Construction of Titanasiloxanes by Incorporation of Silanols to the Metal Oxide Model [{Ti(η 5 ‐C 5 Me 5 )(μ‐O)} 3 (μ 3 ‐CR)]: DFT Elucidation of the Reaction Mechanism

A family of novel titanasiloxanes containing the structural unit {[Ti(η 5 ‐C 5 Me 5 )O] 3 } were synthesized by hydron‐transfer processes involving reactions with equimolecular amounts of μ 3 ‐alkylidyne derivatives [{Ti(η 5 ‐C 5 Me 5 )(μ‐O)} 3 (μ 3 ‐CR)] (R=H ( 1 ), Me ( 2 )) and monosilanols, R 3 ′Si(OH), silanediols, R 2 ′Si(OH) 2 , and the silanetriol t BuSi(OH) 3 . Treatment of 1 and 2 with triorganosilanols (R′=Ph, i Pr) in hexane affords the new metallasiloxane derivatives [{Ti(η 5 ‐C 5 Me 5 )(μ‐O)} 3 (μ‐CHR)(OSiR 3 ′)] (R=H, R′=Ph ( 3 ), i Pr ( 4 ); R=Me, R′=Ph ( 5 ), i Pr ( 6 )). Analogous reactions with silanediols, (R′=Ph, i Pr), give the cyclic titanasiloxanes [{Ti(η 5 ‐C 5 Me 5 )(μ‐O)} 3 (μ‐O 2 SiR′ 2 )(R)] (R=Me, R′=Ph ( 7 ), i Pr ( 8 ); R=Et, R′=Ph ( 9 ), i Pr ( 10 )). Utilization of t BuSi(OH) 3 with 1 or 2 at room temperature produces the intermediate complexes [{Ti(η 5 ‐C 5 Me 5 ) (μ‐O)} 3 (μ‐O 2 Si(OH) t Bu)(R)] (R=Me ( 11 ), Et( 12 )). Further heating of solutions of 11 or 12 affords the same compound with an adamantanoid structure, [{Ti(η 5 ‐C 5 Me 5 )(μ‐O)} 3 (μ‐O 3 Si t Bu)] ( 13 ) and methane or ethane elimination, respectively. The X‐ray crystal structures of 3 , 4 , 6 , 8 , 10 , 12 , and 13 have been determined. To gain an insight into the mechanism of these reactions, DFT calculations have been performed on the incorporation of monosilanols to the model complex [{Ti(η 5 ‐C 5 H 5 )(μ‐O)} 3 (μ 3 ‐CMe)] ( 2 H ). The proposed mechanism consists of three steps: 1) hydron transfer from the silanol to one of the oxygen atoms of the Ti 3 O 3 ring, forming a titanasiloxane; 2) intramolecular hydron migration to the alkylidyne moiety; and 3) a μ‐alkylidene ligand rotation to give the final product.