Dinuclear azolato-bridged complexes of the nickel group metals with haloaryl ligands: a reinvestigation of their behavior in solution

Inorg Chem. 2000 Mar 6;39(5):975-9. doi: 10.1021/ic9911062.

Abstract

A reinvestigation of the NMR spectra of the complexes (NBu4)2[M2(mu-LL)2R4] (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(N1-N2)(acetone)]- + [R2M(N2-N1)(acetone)]- in no case occur. A mixture of the two diastereoisomers (head-to-head, HH, and head-to-tail, HT) is present for the asymmetrically substituted azolates (mpz and indz), in a ratio 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 19F NMR spectra of these diastereoisomers whose boatlike structures place these atoms at short distances.