SYNTHESIS, REACTIVITY, AND RING-OPENING POLYMERIZATION (ROP) OF TIN-BRIDGED [1]FERROCENOPHANES

The first examples of tin-bridged [1]ferrocenophanes, Fe(eta-C5H4)(2)- SntBu(2) (7a) and Fe(eta-C5H4)(2)SnMes(2) (7b) have been synthesized b y the low-temperature reaction of Fe(eta-C5H4Li)(2). nTMEDA (TMEDA= N, N,N',N'-tetramethylethylenediamine) with tBu(2)SnCl(2) and Mes(2)SnCl( 2) (Mes = 2,4,6-trimethylphenyl), respectively. They were isolated in 65% (7a) and 85% (7b) yield as orange crystalline solids, which were c haracterized by multinuclear NMR and UV/Vis spectroscopy, mass spectro metry, elemental analysis, and single-crystal X-ray diffraction. The t ilt angles between the planes of the cyclopentadienyl rings are 14.1(2 )degrees for 7a and 15.2(2)degrees (average) for the three independent molecules of 7b in the unit cell. Although they have significantly sm aller tilt angles than analogous [1]ferrocenophanes with the lighter G roup 14 elements silicon or germanium in the bridge, 7a and 7b still r eadily undergo ring-opening polymerization (ROP) by thermal reaction i n the solid state (7a at 150 degrees C; 7b at 180 degrees C), to give high-molecular-weight poly(ferrocenylstannane)s [Fe(eta-C5H4)(2)SntBu( 2)](n) (8a) and [Fe(eta-C5H4)(2)SnMes(2)](n) (8b). Remarkably, 7a and 7b were also found to polymerize in solution at room temperature in th e absence of externally added initiators. ROP is much more rapid for 7 a than for 7b in solution. The cyclic dimers [Fe(eta-C5H4)(2)SnR2](2) (3; R = tBu, Mes) were formed as by-products in amounts which depended on the solvent. Electrochemical studies of the cyclic dimers and poly mers indicated the presence of significant Fe Fe interactions that are mediated by the tin-atom spacer. When benzene solutions of 7a and 7b were treated with small amounts of Karstedt's catalyst, slower polymer ization was observed. Stoichiometric reaction of Pt(1,5-cod)(2) (cod=c yclooctadiene) with 7a yielded the novel trimetallic 1-stanna-2-platin a[2]ferrocenophane Fe(eta-C5H4)(2)Pt(1,5-cod)SntBu(2) (9), which funct ioned as a sluggish catalyst for the ROP of 7a and 7b.