text: This coordination compound is prepared by the reaction of tungsten hexacarbonyl with 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (Hhpp) in o-dichlorobenzene at 200 °C:
  The reaction gives W(hpp)Cl. Dichlorobenzene provides the chlorine atoms and is itself reductively coupled to 2,2′-dichlorobiphenyl. The bond order between the tungsten centers in W(hpp)Cl is three.
  This dichloride is further reduced by potassium metal to W(hpp). This species has a quadruple bond between the two tungsten centers. Related quadruply bonded complexes include [WCl] and [[Potassium octachlorodimolybdate|[MoCl]]]. Because of its low ionization energy, W(hpp) is easily oxidized back to the dichloride by dichloromethane.  It is readily oxidized to the corresponding cation with the oxidants fullerene and with tetracyanoquinodimethane. (hpp) was proposed to be a potentially useful powerful reducing agent akin to CpCo and CpCr, so far this reagent has not become part of the synthetic chemist's armament. grand total of 7 refs in 5 years-->