Alkyloxy- and aryloxy-titanocenes: Synthesis, solid-state structure and cyclic voltammetric studies |
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Authors: | Stefan Kcher Bernhard Walfort Gerd Rheinwald Tobias Rüffer Heinrich Lang |
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Institution: | aTechnische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie, Lehrstuhl für Anorganische Chemie, Straße der Nationen 62, 09111 Chemnitz, Germany |
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Abstract: | Alkyloxy- and aryloxy-functionalized titanocenes of type Ti](Cl)(OR) (R = Me (2), CH2PPh2 (3), CH2Fc (4), C6H5 (5), C6H4-4-C N (6), C6H4-4-NO2 (7), C6H4-4-Me (8), C6H4-4-OMe (9), C6H4-4-C(O)Me (10), C6H4-4-CO2Me (11), C6H4-3-NO2 (12); Ti] = (η5-C5H4SiMe3)2Ti; Fc = (η5-C5H4)(η5-C5H5)Fe) were synthesized by the reaction of Ti]Cl2 (1) with ROH in a 1:1 molar ratio and in presence of Et2NH. Diaryloxy-titanocenes (e.g., Ti](OC6H4-4-NO2)2 (13)) are accessible, when the ratio of 1 and ROH is changed to 1:2. This synthesis methodology also allowed the preparation of dinuclear complexes of composition (Ti](Cl))2(μ-OC6H4O) (14) and (Ti](Cl)(μ-OC6H4-4))2 (15) by the reaction of 1 with hydroquinone or 1,1′-dihydroxybiphenyl in a 2:1 stoichiometry.Cyclic voltammetric studies show the characteristic Ti(IV)/Ti(III)] reductions. It was found that the potentials of the alkyloxy titanocenes 2–4 do not differ, while for the aryloxy-titanocenes 5–15 the reduction potentials correlate linearly with the σp/m Hammett substituent constants showing a strong influence of the substituents on the electron density at titanium.The structures of titanocenes 4, 5, 9, and 11–13 in the solid state are reported. Typical for these organometallic sandwich compounds is a distorted tetrahedral coordination geometry around titanium with D1–Ti–D2 angles (D1, D2 = centroids of the cyclopentadienyl ligands) of ca. 130 °. In comparison to FcCH2O-functionalized 4, for the aryloxy-titanocenes 5, 9, and 11–13 a significant larger Ti–O–C angle was found confirming electronic interactions between the titanium atom and the appropriate aryl group. |
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Keywords: | Titanocene Alkyloxy Aryloxy Cyclic voltammetry Hammett parameter |
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