Molybdenum and tungsten alkylidene complexes for cis- and trans-selective ring-opening metathesis polymerization

Chapter 1 describes the synthesis of tert-butylimido alkylidene complexes for molybdenum and tungsten. A dimer species [chemical formula] served as a bisimido precursor. After alkylation with Grignard reagent, alkylidene formation is accomplished using pyridinium chloride. [chemical formula] crystallizes as a dimer [chemical formula] with a loss of pyridine for each W center. For the case of molybdenum, addition of pentafluorophenol to the diimido dialkyl precursor affords [chemical formula]. Dipyrrolide complexes for both Mo and W are synthesized and isolated as a 2,2'-bipyridine adduct. Addition of a sterically encumbered terphenol along with ZnCl₂(dioxane) affords monoalkoxide pyrrolide (MAP) complexes [chemical formula]. Chapter 2 investigates Z-selective ring-opening metathesis polymerization (ROMP) of 3- substituted cyclooctenes (3-RCOEs) by Mo and W MAP catalysts. [chemical formula], [chemical formula], and [chemical formula] all produced >98% [chemical formula]. The key in forming high molecular weight polymer instead of cyclic oligomer species was to run the reaction neat. Surprisingly, the fastest initiator was [chemical formula] among all three MAP species. Polymerization proceeds via a propagating species in which the R group is of C2 position of the propagating chain, giving HT polymers with high regioselectivity. Chapter 3 describes the synthesis and reactivity of compounds containing a tert-butylimido ligand. Chelating alkylidenes can be synthesized either by alkylidene exchange or by traditional routes in forming alkylidene complexes from diimido dialkyl species. A W MAP complex containing a chelating alkylidene can be synthesized and its reactivity is comparable to that of neopentylidene analogue in 1-octene homocoupling. Complexes with a chelating diolate ligand [chemical formula] and [chemical formula] were synthesized. However, attempts to remove the pyridine ligand induced C-H activation of one tertbutyl group on Biphen ligand to form alkyl complexes. Chapter 4 presents the synthesis of high sequence-regular alternating trans-AB copolymers by ROMP initiated by [chemical formula]. Monomers employed were 2,3-dicarbomethoxy-7-isopropylidenenorbomadiene (B), [chemical formula] (B'), cyclooctene (A), and cycloheptene (A'). All four combinations afford structures containing a high degree of monomer alternation. Evidence suggests a catalytic cycle proceeding through a syn alkylidene arising from insertion of B (syn-MB) reacting with A to form an anti alkylidene (anti-MA) and a trans-AB linkage. A MAP complex [chemical formula] [chemical formula] was also found to form trans-poly[A-alt-B'] with >90% alternating dyad sequences. Variations on imido and alkoxide ligands were surveyed as well as both A and B type monomers.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2015

Author dc:creator

• Jeong, Hyangsoo

• Chemistry.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/101548

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/101548