Mercury- ligands

Mercury ligands No examples of simple Cu—Hg bonds are known. 

The demercuration of these cyclic mercurials is fraught with more problems than analogous mercurials formed by intermolecular processes. Alkaline sodium borohydride is once again the most common reducing agent, but elimination to the starting unsaturated alcohol is not unusual. The extent of elimination varies with the mercury ligand, the pH and the solvent used.434 Phase transfer approaches offer advant-... 

The list of ligands covered by Ref. 1 (vol. 2) starts with the exotic mercury ligand (Dean, p. 1). Silicon and a series of metals (Ge, Ti, Pb) (Harrison, p. 15) also reveal ligand properties. Hydrogen and a variety of hydride anion complexes (Crabtree, p. 689), as well as the complexes formed by anions with a carbon-donor center (cyanides, fulminates, etc.) (Sharpe, p. 25) are briefly discussed. 

A number of these have been mentioned above. The Hg2+ ion has indeed a strong tendency to complex formation, and the characteristic coordination numbers and stereochemical arrangements are two-coordinate, linear, and four-coordinate, tetrahedral. Octahedral coordination is less common a few three- and five-coordinate complexes are also known. There appears to be considerable covalent character in the mercury—ligand bonds, especially in the two-coordinate compounds. The most stable complexes are those with C, N, P and S as ligand atoms. 

The primary (or characteristic) coordination number, indicating mercury-ligand bond distances appropriate for the sum of their respective covalent radii. 

The effective coordination number, indicating all mercury-ligand interactions that are less than the sum of their respective van der Waals radii, or simply the total number of primary and secondary bonds. 

A variety of new complexes has been described in which [CpM(CO)n] residues (M = Cr, Mo, and W) are attached to phosphorus, arsenic, sulphur, tin, and mercury ligands. The cyclic amino-phosphine PhP(OCH2CHg)aNH has been incorporated both as a mono- and bi-dentate ligand in [CpMo(CO)n] complexes. The diazenido complexes [CpM(CO)gN=NMe] (M = Mo and W) react with (THF)MX [M L = Cr(CO)5 and Mn(CO)gCp] to give thermally stable products of the type [CpM(CO)gN—N(Me)M Ln]. A free-radical mechanism has been proposed for reactions in which the CO ligands in [CpMo(CO)sI] are replaced by alkyl or aryl isonitriles these substitutions are catalysed by [CpMo(CO)s]g. 

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