The Reaction of BeCl2 with Carbodiphosphorane C(PPh3)2; Experimental and Theoretical Studies

The use of 2‐Br‐fluorobenzene as the solvent permitted the isolation of the addition compound [Cl2Be(C{PPh3}2)] (5) from the reaction of the carbodiphosphorane 1 (carbon) with BeCl2 featuring a three coordinate beryllium atom. In other solvents such as THF, DCM, etc. deprotonation occurs with formation of the cations (HC{PPh3}2)+ or (H2C{PPh3}2)2+. Compound 5 was characterized by an X‐ray diffraction analysis. The analysis of the bonding situation in Cl2Be←1 reveals that the orbital donation comes mainly from the σ lone‐pair orbital of 1, whereas the π donation is rather weak. However, the Cl2Be←1 π donation appears strong enough to make the donation of a second donor species 1 unfavorable. The calculation of 1→Cl2Be←1 shows that the latter complex is higher in energy than 1→Cl2Be and free 1. The carbodiphosphorane may bind, albeit weakly, a second BeCl2 species in the complex Cl2Be←1→BeCl2. The bond dissociation energies for the first and second BeCl2 fragments are De = 31.8 kcal·mol–1 and 7.0 kcal·mol–1. The dimerization of Cl2Be←1 is energetically slightly endoenergetic.