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 center dot CH3OH and 5, the 1:1 complexes [In(4)(NO3)(3)], [Pr(4)(NO3)(3)(CH3CN)]center dot 0.5CH(3)CN, [Er(4)(NO3)(3)(CH3CN)]center dot CH3CN, [Pu(4)Cl-4]center dot THF and the 2:1 complex [Nd(4)(2)(NO3)(2)](2)(NO3)(2)center dot(H2O)center dot 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 angstrom 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)center dot 4(CH3OH)}(0.5), although the nonbonded Er center dot center dot center dot O-furan distance is reduced to similar to 3.6 angstrom. 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 (O Phi DiBCMPO) measured under identical conditions.