Stepwise Synthesis of Octamethylferrocene-1,1‘-dicarbaldehyde. Preparation of New Electron Donors for Charge-Transfer Complexes

A stepwise synthesis of octamethylferrocene-1,1‘-dicarbaldehyde ( 3 ), starting from 1,2,3,4-tetramethyl-5-(methoxycarbonyl)cyclopentadiene ( 7 ) is described, involving ferrocene formation, ester reduction to the corresponding bis(hydroxymethyl) derivative 9, and MnO 2 oxidation. The aldehyde 3 readily reacts with different phosphonates derived from sulfur-containing heterocycles in a Wittig−Horner reaction to form new electron donors that may be used in the preparation of various charge transfer complexes. The X-ray crystal structures of 1-[(1,3-benzodithiol-2-ylidene)methyl]-2,2‘,3,3‘,4,4‘,5,5‘-octamethylferrocene ( 11a ), 1-[(1,3-dithiolo[4,5- b ][1,3]dithiol-2-ylidene)methyl]-2,2‘,3,3‘,4,4‘,5,5‘-octamethylferrocene ( 11b ), 1,1‘-bis[(1,3-benzodithiol-2-ylidene)methyl]-2,2‘,3,3‘,4,4‘,5,5‘-octamethylferrocene ( 12a ), and 1,1‘-bis[(5,6-dihydro-1,3-dithiolo[4,5- b ][1,4]dithiol-2-ylidene)methyl]-2,2‘,3,3‘,4,4‘,5,5‘-octamethylferrocene ( 12c ) have been determined. In these compounds the planes of the sulfur heterocycles are oriented at angles of 60−75°, with respect to the plane of the respective Cp ring.