Ferrocenyl-substituted pyridine

The preparation of ferrocenyl substituted pyridines, such as 4-ferrocenylpyiidine and l,r-di(2-pyiidyl)feiTocene (L), allowed the preparation of complexes with formula [Rh(cod)L2]CI04. The multitopic ligands, A,A -bis[(A)-prolyl)phenylenediamine, A,A -bis [(A)-pyrrolidin-2-yl]methyl)phenylenediamine, A,Af -bis[(6 )-A-benzylprolyl]phe-nylenediamine, and A,A -bis [(A)-Af-benzyl-pyrrolidin-2-yl]methyl)phenylenediamine, were synthesized and their coordination properties with Rh(i) studied. The ligand bis(bipyridine)-calix[4]arene (BBPC) reacted with 2 equiv. of [Rh(nbd)2]BF4 or [Rh(nbd)(CH3CN)2]BF4 yielding the bimetallic compound [Rh(nbd)(BBPC)]2[BF4]2 396. ... 

Naturally, it is possible to synthesise a similar ligand system without central chirality and in fact without the unnecessary methylene linker unit. A suitable synthesis starts with planar chiral ferrocenyl aldehyde acetal (see Figure 5.30). Hydrolysis and oxidation of the acetal yields the corresponding carboxylic acid that is transformed into the azide and subsequently turned into the respective primary amine functionalised planar chiral ferrocene. A rather complex reaction sequence involving 5-triazine, bromoacetal-dehyde diethylacetal and boron trifluoride etherate eventually yields the desired doubly ferrocenyl substituted imidazolium salt that can be deprotonated with the usual potassium tert-butylate to the free carbene. The ligand was used to form a variety of palladium(II) carbene complexes with pyridine or a phosphane as coligand. 

It is also possible to design mixed inorganic-organometallic systems by appropriate decoration of such clusters, as in the case of MogBri4 " below. The 6 apical Br ligands can be substituted by triflates, then by functional pyridines to synthesize dicationic cluster-cored ferrocenyl dendrimers ... 

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