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Planar bismuth compounds exhibit tunable Lewis acidity and high catalytic activity for lactone polymerization.

The iron-catalyzed direct arylation of a variety of N-heteroarenes, quinones, and hydroquinones with arylboronic acids is investigated under microwave heating. The reaction proceeds at 70 °C under air using K2S2O8 as an oxidant and FeSO4 as a catalyst. Under microwave heating, reaction times decreased 14- to 115-fold. Reaction scope with N-heteroarenes and quinones is comparable with or slightly expanded when compared with previous reports, but the scope of arylboronic acid utility was slightly limited due to previously unobserved arylboronic acid hydroxydeboronation.

Chromium diamino-bis(phenolate) complexes, CrXL [where L = 6,6'-((1,4-diazepane-1,4-diyl)bis(methylene))bis(2,4-dimethylphenolato) and X = Cl- (1), OH- (2), and N3- (3)], were prepared and characterized by MALDI-TOF MS and single-crystal X-ray diffraction. Complex 1 crystallized as two linkage isomers, specifically a green chloride-bridged dimer (1) and a pink asymmetrically bridged isomer exhibiting one chloride bridging atom and one bridging phenolate oxygen (1'). Adventitious moisture during sample handling causes the formation of hydroxide-containing complex 2. The reaction of 1 with PPNN3 (where PPN = bis(triphenylphosphine)iminium) permits the isolation of a crystalline chromium azide complex, 3, which was structurally authenticated. Complex 1 showed good activity toward the ring-opening copolymerization of cyclohexene oxide and carbon dioxide with an added chloride, azide, or 4-(dimethylamino)pyridine (DMAP) cocatalyst to give a completely alternating polycarbonate with a narrow molecular weight dispersity.

Compounds of Li, Na, K and Ca of a tetradentate amino-bis(phenolato) ligand were prepared. Bimetallic compounds formulated as M2[L](THF)n (where M = Na, n = 1 (1·THF) or Li, n = 1 (2·THF)) were synthesized via the reaction of H2[L] (where [L] = 2-pyridylmethylamino-N,N-bis(2-methylene-4-methoxy-6-tert-butylphenolato) with sodium hydride or n-butyllithium, respectively, in THF. Monometallic complexes MH[L](THF)n (where M = Na, n = 1 (3·THF), Li, n = 0 (4) and K, n = 0 (5)) were obtained by reaction of H2[L] with MN(SiMe3)2 where M = Na, Li, or K. Calcium complex Ca[L](THF) (6·THF) was synthesized in two ways; reaction of Na2[L] with calcium iodide in THF, and reaction of Ca[N(SiMe3)2]2 with H2[L] in toluene. Compounds 1–6 exhibit activity for rac-lactide polymerization under melt and solution conditions. Moderate control of polymer molecular weights was achieved in toluene, whereas polydisperse polymer was obtained under solvent free conditions. MALDI-TOF MS analysis of the polymer end groups revealed a predominantly cyclic nature for the polylactides.

The chromium(III) amino-bis(phenolate) “ate” complex, {Na[CrCl2L1]}, 1, where L1 = 6,6′-((1,4-diazepane-1,4-diyl)bis(methylene))bis(2,4-di-tert-butylphenolato) and its derivatives 2–4 (where the ph...

Waste-derived fish oil (FO) can be epoxidized and reacted with CO2 to produce a cyclic carbonate containing material. Upon reaction with a bioderived amine, this leads to the formation of nonisocyanate polyurethane materials. The FO used is extracted from the by-products produced at fish processing plants, including heads, bones, skin, and viscera. Three different methods are used for the epoxidation of the FO: (i) oxidation by 3-chloroperoxybenzoic acid, (ii) oxidation by hydrogen peroxide and acetic acid, catalyzed by sulfuric acid, and (iii) oxidation by hydrogen peroxide catalyzed by formic acid. Synthesized FO epoxides are reacted with CO2 to yield FO cyclic carbonates with high conversions. The products are characterized by 1 H and 13 C NMR spectroscopy, IR spectroscopy, thermogravimetric analysis, and viscometry. Using a biomass-derived amine, nonisocyanate polyurethane materials are synthesized. This process can lead to new opportunities in waste management, producing valuable materials from a resource that is otherwise underutilized.

The catalytic copolymerization of CO2 with epoxides to give polycarbonates was discovered nearly 50 years ago. The last 10 years have been particularly exciting for the development on highly active homogenous catalyst systems, insights into mechanisms and the design of polymers with promising physical properties. Recent work has identified new copolymerization pathways with increasing diversity in the metals and ligands employed. Cooperative mechanisms with binary catalyst systems using exogenous nucleophiles continue to be studied. Elegant ligand design, however, has been used to generate new, highly active bimetallic or bifunctional catalyst systems. The bimetallic systems allow for “shuttling” of growing polymer chains leading to excellent activity under low CO2 pressures. Bifunctional systems use covalently linked groups that facilitate the role of the nucleophilic co-catalyst. These groups can be neutral Lewis basic sites, such as N-donors, or cationic sites, such as ammonium groups, that improve the association of the anionic nucleophilic co-catalyst components. The cationic groups also improve association of any metal-dissociated anionic polymer chain ends and allow more efficient separation of the catalyst from the polymer products via chromatography. This review gives an overview of the developments of homogeneous catalysts for CO2/epoxide copolymerization grouped by metal site. New mechanistic studies and strategies for future catalyst developments are also discussed.

A series of iron(III) chloride and iron(III) μ-oxo compounds supported by tetradentate amino-bis(phenolate) ligands containing a homopiperazinyl backbone were prepared and characterized by electronic absorption spectroscopy, magnetic moment measurement, and MALDI-TOF mass spectrometry. The solid-state structures of three iron(III) μ-oxo compounds were determined by single crystal X-ray diffraction and revealed oxo-bridged bimetallic species with Fe–O–Fe angles between 171.7 and 180°, with the iron centers in distorted square pyramidal environments. Variable temperature magnetic measurements show the oxo complexes exhibit strong antiferromagnetic coupling between two high-spin S = 5/2 iron(III) centers. The oxo complexes exhibit poor activity for the reaction of carbon dioxide and epoxides in the presence of a cocatalyst, under solvent free conditions to yield cyclic carbonates. The least active iron oxo compound bears tert-butyl groups on the phenolate donors, and we propose that steric congestion around ...

The affinity for nucleophile (azide, N3–, and chloride, Cl–) binding significantly influences the catalytic activity of chromium complexes for the copolymerization of cyclohexene oxide (CHO) and CO2. The binding of N3– and Cl– to two amino-bis(phenolate) Cr(III) chloride complexes [L1Cr(μ-Cl)]2 (1) and [L2CrCl(THF)] (2·THF), where L1 = methoxyethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenolate) and L2 = dimethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenolate), were studied by both matrix assisted laser desorption/ionization time-of-flight and electrospray ionization mass spectrometry (MALDI-TOF-MS and ESI-MS, respectively). Upon reaction with [PPN][N3] ([PPN] = bis(triphenylphosphine)iminium), 1 exhibited greater ability to form six-coordinate bis-azide ions [L1Cr(N3)2]− and produced fewer five-coordinate species detected by MS than 2·THF. This corresponded to 2·THF having a significantly faster rate of polymerization with anionic nucleophile cocatalysts than 1. In the presence of 1 e...

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.

Cobalt(II) and (III) complexes bearing tetradentate amino-bis(phenolate) ligands containing either pendent dimethylaminoethylene or pyridyl groups and phenolates bearing electron-donating alkyl or electron-withdrawing chloro substituents were synthesized. The compounds were characterized by mass spectrometry, elemental analysis and NMR for diamagnetic compounds. The influence of the electron donating ability and steric demand of the ligands on CO2/epoxide ring-opening copolymerization (ROCOP) and coupling reactions was investigated. Of the Co(II) systems studied, complex 3, which has an amino-bis(phenolate) ligand possessing chlorine-functionalized phenolates and a pyridyl pendent group, [L3] = 2-methylene-pyridyl-N,N-bis(2-methylene-2,4-dichlorophenolate), was active for poly(cyclohexene carbonate) formation. The complex showed up to 98% epoxide conversion, up to 98% polymer selectivity and up to 97% carbonate linkages. By comparison, Co(II) compounds 1 and 2 bearing alkyl groups on the phenolate donors were inactive for ROCOP. Structural characterization of 3 by X-ray diffraction (and supported by mass spectrometry and elemental analysis) showed the potassium acetate (KOAc), which formed as a synthetic by-product, remains coordinated to the Co[L3] unit through binding of the K+ ions to the chlorine substituents on the phenolate groups and acetate anions, resulting in a hexacobalt cluster in the solid state. Cobalt(III) compounds were prepared from the Co(II) complexes by aerobic oxidation in the presence of 2,4-dinitrophenol. The resulting 2,4-dinitrophenolate (2,4-DNP) complexes were diamagnetic species of which 7, possessing a dimethylamino-N,N-bis(2-methylene-2-tert-butyl-4-methyl-phenolate) ligand [L4], was characterized by single crystal X-ray diffraction. The Co(III) complexes 5–7 were inactive for ROCOP of cyclohexene oxide or propylene oxide but were active for cyclic carbonate formation for a variety of epoxides studied. A maximum turnover frequency of 20 h−1 was attained for conversion of epichlorohydrin to (chloromethyl)ethylene carbonate.

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.

A series of iron(III) chloride and iron(III) μ-oxo compounds supported by tetradentate amino-bis(phenolate) ligands containing a homopiperazinyl backbone were prepared and characterized by electronic absorption spectroscopy, magnetic moment measurement, and MALDI-TOF mass spectrometry. The solid-state structures of three iron(III) μ-oxo compounds were determined by single crystal X-ray diffraction and revealed oxo-bridged bimetallic species with Fe-O-Fe angles between 171.7 and 180°, with the iron centers in distorted square pyramidal environments. Variable temperature magnetic measurements show the oxo complexes exhibit strong antiferromagnetic coupling between two high-spin S = 5/2 iron(III) centers. The oxo complexes exhibit poor activity for the reaction of carbon dioxide and epoxides in the presence of a cocatalyst, under solvent free conditions to yield cyclic carbonates. The least active iron oxo compound bears tert-butyl groups on the phenolate donors, and we propose that steric congestion around the iron center reduces catalytic activity in this case. We provide evidence that an epoxide deoxygenation step occurs when employing monometallic iron(III) chlorido species as catalysts. This affords the corresponding μ-oxo compounds which can then enter their own catalytic cycle. Deoxygenation of epoxides during their catalytic reactions with carbon dioxide is frequently overlooked and should be considered as an additional mechanistic pathway when investigating catalysts.

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.

Amine-bis(phenolato)chromium(iii) chloride complexes, [LCrCl], are capable of catalyzing the copolymerization of cyclohexene oxide with carbon dioxide to give poly(cyclohexane) carbonate. When combined with 4-(N,N-dimethylamino)pyridine (DMAP) these catalyst systems yield low molecular weight polymers with moderately narrow polydispersities. The coordination chemistry of DMAP with five amine-bis(phenolato)chromium(iii) chloride complexes was studied by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The amine-bis(phenolato) ligands were varied in the nature of their neutral pendant donor-group and include oxygen-containing tetrahydrofurfuryl and methoxyethyl moieties, or nitrogen-containing N,N-dimethylaminoethyl or 2-pyridyl moieties. The relative abundance of mono and bis(DMAP) adducts, as well as DMAP-free ions is compared under various DMAP : Cr complex ratios. The [LCr]+ cations show the ability to bind two DMAP molecules to form six-coordinate complex ions in all cases, except when the pendant group is N,N-dimethylaminoethyl (compound 3). Even in the presence of a 4 : 1 ratio of DMAP to Cr, no ions corresponding to [L3Cr(DMAP)2]+ were observed for the complex containing the tertiary sp3-hybridized amino donor in the pendant arm. The difference in DMAP-binding ability of these compounds results in differences in catalytic activity for alternating copolymerization of CO2 and cyclohexene oxide. Kinetic investigations by infrared spectroscopy of compounds 2 and 3 show that polycarbonate formation by 3 is twice as fast as that of compound 2 and that no initiation time is observed.

A one-pot synthesis of poly(ether-co-carbonates) catalyzed by an amino-bis(phenolate) zinc catalyst [L]Zn2Et2(THF) 1 (where [H2L] = n-propylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol) has been developed. Ring-opening polymerization (ROP) of cyclohexene oxide (CHO) can be performed by 1 with and without addition of BnOH or PPNCl as co-catalysts. The ROP of CHO can be inhibited by CO2 pressurization, which leads to the formation of polycarbonate blocks, or presence of other epoxides, which leads to the formation of poly(ether-co-carbonate) containing carbonate linkages and ether linkages. Polycarbonate formation was observed at 1 bar CO2 giving 23% carbonate linkages at this pressure. At 20 bar CO2, 92% carbonate formation was achieved in the presence of limonene oxide (LO). Poly(ether-co-carbonates) from mixtures of epoxides could be synthesized by changes in reaction temperatures and pressures.

Three complexes were prepared using lithium, sodium and potassium reagents and an amine-(bis)phenol proligand. The proligand, benzylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol) (abbreviated H2[L]), was reacted with n-butyllithium to give the lithium complex, Li2[L] (1), and NaH or KH to give the sodium, Na2[L] (2), and potassium, K2[L] (3), complexes, respectively. The compounds were also found to contain varying numbers of coordinated THF molecules. These complexes were characterized using 1H, 13C, and 7Li NMR (for the lithium complex), MALDI-TOF MS, elemental analysis and FT-IR. The potassium complex (3) was characterized in the solid state and exhibits η6 K-arene bonds as well as η1-bonding of the K ion to the ipso-carbons of the phenolate fragments. The reactivity of 1–3 towards the ring-opening polymerization of rac-lactide to form polylactide (PLA) was explored.

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.

Reaction of benzylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H2L1, with anhydrous ferric chloride in the presence of a base yields FeCl(THF)L1 (1). In the solid state, complex 1 exists as a monomeric iron(III) species with a distorted trigonal bipyramidal geometry. Complex 1 is an air-stable, non-hygroscopic, single-component catalyst for C–C cross-coupling of aryl Grignard reagents with benzyl halides, including chlorides. Moderate to good yields of cross-coupled products can be obtained in diethyl ether at room temperature. Preliminary investigations include the screening of electron-donating and electron-withdrawing groups on both the benzylic substrate and the aryl Grignard reagent.

A diamine-bis(phenolate) chromium(III) complex, {CrCl[O2NN'](BuBu)}2 catalyzes the copolymerization of propylene oxide with carbon dioxide. The synthesis of this metal complex is straightforward and it can be obtained in high yields. This catalyst incorporates a tripodal amine-bis(phenolate) ligand, which differs from the salen or salan ligands typically used with Cr and Co complexes that have been employed as catalysts for the synthesis of such polycarbonates. The catalyst reported herein yields low molecular weight polymers with narrow polydispersities when the reaction is performed at room temperature. Performing the reaction at elevated temperatures causes the selective synthesis of propylene carbonate. The copolymerization activity for propylene oxide and carbon dioxide, as well as the coupling of carbon dioxide and styrene oxide to give styrene carbonate are presented.

Chromium(III) chlorido amine-bis(phenolate) complexes paired with nucleophilic co-catalysts are a promising family of catalysts for the copolymerization of CO

A monumental achievement for coordination chemistry that also re-addresses the role of molybdenum in the nitrogenase FeMo cofactor is the discovery of the catalytic reduction of dinitrogen at a well-defined molybdenum complex by protons and electrons (see picture).

A series of cobalt(II), cobalt(III) and mixed valence cobalt(II/III) compounds has been prepared and characterized. The protonated tripodal tetradentate ligand precursors (dimethylaminoethylamino-N,N-bis(2-methylene-4-tert-butyl-6-methylphenol), H2[O2NN′]BuMeNMe2, dimethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H2[O2NN′]BuBuNMe2, and 2-pyridylamino-N,N-bis(2-methylene-4-tert-butyl-6-methylphenol), H2[O2NN′]BuMePy were reacted with cobaltous acetate tetrahydrate under varying conditions to afford a range of monometallic, bimetallic and trimetallic species. Monometallic compounds, 1 and 2, were obtained with pendant amine-containing ligands [O2NN′]BuMeNMe2 and [O2NN′]BuBuNMe2, respectively. Compound 1 is a trigonal bipyramidal CoII acetone adduct, CoII(OCMe2)[O2NN′]BuMeNMe2, and 2 is a distorted octahedral CoIII acetate complex, CoII(OAc)[O2NN′]BuBuNMe2. A dimethoxo-bridged dicobalt(III) complex, 3, was obtained using the pyridyl group-containing ligand, [O2NN′]BuMePy, after oxidation in air of a methanol solution of {Co[O2NN′]BuMePy}2. Two side-products, 4 and 5 were also obtained from this reaction. Complex 4 contains two octahedrally coordinated cobalt(III) atoms, each bonded to a tetradentate amine-bis(phenolate) ligand and bridged by one syn,syn η1:η1:μ2 acetate ligand, and one hydroxide ligand. Complex 5 is a heterotrimetallic compound and consists of two Co[O2NN′]BuMePy fragments, each bridged by a syn,anti η1:η1:μ2 acetate ligand to a central CaII(HOMe)4 fragment. Mixed valence CoIII–CoII–CoIII trimetallic complexes, 6 and 7, were obtained by reaction of H2[O2NN′]BuMePy or H2[O2NN′]BuBuPy ligands, respectively, with Co(OAc)2·4H2O in 2:3 molar ratios in methanol under nitrogen followed by aerobic oxidation. Diethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H2[O2NN′]AmAmNEt2 was reacted with cobaltous chloride hexahydrate under acidic conditions to give the ionic compound {H3[O2NN′]AmAmNEt2}+2[CoCl4]2−, 8.

A series of (amine)bis(phenolato)iron(III)acac complexes has been prepared and characterized. Reaction of Fe(acac)3 with the diprotonated linear tetradentate proligand N,N′-bis(4,6-di-tert-butyl-2-methylphenol)-N,N′-dimethyl-1,2-diaminoethane, H2[L1], and tripodal tetradentate ligand precursors dimethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H2[L2], dimethylaminoethylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H2[L3], 2-methoxyethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H2[L4], 2-methoxyethylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H2[L5], and 2-methoxyethylamino-N,N-bis(2-methylene-4,6-dimethylphenol), H2[L6], produces the distorted octahedral FeIII complexes [L1]Fe(acac) (1), [L2]Fe(acac) (2), [L3]Fe(acac) (3), [L4]Fe(acac) (4), [L5]Fe(acac) (5), and [L6]Fe(acac) (6). In all of these complexes, the phenolato oxygen atoms are cis-oriented. The paramagnetic FeIII complexes 1–6 were also characterized by UV/Vis and IR spectroscopy, mass spectrometry, cyclic voltammetry, and magnetic measurements. Single crystal X-ray molecular structures have been determined for complexes 1, 2, 3, 5, and the proligand H2[L6]. Preliminary investigations of complexes 1–6 for catalytic cross-coupling reactions of aryl Grignard reagents with cyclic and acyclic secondary alkyl halides and benzyl halides were performed. While the activity for cyclohexyl chlorides and bromides was high, cross-coupling of benzyl halides was moderate and 2-bromo- and 2-chlorobutane gave poor yields of cross-coupled product.

Cross-coupling of Grignard reagents with dichloromethane is achieved using iron(III) catalysts. Aryl- and benzylmagnesium bromides show a range of activity toward double C―Cl bond activation resulting in the insertion of methylene fragments between two equivalents of the nucleophilic partner.

The preparation of tetradentate amine-bis(phenol) proligands with dichloro and difluoro substituted phenol groups and their reaction with FeX3 (X = Cl or Br) is described. The compounds, 2-pyridylamino-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L1]; 2-pyridylamino-N,N-bis(2-methylene-4,6-difluorophenol), H2[L2]; dimethylaminoethylamino-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L3]; 2-tetrahydrofurfuryl-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L4]; and methoxyethylamino-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L5] were prepared in aqueous medium and obtained as white powders in good to excellent yield. Ten new iron(III) halide complexes supported by these tetradentate ligands are reported. Representative single crystal X-ray diffraction structures were obtained for H2[L1] and a water adduct of the iron(III) complex, aquachloro{2-pyridylamino-N,N-bis(2-methylene-4,6-dichlorophenolato)}iron(III), 2·H2O. The structure of the proligand H2[L1] shows intramolecular hydrogen bonding. In the solid-state structure, the iron complex exhibits intermolecular hydrogen bonding between the water ligand and the phenolate oxygen of a neighbouring complex. The anhydrous complexes were studied for catalytic activity towards C–C cross-coupling of Grignard reagent nucleophiles with alkyl halide electrophiles.

Reaction of n-propylamino-N,N-bis(2-methylene-4-tert-butyl-6-methylphenol), H(2)L1, n-propylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)L2, and benzylamino-N,N-bis(2-methylene-4-tert-butyl-6-methylphenol), H(2)L3, with anhydrous ferric chloride in the presence of base yields the products, [FeL1(μ-Cl)](2) (1), [FeL2(μ-Cl)](2) (2) and [FeL3(μ-Cl)](2) (3). In the solid state, these complexes exist as chloride-bridged dimers giving distorted trigonal bipyramidal iron(III) ions. Reaction of H(2)L1 with FeBr(3), however, results in the formation of a tetrahedral iron(III) complex possessing two bromide ligands. The amine-bis(phenolate) ligand is bidentate in this complex and bonds to the iron(III) ion via the phenolate O-donors. The central amine donor is protonated, resulting in a quaternized ammonium fragment and the iron(III) centre possesses a negative formal charge. As a result, this complex is zwitterionic and formulated as FeBr(2)L1H (4). Complex 1 is an air-stable, non-hygroscopic, single-component catalyst for C-C cross-coupling of aryl Grignard reagents with primary and secondary alkyl halides, including chlorides. Good to excellent yields of cross-coupled products are obtained in diethyl ether at room temperature. In some cases where low yields are obtained under these conditions, the use of microwave-assisted heating of the reaction mixture can improve yields.

Two lithium amine-bis(phenolate) and four chromium(III) amine-bis(phenolate) complexes have been prepared. The diprotonated tripodal tetradentate ligand precursors 2-tetrahydrofurfuryl-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)[O(2)NO](BuMe); 2-tetrahydrofurfuryl-N,N-bis(2-methylene-4,6-tert-butylphenol), H(2)[O(2)NO](BuBu); 2-pyridylamino-N,N-bis(2-methylene-4,6-methylphenol), H(2)[O(2)NN'](MeMe); and 2-pyridylamino-N,N-bis(2-methylene-4,6-tert-butylphenol), H(2)[O(2)NN'](BuBu); can be lithiated using n-butyllithium. Isolation of the Li(2)[O(2)NO](RR') compounds generates dimeric {Li(2)[O(2)NO](RR')}(2) (R = t-Bu, R' = Me in 1 and R = R' = t-Bu in 2) in the solid state as shown by single-crystal X-ray diffraction. The lithiated ligands were used to prepare a series of Cr(III) complexes. Monometallic complexes are obtained when prepared and purified under strictly anhydrous conditions, giving CrCl(THF)[O(2)NO](RR') (R = t-Bu, R' = Me in 3 and R = R' = t-Bu in 4). However, bimetallic Cr complexes are obtained upon recrystallization in air, where adventitious water reacts with the complex resulting in protonation of one of the phenolate groups of the ligand and generating hydroxide, which bridges two Cr(III) centres. Solid-state single-crystal X-ray diffraction studies of {CrCl[O(2)NN'](MeMe)}(mu-HO){CrCl[HO(2)NN'](MeMe)}, 5, and {CrCl[O(2)NN'](BuBu)}(mu-HO){CrCl[HO(2)NN'](BuBu)}, 6, were performed. The paramagnetic Cr(III) complexes were also characterized by UV-vis spectroscopy, mass spectrometry and magnetic measurements.

Magnesium compounds of tetradentate amino-bis(phenolato) ligands, Mg[L1] (1) and Mg[L2] (2) (where [L1] = 2-pyridyl-N,N-bis(2-methylene-4-methoxy-6-tert-butylphenolato), and [L2] = dimethylaminoethylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolato)) were prepared. The proligands, H2[L1] and H2[L2] were reacted with di(n-butyl)magnesium in toluene to give the desired compounds in high yields. Compounds 1 and 2 exhibit dimeric structures in solutions of non-coordinating solvents as observed by NMR spectroscopy and in the solid state as shown by the single crystal X-ray structure of 2. These compounds exhibit good activity for rac-lactide polymerization in solution and in molten lactide.

The synthesis and structures of isomeric lithium diamine-bis(phenolate) complexes are reported. Deprotonation of the ligands, H2O2NN′tBu [Me2NCH2CH2N(CH2ArOH)2, Ar = 3,5-C6H2-tBu2] and H2O2N2tBu [HOArCH2NMeCH2CH2NMeCH2ArOH, Ar = 3,5-C6H2-tBu2], in diethyl ether affords base-free lithium complexes Li2O2NN′tBu (1) and Li2O2N2tBu (2) upon solvent removal. The dioxane adduct of (1) exhibits a polymeric structure in the solid-state, whereas the dioxane adduct of (2) possesses a dimeric structure. The syntheses of K2O2NN′tBu (3), K2O2N2tBu (4), Zr(O2NN′tBu)Cl2 (5) and Y(O2NN′tBu)Cl(THF), (6), are also reported. The transition metal complexes were isolated in good yields via salt metathesis reactions using 1 or 3.

The niobium(III) chloride precursors R[P2N2]NbCl stabilized by the bis-(amidophosphine) macrocycle (where R[P2N2]=RP(CH2SiMe2NSiMe2CH2)2PR, R=phenyl, Ph, or cyclohexyl, Cy), react with MeMgCl under argon to form the paramagnetic R[P2N2]NbMe (R=Ph, 1; R=Cy, 2) complexes. The methyl complexes 1 and 2 can be stabilized by the donor solvent pyridine to form the paramagnetic adducts R[P2N2]NbMe(py) (R=Ph, 3; R=Cy, 4). Methyl complexes 1 and 2 readily react with N2 to form the diamagnetic dinuclear dinitrogen compounds, (R[P2N2]NbMe)2(μ-N2) (R=Ph, 5; R=Cy, 6), which have been characterized crystallographically. Dinitrogen complex 5 is fluxional and undergoes enantiomeric inversion of the six-coordinate niobium centres via axial rotation about the NbN2Nb axis. Complex 6 shows no enantiomeric inversion, likely due to the steric effects of the cyclohexyl substituents. The dinitrogen ligand itself is labile at elevated temperatures and undergoes reversible dissociation; the dinitrogen complexes are reformed upon cooling to room temperature. Reaction of 5 and 6 with CO displaces the N2 fragment forming the bridging acyl complexes (R[P2N2]Nb)2(μ-COCH3)2 (R=Ph, 7; R=Cy, 8) where the carbonyl fragments bond to the metal centres in a η2 fashion. Addition of H2 to 5 and 6 results in the formation of the previously reported paramagnetic dinuclear dinitrogen complex, (R[P2N2]Nb)2(μ-N2).

Cobalt complexes of tetradentate amine-phenolate ligands were studied for their potential in coupling carbon dioxide with propylene oxide under neat reaction conditions. Cobalt(II) complexes afforded catalytic systems with higher TONs than analogous cobalt(III) compounds. Tetrabutylammonium bromide (TBAB) and PPN+N3- were effective co-catalysts whereas N,N-dimethylaminopyridine (DMAP) shut down reactivity. Ligands containing a pendant pyridyl donor afforded more active catalysts than those containing dimethylamine groups. Reactions proceeded well at room temperature under moderate pressures of carbon dioxide.

Hydrogenolysis of R[P2N2]NbCH2SiMe3 (where R[P2N2] = RP(CH2SiMe2NSiMe2CH2)2PR; R = cyclohexyl, Cy, or phenyl, Ph) in benzene or toluene causes hydride addition to the aromatic solvent resulting in ...

The coordination chemistry of the two mixed donor macrocyclic ligands R[P2N2] (where R[P2N2] = RP(CH2SiMe2NSiMe2CH2)2PR, R = cyclohexyl (Cy) or phenyl (Ph)) with niobium(III) is presented. The reaction of the dilithio precursors R[P2N2]Li2(S) (R = Cy, S = THF; R = Ph, S = 1,4-dioxane) with NbCl3(DME) (DME = 1,2-dimethoxyethane) generates the complexes R[P2N2]NbCl (R = Cy, 1; R = Ph, 2). For R = Cy, single-crystal X-ray diffraction studies and variable-temperature magnetic susceptibility measurements indicate that 1 is mononuclear in the solid state; however, analogous variable-temperature magnetic data suggest that 2 is dinuclear in the solid state due to the observation of antiferromagnetic exchange. In solution, 2 is apparently monomeric similar to 1. Adduct formation between these mononuclear complexes is also evident; reaction of 2 with neutral donors and coordinating solvents produces the mononuclear derivatives Ph[P2N2]NbCl(L) (L = py, CO, PMe3, THF, MeCN), of which the pyridine adduct, 3e, has been...

The syntheses and X-ray crystal structures of the oxidized indenyl-diphosphines, 1,3-(Ph 2 PX) 2 C 9 H 6 , where X is O, S, are reported. The sulfur complex is readily deprotonated to form the corresponding 1,3-disubstituted indenide anion, which yields a crystallographically-characterized η 5 -Mn(CO) 3 complex upon treatment with bromopentacarbonylmanganese. The relevance of these molecules to mixed-metal catalytic systems is discussed.

The title reaction affords diarylmethanes (III) in highly variable yields and significant amounts of homo-coupled by-products.

International audience; 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.

Lithium compounds of tetradentate amino-bis(phenolato)-tetrahydrofuranyl ligands, Li(2)[L1] (1) and Li(2)[L2] (2) (where [L1] = 2-tetrahydrofuranyl-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate), and [L2] = 2-tetrahydrofuranyl-N,N-bis(2-methylene-4,6-tert-butylphenolate)) were characterized by multinuclear solution NMR and solid-state (6)Li and (7)Li NMR spectroscopy. The proligands, n-propylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), (H(2)[L3]) and benzylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H(2)[L4] were reacted with n-butyllithium in THF to give the related dilithium compounds Li(2)[L3] (4) and Li(2)[L4] (5), respectively. The pyridine adduct of 1, (py)(2)Li(2)[L1] (3) and complexes 4 and 5 have been structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy. The reactivity of these complexes for the ring-opening polymerization of rac-lactide, as well as the influences of monomer concentration, monomer/Li molar ratio, polymerization temperature and time, were studied.

Tetradentate aminebis(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.

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.

The inorganic and coordination chemistry of zirconium and hafnium is described. The physical properties of the metals, as well as their isolation, purification, and commercial and industrial uses are discussed. A section on the binary compounds of zirconium and hafnium containing hydride and main group elements follows. Oxoacid salts of the two metals are described, as well as aqueous chemistry. Examples of zirconium and hafnium coordination chemistry are presented according to ligand type: molecular and silica-supported hydride complexes; ionic and neutral halide complexes; complexes with oxygen donor ligands; complexes with nitrogen donor ligands; dinitrogen complexes; complexes with phosphorus and sulphur donors ligands; complexes with mixed-donor ligands. Lastly, lower oxidation state inorganic, coordination, and cluster compounds are discussed. Keywords: zirconium; hafnium; catalysis; dinitrogen complexes; early transition metals

A simple and practical method for the synthesis of the compounds (II) with a readily available additive is developed.

A dinuclear amine-bis(phenolate) iron complex (I) or FeCl3 are used in the cross-coupling of Grignard reagents with dichloromethane to give diarylmethanes and diarylethanes.

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

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.

Here we demonstrate how para-hydrogen can be used to prepare a two-spin system in an almost pure state which is suitable for implementing nuclear magnetic resonance (NMR) quantum computation. A 12ns laser pulse is used to initiate a chemical reaction involving pure para-hydrogn (the nuclear spin singlet of H2). The product, formed on the microsecond timescale, contains a hydrogen derived two-spin system with an effective spin-state purity of 0.916. To achieve a comparable result by direct cooling would require an unmanageable (in the liquid state) effective spin temperature of 6.4mK or an impractical magnetic field of 0.45MT at room temperature. The resulting spin state has an entanglement of formation of 0.822 and cannot be described by local hidden variable models., Comment: 4 pages including 2 figures. Changes from v.3 at request of referees. Now in press at Physical Review Letters