(eta(5)-C5H4SiMe3)(2)Ti(C C-SiMe2-C CSiMe3)(2): a unique entry to monomeric and oligomeric alkyne-copper(I) and alkyne-silver(I) halides

The reaction of [Ti]Cl-2 (1) ([Ti]=(eta(5)-C5H4SiMe3)(2)Ti) with two equiva lents of LiC=C-SiMe2-C=CSiMe3 (2) produces [Ti](C=C-SiMe2-C=CSiMe3)(2) (3). On treatment with [MX] (M = Cu: 4a X = Cl, 4b X = Br; M = Ag: 5a X = Cl, 5 b X = Br) the tweezer complexes ([Ti](C=C-SiMe2-C=CSiMe3)(2)) MX (M = Cu: 6 a X = Cl, 6b X = Br; M = Ag: 7a X = Cl, 7b X = Br) are formed in which the Ti-C=C-Si units are eta(2)-coordinated to a monomeric copper(I) or silver(I ) halide moiety. When 6b is further reacted with [CuBr] (4b), oligomeric ([ Ti](C=C-SiMe2-C=CSiMe3)(2)(CuBr)(3))(n) (8) is formed. This molecule contai ns a (eta(2)-TiC=CSi)(2)CuBr entity next to two (eta(2)-SiC=CSi)CuBr moieti es, of which the latter building blocks are responsible for the oligomeric structure. In addition, 8 can be prepared by the direct reaction of 3 with an excess of 4b, respectively. However, when an excess of [AgX] is used, th e only formed products are 7; no polymeric material is obtained. A Group 11 metal exchange reaction is noticed, when 7a or 7b are reacted with [CuX]: depending on the amount of [CuX] used, monomeric 6 or oligomeric 8 is produ ced. An explanation is given by a better bonding synergysmus for the alkyne -to-copper interaction. The result of the X-ray structure analysis of compo und Tb is reported. The compound 7b crystallizes in the monoclinic space gr oup C2/c with cell constants a = 25.097(8), b = 11.327(3), c = 19.014(6) An gstrom, beta = 122.36(3)degrees V = 4566(2) Angstrom(3) and Z = 4. The comp ound 7b contains a monomeric (eta(2)-alkyne)(2)AgBr moiety in which the sil ver(I) center possesses a trigonal-planar environment, caused by the eta(2) -coordinated TiC=CSi units as well as a eta(1)-bonded bromine atom. However this differs from the behavior of compounds 6 and 7 in solution, where all four C=C building blocks of the TiC=CSi as well as the SiC=CSi units are c omplexed by the transition metal entities MX (M = Cu, Ag X = Cl, Br). (C) 1 999 Elsevier Science S.A. All rights reserved.