Norbomene molybdenum complexes

Synthetic protein-like polymers containing amino acids find pharmaceutical and biological applications and display self-assembly properties [174], In this aspect, both ROMP and ADMET have been used as tools for the polymerization of amino acid-based monomers. Early ROMP examples date back to 1994 with the synthesis and ROMP of amino acid-derived homochiral norbomene monomers by Coles et al [175], The molybdenum complex [Mo(=CHCMe2Ph)(=NC6H3Pr,2-2,6)(OBu )2]... 

The molybdenum neopentyUdene complex Mo(CHBu )(NR)(OBu )2 is the active catalyst used in a fascinating development for the synthesis of 11-Vt semiconductor clusters (ZnS, CdS, PbS) and silver and gold nanoclusters of predictable size within microdomains in films of block copolymers prepared by ROMP. Block copolymers of norbomene and a functionalized norbomene that wiU complex with a metal-containing compound were prepared and characterized as monodisperse materials. The functionalized component (amine, alkoxide, or thiolate) then sequestered the metal and the metallated block copolymer was cast into a film which was subsequently treated with H2S to convert the metal into the sulfide. The molybdenum complexes have also featured in the development of the synthesis of side-chain liquid crystal polymers by living ROMP.98 99... 

A related complex, Mo(N-t-Bu)(CH-t-Bu)(OCMe(CF3)2)2 (10), was synthesized by Osborn et al. and investigated for the ROMP of norbomene and acyclic internal olefins [146]. Boncella performed metathesis reactions using tris(pyrazolyl)borate stabilized molybdenum complexes in combination with AIQ3 [147]. 

The proposed idea that metal alkyhdene complexes are be able to catalyze olefin metathesis was confirmed in 1980 [8] and consolidated in 1986 by Schrock with the development of the first well-characterized, highly active, neutral tungsten (Cl, Fig. 3) [9] and molybdenum (C2) [10] alkylidene complexes. These complexes were able to catalyze both the metathesis of different olefins and the ROMP of functionalized norbomene to polynorbomene with low polydispersities [11]. Moreover, these catalysts were used by Wagener and coworkers to perform the first quantitative ADMET polymerization [12] and copolymerization [13] of 1,5-hexadiene and 1,9-decadiene. However, the low stability of these catalysts in... 

The second step involved the ROMP of the functionalised PEO macromer using the well-defined Schrock (hexa-fluorinated) or Grubbs initiating complexes. Each initiator had a metal core (molybdenum or ruthenium) with bulky ligands that controlled the approach and co-ordination of the reactive carbene bond to the double bond of the norbomene group... 

Czelusniak I, Szymanska-Buzar T. Ring-opening metathesis polymerization of norbomene and norbomadiene by tungsten(n) and molybdenum(II) complexes. J Mol Catal A Chem 2002 190 131-143. 

More complex heterocyclic structures have been synthesized efficiently and with high stereoselectivities using tandem AROM-RCM sequences [85] similarly, application of tandem AROM/CM to functionalized norbomenes affords enantio-pure highly functionalized cydopentanes [86]. A polymer-supported chiral molybdenum catalyst for enantioselective metathesis effidendy promotes ARCM (kinetic resolution as well as desymmetrization) and AROM reactions and can be recycled [87]. 

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