M. Rosario Díaz

Diphosphanylketenimines: New Reagents for the Synthesis of Unique Phosphorus Heterocycles

Two consecutive [3+2] cycloaddition reactions of the diphosphanylketenimine (PPh(2))(2)C[double bond]C[double bond]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 1 lambda(5),3 lambda(5)-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 H(2)O(2) 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[double bond]PPh(2))(PPh(2))C[double bond]C[double bond]NPh (8) is quantitatively obtained. Compound 8 readily reacts with the alkynes MeO(2)CC[triple bond]CCO(2)Me and MeO(2)CC[triple bond]CH, and with phenyl isocyanate and ethyl isothiocyanate through regiospecific [3+2] cycloaddition processes furnishing several lambda(5)-phosphole and lambda(5)-azaphosphole derivatives. Finally, the reaction of 8 with N-methylpropargylamine yields the new 2,3-dihydro-1,4-lambda(5)-azaphosphinine 15 through a cycloaddition process involving two functional groups from each molecule.

Dithiocarbamyl-substituted diphosphanylmethanide complexes of manganese(I): a new type of ambivalent metalloligands

The diphosphanylmethanide complex [Mn(CO)4[(PPh2)2C-H]] promotes S-S bond breaking in tetramethylthiuram disulfide affording [Mn(CO)4[(PPh2)2C-S-C(S)NMe2)]] (2), which proved to be a valuable host for binding cations through the methanide carbon atom and the thiocarbonyl group, allowing the controlled synthesis of heterometallic compounds.

CrCl2-Promoted Stereospecific and Stereoselective Alkyl- and Silylcyclopropanation of α,β-Unsaturated Amides

An efficient chromium-promoted alkyl- or silylcyclopropanation of alpha,beta-unsaturated amides is described. These reactions can be carried out on (E)- or (Z)-alpha,beta-enamides in which the C-C double bond is di-, or trisubstituted. This process takes place with total stereospecificity and the new stereogenic center is generated with high or total stereoselectivity. Some synthetic applications of the obtained silylcyclopropyl amides are also reported. Two mechanisms based on the generation of carbenoid or carbene complexes have been proposed to explain this cyclopropanation reaction.

P-C versus C-H bond cleavage in coordinated bis(dimethylphosphino)methane: controlled access to either phosphinite or functionalized diphosphine complexes.

Treatment of fac-[Mn(CNPh)(CO)3(dmpm)]ClO4 (1) with KOH affords neutral phosphinite complex fac-[Mn(PMe2O)(CNPh)(CO)3(PMe3)] (2) as a result of P-C bond cleavage on the dmpm ligand, whereas when carrying out the reaction in the presence of iodine the diphosphinoketenimine derivative fac-[MnI(CO)3[(PMe2)2C=C=NPh]] (4) is obtained after deprotonation and further functionalization of the central carbon atom of the diphosphine.

Thiocyanogen Insertion into P−C Bonds of Diphosphinomethanide Complexes, Leading to Rare Functionalized Diphosphine and Tetraphosphine Ligands

The complex fac-[Mn(CNtBu)(CO)3{(PPh2)2C−SCN}] (2) reacts with thiocyanogen, affording the unstable derivative fac-[Mn(CNtBu)(CO)3{(PPh2)C(SCN)C(SSCN)N(PPh2)}] (3), as a result of the insertion of the pseudohalogen molecule into one of the P−C bonds of the diphosphinomethanide ligand. This complex undergoes intermolecular sulfur−sulfur coupling processes, with elimination of the pseudohalogen molecules (SCN)2, S(CN)2, and (CN)2, to yield a mixture of the dinuclear complexes fac-[{Mn(CNtBu)(CO)3(PPh2)C(SCN)C(NPPh2)}2−Sn] (4−6) linked through polysulfide chains of different lengths. Treatment of these dinuclear disulfide and trisulfide derivatives with 1 or 2 equiv of HBF4 resulted in the sequential protonation of the nitrogen atoms of the ligand, yielding cationic and dicationic complexes, respectively. In the case of monoprotonated disulfide derivatives 31P NMR experiments reveal the existence of an intramolecular proton-transfer process between the endocyclic nitrogen atoms of both metallic fragments. Si...