Lead-chromium carbonyl complexes incorporated with group 8 metals: Synthesis, reactivity, and theoretical calculations

The trichromium-lead complex [Pb{Cr(CO)₅}₃] ^2- (1) was isolated from the reaction of PbCl₂ and Cr(CO)₆ in a KOH/MeOH solution, and the new mixed chromium-iron-lead complex [Pb{Cr(CO)₅}{Fe(CO)₄}₂]^2- (3) was synthesized from the reaction of PbCl₂ and Cr(CO)₆ in a KOH/MeOH solution followed by the addition of Fe(CO)₅. X-ray crystallography showed that 3 consisted of a central Pb atom bound in a trigonal-planar environment to two Fe(CO)₄ and one Cr(CO)₅ fragments. When complex 1 reacted with 1.5 equiv of Mn(CO)₅Br, the Cr(CO)₄-bridged dimeric lead-chromium carbonyl complex [Pb ₂Br₂Cr₄(CO)₁₈]^2- (4) was produced. However, a similar reaction of 3 or the isostructural triiron-lead complex [Pb{Fe(CO)₄}₃]^2- (2) with Mn(CO) ₅Br in MeCN led to the formation of the Fe₃Pb ₂-based trigonal-bipyramidal complexes [Fe₃(CO) ₉{PbCr(CO)₅}₂]^2- (6) and [Fe ₃(CO)₉{PbFe(CO)₄}₂]^2- (5), respectively. On the other hand, the Ru₃Pb₂-based trigonal-bipyramidal complex [Ru₃(CO)₉{PbCr(CO) ₅}₂]^2- (7) was obtained directly from the reaction of PbCl₂, Cr(CO)₆, and Ru₃(CO) ₁₂ in a KOH/MeOH solution. X-ray crystallography showed that 5 and 6 each had an Fe₃Pb₂ trigonal-bipyramidal core geometry, with three Fe(CO)₃ groups occupying the equatorial positions and two PbFe(CO)₄ or PbCr(CO)₅ units in the axial positions, while 7 displayed a Ru₃Pb₂ trigonal-bipyramidal geometry with three equatorial Ru(CO)₃ groups and two axial PbCr(CO)₅ units. The complexes 3-7 were characterized spectroscopically, and their nature, formation, and electrochemistry were further examined by molecular orbital calculations at the B3LYP level of density functional theory.