ROMP with Grubbs-Type Initiators

Compared to molybdenum- or tungsten-based Schrock catalysts, the reactivity of ruthenium-based Grubbs catalysts is somewhat different Reactivity in RuCl2(PR3)2(CHPh) may efficiently be tuned rather via the use of different phos-phanes [103] than by the nature of the alkylidene moiety [42] or by substitution of the chlorides by other, more elechon-withdrawing groups [104]. In principle, two 

Piers et al. were able to characterize a 14-electron ruthenacyclobutane obtained from the reaction of [RuCl2(lMesH2)(CHPCy3 ) B(QF5)4 ] with ethylene [109]. In view of these data and the results reported by Snapper et al. [110], a (flattened) intermediary ruthenacyclobutane trans to the phosphane or N-heterocyclic carbene ligand appeared to be the most abundant structure. Recent studies conducted by Grubbs et al. supported these data [111], although side-bound stmctures have also been reported by the same group [112]. 

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FIGURE 3.24 ROMP of norborn-5-ene-2-methanol with a Grubbs-type initiator in... 

ROMP with Grubbs and Crubbs-Hoveyda-Type Initiators... 

Example 3.34 ROMP of norborn-5-ene-2-methano with a Grubbs-Type Initiator in Solution... 

In principle the most common types of polyelectolytes like poly acids or polyamins should be accessible via ROMP with the Grubbs-type initiators. It turned out that direct polymerisation is problematic as both functional groups are able to form complexes with the initiator. So we decided to protect the carboxylic acid with a tetrahydropyrane group. After the polymerisation this group was easily hydrolysed and the polyacid or the respective salt was easily accessible [10]. 

Routes to the important class of well-defined ruthenium initiators of the Grubbs type (20b-22b) are summarized in Eigure 4 for details, see Table 2. COMC (1995) described the first example of this family, vinylalkylidene 20a, prepared by reaction of RuCl2(PPh3)3 with 2,2-diphenylcyclopropene. Subsequent treatment with PCys yields 20b (path (a)). (The corresponding complex 21a was later prepared by reaction of RuHCl(PPh3)3 with propargyl chloride see below). Initiator 20a effected controlled ROMP of and bicyclo[3.2.0]heptene M6, but ROMP of less... 

Possibly the most convenient direct route to polyacetylene, namely the polymerisation of cyclooctatetraene (COT), was introduced by Grubbs and co-workers [4], They initially showed that polyacetylene can be obtained via ROMP of COT using the very active Schrock type tungsten hexafluoro-t-butoxide initiator W(=CHR)(OC(Cp3)2 CH3 )2(=NAr). A freestanding film was obtained when the monomer was polymerised as the neat liquid. A random copolymer was obtained from the polymerisation of a mixture of COT and 1,5-cyclooctadiene (COD) and, as expected, a gradation in colour and Raman shift showed that the conjugation length of the polyene sequences increased with COT... 

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