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 [Pb2Br2Cr4(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 Fe3Pb2-based trigonal-bipyramidal complexes [Fe3(CO)9{PbCr(CO)5}2]2− (6) and [Fe3(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 37 were characterized spectroscopically, and their nature, formation, and electrochemistry were further examined by molecular orbital calculations at the B3LYP level of density functional theory.