Iron(ii) template synthesis of benzannulated triphospha- and triarsamacrocycles

Nine-membered 1,4,7-triphospha- and triarsamacrocycles with unsaturated benzo-backbones have been prepared using the [CpRFe]+ unit as a template. The cyclisation involves the attack of a coordinated phosphide (or arsenide) nucleophile at an activated, electrophilic ortho-fluorophenyl substituent on a neighbouring pnictide donor. The macrocycle assembly is of the 2 + 1 type where two new chelate rings are formed from appropriately derivatised bidentate and monodentate phosphines/arsines. Both [(η5-C5H5)Fe]+ and [(η5-C5Me5)Fe]+ may be employed for the cyclisation with higher yields generally being observed with the unsubstituted Cp. All new compounds have been characterised by spectroscopic and analytical methods including the single-crystal X-ray structure determination of [(η5-C5H5)Fe(tribenzo-9aneP3-Ph,PhF2)]+, 3a, and [(η5-C5H5)Fe(tribenzo-9aneAs3-Ph,PhF2)]+, 5, as the tetraphenylborate salts. The crystal structures are isomorphous and show the unique conformation of these new macrocycles with a ‘cup shaped’ cavity formed by the rigid benzo-backbones. The 9aneAs3 derivative is the first example of a nine-membered triarsamacrocycle