Cyclopentadienyl, indenyl and bis(cyclopentadienyl) titanium imido compounds

The titanium tert-butyl imido compounds [Ti(NBu t )Cl 2 (NC 5 H 4 R-4) n ] (R = H, n = 2 or 3; R = Bu t , n = 2) have been found to be entry points to the half-sandwich η 5 -cyclopentadienyl derivatives [Ti(η 5 -C 5 R′ 4 R″)(NBu t )Cl(NC 5 H 4 R-4)] (R = Bu t , R′ = R″ = H or Me; R = H, R′ = H, R″ = H, Me or Pr i ; R = H, R′ = Me, R″ = Me, Et or C 4 H 7 ), the η 5 -1,2,3-trimethylindenyl species [Ti(η 5 -C 9 H 4 Me 3 )(NBu t )Cl(NC 5 H 4 Bu t -4)] and the bis(η 5 -cyclopentadienyl) compound [Ti(η 5 -C 5 H 5 ) 2 (NBu t )(NC 5 H 5 )], the crystal structure of which has been determined. The complex [Ti(η 5 -C 5 H 5 )(NBu t )Cl(NC 5 H 5 )] readily loses pyridine under vacuum in the solid state to form the binuclear complex [Ti 2 (η 5 -C 5 H 5 ) 2 ( µ-NBu t ) 2 Cl 2 ]. Treatment of [Ti(η 5 -C 5 Me 4 R)(NBu t )Cl(NC 5 H 5 )] (R = Me or Et) with Na[C 5 H 5 ] gives the corresponding mixed-ring sandwich derivatives [Ti(η 5 -C 5 H 5 )(η 5 -C 5 Me 4 R)(NBu t )Cl(NC 5 H 5 )]. Addition of Li[C 9 H 7 ] to [Ti(η 5 -C 5 H 5 )(NBu t )Cl(NC 5 H 5 )] gave the η 5 -cyclopentadienyl, η 3 -indenyl mixed-ring analogue [Ti(η 5 -C 5 H 5 )(η 3 -C 9 H 7 )(NBu t )(NC 5 H 5 )]. The complex [Ti(η 5 -C 5 H 5 ) 2 (NBu t )(NC 5 H 5 )] undergoes a room-temperature cyclopentadienyl ligand-redistribution reaction with [Ti(NBu t )Cl 2 (NC 5 H 5 ) 2 ] forming [Ti(η 5 -C 5 H 5 )(NBu t )Cl(NC 5 H 5 )] 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(η 5 -C 5 H 5 )(η 5 -C 5 Me 4 Et)(NBu t )(NC 5 H 5 )] is also fluxional and exhibits reversible pyridine dissociation at higher temperatures and restricted rotation about the Ti–N (pyridine) bond at lower temperatures.