Synthesis and characterization of the dimercury(I)-linked compound [PPn]4[(Re7C(CO)21Hg)2]. Oxidative cleavage of the mercury-mercury bond leading to carbidoheptarhenate complexes of mercury(II), including [PPN][Re7C(CO)21Hg(S=C(NME2)2)

The reaction of PPN](3)Re(7)C(CO)(21)] with Hg(2)(NO(3))(2).2H(2)O in dichloromethane formed the complex PPN](4)(Re(7)C(CO)(21)Hg)(2)] (PPN](4)1]), isolated in 60% yield. Analogous salts of 1](4-) with PPh(4)](+) and NEt(4)](+) were also prepared. The crystal structure of PPN](4)1] showed that two carbidoheptarhenate cores are linked by a dimercury(I) unit (d(Hg-Hg) = 2.610(4) A), with each individual mercury atom face-bridging. Oxidative cleavage of the Hg-Hg bond in 1](4-) was effected by 4-bromophenyl disulfide to form Re(7)C(CO)(21)HgSC(6)H(4)Br](2-) (4](2-)), by I(2) to form Re(7)C(CO)(21)HgI](2-) (5](2-)), and by Br(2) to form Re(7)C(CO)(21)HgBr](2-) (6](2-)). Oxidation of 1](4-) by ferrocenium ion (2 equiv) in the presence of tetramethylthiourea resulted in the derivative Re(7)C(CO)(21)HgSC(NMe(2))(2)](-) (7](-)). The molecular structure of PPN]7] was determined by X-ray crystallography. This is the first example of a carbidoheptarhenate-mercury complex with a neutral ligand on mercury, and ligand exchange was demonstrated by displacement with triethylphosphine. Complex 7](-) can also be prepared by protonating Re(7)C(CO)(21)HgO(2)CCH(3)](2-) in the presence of tetramethylthiourea. Cyclic voltammetry data to calibrate and compare the redox properties of compounds 1](4-) and 7](-) have been measured.