UNEXPECTED BASICITY OF A HEXACOORDINATE SILICON MINO)METHYL]PHENYL)BIS(1,2-BENZENEDIOLATO)SILICATE

The high basicity of {2,6-bis-[(dimethylamino)methyl]phenyl} bis(1,2-b enzenediolato)silicate (1) was demonstrated by its quantitative proton ation in methanol to give the zwitterion 2. It was found that 1 is muc h more basic (pK(a) in CH2Cl2 = 16.7) than the ''proton sponge'' 1,8-b is(dimethylamino)naphthalene (3) and also much more basic than {2,6-bi s-[(dimethylamino)methyl]phenyl} bis(1,2-benzenediolato)phosphorane (4 ). The stability of the zwitterion 2, the geometry of which correspond s to a more perfect octahedron than 1, can explain the high basicity o f 1. Dynamic NMR studies of 2 in solution show that at low temperature the hydrogen-bonding interaction with one oxygen atom observed in the solid state is maintained. On raising the temperature, firstly the hy drogen bond breaks, then dynamic coordination occurs, in which the NMe (2) groups displace each other in conjunction with transprotonation.