EVIDENCE FOR LONG-RANGE ELECTRONIC EFFECTS IN HEXAPLATINUM CLUSTERS -THE CASE OF PHOSPHITE LIGAND ADDITION AND MIGRATION

The 84-electron cluster [Pt-6(mu(2)-CO)(6)(mu(2)-dppm)] (1) (dppm = Ph 2PCH2PPh2) forms an adduct with the phosphite P(OCH2)(3)CMe to give th e 86-electron cluster [Pt-6(mu(2)-CO)(6)(mu(2)-dppm)(3){P(OCH2)(3)CMe} ] (2). The phosphite ligand in 2 is fluxional as shown by a variable t emperature NMR study between 20 and -90 degrees C. ht low temperatures the spectra indicate a structure in which the phosphite is terminally bound to one platinum atom, while at temperatures above -70 degrees C , the complex is fluxional with the phosphite migrating rapidly around a triangular face of the cluster. The selective formation of only a I :1 complex, coupled with the predictions of EHMO theory, provides good evidence for long-range electronic effects across the hexaplatinum cl uster. (C) 1997 Elsevier Science S.A.