Structural and dynamic studies in solution of anionic dinuclear azolato-bridged palladium(II) complexes

Abstract Detailed analysis of the 19 F-NMR spectra of the boat-shaped complexes (NBu 4 ) 2 [Pd 2 (μ-LL) 2 R 4 ] (R=3,5-C 6 Cl 2 F 3 ) (LL=pyrazolate (pz), 1 ; dimethylpyrazolate (dmpz), 2 ), HH- (head-to-head) and HT- (head-to-tail) (NBu 4 ) 2 [Pd 2 (μ-LL) 2 R 4 ] (LL=3-methylpyrazolate (mpz), 3 ; indazolate (indz), 4 ), (NBu 4 ) 2 [Pd 2 (μ-dmpz)(μ-LL)R 4 ] (LL=mpz, 6 ; indz, 7 ), and (NBu 4 ) 2 [R 2 Pd(μ-LL) 2 Pd(C 6 F 5 ) 2 ] (LL=pz, 8 ; dmpz, 9 ) affords valuable structural information in solution. The substituents of the azolate ligands, which reduce the dihedral angle between the coordination planes of the two metals, place the endo F ortho of different PdR 2 fragments at short distances. A single-crystal X-ray structure has been obtained for compound HT - 4 and the distances between F ortho compared with that calculated from the NMR spectra. The study of the dynamic processes for these complexes reveals the involvement of different mechanisms such as: (a) rotation of the R groups, (b) boat–boat inversion of the six-membered Pd(μ-LL) 2 Pd ring, (c) σ-1,2-metallotropic shift, and (d) associative exchange of PdR 2 fragments between 1 and mononuclear complexes.