Carbodiphosphoranes: The Chemistry of Divalent Carbon(0)

Energy decomposition analysis

“…The parent system is carbodiphosphorane C(PPh 3 ) 2 , which was synthesized already in 1961 . A detailed analysis of the electronic structure of carbodiphosphorane (CDP) revealed that the carbon‐phosphorous bonds come from the donation of the phosphine groups to the carbon atom . The application of the bonding model to carbon suboxide, which is mentioned in the previous section, provided a straightforward explanation for its nonlinear equilibrium structure …”

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“…Experimental and theoretical studies on carbodiphosphoranes show that the geometrical features are already good indicators for the bonding situation in CL 2 compounds 12,14,16,23,24. Figures 1 and 2 show representative examples of calculated and synthesized carbodicarbenes 1 , tetraaminoallenes 2 , and bent allenes 3 together with the most important bonding parameters.…”

“…Although the molecules do not have a mirror plane that prevents the clear definition of σ‐ and π‐orbitals, the local symmetry of the highest lying molecular orbitals (MOs) at the central CCC moiety makes it possible to identify them as σ‐ and π‐type orbital, respectively. The form of these orbitals resembles the orbital shapes of carbodiphosphoranes,12 although the contributions from the orbitals of the ligands NHC to the HOMO and HOMO‐1 in the carbodicarbenes are larger than the contributions of the ligand orbitals in carbodiphosphoranes. The orbitals of tetraaminoallene 2a exhibit a higher degree of delocalization, but the largest coefficient for the occupied frontier orbitals is still found at the central carbon atom.…”

“…The first carbone CL 2 synthesized already in 1961 by Ramirez et al8 is the carbodiphosphorane C(PPh 3 ) 2 . The synthetic chemistry of carbodiphosphoranes was extensively studied experimentally,9–11 but the peculiar donor–acceptor bonding situation Ph 3 P → C ← PPh 3 was only recently recognized in a theoretical study of the complex (PPh 3 ) 2 C → CO 2 12. After recognizing the donor–acceptor bonding in C(PPh 3 ) 2 , the authors searched for other carbones CL 2 , which were not experimentally known at that time.…”

Strong Chemical Bonds

“…Frenking et al [123] have presented experimental and theoretical evidence that formally zero-valent carbon can exist in compounds, for example, in carbodiphosphoranes like C(PPh 3 ) 2 , in which the valence electrons remain as two lone pairs that are not engaged in bonding. In reality, the carbon atom is divalent like in a carbene, but the electron pairs for the carbon-phosphorus bonds are donated entirely by the phosphorus atoms.…”