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 [(CpFe)-Fe-R](+) 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 [(eta(5)-C5H5)Fe](+) and [(eta(5)-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 [(eta(5)-C5H5)Fe(tribenzo-9aneP(3)-Ph, Ph-2(F))](+), 3a, and [(eta(5)-C5H5)Fe(tribenzo-9aneAs(3)-Ph, Ph-2(F))](+), 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 9aneAs(3) derivative is the first example of a nine-membered triarsamacrocycle.