REDOX-ACTIVE MACROCYCLES AS METALLOLIGANDS - SYNTHESIS, ELECTROCHEMISTRY, AND STRUCTURE OF SILVER(I) AND COPPER(I) COMPLEXES OF CP2TI(ETA-S(CH2)NS)2TICP2 (N = 2, 3)

The reactions of Cp2TiCl2 with the dithiols HS(CH2)nSH (n = 2, 3) in the presence of imidazole proceed with formation of imidazole hydrochloride, affording insoluble titanocene dithiolate derivatives 1 and 2, respectively. In the case of propanedithiol, the product 2 can also be synthesized via reaction of Cp2TiCl2 with Mg and (SCH2CH2CH2S)2 or by reaction of Cp2Ti(PMe3)2 with (SCH2CH2CH2S)2. Alternatively, 2 can be prepared via the reaction of Cp2TiPh2 with dithiols. The spectroscopic and analytical data are consistent with the formulation of 1 and 2 as the bimetallic compounds Cp2Ti(mu-S(CH2)n(S))2TiCp2 (n = 2, 1; n = 3, 2). The H-1 NMR data suggest an open macrocyclic structure for 2. In contrast, the temperature dependence of the H-1 NMR spectra for 1 is consistent with a fluxional process involving the twisted conformations of 1 in which two of the four sulfur atoms bridge the two Ti centers. Molecules 1 and 2 are shown to act as metalloligands and react with AgBPh4 and [Cu(NCMe)4]BF4 to yield the complexes [(Cp2Ti(mu-S(CH2)nS)2TiCp2)M]+X- (n = 2, M = Cu(I), 3; n = 3, M = Ag(I), 4). A crystallographic study of 4 confirms the formulation of 4 in which 2 acts as a macrocyclic metalloligand presenting a four-sulfur coordination sphere to the encapsulated silver ion. The complex [(Cp2Ti(mu-SCH2CH2CH2S)2TiCp2)Ag]BPh4 (4) crystallizes as 4.H2O.0.75CH2Cl2 in the space group P2(1)/n with a = 24.610 (9) angstrom, b = 17.098 (5) angstrom, c = 25.453 (15) angstrom, beta = 111.76 (3)-degrees, Z = 8, and V = 9947 (14) angstrom3. Electrochemical studies of 1-4 by cyclic voltammetry are reported. The macrocycles exhibit only irreversible reductions. In contrast, the complexes 3 and 4 undergo quasi-reversible one-electron reductions at -0.93 and -1.26 V vs Ag/AgCl, respectively. A second irreversible wave is also observed at -1.56 and -1.53 V for 3 and 4, respectively. This redox behavior is interpreted in terms of Ti(IV)/Ti(III) redox couples. The chemical generation of the one-electron-reduction products, i.e. [(Cp2Ti(mu-S(CH2)n(S))2TiCp2)M]0 (n = 2, M = Cu(I), 5; n = 3, M = Ag(I), 6) is achieved via reactions of 3 and 4 with Cp2Co. The EPR spectrum of 5 reveals Cu-63, Cu-65 hyperfine coupling, while Ag-107, Ag-109 hyperfine coupling is seen for 6. The results of these studies are discussed, and the implications of the data are considered.