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

Abstract

Nine-membered 1,4,7-triphospha- and triarsamacrocycles with unsaturated benzo-backbones have been prepared using the [Cp^RFe]⁺ 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,Ph^F₂)]⁺, 3a, and [(η⁵-C₅H₅)Fe(tribenzo-9aneAs₃-Ph,Ph^F₂)]⁺, 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.