The development of processable high molecular weight polymers with skeletal transition metal atoms represents a synthetic challenge that, if overcome, can be expected to yield a variety of materials with novel electrical, optical, magnetic, or preceramic properties. Recent work has shown that the ringopening polymerization (ROP) of strained, ring-tilted [ 11or [2]metallocenophanes provides a route to a variety of welldefined, ferrocene-backbone polymers with molecular weights of over 1000000 in several cases.
prepare polymers with transition elements in the main chain are extremely rare.[61 This article focuses on recent discoveries in our group which have demonstrated that [n]metallocenophanes, species which contain a metallocene group with a bridge containing n atoms between the cyclopentadienyl ligands, function as precursors to well-defined high molecular weight macromolecules via ROP processes.[7 -"I containing ceramics.['] However, apart from several, mainly very recent, exceptions, most transition-metal-based polymers reported to date are of low molecular weight, or insoluble, or of poorly defined structure. [33 41 To help facilitate the development of transition-metalbased polymer science we have investigated the synthesis of high molecular weight, well-defined transition-metal-based polymers using ring-opening polymerization (ROP) techniques. ROP represents a powerful route to organic polymers and the ROP of cyclic compounds with skeletons containing atoms of main group elements is of growing importance.[s1 In contrast, reports of the use of ROP to [