Early-transition-metal ketenimine complexes: Synthesis, reactivity, and structure of ketenimine-containing titanocene and zirconocene complexes

Abstract

Reaction of Cp2M(PMe3)(2) complexes (M = Ti, Zr; Cp = eta(5)-C5H5) with the N-(p-tolyl)-diphenylketenimine Ph'N=C=CPh2 (Ph' = p-MeC6H4) in a 1:1 molar ratio affords the ketenimine-containing metallocene derivatives Cp2M(eta(2)-(C,N)-Ph'N=C=CPh2)(PMe3) (M = Ti (1); Zr (2)). The ketenimine ligand reacts in the same way with the ''Cp*M-2'' species (Cp* = eta(5)-C5Me5) generated from the reduction of the corresponding Cp*2MCl2 complexes with (LiBu)-Bu-t (1:2 molar ratio) to give the related complexes Cp*M-2(eta(2)-(C,N)-Ph'N=C=CPh2) (M = Ti (3); Zr (4)). The molecular structure of 3 shows a titanium atom bonded to two eta(5)-cyclopentadienyl rings and a eta(2)-(C,N)-bonded ketenimine ligand. Reaction of ''Cp*Ti-2'' with the ketenimine ligand in a 1:2 molar ratio gives 1,1,5,5-tetraphenyl-3-(p-tolyl)-2-(p-toluidino)-3-aza-1,4-pentadiene, which probably results from the coupling, followed by hydrolysis, of two ketenimine molecules coordinated to one titanocene moiety. Protonation of 3 with Et3NHCl or H2O (1:1 molar ratio) affords the intermediate species Cp*Ti-2(X)(eta(2)-(C,N)-Ph'N=C(H)=CPh2) (X = Cl (5); OH (6)), which on hydrolysis evolves to give the enamine Ph'N(H)-CH=CPh2 as the final product. Finally, 3 reacts reversibly with H-2 to give the hydride enamidate complex Cp*Ti-2(H)(eta(1)-Ph'N-CH=CPh2) (7). The structures of the different compounds have been determined by IR and NMR spectroscopic methods

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