Tungsten atom hexacarbonyl

The mononuclear metal carbonyls contain only one metal atom, and they have comparatively simple structures. For example, nickel tetracarbonyl is tetrahedral. The pentacarbonyls of iron, ruthenium, and osmium are trigonal bipyramidal, whereas the hexacarbonyls of vanadium, chromium, molybdenum, and tungsten are octahedral. These structures are shown in Figure 21.1. 

Most of the work is done with carbonyl complexes of group-VIA metals. Tungsten hexacarbonyl reacts at RT with methyllithium in solvents such as diethylether or THF almost quantitatively with addition of the carbanion to the carbon atom of a coordinated CO to give the lithium salt of acetylpentacarbonyl tungstate. This complex can be converted by aqueous tetramethylammonium bromide into the more stable tetramethyl-ammonium salt ... 

The crystal structure of 2-lithiated l-methyl-l,3-benzazaphosphole 35 showed it to have a dimeric structure with two THF molecules associated with each lithium. The two lithium atoms and the two C-2 atoms form a four-membered ring <20020M912>. In contrast, the N-lithiated derivative of 2,5-dimethyl-l//-l,3-benzazaphosphole exists as a monomeric species 36 in the solid state <2002JOM(646)113>. The carbene-type complex 37 derived from the lithiated species 35 on reaction with tungsten hexacarbonyl was also studied by X-ray crystallography. 

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