{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/20877"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/20877","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Observation of the first titanium alkyl/alkyl complexes: The key intermediate in the Ziegler-Natta mechanism for the polymerization of alkenes","abstract":"The complexes trans-TiX$\\sb2$(dmpe)$\\sb2$ (X = BH$\\sb4,$ Br, Cl, Me, and OPh) react with alkenes to give two diamagnetic products: the mononuclear and dinuclear complexes trans-TiX$\\sb2$ (alkene)(dmpe)($\\eta\\sp1$-dmpe) and trans- (TiX$\\sb2$(alkene)(dmpe)) $\\sb2(\\mu$-dmpe). A crystallographic study of (TiCl$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)) $\\sb2(\\mu$-dmpe) confirms the trans geometry and shows that the ethylene ligand resides in the plane described by the phosphine ligands. The complexes TiMe$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)($\\eta\\sp1$-dmpe) and (TiMe$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)) $\\sb2(\\mu$-dmpe) are the first structural models of the key titanium alkyl/alkene intermediate in the Cossee mechanism for Ziegler-Natta catalysis. Above $-$20$\\sp\\circ$C, the TiX$\\sb2$(dmpe)$\\sb2$ complexes catalyze the dimerization of ethylene to 1-butene with turnover rates of up to 440 hr$\\sp{-1};$ the rates of ethylene dimerization vary according to the nature of the X group (Me $>$ BH$\\sb4 >$ Cl $>$ OPh). Most of the evidence favors a mechanism involving the oxidative coupling of two coordinated ethylenes followed by $\\beta$-hydrogen abstraction and reductive elimination. Interestingly, there is no insertion of ethylene into the Ti-CH$\\sb3$ bonds. This behavior is probably a general feature of d$\\sp2$ metal centers.","abstract_html":"The complexes trans-TiX$\\sb2$(dmpe)$\\sb2$ (X = BH$\\sb4,$ Br, Cl, Me, and OPh) react with alkenes to give two diamagnetic products: the mononuclear and dinuclear complexes trans-TiX$\\sb2$ (alkene)(dmpe)($\\eta\\sp1$-dmpe) and trans- (TiX$\\sb2$(alkene)(dmpe)) <span class=\"etd-inline-math\">\\sb2(&mu;</span>-dmpe). A crystallographic study of (TiCl$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)) <span class=\"etd-inline-math\">\\sb2(&mu;</span>-dmpe) confirms the trans geometry and shows that the ethylene ligand resides in the plane described by the phosphine ligands. The complexes TiMe$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)($\\eta\\sp1$-dmpe) and (TiMe$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)) <span class=\"etd-inline-math\">\\sb2(&mu;</span>-dmpe) are the first structural models of the key titanium alkyl/alkene intermediate in the Cossee mechanism for Ziegler-Natta catalysis. Above $-$20$\\sp\\circ$C, the TiX$\\sb2$(dmpe)$\\sb2$ complexes catalyze the dimerization of ethylene to 1-butene with turnover rates of up to 440 hr$\\sp{-1};$ the rates of ethylene dimerization vary according to the nature of the X group (Me $&gt;$ BH$\\sb4 &gt;$ Cl $&gt;$ OPh). Most of the evidence favors a mechanism involving the oxidative coupling of two coordinated ethylenes followed by <span class=\"etd-inline-math\">&beta;</span>-hydrogen abstraction and reductive elimination. Interestingly, there is no insertion of ethylene into the Ti-CH$\\sb3$ bonds. This behavior is probably a general feature of d$\\sp2$ metal centers.","abstract_has_math":true,"creators":["Spencer, Michael Donald"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Chemistry","degree_department":null,"school":null,"contributors":["Girolami, Gregory S."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2011,"date_issued":"2011-05-07T12:51:53Z","date_published":"2011-05-07T12:51:53Z","updated_at":"2026-07-22T22:25:16Z","subjects":["Chemistry, Inorganic"],"languages":["eng"],"rights":["Copyright 1993 Spencer, Michael Donald"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["AAI9411788","(UMI)AAI9411788"],"render_values":[{"text":"AAI9411788","href":null,"code":true},{"text":"(UMI)AAI9411788","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/20877","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Girolami, Gregory S."]},{"key":"dc:creator","label":"Author","values":["Spencer, Michael Donald"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2011-05-07T12:51:53Z","10000-01-01","1993"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Chemistry"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Chemistry, Inorganic"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 1993 Spencer, Michael Donald"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["AAI9411788","(UMI)AAI9411788","http://hdl.handle.net/2142/20877"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["The complexes trans-TiX$\\sb2$(dmpe)$\\sb2$ (X = BH$\\sb4,$ Br, Cl, Me, and OPh) react with alkenes to give two diamagnetic products: the mononuclear and dinuclear complexes trans-TiX$\\sb2$ (alkene)(dmpe)($\\eta\\sp1$-dmpe) and trans- (TiX$\\sb2$(alkene)(dmpe)) $\\sb2(\\mu$-dmpe). A crystallographic study of (TiCl$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)) $\\sb2(\\mu$-dmpe) confirms the trans geometry and shows that the ethylene ligand resides in the plane described by the phosphine ligands. The complexes TiMe$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)($\\eta\\sp1$-dmpe) and (TiMe$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)) $\\sb2(\\mu$-dmpe) are the first structural models of the key titanium alkyl/alkene intermediate in the Cossee mechanism for Ziegler-Natta catalysis. Above $-$20$\\sp\\circ$C, the TiX$\\sb2$(dmpe)$\\sb2$ complexes catalyze the dimerization of ethylene to 1-butene with turnover rates of up to 440 hr$\\sp{-1};$ the rates of ethylene dimerization vary according to the nature of the X group (Me $>$ BH$\\sb4 >$ Cl $>$ OPh). Most of the evidence favors a mechanism involving the oxidative coupling of two coordinated ethylenes followed by $\\beta$-hydrogen abstraction and reductive elimination. Interestingly, there is no insertion of ethylene into the Ti-CH$\\sb3$ bonds. This behavior is probably a general feature of d$\\sp2$ metal centers.","Addition of butadiene or 1,4-diphenyl-1,3-butadiene to TiMe$\\sb2$(dmpe)$\\sb2$ affords complexes of stoichiometry TiMe$\\sb2(\\eta\\sp4$-C$\\sb4$H$\\sb4$R$\\sb2$)(dmpe) (R = H or Ph); the latter has been isolated and characterized crystallographically. At higher temperatures, the reaction of TiMe$\\sb2$(dmpe)$\\sb2$ with 1,3-butadiene proceeds further to form TiMe$\\sb2$(C$\\sb8$H$\\sb{12})$(dmpe); the C$\\sb8$H$\\sb{12}$ ligand is formed by oxidative coupling of two butadienes and allylic rearrangement to expand the ring. The reaction of TiMe$\\sb2$(dmpe)$\\sb2$ with styrene gives the titanium(0) complex, Ti($\\eta\\sp2$-styrene)($\\eta\\sp4$-C$\\sb4$H$\\sb4$Ph$\\sb2)$(dmpe), via the same oxidative coupling mechanism except that $\\beta$-hydrogen elimination is followed by reductive elimination of methane rather than of diphenylbutene.","The reactions of TiX$\\sb2$(dmpe)$\\sb2$ with carbon monoxide lead to the formation of the eight-coordinate complexes TiX$\\sb2$(CO)$\\sb2$(dmpe)$\\sb2$ for X = Cl or Br, which have been characterized by NMR spectroscopy.","The reaction of TiMe$\\sb2$(dmpe)$\\sb2$ with t-butylsilane yields the zerovalent complex Ti(dmpe)$\\sb3,$ which has been crystallographically characterized. The reaction of TiMe$\\sb2$ (dmpe)$\\sb2$ with phenylsilane yields two complexes in succession that appear to be titanium silyl complexes of stoichiometry Ti(Si$\\sb2$Ph$\\sb2$H$\\sb4)$Me$\\sb2$(dmpe)$\\sb2$ and Ti(Si$\\sb3$H$\\sb5$Ph$\\sb3)$(dmpe)$\\sb2.$","Variable temperature NMR studies of the dinuclear chromium(II) alkyl anion (Li(thf)$\\sb2\\rbrack\\sb2\\lbrack$Cr$\\sb2$(CH$\\sb2$SiMe$\\sb3)\\sb6$) show that the two bridging CH$\\sb2$SiMe$\\sb3$ groups engage in agostic Cr$\\cdots$H-C interactions that are static on the NMR timescale at $-$80$\\sp\\circ$C. At higher temperatures, the molecule undergoes two different dynamic processes. One process, which has activation parameters of $\\Delta$H$\\ddagger$ = 10.6 $\\pm$ 0.5 kcal mol$\\sp{-1}$ and $\\Delta$S$\\ddagger$ = $-$4 $\\pm$ 2 eu, is ascribed to exchange between the terminal and bridging CH$\\sb2$SiMe$\\sb3$ ligands; the other process, which has activation parameters of $\\Delta$H$\\ddagger$ = 14.1 $\\pm$ 0.6 kcal mol$\\sp{-1}$ and $\\Delta$S$\\ddagger$ = 17 $\\pm$ 3 eu, is ascribed to rotation of the bridging CH$\\sb2$SiMe$\\sb3$ ligands about their Cr-C bonds. The latter values give an estimate of the strength of an agostic Cr$\\cdots$H bond.","Made available in DSpace on 2011-05-07T12:51:53Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9411788.pdf: 7665810 bytes, checksum: a5fad8345b9a849d71727fbcad179f49 (MD5) Previous issue date: 1993","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:46:54Z Item is restricted indefinitely.","Restriction data tranferred 2014-07-01T11:21:07-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission","ETDs are only available to UIUC Users without author permission","U of I Only"]},{"key":"dc:title","label":"Title","values":["Observation of the first titanium alkyl/alkyl complexes: The key intermediate in the Ziegler-Natta mechanism for the polymerization of alkenes"]}]}],"canonical_facts":{"dc:contributor":["Girolami, Gregory S."],"dc:creator":["Spencer, Michael Donald"],"dc:date":["2011-05-07T12:51:53Z","10000-01-01","1993"],"dc:description":["The complexes trans-TiX$\\sb2$(dmpe)$\\sb2$ (X = BH$\\sb4,$ Br, Cl, Me, and OPh) react with alkenes to give two diamagnetic products: the mononuclear and dinuclear complexes trans-TiX$\\sb2$ (alkene)(dmpe)($\\eta\\sp1$-dmpe) and trans- (TiX$\\sb2$(alkene)(dmpe)) $\\sb2(\\mu$-dmpe). A crystallographic study of (TiCl$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)) $\\sb2(\\mu$-dmpe) confirms the trans geometry and shows that the ethylene ligand resides in the plane described by the phosphine ligands. The complexes TiMe$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)($\\eta\\sp1$-dmpe) and (TiMe$\\sb2$(C$\\sb2$H$\\sb4)$(dmpe)) $\\sb2(\\mu$-dmpe) are the first structural models of the key titanium alkyl/alkene intermediate in the Cossee mechanism for Ziegler-Natta catalysis. Above $-$20$\\sp\\circ$C, the TiX$\\sb2$(dmpe)$\\sb2$ complexes catalyze the dimerization of ethylene to 1-butene with turnover rates of up to 440 hr$\\sp{-1};$ the rates of ethylene dimerization vary according to the nature of the X group (Me $>$ BH$\\sb4 >$ Cl $>$ OPh). Most of the evidence favors a mechanism involving the oxidative coupling of two coordinated ethylenes followed by $\\beta$-hydrogen abstraction and reductive elimination. Interestingly, there is no insertion of ethylene into the Ti-CH$\\sb3$ bonds. This behavior is probably a general feature of d$\\sp2$ metal centers.","Addition of butadiene or 1,4-diphenyl-1,3-butadiene to TiMe$\\sb2$(dmpe)$\\sb2$ affords complexes of stoichiometry TiMe$\\sb2(\\eta\\sp4$-C$\\sb4$H$\\sb4$R$\\sb2$)(dmpe) (R = H or Ph); the latter has been isolated and characterized crystallographically. At higher temperatures, the reaction of TiMe$\\sb2$(dmpe)$\\sb2$ with 1,3-butadiene proceeds further to form TiMe$\\sb2$(C$\\sb8$H$\\sb{12})$(dmpe); the C$\\sb8$H$\\sb{12}$ ligand is formed by oxidative coupling of two butadienes and allylic rearrangement to expand the ring. The reaction of TiMe$\\sb2$(dmpe)$\\sb2$ with styrene gives the titanium(0) complex, Ti($\\eta\\sp2$-styrene)($\\eta\\sp4$-C$\\sb4$H$\\sb4$Ph$\\sb2)$(dmpe), via the same oxidative coupling mechanism except that $\\beta$-hydrogen elimination is followed by reductive elimination of methane rather than of diphenylbutene.","The reactions of TiX$\\sb2$(dmpe)$\\sb2$ with carbon monoxide lead to the formation of the eight-coordinate complexes TiX$\\sb2$(CO)$\\sb2$(dmpe)$\\sb2$ for X = Cl or Br, which have been characterized by NMR spectroscopy.","The reaction of TiMe$\\sb2$(dmpe)$\\sb2$ with t-butylsilane yields the zerovalent complex Ti(dmpe)$\\sb3,$ which has been crystallographically characterized. The reaction of TiMe$\\sb2$ (dmpe)$\\sb2$ with phenylsilane yields two complexes in succession that appear to be titanium silyl complexes of stoichiometry Ti(Si$\\sb2$Ph$\\sb2$H$\\sb4)$Me$\\sb2$(dmpe)$\\sb2$ and Ti(Si$\\sb3$H$\\sb5$Ph$\\sb3)$(dmpe)$\\sb2.$","Variable temperature NMR studies of the dinuclear chromium(II) alkyl anion (Li(thf)$\\sb2\\rbrack\\sb2\\lbrack$Cr$\\sb2$(CH$\\sb2$SiMe$\\sb3)\\sb6$) show that the two bridging CH$\\sb2$SiMe$\\sb3$ groups engage in agostic Cr$\\cdots$H-C interactions that are static on the NMR timescale at $-$80$\\sp\\circ$C. At higher temperatures, the molecule undergoes two different dynamic processes. One process, which has activation parameters of $\\Delta$H$\\ddagger$ = 10.6 $\\pm$ 0.5 kcal mol$\\sp{-1}$ and $\\Delta$S$\\ddagger$ = $-$4 $\\pm$ 2 eu, is ascribed to exchange between the terminal and bridging CH$\\sb2$SiMe$\\sb3$ ligands; the other process, which has activation parameters of $\\Delta$H$\\ddagger$ = 14.1 $\\pm$ 0.6 kcal mol$\\sp{-1}$ and $\\Delta$S$\\ddagger$ = 17 $\\pm$ 3 eu, is ascribed to rotation of the bridging CH$\\sb2$SiMe$\\sb3$ ligands about their Cr-C bonds. The latter values give an estimate of the strength of an agostic Cr$\\cdots$H bond.","Made available in DSpace on 2011-05-07T12:51:53Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9411788.pdf: 7665810 bytes, checksum: a5fad8345b9a849d71727fbcad179f49 (MD5) Previous issue date: 1993","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:46:54Z Item is restricted indefinitely.","Restriction data tranferred 2014-07-01T11:21:07-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission","ETDs are only available to UIUC Users without author permission","U of I Only"],"dc:identifier":["AAI9411788","(UMI)AAI9411788","http://hdl.handle.net/2142/20877"],"dc:language":["eng"],"dc:rights":["Copyright 1993 Spencer, Michael Donald"],"dc:subject":["Chemistry, Inorganic"],"dc:title":["Observation of the first titanium alkyl/alkyl complexes: The key intermediate in the Ziegler-Natta mechanism for the polymerization of alkenes"],"dc:type":["text"],"thesis:degree_discipline":["Chemistry"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:16Z"}