Mean field slave boson approximation is performed analytically on the extended Emery model for the CuO2 conducting plane. The model is parameterized by Cu-O charge transfer energy Delta(pd), copper-oxygen overlap to, oxygen-oxygen overlap t' and Coulomb interaction U on the copper site taken as infinite. Special emphasis is placed on the role of t' in the renormalization trends of the effective band parameters Delta(pf) and t, replacing Delta(pd) and t(0), at small doping delta. It is shown that small, negative t' expands the range of stability of the metallic phase, changing, through the higher order corrections in t', the nature of the metal-insulator transition point. In the non-perturbative limit, t' modifies qualitatively the renormalization of Delta(pf), making it saturate at the value of 4\t'\. Finite doping suppresses the insulating state approximately symmetrically with respect to its sign. The regime Delta(pf) approximate to 4\t'\ fits very well the ARPES spectra of Y123, Bi2212 and LSCO and also explains, in the latter case, the evolution of the FS with doping accompanied by the spectral weight transfer from the oxygen to the resonant band. (C) 2004 Elsevier B.V. All rights reserved.