1,3,4-Azadiphospholides as building blocks for scorpionate and bidentate ligands in multinuclear complexes.

Annulated oxy-substituted 1,3,4-azadiphospholides such as the anion in Na[1] are readily accessible phosphorus heterocycles made from the phosphaethynolate anion (OCP)- and 2-chloropyridines. The sodium salt Na[1] reacts with oxophilic element halides such as OPCl3, PhSiCl3, PhBCl2 and CpTiCl3 at room temperature to form exclusively the oxygen bound tris-substituted compounds E(1)3 (with E = OP, PhSi, PhB- or CpTi). Six equivalents of Na[1] with group four metal chlorides MCl4 (M = Ti, Zr, Hf) form cleanly the hexa-substituted dianions (Na2[M(1)6]) which are isolated in excellent yields. The titanium complexes are deeply coloured species due to ligand to metal charge transfer (LMCT) excitations. In all complexes, the phosphorus atoms of the azadiphosphole moieties are able to coordinate to a soft metal center as shown in their reactions with [Mo(CO)3Mes], yielding complexes in which the Mo(CO)3 binds in a fac manner. Functionalization of the oxy group with amino phosphanes allows isolation of tridentate ligands, which have been used as synthons for macrocyclic molybdenum carbonyl complexes.

2,6-Bis(benzimidazol-2-yl)pyridine complexes of group 14 elements.

Treatment of MCl2 (M = Ge or Sn) with 2,6-bis(benzimidazol-2-yl)pyridine (G-BZIMPY, G = NBn, N(3,5-CF3)Bn, NAllyl and O) yielded the self-ionization products [G-BZIMPYMCl][MCl3] (1-6) in high yields (75-98%). Reduction reactions are examined and the nickel complexes 8 and 9 ([(NBn-BZIMPY)2Ni][MCl3]2) are isolated from the reaction of Ni(COD)2 with 1 and 2 respectively. [NBn-BZIMPYSnCl][SnCl3] shows a significantly stronger MLCT band in the UV-vis absorption spectrum than its germanium counterparts, with germanium complexes exhibiting negative solvatochromism that is not observed in tin complexes.

Halogen and Sulfur Oxidation of Germanium and Tin Dications.

Herein we present the oxidation of base-stabilized tetrelII dications [LM][OTf]2 [L = BIMEt3 = tris(1-ethyl-benzoimidazol-2-ylmethyl)amine and M = Ge, Sn] with PCl5, SeCl4, Br2, and I2 to access dicationic dihalides [LMX2][OTf]2. The addition of oxygen-rich donor molecules (picoline N-oxide, OPEt3) to dications [LM][OTf]2 yielded donor-acceptor complexes bearing a tetrel(II) dication adjacent to a pnictogen(V) moiety. The addition of elemental sulfur to [LGe][OTf]2 yielded [(LGeS)2][OTf]4 containing a dimeric tetracation.

Transient Dipnictyl Analogues of Acrylamides, R-E=E'-CONR2 , and a Related Diphosphadigalletane from Na[OCP] and (R2 N)2 ECl (E, E'=P, As, Ga).

The reaction of Na[OCP] with (R2 N)2 ECl (E=P or As; R=alkyl) granted direct access to transient amine-substituted diphospha- and arsaphospha-acrylamide analogues, (R2 N)E=P(CONR2 ) 1. Their facile formation allowed for a comprehensive reactivity study. Dimerization yielded the four-membered rings (R2 N)2 E2 P2 (CONR2 )2 , whereas in the presence of excess Na[OCP], a stepwise [2+2] cycloaddition occured, leading to the sodium salts of carboxotripnictides [(R2 N)EP2 CO(CONR2 )]- . These salts served as a reservoir of 1, either by extrusion of Na[OCP] or by reaction with the appropriate (R2 N)2 ECl, giving the [4+2]-cycloaddition products (R2 N)EP(C6 H10 )(CONR2 ) in the presence of 2,3-dimethylbutadiene. The formal conjugate addition product K[(tBuO)(R2 N)PP(CONR2 )] was obtained by reaction of Na[(R2 N)PP2 CO(CONR2 )] with tBuOK. In addition, a rare diphosphadigalletane with a ladder-type (R2 N)2 Ga2 P2 (CONR2 )2 core was isolated from the reaction of Na[OCP] with (R2 N)2 GaCl (R=alkyl). The unprecedented pnictogenyl carboxamide compounds were thoroughly characterized, including single-crystal X-ray structure determinations, and mechanisms for their formation were investigated by DFT calculations.

2,6-Bis(benzimidazol-2-yl)pyridines as more electron-rich and sterically accessible alternatives to 2,6-bis(imino)pyridine for group 13 coordination chemistry.

Treatment of GaCl3 with 2,6-bis(benzimidazol-2-yl)pyridine (G-BZIMPY, G = NBz, N(3,5-CF3)Bz, N-allyl and O) yielded the autoionization products [G-BZIMPYGaCl2][GaCl4] (1-4) in great yields. The Ga(iii) complex 1 was reduced to Ga(i) using K2[Fe(CO)4], resulting in the complex [(NBzBZIMPY)(Cl)Ga-Fe(CO)4] (7). GaCl3 and AlCl3 were complexed by the structurally similar bis(imino)pyridine (DIMPY) and the resulting complexes are compared to those of G-BZIMPY.

Synthesis, characterization and mass-spectrometric analysis of [LSn(IV)F4-x]x+ salts [L = tris ((1-ethyl-benzoimidazol-2-yl)methyl)amine, x = 1-4].

A series of complexes with the formulae [(BIMEt3)SnF4-x][OTf]x with x = 1-4 has been synthesized by successive fluoride abstraction from SnF4 with TMSOTf in the presence of the tetradentate nitrogen donor BIMEt3 (tris ((1-ethyl-benzoimidazol-2-yl)methyl)amine). Single crystal X-ray diffraction and heteronuclear NMR spectroscopic analysis provided insight into these new main group cations. Electrospray ionization mass spectrometric analysis on solutions containing the different salts allowed for successful detection of the cations [(BIMEt3)SnF]3+, [(BIMEt3)SnF2]2+ and [(BIMEt3)SnF3]+.

Tris(benzoimidazol)amine (L) complexes of pnictogen(iii) and pnictogen(v) cations and assessment of the [LP]3+/[LPF2]3+ redox couple.

A series of cationic complexes involving a pnictogen(iii) (Pn = P, As, Sb) centre and the tetradentate ligand tris((1-ethyl-benzoimidazol-2-yl)methyl)amine (BIMEt3) have been synthesized and comprehensively characterized. Oxidation of [P(BIMEt3)]3+ with XeF2 provides access to [PF2(BIMEt3)]3+ representing the first structurally characterized example of a phosphorus(v) centred trication.

Oxidation of a germanium(ii) dication to access cationic germanium(iv) fluorides.

The synthesis and characterization of the tris(1-ethyl-benzoimidazol-2-ylmethyl)amine (BIMEt3 = L) complex of Ge(ii)2+ is described. Oxidation of [LGe]2+ with Selectfluor gives [LGeF2]2+, in a process that is envisaged to involve a tricationic complex [LGeF]3+ as an intermediate, which has been isolated by fluoride ion abstraction from [LGeF2]2+.

Tris(1-methyl-imidazol-2-yl)phosphane Complexes of Pnictogen, Tetrel, and Triel Cations.

cations gallium indium nitrogen ligands pnictogens tetrelThe synthesis and characterization of salts with the generic formula [P(Im)3 M][OTf]x (Im=1-methyl-imidazol-2-yl; M=P, As or Sb and x=3; M=Ge or Sn and x=2) are reported. In all cases, the cations adopt a cage structure with two chemically and energetically distinct apical lone pairs. In contrast, complexes of gallium and indium engage two P(Im)3 ligands resulting in a distorted octahedral geometry for the triel center in compounds of the generic formula [{P(Im)3 }2 M][OTf]3 (M=Ga or In). An assessment of the acidity and basicity of the new compounds is presented.

Synthesis of P2C2O2 and P2CO via NHC-mediated coupling of the phosphaethynolate anion.

The reaction of the chloroimidazolium chloride salt, [NHC-Cl][Cl], NHC = C{N(2,6-iPr2C6H3)CH}2 (1) with two equivalents of sodium phosphaethynolate, Na[OCP]·(dioxane)2.5, results in the formation of NHC-{cyclo-(CO)-P2-C(O)} (2) and NHC-P2-C(O)-NHC (3). Notably, in the presence of free NHC ligand, compound 2 converts to compound 3via extrusion of CO at elevated temperatures. The nature of the bonding in these complexes was probed computationally and spectroscopically.

Substitution Reactions at Dipp BIAN Supported Fluoroantimony Cations Yielding Cyanoantimony and Azidoantimony Cations.

This work presents new cationic coordination complexes of antimony with the 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (Dipp BIAN) ligand system. The fluoroantimony complexes [SbF(Dipp BIAN)][OTf]2 and [SbF2 (Dipp BIAN)][OTf] have been successfully isolated and characterized. The fluorine substituent in the Lewis acidic complex [SbF(Dipp BIAN)][OTf]2 can be selectively replaced without degradation of the Sb-Dipp BIAN interaction to give the first dicationic azido and cyano derivatives, [Sb(CN)(Dipp BIAN)][OTf]2 and [Sb(N3 )(Dipp BIAN)][OTf]2 , which have been isolated and structurally characterized.

Borane-Stabilized Isomeric Dimers of the Phosphaethynolate Anion.

The reactions of the phosphaethynolate anion ([PCO]- ) with a range of boranes were explored. BPh3 and [PCO]- form a dimeric anion featuring P-B bonds and is prone to dissociation at room temperature. The more Lewis acidic borane B(C6 F5 )3 yields a less symmetric dimer of [PCO]- with P-B and P-O bonds. Less sterically demanding HB(C6 F5 )2 and H2 B(C6 F5 ) boranes form a third isomer with [PCO]- featuring both boranes bound to the same phosphorus atom. Despite the unexpected thermodynamic preference for P-coordination, computational data illustrate that electronic and steric features impact the binding modes of the resulting dianionic dimers.

Annulated 1,3,4-Azadiphospholides: Heterocycles with Widely Tunable Optical Properties.

Phosphorus heterocycles find applications in the synthesis of π-conjugated compounds and as precursors for optoelectronic materials such as organic light-emitting diodes (OLEDs), electronic switches, and transistors. A high-yield, one-pot synthesis of anionic annulated 1,3,4-azadiphospholides from Na(OCP) and 2-chloropyridines is presented. The synthesis proceeds without the use of transition metals and tolerates a wide range of substrates. Cyano-substituted compounds are especially deeply colored and have absorption maxima which range from λmax =525 to 596 nm. The optical properties are dominated by the spatial separation of an electron acceptor and donor unit within one molecule (push-pull chromophore). The anionic 1,3,4-azadiphospholides are silylated to neutral siloxy compounds with a strong blue-shifted absorption. This reaction can be reversed by addition of fluoride ions, which allows fluoride ions to be detected in optically low concentrations.

Tris(2-pyridyl)phosphine as a versatile ligand for pnictogen acceptors.

We report cationic complexes of arsenic and antimony with the tris(2-pyridyl)phosphine ligand. Chloride ion abstraction from AsCl3 using TMSOTf in the presence of the ligand gives [P(Pyr)3As][OTf]3, in which the trication adopts a C3v symmetric cage structure. The reaction proceeds via the intermediate [P(Pyr)3AsCl][OTf]2, which undergoes chloride exchange to give [P(Pyr)3As][OTf]3 and [P(Pyr)3AsCl2][OTf]. The rearrangement reaction has been supported by the isolation of the antimony mono fluoride derivative [P(Pyr)3SbF][OTf]2. The asymmetric axial lone pairs in derivatives of [P(Pyr)3Pn]3+ are electronically separated. The HOMO-1 (for arsenic) and HOMO (for antimony) represent the major contribution to the phosphine lone pair indicating the possibility for nucleophilic behaviour despite the +3 charge. Less accessible is the HOMO-7, which represents the lone pair at arsenic or antimony, respectively.

A Planar Ti2 P2 Core Assembled by Reductive Decarbonylation of - O-C≡P and P-P Radical Coupling.

The complex [(nacnac)Ti(OAr)]2 (µ2 :η2 ,η2 -P2 ) (1) is formed via reductive decarbonylation of the phosphaethynolate ion - [OCP], which serves as a P atom source. Complex 1 is the first structurally characterized Group 4 transition metal P2 complex and its structure reveals the rhombic Ti2 P2 core is essentially planar with short bond lengths suggesting some degree of multiple bonding character between the Ti-P and P-P sites. Computational studies of 1 provide an understanding of the Ti2 P2 core as well as the origin of the highly downfield 31 P NMR spectroscopic signal.

2,4,6-Tri(hydroxy)-1,3,5-triphosphinine, P3 C3 (OH)3 : The Phosphorus Analogue of Cyanuric Acid.

Cyanuric acid (C3 H3 N3 O3 ) is widely used as cross-linker in basic polymers (often in combination with other crosslinking agents like melamine) but also finds application in more sophisticated materials such as in supramolecular assemblies and molecular sheets. The unknown phosphorus analogue of cyanuric acid, P3 C3 (OH)3 , may become an equally useful building block for phosphorus-based polymers or materials which have unique properties. Herein we describe a straightforward synthesis of 2,4,6-tri(hydroxy)-1,3,5-triphosphinine and its derivatives P3 C3 (OR)3 which have been applied as strong π-acceptor η6 -ligands in piano stool Mo(CO)3 complexes.

A Convenient Synthesis of 1,2,4- and 1,3,4-Azadiphospholes.

A new synthetic route to functionalized neutral and anionic azadiphospholes from easily accessible starting materials is described. Equimolar reaction of Na(OCP) and N-(2,6-dimethylphenyl)pivalimidoyl chloride 2 a cleanly affords the imidoxy-functionalized 1,2,4-azadiphosphole 3 a. Using Na(OCP) and imidoyl chloride in a 2:1 ratio leads to an anionic four-membered ring Na[4 a], which has been structurally characterized. During 16 h at room temperature, Na[4 a] rearranges to the anionic 1,3,4-azadiphospholide Na[5 a] with release of carbon monoxide. Applying the more sterically demanding N-(2,6-diisopropylphenyl)pivalimidoyl chloride allows isolation of the 1,3,4-azadiphospholide Na[5 b] in good yield (>70 %). Possible mechanisms leading to the new isomeric azadiphospholides have been investigated with the aid of high-level composite calculations.

Isolation of Au-, Co-η1PCO and Cu-η2PCO complexes, conversion of an Ir-η1PCO complex into a dimetalladiphosphene, and an interaction-free PCO anion.

Sodium phosphaethynolate reacts with [MCl(PDI)] (M = Co, Ir; PDI = pyridinediimine) to give metallaphosphaketenes, which in the case of iridium rearranges into a dimetalladiphosphene, via CO migration from phosphorus to the metal. Two different bonding modes of the PCO anion to CAAC-coinage metal complexes [CAAC: cyclic (alkyl)(amino)(carbene)] are reported, one featuring a strong Au-P bond and the other an η2 coordination to copper. The gold complex appears to be mostly unreactive whereas the copper complex readily reacts with various organic substrates. A completely free PCO anion was structurally characterized as the [Cu(La)2]+ (OCP)- salt. It results from the simple displacement of the PCO unit of the cationic (CAAC)Cu(PCO) complex by a second equivalent of CAAC.

The reactivity of acyl chlorides towards sodium phosphaethynolate, Na(OCP): a mechanistic case study.

The reaction of Na(OCP) with mesitoyl chloride delivers an ester functionalized 1,2,4-oxadiphosphole in a clean and P-atom economic way. The reaction mechanism has been elucidated by means of detailed NMR-spectroscopic, kinetic and computational studies. The initially formed acyl phosphaketene undergoes a pseudo-coarctate cyclization with an (OCP)- anion under the loss of carbon monoxide to yield a five-membered ring anion. Subsequently, the nucleophilic attack of the formed heterocyclic anion on a second acyl chloride molecule results in the 1,2,4-oxadiphosphole. The transient acyl phosphaketene is conserved during the reaction in the form of four-membered ring adducts, which act as a reservoir. Consequently, the phosphaethynolate anion has three different functions in these reactions: it acts as a nucleophile, as an en-component in [2 + 2] cycloadditions and as a formal P- transfer reagent.

Sorption enhanced CO2 methanation.

The transformation from the fatuous consumption of fossil energy towards a sustainable energy circle is most easily marketable by not changing the underlying energy carrier but generating it from renewable energy. Hydrocarbons can be principally produced from renewable hydrogen and carbon dioxide collected by biomass. However, research is needed to increase the energetic and economic efficiency of the process. We demonstrate the enhancement of CO2 methanation by sorption enhanced catalysis. The preparation and catalytic activity of sorption catalysts based on Ni particles in zeolites is reported. The functioning of the sorption catalysis is discussed together with the determination of the reaction mechanism, providing implications for new ways in catalysis.