Interaction of 1,3,2,4-Benzodithiadiazines with Aromatic Phosphines and Phosphites

Although an interaction between hydrocarbon and fluorocarbon 1,3,2,4-benzodithiadiazines (1 ) and P(C6H5)3 continuously produces chiral 1,2,3-benzodithiadiazol-2-yl iminophosporanes (2; in this work, 5,7-difluoro derivative 2a ) via 1:1 condensation, an interaction between 1 and other PR3 reagents gives different products. With R OC6H5 and both hydrocarbon and fluorocarbon 1, only X=P(OC6H5)3 (X = S, O) were identified in the complex reaction mixtures by 13С and 31Р NMR and GC-MS. With R = C6F5, no interaction with the archetypal 1 was observed but catalytic addition of atmospheric water to the heterocycle afforded 2-amino-N-sulfinylbenzenesulfenamide (4 ). With electrophilic B(C6F5)3 instead of nucleophilic P(C6F5)3, only adduct H3NB(C6F5)3 and a new polymorph of C6F5B(OH)2 were isolated and identified by X-ray diffraction (XRD). A molecular structure of 2a was confirmed by XRD, and the π-stacked orientation of one of phenyl groups and heterocyclic moiety was observed. This structure is in general agreement with that calculated at the RI-MP2 level of theory, as well as at three different levels of DFT theory with the PBE and B3LYP functionals. Mild thermolysis of 2a in a dilute decane solution gave persistent 5,7-difluoro-1,2,3-benzodithiazolyl (3a ) identified by EPR in combination with DFT calculations.