Synthesis and coordination chemistry of phosphine oxide decorated dibenzofuran platforms

Abstract

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·CH 3OH and 5, the 1:1 complexes [In(4)(NO 3) 3], [Pr(4)(NO 3) 3(CH 3CN)] ·0.5CH 3CN, [Er(4)(NO 3) 3(CH 3CN)]·CH 3CN, [Pu(4)Cl 4]·THF and the 2:1 complex [Nd(4) 2(NO 3) 2] 2(NO 3) 2· (H 2O)·4(CH 3OH) 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(NO 3) 2](NO 3)·4(CH 3OH)} 0.5, although the nonbonded Er⋯O furan 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. © 2012 American Chemical Society.