Cyclopropene polymerization and enyne metathesis catalyzed by high oxidation state molybdenum alkylidenes
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.
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| Format: | Thesis |
| Language: | eng |
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Massachusetts Institute of Technology
2008
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| Online Access: | http://hdl.handle.net/1721.1/43771 |
| _version_ | 1811068393508306944 |
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| author | Singh, Rojendra |
| author2 | Richard R. Schrock. |
| author_facet | Richard R. Schrock. Singh, Rojendra |
| author_sort | Singh, Rojendra |
| collection | MIT |
| description | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008. |
| first_indexed | 2024-09-23T07:55:21Z |
| format | Thesis |
| id | mit-1721.1/43771 |
| institution | Massachusetts Institute of Technology |
| language | eng |
| last_indexed | 2024-09-23T07:55:21Z |
| publishDate | 2008 |
| publisher | Massachusetts Institute of Technology |
| record_format | dspace |
| spelling | mit-1721.1/437712022-01-13T07:54:21Z Cyclopropene polymerization and enyne metathesis catalyzed by high oxidation state molybdenum alkylidenes Singh, Rojendra Richard R. Schrock. Massachusetts Institute of Technology. Dept. of Chemistry. Massachusetts Institute of Technology. Department of Chemistry Chemistry. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008. Vita. Includes bibliographical references. Chapter 1. An olefin metathesis reaction between Mo(NAr)(CHCMe2Ph)(OCMe(CF3)2)2 (Ar = 2,6diisopropylphenyl) and trans-i 1,4-divinylbenzene or trans, trans- 1,4-di-buta- 1,3-dienylbenzene (5) results in the formation of bimetallic ROMP initiators [(DME)((CF3)2MeCO)2(ArN)MoCH]2-1,4-C6H4 (DME = 1,2-dimethoxyethane; la) and [(DME)((CF3)2MeCO)2(ArN)MoCHCHCH]2-1,4-C6H4 (6), respectively. An X-ray study of [(THF)((CF3)2MeCO)2(ArN)MoCH]2-1,4-C6H4 (THF = tetrahydrofuran; ib), which is closely related to la, showed it to be the expected bimetallic species in which each end is approximately a trigonal bipyramidal monoadduct of a syn alkylidene with the THF coordinated to the NOO face of the metal trans to the Mo=C bond. Treatment of la with hium-t-butoxide yielded [(Bu-t-O)2(ArN)MoCH]2-1,4-C6H4 (2). Addition of four equivalents of Me3CCH2MgCl to la produced the bimetallic species [(Me3CCH2)2(ArN)MoCH]2- 1,4-C6H4 (3), which upon treatment with 2,6diisopropylphenol generated a diastereomeric mixture of [(DME)(ArO)(Me3CCH2)(ArN)MoCH]2-1,4-C6H4 (4). The solid state structure of 3 revealed a "syn/syn" bimetallic species related to lb. In solution two resonances can be observed in the alkylidene region of the 1H NMR spectra for the "syn/anti" isomer of la, Ib, 2, 3, 4 and 5. The total amount of the "syn/anti" isomer varies between 4 and 20% of the total. Bimetallic species la, 2, and 6 initiate at both ends upon addition of less than ten equivalents of 4,5-dicarbomethoxynorbornadiene (DCMNBD),and afford homopolymers of DCMNBD and methyltetracyclododecene (MTD) in a living fashion. MALDI-TOF mass spectra of ferrocene-containing homopolymers have been obtained that are consistent with the polymerization process being living. (cont.) Triblock copolymers MTDxDCMNBDyMTDx were prepared by adding y equivalents of DCMNBD to the bimetallic ROMP initiators followed (after consumption of DCMNBD) by 2x equivalents of MTD. These triblocks were shown to be of relatively high purity (free of homopolymer and diblock copolymer) and to have a relatively low polydispersity index. Chapter 2 A series of monomers with side chain liquid crystals (SCLCs) were synthesized for ring opening metathesis polymerization (ROMP). The liquid crystals (LCs) used were 4hydroxybenzoic acid 4-methoxyphenyl ester (MPOB-H), which is known to exhibit a nematic liquid crystalline phase, and biphenyl-4-carboxylic acid 4-(1butoxycarbonylethoxy)phenyl ester (BPP4-H), which is known to exhibit a smectic phase. The side chains differed in spacer length, spacer type, and the nature of the LC. Monomers were polymerized using a bimetallic ROMP initiator [(Bu-t-O)2(ArN)MoCH]2-1,4-C6H4 (where Ar = 2,6-diisopropylphenyl); both homopolymers and ABA type triblock copolymers, where the B block is the LC functional monomer, and A is methyltetracyclodocene (MTD) were prepared. The polymers displayed unimodal peak distributions with polydispersities < 1.22. Incorporation of a polyoxyethylene spacer decreased the glass transition temperature (Tg) of the polymer block to -25 from +20 TC, the Tg when an alkyl spacer was used. Although no distinct LC phase was observed with the polyoxyethylene spacer when MPOB was used, use of BPP4 in conjunction with a polyoxyethylene spacer displayed a distinct liquid crystalline transition. Polymers with an alkyl spacer exhibited liquid crystalline behavior and good phase segregation on the basis of differential scanning calorimetry and small-angle X-ray scattering studies. (cont.) Chapter 3. Molybdenum imido alkylidene complexes supported by 2,6-diisopropylphenyl, 2,6dimethylphenyl, 1-adamantyl, or 2-trifluorophenyl that contain relatively electronwithdrawing phenolate (pentafluoro), binaphtholate (3,3'-bis(9-anthracenyl), 3,3'bispentafluorophenyl, or 3,3'-bis(3,5-bis(trifluoromethyl)phenyl)) or biphenolate (3,3'-ditert-butyl-5,5'-bistrifluoromethyl-6,6'-dimethyl-1,1'-biphenyl) ligands have been prepared to be tested in olefin metathesis reactions. A series of new monomeric pyrrolide complexes, Mo(NR)(CHCMe2R')(2,5-dimethylpyrrolide)2 (where R' = Me or Ph) and Mo(NAd)(CHCMe2Ph)(2,4-dimethylpyrrolide)2, were also synthesized and treated with alcohols, biphenols or binaphthols in order to generate Mo(NR)(CHCMe2Ph)(diolate) species. In several cases the new alkylidene complexes could be prepared only through reaction of two equivalents of pentafluorophenols or an equivalent of binaphthol (3,3'bis(pentafluorophenyl)binaphthol or 3,3'-bis(3,5-bis(trifluoromethyl)phenyl binaphthol) with a bis(2,5-dimethylpyrrolide) complex. The pyrrolide approach can be employed either to isolate catalysts on a preparative scale or to generate catalysts in situ. Several simple preliminary ring-closing metathesis reactions show that the new complexes are catalytically competent. Chapter 4. Living ring opening metathesis polymerization of cyclopropenes using Mo(NAr)(CHCMe2R)(O-t-Bu)2 (where R = Me; la or R = Ph; ib) and Mo(NAr)(CHCMe2Ph)(OCMe(CF3)2)2 (2) has been achieved. The polydispersity indices of the polymers generated are recorded to be < 1.10 for la and lb based on gel permeation chromatography (GPC). Living polymerization of 3-methyl-3phenylcyclopropene (MPC) by t-butoxide derived molybdenum imido alkylidene initiators is utilized in the synthesis of block copolymers. (cont.) Diblock copolymers MPCPxDCMNBDy (where DCMNBD = 2,3- dicarbomethoxynorbornadiene and x and y are the number of equivalents of MPC and DCMNBD, respectively) were prepared in quantitative yield with unimodal peak distribution via sequential addition of monomers to the initiator 1b. Triblock copolymers MPC100MEMC100MPCoo0 and MTDiooMEMCIooMTDjoo were prepared using [(O-t-Bu)2(ArN)MoCH]2-1,4-C6H4 (IC) as an initiator. The block copolymers revealed good phase segregation based on the differential scanning calorimetry (DSC). ROMP of MPC by molybdenum imido alkylidene initiators containing electron-withdrawing diolates resulted in highly tactic polymers as determined by 'H and 13C NMR spectroscopy. IR spectroscopy of all MPCl00 revealed absorptions at 963 and/or 982 cm-1 of approximately equal intensity that are most consistent with a trans structure. Chapter 5. Addition of one equivalent of ROH to Mo(NAr)(CHCMe2Ph)(2,5-dimethylpyrrolide)2 (Ar = 2,6-diisopropylphenyl) in diethyl ether or THF yielded Mo(NAr)(CHCMe2Ph)(OR)(2,5-dimethylpyrrolide) species where R = (CH3)3C (1), (CH3)2CH (2), Ar (3), (CF3)2CH (4), (CF3)2MeC (5), (Bu-t-O)3SiO (6) or C6F50 (7). Treatment of an equivalent of PMe3 to 5 resulted in the formation of (Me3P)Mo(NAr)(CHCMe2Ph)(OCMe(CF3)2)(PyrMe) (Me3P-5), which showed trans binding of PMe3 with respect to 2,5-dimethylpyrrolide ligand as determined by the 'H NOESY spectrum. The solid state structure of 3 depicts a psuedo-tetrahedral geometry around the metal center with the 2,5-dimethylpyrrolide ligand bound rq' to the metal cener. (cont.) Complexes 1-6 show rapid reaction when treated with one atmosphere of ethylene and catalyze ring-closing metathesis reactions. Hetereogenous analogs of 6, Mo(NAr)(CHCMe2Ph)(PyrMe)(OSisurf) (10a), Mo(NAd)(CHCMe2Ph)(PyrMe)(OSisurf) (10b) and Mo(NArF)(CHCMe2Ph)(PyrMe)(OSisurf) (10c) (Ad = 1-adamantyl and ArF = 2trifluoromethylphenyl) showed great enhancement in the catalytic activity when employed in self-metathesis of propene and ethyloleate. Ring-closing enyne metathesis catalyzed by 1 - 6 leads to cyclic products that arise through initial addition of the triple bond to a methylene species (initially neophylidene) to yield an cC- or a 3-substituted metallacyclobutene intermediate. by Rojendra Singh. Ph.D. 2008-12-11T18:25:00Z 2008-12-11T18:25:00Z 2008 2008 Thesis http://hdl.handle.net/1721.1/43771 260401395 eng 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. http://dspace.mit.edu/handle/1721.1/7582 242 leaves application/pdf Massachusetts Institute of Technology |
| spellingShingle | Chemistry. Singh, Rojendra Cyclopropene polymerization and enyne metathesis catalyzed by high oxidation state molybdenum alkylidenes |
| title | Cyclopropene polymerization and enyne metathesis catalyzed by high oxidation state molybdenum alkylidenes |
| title_full | Cyclopropene polymerization and enyne metathesis catalyzed by high oxidation state molybdenum alkylidenes |
| title_fullStr | Cyclopropene polymerization and enyne metathesis catalyzed by high oxidation state molybdenum alkylidenes |
| title_full_unstemmed | Cyclopropene polymerization and enyne metathesis catalyzed by high oxidation state molybdenum alkylidenes |
| title_short | Cyclopropene polymerization and enyne metathesis catalyzed by high oxidation state molybdenum alkylidenes |
| title_sort | cyclopropene polymerization and enyne metathesis catalyzed by high oxidation state molybdenum alkylidenes |
| topic | Chemistry. |
| url | http://hdl.handle.net/1721.1/43771 |
| work_keys_str_mv | AT singhrojendra cyclopropenepolymerizationandenynemetathesiscatalyzedbyhighoxidationstatemolybdenumalkylidenes |