Mixed-cyclopentadienyl aryloxide and arylsulfide derivatives of titanium: Synthesis, reactivity, and application to olefin polymerization

Andrew E Fenwick, Purdue University

Abstract

A series of dimethyltitanium compounds [CpTi(OAr)Me2] ligated by one cyclopentadienyl (Cp) and one 2,6-disubstituted-aryloxide (OAr) have been prepared by the addition of parent phenol (HOAr) to a cold ether solution of [CpTiMe3]. Reaction of the dimethyl compounds with [B(C 6F5)3] generated the corresponding cationic methyl species [CpTi(OAr)Me][MeB(C6F5)3]. The compound [CpTi(OC6HPh4-2,3,5,6)Me][MeB(C6F5) 3] was studied via solution VT-NMR spectroscopy, and a free energy of activation for methyl exchange was estimated to be 14.4(5) Kcal·mol −1 at 10°C. These cationic derivatives were capable of polymerizing 1-hexene and styrene, yielding regioregular, atactic homopolymers. In the absence of olefin, these thermally unstable cationic derivatives readily eliminated methane at room temperature affording compounds of the type [CpTi(OAr)(C 6F5){CH2B(C6F5)2}]. A kinetic study of the conversion of [CpTi(OC6HPh4-2,3,5,6)Me][MeB(C 6F5)3] to [CpTi(OC6HPh4-2,3,5,6)(C 6F5){CH2B(C6F5)2}] was undertaken. By 1H NMR spectroscopy, a first order rate constant of 7.6(2) × 10−4s−1 was observed at 25.0(5)°C. The corresponding arylsulfide derivatives [CpTi(SAr)X2] (X = Cl, Me) have also been prepared. The dichlorides were synthesized from the reaction of [CpTiCl3] with one equivalent of the lithium salt of the corresponding arylsulfide in benzene. The one electron reduction produced sulfur-bridged dimers of the type [CpTiCl(μ-SAr)]2. The dimethyl derivatives [CpTi(SAr)Me2] were prepared by the addition of substituted thiophenol (HSAr) to a cold ether solution of [CpTiMe3]. Reaction of the dimethyl compounds with [B(C6F5)3] generated a cationic species which would oligomerize 1-hexene, but rapidly deactivated through cyclometallation (intramolecular C-H bond activation) as determined by NMR spectroscopy.

Degree

Ph.D.

Advisors

Rothwell, Purdue University.

Subject Area

Chemistry|Polymers

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