Solution structures and dynamic properties of chelated d(0) metal olefin complexes {eta(5):eta(1)-(C5R4SiMe2NBu)-Bu-t}Ti(OCMe(2)CH(2)Ch(2)CH=CH2)(+) (R = H, Me): Models for the {eta(5):eta(1)-(C5R4SiMe2NBu)-Bu-t}Ti(R ')(olefin)(+) intermediates in "constrained geometry" catalysts

To model the Ti-olefin interaction in the putative {eta (5): eta (1)-(C5R4S iMe2NBu)-Bu-t}Ti(R')(olefin)(+) intermediates in "constrained geometry" Ti- catalyzed olefin polymerization, chelated alkoxide olefin complexes {eta (5 ): eta (1)-(C5R4SiMe2NBu)-Bu-t}Ti(OCMe2CH2CH2CH=CH2)(+) have been investiga ted. The reaction of (eta (5): eta (1)-(C5R4SiMe2NBu)-Bu-t)TiMe2 (la,b; R = H, Me) with HOCMe2CH2CH2CH=CH2 yields mixtures of {eta (5)-(C5R4SiMe2NHBu) -Bu-t}TiMe2(OCMe2CH2CH2CH=CH2) (2a,b) and {eta (5): eta (1)-(C5R4SiMe2NBu)- Bu-t}TiMe(OCMe2CH2CH2CH=CH2) (3a,b). The reaction of 2a/3a and 2b/3b mixtur es with B(C6F5)(3) yields the chelated olefin complexes [{eta (5): eta (1)- (C5R4SiMe2NBu)-Bu-t}Ti(OCMe2CH2CH2CH=CH2)] [MeB(C6F5)(3)] (4a,b; 71 and 89% NMR yield). The reaction of 2b/3b with [Ph3C][B(C6F5)(4)] yields [{eta5: e ta (1)-(CsMe4SiMe2NBu)-Bu-t}Ti(OCMe2CH2CH2CH=CH2)] [B(C6F5)(4)] (5b, 88% NM R yield). NMR studies establish that 4a,b and 5b exist as mixtures of diast ereomers (isomer ratios: 4a/4a', 62/38; 4b/4b', 75/25; 5b/5b', 75/25), whic h 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 i n an unsymmetrical fashion primarily through Ct,, such that the C=C pi bond is polarized with positive charge buildup on C-int. Dynamic NMR studies sh ow that 4b/4b' undergoes olefin face exchange by a dissociative mechanism w hich is accompanied by fast inversion of configuration at Ti ("O-shift") in the olefin-dissociated intermediate. The activation parameters for the con version of 4b to 4b' (i.e., 4b/4b' face exchange) are: DeltaH(double dagger ) = 17.2(8) kcal/mol; DeltaS(double dagger): = 8(1) eu. 4a/4a' also undergo es olefin face exchange but with a lower barrier (DeltaH(double dagger) 12. 2(9) kcal/mol; AS' = -2(3) eu), for the conversion of 4a to 4a'.