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摘要
This paper reports that (a-diimine)PdMe(+) species (1) (a-diimine (2,6-(i)Pr(2)-C(6)H(3))N=CMeCMe =N(2,6-(i)Pr(2)-C(6)H(3))) undergo multiple insertions of CH(2)=CHOSiPh(3) (2), ultimately forming Pd allyl products. The reaction of (a-diimine)PdMeCl, [Li(Et(2)O)(2.8)][B(C(6)F(5))(4)] (1 equiv), and 2 (8 equiv) in CH(2)Cl(2) yields [(alpha-diimine)Pd(eta(3)-CH(2)CHCHCH(OSiPh(3))CH(2)CH(OSiPh(3))Me)][B(C(6)F(5))(4)](7-B(C(6)F(5))(4)) in 83% NMR yield. 7 is formed as a 95/5 mixture of isomers (7a/b), which converts to an equilibrium 40/60 mixture at 23 degrees C. X-ray diffraction analysis established that the configuration of the kinetically favored isomer 7a is S,S,S (ent-R,R,R), where the descriptors refer to the configurations of the substituted allyl carbon and the side chain methine carbons, respectively. 7b has an R,S,S (ent-S,R,R) configuration and differs from 7a in that the Pd is coordinated to the opposite allyl enantioface. The reaction of (alpha-diimine)PdMeCl, Ag[SbF(6)] (1 equiv), and 2 (8 equiv) under the same conditions yields [(a-diimine)Pd {(eta(3)-CH(2)CHCHCH(OSiPh(3))Me)}][SbF(6)] (8-SbF(6)) in 90-100% NMR yield. 8 is formed as a 90/10 mixture of isomers (8a/b) that differ in the configuration of the substituted allyl carbon and evolve to a 70/30 equilibrium mixture at 23 degrees C. These results are consistent with a mechanism involving generation of 1 and insertion of 2 to give (alpha-diimine)PdCH(2)CH(OSiPh(3))Me(+) (4). In the absence of 2, 4 undergoes beta-OSiPh(3) elimination and allylic C-H activation to give (alpha-diimine)Pd(eta(3)-CH(2)CHCH(2))(+) (6) and Ph(3)SiOH, In the presence of excess 2, 4 undergoes a second insertion of 2 to form (a-diimine)Pd(C(H)2CH (OSiPh(3))CH(2)CH(OSiPh(3))Me(+) (9), which can undergo beta-OSiPh(3) elimination/allylic C-H activation to form 8, or insert a third equivalent of 2 ultimately leading to 7. Further chain growth is probably disfavored by steric crowding.
- 出版日期2008-10-1
