ALKALI-METAL INDUCED RUPTURE OF A PHOSPHORUS-PHOSPHORUS DOUBLE-BOND -ELECTROCHEMICAL AND EPR INVESTIGATIONS OF NEW STERICALLY PROTECTED DIPHOSPHENES AND RADICAL-ANIONS [ARPPAR](CENTER-DOT-)

The synthesis and characterization of the new diphosphenes DmtP + PDmt (2a) (Dmt = 2,6-dimesityl-p-tolyl) and DxpP=PDxp (3a) (Dxp = 2,6-di(m -xylyl)phenyl) are described. The electrochemical behavior of 2a, 3a, Emd DmpP=PDmp (1a) (Dmp = 2,6-dimesitylphenyl) has been examined by cy clic voltammetry. Compounds 1a-3a display reversible reductions in THF (room temperature, 0.1 M (Bu4NBF4)-Bu-n) at -2.08, -2.15, and -2.08 V vs SCE, respectively. Chemical and electrochemical reduction of solut ions of 1a-3a led to the stable radical anions [DmpPPDmp](.-) (1b),[Dm tPPDmt](.-) (2b), and [DxpPPDxp](.-) (3b) which were studied by EPR sp ectroscopy. The EPR data indicate the unpaired spins reside in P=P pi( ) molecular orbitals. Chemical reduction of 1a-3a with either Na meta l or sodium naphthalenide yields sodium salts Na[ArPPAr], which show a dditional EPR signals that have been attributed to the presence ofion- paired species. No ion pairing was detected by EPR spectroscopy for th e corresponding magnesium, potassium, or lithium salts of la. Reductio n of DmpP=PDmp with excess potassium metal in THF led to dark, EPR sil ent, solutions. Analysis of such solutions by P-31 NMR indicated the p resence of DmpP(H)K. Quenching of this species with degassed H2O or CF 3COOH affords DmpPH(2).