Synthesis and Coordination Chemistry of Phosphine Oxide Decorated Dibenzofuran Platforms

A four-step synthesis for 4,6-bis­(diphenylphosphinoylmethyl)­dibenzofuran (4) from dibenzofuran and a two-step synthesis for 4,6-bis­(diphenylphosphinoyl)­dibenzofuran (5) are reported along with coordination chemistry of 4 with In­(III), La­(III), Pr­(III), Nd­(III), Er­(III), and Pu­(IV) and of 5 with Er­(III). Crystal structure determinations for the ligands, 4·CH3OH and 5, the 1:1 complexes [In­(4)­(NO3)3], [Pr­(4)­(NO3)3(CH3CN)]·0.5CH3CN, [Er­(4)­(NO3)3(CH3CN)]·CH3CN, [Pu­(4)­Cl4]·THF and the 2:1 complex [Nd­(4)2(NO3)2]2(NO3)2·(H2O)·4­(CH3OH) are described. In these complexes, ligand 4 coordinates in a bidentate POP′O′ mode via the two phosphine oxide O-atoms. The dibenzofuran ring O-atom points toward the central metal cations, but in every case it is more than 4 Å from the metal. A similar bidentate POP′O′ chelate structure is formed between 5 and Er­(III) in the complex, {[Er­(5)2(NO3)2]­(NO3)·4­(CH3OH)}0.5, although the nonbonded Er···Ofuran distance is reduced to ∼3.6 Å. The observed bidentate chelation modes for 4 and 5 are consistent with results from molecular mechanics computations. The solvent extraction performance of 4 and 5 in 1,2-dichloroethane for Eu­(III) and Am­(III) in nitric acid solutions is described and compared against the extraction behavior of n-octyl­(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (OΦDiBCMPO) measured under identical conditions.