Alkylidyne ligand iron complex

The Iron Triad.—Mild protonation of the anion [Fe4(CO)u(/t-CO)(/e3-COMe)] yields [Fe4H(CO)i2(i -COMe)], which in turn reacts with strong acid to generate methane from the iy -COMe liquid X-ray crystal structures are reported for both iron complexes. Methods for the s mthesis of triangular metal-cluster complexes containing iUg-alkylidyne ligands have been reported and structures of this tsrpe have been established by X-ray diffraction methods for... 

Given the isoelectronic relationship between [CR] and [NO] and the ubiquity of this latter ligand in the coordination chemistry of later transition metals, the scarcity of mononuclear alkylidyne complexes of metals from groups 8-10 is surprising [1-4]. Isolated examples have been reported for iron [5], cobalt [6], ruthenium [4,7], osmium [4,8-9] and iridium [10]. Most of the examples known employ routes with extensive precedent in early transition metal systems, i.e., either electrophilic attack at the p-atom of a hetero carbonyl (CS [5], CTe [4], or C=CH2 [10]) or the Lewis-acid assisted abstraction of an alkoxide group from a carbene precursor [5] (Scheme 1). The one approach which is, too date, peculiar to group 8 metals involves reduction of a divalent dichlorocarbene complex by lithium aryls [4]. The limitation of this procedure to ruthenium and osmium is presumably not a feature of these metals but rather a result of the present lack of synthetic routes to suitable dihalocarbene precursor complexes of earlier metals. 

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