Synthesis of 1,1′,2-Trisubstituted Aryl-Based Ferrocenyl Phosphines as Precursors for Immobilized Ligands

Ferrocenylaryl or ferrocenylheteroaryl phosphines bearing a carboxaldehyde group, [Fe­{1-PPh2(spacer)-2-NMe2CH2C5H3}­(C5H4CHO)] (spacer = none (rac-12), 1,4-phenylene (rac-13), 1,3-phenylene (rac-14), 2,5-thienylene (rac-15)), were prepared in a facile four-step sequence starting with dibromination of N,N-dimethylaminomethylferrocene (1) followed by Negishi cross-coupling between 1,1′-dibromo-2-N,N-dimethylaminomethylferrocene (rac-2) and aryl or heteroaryl bromide phosphine oxides, Br-spacer-P­(O)­Ph2 (spacer = 1,4-phenylene, 1,3-phenylene, 2,5-thienylene), reduction with trichlorosilane, and functionalization of the 1′-position of the cyclopentadienyl ring. All products were fully characterized by spectroscopy (1H, 13C, and 31P NMR, MS, IR) and for rac-3, rac-7 and rac-11 also by X-ray crystallography. Furthermore, preliminary studies on the grafting of rac-12 on silica were conducted.