BORA AROMATIC SYSTEMS .14. THE NATURE OF KRAUSE ADDUCTS - THE STRUCTURE OF THE 1 1 ADDUCT OF TRIPHENYLBORANE WITH SODIUM METAL/

Triphenylborane (7) undergoes reductive dimerization with sodium metal in diethyl ether solution to form a yellow solid (3) having the empir ical composition Ph3B.Na.(C2H5)2O. By H-1 NMR spectroscopy, 3 has now been shown to have the structure depicted. By the [GRAPHICS] action of heat or strongly donor ethers, 3 rearranges into 6, whose structure w as likewise determined by H-1 and B-11 NMR spectroscopy and by deuteri ode-boronation with DOAc. Prolonged reaction of sodium metal with 7 or with diphenylboron chloride (8) in DME leads to biphenyl precursors, sodium tetraphenylborate (9), and sodium phenylborohydrides. All these results can be reconciled by the formation of the radical-anion 10 fr om 7 and its subsequent coupling or fragmentation. The coupling of 10 to form 3 and the rearrangement of 3 to yield 6 shows that there is a striking parallel in behavior between the isoelectronic (Ph3B.)- and t he triphenylmethyl radical (Ph3C.). In this light, the solution of the ''hexaphenylethane riddle'' is also applicable to the solution of the ''hexaphenyldiborate dianion riddle,'' which was posed by the discove ry of Krause's adduct over 68 years ago.