C–H Activation of Pyrazolyl Ligands by Ru(II)
Abstract
Previously, hydridotris(pyrazolyl)borate (Tp) Ru(II) alkyl and aryl complexes of the type TpRu(L)(NCMe)R (R = methyl or aryl; L = charge-neutral two-electron donating ligand) were demonstrated to activate aromatic C–H bonds. To determine the impact of replacing the anionic Tp ligand with charge-neutral poly(pyrazolyl)alkane ligands, [(C(pz)<sub>4</sub>)Ru(P(OCH<sub>2</sub>)<sub>3</sub>CEt)(NCMe)Me][BAr′<sub>4</sub>] (pz = pyrazolyl, BAr′<sub>4</sub> = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) was prepared. Heating a C<sub>6</sub>D<sub>6</sub> solution of [(C(pz)<sub>4</sub>)Ru(P(OCH<sub>2</sub>)<sub>3</sub>CEt)(NCMe)Me][BAr′<sub>4</sub>] with 1 equiv of NCMe resulted in C–H activation of the 5-position of a pyrazolyl ring to yield [(κ<sup>3</sup>-(<i>N</i>,<i>C</i><sup>5</sup>,<i>N</i>)C(pz)<sub>4</sub>)Ru(P(OCH<sub>2</sub>)<sub>3</sub>CEt)(NCMe)<sub>2</sub>][BAr′<sub>4</sub>] and CH<sub>4</sub>. Intramolecular C–H activation of the 5-position of a pyrazolyl ring also occurred when (η<sup>6</sup>-<i>p</i>-cymene)Ru(P(OCH<sub>2</sub>)<sub>3</sub>CEt)(Br)Ph was heated in the presence of C(pz)<sub>4</sub> to yield [(κ<sup>3</sup>-<i>N</i>,<i>C</i><sup>5</sup>,<i>N</i>)C(pz)<sub>4</sub>]Ru(P(OCH<sub>2</sub>)<sub>3</sub>CEt)(NCMe)Br and C<sub>6</sub>H<sub>6</sub>. Density functional theory calculations revealed that the different reactivities of TpRu(P(OCH<sub>2</sub>)<sub>3</sub>CEt)(NCMe)R and [(C(pz)<sub>4</sub>)Ru(P(OCH<sub>2</sub>)<sub>3</sub>CEt)(NCMe)Me][BAr′<sub>4</sub>] result from the stronger binding of the Tp pyrazolyl rings to Ru(II) compared to that of C(pz)<sub>4</sub>Similar works
This paper was published in FigShare.
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