Reaction of C5R1 4(SiMe3)CHR2CH2CR3R4OR5 with titanium tetrachloride gives the bidentate η5-σ-cyclopentadienyl−alkoxide complexes of titanium (η5-σ-C5R1 4CHR2CH2CR3R4O)TiCl2 through elimination of chlorotrimethylsilane and RCl (R = SiMe3, CH2Ph, CMe3). A potentially tridentate system (R1, R2, R3 = H, R4 = −(CH2)2OMe) was synthesized in optically pure form and its structure determined by X-ray diffraction. The pendant ether oxygen does not coordinate to the metal, and hydride transfer reactions catalyzed by the complex gave racemic products. Efficient routes to tetramethylcyclopentadienyl-substituted ligands (R1 = Me) were developed on the basis of the addition of 2-butenylmagnesium bromide to γ-lactones to give the dienyl alcohols [C(CH3)CH(CH3)]2C(OH)CHR2(CH2)2OH, which could be functionalized on the primary alcohol before acid-catalyzed cyclization to afford the 3-alkoxypropyl-substituted tetramethylcyclopentadienes.

A rhenium(I) tricarbonyl complex with a 3-(pyridin-2-yl)pyrazole chromophoric ligand and a functionalized organosilane spectator ligand, [Re(py-pzH)(CO) 3 (L 1 )](CF 3 SO 3 ) (1) [where py-pzH~3-(pyridin-2-yl)pyrazole, L 1 ~3-N-(pyridin-4-ylmethylene)aminopropyltriethoxysilane], as well as its analog, [Re(py-pzH)(CO) 3 (py)](CF 3 SO 3 ) (2) (where py~pyridine) have been synthesized. The room temperature MLCT luminescence properties of 1 and 2 (l max at 484 and 489 nm, respectively) were found to be sensitive to the protonation±deprotonation status of the 3-(pyridin-2-yl)pyrazole ligand. Spectro¯uorometric pH titration of 2 in aqueous media revealed an excited state pK a of 7.05. Sol±gel material formed from hydrolysis of 1 was successfully spin-coated onto glass microscope slides. The result was a sol±gel based luminescent pH sensor capable of responding over a wide pH range from pH 2.3 to 12 in air. The applicability of the principle of direct perturbation of electronic factors of sensor molecules in the development of luminescent chemical sensing materials is demonstrated.

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