The Reaction of BeCl 2 with Carbodiphosphorane C(PPh 3 ) 2 ; Experimental and Theoretical Studies

The use of 2‐Br‐fluorobenzene as the solvent permitted the isolation of the addition compound [Cl 2 Be(C{PPh 3 } 2 )] ( 5 ) from the reaction of the carbodiphosphorane 1 (carbon) with BeCl 2 featuring a three coordinate beryllium atom. In other solvents such as THF, DCM, etc. deprotonation occurs with formation of the cations (HC{PPh 3 } 2 ) + or (H 2 C{PPh 3 } 2 ) 2+ . Compound 5 was characterized by an X‐ray diffraction analysis. The analysis of the bonding situation in Cl 2 Be← 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 Cl 2 Be← 1 π donation appears strong enough to make the donation of a second donor species 1 unfavorable. The calculation of 1 →Cl 2 Be← 1 shows that the latter complex is higher in energy than 1 →Cl 2 Be and free 1 . The carbodiphosphorane may bind, albeit weakly, a second BeCl 2 species in the complex Cl 2 Be← 1 →BeCl 2 . The bond dissociation energies for the first and second BeCl 2 fragments are D e = 31.8 kcal · mol –1 and 7.0 kcal · mol –1 . The dimerization of Cl 2 Be← 1 is energetically slightly endoenergetic.