Elsevier, Journal of Organometallic Chemistry, (545-546), p. 131-137
DOI: 10.1016/s0022-328x(97)00232-5
Full text: Unavailable
Exocyclic six-membered cyclopalladated dimers 2a-2c, , have been prepared by reaction of palladium(II) acetate with N-benzylidene-2-phenylanilines 1a-1c, RCH=NC6H4-2-C6H5 {1a, R = 2,6-Cl2C6H3; 1b, R = 2,6-F2C6H3 and 1c, R = 2,4,6-(CH3O)3C6H2}, and a subsequent metathesis reaction with LiBr. Reaction of 2 with PPh3 produced mononuclear compounds 3, . Analysis of the 1H NMR methinic region of 2 and 3 revealed their E/Z composition. 2a and 2b present imines in E and Z configuration in an approximate ratio of 1:1, white 2c consists almost exclusively of imines in E configuration. Compounds 3 also present imines in E and Z configuration, the former are more abundant in all cases (≥ 4:1). The crystal structure of 3c with the imine in E configuration has been determined. It crystallizes in the monoclinic space group P21/a with a = 19,258(3) Å, b = 13.177(2) Å, c = 14.660(2) Å and β = 113.78(2)°. Steric and electronic effects on the E/Z composition of 2 and 3 and related exocyclic cyclopalladated N-benzylidenebenzylamines suggest that, for compounds of this type, the E → Z isomerization takes place via a rotation through the N=C bond which is assisted by π back bonding of the palladium(II) center to the iminic function.