Christopher M. Kozak

Iron(III) amine-bis(phenolate) complexes as catalysts for the coupling of alkyl halides with aryl Grignard reagents

Catalytic cross-coupling of aryl Grignard reagents with primary and secondary alkyl halides bearing beta-hydrogens is achieved using Fe(III) amine-bis(phenolate) halide complexes.

Controlled Radical Polymerization Mediated by Amine–Bis(phenolate) Iron(III) Complexes

Tetradentate amine-bis(phenolate) iron(III) halide complexes containing chloro substituents on the aromatic ring are extremely efficient catalysts for controlled radical polymerization. Molecular weights are in good agreement with theoretical values and polydispersity indexes (PDIs) are as low as 1.11 for styrene and methyl methacrylate polymerizations. Complexes containing alkyl substituents on the aromatic ring are less efficient. Kinetic data reveal activity for styrene polymerization among the fastest reported to date and initial studies implicate a multimechanism system. Despite the highly colored polymerization media, simple work-up procedures yield pure white polymers.

Alkali aminoether-phenolate complexes: synthesis, structural characterization and evidence for an activated monomer ROP mechanism

Several monometallic {LO(i)}M complexes of lithium (M = Li; i = 1 (1), 2 (2), 3 (3)) or potassium (M = K, i = 3 (4)) and the heteroleptic bimetallic lithium complex {LO(3)}Li·LiN(SiMe2H)2 (5), all supported by monoanionic aminoether-phenolate {LO(i)}(-) (i = 1-3) ligands, have been synthesized and structurally characterized. A large range of coordination motifs is represented in the solid state, depending on the chelating ability of the ligand, the size of the metal and the number of metallic centres found in the complex. Pulse-gradient spin-echo NMR showed that 1-4 are monomeric in solution, irrespective of their (mono- or di)nuclearity in the solid-state. VT (7)Li and DOSY NMR measurements conducted for 5 indicated that the two Li atoms in the complex do not exchange positions even at 80 °C. Upon addition of 1-10 equiv. of BnOH, the electron-rich and sterically congested {LO(3)}Li complex (3) promotes the controlled living and immortal ring-opening polymerisation of L-lactide. The combination of polymer end-group analyses and stoichiometric model reactions unambiguously provided evidence that ROP reactions catalyzed by these two-component {LO(i)}Li/BnOH catalyst systems operate according to an activated monomer mechanism, and not via the coordination-insertion scenario frequently assumed for similar alkali phenolate-alcohol systems.

Iron-catalyzed epoxidation of olefins using hydrogen peroxide

A practical method of olefin epoxidation was developed by combining FeCl3·6H2O and 1-methylimidazole in acetone using H2O2 as the terminal oxidant. This system showed very good reactivity toward epoxidation of both terminal and substituted alkenes. The use of tridentate and tetradentate amine-bis(phenolate) ligands as additives was also examined. Modest improvement in selectivity was achieved if a bulky tridentate ligand was used. Generally, however, the simple catalyst system involving ferric chloride, 1-methylimidazole and dilute H2O2 in acetone proved most successful in achieving good to excellent yields of epoxide products for a number of substrates, including aromatic and aliphatic alkenes.

Magnetic, electrochemical and spectroscopic properties of iron(III) amine–bis(phenolate) halide complexes

Eight new iron(III) amine-bis(phenolate) complexes are reported. The reaction of anhydrous FeX(3) salts (where X = Cl or Br) with the diprotonated tripodal tetradentate ligands 2-tetrahydrofurfurylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)L1, 2-tetrahydrofurfurylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)L2, and 2-methoxyethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)L3, 2-methoxyethylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)L4 produces the trigonal bipyramidal iron(III) complexes, L1FeCl (1a), L1FeBr (1b), L2FeCl (2a), L2FeBr (2b), L3FeCl (3a), L3FeBr (3b), L4FeCl (4a), and L4FeBr (4b). All complexes have been characterized using electronic absorption spectroscopy, cyclic voltammetry and room temperature magnetic measurements. Variable temperature magnetic data were acquired for complexes 2b, 3a and 4b. Variable temperature Mössbauer spectra were obtained for 2b, 3a and 4b. Single crystal X-ray molecular structures have been determined for proligand H(2)L4 and complexes 1b, 2b, and 4b.

Chromium(III) amine-bis(phenolate) complexes as catalysts for copolymerization of cyclohexene oxide and CO2

Amine-bis(phenolate) chromium(III) complexes catalyze the copolymerization of cyclohexene oxide with carbon dioxide. These catalysts incorporate tetra- or tridentate amine-bis(phenolate) ligands and when combined with dimethylaminopyridine (DMAP) or bis(triphenylphosphoranylidene)ammonium chloride or azide, (PPNCl or PPNN3), yield low molecular weight polymers with moderately narrow polydispersities. The tetradentate ligand containing catalysts show higher conversions and yields of polycyclohexene carbonate, but with a wide variety of polymer end groups as shown by MALDI-TOF mass spectrometry.

Mechanistic Studies of Cyclohexene Oxide/CO2 Copolymerization by a Chromium(III) Pyridylamine-Bis(Phenolate) Complex

Chromium(III) chlorido amine-bis(phenolate) complexes paired with nucleophilic co-catalysts are a promising family of catalysts for the copolymerization of CO2 and epoxides to selectively produce polycarbonates with a very high degree of carbonate linkages. Single-component catalyst systems can be prepared, where the neutral nucleophile, 4-dimethylaminopyridine (DMAP), is coordinated to the metal site to provide a stable octahedral CrIII complex. These complexes possess the potential for both anionic (from the chlorido ligand) or neutral (DMAP) nucleophilic epoxide ring-opening during the proposed rate-determining initiation step. Concentration effect studies support a first-order dependence of the polymerization rate on the concentration of single-component catalyst. End-group analysis of polycarbonates by MALDI-TOF MS indicate the presence of predominantly DMAP-initiated chains as well as the occurrence of chain-transfer events resulting in ether linkages, likely from the presence of cyclohexene diol formed by the reaction of cyclohexene oxide and adventitious water.

Cyclohexene oxide/carbon dioxide copolymerization by chromium(III) amino-bis(phenolato) complexes and MALDI-TOF MS analysis of the polycarbonates

Amine-bis(phenolate) chromium(III) chloride complexes 1·THF, 2·THF and 1·DMAP catalyze the copolymerization of cyclohexene oxide and carbon dioxide. These catalysts incorporate tetradentate amine-bis(phenolate) ligands [L1] and [L2], (where [L1] = 2-pyridyl-N,N-bis(2-methylene-4-methoxy-6-tert-butylphenolato) and [L2] = dimethylaminoethylamino-N,N-bis(2-methylene-4-methoxy-6-tert-butylphenolato)) and when combined with 4-(N,N-dimethylamino)pyridine (DMAP) or bis(triphenylphosphoranylidene)ammonium chloride or azide (PPNCl or PPNN3), yield low molecular weight polycarbonate with narrow dispersities. The structure of 1·DMAP incorporates one molecule of 4-(N,N-dimethylamino)pyridine (DMAP) and can be used as a single-component catalyst precursor. Polymer end group analysis by MALDI-TOF mass spectrometry reveals possible initiation pathways.

Kinetic Studies of Copolymerization of Cyclohexene Oxide with CO2 by a Diamino-bis(phenolate) Chromium(III) Complex

A diamino-bis(phenolate) chromium(III) complex, CrCl(THF)[L], 1, where [L] = dimethylaminoethylamino- N, N-bis(2-methylene-4,6- tert-butylphenolate), has been synthesized in high yield and characterized by MALDI-TOF mass spectrometry, elemental analysis, UV-vis spectroscopy and single crystal X-ray diffraction. This complex combined with 4-dimethylaminopyridine (DMAP) or bis(triphenylphosphoranylidene)ammonium chloride or azide salts (PPNCl or PPNN3) shows improved activity over previously reported amine-bis(phenolate) chromium(III) complexes for copolymerization of cyclohexene oxide (CHO) and CO2 to yield poly(cyclohexene) carbonate (PCHC). Kinetic studies of the complex/DMAP system showed the activation energy for polycarbonate formation to be 62 kJ/mol. End group analysis of resulting polycarbonates by MALDI-TOF MS reveals either the chloride of the Cr(III) complex or the external nucleophile initiates the copolymerization reaction.

Acetato­aqua­{4,4′,6,6′-tetra-tert-butyl-2,2′-[(2-pyridyl­meth­yl)imino­dimethyl­ene]diphenolato}manganese(III) ethanol solvate

In the title complex, [Mn(C36H50N2O2)(CH3COO)(H2O)]·CH3CH2OH, the MnIII atom is in an octahedral environment and is coordinated by the tetradentate amine–bis(phenolate) ligand, a monodentate acetate anion and a water molecule. An ethanol solvent molecule is also found in the asymmetric unit. The structure displays O—H⋯O and C—H⋯O hydrogen bonding.