Two consecutive [3+2] cycloaddition reactions of the diphosphanylketenimine (PPh2)2CCNPh (3), involving the phosphanyl groups, with two equivalents of the electron‐poor alkynes dimethyl acetylenedicarboxylate or methyl acetylenecarboxylate give rise to the formation of the bicyclic 1λ5,3λ5‐diphospholes 5 a,b, which contain a phosphorane unit with five carbon substituents attached to the phosphorus center. Compound 3 undergoes cyclodimerization by crystallization, affording the unsymmetrical dimer 6, which is converted back to 3 by heating in toluene. Compound 6 can be oxidized stepwise on the three trivalent phosphorus atoms by treatment with H2O2 affording 7, 9, and the transient species 10, which are transformed into their corresponding ketenimine monomers either spontaneously (10) or by heating in toluene (7, 9). In this way, the compound (OPPh2)(PPh2)CCNPh (8) is quantitatively obtained. Compound 8 readily reacts with the alkynes MeO2CCCCO2Me and MeO2CCCH, and with phenyl isocyanate and ethyl isothiocyanate through regiospecific [3+2] cycloaddition processes furnishing several λ5‐phosphole and λ5‐azaphosphole derivatives. Finally, the reaction of 8 with N‐methylpropargylamine yields the new 2,3‐dihydro‐1,4‐λ5‐azaphosphinine 15 through a cycloaddition process involving two functional groups from each molecule.

Just by crystallization at room temperature the diphosphanylketenimine 1 is transformed into the unsymmetrical dimer 2 through a novel [2+3] cycloaddition reaction; a phosphanyl substituent is involved in the annelation process. This dimerization is fully reversible and appears to be promoted by intramolecular CH⋅⋅⋅N hydrogen bonds.

The next generation: Diphosphinocarbene (Arduengo carbene) and imidazol‐2‐ylidene (Bertrand carbene) are combined in complex 2, which was prepared by reaction of the diphosphinoketenimine complex 1 with propargylamine to form a new type of P2CCN2 electron‐rich olefin, which behaves as a strongly basic diphosphine.

The diphosphinoketenimine ligand in the neutral complexes fac-[MnI(CO)(3){(PPh(2))(2)C=C=NR}] (1 a: R = Ph; 1 b: R = p-tolyl) undergoes nucleophilic attack by MeLi and nBuMgCl yielding, after hydrolysis, the diphosphinoenamine-containing complexes fac-[MnI(CO)(3){(PPh(2))(2)C=C(R')NHR}] (3 a,b: R' = Me; 4 a,b: R' = nBu). Complex 1 a reacts under the same conditions with H(2)C=C=CHMgBr to afford fac-[MnI(CO)(3){(PPh(2))(2)C=C(CH(2)CC[triple chemical bond]CH)NHR}] (5 a), which contains a terminal alkyne group on the alpha-carbon atom of the diphosphinoenamine ligand. The cationic complexes fac-[Mn(CO)(4){(PPh(2))(2)C=C=NR}](+) (6) react with H(2)C=C=CHMgBr to afford diphosphinomethanide derivatives bearing three different types of functional groups, depending upon the substituent on the nitrogen atom of the ketenimine: cumulene in fac-[Mn(CO)(4){(PPh(2))(2)C--C(CH=C=CH(2))=N-xylyl}] (7 d), internal alkyne in fac-[Mn(CO)(4){(PPh(2))(2)C--C(C[triple chemical bond]CCH(3))=NtBu}] (8), and quinoline in 9 (R = Ph), whose formation implies an unusual cyclization process. Protonation of 7 d, 8, and 9 with HBF(4) occurs at the nitrogen atom to give the cationic derivatives 10 d, 11, and 12, respectively, which contain the corresponding functionalized diphosphine ligands. Irradiation of 3 a,b and 4 a,b with Vis/UV light makes it possible to isolate the free ligands (PPh(2))(2)C=C(R')NHR (13 a,b and 14 a,b), completing the metal-assisted synthesis of these novel functionalized diphosphines. Irradiation of 12 with Vis/UV light generates free phosphinoquinoline ligand 15, which readily affords a complex 16 containing 15 as a P,N-chelating ligand when treated with [PdCl(2)(NCMe)(2)], thus demonstrating its coordination capability.

Einfach bei der Kristallisation bei Raumtemperatur reagiert das Diphosphanylketenimin 1 zum unsymmetrischen Dimer 2, und zwar über eine neuartige [2+3]‐Cycloaddition; einer der beiden Phosphanylsubstituenten ist an der Anellierung beteiligt. Diese Dimerisierung ist vollständig reversibel und scheint durch die Bildung intramolekularer CH⋅⋅⋅N‐Wasserstoffbrückenbindungen gefördert zu werden.