Cyclopentadienyl, indenyl and bis(cyclopentadienyl) titanium imido compounds

Abstract

The titanium tert-butyl imido compounds [Ti(NBu^t)Cl₂(NC₅H₄R-4) _n] (R = H, n = 2 or 3; R = Bu^t, n = 2) have been found to be entry points to the half-sandwich η⁵-cyclopentadienyl derivatives [Ti(η⁵-C₅R′₄R″)(NBu^t )Cl(NC₅H₄R-4)] (R = Bu^t, R′ = R″ = H or Me; R = H, R′ = H, R″ = H, Me or Prⁱ; R = H, R′ = Me, R″ = Me, Et or C₄H₇), the η⁵-1,2,3-trimethylindenyl species [Ti(η⁵-C₉H₄Me₃)(NBu^t )Cl(NC₅H₄Bu^t-4)] and the bis(η⁵-cyclopentadienyl) compound [Ti(η⁵-C₅H₅)₂(NBu^t )(NC₅H₅)], the crystal structure of which has been determined. The complex [Ti(η⁵-C₅H₅)(NBu^t)Cl(NC ₅H₅)] readily loses pyridine under vacuum in the solid state to form the binuclear complex [Ti₂(η⁵-C₅H₅)₂( µ-NBu^t)₂Cl₂]. Treatment of [Ti(η⁵-C₅Me₄R)(NBu^t)Cl(NC ₅H₅)] (R = Me or Et) with Na[C₅H₅] gives the corresponding mixed-ring sandwich derivatives [Ti(η⁵-C₅H₅)(η⁵-C ₅Me₄R)(NBu^t)Cl(NC₅H₅ )]. Addition of Li[C₉H₇] to [Ti(η⁵-C₅H₅)(NBu^t)Cl(NC ₅H₅)] gave the η⁵-cyclopentadienyl, η³-indenyl mixed-ring analogue [Ti(η⁵-C₅H₅)(η³-C ₉H₇)(NBu^t)(NC₅H₅)]. The complex [Ti(η⁵-C₅H₅)₂(NBu^t )(NC₅H₅)] undergoes a room-temperature cyclopentadienyl ligand-redistribution reaction with [Ti(NBu^t)Cl₂(NC₅H₅)₂ ] forming [Ti(η⁵-C₅H₅)(NBu^t)Cl(NC ₅H₅)] in quantitative yield. Variable-temperature NMR spectra for the half-sandwich complexes show that the co-ordinated pyridine exchanges with free pyridine via an associative mechanism. The compound [Ti(η⁵-C₅H₅)(η⁵-C ₅Me₄Et)(NBu^t)(NC₅H₅ )] is also fluxional and exhibits reversible pyridine dissociation at higher temperatures and restricted rotation about the Ti–N (pyridine) bond at lower temperatures.

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