Synthesis, Structure, and Reactivity of Hydroxylaminato Alkyltitanium Complexes

Mahesh K. Mahanthappa, Adam P. Cole, Robert M. Waymouth

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17 Scopus citations

Abstract

Alkyltitanium complexes bearing hydroxylaminato ligands were synthesized by two methods: (i) reaction of the stable nitroxide radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) with TiCl 3 to generate (TEMPO)TiCl 3 (1) followed by alkylation with PhCH 2MgCl to furnish (TEMPO)Ti(CH 2Ph) 3 (2), and (ii) protonolysis of Ti(CH 2Ph) 4 (3) with hydroxylamines to yield (R 2NO) 2Ti(CH 2Ph) 2 (R = CH 2Ph (4), Et (5)). 1H NMR studies of these compounds demonstrate that the hydroxylaminato ligands exhibit both η 1- and η 2-binding modes with varying degrees of hemilability. X-ray crystallographic analysis of 5 shows that titanium adopts a six-coordinate "propeller" conformation in which the hydroxylamine anions are η 2-bound. The reaction of the complex 2 with B(C 6F 5) 3 at 20°C forms 1 equiv of toluene and a cationic benzyltitanium complex exhibiting strong η 6-PhCH 2B(C 6F 5) 3 anion coordination, in which one of the TEMPO methyl groups has undergone C-H bond activation as evidenced by 1H, 13C NMR, gHSQC, gHMBC, and gROESY experiments. Complexes 2-5 exhibit very low activities for propylene polymerization.

Original languageEnglish (US)
Pages (from-to)1405-1410
Number of pages6
JournalOrganometallics
Volume23
Issue number6
DOIs
StatePublished - Mar 15 2004

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