Synthesis and Coordination Chemistry of Iminophosphanes.

Iminophosphanes are a new group of 1,3-P,N-ligands, readily obtainable from secondary phosphanes and nitrilium ions, having a tunable N-donor site by means of varying the imine substituents. These ligands give, in high yields, monodentate gold complexes and bidentate rhodium and iridium complexes. Crystal structures are reported for both the ligands and the complexes.

Facile synthesis of phosphaamidines and phosphaamidinates using nitrilium ions as an imine synthon.

Readily accessible nitrilium triflates are convenient imine building blocks for the expedient synthesis of a novel class of 1,3-P,N ligands as demonstrated for the reaction with primary phosphanes. This procedure allows variation of all substituents. X-ray crystal structures are reported for nitrilium ions, phosphaamidines, and three phosphaamidinate complexes.

Towards spontaneous heterolysis of the homonuclear P-P bond in diphosphines: the case of diazaphospholeniumtriphospholides.

Computational studies on a series of polyphospholyl-substituted N-heterocyclic phosphines (CH)(2)(NR)(2) P-P(n)(CH)(5-n) (R=Me, n=1-5) disclosed that increasing formal replacement of CH units in the phosphole ring by phosphorus atoms is associated with an increase in P-P distances and charge separation, and a decrease in covalent bond orders. Altogether, these trends imply that the CH versus P substitution enhances ionic P-P bond polarization in these compounds. Experimental verification of this hypothesis was obtained for the triphospholyl diazaphospholenes (CR)(2)(NR')(2)P-P(3)(CtBu)(2) (8a: R=H, R'=tBu; 8b: R=Me, R'=Mesityl [Mes]), which were prepared through metathesis reactions from suitable precursors and identified by solution and solid-state NMR data and a single-crystal X-ray diffraction study of 8a.

Ambident PCN heterocycles: N- and P-phosphanylation of lithium 1,3-benzazaphospholides.

Synthetic and structural aspects of the phosphanylation of 1,3-benzazaphospholides 1(Li), ambident benzofused azaphosphacyclopentadienides, are presented. The unusual properties of phospholyl-1,3,2-diazaphospholes inspired us to study the coupling of 1(Li) with chlorodiazaphospholene 2, which led to the N-substituted product 3. Reaction of 1(Li) with chlorodiphenyl- and chlorodicyclohexylphosphane likewise gave N-phosphanylbenzazaphospholes 4 and 5, whereas with the more bulky di-tert-butyl- and di-1-adamantylchlorophosphanes, the diphosphanes 6 and 7 are obtained; in the case of 7 they are isolated as a dimeric LiCl(THF) adduct.

Bisphosphine-functionalized cyclic decapeptides based on the natural product Gramicidin S: a potential scaffold for transition-metal coordination.

The natural product Gramicidin S is a promising scaffold for novel oligopeptide-based bisphosphine ligands, combining the advantageous rigid chiral backbone with the close proximity of phosphine substituents. The required unnatural, phosphine-containing, amino acid building blocks were synthesized by means of a novel protocol that involves the enantioselective alkylation of a chiral nickel Schiff base template. Three Ni complexes were prepared with different alkyl chains between the phosphine group and the alpha-carbon atom of the incorporated glycine; the absolute stereochemistry of two of them was determined by single-crystal X-ray structure analysis.

Diphosphines with strongly polarized P-P bonds: hybrids between covalent molecules and donor-acceptor adducts with flexible molecular structures.

A series of P-phospholyl-substituted N-heterocyclic phosphines was prepared and characterized by single-crystal X-ray diffraction and solution and solid-state (31)P NMR spectroscopy. The molecular structures are distinguished by the presence of P-P bonds of exceptionally variable lengths (2.35-2.

Pyrido-annellated diazaphospholenes and phospholenium ions.

Pyrido-annulated 1,3,2-diazaphospholenium ions and P-bis(trimethylsilyl)amino substituted 1,3,2-diazaphospholenes were synthesised and characterised by spectroscopic methods and single-crystal X-ray diffraction studies. The distribution of bond distances provided evidence for pi-electron delocalisation in the fused ring system. This hypothesis was confirmed by calculations of magnetic (NICS, nucleus independent chemical shift) and geometrical (Bird index, bond shortening index) aromaticity indexes which attest aromatic character of the five-membered rings in the cations that is lost upon introduction of a substituent at the phosphorus atom.

Phosphazene vs.diazaphospholene PN-bond cleavage in spirocyclic cyclodiphosphazenes.

Thermolysis of 2-azido-1,3,2-diazaphospholenes offers access to novel and rare spirocyclic cyclodiphosphazenes. The spectroscopic data and X-ray structure of one representative of the 2-azido-1,3,2-diazaphospholenes reveals an ionic bonding situation explaining sufficiently its rather high thermal stability. The cyclodiphosphazenes were characterised by NMR, mass spectrometry, and X-ray diffractometry.

Structural alternatives for the formation of halogenophosphine-phosphenium complexes.

NMR studies of reactions between some N-heterocyclic and acyclic diamino phosphenium ions (R2N)2P+ and P-chlorophosphines (R2N)2PCl suggest that the reactants interact via chloride scrambling rather than by formation of P-P bonded phosphenium-phosphine complexes. Computational studies of reactions between model ions (R'2N)2P+ and neutral phosphines (R'2N)2PX (X = F, Cl, Br) confirm that in the gas phase the formation of halide-bridged adducts is indeed preferred and only for the most electrophilic cation an alternative but energetically less favorable P-P bonded structure was found. The halide-bridged adducts feature nearly C2-symmetrical P.

Structures, dynamic behaviour, and reactivity of P-cyclopentadienyl-substituted 1,3,2-diazaphospholenes.

P-Cyclopentadienyl-substituted 1,3,2-diazaphospholenes were prepared by salt metathesis from NaCp or LiCp* and 2-chloro-1,3,2-diazaphospholenes. Comprehensive spectroscopic and X-ray diffraction studies revealed a significant lengthening of the phosphorus-carbon bonds as compared with typical P-C bond distances, and the presence of fluxional molecular structures in solution and solid state as a consequence of circumambulatory migration of the diazaphospholene moiety around the Cp-ring. The P-C bond lengthening is accompanied by the capability to react with transition metal complexes under P-C bond activation and cyclopentadienyl transfer.

Phosphorus-carbon bond formation catalysed by electrophilic N-heterocyclic phosphines.

A P-chloro-diazaphospholene catalyses the phosphorus-carbon bond formation reaction between diphenylsilylphosphine and various alkyl chlorides.

P-hydrogen-substituted 1,3,2-diazaphospholenes: molecular hydrides.

P-Hydrogen-substituted 1,3,2-diazaphospholenes 1 were prepared by an improved procedure from diazadienes and were characterized by spectroscopy and in one case by X-ray diffraction. A unique hydride-type reactivity of the P-H bonds was documented by extensive reactivity studies. Aldehydes and ketones were readily reduced to diazaphospholene derivatives of the corresponding alcohols, with alkyl-substituted ketones being converted at much lower rates than aldehydes or diaryl ketones.