Reactions of complex ligands, Part 86 - Benzannulation of axial chiral biscarbene complexes of chromium: An approach to novel C-2-symmetrical redox-active bi(phenanthrenequinones)

The biscarbene chromium complex 1 (derived from binaphthol) undergoes benza nnulation upon reaction with 1- and 3-hexyne to give the biphenanthrenes 2- 5, Subsequent column chromatography and recrystallisation yield two diaster eomeric Cr(CO)(3) complexes 3a and 3b, which bear elements of both axial an d planar chirality. The annulation products have been characterized by CD s pectroscopy. Oxidative workup of the primary annulation product 2 affords t he C-2-symmetrical axial chiral bi(phenanthrenequinones) 4 and 5, Deprotect ion of 4 with boron tribromide or aluminium trichloride gives the binaphtho l-related skeletons 6 and 8, whereas reaction of 4 with trimethylsilyl iodi de (TMSI) results in the unexpected formation of the helicene 7 X-ray struc ture analysis of 7 indicates pi stacking of the arene and quinone rings, as well as a unit cell in which two molecules of the helicene and two molecul es of chloroform are connected by C-H ... O hydrogen bonding. Comparative c yclovoltammetric studies on 4, 5, 7 and the 'monomer' 9 show that the angul ar quinone moieties are electrochemically independent.