Heterobi- to heterotetrametallic transition metal complexes constructed from ferrocenecarboxylate and [{[Ti](μ-σ,π-CCSiMe3)2}M]+ units

A series of copper(I) and silver(I) carboxylates received from various ferrocenecarboxylic acids was synthesized and used in the preparation of heterooligometallic Ti–Cu(Ag)–Fe complexes. The silver(I) salts [FcCO2Ag] (2a) and [FcCHCHCO2Ag] (2b) (Fc = ferrocenyl, (η5-C5H4)Fe(η5-C5H5)) were obtained through deprotonation of the respective acids FcCO2H (1a) and FcCHCHCO2H (1b) with NEt3, followed by a reaction with [AgNO3]. The heterotrimetallic complexes {[Ti](μ-σ,π-CCSiMe3)2}AgO2CFc (4a) and {[Ti](μ-σ,π-CCSiMe3)2}AgO2CCHCHFc (4b), where [Ti] denotes the (η5-C5H4SiMe3)2Ti unit, were obtained from the reaction of 2a and 2b with the organometallic π-tweezer compound [Ti](CCSiMe3)2 (3). The related heterotrimetallic copper(I) complex {[Ti](μ-σ,π-CCSiMe3)2}CuO2CFc (9a) was prepared via two synthetic routes. First, salt 2a was reacted with [(η2-Me3SiCCSiMe3)CuBr]2 (10) to give the alkyne-stabilized copper(I) carboxylate [(η2-Me3SiCCSiMe3)(CuO2CFc)2]2 (11). Subsequent reaction of 11 with four equivalents of 3 afforded 9a. Alternatively, 9a and its analogues {[Ti](μ-σ,π-CCSiMe3)2}CuO2C–E–Fc (E = trans-CHCH (9b), CH2CH2 (9c)), were prepared from acidolysis of the Cu–CMe bond in {[Ti](μ-σ,π-CCSiMe3)2}CuMe (8) with acids 1a–1c. An analogous reaction between HO2CfcPPh2M(CO)5 (M = Cr (14a), Mo (14b), W (14c); fc = ferrocene-1,1′-diyl) and 8 at−30 °C gave the alkyne/ferrocene-bridged heterotetrametallic compounds {[Ti](μ-σ,π-CCSiMe3)2}CuO2CfcPPh2M(CO)5 (M = Cr (15a), Mo (15b), W (15c)). Reversing the reaction steps so that {[Ti](μ-σ,π-CCSiMe3)2}CuO2CfcPPh2 (12) was prepared first and then reacted with M(CO)5(thf) (M = Cr (13a), Mo (13b), W (13a)) gave complicated reaction mixtures from which pure 15a–15c could not be isolated. The solid-state structures of 5, 7, 9a, and 11 have been corroborated by single-crystal X-ray structural studies and the electrochemical behavior of acids 1a–1c and of complexes 4a, 4b and 9a–9c was studied by cyclic voltammetry.

Graphical abstractThe synthesis, properties and reaction chemistry of heterotri- and tetrametallic complexes based on ferrocenecarboxylic and organometallic π-tweezer building blocks including Ti, Fe, Cu, Ag, Cr, Mo and W transition metal atoms is reported. The solid state structure of four compounds is discussed as well.Figure optionsDownload full-size imageDownload as PowerPoint slide