The Azide-Wittig Reaction.

The introduction of heteroatoms into conjugated organic molecules is an important strategy to tune their reactivity and physical properties. In this realm triazabutadienes (TBDs) of the general from RC=N-N=NR' are an interesting class of compounds, however, general synthetic protocols for their generation are limited. Based on the serendipitous finding that the sterically encumbered azide Mes*N (Mes*=2,4,6-tBuCH) reacted with PMe in the presence of an aromatic aldehyde to form a TBD, we now report on the "Azide-Wittig" reaction.

1,3-Dipolar cyclisation reactions of nitriles with sterically encumbered cyclic triphosphanes: synthesis and electronic structure of phosphorus-rich heterocycles with tunable colour.

We describe the synthesis, solid state and electronic structures of a series of tunable five-membered cationic and charge-neutral inorganic heterocycles featuring a PCN core. 1-Aza-2,3,4-triphospholenium cations [(PR)N(H)CR'], [1] (R' = Me, Ph, 4-MeOCH, 4-CFCH) were formed as triflate salts by the formal [3 + 2]-cyclisation reactions of strained cyclic triphosphanes (PR) (R = Bu, 2,4,6-MeCH (Mes), 2,6- PrCH (Dipp), 2,4,6- PrCH (Tipp)) with nitriles R'CN in the presence of triflic acid. The corresponding neutral free bases (PR)NCR' (2) were readily obtained by subsequent deprotonation with NEt.

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'.

On Haptotropic Rearrangements of Diphosphene and Diarsene Ligands in Titanium Complexes.

Dipnictenes of the type RE=ER (E=P, As, Sb, Bi) are the isovalence electronic heavier analogs of alkenes. Although diphosphenes and dipnictenes in general show a variety of binding modes in metal complexes, little is known about haptotropic shift reactions involving these ligands. Herein, we report an unprecedented η to η rearrangement of the dipnictene ligands in titanocene complexes of the type CpTi(PnAr) (Pn=P, As; Ar=2,4,6-Me-CH, Mes; 2,6-iPr-CH, Dip; 2,4,6-iPr-CH, Tip), initiated by Lewis basic ligands (L=MeCN, PMe, AdNC, CO).

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.

Unusual selectivity in the ring-opening of γ-valerolactone oxide by amines.

Primary and secondary amines selectively react with the lactone moiety of γ-valerolactone oxide (GVLO). Several primary amines afforded the resulting epoxyamides with an intact epoxy group. In some cases addition of two equivalents of amine resulted in additional epoxide opening to give α,γ-dihydroxy-β-amino-amides.

Photochemical formation and reversible base-induced cleavage of a phosphagallene.

The reactivity of Cp*Ga (Cp* = CMe) towards phosphanylidenephosphoranes of the type TerP(PMe) (Ter = Ter 2,6-(2,6-iPrCH)CH), Ter 2,6-(2,4,6-iPrCH)CH was investigated. While no thermal reaction was observed (in line with DFT results), irradiation at 405 nm at low temperatures resulted in the formation of phosphagallenes TerP = GaCp* (1a) and TerP = GaCp* (1b) accompanied by release of PMe. When warming the reaction mixture to ambient temperatures without irradiation, the clean re-formation of TerP(PMe) and Cp*Ga in a second-order reaction was observed.

On the Reactivity of Mes*P(PMe ) towards Aluminum(I) Compounds - Evidence for the Intermediate Formation of Phosphaalumenes.

Phosphaalumenes are the heavier isoelectronic analogs of alkynes and have eluded facile synthesis until recently. We have reported that the combination of a phosphinidene transfer agent, TerP(PMe ) ( Ter=2,6-Ar -C H ), with (Cp*Al) (Cp*=C (CH ) ) afforded the phosphaalumenes TerPAlCp* as isolable, violet, thermally stable compounds. In here we describe attempts to utilize Mes*P(PMe ) (Mes*=2,4,6-tBu -C H ) as a phosphinidene source in combination with different Al(I) precursors, namely NacnacAl ( Nacnac=HC[C(Me)NDip] , Dip=2,6-iPr -C H ), (Cp*Al) and Cp Al (Cp =1,2,4-tBu -C H ).

On the Reactivity of Phosphaalumenes towards C-C Multiple Bonds.

Heterocycles containing group 13 and 15 elements such as borazines are an integral part of organic, biomedical and materials chemistry. Surprisingly, heterocycles containing P and Al are rare. We have now utilized phosphaalumenes in reactions with alkynes, alkenes and conjugated double bond systems.

Deoxygenation of chalcogen oxides EO (E = S, Se) with phospha-Wittig reagents.

In here we present the deoxygenation of the chalcogen oxides EO (E = S, Se) with R-P(PMe), so-called phospha-Wittig reagents. The reaction of DABSO (DABCO·2SO) with R-P(PMe) (R = Mes*, 2,4,6-Bu-CH; Ter, 2,6-(2,4,6-Me-CH)-CH) resulted in the formation of thiadiphosphiranes (RP)S (1:R), while selenadiphosphiranes (RP)Se (2:R) were afforded with SeO, both accompanied by the formation of OPMe. Utilizing the sterically more encumbered Ter-P(PMe) (Ter = 2,6-(2,6-iPr-CH)-CH) a different selectivity was observed and (TerP)Se (2:DipTer) along with [Se(μ-PTer)] (3:DipTer) were isolated as the Se-containing species in the reaction with SeO.

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.

Modulating the reactivity of phosphanylidenephosphoranes towards water with Lewis acids.

Phosphanylidenephosphoranes of the type R-P(PR'), also known as phospha-Wittig reagents, can be utilized in a variety of bond activation reactions exploiting their phosphinidenoid reactivity. Herein, we thoroughly show that a facile PMe for HO exchange gives access to various primary phosphine oxides of the general formula RP(H)O (R = Mes*, Ter, Ter) and the molecular structure of TerP(O)H was determined. However, phosphanylidenephosphoranes are described to be highly nucleophilic as well.

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' ).

Heavier group 13/15 multiple bond systems: synthesis, structure and chemical bond activation.

Heavier group 13/15 multiple bonds have been under investigation since the late 80s and to date, several examples have been published, which shows the obsoleteness of the so-called double bond rule. Especially in the last few years, more and more group 13/15 multiple bonds became synthetically feasible and their application in terms of small molecule activation has been demonstrated. Our group has recently shown that the combination of the pnictinidene precursor Ter-Pn(PMe) (Pn = P, As) in combination with Al(I) synthons afforded the first examples of phospha- and arsaalumenes as isolable and thermally robust compounds.

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.

On 1,3-phosphaazaallenes and their diverse reactivity.

1,3-Phosphaazaallenes are heteroallenes of the type RP[double bond, length as m-dash]C[double bond, length as m-dash]NR' and little is known about their reactivity. In here we describe the straightforward synthesis of ArPCNR (Ar = Mes*, 2,4,6-Bu-CH; Ter, 2.6-(2,4,6-MeCH)-CH; Ter, 2.

Titanocene pnictinidene complexes.

The phospha-Wittig reagent MesTerPPMe3 (MesTer = 2,6-{2,4,6-Me3-C6H2}-C6H3) and arsa-Wittig reagent DipTerAsPMe3 (DipTer = 2,6-{2,6-iPr2-C6H3}-C6H3) have been employed to synthesize the titanocene complexes Cp2Ti(PMe3)PnAr (Pn = P, As) with terminal phosphinidene or arsinidene ligands, respectively. Ab initio studies show that the description as singlet biradicaloids in their ground state is warranted.

Isolable Phospha- and Arsaalumenes.

The combination of (AlCp*), a source of monomeric :AlCp* at elevated temperatures, with TerPnPMe (Pn = P, As), so-called pnicta-Wittig reagents, at 80 °C cleanly gives the pnictaalumenes TerPnAlCp* with polarized Pn-Al double bonds and intramolecular stabilization through interactions of Al with a flanking aryl group of the terphenyl substituent on Pn. In contrast, using TerPPMe, the reaction with 2 equiv of :AlCp or :AlCp* afforded the three-membered 2π-aromatic ring systems TerP(AlCp) ( = 3t, *).

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.

Aryl-substituted triarsiranes: synthesis and reactivity.

Cyclotriarsanes are rare and described herein is a scalable synthetic protocol towards (AsAr)3, which allowed to study their reactivity towards [Cp2Ti(C2(SiMe3)2)], affording titanocene diarsene complexes, and towards N-heterocyclic carbenes (NHCs) to give straightforward access to a variety of NHC-arsinidene adducts.

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.