Tungsten complexes seven-coordinate

A number of attempts have been made over the years to develop reproducible synthetic routes to six- and seven-coordinate isocyanide complexes of molybdenum and tungsten. Two of the older methods, namely, the reaction of the hexacarbonyls with halogens in the presence of an isocyanide (775,116) or reactions of the salt Ag4Mo(CN)8 with isocyanides (74), have given six- and seven-coordinate products. Recently, however, the discovery of the reductive or nonreductive cleavage of multiple metal - metal bonds in dinuclear group VIA compounds by isocyanides has provided a facile route to the synthesis of a variety of homoleptic and related isocyanide complexes of these metals in reasonable yields. 

C. Preparation of Six- and Seven-Coordinate Complexes of Molyb-denum(II) and Tungsten(II) by Halogen Oxidation of Zero-Valent Carbonyl Complexes Containing at Least One Other Donor Ligand 49... 

This article is concerned with six- and seven-coordinate halocarbonyl complexes of molybdenum(II) and tungsten(II) (Section II), of which earlier reviews by Colton et al.2 on substituted halocarbonyls of group 6 transition metals and on steric effects in substituted halocarbonyls of molybdenum and tungsten3 have been published. Also, reviews on the structures of seven-coordinate compounds by Drew in 19774 and by Melnik and Sharrock in 1985s contain relevant material. 

SIX- AND SEVEN-COORDINATE HALOCARBONYL COMPLEXES OF MOLYBDENUM(II) AND TUNGSTEN(II)... 

Thus far, the reactions of the diiodo-complexes [MI2(CO)3(NCMe)2] with alkynes have been described. In this section the reactions of other seven-coordinate molybdenum(II) and tungsten(II) halocarbonyls with alkynes are described. 

The very air-sensitive compounds [Mo(terpy)2] (purple) and [W(terpy)2] (green) have been described by a number of workers 44,174). The chromium compound may be prepared by the reaction of [Cr(CO)g] 44), [Cr(CN)g] 42,47), [Cr(CO)3(C6H6)] 47), or [Cr(bipy)3] 44) with two equivalents of terpy. The molybdenum 44,174) and tungsten 44) compounds have been prepared from [M(CO)g] in a similar manner. Electrochemical studies on [Mo(terpy)2] indicate three one-electron oxidations 8). Photosubstitution reactions of [M(CO)g] in the presence of limited amounts of terpy lead to the formation of [M(CO)4(terpy)] (M = Cr, Mo, or W) 205). It is unlikely that these compounds are seven-coordinate, and they may well provide examples of a bidentate terpy. [Mo(CO)3(terpy)] may be prepared by the reaction of terpy with [Mo(CO)3(mesitylene)], but attempts to prepare the other group VI complexes of this stoichiometry lead to the formation of [M(CO)4(terpy)] 205). 

Six- and Seven-Coordinate Halocarbonyl Complexes of Molybdenum(II) and Tungsten(II). 47... 

HgX)(CO)2Cp] (X = Cl, Br, I, SCN, N3) to give the seven-coordinate molybdenum and tungsten complexes [CpFe(CO)2HgMX(CO)3(N"N)], with Fe-Hg-M-X arrays. Riera et have described the reactions... 

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