Letter: A new measurement of surface charge in model and biological lipid membranes.

of the p-N2 of 2 is observed, an indication that the terminal dinitrogen ligands are playing roles beyond that of mere spectators in the reaction of 1 with HC1. The data require a reaction sequence mediated by a symmetric species in which one terminal N2 and the p-N2 have become e q ~ i v a l e n t. ~ While a number of mechanisms satisfying this requirement could be formulated, we favor one involving protonation of a terminal dinitrogen of 1, loss of the other terminal N2, and generation of the symmetric reaction intermediate (C5Me5)2Zr(N~H)2 (3).1° Consistent with the labeling experiments, 3 would then lead to 1 mol each of N2 and N2H4 (eq 3). Generation of the neutral, monomeric species 3 from 1 would require a formal two-electron transfer to the N2-bearing Zr accompanied by release of the other zirconium in the fully oxidized state, i.e., as (CsMes)zZrC12. Strong electronic coupling of the two Zr(I1) centers through the p-N2 of 1 as suggested by its structural features, ir, and visible spectra should facilitate such a Zr-to-Zr charge transfer.