Mixed-Sandwich (Cp*/(HMB))Ru
Complexes Containing Bis(methimazolyl)(pyrazolyl)borate (Cp* = η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>, HMB = η<sup>6</sup>-C<sub>6</sub>Me<sub>6</sub>)
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Abstract
Reaction of the scorpionate salt Li[HB(mt)<sub>2</sub>(pz)] (mt = <i>N</i>-methyl-2-mercaptoimidazol-1-yl, pz
= pyrazolyl) with the organometallic complexes [Cp*RuOMe]<sub>2</sub> (Cp* = η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>) (<b>1</b>) and [(HMB)RuCl<sub>2</sub>]<sub>2</sub> (HMB = η<sup>6</sup>-C<sub>6</sub>Me<sub>6</sub>) (<b>2</b>) gave the 18-electron
Ru(II) complexes [Cp*Ru(κ<sup>3</sup><i>-H,S,S′</i>)<i>-</i>{HB(mt)<sub>2</sub>(pz)}] (<b>3</b>) and
[(HMB)Ru(κ<sup>3</sup><i>-H,S,S′</i>)<i>-</i>{HB(mt)<sub>2</sub>(pz)}](<b>4B</b>)PF<sub>6</sub> in moderate yields. In the absence of the PF<sub>6</sub><sup>–</sup> anion, [(HMB)Ru(κ<sup>2</sup>-<i>S</i>,<i>S</i>′-{HB(mt)<sub>2</sub>(pz)})(Cl)] [<b>4C</b>] was isolated
as a coproduct with (<b>4B</b>)Cl. These complexes are the first
examples of organoruthenium(II) complexes containing bis(methimazolyl)(pyrazolyl)borate
ligands. Isomers of <b>4B</b> were observed in solution, and
the isomerization process was studied using variable-temperature <sup>1</sup>H NMR spectroscopy. The reactivity of <b>3</b> toward
O<sub>2</sub> and CO was investigated, and in the process we isolated
the first Ru(IV) peroxo complex containing a poly(methimazolyl)borate
ligand, [Cp*Ru(κ<sup>2</sup>-<i>S</i>,<i>S</i>′-{HB(mt)<sub>2</sub>(pz)})(η<sup>2</sup>-O<sub>2</sub>)] (<b>5</b>), and a CO adduct, [Cp*Ru(κ<sup>2</sup>-<i>S</i>,<i>S</i>′-{HB(mt)<sub>2</sub>(pz)})(CO)]
(<b>6</b>), respectively. The oxidation process was reversible,
but treatment of <b>5</b> with CO converted it irreversibly
to <b>6</b>. All the new compounds were fully characterized,
including by X-ray diffraction analyses. Cyclic voltammetric studies
were also conducted for complexes <b>3</b>, <b>5</b>,
and <b>6</b>
