Inorganic Chemistry, Vol.33, No.8, 1709-1718, 1994
Synthesis, Structures, and the Redistribution and Skeletal Cleavage Reactions of Siloxane-Bridged Ferrocenophanes
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.
Keywords:RING-OPENING POLYMERIZATION;GLASS-TRANSITION BEHAVIOR;RAY CRYSTAL-STRUCTURES;HIGH-MOLECULAR-WEIGHT;INORGANIC POLYMERS;ATOMS;POLY(FERROCENYLSILANES);PHOSPHORUS;(2)FERROCENOPHANES;MACROMOLECULES