Synthesis, electrochemistry and electronic spectra of tetranuclear bis(η2-alkynyl) transition-metal complexes.: The molecular structure of [(η5-C5H4SiMe3)3Ti(CCFc)2]CuBr

Tetrametallic complexes of type {[Ti](C=CFc)(2)}MX (M = Cu: 2a, X = Cl; 2b, X = Br; 2c: X = OTf; M = Ag: 3a, X = Cl; 3b, X = BF4; [Ti] = (eta(5)-C5H4SiMe3)(2)Ti, Fc = (eta(5)-C5H4)Fe(eta(5)-C5H5), OTf = OSO2CF3) were synthesised by the reaction of trinuclear [Ti](C=CFc)(2) (1) with one equivalent of [MX] (M = Cu, Ag; X = Cl, Br, OTf, BF4). The solid-state structure of {[Ti](C=CFc)(2)}CuBr (2b) displays a three-coordinate Cu(I) centre with two eta(2)-coordinated C=CFc units and a eta(1)-bound Br ligand. The Fc groups are both positioned on one side of the Ti(C=C)(2)Cu plane, while the Br ligand points towards the opposite side and is located 0.2566(57) Angstrom out of this array. The electronic spectra of complexes 2b (M = Cu) and 3a (M = Ag) show a bathochromic shift of lambda(max) upon eta(2)-coordination of the FcC=C units in 1 to the M(I) centre in 2b or 3a. Cyclic voltammetric studies reveal a behaviour dependent on M(I). In the case of Cu(I), the Ti sigma-acetylide bonds are retained upon oxidation of the remote Fc units, while with Ag(I) immediate Ti-C-C=C sigma-bond cleavage is observed. (C) 2000 Elsevier Science S.A. All rights reserved.