Lead−Chromium Carbonyl Complexes Incorporated with Group 8 Metals: Synthesis, Reactivity, and Theoretical Calculations

The trichromium−lead complex [Pb{Cr(CO)<sub>5</sub>}<sub>3</sub>]<sup>2−</sup> (<b>1</b>) was isolated from the reaction of PbCl<sub>2</sub> and Cr(CO)<sub>6</sub> in a KOH/MeOH solution, and the new mixed chromium−iron−lead complex [Pb{Cr(CO)<sub>5</sub>}{Fe(CO)<sub>4</sub>}<sub>2</sub>]<sup>2−</sup> (<b>3</b>) was synthesized from the reaction of PbCl<sub>2</sub> and Cr(CO)<sub>6</sub> in a KOH/MeOH solution followed by the addition of Fe(CO)<sub>5</sub>. X-ray crystallography showed that <b>3</b> consisted of a central Pb atom bound in a trigonal-planar environment to two Fe(CO)<sub>4</sub> and one Cr(CO)<sub>5</sub> fragments. When complex <b>1</b> reacted with 1.5 equiv of Mn(CO)<sub>5</sub>Br, the Cr(CO)<sub>4</sub>-bridged dimeric lead−chromium carbonyl complex [Pb<sub>2</sub>Br<sub>2</sub>Cr<sub>4</sub>(CO)<sub>18</sub>]<sup>2-</sup> (<b>4</b>) was produced. However, a similar reaction of <b>3</b> or the isostructural triiron−lead complex [Pb{Fe(CO)<sub>4</sub>}<sub>3</sub>]<sup>2−</sup> (<b>2</b>) with Mn(CO)<sub>5</sub>Br in MeCN led to the formation of the Fe<sub>3</sub>Pb<sub>2</sub>-based trigonal-bipyramidal complexes [Fe<sub>3</sub>(CO)<sub>9</sub>{PbCr(CO)<sub>5</sub>}<sub>2</sub>]<sup>2−</sup> (<b>6</b>) and [Fe<sub>3</sub>(CO)<sub>9</sub>{PbFe(CO)<sub>4</sub>}<sub>2</sub>]<sup>2−</sup> (<b>5</b>), respectively. On the other hand, the Ru<sub>3</sub>Pb<sub>2</sub>-based trigonal-bipyramidal complex [Ru<sub>3</sub>(CO)<sub>9</sub>{PbCr(CO)<sub>5</sub>}<sub>2</sub>]<sup>2−</sup> (<b>7</b>) was obtained directly from the reaction of PbCl<sub>2</sub>, Cr(CO)<sub>6</sub>, and Ru<sub>3</sub>(CO)<sub>12</sub> in a KOH/MeOH solution. X-ray crystallography showed that <b>5</b> and <b>6</b> each had an Fe<sub>3</sub>Pb<sub>2</sub> trigonal-bipyramidal core geometry, with three Fe(CO)<sub>3</sub> groups occupying the equatorial positions and two PbFe(CO)<sub>4</sub> or PbCr(CO)<sub>5</sub> units in the axial positions, while <b>7</b> displayed a Ru<sub>3</sub>Pb<sub>2</sub> trigonal-bipyramidal geometry with three equatorial Ru(CO)<sub>3</sub> groups and two axial PbCr(CO)<sub>5</sub> units. The complexes <b>3</b>−<b>7</b> were characterized spectroscopically, and their nature, formation, and electrochemistry were further examined by molecular orbital calculations at the B3LYP level of density functional theory.