(N-Arylaminomethyl)pyridine-N-oxides: Synthesis and characterization of potential ligand systems and the formation of their N,O-chelate aluminum complexes

Pyridine-N-oxide-2-carbaldehyde (4a) was converted to the corresponding imine (5a) by treatment with 2,6-diisopropylaniline. Subsequent reduction with a sodium borohydride gave the corresponding (N-arylaminomethyl)pyridine-N-oxide derivative (6a). A series of analogous compounds was prepared starting from the respective (aldimino)quinoline-N-oxide (4b) or (ketimino)pyridine-N-oxide (10) systems. Deprotonation of the (aminomethyl)pyridine-N-oxides resulted in a series of unexpected reactions, such as coupling, internal redox reactions or fragmentation. Eventually, the N,O-chelate aluminum complexes (22, 23) derived from the (aminoethyl)pyridine-N-oxide ligand systems could be obtained by treatment of the respective iminopyridine-N-oxides with trimethylaluminum. Many products were characterized by X-ray diffraction.     

Synthesis, characterisation and solid state structures of α-diimine cobalt(II) complexes: Ethylene polymerisation tests

A series of cobalt(II) compounds of the type [CoX₂(α-diimine)] were synthesised by direct reaction of anhydrous CoCl₂ or CoI₂ and the corresponding α-diimine ligand, in CH₂Cl₂: [CoI₂(o,o′,p-Me₃C₆H₂-DAB)] (1), [CoI₂(o,o′-ⁱPr₂C₆H₃-DAB)] (2), (where Ar-DAB = 1,4-bis(aryl)-2,3-dimethyl-1,4-diaza-1,3-butadiene), and [CoCl₂(o,o′,p-Me₃C₆H₂-BIAN)] (3), [CoCl₂(o,o′-ⁱPr₂C₆H₃-BIAN)] (4), and [CoI₂(o,o′-ⁱPr₂C₆H₃-BIAN)] (5) (where Ar-BIAN = bis(aryl)acenaphthenequinonediimine). All compounds were characterised by elemental analyses, IR, mass spectrometry, and X-ray diffraction whenever possible. The crystal structures of compounds 2-4 showed, in all cases, distorted tetrahedral geometries about the Co, built by two halogen atoms and two nitrogen atoms of the α-diimine ligand. Compounds 3 and 4, as well as [CoCl₂(o,o′,p-Me₃C₆H₂-DAB)] (1a), and [CoCl₂(o,o′-ⁱPr₂C₆H₃-DAB)] (2a), were activated by methylaluminoxane (MAO) and tested as catalysts for ethylene polymerisation, showing low catalytic activities. Selected polyethylene (PE) samples were characterised by ¹H and ¹³C NMR and FT-IR spectroscopies, and by differential scanning calorimetry (DSC), revealing branching microstructures (2.5-5.5%).     

Synthesis and thermal behavior of dimethyl scandium complexes featuring anilido-phosphinimine ancillary ligands

A family of N,N donor ligands [1-(NHAr)-2-(PR₂NAr′)C₆H₄] (1a-d; Ar = 2,6-ⁱPr₂-C₆H₃, R = Me, Ph, Ar′ = 2,4,6-Me₃-C₆H₂, 2-ⁱPr-C₆H₄, 2,6-ⁱPr₂-C₆H₃) has been prepared and fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. Lithiation of the N-H unit and subsequent salt metathesis protocols with ScCl₃THF₃ provides an avenue to organometallic scandium complexes. The resultant base-free monomeric dichlorides LScCl₂, 3a-d, have been fully characterized by NMR spectroscopy as well as X-ray crystallography (3a,c,d). Alkylation of the dichlorides using LiMe results in clean formation of dialkyl complexes LScMe₂4a-c. Thermolysis of these materials under argon and hydrogen leads to decomposition products as a result of C-H activation of the ligand. Analysis of these results provides a qualitative assessment of the metalative resistance of each ligand framework.     

N-tripodal ligands to generate copper catalysts for the syndiotactic polymerization of methyl-methacrylate: Crystal structures of copper complexes

A library of N-tripodal ligands, based on a central nitrogen atom connected to three different functionalized arms, was investigated via a parallel approach for the polymerization of methyl-methacrylate (MMA) in presence of late transition metal salts. Copper salts CuCl₂ and Cu(OAc)₂ in combination with N-(2-furanylmethyl)-N-(1-3,5-dimethyl-1H-pyrazolylmethyl)-N- (phenylmethyl)amine were detected as efficient catalysts for the syndiotactic polymerization of MMA ([rr] up to 78%). Kinetic studies and X-ray structures of the best catalysts were reported.     

Reactivity of a triruthenium alkenyl cluster complex with conjugated diynes: Coupling of two diyne molecules via a face-capping diyne intermediate

The cluster [Ru₃(μ₃-κ²-HNNMe₂)(μ-κ²-PhCHCPh)(μ-CO)₂(CO)₆], which has a face-capping 1,1-dimethylhydrazido and an edge-bridging 1,2-diphenylethenyl ligand, reacts with diphenylbutadiyne or 2,4-hexadiyne to give the isomeric triruthenium carbonyl cluster complexes [Ru₃(μ₃-κ²-HNNMe₂)(μ-κ²-PhCHCPh){μ₃-κ⁴-RCCCC(R)C(R)CCCR}(CO)₆] (3a, R = Ph; 3b, R = Me) and [Ru₃(μ₃-κ²-HNNMe₂)(μ-κ²-PhCHCPh){μ₃-κ⁴-RCCCC(R)C(CCR)CR}(CO)₆] (4a, R = Ph; 4b, R = Me). These compounds contain a large unsaturated hydrocarbyl ligand that arises from a metal-cluster-mediated head-to-head (3) or head-to-tail (4) coupling of two diyne molecules and maintain the original hydrazido and ethenyl ligands. Metal clusters that contain a face-capping diyne coordinated through only one alkyne fragment, such as [Ru₃(μ₃-κ²-HNNMe₂)(μ-κ²-PhCHCPh)(μ₃-κ²-RCCCCR)(CO)₇], have also been isolated (2a, R = Ph; 2b, R = Me). They are the intermediates that incorporate a second diyne reagent to give 3 and 4. The structural parameters of intermediate 2b have been obtained from DFT calculations.     

Alkene and alkyne insertion into the Ir-H bond: Synthesis of new mono- and dinuclear alkyl and alkenyl iridium-pybox complexes

The treatment of the complex [Ir(η²-C₂H₄)₂(L)][PF₆] (L = κ³-N,N,N-(S,S)-ⁱPr-pybox) with acetic acid (1:1 molar ratio) at −10 °C affords the complex [Ir(C₂H₅)(κ²-O,O-O₂CCH₃)(L)][PF₆] (1). The dinuclear iridium(III) complex [Ir₂(μ-Cl)₂(C₂H₅)₂(L)₂][PF₆]₂ (2) is stereoselectively obtained by spontaneous intramolecular insertion of ethylene into the iridium-hydride bond of the mononuclear complex [IrClH(η²-C₂H₄)(L)][PF₆]. The single bridging chloride dinuclear derivative [Ir₂(μ-Cl)(C₂H₅)₂Cl₂(L)₂][PF₆] (3) is prepared by reaction of 2 with one equivalent of NaCl. The intramolecular insertion reaction of methyl and ethyl propiolate into the Ir-H bond of the complex [IrClH(MeCN)(L)][PF₆] gives stereoselectively the dinuclear complexes [Ir₂(μ-Cl)₂(HCCHCO₂R)₂(L)₂][PF₆]₂ (R = Me (4), Et (5)). The reaction of the complexes 4, 5 with one equivalent of NaCl or with an excess of sodium acetate yields the dinuclear [Ir₂(μ-Cl)(HCCHCO₂R)₂Cl₂(L)₂][PF₆] (R = Me (6), Et (7)) or the mononuclear [IrCl(HCCHCO₂Et)(κ¹-O-O₂CMe)(L)] (8) complexes, respectively. The structure of the dinuclear complex 3 · CH₂Cl₂ has been determined by an X-ray monocrystal study.     

Palladium complexes of 8-(di-tert-butylphosphinooxy) quinoline

The preparation of the new ligand 8-(di-tert-butylphosphinooxy)quinoline (1) and the palladium derivatives [PdCl₂(1)] (2), [Pd(η³-all)(1)]⁺ [all = C₃H₅ (3a), 1-PhC₃H₄ (3b) and 1,3-Ph₂C₃H₃ (3c)] and [Pd(η²-ol)(1)] [ol = dimethyl fumarate (4a) and fumaronitrile (4b)] is reported. The cationic species 3a-3c have been isolated as salts. The complex 3a(BF₄) is obtained either from the reaction of 1 with [Pd(μ-Cl)(η³-C₃H₅)]₂ or from the reaction of ClP(CMe₃)₂ with [Pd(η³-C₃H₅)(8-oxyquinoline)], followed in both cases by chloride abstraction with NaBF₄. In the complexes, the ligand 1 is P,N chelated to the central metal, as shown by the X-ray structural analysis of 3a(BF₄). At 25 °C in solution, 3a(BF₄) and 3b(BF₄) undergo a fast η³−η¹−η³ dynamic process which brings about a syn-anti exchange only for the allylic protons cis to phosphorus, while for 4a and 4b a slow rotation of the olefin around its bond axis to palladium takes place. The complexes 2 and 3a(BF₄) are efficient catalyst precursors in the coupling of the phenylboronic acid with aryl bromides and chlorides.     

Imidazolium salicylaldimine frameworks for the preparation of tridentate N-heterocyclic carbene ligands

Sterically hindered salicylaldimine functionalized imidazolium salts 2 have been prepared. The structures of the synthesized compounds were determined by spectroscopic techniques. The reaction of these salts containing arylmethyl-N chain (aryl: phenyl (2a), 2,4,6-trimethylphenyl (2b), 2,3,4,5,6-pentamethylphenyl (2c)) with Pd(OAc)₂ in boiling toluene afforded Pd(II) complexes 3 in high yields. The X-ray structure of 1-[3-(3,5-di-tert-butyl-2-oxophenyl)propyliminato]-3-(2,4,6-trimethylbenzyl)imidazol-2-ylidenebromopalladium(II) (3b) has been determined. The Suzuki-Miyaura reaction was used to investigate their activity as catalysts either prepared in situ or from well-defined complexes. They are efficient when activated arylbromides are used as substrates.     

Synthesis, coordination studies and redox properties of a novel ditertiary phosphine bearing two ferrocenyl groups

The new ferrocenyl substituted ditertiary phosphine {FcCH₂N(CH₂PPh₂)CH₂}₂ [Fc = (η⁵-C₅H₄)Fe(η⁵-C₅H₅)] (1) was prepared, in 72% yield, by Mannich based condensation of the known bis secondary amine {FcCH₂N(H)CH₂}₂ with 2 equiv. of Ph₂PCH₂OH in CH₃OH. Phosphine 1 readily coordinates to various transition-metal centres including Mo⁰, Ru^II, Rh^I, Pd^II, Pt^II and Au^I to afford the heterometallic complexes {RuCl₂(p-cym)}₂(1) (2), (AuCl)₂(1) (3), cis-PtCl₂(1) (4), cis-PdCl₂(1) (5), cis-Mo(CO)₄(1) (6), trans,trans-{Pd(CH₃)Cl(1)}₂ (7) and trans,trans-{Rh(CO)Cl(1)}₂ (8). In complexes 2, 3, 7 and 8 ligand 1 displays a P,P′-bridging mode whilst for 4-6 a P,P′-chelating mode is observed. All new compounds have been fully characterised by spectroscopic and analytical methods. Furthermore the structures of 1, 2 · 2CH₂Cl₂, 3 · CH₂Cl₂, 4 · CH₂Cl₂, 6 · 0.5CHCl₃ and 8 have been elucidated by single crystal X-ray crystallography. Electrochemical measurements have been undertaken, and their redox chemistry discussed, on both noncomplexed ligand 1 and representative compounds containing this new ditertiary phosphine.     

Platinum chloride/Xphos-catalyzed regioselective hydrosilylation of functionalized terminal arylalkynes

Totally regioselective hydrosilylation of functionalized terminal arylalkynes was achieved using PtCl₂ associated with the air-stable and bulky Xphos ligand with various silanes. Regardless of the electronic nature of the substituents on the aromatic ring, a single β-(E)-vinylsilane was obtained in excellent yields.