Synthesis, characterization, and ring-opening polymerization of a novel [1] silaferrocenophane with two ferrocenyl substituents at silicon

Reaction of dichlorodiferrocenylsilane, Fc(2)SiCl(2) (4) (Fc = ( eta-C5H4)Fe(eta-C5H5)), with dilithioferrocene fcLi(2). TMEDA (fc=(eta-C5H5)(2)Fe, TMEDA = N,N,N,N-tetramethylethylenediamine) afforded the novel trimetallic [1] silaferrocenophane 5, fcSiFc(2), in 77% yield. A single crystal X-ray diffraction study of ferrocenophane 5 showed the presence of significant disorder but revealed that the molecule possesses a highly strained structure where the tilt-angle between the planes of the cyclopentadienyl rings of the ferrocenophane is 20-22 degrees, typical of strained silicon-bridged [1] ferrocenophanes. The Fe...Fe distances in 5 are 5.434, 5.537, and 5.687 Angstrom, and metal-metal interactions are evident as redox coupling was detected in the cyclic voltammogram of this species. Differential pulse voltammetry resolved three oxidation waves at 0, 0.22, and 0.45 V relative to the ferrocene/ferrocenium couple. Mossbauer spectroscopy proved useful in corroborating the structure of 5, as the two distinct Fe environments present were readily resolved ( delta = 0.424( 5) mm s (-1), d, Delta E-q = 2.242( 5) mm s (-1), 2 Fe; delta = 0.414(5) mm s (-1), d, Delta E-q = 1.930(5) mm s (-1), 1 Fe). Further characterization of 5 by IR and Raman spectroscopy was also undertaken. Ring-opening addition of HCl across a strained Si-C bond of 5 afforded chlorotrifenocenylsilane, Fc(3)SiCl (6), in 81% yield. Subsequent hydrolysis of 6 afforded a silanol Fc(3)SiOH (7) with three ferrocenyl substituents. Single crystal X-ray diffraction of 7 revealed that the compound crystallizes as hydrogen-bonded dimers. When heated, 5 was found to undergo thermal ring-opening polymerization (ROP) to afford cyclic oligomeric species [fcSiFc(2)](x) (9(x),x = 2 or 3) and an insoluble polymeric material [fcSiFc(2)](n) (8). Copolymers 10 were obtained when 5 was heated in the presence of dimethyl [1] silaferrocenophane, fcSiMe(2) (1a). (C) 2000 Elsevier Science Ltd All rights reserved.