Stuart R. Dubberley

A remarkable inversion of structure–activity dependence on imido N-substituents with varying co-ligand topology and the synthesis of a new borate-free zwitterionic polymerisation catalyst

Ethylene polymerisation productivities of tris(pyrazolyl)methane-supported catalysts [Ti(NR){HC(Me2pz)3}Cl2] show a dramatically different dependence on the imido R-group compared to those of their TACN analogues, attributed to differences in fac-N3 donor topology; when treated with AliBu3, the zwitterionic tris(pyrazolyl)methide compound [Ti(N-2-C6H4tBu){C(Me2pz)3}Cl(THF)] also acts as a highly active, single site catalyst (TACN = 1,4,7-trimethyltriazacyclononane).

Discovery and evaluation of highly active imidotitanium ethylene polymerisation catalysts using high throughput catalyst screening

A family of ca. 50 imidotitanium precatalysts [Ti(NR)(Me(3)[9]aneN(3))Cl(2)](R = alkyl or aryl; Me(3)[9]aneN(3)= 1,4,7-trimethyltriazacyclononane) were prepared in good yields using semi-automated procedures; high-throughput screening techniques identified seven highly active ethylene polymerisation precatalysts with activities in the range ca. 3 400 to 10 000 kg(PE) mol(-1) h(-1) bar(-1).

Synthesis of TiN thin films from titanium imido complexes

Thin films have been formed on glass by low pressure chemical vapour deposition from eleven closely related single-source precursors of generic form [TiCl2(NR)(L)x] (where x = 1, L = tridentate N-ligand; x = 2, 3, L = monodentate N-ligand). Most of the precursors formed titanium nitride films, however, bulkier imido complexes and those with chelating ligands tended to produce thin films with significant oxygen and carbon contamination, suggesting incomplete decomposition and post reaction oxidation. The best single-source precursor was found to be [TiCl2(NtBu)(py)3], which gave gold-coloured films of stoichiometric TiN1.0. Despite the coordination environment around the metal being essentially the same and the materials having comparable volatility, significant differences in film quality were observed.

Unexpected features of stretched Si–H⋯Mo β-agostic interactions

Coupling of silanes with the imido group of (Ar′N)2Mo(PMe3)3 gives either the silanimine dimer (ArN–SiHCl)2 or Si–H agostic silylamido complexes which do not exhibit the commonly expected correlation between the nature of the substituents on silicon, the degree of Si–H addition and the value of the Si–H coupling constant.

Lanthanide mono(borohydride) complexes of diamide-diamine donor ligands: novel single site catalysts for the polymerisation of methyl methacrylate

Samarium chloride and borohydride complexes of the diamide-diamine ligands (2-C5H4N)CH2N(CH2CH2NR)2(R = SiMe3 or mesityl) are described; the borohydride compounds are the first polydentate amide-supported single component lanthanide catalysts for the controlled polymerisation of polar monomers, and also represent the first lanthanide borohydride complex for the polymerisation of methyl methacrylate.

A new diamido-amine ligand based on three-carbon atom “arms”: synthesis, structures and polymerisation capability of zirconium derivatives of MeN(CH2CH2CH2NSiMe3)2

Zirconium compounds of the new diamido-amine ligand MeN(CH(2)CH(2)CH(2)NSiMe(3))(2) feature significantly different molecular structures and considerably improved olefin polymerisation characteristics in comparison with analogous compounds based on the two-carbon arm homologues.

Synthesis and reactivity of the imidotungsten methyl cation [W(N2Npy)(NPh)Me]+: CO2 adds to the WNPh bond and does not insert into the W–Me bond

The imidotungsten dimethyl compound [W(N2Npy)(NPh)Me2] 2 reacts with BArF3 to form the cationic complex [W(N2Npy)(NPh)Me]+ 3+ [anion = [MeBArF3]-; ArF = C6F5; N2Npy = MeC(2C5H4N)(CH2NSiMe3)2] which undergoes methyl group exchange with added 2, [Cp2ZrMe2] or ZnMe2; treatment of cation 3+ with CO2 or isocyanates leads to cycloaddition reactions at the W=NPh bond and not insertion into the W-Me bond, despite the latter product being the most thermodynamically favourable according to DFT calculations.

Group 1 and mixed Group 1 and 2 metal complexes of dianionic p-tert-butylcalix[4]arenes

Group 1 and related complexes of 1,3-O,O′-disubstituted p-tert-butylcalix[4]arene dianions [tBu-calix[4](OR)2(O)2]2− are reported. Reaction of tBu-calix[4](OMe)2(OH)2 with NaH, K, Rb or Cs gave dimeric [M2{tBu-calix[4](OMe)2(O)2}]2 (M = Na 1, K 2, Rb 3 or Cs 4). The X-ray structure of 1 shows that two Na+ ions are exo-bound between the two calix[4]arene ligands while the other two are endo-bound within the calix[4]arene cavities. Reaction of tBu-calix[4](OMe)2(OH)2 with nBuLi (2 equiv.) gave a mixture of dimeric and monomeric compounds. Complex 1 is cleaved by 15-crown-5 forming [Na2{tBu-calix[4](OMe)2(O)2}(15-crown-5)]. The complexes 2–4 are cleaved by dibenzo-18-crown-6 forming [M2{tBu-calix[4](OMe)2(O)2}(dibenzo-18-crown-6)]. Reactions of tBu-calix[4](OR)2(OH)2 (R = CH2Ph or SiMe3) with Li or Na reagents gave monomeric [M2{tBu-calix[4](OR)2(O)2}]. The reaction of 1 with CsCl gave [NaCs{tBu-calix[4](OMe)2(O)2}]213 in which the two Cs+ ions are endo-bound. Reaction of 1 with CaCl2 formed [Na2Ca{tBu-calix[4](OMe)2(O)2}2].

Highly efficient ethylene polymerisation by scandium alkyls supported by neutral fac-?3 coordinated N3 donor ligandsElectronic supplementary information (ESI) available: experimental details, characterising data, crystallographic data for 5 and GPC data. See http://www.rsc.org/suppdata/cc/b3/b310867h/

Reaction of [M(CH2SiMe3)3(THF)2] (M = Sc or Y) with the neutral fac-kappa3 N3 donor ligands (L) Me3[9]aneN3 or HC(Me2pz)3 gave the corresponding trialkyls [M(L)(CH2SiMe3)3]; activation of the scandium congeners with B(C6F5)3 in the presence of ethylene afforded highly active polymerisation catalysts (Me3[9]aneN3 = 1,4,7-trimethyltriazacyclononane).

Titanium imido complexes of pendant arm functionalised benzamidinate ligands

Reactions of the lithiated pendant arm functionalised benzamidinates Li{Me2NCH2CH2NC(Ph)NSiMe3} and Li{Me2NCH2CH2CH2NC(Ph)NSiMe3} with the compounds [Ti(NR)Cl2(py)3] (R = tBu, 2,6-Me2C6H3, 2,6-iPr2C6H3) afforded five-coordinate [Ti(NR){Me2NCH2CH2NC(Ph)NSiMe3}Cl] 1–3 and [Ti(NR){Me2NCH2CH2CH2NC(Ph)NSiMe3}Cl] 4–6, respectively. Reaction of [Ti(NtBu){Me2NCH2CH2CH2NC(Ph)NSiMe3}Cl] 4 with C6F5NH2 gave elimination of tBuNH2 and the corresponding perfluoroarylimido complex 7. The X-ray crystal structures of [Ti(NtBu){Me2NCH2CH2NC(Ph)NSiMe3}Cl] 1 and [Ti(N-2,6-R2C6H3){Me2NCH2CH2CH2NC(Ph)NSiMe3}Cl] (R = Me 5 or iPr 6) have been determined. Reaction of either 1 or 4 with H2N-2,6-Me2C6H3 in C6D6 afforded the corresponding arylimido compounds 2 and 5, but this route is not amenable to easy scale-up. For better evaluation of the effects of the pendant NMe2 donor group in 1–6, the bis(pyridine) compound [Ti(NtBu){MeCH2CH2NC(Ph)NSiMe3}Cl(py)2] 9 was prepared from Li{MeCH2CH2NC(Ph)NSiMe3} 8 and [Ti(NtBu)Cl2(py)3]. The compounds 1–3 with two-carbon pendant arms are quite sensitive to adventitious protonation, and the X-ray crystal structures of the products of two such reactions, namely [Ti2{Me2NCH2CH2NC(Ph)N(H)SiMe3}2(NtBu)2Cl2(μ-Cl)2] 10 and [Ti2(N-2,6-C6H3Me2)2Cl2(μ-O){Me2NCH2CH2NC(Ph)N(H)SiMe3}2] 11, have been determined. Both possess amidine ligands that show interesting intramolecular N–H⋯X (X = μ-Cl or μ-O) hydrogen bonds.