John A. Segal

Low coordinate magnesium chemistry supported by a bulky β-diketiminate ligand

A series of magnesium(II) alkyl, alkoxide, carboxylate, amide and halide complexes stabilised by the bulky β-diketiminate ligand, HC(C(Me)N-2,6-iPr2C6H3)2 (BDI), have been synthesised and structurally characterised. (BDI)H reacts with MgMe2 in Et2O to give the four-coordinate complex (BDI)MgCH3(Et2O), 1, and in toluene to afford [(BDI)Mg(μ-CH3)]2, 2. Three coordinate complexes may be accessed by increasing the size of the alkyl ligand; hence, the reaction of (BDI)H with tBu2Mg yields (BDI)MgtBu, 3, while Li(BDI) reacts with iPrMgCl to afford (BDI)MgiPr, 4; a similar reaction with PhMgCl affords the diethyl ether adduct (BDI)MgPh(Et2O), 5. The etherates 1 and 5 may be converted into the base-free complexes, 2 and (BDI)MgPh, 6, respectively, upon heating in vacuo. The direct reaction of (BDI)H with RMgX (X = Cl or Br) results in relatively inert halide-bridged dimers of formula [(BDI)Mg(μ-X)]2, (X = Cl, 7; X = Br, 8). The alkylmagnesium derivatives react readily with alcohols, amines or carboxylic acids to yield alkoxide, amide and carboxylate complexes, respectively. For example, 4 reacts with iPrOH (or O2) to form [(BDI)Mg(μ-OiPr)]2, 9. Convenient one-pot synthetic procedures have been developed using commercially available Bu2Mg. Treatment of Bu2Mg with (BDI)H, followed by its reaction with MeOH, tBuOH, iPr2NH, (Me3Si)2NH, MeCO2H or PhCO2H affords [(BDI)Mg(μ-OMe)]2, 10, [(BDI)Mg(μ-OtBu)]2, 11, (BDI)Mg(NiPr2), 12, (BDI)Mg(NTMS2), 13, [(BDI)Mg(μ-O2CMe])]2, 14, and [(BDI)Mg(μ-O2CPh)]2, 15, respectively. The molecular structures of complexes 4–8 and 12–15 are reported.

Pendant arm Schiff base complexes of aluminium as ethylene polymerisation catalysts

The potentially tridentate Schiff base ligands [3,5-But2-2-(HO)C6H2CHNL] 1, on reaction with Me3Al at room temperature, afford the complexes [(3,5-But2-2-(O)C6H2CHNL)AlMe2] [L = CH2CH2NMe2 2a, (2-PhO)C6H4 2b, 2-CH2C5H4N 2c and 8-C9H6N (quinoline) 2d], 2a and 2c have been characterised crystallographically; further reaction of the dimethyl compounds with B(C6F5)3 affords the cationic systems [(3,5-But2-2-(O)C6H2CHNL)AlMe]+ 3a–d of which 3a and 3b are ethylene polymerisation catalysts.

Mono(η-cyclopentadienyl)molybdenum chemistry: acetylene, tertiary phosphine, and related derivatives

Displacement of chloride in [Mo(η-C5H5)(η-C6H6)Cl] gives [Mo(η-C5H5)(η-C6H6)L][PF6], [L = PPh3, PMe2Ph, CO, C2H4, C2H2, or C2(CO2Me)2] or [Mo(η-C5H5)(η-C6H6)X](X = H or Me). Loss of benzene gives rise to [Mo(η-C5H5)(dppe)2][PF6], [Mo(η-C5H5)Cl(O)2], [Mo(η-C5H5)Cl2O], and [Mo(η-C5H5)(η-C8H8)][PF6]. Replacement of dppe in [Mo(η-C5H5)(dppe)2][PF6](or [BF4]) leads to the salts [Mo(η-C5H5)(dppe)L2][PF6], [L2=(CO)(NCMe), (CO)2, η4-C6H8, C4H6, C2Me2· or C2Ph2]. Oxidation of [Mo(η-C5H5)(dppe)2][BF4] by iodine gives paramagnetic [Mo(η-C5H5)(dppe)2][PF6]2. The compound [Mo(η-C5H5)(η-C8H8)][PF6] reacts with L = CO or PPh3 giving [Mo(η-C5H5)(η-C8H8)L][PF6] and with Ph2P[CH2]2PPh2(dppe) giving [Mo(η-C5H5)(η4-C8H8)-(dppe)][PF6]. The compound [Mo(η-C5H5)(η4-C4H6)(dppe)][PF6] exists in solutions as a mixture of isomers. These react with Na[Al H2(OCH2CH2OMe)2] giving a separable mixture of the η3-3-methylally compounds [Mo-(η-C5H5)(η3-MeCHCHCH2)(dppe)] where the allyllc group is oriented ‘up’ or ‘down’ relative to the η-C5H5 ring.

Synthesis and characterisation of neutral and cationic alkyl aluminium complexes bearing N,O-Schiff base chelates with pendant donor arms

The Schiff base ligands [3,5-But2-2-(OH)C6H2CHNL] [L = CH2CH2NMe2 (1a), 2-(PhO)C6H4 (1b), 2-CH2C5H3N (1c), 8-C9H6N (quinoline) (1d) and 2-(PPh2)C6H4 (1e)] are accessed in good yields (>85%) via standard imine condensation reactions. Reaction of 1a–e with Me3Al at room temperature affords the corresponding complexes [(3,5-But2-2-(O)C6H2CHNL)AlMe2] (2a–e); in the case of L = 8-quinoline, the same reaction conducted in refluxing toluene affords binuclear {[3,5-But2-2-(O)C6H2CHMeN-8-C9H6N]AlMe}2 (3) by methyl migration from metal to ligand. Further reaction of the dimethyl compounds with B(C6F5)3 in CD2Cl2 or C6D6 affords the cationic systems [(3,5-But2-2-(O)C6H2CHNL)AlMe]+ (4a–e). The crystal structures of 2a, 2c, 2e and 3 have been determined. In 2a and 2c the respective ligands bind to the metal centre via all three heteroatoms, the aluminium having a trigonal bipyramidal geometry, whereas in 2e coordination is via nitrogen and oxygen only, and the aluminium is tetrahedral. Complex 3 has a dimeric structure with the ligand adopting both tridentate and binucleating roles; the aluminium centres are trigonal bipyramidal.

Synthesis of fluorinated block copolymers and their application asnovel polymerisation surfactants in supercritical carbon dioxide

Screened anionic copolymerisation of methyl methacrylate with the perfluoroalkyl methacrylates 2 affords well-defined AB block copolymers 4–6, which serve as effective surfactants in the dispersion polymerisation of methyl methacrylate in supercritical carbon dioxide.

Formation of substituted cyclohexadienyl tricarbonylmanganese complexes by nucleophilic addition reactions of functionally substituted (η-arene)tricarbonylmanganese cations

Cyclohexadienyl and 6-exo-methyl- or -phenyl-cyclohexadienyl complexes bearing halogeno-, alkoxy-, or dialkyl-amino-substituents in the 1- or 2-positions are obtained by reaction of lithium tetrahydridoaluminate or methyl-or phenyl-lithium with the appropriately substituted (η-arene)tricarbonylmanganese salt. Directive effects in these nucleophilic additions are compared with those observed for arene complexes of iron and chromium.

Some reactions of nitrosyl complexes of nickel, palladium, and platinum

The reactions of [Ni(NO2)XL2][X = Cl, L =½ dppe (dppe = Ph2PCH2CH2PPh2), PPh3, PPrn3, OPPh3, or NC5H5; X = Br, L =½ dppe or PPh3; X = NO2, L =½ dppe] and trans-[M(NO2)2L2](M = Pd, L = PEt2Ph or PEt3; M = Pt, L = PEt2Ph, PEt3, or PBun3) with carbon monoxide have been examined. The nickel compounds react to produce the corresponding nitrosyl compounds [Ni(NO)XL2] and CO2. The palladium and platinum compounds react with CO to form [M(CO)2L2] complexes and subsequently higher clusters, except for [Pt(NO2)2(PEt3)2] where evidence for the formation of [Pt(NO)(NO2)(PEt3)2] and [Pt(NCO)(NO2)(PEt3)2] has been found. On reaction with dioxygen the compounds [Ni(NO)XL2] afford the nitro-complexes [Ni(NO2)XL2] exclusively, the rate of the reaction depending on L. The compound [Pt(NO)(NO3)(PPh3)2], prepared from the reaction of N2O4 with [Pt(PPh3)4] in toluene, reacts with O2 to produce trans-[Pt(NO3)2(PPh3)2]. In solution, [Pt(NO)(NO3)(PPh3)2] undergoes an intramolecular reaction to form [Pt(NO2)2(PPh3)2]. The complex [Pt(N2O2)(PPh3)2] reacts with [NO][PF6] to form [{Pt(PPh3)2}2N2O2][PF6]2.

Transition-metal nitrosyl compounds. Part IX. The preparation and study of the osmium cation [OsH2(CO)(NO)L2]+(L = triphenyl- or tricyclohexyl-phosphine

The dihydrides [OsH2(CO)(NO) L2] PF6[L = PPh3(1) or P(C6H11)3(2)] have been prepared from the reaction of Os(CO)(NO)L2Cl and AgPF6 in the presence of H2. 1H N.m.r. data indicate that these compounds are stereo-chemically non-rigid and ΔG‡Tc values of 48·5 ± 0·8 kJ mol–1 and 53·1 ± 0·8 kJ mol–1 have been determined for (1) and (2) respectively. On reaction with CO the dihydrides readily undergo H2 displacement to give the salts [Os(CO)2(NO) L2] PF6. Complex (1) reacts similarly with PPh3 to give [Os(CO)(NO)(PPh3)3]PF6 but complex (2) reacts with P(C6H11)3 to form the neutral complex OsH(CO)(NO){P(C6H11)3}2 by H+ abstraction.

Titanium mediated anionic polymerisation of methyl methacrylate

Polymerisation of methyl methacrylate using a tris(isopropoxy)titanium ester enolate and an analogous ‘ate’ complex is investigated; the latter affords poly(methyl methacrylate) in high yields with narrow polydispersity.

Syntheses and structures of nickel(0) complexes containing the methyl methacrylate monomer as ligand

The reaction of [Ni(η4-C8H12)2] with the industrially important monomer methyl methacrylate, CH2C(Me)CO2Me, in the presence of 1 or 2 mol equivalents of tricyclohexylphosphine leads to the formation of [Ni{η2-CH2C(Me)CO2Me}{P(C6H11)3}2]1 and [Ni{η2-CH2C(Me)CO2Me}2{P(C6H11)3}]2, respectively. The crystal structures of 1 and 2 have been determined and reveal an η2-CC mode of co-ordination of the methyl methacrylate ligands, with the CO2Me groups pendant and outside the nickel co-ordination sphere. Complexes 1 and 2 represent the first structurally characterised methyl methacrylate complexes; 2 is formed as a mixture of meso and DL diastereomers in the ratio 2.34:1. Solution NMR studies indicate that the diastereomers interconvert rapidly, via an intramolecular mechanism, which is proposed to proceed via an O-co-ordinated intermediate. Reaction of 1 with an excess of tert-butyl acrylate CH2CHCO2But yields [Ni(η2-CH2CHCO2But)2{P(C6H11)3}]4, which may be prepared independently from [Ni(η4-C8H12)2], P(C6H11)3 and tert-butyl acrylate.