Synthesis,characterization, and reactivity of monomeric,arylpalladium halide complexes with a hindered phosphine as the only dative ligand

We report the isolation and structural characterization of several monomeric arylpalladium(II) halide complexes containing tri-tert-butyl phosphine, 1-adamantyl-di-tert-butylphosphine, or 2-adamantyl-di-tert-butylphosphine. X-ray diffraction, IR spectroscopy, and theoretical studies indicated that the complexes may be stabilized by agostic interactions. For example, the distance from the closest hydrogen atom to the palladium metal center in the X-ray structure of the 1-adamantyl-phenylpalladium bromide complex 1 was 2.26(3) A. The calculated Pd-H distance of 2.28 A and harmonic vibrational frequencies were in agreement with the measured distance, but Wiberg bond indices indicated only weak M-H-C interactions. Addition of 2-adamantyl-di-tert-butyl phosphine to 1 led to ligand exchange and formation of 2-adamantyl-di-tert-butyl phosphine complex 2. Addition of P(t-Bu)(3) generated free aryl bromide and Pd[P(t-Bu)(3)](2). Reactivity of complex 1 with nucleophiles provided evidence of the intermediacy of these complexes in palladium-catalyzed cross-coupling reactions. Complex 1 reacted with amine and base to form the corresponding arylamine, with tert-butoxide to form the corresponding ether, with boronic acid and fluoride to form the corresponding biaryl, and with styrene to form stilbene. This complex also catalyzed the reaction of bromobenzene with diphenylamine in the presence of base to produce 94% of the amination product in 45 min at room temperature. This rate is comparable to the reaction rate of in situ generated catalysts.     

Polymer-bound metal complexes as catalysts: Synthesis, characterization, reactivity and catalytic activity in E-H bond activation

An account of recent research of our groups is presented, focusing on the preparation of several polystyrene anchored complexes and their use as catalysts in functionalization of alkenes. The procedures for covalently binding the ligands or ligand precursors are outlined, as well as for coordination of the metal ions. Instrumental techniques used for the characterization of the polymer-bound complexes have been highlighted. The heterogenized complexes are used as catalysts for the functionalization of alkenes, namely for oxidative aminations, hydroaminations and several types of oxidations, and results obtained using the catalysts prepared are presented. The main advantages of the use of the prepared supported catalyst are specified, namely their recyclability and their higher activity, also confirmed in many cases by comparison with their homogeneous counterparts. An account of the success in the use of EPR to characterize the V^IVO- and Cu^II-systems is also given.     

Salen-iron complexes: Synthesis,characterization and their reactivity with lactide

Schiff-base metal complexes as efficient catalysts are widely used in ring-opening polymerization of cycle esters.The salen Fe complexes were formed with their excellent biocompatibility and less toxicity.A series of salen Fe complexes were designed in this work in order to study the activity and control of polymerization of lactide.The salen Fe complexes' activities changed with the ligands configuration and substituent groups.     

Synthesis, characterization and reactivity of tetramethylphospholyl complexes of scandium

Reaction of 2 equiv. of (C₄Me₄P)Li(tmeda) (tmeda = tetraethylenediamine) with 1 equiv. of ScCl₃(THF)₃ gave the new compound (η⁵-C₄Me₄P)₂ScCl₂Li(tmeda) (1), which was characterized by X-ray crystallography. A phospholyl moiety in 1 is labile, as demonstrated by reactions of 1 with LiCH(SiMe₃)₂ and Cp^∗Li (Cp^∗ = C₅Me₅) to afford, respectively, (η⁵-Me₄C₄P)Sc[CH(SiMe₃)₂]Cl₂Li(tmeda) (4) and (η⁵-Me₄C₄P)Cp^∗ScCl₂Li(tmeda) (5). Attempts to generate alkyl derivatives of the general type (η⁵-C₄Me₄P)₂ScR (R = alkyl) were unsuccessful.     

Synthesis,characterization and reactivity of some rhenium phosphite complexes

The preparation and characterization of some Re(III), Re(IV) and Re(V) chloro phosphite complexes are reported. Both Re(III) and Re(IV) complexes react with sodium borohydride, yielding the corresponding polyhydrides, ReH₅[P(OEt)₃]₃ and ReH₇[P(OEt)₃]₂. The thermal and photochemical reactivity of these complexes is described.     

Synthesis, characterization and reactivity of tribenzylphosphine rhodium and iridium complexes

New rhodium and iridium complexes, with the formula [MCl(PBz₃)(cod)] [M = Rh (1), Ir (2)] and [M(PBz₃)₂(cod)]PF₆ [M = Rh (3), Ir (4)] (cod = 1,5-cyclooctadiene), stabilized by the tribenzylphosphine ligand (PBz₃) were synthesized and characterized by elemental analysis and spectroscopic methods. The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. The addition of pyridine to a methanol solution of 1or 2, followed by metathetical reaction with NH₄PF₆, gave the corresponding derivatives [M(py)(PBz₃)(cod)]PF₆ [M = Rh (5), Ir (6)]. At room temperature in CHCl₃ solution, 4 converted spontaneously to the ortho-metallated complex [IrH(PBz₃)(cod){η²-P,C-(C₆H₄CH₂)PBz₂}]PF₆ (7) as a mixture of cis/trans isomers via intramolecular C-H activation of a benzylic phenyl ring. The reaction of 3 or 4 with hydrogen in coordinating solvents gave the dihydrido bis(solvento) derivative [M(H)₂(S)₂(PBz₃)₂]PF₆ (M = Rh, Ir; S = acetone, acetonitrile, THF), that transformed into the corresponding dicarbonyls [M(H)₂(CO)₂(PBz₃)₂]PF₆ by treatment with CO. Analogous cis-dihydrido complexes [M(H)₂(THF)₂(py)(PBz₃)₂]PF₆ (M = Rh, Ir) were observed by reaction of the py derivatives 5 and 6 with H₂.     

Synthesis,characterization and reactivity of thiolate-bridged cobalt-iron and ruthenium-iron complexes

Thiolate-bridged hetero-bimetallic complexes [Cp*M（Me CN）N₂S₂Fe Cl][PF₆]（2, M = Ru; 3, M = Co, Cp*= η⁵-C₅Me₅, N₂S₂= N,N’-dimethyl-3,6-diazanonane-1,8-dithiolate） were prepared by self-assembly of dimer [N₂S₂Fe]₂ with mononuclear precursor [Cp*Ru（MeCN）₃][PF₆] or [Cp*Co（Me CN）₃][PF₆]₂ in the presence of CHCl₃ as a...     

Synthesis, structure, and reductive elimination chemistry of three-coordinate arylpalladium amido complexes

Four three-coordinate arylpalladium amido complexes with a single hindered phosphine were isolated and structurally characterized. Each possessed a T-shaped geometry. Several of these complexes possessed true three-coordinate structures that lacked any additional coordination by ligand C-H bonds. All of the three-coordinate complexes underwent reductive elimination to form the corresponding triarylamine. A comparison of the rate of reaction of the three-coordinate compounds demonstrated that the rate of elimination from the pentaphenylferrocenyl di-tert-butylphosphine complex were the fastest. A comparison of the rates of reactions between three-coordinate and four-coordinate complexes showed that the rates were much faster from the three-coordinate complexes.     

Synthesis, characterization and ethylene reactivity of 2-diphenylphosphanylbenzamido nickel complexes

Addition of primary amines to N-[2-(diphenylphosphanyl)benzoyloxy]succinimide affords 2-diphenylphosphanylbenzamides, Ph2PC6H4C(O)NHR (R = C(CH3)3, 3; R = H, 4; R = CH2CH2CH3, 5; R = CH(CH3)2, 6). Addition of NiCl(eta3-CH2C6H5)(PMe3) to the deprotonated potassium salts of the amides and subsequent treatment of two equivalents of B(C6F5)3 to the resulting products furnishes eta3-benzyl zwitterionic nickel(II) complexes, [Ph2PC6H4C(O)NR-kappa2N,P]Ni(eta3-CH2C6H5) (R = C6H5, 9; R = C(CH3)3, 10; R = H, 11; R = CH2CH2CH3, 12; R = CH(CH3)2, 13). Solid structures of 9, 11, 13 and the intermediate eta1-benzyl nickel(II) complexes, [Ph2PC6H4C(O)NR-kappa2N,P]Ni(eta1-CH2C6H5)(PMe3) (R = C6H5, 7; R = C(CH3)3, 8) were determined by X-ray crystallography. When ethylene is added to the eta3-benzyl zwitterionic nickel(II) complexes, butene is obtained by the complexes 9-12 but complex 13 provides very high molecular-weight branched polyethylene (Mw, approximately 1300000) with excellent activity (up to 5200 kg mol-1 h-1 at 100 psi gauge).     

Ketiminate supported aluminum(III) complexes: Synthesis, characterization and reactivity

The reaction of LLi, (L = [RNC(Me)CHC(Me) = O] (R = C₂H₄NEt₂)), with AlCl₃ at −78 °C forms the mono-ketiminate product, LAlCl₂, 1, while the same reaction at 0 °C affords the bis-ketiminate complex, [{(LH)₂AlCl}(Cl₂)], 2, Reduction of 1 with Li^o, K^o or Mg^o yielded an unusual dimeric aluminum(III) species, [L′AlCl]₂, 3, where C-C coupling of the ligand backbone is observed.     

Mild and practical method for the alpha-arylation of nitriles with heteroaryl halides

[reaction: see text] A mild and transition-metal-free method for the alpha-arylation of aliphatic nitriles with activated heteroaryl halides was developed using NaHMDS or KHMDS as base at ambient temperature. The key to the success of this method is generation of the nitrile anion in the presence of the heteroaryl halide. The method is applicable to both primary and secondary carbonitriles and a wide range of heteroaryl halides. Selective monoarylation was observed with primary carbonitriles. The operational simplicity and the mild reaction conditions add to the value of this method as a practical alternative to the preparation of alpha-heteroaryl carbonitriles.     

Synthesis and characterization of zinc complexes and reactivity with primary phosphines

Zinc complexes of chelating monoanionic N-donors and neutral diphosphine ligands were synthesized by reaction of diethylzinc with 1,3-diketimine, diazabutadiene, and diphosphine ligand precursors. These complexes were reacted with primary phosphines in an attempt to solicit phosphine dehydrocoupling reactivity. In most cases, insoluble zinc-containing precipitates were formed and ligands were liberated. For the most sterically encumbered complex, (^DippL)ZnEt (3, ^DippL = [(2,6-ⁱPrC₆H₃)NC(CH₃)]₂CH^?), a product assigned as the zinc-phosphide (^DippL)ZnPHPh (6) was observed but could not be isolated as a pure compound. A new, less bulky β-diketiminate complex (^TolL)ZnEt (2, ^TolL = [(p-CH₃C₆H₄)NC(CH₃)]₂CH^?) was reacted with primary phosphines to give a precipitate and the bis(β-diketiminate)zinc complex (^TolL)₂Zn (5), an apparent product of comproportionation. (^MesAI)ZnEt (1, ^MesAI = MesNC(Me)(Et)C(Me) = NMes) and 2 were structurally characterized.     

Synthesis of cyanoalkyl indolines through cyanoalkylarylation of N-allyl anilines with alkyl nitriles under metal-free and neutral conditions

An α-C(sp³)−H functionalization of alkyl nitriles under metal-free and neutral conditions is presented. In the presence of di-tert-butyl peroxide (DTBP), N-allyl anilines underwent exo-selective cyanoalkylation/cyclization cascade, providing a direct access to 3-cyanoalkyl indolines. Previously, a transition-metal catalyst and/or a strong base were generally required to activate nitrilic α-C−H bonds. This reaction features a broad substrate scope and low cost, and primary, secondary and tertiary indolin-3-yl nitriles could all be assembled.     

Synthesis and characterization of zinc complexes and reactivity with primary phosphines

Zinc complexes of chelating monoanionic N-donors and neutral diphosphine ligands were synthesized by reaction of diethylzinc with 1,3-diketimine, diazabutadiene, and diphosphine ligand precursors. These complexes were reacted with primary phosphines in an attempt to solicit phosphine dehydrocoupling reactivity. In most cases, insoluble zinc-containing precipitates were formed and ligands were liberated. For the most sterically encumbered complex, (^DippL)ZnEt (3, ^DippL = [(2,6-ⁱPrC₆H₃)NC(CH₃)]₂CH⁻), a product assigned as the zinc-phosphide (^DippL)ZnPHPh (6) was observed but could not be isolated as a pure compound. A new, less bulky β-diketiminate complex (^TolL)ZnEt (2, ^TolL = [(p-CH₃C₆H₄)NC(CH₃)]₂CH⁻) was reacted with primary phosphines to give a precipitate and the bis(β-diketiminate)zinc complex (^TolL)₂Zn (5), an apparent product of comproportionation. (^MesAI)ZnEt (1, ^MesAI = MesNC(Me)(Et)C(Me) = NMes) and 2 were structurally characterized.     

Synthesis, characterization and catalytic activity of magnesium and zinc aminophenoxide complexes: catalysts for ring-opening polymerization of L-lactide

A series of novel magnesium and zinc aminophenoxide complexes were successfully synthesized and one zinc complex was characterized by X-ray crystallography. They were also investigated as initiators for the ring opening polymerization of L-lactide. The complexes are effective in forming polylactides with good conversions. The nature and steric bulk of the ligands coordinated to the central metal ions enormously influenced the polymer properties. Among all the complexes, the zinc aminophenoxide complexes as initiators produced polymers with good molecular weight control and relatively narrow PDIs.     

Synthesis, characterization and dioxygen reactivity of copper(I) complexes with glycoligands

A new family of copper(I) complexes with "glycoligands" containing a central saccharide scaffold, with 2-picolyl ether groups or 2-picolylamine or N-imidazolylamine groups, has been prepared and characterized. For this purpose, the following tetradentate ligands have been synthesized: methyl 2,3-di-O-(2-picolyl)-alpha-D-lyxofuranoside (L1), 1,5-anhydro-2-deoxy-3,4-di-O-(2-picolyl)-d-galactitol (L2), 5-(amino-N-(2-salicyl))-5-deoxy-1,2-O-isopropylidene-3-O-(2-picolyl)-alpha-D-xylofuranose (L3), and 5-(amino-N-(2-salicyl))-5-deoxy-1,2-O-isopropylidene-3-O-(methylimidazol-2-yl)-alpha-D-xylofuranose (L4). The ligands and the complexes were characterized by elemental analysis, IR, 1H and 13C NMR spectroscopies, ESI mass spectrometry, and cyclic voltammetry. Collaterally with the experimental work, HF-DFT(B3LYP/6-31G*) computations were performed to obtain additional structural information. The Cu(I) complexes are found to be pentacoordinated. The redox properties and the O2-reactivity of the Cu(I)Ln complexes have been studied. Reactions of Cu(I) complexes with dioxygen in ethanol yield stable Cu(II) complexes as confirmed by UV-visible spectrophotometry and EPR spectroscopy.     

Synthesis,characterization and C–H amination reactivity of nickel iminyl complexes

Metalation of the deprotonated dipyrrin (^AdFL)Li with NiCl₂(py)₂ afforded the divalent Ni product (^AdFL)NiCl(py)₂ (1) (^AdFL: 1,9-di(1-adamantyl)-5-perfluorophenyldipyrrin; py: pyridine). To generate a reactive synthon on which to explore oxidative group transfer, we used potassium graphite to reduce 1, affording the monovalent Ni synthon (^AdFL)Ni(py) (2) and concomitant production of a stoichiometric equivalent of KCl and pyridine. Slow addition of mesityl- or 1-adamantylazide in benzene to 2 afforded the oxidized Ni complexes (^AdFL)Ni(NMes) (3) and (^AdFL)Ni(NAd) (4), respectively. Both 3 and 4 were characterized by multinuclear NMR, EPR, magnetometry, single-crystal X-ray crystallography, theoretical calculations, and X-ray absorption spectroscopies to provide a detailed electronic structure picture of the nitrenoid adducts. X-ray absorption near edge spectroscopy (XANES) on the Ni reveals higher energy Ni 1s → 3d transitions (3: 8333.2 eV; 4: 8333.4 eV) than Ni^I or unambiguous Ni^II analogues. N K-edge X-ray absorption spectroscopy performed on 3 and 4 reveals a common low-energy absorption present only for 3 and 4 (395.4 eV) that was assigned via TDDFT as an N 1s promotion into a predominantly N-localized, singly occupied orbital, akin to metal-supported iminyl complexes reported for iron. On the continuum of imido (i.e., NR²⁻) to iminyl (i.e., ²NR⁻) formulations, the complexes are best described as Ni^II-bound iminyl species given the N K-edge and TDDFT results. Given the open-shell configuration (S = 1/2) of the iminyl adducts, we then examined their propensity to undergo nitrenoid-group transfer to organic substrates. The adamantyl complex 4 readily consumes 1,4-cyclohexadiene (CHD) via H-atom abstraction to afford the amide (^AdFL)Ni(NHAd) (5), whereas no reaction was observed upon treatment of the mesityl variant 3 with excess amount of CHD over 3 hours. Toluene can be functionalized by 4 at room temperature, exclusively affording the N-1-adamantyl-benzylidene (6). Slow addition of the organoazide substrate (4-azidobutyl)benzene (7) with 2 exclusively forms 4-phenylbutanenitrile (8) as opposed to an intramolecular cyclized pyrrolidine, resulting from facile β-H elimination outcompeting H-atom abstraction from the benzylic position, followed by rapid H₂-elimination from the intermediate Ni hydride ketimide intermediate.

Nickel-supported nitrenoids exhibit iminyl character, as determined by multi-edge XAS and TDDFT analysis, demonstrate efficacy for C–H activation and nitrene transfer chemistry.     

Supported metallocene catalysts by surface organometallic chemistry. Synthesis, characterization, and reactivity in ethylene polymerization of oxide-supported mono- and biscyclopentadienyl zirconium alkyl complexes: establishment of structure/reactivity relationships

The reactions of CpZr(CH(3))(3), 1, and Cp(2)Zr(CH(3))(2), 2, with partially dehydroxylated silica, silica-alumina, and alumina surfaces have been carried out with careful identification of the resulting surface organometallic complexes in order to probe the relationship between catalyst structure and polymerization activity. The characterization of the supported complexes has been achieved in most cases by in situ infrared spectroscopy, surface microanalysis, qualitative and quantitative analysis of evolved gases during surface reactions with labeled surface, solid state (1)H and (13)C NMR using (13)C-enriched compounds, and EXAFS. 1 and 2 react with silica(500) and silica-alumina(500) by simple protonolysis of one Zr-Me bond by surface silanols with formation of a single well-defined neutral compound. In the case of silica-alumina, a fraction of the supported complexes exhibits some interactions with electronically unsaturated surface aluminum sites. 1 and 2 also react with the hydroxyl groups of gamma-alumina(500), leading to several surface structures. Correlation between EXAFS and (13)C NMR data suggests, in short, two main surface structures having different environments for the methyl group: [Al](3)-OZrCp(CH(3))(2) and [Al](2)-OZrCp(CH(3))(mu-CH(3))-[Al] for the monoCp series and [Al](2)-OZrCp(2)(CH(3)) and [Al]-OZrCp(2)(mu-CH(3))-[Al] for the bisCp series. Ethylene polymerization has been carried out with all the supported complexes under various reaction conditions. Silica-supported catalysts in the absence of any cocatalyst exhibited no activity whatsoever for ethylene polymerization. When the oxide contained Lewis acidic sites, the resulting surface species were active. The activity, although improved by the presence of additional cocatalysts, remained very low by comparison with that of the homogeneous metallocene systems. This trend has been interpreted on the basis of various possible parameters, including the (p-pi)-(d-pi) back-donation of surface oxygen atoms to the zirconium center.     

Platinum complexes with diamino-substituted phosphorus ligands: Synthesis,characterization, and their reactivity with a Lewis acid

Reaction of dialkyl- or diaryl-platinum complexes PtR₂(cod) (cod = η², η²-1,5-cyclooctadiene, R = Me, p-tol) with diamino-substituted phosphorus ligands P(NMeCH₂)₂(R′) (R′ = OMe, NEt₂) produced neutral complexes, cis-[Pt(R)₂{P(NMeCH₂)₂(R′)}₂]. On the other hand, reaction of dihalogeno platinum complex PtX₂(cod) (X = Cl, I) with P(NMeCH₂)₂(OMe) yielded a cationic complex [PtX{P(NMeCH₂)₂(OMe)}₃]X. A platinum complex having both methyl and halogeno ligands, PtMeX(cod), reacted with P(NMeCH₂)₂(OMe) to give a cationic methyl complex [PtMe{P(NMeCH₂)₂(OMe)}₃]X, by contrast, it reacted with P(NMeCH₂)₂(NEt₂) to yield a neutral methyl complex [PtMeX{P(NMeCH₂)₂(NEt₂)}₂]. Reaction of [PtMe{P(NMeCH₂)₂(OMe)}₃]X with BF₃·OEt₂ and then NaBPh₄ afforded [PtX{P(NMeCH₂)₂(OMe)}₃]BPh₄, showing preferential Me group abstraction on the Pt center rather than the OMe abstraction on the phosphorus atom, followed by the coordination of X to the Pt center. All new complexes were fully characterized using ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR measurements and elemental analyses. In addition, structures of several complexes were determined by single crystal X-ray diffraction studies.