Synthesis and reactivity of a very strong reducing agent containing a quadruple bond: structures of W_2 (hpp)_4 and W_2(hpp)_4Cl_2·4CH_2Cl_2

摘要

The preparation and structural characterization of the very strong reducing agent W_2(hpp)_4, hpp = the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, 1, has been accomplished. It has a short distance of 2.1617(4)A for the quadruplybonded W_2~(4+) unit. Compound 1 is very reactive and gives the triple bonded W_2(hpp)_4Cl_2·4CH_2Cl_2, 2·4CH_2Cl_2, upon crystallization after mere contact with haloalkane CH_2CL_2. The change in electronic configuration from the sigma~2pi~4delta~2 in 1 to the sigma~2pi~4 system in 2 increases the W-W distance by ca. 0.09 to 2.2497(8) A. W_2(hpp)_4 also reduces C_(60) and 7,7',8,8'-tetracyanoquinodimethhide, TCNQ. The latter is reduced to the TCNQ~~(2-) anion while the W_2~(4+) unit is oxidized to the W_2~(6+) state.