Simon J. Lancaster

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

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).

Role of B(C 6 F 5 ) 3 in catalyst activation, anion formation, and as C 6 F 5 transfer agent* , **

The versatile reactivity of B(C6F5)3 in alkene polymerization reactions is summarized. Adduct formation with basic anions such as CN– and NH2– gives extremely weakly co- ordinating diborates, which are the basis of some of the most active polymerization catalysts known to date. By contrast, the reaction of B(C6F5)3 with zirconium half-sandwich complexes leads to extensive C6F5 transfer, including the surprising formation of borole-bridged triple decker complexes. Main group alkyls undergo such C6F5 exchange reactions very readily unless donor ligands are present. Borate salts of new three-coordinate zinc alkyl cations proved to be highly effective catalysts for the ring-opening polymerization of epoxides and lactones.

Highly Selective and Immortal Magnesium Calixarene Complexes for the Ring‐Opening Polymerization of rac‐Lactide

The lithiation of 1,3‐dipropoxy‐p‐tert‐butylcalix[4]arene (LH2) followed by reaction with nBuMgBr in THF resulted in the formation of the hetero‐bimetallic complex [Li(THF)Mg(nBu)L] (1). By contrast, the treatment of tripropoxy‐p‐tert‐butylcalix[4]arene (L′H) with nBu2Mg afforded a mononuclear complex [L′Mg(nBu)] (2). Single‐crystal XRD studies revealed that in both structures the calix[4]arene adopts a cone conformation, and a Li cation resides in the cavity for 1. Both 1 and 2 were active for the ring‐opening polymerisation of rac‐lactide. Compound 2 displayed not only exceptional activity (100 equivalents, 3 min, 92 % conversion, BnOH, room temperature) but also high selectivity (probability to form an r dyad, Pr=0.85) and exhibited an immortal character in THF. Surprisingly, compound 2 also showed isotactic bias (Pr=0.30–0.36) and an immortal character if toluene was employed as the solvent; 2 D J‐resolved 1H NMR spectroscopy was employed for the assignment of the stereoselectivity.

Luminescent Gold(III) Thiolates: Supramolecular Interactions Trigger and Control Switchable Photoemissions from Bimolecular Excited States

Abstract A new family of cyclometallated gold(III) thiolato complexes based on pyrazine‐centred pincer ligands has been prepared, (C^Npz^C)AuSR, where C^Npz^C=2,6‐bis(4‐ButC6H4)pyrazine dianion and R=Ph (1), C6H4 tBu‐4 (2), 2‐pyridyl (3), 1‐naphthyl (1‐Np, 4), 2‐Np (5), quinolinyl (Quin, 6), 4‐methylcoumarinyl (Coum, 7) and 1‐adamantyl (8). The complexes were isolated as yellow to red solids in high yields using mild synthetic conditions. The single‐crystal X‐ray structures revealed that the colour of the deep‐red solids is associated with the formation of a particular type of short (3.2–3.3 Å) intermolecular pyrazine⋅⋅⋅pyrazine π‐interactions. In some cases, yellow and red crystal polymorphs were formed; only the latter were emissive at room temperature. Combined NMR and UV/Vis techniques showed that the supramolecular π‐stacking interactions persist in solution and give rise to intense deep‐red photoluminescence. Monomeric molecules show vibronically structured green emissions at low temperature, assigned to ligand‐based 3IL(C^N^C) triplet emissions. By contrast, the unstructured red emissions correlate mainly with a 3LLCT(SR→{(C^Npz^C)2}) charge transfer transition from the thiolate ligand to the π⋅⋅⋅π dimerized pyrazine. Unusually, the π‐interactions can be influenced by sample treatment in solution, such that the emissions can switch reversibly from red to green. To our knowledge this is the first report of aggregation‐enhanced emission in gold(III) chemistry.

Mononuclear Ti[triple bond]N complexes formed by the facile multiple deprotonation of H3N x B(C6F5)3: the importance of chloride ligands.

The crystalline ion-pair [TiCl(NMe(2))(2)(NMe(2)H)(2)](+)[TiCl(2){NB(C(6)F(5))(3)}(NMe(2)H)(2)](-), in which the anion has a triply bonded nitridoborate ligand, is formed through the multiple activation of H(3)N x B(C(6)F(5))(3) when treated with [Ti(NMe(2))(3)Cl].

Tris(dimethylamido)bis(dimethylamine)titanium(IV) chloridobis(dimethylamine)[tris(pentafluorophenyl)boron-amido][tris(pentafluorophenyl)boron-nitrido]titanate(IV) toluene solvate.

The title ionic solid, [Ti(C(2)H(6)N)3(C(2)H(7)N)2][Ti(C(18)BF(15)N)(C(18)H(2)BF(15)N)Cl(C(2)H(7)N)(2)].C(7)H(8), (I), comprises a cation with three dimethylamide ligands in the equatorial plane and two dimethylamine ligands positioned axially in a trigonal-bipyramidal geometry about the central Ti(IV) atom. The anion has a highly distorted octahedral structure. The two dimethylamine ligands are coordinated mutually trans. The chloride is trans to the tris(pentafluorophenyl)boron-amide, while the sixth coordination site is occupied by an ortho-F atom of the tris(pentafluorophenyl)boron-amide group in a trans disposition with respect to the tris(pentafluorophenyl)boron-nitride ligand. The most significant feature of the anion is the presence of an unprecedented terminal Ti[triple-bond]N moiety [1.665 (2) A], stabilized by coordination to B(C(6)F(5))(3), with a Ti[triple-bond]N-B angle of 169.50 (19) degrees.

New titanium and zirconium complexes with M-NH2 bonds formed by facile deprotonation of H3N.B(C6F5)3.

Facile deprotonation of H3N.B(C6F5)3 with [M(NMe2)4](M = Zr or Ti) yields the novel amidoborate complexes [Zr(NMe2)3{NH2B(C6F5)3}(HNMe2)] and [Ti(NMe2)3{NH2B(C6F5)3}].

Anionic and zwitterionic metallocene complexes derived from novel boratocyclopentadienyl ligands

Borate-substituted di- and tri-anionic cyclopentadienyi ligands [X3B–C5H4]2– and [X2B(C5H4)2]3–-(X = C6F5) give anionic group 4 metallocene complexes which provide a facile route to zwitterionic ‘single-component’ alkene polymerisation catalysts.