Elaborate Network of Hydrolysis and Methanolysis Reactions Involving the 2,5-Dimethylthiophene Ligand in Cp*Ir(η<sup>5</sup>-2,5-Me<sub>2</sub>T)<sup>2+</sup>
journal contribution
posted on 2004-03-15, 00:00 authored by M. Angeles Paz-Sandoval, Marisol Cervantes-Vasquez, Victor G. Young,, Ilia A. Guzei, Robert J. AngeliciReactions of aqueous base with the dicationic iridium and rhodium thiophene complexes
[Cp*Ir(η<sup>5</sup>-2,5-Me<sub>2</sub>T)](X)<sub>2</sub> (X = BF<sub>4</sub>, <b>1(BF</b><b><sub>4</sub></b><b>)</b>; X = OSO<sub>2</sub>CF<sub>3</sub>, <b>1(OTf)</b>) and [Cp*Rh(η<sup>5</sup>-2,5-Me<sub>2</sub>T)](BF<sub>4</sub>)<sub>2</sub> (<b>8(BF</b><b><sub>4</sub></b><b>)</b>) and the acid/base reactivity of these products are discussed. The reaction of
<b>1(BF</b><b><sub>4</sub></b><b>) </b>with 1 equiv of aqueous KOH (0.01 M) affords the following mixture of mono-, di-,
and tetranuclear compounds: [Cp*Ir(η<sup>4</sup>-SC(Me)CHCHC(O)Me)] (<b>3</b>), (Cp*Ir)[Cp*Ir(η<sup>4</sup>-SC(Me)CHCHC(O)Me)]<sub>3</sub>(BF<sub>4</sub>)<sub>2</sub> (<b>4(BF</b><b><sub>4</sub></b><b>)</b>), [(Cp*Ir)<sub>2</sub>(μ<sub>2</sub>,η<sup>4</sup>-SC(Me)CHCC(O)Me)](BF<sub>4</sub>) (<b>5(BF</b><b><sub>4</sub></b><b>)</b>), and
[Cp*Ir(μ<sub>2</sub>,η<sup>3</sup>-SC(Me)CHCH<sub>2</sub>C(O)Me)]<sub>2</sub>(BF<sub>4</sub>)<sub>2</sub> (<b>6(BF</b><b><sub>4</sub></b><b>)</b>). The <sup>1</sup>H and <sup>13</sup>C NMR data are
consistent with the single-crystal X-ray diffraction structures of the cationic complexes <b>4(BF</b><b><sub>4</sub></b><b>)</b>, <b>5(OTf)</b>, and <b>6(BF</b><b><sub>4</sub></b><b>)</b>. These products are formed by a complex series of reactions that
begin with the displacement of the 2,5-dimethylthiophene (2,5-Me<sub>2</sub>T) ligand from <b>1</b> and
reaction of the resulting “[Cp*Ir]<sup>2+</sup>” fragment with <b>3</b>. In the synthesis of <b>8(BF</b><b><sub>4</sub></b><b>)</b>, the new
complex [(Cp*Rh)<sub>2</sub>(μ<sub>2</sub>,η<sup>4</sup>-SC(Me)CHCC(O)Me)](BF<sub>4</sub>) (<b>9(BF</b><b><sub>4</sub></b><b>)</b>), analogous to <b>5(BF</b><b><sub>4</sub></b><b>)</b>, is produced. Studies of the reactions of [Cp*Rh(η<sup>5</sup>-2,5-Me<sub>2</sub>T)](BF<sub>4</sub>)<sub>2</sub> (<b>8(BF</b><b><sub>4</sub></b><b>)</b>) with OH<sup>-</sup> and MeO<sup>-</sup>
show a type of reactivity quite different from that observed for <b>1(BF</b><b><sub>4</sub></b><b>) </b>and <b>1(OTf)</b>. The
solvolysis of <b>8(BF</b><b><sub>4</sub></b><b>) </b>in acetone affords the mononuclear complex [Cp*Rh(OCMe<sub>2</sub>)<sub>2</sub>(OH)](BF<sub>4</sub>)
(<b>10(BF</b><b><sub>4</sub></b><b>)</b>), whose crystal structure is described. Detailed NMR studies establish the pathways
by which [Cp*Ir(η<sup>5</sup>-2,5-Me<sub>2</sub>T)]<sup>2+</sup> (<b>1</b>) and [Cp*Rh(η<sup>5</sup>-2,5-Me<sub>2</sub>T)]<sup>2+</sup> (<b>8</b>) react with H<sub>2</sub>O/OH<sup>-</sup> and
MeOH/MeO<sup>-</sup> to give the variety of observed products.
