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Reactions of titanapinacolate complexes [(DMSC)Ti(OCAr 2 CAr 2 O)] (1, Ar ) Ph; 2, Ar ) p-MeC 6 H 4 ; DMSC ) 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion) with 1 equiv of a delocalized diimine furnished titanium η 2 -ketone complexes [(DMSC)Ti-(η 2 -OCAr 2 )L 2 )] 3-6 (L 2 ) bpy, dmbpy, or phen). The ketone is weakly bound in 3-6, and it is readily dissociated. The compounds dissolve in aromatic hydrocarbon solvents to give intense green solutions and undergo a photochemically assisted transformation into 1-aza-5-oxa-titanacyclopentene derivatives 8-11, in which C-H activation of the heterocyclic diimine ligand and hydride migration to a Ti-bound ketone to form an alkoxide group has occurred. The reaction of 3-6 with one or more equivalents of appropriate ketone gave 8-11 in high yield. The compounds were characterized by NMR ( 1 H and 13 C) and microanalysis data, as well as by X-ray crystallography for [(DMSC)Ti{κ 3 -OC(p-MeC 6 H 4 ) 2 C 10 H 7 N 2 }{OCH-(p-MeC 6 H 4 ) 2 }] (9). The ease of transformation of [(DMSC)Ti{η 2 -OC(p-MeC 6 H 4 ) 2 }L 2 ] complexes (4, L 2 ) bpy; 5, L 2 ) dmbpy; 6, L 2 ) phen) into 9-11 tracks the facility of metal to diimine ligand charge transfer (MLCT) transition and increased in the order 5 < 4 , 6. This transformation is suggested to occur by a mechanism that involves reversible coordination of ketone to titanium and a rate-limiting step that is dependent on ketone concentration.

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