Dinuclear Azolato-Bridged Complexes Of The Nickel Group Metals With Haloaryl Ligands: A Reinvestigation Of Their Behavior In Solution

A reinvestigation of the NMR spectra of the complexes (NBU4)(2)[M-2(mu-LL)(2)R-4] (M = Pd, Ni, Pt, LL = pyrazolate (pz), 3,5-dimethylpyrazolate (dmpz), 3-methylpyrazolate (mpz), indazolate (indz), R = C6F5; M = Pd, LL = pz, dmpz, mpz, indz, R = 2,4,6-C6F3H2) shows that the boat-shaped dimeric structures of their anions are quite stable in solution, and the previously proposed fast:equilibria or dissociations to give species such as [R2M(N-N)(acetone)](-), [R2M(acetone)(2)] + 2dmpz(-), or [R2M(N-1-N-2)(acetone)](-) [R2M(N-2-N-1)(acetone)](-) in no case occur. A mixture of the two diastereoisomers (head-to-head, KH, and head-to-tail, HT) is present for the asymmetrically substituted azolates (mpz and indz), in a patio ranging from 1:7 to 1:30 for the different complexes. Strong through-space coupling between the endo ortho fluorine nuclei of different MR2 fragments is observed in the F-19 NMR spectra of these diastereoisomers whose boatlike structures place these atoms at short distances.