Copolymerization studies of vinyl chloride and vinyl acetate with ethylene using a transition-metal catalyst

Since the advent of Ziegler-Natta polymerization of ethylene, attempts have been made to extend coordination polymerization to commercially important monomers with polar functionality. In this study we examined the copolymerization of perdeuterated vinyl chloride (VC) and perdeuterated vinyl acetate (VA) with ethylene using a tridentate Fe(II) dichloride pyridine diimine metal catalyst. The resulting ethylene oligomers were examined by GC/MS and 2H NMR spectroscopy. It was shown that VC was inserted once for every approximately 180 ethylene monomers and VA was inserted once for every approximately 350 ethylene monomers. VC and VA behave as comonomers for coordination/insertion polymerizations with ethylene. However, we find that insertion with either monomer leads to termination of the growing chain via beta-elimination processes. The deuterium atoms are exclusively located at the olefin terminus for each of the monomers.     

Synthesis and structures of nickel and palladium salicylaldiminato 1,3,5-triaza-7-phosphaadamantane (PTA) complexes

The synthesis of nickel(II) and palladium(II) salicylaldiminato complexes incorporating the water-soluble phosphine 1,3,5-triaza-7-phosphaadamantane(PTA) has been achieved employing two preparative routes. Reaction of the original ethylene polymerization catalyst developed by Grubbs and co-workers (Organometallics 1998, 17, 3149), (salicylaldiminato)Ni(Ph)PPh(3), with PTA using a homogeneous methanol/toluene solvent system resulted in the formation of the PTA analogues in good yields. Alternatively, complexes of this type may be synthesized via a direct approach utilizing (tmeda)M(CH(3))(2) (M = Ni, Pd), the corresponding salicylaldimine, and PTA. Yields by this method were generally near quantitative. The complexes were characterized in solution by (1)H/(13)C/(31)P NMR spectroscopy and in the solid-state by X-ray crystallography. All derivatives exhibited square-planar geometry with the bulky isopropyl groups on the aniline being perpendicular to the plane formed by the metal center and its four ligands. Such orientation of these sterically encumbering groups is responsible for polymer chain growth during olefin polymerization in favor of chain termination via beta-hydride elimination. Polymerization reactions were attempted using the nickel-PTA complexes in a biphasic toluene/water mixture in an effort to initiate ethylene polymerization by trapping the dissociated phosphine ligand in the water layer, thereby eliminating the need for a phosphine scavenger. Unfortunately, because of the strong binding ability of the small, donating phosphine(PTA) as compared to PPh(3), phosphine dissociation did not occur at a temperature where the complexes are thermally stable.     

Enhancement on Hemilabile Phosphine-Amide Palladium and Nickel Catalysts for Ethylene (Co)Polymerization with Polar Monomers Using a Cyclizing Strategy

To address the issue of hemilabile catalyst in olefin polymerization catalysis, a cyclizing strategy was used to construct novel N-bridged phosphine-carbonyl palladium and nickel catalysts, resulting in improvements on ethylene(co)polymerizations. The N-bridged phosphinecarbonyl Pd catalysts(Pd1-Pd5) and Ni catalysts(Ni1-Ni5) bearing five-to eight-membered-ring structures were designed and synthesized.Catalytic performance for ethylene(co)polymerization became better as the size of N-containing bridge increased. The seven-membered-ring bridged catalysts Pd4 and Ni4 exhibited the best performance in terms of catalytic activity, polymer molecular weight and incorporation of acrylates and acrylic acid. The better performance of these catalysts bearing larger-size bridges was tentatively attributed to the methyleneinduced higher electron density around nitrogen, which strenghtens the coordination of carbonyl group to metal center, and also to the steric effect offered by this cyclization. This work provides a new strategy to enhance hemilabile polymerization catalysts.     

Dinuclear nickel and palladium complexes with bridging 2,5-diamino-1,4-benzoquinonediimines: synthesis, structures, and catalytic oligomerization of ethylene

Dinuclear, divalent acetylacetonato (acac) complexes of the type [M(acac){mu-C6H2(--NR)4}M(acac)] (M = Ni, Pd) have been prepared by the reaction of the corresponding bis(acac) metal precursor with 2,5-diamino-1,4-benzoquinonediimines C6H2(NHR)2(=NR)2 (4a, R = CH2-t-Bu; 4b, R = CH2Ph; 4c, R = Ph), which are metalated and become bridging ligands, also like in the complex [(C8H11)Pt{mu-C6H2(--NCH2-t-Bu)4}Pt(C8H11)] (6) obtained by the reaction of 4a with [PtCl2(COD)]. The complexes were fully characterized, including by X-ray diffraction for [Ni(acac){mu-C6H2(--NCH2Ph)4}Ni(acac)] (9b) and [Pd(acac){mu-C6H2(--NCH2-t-Bu)4}Pd(acac)] (10a). The coordination geometry around the metal ions is square-planar, and a complete electronic delocalization of the quinonoid pi system occurs between the metal centers over the two N--C--C--C--N halves of the ligand. The nature of the N substituent explains the differences between the supramolecular stacking arrangements found for [Ni(acac){mu-C6H2(--NR)4}Ni(acac)] (9a; R = CH2-t-Bu; 9b, R = CH2Ph). The Ni complexes were evaluated as catalyst precursors for ethylene oligomerization in the presence of AlEtCl(2) or MAO as the cocatalyst, in particular in order to study possible cooperative effects resulting from electronic communication between the metal centers and to examine the influence of the N substituent on the activity and selectivity. These catalysts afforded mostly ethylene dimers and trimers.     

Reaction of vinyl chloride with late transition metal olefin polymerization catalysts

The reactions of vinyl chloride (VC) with representative late metal, single-site olefin dimerization and polymerization catalysts have been investigated. VC coordinates more weakly than ethylene or propylene to the simple catalyst (Me(2)bipy)PdMe(+) (Me(2)bipy = 4,4'-Me(2)-2,2'-bipyridine). Insertion rates of (Me(2)bipy)Pd(Me)(olefin)(+) species vary in the order VC > ethylene > propylene. The VC complexes (Me(2)bipy)Pd(Me)(VC)(+) and (alpha-diimine)Pd(Me)(VC)(+) (alpha-diimine = (2,6-(i)Pr(2)[bond]C(6)H(3))N[double bond]CMeCMe[double bond]N(2,6-(i)Pr(2)[bond]C(6)H(3))) undergo net 1,2 VC insertion and beta-Cl elimination to yield Pd[bond]Cl species and propylene. Analogous chemistry occurs for (pyridine-bisimine)MCl(2)/MAO catalysts (M = Fe, Co; pyridine-bisimine = 2,6-[(2,6-(i)Pr(2)[bond]C(6)H(3))N[double bond]CMe](2)-pyridine) and for neutral (sal)Ni(Ph)PPh(3) and (P[bond]O)Ni(Ph)PPh(3) catalysts (sal = 2-[C(H)[double bond]N(2,6-(i)Pr(2)-C(6)H(3))]-6-Ph-phenoxide; P[bond]O = [Ph(2)PC(SO(3)Na)[double bond]C(p-tol)O]), although the initial metal alkyl VC adducts were not detected in these cases. These results show that the L(n)MCH(2)CHClR species formed by VC insertion into the active species of late metal olefin polymerization catalysts undergo rapid beta-Cl elimination which precludes VC polymerization. Termination of chain growth by beta-Cl elimination is the most significant obstacle to metal-catalyzed insertion polymerization of VC.     

新型Ni催化剂催化乙烯聚合的中性机理

用密度泛函理论中的B3LYP LANL2MB方法 ,研究了Ni 水杨亚胺催化剂催化乙烯聚合的中性反应机理并和阳离子活性中心的催化反应机理进行了比较 .计算结果表明 ,整个中性催化机理类似于阳离子催化机理 ,但是也有不同 .两种机理都是从带空位的活性催化剂开始 ,乙烯以垂直于催化剂平面的方式占据空位 ,为了有利于甲基的迁移 ,乙烯向甲基的方向旋转 90° ,形成四元环过渡态 .插入反应发生后 ,Ni和 β C之间形成一种氢桥键 ,协助新空位的形成 ,实现链的增长 .乙烯与中性活性中心的相互作用远远强于乙烯与阳离子活性中心的相互作用 .中性催化机理较阳离子催化机理容易引发 .阳离子催化的过渡态所需的活化能比中性催化所需的活化能低 ,表明阳离子反应机理比中性反应机理容易进行 ,甲基在中性催化过渡态中的迁移明显不同于在酸性液化过渡态中的迁移 .β agostic相互作用在中性催化反应机理中 ,在主导烷基给合物中Ni所带的电荷方面 ,起着关键性的作用 .     

Synthesis,Characterization, and Reaction Studies of Pd(II) Tripeptide Complexes

The aqueous synthesis of Pd(II) complexes with alkylated tripeptides led to the hydrolysis of the peptides at low pH values and mixtures of complexed peptides were formed. A non-aqueous synthetic route allowed the formation and isolation of single products and their characterization. Pd(II) complexes with α-Asp(OR)AlaGly(OR), β-Asp(OR)AlaGly(OR), and TrpAlaGly(OR) (R = H or alkyl) as tri and tetradentate chelates were characterized. The tridentate coordination mode was accompanied by a fourth monodentate ligand that was shown to participate in both ligand exchange reactions and a direct removal to form the tetradentate coordination mode. The tetradentate coordination revealed a rare a hemi labile carbonyl goup coordination mode to Pd(II). Reactivity with small molecules such as ethylene, acids, formate, and episulfide was investigated. Under acidic conditions and in the presence of ethylene; acetaldehyde was formed. The Pd(II) is a soft Lewis acid and thiophilic and the complexes abstract sulfur from episulfide at apparent modest catalytic rates. The complexes adopt a square planar geometry according to a spectroscopic analysis and DFT calculations that were employed to evaluate the most energetically favorable coordination geometry and compared with the observed infrared and NMR data.     

Synthesis and characterization of Ni(II), Pd(II) and Pt(II) complexes of 2,4-diamino-5-(3, 4, 5-trimethoxybenzyl)pyrimidine complexes

The Ni(II), Pd(II) and Pt(II) complexes of 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine (trimethoprim) have been synthesized and characterized by elemental analysis, electronic and IR spectroscopy, and magnetic susceptibility measurements. The single-crystal X-ray structure of the Ni(II) complex is reported. Ni(II) is coordinated to the N(1) atoms of two trimethoprim molecules that act as monodentates. Octahedral coordination around the nickel atom is completed by coordination to two molecules of methanol and two acetate ions. Pd(II) and Pt(II) complexes are square planar and the metal ions coordinate one molecule of trimethoprim, two chloride ions and a molecule of water.     

Computational insights on the challenges for polymerizing polar monomers

Taking Pd di-imine catalysts as an example, we use first principles density functional theory (B3LYP/6-31G) to investigate the chain propagation steps for polymerization of polar monomers. We start with the complex formed from insertion of ethylene into the polymer chain and consider insertion into the Pd-C bond for each of four polar monomers: methyl acrylate, vinyl acetate, vinyl chloride, and acrylonitrile. We find 2,1-insertion is favored in each case (by 3 to 5 kcal/mol), resulting in a product with a strong interaction of the polar group for the growing polymer chain with the metal. Next, we insert another unit of the same polar monomer or an ethylene unit (except for acrylonitrile). We optimize the structures for all important intermediates and transition states using a continuum dielectric to account for solvation effects. These studies pinpoint the critical difficulties in designing catalysts to polymerize polar monomers.     

后过渡金属催化降冰片烯加成聚合

综述了后过渡金属催化剂催化降冰片烯加成聚合的研究进展。主要介绍了Ni、Pd、Co三种金属催化剂各自的结构以及其催化降冰片烯聚合的特点,同时也阐述了Ni、Pd催化剂催化降冰片烯聚合的机理。     

α-二亚胺镍/Cp*TiCl3复式催化剂制备双峰长支链聚乙烯

合成了一种后过渡金属镍化合物 [二 N ,N′ (α 萘基 ) 2 ,3 丁二亚胺镍二溴化物 ][C1 0 H7—NC(CH3)C(CH3)N—C1 0 H7]NiBr2 ,此化合物在MAO活化下催化乙烯聚合能得到含有末端双键的低分子量聚乙烯 ,即长链α 烯烃 .此化合物和一种单茂钛化合物五甲基环戊二烯基三氯化钛 (Cp TiCl3)所组成的复式催化剂 ,用MAO活化后两种主催化剂具有良好协同作用 ,能使单一乙烯聚合制备出双峰型长支链的聚乙烯 .1 3C NMR表明由此复式催化剂制得的聚乙烯不但含有甲基、乙基、丙基、丁基、戊基支链而且还含有相当多的长支链 (支链长度大于或等于 6 ) .催化剂的摩尔比 (Ni Ti)、Al(MAO) (Ni+Ti)摩尔比和聚合温度等聚合条件对催化活性及聚合物的结构与性能有明显影响 .GPC测试表明所得到的支化聚乙烯分子量呈双峰分布 .     

Development of catalyst‐transfer condensation polymerization. Synthesis of π‐conjugated polymers with controlled molecular weight and low polydispersity

We describe the development of chain‐growth condensation polymerization for the synthesis of well‐defined π‐conjugated polymers via a new polymerization mechanism, catalyst‐transfer polymerization. We first studied the condensation polymerization of Grignard‐type hexylthiophene monomer with a Ni catalyst as a part of our research on chain‐growth condensation polymerization, and found that this polymerization also proceeded in a chain‐growth polymerization manner. However, the polymerization mechanism involving the Ni catalyst was different from that of previous chain‐growth condensation polymerizations based on substituent effects; the Ni catalyst catalyzed the coupling reaction of the monomer with the polymer, followed by the transfer of Ni(0) to the terminal C? Br bond of the elongated molecule. This catalyst‐transfer condensation polymerization is generally applicable for the synthesis of polythiophene with an etheric side chain and poly(p‐pheneylene), as well as for the synthesis of polyfluorene via the Pd‐catalyzed Suzuki–Miyaura coupling reaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 753–765, 2008     

A stepwise approach to the formation of heterometallic discrete complexes and infinite architectures

A strategy for the controlled construction of heterobimetallic discrete complexes and 1-D coordination networks is presented. The organic ligand based on the methanedithiolate group and the 4,5-diazafluorene moiety behaving as primary and secondary coordination poles respectively leads to the formation of a series of discrete metal complexes with various geometries via binding through the dithiolate site. The observed coordination geometries range from square-planar for Ni(ii) and Pd(ii) to distorted tetrahedral for Zn(ii) and Hg(ii). The square-planar Pd(ii) complex affords a discrete bimetallic trinuclear complex when treated with a capped Ni(ii) center. All three Ni(ii), Pd(ii) and Hg(ii) discrete complexes have been also shown to behave as metallatectons leading to the generation of infinite networks in the presence of bridging cations such as sodium.     

Pt(Ⅱ), Pd(Ⅱ) and Ni(Ⅱ) Complexes Binding to the N(7) Position of Guanine: Influence on the Guanine and Watson-crick GC Base Pair

Comprehensive ab initio calculations were performed on the coordination of Pt(Ⅱ),Pd(Ⅱ) and Ni(Ⅱ) adducts to the N(7) of guanine and guanine-cytosine (GC) base pair at the DFT level. The fully optimized geometries of the metal complexes were obtained and the stabilization energies of the interaction between metal adducts and nucleobase were calculated with B3LYP method by using 6-31^* basis set for the light atom. While the effective core potential (ECP) is used for metal cation. The results show that both cispalladium and cisnickel cause similar geometric changes of the base pair as cisplatin. For the coordination of metal adducts to guanine, platinum adduct possesses the highest stabilization energy; but the interaction between metal-guanine and cytosine for nickel is larger than that for platinum and palladium. It is worthy to note that hydrolysis effect can also cause significant changes in H-bonds.     

A nickel(II) coordination polymer derived from a tridentate Schiff base ligand with N,O-donor groups: synthesis,crystal structure,spectroscopy, electrochemical behavior and electrocatalytic activity for H<Subscript>2</Subscript>O<Subscript>2</Subscript> electroreduction in alkaline medium

A Ni(II) coordination polymer [C₄₂H₄₂K₂N₄Ni₄O₂₇] has been synthesized under open-air mild reaction conditions and characterized by physicochemical and spectroscopic methods. The X-ray crystal structure of the complex has been obtained. The crystallographic data revealed that each metal center is in a distorted octahedral geometry where the ligand coordinates to the metal centers by a nitrogen from the imine group, an oxygen from the carboxylic acid and a phenoxide group as an endogenous bridge to the metal centers. The coordination sphere is completed by an acetate, coordinated as an exogenous bridging ligand to both nickel centers, plus one terminal water ligand on each nickel. The polymeric structure is an infinite chain involving the binuclear nickel structure and K⁺ ions. Carbon paste electrodes modified with the Ni(II) coordination polymer were prepared, and the electrochemical behavior and electrocatalytic activity toward H₂O₂ reduction were investigated. The electrochemical results suggest that this Ni(II) coordination polymer has good catalytic activity with respect to H₂O₂ reduction.     

后过渡金属配合物催化乙烯齐聚与聚合的研究进展

后过渡金属配合物催化乙烯齐聚和聚合研究,不仅拓展了后过渡金属配合物的应用 ,而且为探求烯烃聚合催化剂提供了新机遇,成为当前催化研究中的热点课题.本文综述了后过渡金属铁、钴、镍配合物催化乙烯齐聚和聚合的国内外最新研究进展.     

DFT Investigation of H2 activation by [M(NHPnPr3)('S3')] (M = Ni, Pd). Insight into key factors relevant to the design of hydrogenase functional models

Density functional theory has been used to investigate the reaction between H(2) and [Ni(NHPnPr(3))('S3')] or [Pd(NHPnPr(3))('S3')], where 'S3' = bis(2-sulfanylphenyl)sulfide(2-), which are among the few synthetic complexes featuring a metal coordination environment similar to that observed in the [NiFe] hydrogenase active site and capable of catalyzing H(2) heterolytic cleavage. Results allowed us to unravel the reaction mechanism, which is consistent with an oxidative addition-hydrogen migration pathway for [Ni(NHPnPr(3))('S3')], whereas metathesis is also possible with [Pd(NHPnPr(3))('S3')]. Unexpectedly, H(2) binding and activation implies structural reorganization of the metal coordination environment. It turns out that the structural rearrangement in [Ni(NHPnPr(3))('S3')] and [Pd(NHPnPr(3))('S3')] can take place due to the peculiar structural features of the Ni and Pd ligands, explaining the remarkable catalytic properties. However, the structural reorganization is the most unfavorable step along the H(2) cleavage pathway (DeltaG > 100 kJ mol(-1)), an observation that is relevant for the design and synthesis of novel biomimetic catalysts.     

Effect of the conformation of the alkyl chain on the catalytic miniemulsion copolymerization of ethylene and acrylates

The catalytic copolymerization of ethylene and acrylic monomers is a promising way of incorporating polar functionality into polyolefins and therefore enlarging the range of properties of these materials. This work shows that for the copolymerization of ethylene and C4 acrylates using a sterically encumbered Pd catalyst, the degree of incorporation of the acrylic monomer decreases with the degree of branching of the alkyl chain of the acrylate, the main reason being the difficulty for coordination of bulky acrylates to the catalytic site. This strongly affects the polymerization rate as well as the molecular weight, crystallinity and melting point temperature of the copolymers.     

2D hydrogen-bonded square-grid coordination networks with a substitution-active metal site

Reported here is the preparation and property of 2D coordination networks composed of rodlike ligands with ethylene glycol side chains (1). Two 2D coordination networks, [[Co(1)2(H2O)2](NO3)2.1.5H2O]n and [[Ni(1)2(H(2)O)2](NO3)2.1.5H2O]n, have been synthesized and characterized by single-crystal X-ray diffraction, TG, DSC, UV-vis spectroscopy, and magnetic measurements. The structural analyses clarified that infinite 1D hydrogen-bond arrays composed of ethylene glycol chains contribute to the stabilization of 2D coordination frameworks, keeping the environment of substitution-active metal sites unchanged. They are more stable than a similar square-grid coordination network that does not possess an ethylene glycol chain on the ligand. We also succeeded in the direct observation of a reversible apical-ligand-exchange reaction at the cobalt(II) and nickel(II) ions in a single-crystal-to-single-crystal fashion because of the considerable stability as well as moderate flexibility of the framework. The cobalt-containing coordination network crystal showed chromic behavior depending on temperatures. Crystallographic and spectroscopic studies revealed that the color change of the crystal was attributed to the ligand-exchange process between H2O and a NO3 anion on the cobalt metal. Magnetic measurements indicated weak antiferromagnetic nearest-neighbor spin coupling between cobalt(II) ions.