Manganese(i) templates for the construction of benzannulated triphosphamacrocycles

Abstract

Nine-membered 1,4,7-triphosphamacrocycles with unsaturated benzo-backbones have been prepared using the [(CO)₃Mn]⁺ unit as a template. Two synthetic methods have been employed for the macrocyclisation both of which involve the attack of a coordinated phosphide at an activated, electrophilic ortho-fluorophenyl substituent on a neighbouring pnictide donor. Addition of base to the precursor complex fac-[(CO)₃Mn(dfppb)(PhPH₂)]⁺, 1, where dfppb = 1,2-bis[di(2-fluorophenyl)phosphino]benzene, results in the direct formation of the macrocyclic compound fac-[Mn(CO)₃(tribenzo-9aneP₃-Ph,Ph^F₂)]⁺, 3. A second precursor, namely fac-[(CO)₃Mn(1,2-bpb){P(Ph^F)₃}]⁺, 5, where 1,2-bpb = 1,2-bis(phosphino)benzene, undergoes spontaneous partial macrocyclisation when dissolved in THF to give the intermediate complex fac-[(CO)₃Mn{H₂PC₆H₄P(H)C₆H₄P(Ph^F)₂}]⁺, 6, which contains a linear tridentate phosphine with the unusual combination of a primary, secondary and tertiary phosphine donor. Addition of base to 6 gives the desired macrocyclic complex fac-[Mn(CO)₃(tribenzo-9aneP₃-H₂,Ph^F)]⁺, 7, which is converted in situ to the more stable dimethylated fac-[Mn(CO)₃(tribenzo-9aneP₃-Me₂,Ph^F)]⁺, 8. The new complexes have been fully characterised by spectroscopic and analytical methods including single crystal X-ray structure determinations for 1, 3, 5, 6 and 8.