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

Complex fac-Ru(PMe<INF>3</INF>)(CO)<INF>3</INF>(Me)I (<BO>1</BO>) reacts with tris- and bis(pyrazol-1-yl)methane, in the presence of NaBPh<INF>4,</INF> affording cis-[Ru(PMe<INF>3</INF>)(CO)<INF>2</INF>(COMe)(η²-pz<INF>3</INF>-CH)]BPh<INF>4</INF> (<BO>2</BO>) and cis-[Ru(PMe<INF>3</INF>)(CO)<INF>2</INF>(COMe)(pz<INF>2</INF>-CH<INF>2</INF>)]BPh<INF>4</INF> (<BO>4</BO>), respectively. Complexes <BO>2</BO> and <BO>4</BO> decarbonylate leading to [Ru(PMe<INF>3</INF>)(CO)(COMe)(η³-pz<INF>3</INF>-CH)]BPh<INF>4</INF> (<BO>3</BO>) and a mixture of three methyl stereoisomers of cis-[Ru(PMe<INF>3</INF>)(CO)<INF>2</INF>(Me)(pz<INF>2</INF>-CH<INF>2</INF>)]BPh<INF>4</INF> (<BO>5</BO>−<BO>7</BO>), respectively. The byproduct of the synthesis of <BO>1</BO>, fac,cis-Ru(PMe<INF>3</INF>)(CO)<INF>3</INF>(I)<INF>2</INF> (<BO>8</BO>), reacts with bis(pyrazol-1-yl)methane affording cis-[Ru(PMe<INF>3</INF>)(CO)<INF>2</INF>(I)(pz<INF>2</INF>-CH<INF>2</INF>)]BPh<INF>4</INF> (<BO>9</BO>). 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 CD<INF>2</INF>Cl<INF>2</INF>. The solid-state crystal structure of <BO>4</BO>, 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 (ΔE<INF>el</INF> > 2.5 kcal/mol) and “sterically” (ΔE<INF>st</INF> > 3.7 kcal/mol) favored in the solid state.