ADDUCTS OF FERROCENYLBORANES AND PYRIDINE BASES - GENERATION OF CHARGE-TRANSFER COMPLEXES AND REVERSIBLE COORDINATION POLYMERS

Compared to parent ferrocene, the redox potential of the Fe-II/Fe-III transition is shifted to much more cathodic values in B-N adducts 1.Do and 2.(Do)(2) of borylated ferrocenes FcBMe(2) (1) and 1,1'-fc(BMe2)( 2) (2) with pyridine bases Do [Fc: (C5H5)Fe(C5H4); fc: (C5H4)Fe(C5H4); Do: gamma-Picoline, 4-(dimethylamino) pyridine, N-(n-propyl)-4-(4'-py ridyl)pyridinium hexafluorophosphate]. Electron donation by one single BMe2 Do substituent at the cyclopentadienyl Ligand is approximately e qual to the positive inductive effect of the five methyl groups in a C 5Me5 (cp) moiety. Using the bidentate nitrogen ligand 4,4'-bipyridine (bipy), the dark-purple dimetallic complex 1.bipy.1 is obtained upon reaction with 2 equiv, of 1. 1.bipy.1 has been structurally characteri zed by X-ray crystallography. The compound tolerates loss of two elect rons at the ferrocene groups, as well as two one-electron reductions a t the bipy linker. Dark purple coloured coordination polymers [2 bipy] (n) are accessible from bipy and 1 equiv, of the diborylated derivativ e 2. The intense colours of 1.bipy.1 and [2.bipy](n) are indicative of charge-transfer interactions between the electron-rich ferrocene frag ments and the viologen-like R3B-bipy-BR3 acceptor. Neat, solid [2 bipy ](n) is thermally stable up to 240 degrees C, but in the presence of t oluene, polymerization is fully reversible at about 85 degrees C.