| Abstract
| - Mononuclear and only the symmetric dinuclear Pd(II) complexes with 4,6-bis(pyrazol-1-yl)pyrimidine ligands (R = H, Me) have been synthesized. Molecular recognition plays a role in the formation of only the symmetric binuclear complexes. Restricted rotation of m-C6HF4 groups in mono and dinuclear complexes gives rise to several atropoisomers. An intramolecular apparent allyl rotation and an intermolecular exchange of allylpalladium fragments have been demonstrated in the complex [{Pd(η3-C4H7)}(bpzpm)]Tf.
- The ligands 4,6-bis(pyrazol-1-yl)pyrimidine (bpzpm) and 4,6-bis(4-methylpyrazol-1-yl)pyrimidine (Me−bpzpm)were synthesized and their reactions with some palladium derivatives explored. Mononuclear or dinuclear neutralor cationic complexes were obtained by reaction of the ligands with 1 or 2 equiv of Pd(C6XF4)2(cod) (cod =1,5-cyclooctadiene; X = F, H) or the palladium fragment [Pd(η3-2-Me-C3H4)(S)2]+ (S = acetone). The reactionof the dinuclear derivatives with 1 equiv of the respective free ligand immediately led to the regeneration of themononuclear complexes. Except in the case of the synthesis of [{Pd(C6HF4)2}{Pd(C6F5)2}(bpzpm)], where twosimilar metallic groups are present, all attempts to obtain dinuclear asymmetric complexes with two differentpalladium fragments failed. Instead, the dinuclear symmetric complexes were formed. This result could beconsidered as an example of molecular recognition with the ligand acting as a ditopic receptor. This behavior iscomparable to chemical symbiosis but in this case applied to the ligand rather than to the metal center as occursnormally. The polyfluorophenyl rings are situated on average in a perpendicular orientation with respect to thecoordination plane. Their restricted rotation results in several atropoisomers for the complexes with m-C6HF4.Different cross-reaction experiments were carried out, and these showed the mobility of the metallic fragments,with the more difficult process being that involving the more strongly bonded polyfluorophenyl palladium groups.By means of 1H NMR variable temperature studies, the interconversion of the two isomers of [{Pd(η3-C4H7)}2(bpzpm)]Tf2 (Tf = CF3SO3) was analyzed. In the case of [{Pd(η3-C4H7)}(bpzpm)]Tf the existence of two processes,an intramolecular apparent allyl rotation and an intermolecular exchange of the allylpalladium fragments, hasbeen demonstrated. Different ΔGc⧧ values at the coalescence temperatures have also been determined. An X-raysingle-crystal analysis was carried out on [{Pd(η3-C4H7)}2(bpzpm)]Tf2, which crystallizes in the monoclinic system,space group I2/m, with a = 9.368(2), b = 16.191(3), c = 20.228(6) Å, β = 101.26(3), and Z = 4. Compound[{Pd(C6HF4)2}(bpzpm)] crystallized in the triclinic system, space group P1̄, with a = 8.845(6), b = 12.6609(9),c = 12.826(3) Å, α = 88.45(2), β = 74.36(3), γ = 89.32(2), and Z = 2.
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