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, d mpz, mpz, indz, R = 2,4,6-C6F3H2) shows that the boat-shaped dimeric struct ures of their anions are quite stable in solution, and the previously propo sed fast:equilibria or dissociations to give species such as [R2M(N-N)(acet one)](-), [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 diastereoisome rs (head-to-head, KH, and head-to-tail, HT) is present for the asymmetrical ly 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 end o 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.