COORDINATED ASYMMETRIC NITROGEN DONOR CENTERS . [PT11(MEEN)(EN)]2+ AND [PT4(MEEN)(EN)CL2]2+ IONS

The ions [Pt11(Meen)(en)]2+ and [PtIV(Meen)(en)Cl2]2+ have been obtained in optically active forms, and their rates of proton exchange and racemization at nitrogen have been measured. For both species, the rate expression for racemization is R = KR[Pt][OH-]; at 34° kMr = 7.9 X 102 M−1 sec−1 and 6.5 X 105 M−1sec−1 for Pt(II) and Pt(IV), respectively. The rate expression for H exchange for Pt(II) in acetate-D20 buffers at 34° is R =(Kd+Koac-[OAc-] + KoD-[OD-])[Pt] with Kd= 1.5 X 10−5 sec−1, k0ac- = 1.6 X 10−3 M−1 sec−1, and k0d- = 1.9 X 105 M−1 sec−1. In D20-DC1 solution, the rate dependence of Pt(IV)-H exchange has the form R = (kd + koD-[OD-])[Pt] with kD ≄ 2 X 10−4 sec−1 and K0D- = 2 X 1010 M−1sec−1. The retention ratio, k0D-kR ≄ 102, is small for square-planar Pt(II), but the larger value for Pt(IV), 104, is similar to those found for octahedral Co(III) complexes. Although the PKafor the Pt(II) complex cannot be measured >14, the Pt(IV) complex is more acidic, PKa 10.6 at 30°, and this result allows the inversion rate at nitrogen to be estimated as 490 sec−1. The results are interpreted mechanistically by invoking a common deprotonated intermediate. © 1969, American Chemical Society. All rights reserved.