Synthesis and Structural Studies of Cationic Bis- and Tris(pyrazol-1-yl)methane Acyl and Methyl Complexes of Ruthenium(II): Localization of the Counterion in Solution by NOESY NMR Spectroscopy

Abstract

Complex fac-Ru(PMe3)(CO)3(Me)I (1) reacts with tris- and bis(pyrazol-1-yl)methane, in the presence of NaBPh4, affording cis-[Ru(PMe3)(CO)2(COMe)(η2-pz3-CH)]BPh4 (2) and cis-[Ru(PMe3)(CO)2(COMe)(pz2-CH2)]BPh4 (4), respectively. Complexes 2 and 4 decarbonylate leading to [Ru(PMe3)(CO)(COMe)(η3-pz3-CH)]BPh4 (3) and a mixture of three methyl stereoisomers of cis-[Ru(PMe3)(CO)2(Me)(pz2-CH2)]BPh4 (5−7), respectively. The byproduct of the synthesis of 1, fac,cis-Ru(PMe3)(CO)3(I)2 (8), reacts with bis(pyrazol-1-yl)methane affording cis-[Ru(PMe3)(CO)2(I)(pz2-CH2)]BPh4 (9). The stereochemistry of the complexes, the dynamic processes existing between them, and the interionic structures of all of the cationic complexes were investigated by the phase-sensitive 1H NOESY NMR spectra in CD2Cl2. The solid-state crystal structure of 4, obtained by single-crystal X-ray studies, was compared from the intramolecular and interionic point of views with that in solution with the help of 3-21G* ab initio and AMI−SM2 semiempirical quantum mechanical and docking mechanic calculations. In particular, the differences of interaction energy of the six solid-state ion pairs determined by the cation and the six symmetry-related anions surrounding it were estimated. The main result is that the averaged preferred position of the counterion in solution corresponds to the ion-pair electrostatically (ΔEel > 2.5 kcal/mol) and “sterically” (ΔEst > 3.7 kcal/mol) favored in the solid state.