Z-selective olefin metathesis processes and Cis/syndioselective ROMP with high oxidation state molybdenum alkylidenes
Author(s)Flook, Margaret McGuigan
Massachusetts Institute of Technology. Dept. of Chemistry.
Richard R. Schrock.
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Chapter 1: Reaction of W(CCMe3)Cl 3(dme) with one equivalent of (3,5-Me 2C6H3NCH2CH 2)3N)Li3 affords yellow, crystalline W(CCMe3)(N3N) in good yield. The reactivity of this new alkylidyne complex towards terminal alkynes was investigated. Two other new tungsten alkylidynes, W(CCMe3)(pyr) 3 (pyr = 2,5-dimethylpyrrolide) and W(CCMe3)(Ph 2N)3 were prepared by the addition of three equivalents of lithium dimethylpyrrolide or lithium diphenylamide, respectively, to W(CCMe3)Cl 3(dme). The reactivity of these new alkylidynes with various alcohols is reported. The reactivity of several tungsten alkylidyne compounds towards ligand displacement by surface silanols is reported, resulting in the synthesis of several new silicasupported tungsten alkylidynes. The alkyne metathesis activity of all new homogeneous and heterogeneous alkylidyne complexes is reported. Chapter 2: Addition of one equivalent of 2,4,6,2',4',6'-hexaisopropylterphenol to Mo(NAd)(CHCMe 2Ph)(pyr)2 results in the formation of Mo(NAd)(CHCMe 2Ph)(pyr)(HIPTO) (HIPTO = hexaisopropylterphenoxide). This new alkylidene compound was found to catalyze the metathesis of 1-hexene in 20% yield to 95% cis 5-decene, which represents the first report of highly Z-selective metathesis homocoupling of a terminal olefin. The decomposition of the catalyst in the presence of ethylene is explored. The syntheses of several new bulky achiral phenoxide ligands are presented, along with the syntheses of the corresponding MAP (monoalkoxide monopyrrolide) molybdenum imido alkylidene compounds. The reactivity of new MAP compounds containing bulky phenoxide ligands towards the Z-selective metathesis of terminal and internal olefins is presented. The cis-selectivity of this system is proposed to arise from the combination of a relatively small imido ligand in conjunction with a very bulky alkoxide forcing the substituents of the substrate to point in this same direction with each insertion. Photolysis of MAP compounds with 366 nm radiation was found to produce significant amounts of anti alkylidenes, and the kinetics of decay of unstable anti alkylidenes are investigated. Chapter 3: The reaction of 2,3-dicarbomethoxynorbomadiene (DCMNBD) with Mo(NAd)(CHCMe 2Ph)(pyr)(HIPTO) (Ad = 1-adamantyl, HIPTO = hexaisopropylterphenoxide) affords >98% cis, >98% tactic polyDCMNBD. The tacticity of this polymer is proved to be syndiotactic through polymerization of DCMenthNBD (2,3-dicarbomenthoxynorbomadiene) and IH- H COSY. A variety of related MAP alkylidene compounds are also investigated towards the ROMP of DCMNBD and found to produce polyDCMNBD in a range of tacticities and cis contents. Highly cis polyNBDF6 (poly-bis(CF 3)-norbomadiene) was also prepared using molybdenum MAP compounds, and the resulting polymer was found to be essentially insoluble in common organic solvents. Solid state CPMAS 13C NMR spectroscopy revealed insoluble polyNBDF6 to be highly tactic, and the tacticity is proposed to be syndiotactic. Cis, tactic polymer was prepared through the addition of 3,3-methylphenylcyclopropene (MPCP) to molybdenum MAP compounds. Attempts towards determination of the tacticity of cispolyMPCP are presented, including the synthesis of three 3,3-disubstituted cyclopropene monomers containing chiral tags. The cis-selective ROMP of cyclooctene and 1,5- cyclooctadiene are reported. The syndioselectivity of the catalysts is proposed to be controlled by the configuration of the 4-coordinate metal center, which alternates with each insertion of monomer. Chapter 4: Racemic 2,3-dicarbomethoxynorbornene (rac-DCMNBE) is polymerized by Mo(NAd)(CHCMe 2Ph)(pyr)(HMTO) (Ad = 1-adamantyl, pyr = pyrrolide, HMTO = hexamethylterphenoxide) to afford an all-cis polymer that is syndiotactic and composed of alternating enantiomers. The cis, syndiotactic ROMP of several other racemic chiral monomers are reported, also affording structures containing a high degree of enantiomer alteration. Attempts towards the alternating copolymerization of two different monomers are reported. The ROMP of enantiomerically pure (+)-dicarbomethoxynorbornene with Mo(NAd)(CHCMe 2Ph)(pyr)(HIPTO) leads to the production of 92% trans-isotactic polyDCMNBE. The structure of trans-isotactic polyDCMNBD is proved through hydrogenation and comparison of its 3C NMR spectrum with that of known cis-isotactic polyDCMNBE. Both cis/syndiotactic/alternating poly-rac-DCMNBE and trans/isotactic poly-(+)-DCMNBE are polymer structures that have not been previously reported. The thermal properties of all new polymers and their hydrogenated counterparts are reported and are found to correlate closely with polymer structure.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2012.Vita. Cataloged from PDF version of thesis.Includes bibliographical references.
DepartmentMassachusetts Institute of Technology. Dept. of Chemistry.
Massachusetts Institute of Technology