Ring-opening Metathesis Polymerization Molybdenum(vi) Alkylidene Catalysts

S Chapter 1 Study of Chiral Arylimido Molybdenum ROMP Catalysts. Molybdenum ROMP catalysts with a chiral ortho-(phenethyl)phenylimido ligand have been prepared. Mo(CHCMe2Ph)(N-2-C 6H4-CHMePh)(O-2,6-C 6H3-Ph2)2 (1la) and Mo(CHMe 2Ph)(N2-C6H4-CHMePh)[BIPHENO(Me) 2(t-Bu) 4] (11b) were isolated and shown to effect the polymerization of 2,3-dicarbomethoxynorbonadienes. Highly-trans syndiotactic polymers and highly-cis isotactic polymers were isolated when Ila and lib were used as initiators, respectively. Surprisingly, Mo(CHCMe2Ph)(N-2-C 6H4-Me)(O-2,6-C 6H3-Ph2)2 (12) which bears a less bulky phenylimido substituent generated high-cis polymers with good tacticity depending on the monomer reactivity. This dramatic effect of the orthosubstituent is explained in terms of rate of rotamer isomerization and rehybridization of the nitrogen atom. Consequences on the role of chiral arylimido in the control over polymer tacticity are discussed. Attempts to isolate chiral catalysts with the previously studied tert-butoxido ligands only led to decomposition products. Chapter 2 Study of Chiral Alkylimido Molybdenum ROMP Catalysts. Molybdenum ring-opening metathesis polymerization catalysts with chiral alkylimido ligands have been prepared. Primary amines with a secondary a -carbon atom, such as a -methylbenzylamine (PhCHMeNH 2) do not give isolable products. tert-Alkylamines were prepared by reduction of the corresponding azides. a,a-Isopropyl-methyl-benzylamine (R*NH2 = MePh-i-PrNH 2, Ic) was used in further reactions to give a series of chiral alkylidene complexes Mo(CHCMe2Ph)(NR*)(OR) 2 (5) (where OR = OCMe 3, OCMe2CF 3, OCMe(CF3)2, O-2,6-C6H 3-Me2 , O-2,6-C 6H 3-Ph2). Nucleophilic attacks on Mo(CHCMe2Ph)(NR*)(OTf) 2 (DME) (4) and ligand substitutions on Mo(CHCMe2Ph)(NR*)(OCMe(CF 3)2)2 (5c) led to the proposal of two mechanisms that might be involved in the synthesis of molybdenum alkylidene ROMP initiators, based on the observation of the alkylidyne amido complex Mo(CCMe 2Ph)(NHR*)(OR) 2 (6) (where OR = OCMe3, OCMe(CF 3)2). Poly(2,3-dicarbomethoxynorbomrnadiene) and poly(2,3-bis((trifluoromethyl)norbomadiene) showed a bias towards trans double bonds. Further tacticity study using 5b suggested that the stereoregularity of the polymers was controlled by chain-end of the growing polymer, rather than by the chiral tert-alkylimido ligand. Implications for the role of chiral alkylimido in the control of polymer tacticity are discussed. Chapter 3 Study of Chiral Biphenoxido Molybdenum ROMP Catalysts. A ligand variation which assures a "locked" configuration of BIPHENO-based molybdenum ROMP catalysts is described. Three complexes were prepared and their activity toward norbornadiene monomers examined. Mo(CHCMe 2Ph)(N-2,6-C 6H3-Me2)[BIPHENO(Me)2(t-Bu)4] (5) and Mo(CHCMe2Ph)(N-2-C 6H4-CHMePh)[BIPHENO(Me) 2(t-Bu) 4] (6) both gave highcis highly-isotactic polymers by enantiomorphic metal-site control. On the other hand, polymers with little double bond stereoselectivity were isolated from Mo(CHCMe 2Ph)(N-2-C6H 4-t-Bu)[BIPHENO(Me) 2(t-Bu) 4] (7). Complexes 5-7 were all isolated in the absence of coordinating bases. BIPHENOand BINO-based complexes are compared and their efficiency at generating stereoregular polymers is further discussed. Chapter 4 Investigation of Copper Nanoclusters Prepared within Microphase-Separated ROMP Diblock Copolymer Films. Attempts to prepare copper nanoclusters within microphase-separated ROMP diblock copolymers are described. Three metal-organic chemical vapor deposition (MOCVD) systems are presented and were used in the study. Phosphine(CuCp) (1) and phosphine(Cu(hfac)) (2) (hfac = hexafluoroacetylacetonato) were first investigated as precursors to elemental copper. Spherical microdomains were obtained by blending with methyltetradodecene homopolymer ([MTD]m) to achieve 10% w/w of the Cu-containing block. The polymers were dissolved in benzene. Good quality films were cast by transferring the solvent under vacuum, and well-behaved microphase separation was observed by transmission electron microscopy (TEM). However, pyrolysis of the films did not result in aggregation to clusters, as judged by TEM, probably due to passivation of the surface by the phosphine atoms. A third attempt using alkyne(Cu)(hfac) (3), where no Lewis base is present, did not give satisfactory results owing to coordination of the Cu(hfac) moiety to alkenes. Chapter 5 Synthesis of Electroluminescence-Active Species. The synthesis of norbornene-type monomers with pendent electroluminescence-active moieties is presented. Two oxadiazole monomers (4, 10) were prepared and subjected to ring-opening metathesis polymerization (ROMP) using Mo(CHCMe2Ph)(N-2,6-C 6H3-i-Pr 2)(O-t-Bu)2 to give polymers with a narrow molecular weight distribution (Mw/Mn < 1.12). In addition to the monomers functionalized with the oxadiazole moiety as electron-transport material, phenanthrene-based monomers (13, 16endo, and 18) were prepared. ROMP of 13 using Mo(CHCMe 2Ph)(N-2,6-C 6H3-i-Pr 2)(0-t-Bu)2 gave a well-behaved polymer with MwlMn = 1.25. However, attempts to polymerize 16endo with Mo(CHCMe 2Ph)(N-2,6-C 6H3-iPr2)(O-t-Bu) 2 or the more reactive Mo(CHCMe 2Ph)(N-2,6-C 6H3-Me2)(OCMe(CF 3)2) gave poor results. The synthesis of the pure exo homologue 18 was not successful. Some preliminary work toward para-terphenyl monomers is also described. The charge-block principle is introduced and discussed in context of the monomer choices. Thesis Supervisor: Dr. Richard R. Schrock Title: Frederick G. Keyes Professor of Chemisty