Synthesis and reactivity of a very strong reducing agent containing a quadruple bond: structures of W2(hpp)4 and W2(hpp)4Cl2·4CH2Cl2

The preparation and structural characterization of the very strong reducing agent W2(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) Å for the quadruply-bonded W24+ unit. Compound 1 is very reactive and gives the triple bonded W2(hpp)4Cl2·4CH2Cl2,2·4CH2Cl2, upon crystallization after mere contact with the haloalkane CH2Cl2. The change in electronic configuration from the σ2π4δ2 in 1 to the σ2π4 system in 2 increases the W–W distance by ca. 0.09 to 2.2497(8) Å. W2(hpp)4 also reduces C60 and 7,7′, 8,8′-tetracyanoquinodimethide, TCNQ. The latter is reduced to the TCNQ2− anion while the W24+ unit is oxidized to the W26+ state.