Tungsten carbonyl structure

The stability of complexes of the type [W(OR)6] is quite remarkable. It has been shown28 that short exposure of [W2(OPri)6py2] to approximately two molar equivalents of CO gives two products, one of which is (1). This structure can best be viewed as a substituted tungsten carbonyl in which two cis CO groups have been replaced by donor atoms of the bidentate neutral ligand [W(OPr )6], This complex is unusual in that it contains two atoms of the same element in oxidation states that differ by six units. 

With chromium, molybdenum, and tungsten carbonyls, 1 and 2 displace two CO molecules and form the trans complexes, (l)2M(CO)4 and (2)2M(CO)4 (M = Mo, Cr and W). As an example, the structure of (l>2Cr(CO)4 is shown in Fig. 6. To provide a measure of the strength of these ligands as electron donors, the C=0 stretching frequencies for these complexes were determined by IR spectroscopy [9]. The frequencies for the molybdenum complexes, and for a number of isostmctural Mo compounds, are shown in Table 1. The data indicate that toward Mo(CO)4 as a reference acid, 1 is about equal to triphenylphosphine in donor ability, whUe 2 is slightly weaker, more resembling a trialkoxyphosphine. The stable carbene isostmctural with 1 is an extremely powerful Lewis base toward molybdenum, however, surpassing even trialkylphosphines. 

The reactivity of molybdenum carbonyls in reaction with Lewis acids is comparable to the reactivity of tungsten carbonyls. The treatment of a nitrile carbonyl compound with an equimolar amount of tetrachlorotin in dichloromethane gives the oxidative-addition product, a mononuclear seven-coordinate compound [MoCl(SnCl3)(CO)3(NCMe)2], in good yield [36, 40]. The same compound was isolated from the reaction of a binuclear compound and acetonitrile. The crystal structure of the reaction product is similar to that... 

Tungsten carbide from the decomposition of tungsten carbonyl (W(CO)5 at 350-400 C although carbon tends to remain incorporated in the structure... 

---