Polymer-supported reagents reactions reviewed

This chapter deals with both initial developments as well as more recent advances in the area of polymer-supported nucleophilic and electrophilic reagents, and reagents intended for radical-mediated reactions. Reviews by Kirschning [1] and Ley [2] cover this area up to 2001, and we also refer to the Ley group for reports on the application of polymer-supported reagents in total synthesis [3-5]. More details can also be found in reviews by Bradley [6] and Drewry [7]. 

There has been the anticipated increase in reports of the use of supported reagents to effect functional group transformations or remove excess reagents and by-products from crude solution phase reaction products. Combinatorial approaches using polymer supported reagents have been recently reviewed by Kaldor and Siegel [17]. 

A wide variety of reagents, catalysts, protecting groups, auxiliaries, etc. have been immobilised on polymer supports (Figure 6.1). The literature has been reviewed fairly comprehensively up to 1988 [18], but thereafter the number of papers appearing has escalated so that full coverage has become difficult. One particularly useful summary appeared in 1981 [70] with an up-date in 1983 [71], and the value of this lay in the convenient tabulation of the polymer structures which had been explored, and the reactions in which the supported species had been exploited. 

These polymers constitute the largest group to be discussed in this report and this is mainly because polystyrene and poly(chloromethylstyrene), often crosslinked with divinylbenzene, continue to be widely used in the preparation of functional polymers and resin-supported reagents. In fact most of the examples given here refer to the preparation of functional polymers rather than to new materials. This is a rapidly growing area of polymer chemistry and it is not possible to refer, in a compressed review of this nature, to all reports of functionalized styrene-based resins that have appeared in the past two years. This section falls naturally into three parts the first deals with styrene polymers and copolymers, the second with reactions on chloromethylated polystyrenes, and the third deals with styrene-related polymers. 

Support-bound transition metal complexes have mainly been prepared as insoluble catalysts. Table 4.1 lists representative examples of such polymer-bound complexes. Polystyrene-bound molybdenum carbonyl complexes have been prepared for the study of ligand substitution reactions and oxidative eliminations [51], Moreover, well-defined molybdenum, rhodium, and iridium phosphine complexes have been prepared on copolymers of PEG and silica [52]. Several reviews have covered the preparation and application of support-bound reagents, including transition metal complexes [53-59]. Examples of the preparation and uses of organomercury and organo-zinc compounds are discussed in Section 4.1. 

Resins can also be used to hold and deliver reagents or catalysts to facilitate selective reaction chemistry. A review of the application of supported catalysts to organic synthesis has been recently published [21] and references many additional review articles covering polymer-based synthesis. 

---