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Download file# Solution Structures and Dynamic Properties of Chelated d^{0} Metal
Olefin Complexes
{η^{5}: η^{1}-C_{5}R_{4}SiMe_{2}N^{t}Bu}Ti(OCMe_{2}CH_{2}CH_{2}CHCH_{2})^{+} (R = H, Me):
Models for the {η^{5}: η^{1}-C_{5}R_{4}SiMe_{2}N^{t}Bu}Ti(R‘)(olefin)^{+} Intermediates
in “Constrained Geometry” Catalysts

journal contribution

posted on 2001-01-09, 00:00 authored by Jean-François Carpentier, Vladimir P. Maryin, Jeffrey Luci, Richard F. JordanTo model the Ti−olefin interaction in the putative {η

^{5}: η^{1}-C_{5}R_{4}SiMe_{2}N^{t}Bu}Ti(R‘)(olefin)^{+}intermediates in “constrained geometry” Ti-catalyzed olefin polymerization, chelated alkoxide olefin complexes {η^{5}: η^{1}-C_{5}R_{4}SiMe_{2}N^{t}Bu}Ti(OCMe_{2}CH_{2}CH_{2}CHCH_{2})^{+}have been investigated. The reaction of {η^{5}: η^{1}-C_{5}R_{4}SiMe_{2}N^{t}Bu}TiMe_{2}(**1a**,**b**; R = H, Me) with HOCMe_{2}CH_{2}CH_{2}CHCH_{2}yields mixtures of {η^{5}-C_{5}R_{4}SiMe_{2}NH^{t}Bu}TiMe_{2}(OCMe_{2}CH_{2}CH_{2}CHCH_{2}) (**2a**,**b**) and {η^{5}: η^{1}-C_{5}R_{4}SiMe_{2}N^{t}Bu}TiMe(OCMe_{2}CH_{2}CH_{2}CHCH_{2}) (**3a**,**b**). The reaction of**2a**/**3a**and**2b**/**3b**mixtures with B(C_{6}F_{5})_{3}yields the chelated olefin complexes [{η^{5}: η^{1}-C_{5}R_{4}SiMe_{2}N^{t}Bu}Ti(OCMe_{2}CH_{2}CH_{2}CHCH_{2})][MeB(C_{6}F_{5})_{3}] (**4a**,**b**; 71 and 89% NMR yield). The reaction of**2b**/**3b**with [Ph_{3}C][B(C_{6}F_{5})_{4}] yields [{η^{5}: η^{1}-C_{5}Me_{4}SiMe_{2}N^{t}Bu}Ti(OCMe_{2}CH_{2}CH_{2}CHCH_{2})][B(C_{6}F_{5})_{4}] (**5b**, 88% NMR yield). NMR studies establish that**4a**,**b**and**5b**exist as mixtures of diastereomers (isomer ratios:**4a**/**4a**‘, 62/38;**4b**/**4b**‘, 75/25;**5b**/**5b**‘, 75/25), which differ in the enantioface of the olefin that is coordinated. NMR data for these d^{0}metal olefin complexes show that the olefin coordinates to Ti in an unsymmetrical fashion primarily through C_{term}such that the CC π bond is polarized with positive charge buildup on C_{int}. Dynamic NMR studies show that**4b**/**4b**‘ undergoes olefin face exchange by a dissociative mechanism which is accompanied by fast inversion of configuration at Ti (“O-shift”) in the olefin-dissociated intermediate. The activation parameters for the conversion of**4b**to**4b**‘ (i.e.,**4b**/**4b**‘ face exchange) are: Δ*H*^{⧧}= 17.2(8) kcal/mol; Δ*S*^{⧧}= 8(1) eu.**4a**/**4a**‘ also undergoes olefin face exchange but with a lower barrier (Δ*H*^{⧧}= 12.2(9) kcal/mol; Δ*S*^{⧧}= −2(3) eu), for the conversion of**4a**to**4a**‘.