Phosphaarsenes - Combining Phospha- and Arsa-Wittig-Reagents.

Dipnictenes of the type RPn=PnR (Pn=P, As, Sb, Bi) can be viewed as dimers of the corresponding pnictinidenes R-Pn. Phosphanylidene- and arsanylidenephosphoranes (R-Pn(PMe); Pn=P, As) have been shown to be versatile synthetic surrogates for the delivery of pnictinidene fragments. We now report that thermal treatment of 1 : 1 mixtures of R-P(PMe) and R'-As(PMe) gives access to arsaphosphenes of the type RP=AsR'.

Triphosphiranes as phosphinidene-transfer agents - synthesis of regular and chelating NHC phosphinidene adducts.

In this contribution we describe the general use of aryl-substituted triphosphiranes (ArP; Ar = Mes, Dip, Tip) as phosphinidene transfer reagents towards N-heterocyclic carbenes (NHCs) to give a library of twelve N-heterocyclic carbene phosphinidene adducts of the type ArPNHC (NHCPs), in which the NHCs have varying steric profiles, allowing a systematic evaluation of their structural and NMR-spectroscopic properties. In the next series of experiments we utilized 1,3- and 1,4-phenylene bridged bis-NHCs to access a new class of chelating bis(NHCP)s, of which three derivatives could be structurally characterized. The 1,4-phenylene derivatives were shown to be susceptible to P-C bond cleavage when irradiated with an LED (396 nm), providing a rare example of phosphinidene release from NHCPs.

Synthesis and Ligand Properties of Chelating Bis(-heterocyclic carbene)-Stabilized Bis(phosphinidenes).

NHC-phosphinidene (NHCP) adducts are an emerging class of ligands with proven binding ability for main group and transition metal elements. They possess electron-rich P atoms with two lone pairs (LPs) of electrons, making them interesting platforms for the formation of multimetallic complexes. We describe herein a modular, high-yielding synthesis of bis(NHCP)s, starting from alkylidene-bridged bis(NHC)s ((IMe)CH; = 1,3) and triphosphirane (PDip) (Dip = 2,6-PrCH) as phosphinidene transfer reagent.

A diarsene radical anion.

The isolation of the first diarsene radical anion by reduction of a neutral diarsene is presented. Comprehensive characterisation in conjunction with DFT calculations reveals unpaired spin density residing in the antibonding π*-orbital with involvement of the terphenyl ligands. First reactivity studies reveal no pronounced radical, but rather reducing properties.

Synthesis, Coordination Chemistry, and Mechanistic Studies of P,N-Type Phosphaalkene-Based Rh(I) Complexes.

The synthesis of P,N-phosphaalkene ligands, py-CH═PMes* (, py = 2-pyridyl, Mes* = 2,4,6-Bu-CH) and the novel quin-CH═PMes* (, quin = 2-quinolinyl) is described. The reaction with [Rh(μ-Cl)cod] produces Rh(I) bis(phosphaalkene) chlorido complexes and with distorted trigonal bipyramidal coordination environments. Complexes and show a pronounced metal-to-ligand charge transfer (MLCT) from Rh into the ligand P═C π* orbitals.

Metal-Free N-H Bond Activation by Phospha-Wittig Reagents.

N-containing molecules are mostly derived from ammonia (NH ). Ammonia activation has been demonstrated for single transition metal centers as well as for low-valent main group species. Phosphinidenes, mono-valent phosphorus species, can be stabilized by phosphines, giving so-called phosphanylidenephosphoranes of the type RP(PR' ).

Phosphine-catalysed reductive coupling of dihalophosphanes.

Classically tetraaryl diphosphanes have been synthesized through Wurtz-type reductive coupling of halophosphanes RPX or more recently, through the dehydrocoupling of phosphines RPH. Catalytic variants of the dehydrocoupling reaction have been reported, but are limited to RPH compounds. Using PEt as a catalyst, we now show that TipPBr (Tip = 2,4,6-PrCH) is selectively coupled to give the dibromodiphosphane (TipPBr) (1), a compound not accessible using classic Mg reduction.

Cyclo-Dipnictadialanes.

Using the Al precursor Cp Al in conjunction with triphosphiranes (PAr) (Ar=Mes, Dip, Tip) we have succeeded in preparing Lewis base-free cyclic diphosphadialanes with both the Al and P atoms bearing three substituents. Using the sterically more demanding Dip and Tip substituents the first 1,2-diphospha-3,4-dialuminacyclobutanes were obtained, whereas with Mes substituents [Cp Al(μ-PMes)] is formed. This divergent reactivity was corroborated by DFT studies, which indicated the thermodynamic preference for the 1,2-diphospha-3,4-dialuminacyclobutane form for sterically more demanding groups on phosphorus.

Reactivity of phospha-Wittig reagents towards NHCs and NHOs.

Phospha-Wittig reagents, RPPMe3 (R = Mes* 2,4,6-tBu3-C6H2; MesTer 2,6-(2,4,6-Me3C6H2)-C6H3; DipTer 2,6-(2,6-iPr2C6H3)-C6H3), can be considered as phosphine-stabilized phosphinidenes. In this study we show that PMe3 can be displaced by NHCs or NHOs. Interestingly, phosphinidene-like reactivity results in a subsequent C(sp2)-H activation of the exocyclic CH2 group in NHOs.

Terphenyl(bisamino)phosphines: electron-rich ligands for gold-catalysis.

Terphenyl(bisamino)phosphines have been identified as effective ligands in cationic gold(i) complexes for the hydroamination of acetylenes. These systems are related to Buchwald phosphines and their steric properties have been evaluated. Effective hydroamination was noted even at low catalyst loadings and a series of cationic gold(i) complexes has been structurally characterized clearly indicating stabilizing effects through gold-arene interactions.

A selective route to aryl-triphosphiranes and their titanocene-induced fragmentation.

Triphosphiranes are three-membered phosphorus cycles and their fundamental reactivity has been studied in recent decades. We recently developed a high-yielding, selective synthesis for various aryl-substituted triphosphiranes. Variation of the reaction conditions in combination with theoretical studies helped to rationalize the formation of these homoleptic phosphorus ring systems and highly reactive intermediates could be isolated.