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A low-valent trinuclear iron complex with an unusual linear Fe(i)–Fe(ii)–Fe(i) unit is presented. It is accessed in a rational approach using a salt metathesis reaction between a new anionic Fe(i) containing heterocycle and FeCl2. Its electronic structure was studied by single crystal XRD analysis, EPR and Mössbauer spectroscopy, and magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

Reflecting on Giacomo Ciamician's revolutionary vision of harnessing sunlight to drive photochemical transformations, the field of materials science has evolved significantly, yet it has been constrained by the misconception that the highest reactivity in photochemical systems is achieved at the absorption maxima. Here, we explore this notion further with evidence from photochemical action plots, demonstrating that reactivity can indeed be maximal at wavelengths significantly separated from the absorption peak. By examining the implications of the disparity between absorptivity and photochemical reactivitiy, we explore its impact for the enhanced penetration depth of light in photoresists, the reduction of energy requirements for photochemical reactions, and its transformative potential for volumetric 3D printing. Ultimately, we argue for a renewed appreciation of light's capability to facilitate photochemical reactions across the entire volume of a material.

This report presents a selective synthetic approach towards borazine from ammonia borane using a dinuclear rhodium olefin homogeneous catalyst. The synthesis and spectroscopic characterization of a dirhodium ammonia borane complex as an intermediate provides insight into a possible mode of activation.

Distonic radical cations (DRCs) with spatially separated charge and radical sites are expected to show both radical and cationic reactivity at different sites within one molecule. However, such "dual" reactivity has rarely been observed in the condensed phase. Herein we report the isolation of crystalline 1λ 2 ,3λ 2 -1-phosphonia-3-phosphinyl-cyclohex-4-enes 2a,b˙ + , which can be considered delocalized DRCs and were completely characterized by crystallographic, spectroscopic, and computational methods. These DRCs contain a radical and cationic site with seven and six valence electrons, respectively, which are both stabilized via conjugation, yet remain spatially separated. They exhibit reactivity that differs from that of conventional radical cations (CRCs); specifically they show sequential radical and cationic reactivity at separated sites within one molecule in solution., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Dehydrogenation of ammonia borane to well-defined products is an important but challenging reaction. A dinuclear ruthenium complex with a Ru-Ru bond bearing a diazadiene (dad) unit and olefins as non-innocent ligands catalyzes the highly selective formation of conjugated polycondensed borazine oligomers (B x N x H y ), predominantly B 21 N 21 H 18 , the BN analogue of superbenzene.

E , Z -isomers display distinct physical properties and chemical reactivities. However, investigations on heavy main group elements remain limited. In this work, we present the isolation and X-ray crystallographic characterization of N-heterocyclic vinyl (NHV) substituted diphosphenes as both E - and Z -isomers (L[double bond, length as m-dash]CH-P[double bond, length as m-dash]P-CH[double bond, length as m-dash]L, E , Z -2b; L = N-heterocyclic carbene). E -2b is thermodynamically more stable and undergoes reversible photo-stimulated isomerization to Z -2b. The less stable Z -isomer Z -2b can be thermally reverted to E -2b. Theoretical studies support the view that this E ↔ Z isomerization proceeds via P[double bond, length as m-dash]P bond rotation, reminiscent of the isomerization observed in alkenes. Furthermore, both E , Z -2b coordinate to an AuCl fragment affording the complex [AuCl(η 2 - Z -2b)] with the diphosphene ligand in Z -conformation, exclusively. In contrast, E , Z -2b undergo [2 + 4] and [2 + 1] cycloadditions with dienes or diazo compounds, respectively, yielding identical cycloaddition products in which the phosphorus bound NHV groups are in trans -position to each other. DFT calculations provide insight into the E / Z -isomerisation and stereoselective formation of Au(i) complexes and cycloaddition products., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A number of stable group 6 metal complexes bearing 2,4,6-oxy functionalised 1,3,5-triphosphinines, phosphorus containing heterocyclic ligands with a central C 3 P 3 core, were synthesised such that a complete series of [M{P 3 C 3 (OX) 3 }(CO) 3 ] compounds is obtained [M = Cr(0), Mo(0), W(0); X = H, Si t BuPh 2 , B(ipc) 2 ]. In all complexes, the triphosphinine coordinates in a η 6 -binding mode via the delocalized 6π-system of the ring. The ligand properties can be tuned by changing the substituent on the oxygen centre. The π-electron accepting properties of the ligand increases in the following order: P 3 C 3 (OH) 3 < P 3 C 3 (OSi t BuPh 2 ) 3 < P 3 C 3 (OB(ipc) 2 ) 3 . This trend is reflected in the structures determined by X-ray crystallography, and the ν (CO) stretching frequencies determined by IR spectroscopy. The collected data raise questions with respect to the frequently made assumption that phosphinines act as stronger π-acceptors with respect to arenes and thereby deplete electron density at the metal centres. With P 3 C 3 (OH) 3 as an η 6 -coordinated ligand further molecules can be coordinated in the second coordination sphere via hydrogen bonds, which may be of interest for the construction of coordination polymers.

The synthesis and reactivity of the heavier group 13 phosphaketene complexes (2,6-Mes 2 C 6 H 3 ) 2 EPCO (1, E = Ga; 2, E = In) were reported. The reaction of 1 and 2 with 1,2,3,4-tetramethylimidazolin-2-ylidene, IMe 4 , gave rise to the formation of (2,6-Mes 2 C 6 H 3 ) 2 EP(O)C(IMe 4 ) (3, E = Ga; 4 E = In; Mes = mesityl). Subsequent addition of elemental tellurium proceeded via insertion into the E-P bond and provided (2,6-Mes 2 C 6 H 3 ) 2 ETeP(O)C(IMe 4 ) (5, E = Ga; 6, E = In) comprising five-membered ETePCO-heterocycles. Compounds 1-6 were fully characterized by X-ray crystallography and heteronuclear NMR spectroscopy. The electronic structures of 1-6 were studied by DFT calculations and analyses of a complementary set of real-space bonding indicators (AIM, ELI-D, NCI) derived from the electron and pair densities, with focus on the bond characteristics of the PCO fragment.

The dinuclear Ru diazadiene olefin complex, [Ru 2 (OTf)(μ-H)(Me 2 dad)(dbcot) 2 ], is an active catalyst for hydrogen evolution in a Polymer Exchange Membrane (PEM) water electrolyser. When supported on high surface area carbon black and at 80 °C, [Ru 2 (OTf)(μ-H)(Me 2 dad)(dbcot) 2 ]@C evolves hydrogen at the cathode of a PEM electrolysis cell (400 mA cm -2 , 1.9 V). A remarkable turn over frequency (TOF) of 7800 mol H 2 mol catalyst h -1 h -1 (OTf)(μ-H)(Me 2 (OTf)(μ-H)(Me 2 dad)(dbcot) 2 ]., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

A reaction of trisodium phosphide (Na 3 P) with chlorosilanes allows for simple derivatization into silyl- and cyano-substituted phosphanide species which were compared with each other. The recently discovered cyano(triphenylsilyl)phosphanide shows unique coordination properties compared to bis(silyl)phosphides.

Homogeneous ruthenium catalysed methanol dehydrogenation could become a key reaction for hydrogen production in liquid fuel cells. In order to improve existing catalytic systems, mechanistic insight is paramount in directing future studies. Herein, we describe what computational mechanistic research has taught us so far about ruthenium catalysed dehydrogenation reactions. In general, two mechanistic pathways can be operative in these reactions: a metal-centered or a metal-ligand cooperative (Noyori-Morris type) minimum energy reaction pathway (MERP). Discerning between these mechanisms on the basis of computational studies has proven to be highly input dependent, and to circumvent pitfalls it is important to consider several factors, such as solvent effects, metal-ligand cooperativity, alternative geometries, and complex electronic structures of metal centres. This Frontiers article summarizes the reported computational research performed on ruthenium catalyzed dehydrogenation reactions performed in the past decade, and serves as a guide for future research.

The vibrational spectra of the simplest phosphaketene HPCO and its isotopologue DPCO in solid Ar-matrices at 12.0 K have been analyzed with the aid of the computations at the CCSD(T)-F12a/cc-pVTZ-F12 level using configuration-selective vibrational configuration interaction (VCI). In addition to the four IR fundamentals, four overtone and ten combination bands have been unambiguously identified. Furthermore, the photochemistry of HPCO in the matrix has been investigated for the first time. Upon UV-light irradiation (365 or 266 nm), CO-elimination occurs by forming the parent phosphinidene HP that can be trapped by ˙NO to yield the elusive phosphinimine- N -oxyl radical HPNO˙. In contrast, an excimer laser (193 nm) irradiation of HPCO causes additional decomposition to H˙ and ˙PCO with concomitant formation of the long-sought phosphaethyne HOCP.

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.

A new multi-photoactive γ-cyclodextrin substituted bis(acyl)phosphane oxide derivative (BAPO-γ-CyD) was successfully prepared via a convergent synthesis using a phospha-Michael-addition, as confirmed by 1H-, 13C-, 31P-NMR and IR spectroscopy and mass spectrometry. Kinetic studies carried out by photo-DSC and photo-rheology demonstrated its outstanding efficiency as a photoinitiator for free-radical polymerization. Remarkably, it is found that BAPO-γ-CyD also acts as a crosslinking agent to convert monofunctional methacrylate monomers into self-standing thermosetting networks with extensive swelling capability in water.

Supporting two metal binding sites by a tailored polydentate trop-based (trop = 5 H -dibenzo[ a , d ]cyclohepten-5-yl) ligand yields highly unsymmetric homobimetallic rhodium(i) complexes. Their reaction with hydrogen rapidly forms Rh hydrides that undergo an intramolecular semihydrogenation of two C[triple bond, length as m-dash]C bonds of the trop ligand. This reaction is chemoselective and converts C[triple bond, length as m-dash]C bonds to a bridging carbene and an olefinic ligand in the first and the second semihydrogenation steps, respectively. Stabilization by a bridging diphosphine ligand allows characterization of a Rh hydride species by advanced NMR techniques and may provide insight into possible elementary steps of H 2 activation by interfacial sites of heterogeneous Rh/C catalysts., (This journal is © The Royal Society of Chemistry 2019.)

Transmetallation studies with the phosphaethynolate ion, [OCP] - , have largely resulted in coordination according to classical Lewis acid-base theory. That is, for harder early transition metal ions, O-bound coordination has been observed, whereas in the case of softer late transition metal ions, P-bound coordination predominates. Herein, we report the use of a V(iii) complex, namely [(nacnac)VCl(OAr)] (1) (nacnac - = [ArNC(CH 3 )] 2 CH; Ar = 2,6- i Pr 2 C 6 H 3 ), to transmetallate [OCP] - and bind via the P-atom as [(nacnac)V(OAr)(PCO)] (2), the first example of a 3d early transition metal that binds [OCP] - via the P-atom. Full characterization studies of this molecule including HFEPR spectroscopy, SQuID measurements, and theoretical studies are presented.

The first OCP adducts of aluminium and gallium are reported. The complexes are supported by sterically encumbered salen ligands and reveal a selective binding to O and P, respectively. Their reactivity with diazaphosphenium Lewis acids and N-heterocyclic carbene Lewis bases is described, in addition to cycloaddition reactions with s-tetrazines.

The transition metal mediated functionalization of P4 is an approach to develop a more sustainable production of organophosphorus compounds. In this paper a ruthenium complex is presented, in which the P4 unit can be selectively converted into new P4R2 molecules in a two-step synthesis. The unsaturated 16 electron species [RuX(Cp*)(PCy3)] (Cp* = C5Me5, X = Cl, Br) reacts with a half equivalent of P4 affording a bimetallic complex bearing a planar P4X2 moiety as a ligand. The latter eliminates chloride anions under reduction with magnesium. In this process the butadiene-like P4Cl2 ligand is converted into two weakly bound P2 units which bridge the ruthenium centers. In the presence of n-BuLi, the P4Cl2 unit can be selectively alkylated, yielding the planar organophosphorus ligand P4nBu2. A detailed analysis of the electronic properties and solid state structures of the compounds combined with DFT calculations and AIM analyses demonstrate that the P4 unit in all complexes acts as an electronically highly flexible, non-innocent ligand.

Insertion of a P- anion into a P-P bond yielding the first carborane-substituted 1,2,3-triphospholanide 1 was achieved by treating a carborane-substitued 1,2-diphosphetane with sodium phosphaethynolate. The triphospholanide 1 can serve as a versatile nucleophilic building block for unprecedent functionalised triphospholanes and carborane-substituted polyphosphanes.

Phosphinines, as aromatic heterocycles, usually engage in coordination as η 1 -P σ-complexes or η 6 -phosphinine π-complexes. The μ 2 -P bridging coordination mode is rarely observed. With the aim to study the effect of different electronic configurations of phosphinines on the coordination modes, a series of anionic phosphinin-2-olates and neutral phosphinin-2-ols were prepared with moderate to high yield. Then the coordination chemistry of these two series was studied in detail towards coinage metals (Au(i) and Cu(i)). It is observed that the anionic phosphinin-2-olates possess a higher tendency to take a bridging position between two metal centers compared to the neutral phosphinin-2-ols. Based on these experimental findings bolstered by DFT calculations, some insight is gained on how the unconventional μ 2 -P phosphinine bridging coordination mode can be made more conventional and used for the synthesis of polynuclear complexes.

The dinuclear ruthenium complex [Ru 2 H(μ-H)(Me 2 dad)(dbcot) 2 ] contains a 1,4-dimethyl-diazabuta-1,3-diene (Me 2 dad) as a non-innocent bridging ligand between the metal centers to give a [Ru 2 (Me 2 dad)] core. In addition, each ruthenium is bound to one dibenzo[ a , e ]cyclooctatetraene (dbcot) ligand. This Ru dimer converts H 2 to protons and electrons. It also catalyzes reversibly under mild conditions the selective hydrogenation of vitamins K 2 and K 3 to their corresponding hydroquinone equivalents without affecting the C[double bond, length as m-dash]C double bonds. Mechanistic studies suggest that the [Ru 2 (Me 2 dad)] moiety, like hydrogenases, reacts with H 2 and releases electrons and protons stepwise., (This journal is © The Royal Society of Chemistry 2019.)

In large-scale, hydrogen production from water-splitting represents the most promising solution for a clean, recyclable, and low-cost energy source. The realization of viable technological solutions requires suitable efficient electrochemical catalysts with low overpotentials and long-term stability for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) based on cheap and nontoxic materials. Herein, we present a unique molecular approach to monodispersed, ultra-small, and superiorly active iron phosphide (FeP) electrocatalysts for bifunctional OER, HER, and overall water-splitting. They result from transformation of a molecular iron phosphide precursor, containing a [Fe 2 P 3 ] core with mixed-valence Fe II Fe III sites bridged by an asymmetric cyclo-P (2+1) 3- ligand. The as-synthesized FeP nanoparticles act as long-lasting electrocatalysts for OER and HER with low overpotential and high current densities that render them one of the best-performing electrocatalysts hitherto known. The fabricated alkaline electrolyzer delivered low cell voltage with durability over weeks, representing an attractive catalyst for large-scale water-splitting technologies.

A bis(acyl)phosphane oxide (BAPO) photoinitiator was conveniently synthesized in an efficient one-pot process. It shows excellent dispersibility in water, good storage stability, and high photo-reactivity in 3D printing of hydrogels under visible-light irradiation (460 nm).

The reaction of magnesium chloride with two equivalents of sodium phosphaethynolate, Na[OCP]·(dioxane) 2.5 (1), yields a magnesium diphosphaethynolate complex, [(THF) 4 Mg(OCP) 2 ] (3). The formation of compound 3 goes through a monosubstituted chloromagnesium phosphaethynolate Mg(OCP)Cl (2). The structure of 3 was determined via a single crystal X-ray diffraction study. For comparison, we also report the structure of a monomeric sodium phosphaethynolate complex, [Na(OCP)(dibenzo-18-crown-6)] (4).

The reaction of the chloroimidazolium chloride salt, [NHC-Cl][Cl], NHC = C{N(2,6- i Pr 2 C 6 H 3 )CH} 2 (1) with two equivalents of sodium phosphaethynolate, Na[OCP]·(dioxane) 2.5 , results in the formation of NHC-{cyclo-(CO)-P 2 -C(O)} (2) and NHC-P 2 -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.

Reaction of the zirconium-benzyne complex [Cp 2 Zr(PMe 3 )(C 6 H 4 )] with sodium phosphaethynolate, Na[OCP], affords a zircono-phosphaalkene complex. Notably, unlike reactions of other transition metal complexes with Na[OCP] that yield the products of simple salt metathesis, this transformation represents novel Na[OCP] insertion chemistry and formation of an unusual solid state coordination polymer. The polymer is disrupted upon addition of Me 3 SiCl to afford a silyl-capped dimer that retains the zirconophosphaalkene functionality. Protonation of either form of zirconophosphaalkenes results in the formation of benzoylphosphine, PhC([double bond, length as m-dash]O)PH 2 .

A rhodium complex containing a tetrapodal triolefin ligand (trop 3 P) and a phosphanyl ligand (PPh 2 - ) has been prepared and characterised. The special structural confinements of the tetradentate ligand impose an unusually long Rh-PPh 2 bond. Chemical oxidation of the complex with FcOTf affords [Rh(OTf)(trop 3 P)] and plausibly phosphanyl radicals, which react instantly with a spin trap reagent forming a nitroxide-based persistent radical, undergo HAT with silanes or dimerise to the corresponding diphosphine (PPh 2 ) 2 . Chemical oxidation with a peroxide leads to complex [Rh(POPh 2 )(trop 3 P)] which is photolabile and loses the Ph 2 PO moiety upon irradiation with UV/Vis light in CH 2 Cl 2 .

The nucleophilic attack of NHCs on the electron deficient carbon of tetryl substituted phosphaketenes Ph3E-P[double bond, length as m-dash]C[double bond, length as m-dash]O (E = Sn-Si), leads quantitatively to the formation of NHC-phosphaketene adducts. With E = Sn or Ge, these zwitterionic adducts decompose upon thermolysis under the release of carbon monoxide to give zwitterionic NHC-phosphinidene adducts. With E = Si an OCP to CPO rearrangement occurs which leads to the formation of a linear π-conjugated molecule, NHC[double bond, length as m-dash]C[double bond, length as m-dash]P-O-SiPh3.

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.

Bis(mesitoyl)phosphinic acid and its sodium salt display a unique photo-induced reactivity: both derivatives stepwise release two mesitoyl radicals and, remarkably, metaphosphorous acid (previously postulated as transient species in the gas phase), providing a new phosphorus-based reagent.

A four-coordinate, sixteen-electron Ru(0) complex containing the tetradentate diamino-diolefin ligand (±)-trans-N,N-bis(5H-dibenzo[a,d]cyclohepten-5-yl)-1,2-diaminocyclohexane (trop2dach) has been synthesised. Deprotonation of one amino N-H functional group generates an unprecedented four-coordinate ruthenate species which has been characterised in solution and in the solid state. The newly formed ruthenate complex undergoes intramolecular metal-ligand N-H addition/elimination in solution to generate a transient diamido ruthenium hydride species, as supported by NMR spectroscopy and density functional theory.

PH3 reacts with the in situ generated N-heterocyclic carbene DippNHC* (DippNHC* = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) to give the phosphanyl-imidazolidine [(Dipp)NHC*-H]-[PH2]. Upon treatment with an ortho-quinone, [(Dipp)NHC*-H]-[PH2] is dehydrogenated to give the parent phosphinidene-carbene adduct (Dipp)NHC*[double bond, length as m-dash]PH. Alternative routes to [(Dipp)NHC*-H]-[PH2] and (Dipp)NHC*[double bond, length as m-dash]PH employ NaPH2 and (TMS)3P7 (TMS = trimethylsilyl), respectively, as phosphorus sources. The adduct (Dipp)NHC*[double bond, length as m-dash]PH and the related adduct (Dipp)NHC[double bond, length as m-dash]PH ((Dipp)NHC = bis(2,6-diisopropylphenyl)imidazol-2-ylidene) possessing an unsaturated NHC backbone both react with HgCl2 to give the bis(carbene-phosphinidenyl) complexes [((Dipp)NHC*[double bond, length as m-dash]P)2Hg] and [((Dipp)NHC[double bond, length as m-dash]P)2Hg].

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 η 2 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(L a ) 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.

A new synthesis of bis(acyl)phosphane oxide (BAPO) photoinitiators was developed which can be used to functionalize cellulose nanocrystal surfaces for polymer grafting. Hybrid materials with excellent graft yields can be rapidly obtained under mild and acid-free conditions.

Reactions of the parent phosphinidene-carbene adduct (Dipp)NHC = PH with chlorophosphanes are reported herein. The obtained (Dipp)NHC-substituted chlorodiphosphanes, (Dipp)NHC = P-PClR, and the formation of their cationic derivatives, [(Dipp)NHC-P = PR](+), were also explored. Depending on the steric demand of their substituents, these cations were found to be monomeric [(Dipp)NHC-PP-N(i)Pr2][GaCl4] or to dimerise to cyclotetraphosphanes [(Dipp)NHC-PP-R]2[GaCl4]2 (R = Ph, NMe2). For R = NMe2, this dication is the first isolated example of a tetrasubstituted all-σ(3) cyclotetraphosphane. Finally, the hetero-Diels-Alder reactivity of these cations was studied with 2,3-dimethylbuta-1,3-diene and cyclopentadiene, resulting in the isolation of a number of cationic 1,2-diphosphinanes.

A diolefin ether, trop2O (2), and a diolefin thioether, trop2S (3), have been investigated as ligand analogues of the well-established diolefin amine, trop2NH (1). Compounds 2 and 3 form different conformers in solution and in the solid state. Whereas 2 could be coordinated to Ni(0), 3 was found to be more suited for coordination to Rh(I). The coordination chemistry, electrochemical properties, and ligand exchange phenomena of the resulting complexes, [Ni(trop2O)(PPh3)] (5) and [Rh(trop2S)(L)n][OTf] (6: L = NCMe, n = 2; 7: L = 2,2'-bipy, n = 1) were investigated by analytical techniques including NMR spectroscopy, single crystal X-ray analysis, and cyclic voltammetry. The results were compared with those obtained for the amine analogues of 5, 6, and 7.

We show that the 2-phosphaethynolate anion, OCP - , is a simple and efficient catalyst for the cyclotrimerization of isocyanates. This process proceeds step-wise and involves five-membered heterocycles, namely 1,4,2-diazaphospholidine-3,5-dionide anions and spiro-phosphoranides as detectable intermediates, both of which were also found to be involved in the catalytic conversion. These species can be considered as adducts of a phosphide anion with two and four isocyanate molecules, respectively, demonstrating that the OCP - anion acts as a formal "P - " source. The interconversion between these anionic species was found to be reversible, allowing them to serve as reservoirs for unique phosphorus-based living-catalysts for isocyanate trimerization.

Sodium phosphaethynolate, Na(OCP), reacts with the bulky P-chloro-diazaphosphole yielding a phosphanyl phosphaketene, which is stable for weeks under an inert atmosphere in the solid state. This compound is best described as a tight ion pair with a remarkably long P-P bond distance (2.44 Å). In solution, this phosphaketene dimerizes under loss of CO to give 1,2,3-triphosphabicyclobutane identified by an X-ray diffraction study. As an intermediate, a five-membered heterocyclic diphosphene was trapped in a Diels-Alder reaction with 2,3-dimethylbutadiene. The formation of this intermediate in a hetero-Cope-rearrangement as well as dimerization/CO loss were computed with various DFT methods which allowed us to understand the reaction mechanisms.

The reactivity of Na(OCP) was investigated towards triorganyl compounds of the heavier group 14 elements (R3EX R = Ph or (i)Pr; E = Si, Ge, Sn, Pb; X = Cl, OTf). In the case of E = Si two constitutional isomers were formed and characterised in situ: R3Si-O-C[triple bond, length as m-dash]P is the kinetic and R3Si-P[double bond, length as m-dash]C[double bond, length as m-dash]O is the thermodynamic product, representing experimental evidence of the ambident character of the (OCP)(-) anion. Applying theoretical calculations and spectroscopic methods, the compound previously reported as (i)Pr3Si-O-C[triple bond, length as m-dash]P can now unambiguously be identified as (i)Pr3Si-P[double bond, length as m-dash]C[double bond, length as m-dash]O. The heavier analogues form exclusively the phosphaketene isomer R3E-P[double bond, length as m-dash]C[double bond, length as m-dash]O (E = Ge, Sn, Pb). DFT calculations were performed to gain deeper insight into the bonding and thermodynamic stability of these compounds.

Carbon dioxide and two equivalents of Na(OCP) form, in an equilibrium reaction, a CO2 adduct of the composition Na2(P2C3O4). The anion of this salt, [O2C-P(CO)2P](2-), is built up by a four-membered 1,3-diphosphetane-2,4-dione ring and a carboxylate unit attached to one of the phosphorus atoms. A remarkable π-delocalization was observed within the OCPCO moiety. The stepwise reaction mechanism leading to Na2(P2C3O4) was investigated with quantum chemical calculations. Accompanied by the release of CO2, Na2(P2C3O4) reacts with both 2-iodopropane and 4,4',4''-trimethoxytriphenylmethyl chloride to form four-membered cyclic anions. For comparison the analogous reactions were performed with Na(OCP) instead of Na2(P2C3O4) and the results are discussed in detail.

Acids, esters and amides have to date been the only isolated products from the dehydrogenation of primary alcohols with [Rh(trop(2)N)(L)] (trop = 5-H-dibenzo[a,d]cyclohepten-5yl) type complexes. With the reported method the available product family is finally to aldehydes. Using nitrosobenzene as a hydrogen acceptor the aldehydes could be isolated in up to 96% yield with substrate to catalyst ratios of up to 1000. Nitrosobenzene was found to be reductively coupled to azoxybenzene under the reaction conditions. Several symmetrically substituted azoxybenzene derivatives could be isolated in generally high yields after 2 to 4 h reaction time using a low catalyst loading.

The mono-phosphanes 5-(diphenyl)-phosphanyl-5H-dibenzo[a,d]cycloheptene (TROPP(Ph)) and 5-((2-methoxy)phenyl)-phosphanyl-5H-dibenzo[a,d]cycloheptene (TROPP((2-MeOPh))) have been employed to coordinate PdCl(2), yielding [PdCl(2)(TROPP(Ph))] (1a) and [PdCl(2)(TROPP((2-MeOPh)))] (1b), respectively. The corresponding tosylate (OTs) complexes [Pd(OTs)(2)(TROPP(Ph))] (2a) and [Pd(OTs)(2)(TROPP((2-MeOPh)))] (2b) have been successfully applied in the p-benzoquinone (BQ)-assisted methoxycarbonylation of terminal alkynes to give chemoselectively the corresponding alkynylcarboxylic acid methyl ester with high TOF (up to 980 h(-1)). Unlike 2a/b, the Pd(II)-(tosylate)-diphosphane complexes [Pd(OTs)(H(2)O)(dppp)](OTs) 2c (dppp = 1,3-bis-di(phenylphosphanyl)propane and [Pd(H(2)O)(2)(MeO-dppp)](OTs)(2) 2d (MeO-dppp = 1,3-bis(di(2-methoxyphenyl)phosphanyl)propane) preferentially catalyzed a double alkyne insertion. The "in situ" spectroscopic observation of the Pd-methoxycarbonyl compound [Pd(COOMe)(TROPP(Ph))](OTs) (3a) in conjunction with the evidence of the fast beta-hydride elimination reaction of TROPP-based Pd-catalysts in the dimerization reaction of ethene are indicative for a strongly electrophilic metal centre. The X-ray crystal structures of 1a x 0.5 C(2)H(4)Cl(2) and of the neutral and cationic Pd-alkyl complexes [Pd(Me)(Cl)(TROPP(Ph)) (7a x 0.5 CH(2)Cl(2)) and [Pd(CH(2)CH(2)COMe)(TROPP(Ph))](PF(6)) (10a x 0.5 C(6)H(6)), respectively, confirm unambiguously the bidentate coordination mode of TROPP-ligands to Pd(II), that persists even in the presence of CO pressure.

In context of an analysis of the effect of the central atom E of gaseous radical cations of phenyl pnictogens C(6)H(5)EH(2), E = N (1), P (2), and As (3), the mass spectrometric reactions of phenyl phosphane 2 have been re-investigated by D-labeling and by using methods of tandem mass spectrometry. The 70 eV mass spectrum of 2 shows the base peak for ion [M-2H](*+) and significant peaks for ions [M-H](+), [M-(2C,3H)](+), [M-PH] (*+), and [M-(C,P,2H)](+). Metastable 2(*+) fragments exclusively by loss of H(2), and the investigation of deuterated 2-d(2) shows that excessive H/D migrations occur before fragmentation. Other significant fragment ions in the mass spectrum of 2 arise by losses of C(2)H(2,) P, or HCP from the ion [M-H](+). This mass spectrometric behavior puts the radical cation 2(*+) in between the fragmentation reactions of aniline radical cation 1(*+) (loss of H and subsequent losses of C(2)H(2,) or HCN) and phenyl arsane radical cation 3(*+) (elimination of H(2) and loss of As from ion [M-H](+)). The fragmentation mechanisms of the radical cations 1(*+) -3(*+) and of related ions were analyzed by calculations of the enthalpy of relevant species at the stationary points of the minimum enthalpy reaction pathways using the DFT hybrid functionals UBHLYP/6-311+G(2d,p)//UBHLYP/6-311+G(d). The results show that, in contrast to ionized aniline 1(*+), the reactions of the derivatives 2(*+) and 3(*+) of the heavier main group elements P and As are characterized by an easy elimination of H(2)via a reductive elimination of group C(6)H(5)-E (E = P, As) and by a special stability of bicyclic isomers of 2(*+) and 3(*+). Thus, while 1(*+) rearranges by ring expansion and formation an 7-aza-tropylium cation by loss of H., the increased stability of bicyclic intermediates in the rearrangement of 2(*+) and in particular of 3(*+) results in separate rearrangement pathways. The origin of these effects is the more extended and diffuse nature of the 3p and 4p AO of P and As.

The unimolecular reactions of radical cations and cations derived from phenylarsane, C6H5AsH2 (1) and dideutero phenylarsane, C6H5AsD2 (1-d2), were investigated by methods of tandem mass spectrometry and theoretical calculations. The mass spectrometric experiments reveal that the molecular ion of phenylarsane, 1*+, exhibits different reactivity at low and high internal excess energy. Only at low internal energy the observed fragmentations are as expected, that is the molecular ion 1*+ decomposes almost exclusively by loss of an H atom. The deuterated derivative 1-d2 with an AsD2 group eliminates selectively a D atom under these conditions. The resulting phenylarsenium ion [C6H5AsH]+, 2+, decomposes rather easily by loss of the As atom to give the benzene radical cation [C6H6]*+ and is therefore of low abundance in the 70 eV EI mass spectrum. At high internal excess energy, the ion 1*+ decomposes very differently either by elimination of an H2 molecule, or by release of the As atom, or by loss of an AsH fragment. Final products of these reactions are either the benzoarsenium ion 4*+, or the benzonium ion [C6H7]+, or the benzene radical cation, [C6H6]*+. As key-steps, these fragmentations contain reductive eliminations from the central As atom under H-H or C-H bond formation. Labeling experiments show that H/D exchange reactions precede these fragmentations and, specifically, that complete positional exchange of the H atoms in 1*+ occurs. Computations at the UMP2/6-311+G(d)//UHF/6-311+G(d) level agree best with the experimental results and suggest: (i) 1*+ rearranges (activation enthalpy of 93 kJ mol(-1)) to a distinctly more stable (DeltaH(r)(298) = -64 kJ mol(-1)) isomer 1 sigma*+ with a structure best represented as a distonic radical cation sigma complex between AsH and benzene. (ii) The six H atoms of the benzene moiety of 1 sigma*+ become equivalent by a fast ring walk of the AsH group. (iii) A reversible isomerization 1+<==>1 sigma*+ scrambles eventually all H atoms over all positions in 1*+. The distonic radical cation 1*+ is predisposed for the elimination of an As atom or an AsH fragment. The calculations are in accordance with the experimentally preferred reactions when the As atom and the AsH fragment are generated in the quartet and triplet state, respectively. Alternatively, 1*(+) undergoes a reductive elimination of H2 from the AsH2 group via a remarkably stable complex of the phenylarsandiyl radical cation, [C6H5As]*+ and an H2 molecule.

Copper phosphide or arsenide complexes, [Cu(EPh(2))(neo)] (E = P, As, neo = 2,9-dimethyl-1,10-phenanthroline; trivial name: neocuprine) react selectively with the N-protected brominated serine derivatives, 2-(S)-(alkoxycarbonylamino)-3-bromomethylpropionates ((ROCO)SerBr, : R = PhCH(2), : tBu, : Me) to give the corresponding phosphanylated or arsanylated amino acids, (ROCO)SerPhos (: Phos = PPh(2)) and (Z)SerArs (Ars = AsPh(2), Z = PhCH(2)OCO). The dipeptide (Z)AlaSerPhos was likewise prepared. The phosphanes , and the arsane reacted cleanly with [Rh(2)(micro-Cl)(2)(cod)(2)] to give the rhodium(I) complexes [RhCl(cod)((Z)SerPhos)] , [RhCl(cod)((Boc)SerPhos)] (Boc = tBuOCO), [RhCl(cod)((Z)AlaSerPhos)] , and [RhCl(cod)((Z)SerArs)] which were characterized by X-ray diffraction studies. A common structural feature is an intramolecular (N)H[dot dot dot]Cl(Rh)-hydrogen bridge which according to NMR investigations remains intact in solution. The abstraction of chloride from the coordination sphere of Rh(I) in or has a profound structural impact. While in and , the ligands bind in a monodentate fashion, via the phosphorus atom only, they serve as bidentate ligands via the phosphorus centre and the peptidic C=O group in [Rh(cod)(kappa(2)-(Z)SerPhos)]PF(6) and [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6). This causes also the amino acid residue structures to change from alpha-helix type in and to a beta-sheet type in both. Addition of chloride to and fully re-establishes the structures of both. The complexes [RhCl(cod)((Z)SerPhos)] and [RhCl(cod)((Boc)SerPhos)] show good activities in homogeneously catalyzed hydrogenations of olefins while the dipeptide complex is less active. Phosphane addition to greatly diminishes the catalytic activity. The cationic complex [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6) shows low activity which, however, is greatly increased by addition of one equivalent of phosphane.

The benzophenone dianion [diphenyloxidomethanide, (Ph(2)CO)(2-)], which occurs in the well known deeply violet sodium/benzophenone tetrahydrofuran solutions, was crystallised with sodium cations in form of the two polymeric chain compounds [Na(2)(Ph(2)CO)(tetraglyme)](infinity) and [Na(2)(Ph(2)CO)(thf)(2)](infinity). It was found to aggregate with its conjugated acid, the alcoholate (Ph(2)CHO)(-), around a central unit of sodium hydroxide, resulting in the mixed cage compound [Na(13)(Ph(2)CO)(4)(Ph(2)CHO)(4)(OH)(mtbe)(4)].mtbe. The structural parameters of the benzophenone dianion indicate that a considerable amount of its negative charge is located within the phenyl rings, rather than on the formally anionic benzylic carbon atom. The topological analysis of the electron density of the monomeric model structure [Na(2)(Ph(2)CO)] reveals an even positive charge for this particular atom, hence (Ph(2)CO)(2-) is, despite its usual representation, not a vicinal dianion.

A highly rigid dibenzo[a,d]cycloheptenyl dibenzophosphole with a pre-organized concave shaped binding site acts as an efficient ligand in the palladium catalyzed Suzuki-Miyaura coupling process between halogenoaromatics and phenylboronic acid.

A combination of the rigid bis(5H-dibenzo[a,d]cyclohepten-5-yl)amine (trop(2)NH) and 5-amino-5H-dibenzo[a,d]cycloheptene (tropNH(2)) ligand allowed the synthesis of the stable pentacoordinated 18 electron amine olefin rhodium(i) complex [Rh(trop(2)NH)(tropNH(2))]O(3)SCF(3)(); this complex can be cleanly deprotonated [pK(a)(DMSO) = 20.6(1)] to the corresponding amide [Rh(trop(2)N)(tropNH(2))](6) which is reversibly oxidised at -0.466 V (vs. Fc/Fc(+)). The coordinated NH bond strength in is estimated to be 379 +/- 10 kJ mol(-1).

[Na11(OtBu)10(OH)], a hydroxide enclosing 21-vertex cage compound, was found to crystallize from mixtures of sodium tert.butanolate with sodium hydroxide. Its structure can be derived from the known (NaOtBu)6-hexaprismane by replacing one butanolate unit with OH- and capping the latter with five additional units of NaOtBu. The hydroxide shows a signal at -3.21 ppm in the 1H NMR spectrum.