Synthesis, Structure, and Ethylene/α-Olefin Polymerization Behavior of (Cyclopentadienyl)(nitroxide)titanium Complexes

Abstract

Mono-Cp titanium coordination compounds bearing monoanionic ligands derived from stable nitroxyl radicals have been synthesized by two methods: (i) trapping of CpTi(III) species with the stable nitroxyl radical TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) to provide Cp‘TiCl2(TEMPO) (Cp‘ = Cp (1) and Cp* (2)) and (ii) salt metathesis of Ti(IV) halides with a nitroxide anion generated by the in situ methylation of tert-butyl-α-phenylnitrone. Alkylation of these complexes with MeLi or MeMgBr furnishes Cp*TiMe2(TEMPO) (3) and Cp‘TiMe2(ON( t Bu)(CHMePh)) (Cp‘ = Cp(4) and Cp* (5)). The molecular structure of 2 has been determined by X-ray crystallography to reveal a monoanionic η1-TEMPO ligated to titanium. Complexes 3 and 4 activated with iprAFPB (2,6,-diisopropyl-N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate) efficiently copolymerize ethylene and 1-hexene to provide copolymers having higher 1-hexene contents and higher productivities than the related Cp*Ti(CH2Ph)3 under identical conditions. Comparison of structural and electronic features as well as the ethylene/1-hexene copolymerization behavior of 3 and 4 with the constrained geometry catalyst [MeSi2(η5-Me4Cp)(η1-N-tBu)]TiMe2 (6) provides insights into factors governing high comonomer incorporation by mono-Cp titanium complexes.

Photochemistry of tris(pyrazolyl)borate titanium(IV) complexes

“…ESR study of solutions of 5 and 6 indicate that these complexes are ESR silents. These results are consistent with the assignment of 5 and 6 as Ti(IV) complexes containing a reduced g 1 TEMPO ligand similar to what was reported by Waymouth for the complex CpTiCl 2 TEMPO [17]. Due to the high oxophylicity of the Ti center, and on the basis of the methyl group resonances, we felt that the reduced TEMPO as oxyaminato ligand, is g 1 bonded to Ti(IV) forming a Ti-O bond [18].…”

“…Ti LMCT. Since the Ti-O bond is normally very strong [17,19], the associated LMCT absorption is predicted to occur at high energy.…”

“…Our studies in this direction were guided by WaymouthÕs [17] recent work which indicates that CpTi(III) species can be trapped by nitroxyl radical TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) to form the complex CpTiCl 2 (TEMPO). Thus, in this study we have focused attention on systems fTpTiCl Å 2 TEMPOg ð5Þ and fTp à TiCl Å 2 TEMPOg ð6Þ which pair the metal acceptor {TpTiCl 2 } and {Tp*TiCl 2 } fragments with the donor Lewis base TEMPO.…”

Reactivity of Organothorium Complexes with TEMPO

“…The metrical parameters of the [(η 5 -C 5 Me 5 ) 2 ThMe] 1+ part of complex 1, i.e., the 2.546 and 2.578 Å Th−(η 5 -C 5 Me 5 ring centroid) distances (Table 3) 16,17,21,23,25,27 The sum of the angles around nitrogen, 336.4°, is consistent with a pyramidal geometry about the nitrogen in a fully reduced TEMPO − anion. 16,17,21 (η 5 -C 5 Me 5 ) 2 Th(η 1 -C 3 H 5 )(η 3 -C 3 H 5 ), 2, and (η 5 -C 5 Me 5 ) 2 Th-(η 1 -C 3 H 5 )(TEMPO), 3.…”

Synthesis, crystal structure and ethylene polymerization activity of zirconium complexes bearing mono-Cp and tridentate Schiff base [ONO] ligands

“…There are many reports concerning this topic especially using metallocene and non-Cp (cyclopentadienyl) catalysts [3][4][5]. Among them, mixed ligands titanium complexes of the type Cp 0 Ti(L)X 2 containing cyclopentadienyl ligand and non-Cp ligand have attracted considerable attention, because this type of catalyst has been expected to exhibit unique characteristics as olefin polymerization catalyst that would combine the merits of metallocene and non-Cp catalyst type [6][7][8][9][10][11][12]. However, there have been only a few reports on the use of mixed ligands zirconium complexes for the olefin polymerization [13,14].…”