Construction of titanasiloxanes by incorporation of silanols to the metal oxide model [{Ti(eta(5)-C5Me5)(mu-O)}(3)(mu(3)-CR)]: DFT elucidation of the reaction mechanism

A family of novel titanasiloxanes containing the structural unit {[Ti-(eta(5)-C5Me5)O](3)} were synthesized by hydron-transfer processes involving reactions with equimolecular amounts of mu(3)-alkylidyne derivatives [{Ti(eta(5)-C5Me5)(mu-O)}(3)(mu(3)-CR)] (R = H (1), Me (2)) and monosilanols, R-3'Si(OH), silanediols, R-2'Si(OH)(2), and the silanetriol tBuSi(OH)(3). Treatment of 1 and 2 with triorganosilanols (R' = Ph, iPr) in hexane affords the new metallasiloxane derivatives [{Ti(eta(5)-C5Me5)(mu-O)}(3) CHR)(OSiR3')] (R = H, R' = Ph (3), iPr (4): R = Me, R' = Ph (5), iPr (6)). Analogous reactions with silanediols, (R' = Ph. iPr), give the cyclic titanasiloxanes [{Ti(eta(5)-C5Me5)(mu-O)}(3) (mu-O,SiR2') (R)] (R = Me, R' = Ph (7), iPr (8); R = Et, R' = Ph (9), iPr (10)). Utilization of tBuSi(OH)(3) with 1 or 2 at room temperature produces the intermediate complexes [{Ti(eta(5)-C5Me5) (mu-O)}(3)(mu-O2Si(OH)tBu)(R)] (R = Me (11), Et(12)). Further heating of solutions of 11 or 12 affords the same compound with an adamantanoid structure, [{Ti(eta(5)-C5Me5)(mu-O)}(3)(mu-O(3)SitBu)] (13) and methane or ethane elimination, respectively. The X-ray crystal structures of 3, 4 61 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(eta(5)-C2H5)(mu-O)}(3)- (mu(3)-CMe)] (2H). The proposed mechanism consists of three steps: 1) hydron transfer from the silanol to one of the oxygen atoms of the Ti3O3 ring, forming a titanasiloxane ; 2) intramolecular hydron migration to the alkylidyne moiety; and 3) a mu-alkylidene ligand rotation to give the final product.