Experimental and theoretical investigation of the reactivity of [(BDI*)Ti(Cl){η2-P(SiMe3)-PiPr2}] towards selected ketones

Abstract

In this work, we report a new type of reactivity of [(BDI*)Ti(Cl){η²-P(SiMe₃)-PiPr₂}] (1) towards ketones (BDI* = 2,6-diisopropylphenyl-β-methyldiketiminate ligand). In the reaction of 1 with acetone, cyclopentanone or cyclohexanone, a ketone moiety is inserted into Ti–P_phosphanyl or Ti–P_phosphido bonds to form complexes with a new C–P–P moiety, providing [(BDI*)Ti(Cl){η²-P(SiMe₃)-PiPr₂-C(Me)₂O}] (2a), [(BDI*)Ti(Cl){η²-OC(Me)₂P(SiMe₃)-PiPr₂}] (2b), [(BDI*)Ti(Cl){η²-P(SiMe₃)-P(iPr)₂-{C(CH₂)₄}O}] (3a), and [(BDI*)Ti(Cl){η²-P(SiMe₃)-P(iPr)₂-{C(CH₂)₅}O}] (4a). Starting complex 1 reacts with cyclohexanone, yielding a monocrystalline complex [{(ArNC(Me)CHC(Me)NAr)C(CH₂)₅O}Ti(Cl){PiPr₂-P(SiMe₃)C(CH₂)₅O}] (4d) with the insertion of two ketone molecules. Interestingly, we found that monoinserted complexes 2a and 3a may be oxidized via a reaction with AgCl, leading to elimination of the –SiMe₃ group and oxidation of the titanium atom. This reaction led us to isolate the Ti(IV) complex [(BDI*)Ti(Cl){η²-P-P(iPr)₂-{C(CH₂)₅}O}] (5) in crystalline form. To identify the kinds of products that may be formed and determine which products are the most energetically favoured ones, we conducted a thermodynamic DFT study of 1 towards acetone, cyclopentanone and cyclohexanone. Structures 2a, 2b, 3a, 3e, 4a, 4d, and 5 were characterized by X-ray crystallography, and complex 5 was also identified by NMR spectroscopy.