Synthesis and Reactivity of [(DMSC)Ti(η 2 -OCAr 2 )L 2 ] Complexes (DMSC = Dimethylsilyl-Bridged p-tert- Butylcalix[4]arene Dianion, Ar = Aryl Group, and L 2 = Delocalized Diimine)
2002; American Chemical Society; Volume: 22; Issue: 1 Linguagem: Inglês
10.1021/om020487f
ISSN1520-6041
AutoresJ.V. Kingston, V. Sarveswaran, Sean Parkin, Folami T. Ladipo,
Tópico(s)Asymmetric Hydrogenation and Catalysis
ResumoReactions of titanapinacolate complexes [(DMSC)Ti(OCAr2CAr2O)] (1, Ar = Ph; 2, Ar = p-MeC6H4; DMSC = 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion) with 1 equiv of a delocalized diimine furnished titanium η2-ketone complexes [(DMSC)Ti(η2-OCAr2)L2)] 3−6 (L2 = 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 (1H and13C) and microanalysis data, as well as by X-ray crystallography for [(DMSC)Ti{κ3-OC(p-MeC6H4)2C10H7N2}{OCH(p-MeC6H4)2}] (9). The ease of transformation of [(DMSC)Ti{η2-OC(p-MeC6H4)2}L2] complexes (4, L2 = bpy; 5, L2 = dmbpy; 6, L2 = 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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