A study of nerve agent model organophosphonate binding with manganese-A2B-corrole and -A2B2-porphyrin systems

Herein the synthesis and binding studies of novel trans-A2B-corrole and trans-A2B2-porphyrin derivatives are presented in comparing manganese(III)-organophosphonate (OP) binding (e.g., Mn+ ← OPR(OR)2) capabilities. H3(PFP-VC) [PFP-VC = 5,15-di(pentafluorophenyl)-10-(3-vinylphenyl)corrolate] was synthesized by way of literature procedures and was characterized by a variety of 2-D NMR spectroscopic techniques and single-crystal X-ray diffraction. These compounds represent the first example of 3-vinyl-phenyl-containing meso-substituted corroles or porphyrins. Mn(PFP-VC) (3) was treated separately with (CH3CH2O)2PO(C3H6NMe2), (C4H9O)2PO(Me), (C2H5O)2PO(CH2COCH3), (CH3CH2O)2PO(Me), to give 1:1 adducts, as determined by UV–Vis spectroscopy (Job Plot), giving a red shift; Ph3PO, was also found to bind, but very weakly. The trans-A2B2-porphyrin analogue Mn(PFP-VP) (4) was also prepared by way of a literature procedure; related binding studies gave 1:1 organophosphonate-Mn(PFP-VP) adducts (Job Plot). A clean blue shift occurred for the Mn-porphyrins at higher organophosphonate loadings (Ka values: 6.7 (0.9)–11.9 (0.4) M−1). DFT geometry optimizations of OP(OMe)2Me binding and formal Mn–O or P–O cleavage products in the unsubstituted neutral Mn-corrolato and -porphyrinato systems with a range of metal-based spin states revealed greatest stability in formal phosphoryl oxygen binding (energies: 11–13 kcal/mol) for the Mn-corrole (singlet); the Mn-porphyrin (sextet) was also quite stable.

Graphical abstractMn A2B-corrole and trans-A2B2-porphyrin derivatives have been prepared for a comparison of experimental organophosphonate (OP) binding (e.g., Mn+ ← OPR(OR)2). Job plots give a 1:1 metal: ligand stochiomietry which is preferable for the Mn-corrole. Theoretical studies with unsubstituted Mn-corroles/-porphyrins and cyclic voltammetry were also undertaken.Figure optionsDownload full-size imageDownload as PowerPoint slide