A combined experimental/theoretical study gives strong evidence that carbodiphosphoranes are divalent carbon(0) compounds. The calculations show that carbodiphosphoranes have two lone pairs of electrons (see picture), which give rise to unusual properties as confirmed by experiment. The synthesis of a triply charged molecules in which two protonated carbodiphosphoranes serve as donor ligands to an Ag+ center supports the bonding model.

Eine theoretisch/experimentelle Untersuchung liefert Hinweise, dass Carbodiphosphorane als Verbindungen mit zweibindigem Kohlenstoff(0)‐Atom einzuordnen sind. Carbodiphosphorane haben zwei freie Elektronenpaare (siehe Schema), die den Molekülen ungewöhnliche Eigenschaften verleihen. Die Synthese eines dreifach geladenen Moleküls, bei dem zwei protonierte Carbodiphosphorane als Elektronendonoren für Ag+ wirken, stützt dieses Bindungsmodell.

The donor‐acceptor complex [(H3B){C(PPh3)2}] (2) has been synthesized by treating B2H6 with C(PPh3)2 and its geometry determined by X‐ray structure analysis. Treatment of 2 with DME yields the complex [{(μ‐H)H4B2}{C(PPh3)2}][B2H7] (4), which has also been isolated and structurally characterized. Compound 4 is the first complex of a carbodiphosphorane where the carbon donor atom binds with its two‐electron lone pairs to two main‐group Lewis acids larger than protons. This reaction is likely to occur via initial formation of [(H3B)2{C(PPh3)2}] (6), which subsequently reacts with B2H6, with loss of a hydride, to yield 4. Quantum chemical calculations of 2, 4+ and 6 show that the carbon–boron bonds in these complexes are very strong, and analysis of the bonding situation using the EDA, NBO and AIM methods reveals typical bonding patterns between the divalent carbon(0) moieties and one or two Lewis acids. The carbon donor atom of the carbodiphosphorane moiety remains strongly negatively charged even in the cation 4+. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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