The 1,3-disila-2-oxaferrocenophanes Fe(eta5-C5H4)2(SiR2)20 (1) (a, R = Me; b, R = Ph), the 1,3,5-trisila-2,4-dioxaferrocenophane Fe(eta5-C5H4)2(SiMe2O)2SiMe2 (2), and the 1,3,5,7-tetrasila-2,4,6-trioxaferrocenophane Fe(eta-C5H4)2(SiMe2O)3SiMe2 (3) have been prepared in low to good yield from the reaction of the appropriate alpha,omega-dichlorooligosiloxane Cl(SiR2O)xSiR2Cl (R = Me or Ph) with dilithioferrocene-tetramethyletbylenediamine. The methylated species 1a, 2, and 3 were found to undergo redistribution and skeletal cleavage reactions rather than ring-opening polymerization when heated in the melt at elevated temperatures in the presence of small quantities of K[OSiMe3]. Similar reactions were detected for 2 in solution in the presence of K[OSiMe3] or triflic acid as initiator and in attempts to copolymerize 2 with either the cyclotrisiloxane [Me2SiO]3 or the [1]ferrocenophane Fe(eta5-C5H4)2SiMe2. Analysis of the reaction products by Si-29 NMR and mass spectrometry showed that varying amounts of other siloxane-bridged [n]ferrocenophanes were formed together with cyclic and oligomeric siloxanes, small quantities of the linear species Fc(SiMe2O)xSiMe2Fc (4) (Fc = Fe(eta5-C5H4)(eta5-C5H5), X = 1-3), and ferrocene. In contrast to the behavior of 1a, 2, and 3, no redistribution reactions were detected for the more sterically encumbered phenylated 1,3-disila-2-oxaferrocenophane 1b under similar conditions. In order to examine structural trends as the ring size and the substituents are varied the molecular structures of 1a, 1b, 2, and 3 were determined by single-crystal X-ray diffraction. Because of the short siloxane bridge present, the cyclopentadienyl carbon-silicon bonds in 1a and 1b are almost eclipsed. In contrast, in 2 and 3 the presence of a longer siloxane bridge allows the cyclopentadienyl ligands in the ferrocenyl moiety to rotate relative to one another, which permits the adoption of a more stable staggered conformation. Crystals of 1a are triclinic, space group P1BAR with a = 8.5893(14) angstrom, b = 15.703(2) angstrom, c = 19.098 (4) angstrom, alpha = 69.684(13)degrees, beta = 77.860(15)degrees, gamma = 74.889(11)degrees, V = 2311.5(12) angstrom3, and Z = 6. Crystals of 1b are orthorhombic, space group P2(1)2(1)2, with a = 10.782(2) angstrom, b = 13.006(3) angstrom, c = 20.082(4) angstrom, V= 2816.1(14) angstrom3, and Z = 4. Crystals of 2 are triclinic, space group P1BAR with a = 9.0693(6) angstrom, b = 14.2473(9) angstrom, c = 17.3733(10) angstrom, alpha = 68.004(5)degrees, beta = 86.027(5)degrees, gamma = 75.733(5)degrees, V = 2016.6 (2) angstrom3, and Z = 4. Crystals of 3 are monoclinic, space group P2(1)/c, with a = 13.521(5) angstrom, b = 18.035(5) angstrom, c = 20.265(5) angstrom, beta = 94.010(2)degrees, V = 4930(3) angstrom3, and Z = 8.
