Manfred Bochmann

Titanium, zinc and alkaline-earth metal complexes supported by bulky O,N,N,O-multidentate ligands: syntheses, characterisation and activity in cyclic ester polymerisation.

The reactions of the bulky amino-bis(phenol) ligand Me(2)NCH(2)CH(2)N[CH(2)-3,5-Bu(t)(2)-C(6)H(2)OH-2](2)(1-H(2)) with Zn[N(SiMe(3))(2)](2)(4), [Mg[N(SiMe(3))(2)](2)](2)(5) and Ca[N(SiMe(3))(2)](2)(THF)(2)(6) yield the complexes 1-Zn, 1-Mg and 1-Ca in good yields. The X-ray structure of 1-Ca showed the complex to be dimeric, with calcium in a distorted octahedral coordination geometry. Five of the positions are occupied by an N(2)O(3) donor set, while the sixth is taken up by an intramolecular close contact to an o-Bu(t) substituent, a rare case of a Ca...H-C agostic interaction (Ca...H distances of 2.37 and 2.41 Angstroms). Another sterically hindered calcium complex, Ca[2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)O](2)(THF)(2).(C(7)H(8))(2/3)(7), was prepared by reaction of 6 with the iminophenol 2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)OH (3-H). According to the crystal structure 7 is monomeric and octahedral, with trans THF ligands. The complex Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(2)(2-Ti) was prepared by treatment of Ti(OPr(i)(4)) with the new amino-bis(phenol) Me(2)NCH(2)CH(2)N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)OH-2](2)(2-H(2)). The reduction of 2-Ti with sodium amalgam gave the titanium(III) salt Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(2).Na(THF)(2)(8). A comparison of the X-ray structures of 2-Ti and 8 showed that the additional electron in 8 significantly reduced the intensity of the pi-bonding from the oxygen atoms of the isopropoxide groups to titanium. 1-Ca and 8 were active initiators for the ring-opening polymerisation of epsilon-caprolactone (up to 97% conversion of 200 equivalents in 2 hours) and yielded polymers with narrow molecular weight distributions.

Gold peroxide complexes and the conversion of hydroperoxides into gold hydrides by successive oxygen-transfer reactions

Gold catalysts are widely studied in chemical and electrochemical oxidation processes. Computational modelling has suggested the participation of Au-OO-Au, Au-OOH or Au-OH surface species, attached to gold in various oxidation states. However, no structural information was available as isolable gold peroxo and hydroperoxo compounds were unknown. Here we report the syntheses, structures and reactions of a series of gold(III) peroxides, hydroperoxides and alkylperoxides. The Au-O bond energy in peroxides is weaker than in oxides and hydroxides; however, the Au-OH bond is also weaker than Au-H. Consequently Au-OH compounds are capable of oxygen-transfer generating gold hydrides, a key reaction in a water splitting cycle and an example that gold can react in a way that other metals cannot. For the first time it has become possible to establish a direct connection from peroxides to hydrides: Au-OO-Au→Au-OOH→Au-OH→Au-H, via successive oxygen-transfer events.

A Thermally Stable Gold(III) Hydride: Synthesis, Reactivity, and Reductive Condensation as a Route to Gold(II) Complexes†

Going for gold: The first thermally stable gold(III) hydride [(C N C)*AuH] is presented. It undergoes regioselective insertions with allenes to give gold(III) vinyl complexes, and reductive condensation with [(C N C)*AuOH] to the air-stable Au(II) product, [(C N C)*(2)Au(2)], with a short nonbridged gold-gold bond.

Cyclometallated gold(III) hydroxides as versatile synthons for Au–N, Au–C complexes and luminescent compounds

The gold(III) hydroxide κ(3)-(C^N^C)*Au(OH) reacts with C-H and N-H compounds and arylboronic acids to produce a range of perfluoroaryls, N-heterocyclic and alkynyl compounds in high yields; some of which show unexpectedly strong modulation of their photoluminescence from yellow to blue [(C^N^C)* = 2,6-(C(6)H(3)Bu(t))(2)pyridine].

Monocyclopentadienyl phenoxy-imine and phenoxy-amine complexes of titanium and zirconium and their application as catalysts for 1-alkene polymerisation

Abstract Deprotonation of the phenol-imines 2-But-6-(RNCH)C6H3OH (R=2,4,6-Me3C6H2 (1a), C6F5 (1b), C6H11 (1c) and phenol-amines 2,4-But2-6-(R′NCH2)C6H2OH (R′=C4H8 (1d), C5H10 (1e)) with n-BuLi gives the corresponding lithium phenoxides. The reaction with MCl4 in THF solution leads to the bis(ligand) complexes {2-But-6-(RNCH)C6H3O}2MCl2 and {2,4-But2-6-(R′NCH2)C6H2O}2MCl2 (M=Ti: 2a, 2d, 2e, Zr: 3a, 3d and 3e). The cyclopentadienyl phenoxy-imine and -amine complexes Cp{2-But-6-(RNCH)C6H3O}MCl2 and Cp{2,4-But2-6-(R′NCH2)C6H2O}MCl2 (M=Ti: 4a–4e, Zr: 5a–5e) were prepared similarly through reaction with CpMCl3. The crystal and molecular structures of 2a, 3a, 4a and 4e have been determined. 2a and 3a are isostructural and exhibit a distorted octahedral geometry. 4a has a distorted square-pyramidal structure whereas 4e is essentially tetrahedral and the nitrogen does not coordinate. All new complexes are active for the polymerisation of ethene when activated with methyaluminoxane. 4b, 5a, 5d and 5e are active for the copolymerisation of ethene and 1-hexene and the oligomerisation of 1-hexene.

Cationic group IV metal alkyl complexes and their role as olefin polymerization catalysts: The formation of ethyl-bridged dinuclear and heterodinuclear zirconium and hafnium complexes

Abstract Bis(cyclopentadienyl)hafnium diethyl (1) reacts with [CPh3][B(C6F5)4] in dichloromethane at −60 °C with hydride rather than alkyl transfer to give triphenylmethane and the ethyl-bridged dinuclear complex [(Cp2HfEt)2(μ-Et)][B(C6F5)4] (2). The complex is less stable than analogous methyl complexes but is stabilized by the presence of excess Cp2HfEt2. The reaction between Cp2HfEt2, [CPh3][B(C6F5)4], and AlEt3 under analogous conditions leads to [Cp2Hf(μ-Et)2AlEt2][B(C6F5)4] (3). The reaction between Cp2 HfMe2 and AlEt3 leads to alkyl ligand exchange to give, successively, Cp2Hf(Me)(Et) and Cp2 HfEt2. Similar fast ligand exchange reactions, take place between Cp′2ZrMe2 and AlEt3 and can be used for generating the thermally labile complex Cp′2ZrEt2 as a precursor for cationic polymerization catalysts [Cp′2 = Cp2, rac-Me2Si(Ind)2]. Polymerization activities of rac-[Me2Si(Ind)2Zr(μ-R)2AlR2][B(C6F5)4] increase in the order R = Me

Cationic Group 4 metallocene complexes and their role in polymerisation catalysis: the chemistry of well defined Ziegler catalysts

Cationic alkyl complexes of Group 4 metallocenes of the type [MCp2R]+(M = Ti, Zr or Hf, Cp = C5H5) have been recognised as the catalytically active species in metallocene-based olefin polymerisation catalysts. These highly electrophilic 14-electron species possess a very complex chemistry in which the formation of temporarily dormant stabilised adducts plays a dominant role. Cationic metal alkyls of this kind are found to be extremely active polymerisation catalysts, with high stereoselectivities and the potential to produce numerous previously inaccessible polymeric materials. A detailed understanding of the chemistry of these species promises to lead to a new generation of well defined polymerisation catalysts. Metallocene-based catalysts already play an increasing role in major industrial polymerisation processes.

Gold(III) Olefin Complexes

Zeises salt gets company: 185 years after the report of the well-known platinum(II) ethylene compound, examples of isolable olefin complexes of its isoelectronic neighbor in the periodic table, gold(III), have been prepared (see picture). The complexes are very susceptible towards nucleophilic attack; there is also structural evidence for Au-Ag interactions. Copyright

Base-free cationic 14-electron alkyls of Ti, Zr and Hf as polymerisation catalysts: A comparison

The reaction of CP′2MMe2 (M  Ti, Zr, or Hf) with either [CPh3]+ or [PhNHEt2]+ salts of non-coordinating anions gives new cationic [Cp′2MMe]+ catalysts. The ethene polymerisation activity increases in the order M  Ti « Hf < Zr; the activity of the Zr and Hf complexes is comparable with that of CP2MCl2 /methylaluminoxane systems (Cp′  C5H4SiMe3).

Half-sandwich complexes of titanium and zirconium with pendant phenyl substituents. The influence of ansa-aryl coordination on the polymerisation activity of half-sandwich catalysts

Abstract Benzyl-substituted Group 4 half-sandwich complexes (η5-C5H4R)TiCl3 (1a, R=CMe2Ph; 2a, R=CMe2CH2Ph; 4a, R=SiMe2Ph; 5a, R=CHPh2) are readily accessible from C5H4(R)SiMe3 and TiCl4, while the reaction of C5H4(CMe2CH2Ph)SiMe3 with ZrCl4(SMe2)2 affords (C5H4CMe2CH2Ph)ZrCl3·dme (3a). The structures of 1a, 4a and 5a have been determined by X-ray diffraction; the compounds are monomeric in the solid state. Alkylation readily affords the corresponding trimethyl and tribenzyl derivatives; the crystal structure of (η5-C5H4CHPh2)Ti(CH2Ph)3 (5b) has been determined. Treatment of (η5-C5H4R)MMe3 with [Ph3C]+[B(C6F5)4]− in dichloromethane at low temperatures generates cationic [(η5-C5H4R)MMe2]+ complexes; the complexes are stabilised by π-coordination to the phenyl ring to give ansa-arene complexes with one- and two-carbon linkages. The complexes catalyse the polymerisation of propene. Compared to the system Cp*TiMe3/B(C6F5)3 the ansa complexes show reduced catalytic activity and enhanced chain termination.