219832-12-9Relevant articles and documents
Carbon-carbon bond activation by Rhodium(I) in solution. Comparison of sp2-sp3 vs sp3-sp3 C-C, C-H vs C-C, and Ar-CH3 vs Ar-CH2CH3 activation
Van Der Boom, Milko E.,Liou, Shyh-Yeon,Ben-David, Yehoshoa,Gozin, Michael,Milstein, David
, p. 13415 - 13421 (2007/10/03)
Reaction of [RhCIL2]2 (L = cyclooctene or ethylene) with 2 equiv of the phosphine {1-Et-2,6(CH2P(t)Bu2)2C6H3} (1) in toluene results in a selective metal insertion into the strong Ar-Et bond. This reaction proceeds with no intermediacy of activation of the weaker sp3-sp3 ArCH2-CH3 bond. The identity of complex Rh(Et){2,6-(CH2P(t)Bu2)2C6H3}Cl (3) was confirmed by preparation of the iodide analogue 6 by reaction of the new Rh(η(I)-N2){2,6-(CH2P(t)Bu2)2C6H3} (7) with EtI. It is possible to direct the bond activation process toward the benzylic C-H bonds of the aryl- alkyl group by choice of the Rh(I) precursor, of the substituents on the phosphorus atoms ((t)Bu vs Ph), and of the alkyl moiety (Me vs Et). A Rh(III) complex which is analogous to the product of insertion into the ArCH2-CH3 bond (had it taken place) was prepared and shown not to be an intermediate in the Ar-CH2CH3 bond activation process. Thus, aryl-C activation by Rh(I) is kinetically preferred over activation of the alkyl-C bond in this system. Moreover, cleavage of an Ar-CH2CH3 bond, followed by β-H elimination, may be preferred over sp2-sp3 C-C activation of an Ar-CH3 group.
