Three-, four-, and five-coordinate cyclic phosphites, phosphonates, and phosphonium salts containing sulfuryl groups

Reaction of the sulfuryl diphenol O2S[(t-Bu)MeC6H2OH](2) (10) with phosphorus trihalides in the presence of amines yielded the phosphites O2S[(t-Bu)MeC6H2O](2)PR where R = Cl for 1 and R = Br for 2. Treatment of 1 with 2,6-dimethylphenol in a halide displacement reaction gave 3 (R = OXyl). In a similar diol reaction with O2S[Me2C6H2OH](2) (11), the hydrogenphosphonate O2S[Me2C6H2O](2)P(O)H (5) formed. A related hydrogenphosphonate O2S[(t-Bu)MeC6H2O](2)P(O)H (4) was obtained by hydrolysis of either 1 or 2. The phosphonium bromide salt O2S[(t-Bu)MeC6H2O](2)PPhBr+Bi- (7) formed from the bromination of the phenylphosphonite derivative O2S[(t-Bu)MeC6H2O](2)PPh (9), the hydrolysis of which yielded the phosphonate O2S[(t-Bu)MeC6H2O](2)P(O)Ph (6). A related phosphonium bromide O2S [(t-Bu)MeC6H2O](2)PB2+Br- (8) was prepared by the reaction of the diphenol 10 with PBr3 in the presence of N-bromodiisopropylamine. All of the cyclic phosphorus derivatives 1-8 were characterized by x-ray studies and NMR measurements. All of the compounds lack donor-acceptor interaction that is potentially available via the oxygen atom of the sulfuryl group present as part of the ring system except for 4. For 3, the structure is pentacoordinated with a displacement from a tetrahedral geometry toward a trigonal bipyramid, The ring conformation is a syn twist-boat whereas the others lacking donor coordination reside in an anti chair-like ring arrangement. Solution P-31 NMR chemical shifts are in appropriate ranges indicating retention of the coordination geometry that was found in the solid state. Weak P-Br bond strength is suggested to account for formation of the phosphonium bromides 7 and 8 which contrasts with the hexacoordinate structure obtained previously for an analogous chlorophosphorane. Comparisons with similar formulations of cyclic phosphites and phosphates having ring sulfur atoms show that there is a preponderance of donor-acceptor interactions involving sulfur compared to that experienced with the sulfuryl group.