Reactivity of a Terminal Ti(IV) Imido Complex toward Alkenes and Alkynes: Cycloaddition vs C−H Activation

Abstract

This paper describes the reactivity of the base-free titanium imido complex Cp*2TiNPh (1) (Cp* = pentamethylcyclopentadienyl) toward alkenes and alkynes. Complex 1 reacts with ethylene and acetylene to generate the azametallacycles Cp*2Ti(N(Ph)CH2CH2) (2) and Cp*2Ti(N(Ph)CHCH) (3), respectively. In the case of ethylene, the cycloaddition is readily reversible, and 2 was characterized spectroscopically under an ethylene atmosphere. We have also examined the reactivity of 1 toward phenyl- and trimethylsilylacetylene and have found that 1 activates the alkynyl C−H bond to give anilido−acetylide complexes Cp*2Ti(N(Ph)H)C⋮CR (6, R = Ph; 7, R = SiMe3). This reaction proceeds without observable intermediate metallacyclobutene complexes such as those observed previously for the reaction of the related oxo complex Cp*2Ti(O)pyr (pyr = pyridine) with terminal alkynes. Thermolysis of azametallacyclobutene 3 results in formation of the novel ring-activated complex Cp*(η5,η1-C5Me4CH2CHCH)TiN(Ph)H (5).