Metallorganische π-liganden: cluster als tripeldeckerkomplexe

Clusters (R′P)(RCCR)Fe₃(CO)₉ (1) have a pentagonal pyramidal cage structure with a planar C₂Fe₂P cycle acting as a organometallic 4π ligand towards a side-on η⁵-coordinated Fe(CO)₃ entity. Compounds of this type, which may be considered halfsandwich complexes, undergo transformation to clusters (R′P)(RCCR)Fe₄(CO)₁₁ (2) which correspond to triple-decker compounds with a planar central C₂Fe₂P 4π ligand. Compounds 2 can also be described as pentagonal bipyramidal clusters. Since compounds 1 are chemically related to a number of different cage molecules containing a C₂PFe₃ core and also to binuclear complexes with a C₂PFe₂ core, the triple-decker clusters 2 can also be prepared from these starting materials. Several examples of this type are given. The isoelectronic analogy between RP and S as cluster constituents is exemplified by the synthesis of a sulfur-containing analogue of 2 by similar procedures.