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 H₃N→B(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.