Electron Counts of Ligand Contributions

3 CONSTRUCTION OF TRANSITION METAL COMPLEXES THAT OBEY THE 18e RULE 

Once we know the electron counts and connectivities of various transition metals and ligands, we can proceed to systematically construct a few beautiful complexes. 

SCHEME 9.4 Construction of (a) the piano stool complex, Cr(CO)3(CgH6), and (b) ferrocene, Fe(C5H5)2. On the top, the respective TM fragments and ligand molecules are shown along with their connectivities. 

SCHEME 9.5 Construction of transition metal carbonyl compounds, TM(CO) , where the TM is neutral, that approach the 18e requirement as much as possible (a) The connectivities of CO and various TM atoms (TM atoms connectivities are specified beneath the atoms), (b) Construction of Cr(CO)6, Mn(CO)5, Fe(CO)5, Co(CO)4, andNi(CO)4, and the corresponding electron counts on the TM centers. The different geometric structures will be further explored later, (c) Formation of complexes with TM—TM bonds from the radicals in (b). 

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