl)ethanedione dioximato]nickel(II) complexes and evaluation of the fastener effect

Bis[1,2-bis(4-methylphenyl)ethanedione dioximato]nickel(II), [Ni{(C₁)₂dpg}₂] (1), was found to exhibit shift in diffuse reflectance spectra from the corresponding non-methyl species. Characterization by X-ray crystal structural analysis on 1 and bis[1,2-bis(4-n-hexylphenyl)ethanedione dioximato]nickel(II), [Ni{(C₆)₂dpg}₂] (2), revealed the presence of the edge-to-face aromatic interactions caused by the electron-donating effect of the methyl and hexyl groups. The Ni(dpg)₂ units of complex 2 stack (staggered by 90°) at alternate intervals of 3.151 Å and 3.253 Å. Thus, the shift in the d-p transition of 2 was found to contain 43% of the effect of the edge-to-face aromatic interaction, together with 57% of the reported fastener effect.     

1-Methylisocytosine as a ligand for (dien)M (M = Pt, Pd) and Pt-promoted deamination to 1-methyluracil

1-Methylisocytosine (1-MeIC) can be protonated at the endocyclic N(3) position (pK_a of 1-MeICH⁺, 4.02 ± 0.04) or complexed at this position with (dien)M^II (M = Pt, Pd). X-ray crystal structures of the protonated species 1 as well as the Pd (2) and Pt (3) complexes are reported, and gas phase structures of the cation 2 and 3 have been calculated by ab initio methods. These results are compared with results from X-ray crystallography. At high pH, the Pt complex 3 undergoes deamination of the exocyclic N(2)H₂ group to the 1-methyluracilate complex. As compared to the situation with 1-methylcytosine (1-MeC), the accelerating effect of (dien)Pt^II is much less pronounced, however.     

Construction of crystal structures of metal(II)-benzoates (M = Mn, Ni, Co, Cu, Zn, and Cd) and 1,2-bis(4-pyridyl)ethane: Effects of metal coordination modes and their catalytic activities

Five polymeric metal(II)-benzoate complexes of formula [Mn(O₂CPh)₂(CH₃OH)₂(bpa)]_n (1-Mn), [Co(O₂CPh)₂(H₂O)(bpa)_1.5]_n (2-Co), [Ni(O₂CPh)₂(H₂O)(bpa)_1.5]_n (3-Ni), [Cu(O₂CPh)₂(CH₃OH)₂(bpa)]_n (4-Cu), and [Cd(O₂CPh)₂(bpa)_1.5]_n (6-Cd) have been synthesized and characterized (bpa = 1,2-bis(4-pyridyl)ethane). They showed two kinds of structures: parallelogram-like two-dimensional sheets for Co, Ni, and Cd, and one-dimensional chains for Mn, Cu, and Zn. Since similar structures provide similar coordination geometries, the structures depend on the coordination geometries of metal ions. The compounds 1-Mn, 2-Co, 4-Cu, 5-Zn, and 6-Cd have catalyzed efficiently the transesterification of a variety of esters, while 3-Ni has displayed a very slow conversion. The reactivity of catalyst 6-Cd containing Cd ion, well known as an inert metal ion for the ligand substitution, was found to be comparable to that of 5-Zn. The reactivities of the compounds used in this study are in the order of 5-Zn > 6-Cd > 1-Mn > 4-Cu > 2-Co ? 3-Ni, indicating that the non-redox metal-containing compounds (5-Zn and 6-Cd) show better activity than the redox-active metal-containing compounds (1-Mn, 4-Cu, 2-Co, and 3-Ni).     

Heterobimetallic Fe-Pd and Fe-Pt NCN pincer complexes (NCN = [C6H2(CH2NMe2)2-2,6])

The meta-diaminoaryl ferrocenes Fc-NCN-H (3) and Fc-CC-NCN-H (5) (Fc = (η⁵-C₅H₅)(η⁵-C₅H₄)Fe, NCN-H = C₆H₃(CH₂NMe₂)₂-3,5) can be used as precursors in the preparation of heterobimetallic transition metal complexes of structural type Fc-NCN-MX (NCN = [C₆H₂(CH₂NMe₂)₂-2,6]⁻; MX = PdCl (7), PtCl (8), PtI (9)) and Fc-CC-NCN-MX (MX = PdCl (11), PdI (12), PtCl (13)), respectively. They are accessible by applying different synthesis procedures, including oxidative addition and metallation-transmetallation processes.Cyclovoltammetric studies show that the ferrocene moieties in 3, 5, 7-9 and 11-13 can reversibly be oxidised. The potential of the Fe(II)/Fe(III) redox couple decreases with increasing electron density at the NCN pincer unit. The use of 8 as a possible (electro)chemical sensor in the detection of SO₂ is discussed as well.The solid-state structures of 8 and 13 are reported. The crystals of 8 contain two molecules of 8 in the asymmetric unit. The plane of the C₆H₂ moiety is with 27.2(3)° and 38.2(3)° tilted towards the C₅H₄ entity, while in 13 an angle of 45.9(3)° can be found. The d⁸-electron configured platinum atoms possess a somewhat distorted square-planar surrounding, setup by two Me₂NCH₂ortho-substituents, the NCN C_ipso carbon atom and the chloride ligand.