A Simple Manganese(I) Catalyst for the Efficient and Selective Hydrophosphination of Olefins with PH3, Primary, and Secondary Phosphanes.

A tridentate ligand L with a P,NH,N donor motif was synthesized in few steps from commercially available precursors. Upon reaction with [MnBr(CO)5], an octahedral 18-electron complex [Mn(CO)3(L)]Br (1) is obtained in which L adopts a facial arrangement. After deprotonation of the NH group in the cationic complex unit, a neutral Mn(I) amido complex [Mn(CO)2(L-H)] (2) is formed under loss of CO. Rearrangement of L-H leads to a trigonal bipyramidal structure in which the P and N donor centers are in trans position. Further deprotonation of 2 results in a dep-blue anionic complex fragment [Mn(CO)2(L-2H)]- (3). DFT calculations and a QTAIM analysis show that the amido complex 2 contains a Mn-N bond with partial double bond character and 3 an aromatic MnN2C2 ring. The anion [Mn(CO)2(L-2H)]- reacts with Ph2PH to give a phosphido complex, which serves as phosphide transfer reagent to activated olefins. But the catalytic activity is low. However, the neutral amido complex 2 is an excellent catalyst and with loadings as low as 0.04 mol %, turn over frequencies of >40'000 h-1 can be achieved. Furthermore, secondary and primary alkyl phosphines as well as PH3 can be added in a catalytic hydrophosphination reaction to a wide range of activated olefins such as α,ß-unsaturated aldehydes, ketones, esters, and nitriles. But also, vinyl pyridine and some styrene derivatives are converted into the corresponding phosphanes.

Reduction of Nitrous Oxide by Light Alcohols Catalysed by a Low-Valent Ruthenium Diazadiene Complex.

Decomposition of the environmentally harmful gas nitrous oxide (N2 O) is usually performed thermally or catalytically. Selective catalytic reduction (SCR) is currently the most promising technology for N2 O mitigation, a multicomponent heterogeneous catalytic system that employs reducing agents such as ammonia, hydrogen, hydrocarbons, or a combination thereof. This study reports the first homogenous catalyst that performs the reduction of nitrous oxide employing readily available and cheap light alcohols such as methanol, ethanol or ethylene glycol derivatives. During the reaction, these alcohols are transformed in a dehydrogenative coupling reaction to carboxylate derivatives, while N2 O is converted to N2 and H2 O, later entering the reaction as substrate. The reaction is catalysed by the low-valent dinuclear ruthenium complex [Ru2 H(µ-H)(Me2 dad)(dbcot)2 ] that carries a diazabutadiene, Me2 dad, and two rigid dienes, dbcot, as ligands. The reduction of nitrous oxide proceeds with low catalyst loadings under relatively mild conditions (65-80 °C, 1.4 bar N2 O) achieving turnover numbers of up to 480 and turnover frequencies of up to 56 h-1 .

Organocatalyzed Phospha-Michael Addition: A Highly Efficient Synthesis of Customized Bis(acyl)phosphane Oxide Photoinitiators.

Addition of the P-H bond in bis(mesitoyl)phosphine, HP(COMes)2 (BAPH), to a wide variety of activated carbon-carbon double bonds as acceptors was investigated. While this phospha-Michael addition does not proceed in the absence of an additive or catalyst, excellent results were obtained with stoichiometric basic potassium or caesium salts. Simple amine bases can be employed in catalytic amounts, and tetramethylguanidine (TMG) in particular is an outstanding catalyst that allows the preparation of bis(acyl)phosphines, R-P(COMes)2 , under very mild conditions in excellent yields after only a short time. All phosphines RP(COMes)2 can subsequently be oxidized to the corresponding bis(acyl)phosphane oxides, RPO(COMes)2 , a substance class belonging to the most potent photoinitiators for radical polymerizations known to date. Thus, a simple and highly atom economic method has been found that allows the preparation of a broad range of photoinitiators adapted to their specific field of application even on a large scale.

ACTIVE-BAPO - A Versatile Transfer Agent for Photoactive Bis(acyl)phosphane Oxide Units.

A N-hydroxy succinimide (NHS) ester substituted bis(acyl)phosphane oxide (ACTIVE-BAPO) was prepared by phospha-Michael addition and used for an easy one-step BAPO ligation with substrates containing primary amino groups, such as amino acids, proteins, and poly(amidoamine) (PAMAM) dendrimers. Thereby, a range of new molecular and polymeric photoinitators was obtained. Real-time photo-rheology experiments demonstrated the outstanding efficiency of the PAMAM BAPOs as photoinitiators for free radical polymerization. Remarkably, it is found that PAMAM BAPOs also act as crosslinking agents to convert monofunctional methacrylate monomers into thermosetting networks without any further additives. Depending on the number of the attached BAPOs, thermosets with a different degree of crosslinking and swelling capability in water were obtained.

Symmetrical and Mixed Tris(acyl)phosphines: Synthesis, Oxidation and Photochemistry.

Herein, we present a convenient synthesis for symmetrical and mixed substituted tris(acyl)phosphines (TAPs) starting from red phosphorus. All TAPs exhibit a phosphaalkene-acylphosphine equilibrium, which was investigated in detail by variable-temperature (VT) NMR spectroscopy supported by density-functional theory (DFT) calculations. Depending on the substituents, two phosphaalkene derivatives and ten acylphosphine derivatives could be isolated. NMR spectroscopy and single-crystal X-ray crystallography enabled a clear structural assignment of these compounds. Oxidation of selected TAPs led to the formation of the corresponding tris(acyl)phosphine oxides (TAPOs). Furthermore, their spectroscopic properties as well as their photochemistry was investigated. Especially, the TAPO compounds were evaluated for their suitability as photoinitiators by CIDNP spectroscopy, photobleaching measurements and by storage stability tests.

Symmetrical and Mixed Tris(acyl)phosphines: Synthesis, Oxidation and Photochemistry.

Invited for the cover of this issue are the groups of M. Haas, G. Gescheidt and H. Grützmacher from the Graz University of Technology and the ETH Zürich. The image depicts a phosphorus mine, where the workers are acid chlorides using their shovels and red phosphorus to provide the chemicals necessary to produce novel reagents. Read the full text of the article at 10.1002/chem.202302535.

Reversible Single Electron Redox Steps Convert Polycycles with a C3 P3 Core to a Planar Triphosphinine.

Reaction of the imidazolium-stabilized diphosphete-diide IDP with trityl phosphaalkyne affords a mixture which contains the molecules 1 a and 1 b with a central C3 P3 core, which formally carries a two-fold negative charge. In order to avoid the formation of an antiaromatic 8π electron system within a conjugated dianionic six-membered [C3 P3 ]2- ring, 1 a adopts a bicyclic [3.1.0] and 1 b a tricyclic [2.2.0.0] structure which are in a dynamic equilibrium. 1 a, b can be reversibly oxidized to a triphosphinine dication [5]2+ with a central flat aromatic six-membered C3 P3 ring. This two-electron redox reaction occurs in two single-electron transfer steps via the 7π-radical cation [4]⋅+ , which could also be isolated and fully characterized. The profound reversible structural change observed for the two-electron redox couple [5]2+ /1 a, b is in sharp contrast to the C6 H6 /[C6 H6 ]2- couple, which undergoes only a modest structural deformation.

The Chemistry of the Cyaphide Ion.

We review the known chemistry of the cyaphide ion, (C≡P)- . This remarkable diatomic anion has been the subject of study since the late nineteenth century, however its isolation and characterization eluded chemists for almost a hundred years. In this mini-review, we explore the pioneering synthetic experiments that first allowed for its isolation, as well as more recent developments demonstrating that cyaphide transfer is viable in well-established salt-metathesis protocols. The physical properties of the cyaphide ion are also explored in depth, allowing us to compare and contrast the chemistry of this ion with that of its lighter congener cyanide (an archetypal strong field ligand and important organic functional group). Recent studies show that the cyaphide ion has the potential to be used as a versatile chemical regent for the synthesis of novel molecules and materials, hinting at many interesting future avenues of investigation.

Solid-State Investigation, Storage, and Separation of Pyrophoric PH3 and P2 H4 with α-Mg Formate.

Phosphane, PH3 -a highly pyrophoric and toxic gas-is frequently contaminated with H2 and P2 H4 , which makes its handling even more dangerous. The inexpensive metal-organic framework (MOF) magnesium formate, α-[Mg(O2 CH)2 ], can adsorb up to 10 wt % of PH3 . The PH3 -loaded MOF, PH3 @α-[Mg(O2 CH)2 ], is a non-pyrophoric, recoverable material that even allows brief handling in air, thereby minimizing the hazards associated with the handling and transport of phosphane. α-[Mg(O2 CH)2 ] further plays a critical role in purifying PH3 from H2 and P2 H4 : at 25 °C, H2 passes through the MOF channels without adsorption, whereas PH3 adsorbs readily and only slowly desorbs under a flow of inert gas (complete desorption time≈6 h). Diphosphane, P2 H4 , is strongly adsorbed and trapped within the MOF for at least 4 months. P2 H4 @α-[Mg(O2 CH)2 ] itself is not pyrophoric and is air- and light-stable at room temperature.

Recyclable Mn(I) Catalysts for Base-Free Asymmetric Hydrogenation: Mechanistic, DFT and Catalytic Studies.

We report here a mechanistic, DFT and catalytic study on a series of Mn(I) complexes 1, 2(a-d), 3, 4. The studies apprehended the requirements for Mn(I) complexes to be active in both asymmetric direct (AH) and transfer hydrogenations (ATH). The investigations disclosed 6 vital factors accelerating the formation of a resting species, which plays a significant role in lowering the activities of the Mn(I) complex 1 in ATH and AH, respectively. In addition, we also report here a base free Mn(I) catalyzed ATH of aryl alkyl ketones with high enantioselectivity (up to 98 % ee) and improved activity. More significantly, a novel and simple single-step process for recycling the resting species from the catalytic leftover has been discovered. Notably, the studies provide evidence for the existence of two different temperature dependent mechanisms for AH and ATH, in contrast to previous studies on related systems.

A Germapyramidane Switches Between 3D Cluster and 2D Cyclic Structures in Single-Electron Steps.

Reaction of the imidazolium-substituted iphosphate-diide, (Ipr)2 C2 P2 (IDP), with GeCl2 ⋅ dioxane and KBArF24 [(BarF24 )- =tetrakis[(3,5-trifluoromethyl)phenyl]borate)] afforded the dicationic spherical-aromatic nido-cluster [Ge(η4 -IDP)]2+ ([1]2+ ) (Ipr=1,3-bis(2,6-diisopropylphenyl)imidazolium-2-ylidene). This complex is a rare heavy analogue of the elusive pyramidane [C(η4 -C4 H4 )]. [1]2+ undergoes two reversible one-electron reductions, which yield the radical cation [2]⋅+ and the neutral GeII species 3. Both [2]⋅+ and 3 rearrange in solution forming the 2D aromatic and planar imidazolium-substituted digermolide [4]2+ and germole-diide 5, respectively. Both planar species can be oxidized back to [1]2+ using AgSbF6 . These redox-isomerizations correspond to the fundamental transformation of a 3D aromatic cluster into a 2D aromatic ring compound upon reduction and vice versa. The mechanism of these reactions was elucidated using DFT calculations and cyclic voltammetry experiments.

Bis(imidazolium)-1,3-diphosphete-diide: A Building Block for FeC2 P2 Complexes and Clusters.

Reaction of the 6π-electron aromatic four-membered heterocycle (IPr)2 C2 P2 (1) (IPr=1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) with [Fe2 CO9 ] gives the neutral iron tricarbonyl complex [Fe(CO)3 -η3 -{(IPr)2 C2 P2 }] (2). Oxidation with two equivalents of the ferrocenium salt, [Fe(Cp)2 ](BArF24 ), affords the dicationic tricarbonyl complex [Fe(CO)3 -η4 -{(IPr)2 C2 P2 }](BArF24 )2 (4). The one-electron oxidation proceeds under concomitant loss of one CO ligand to give the paramagnetic dicarbonyl radical cation complex [Fe(CO)2 -η4 -{(IPr)2 C2 P2 }](BArF24 ) (5). Reduction of 5 allows the preparation of the neutral dicarbonyl complex [Fe(CO)2 -η4 -{(IPr)2 C2 P2 }] (6). An analysis by various spectroscopic techniques (57 Fe Mössbauer, EPR) combined with DFT calculations gives insight into differences of the electronic structure within the members of this unique series of iron carbonyl complexes, which can be either described as electron precise or Wade-Mingos clusters.

Vibrational spectrum and photochemistry of phosphaketene HPCO.

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.

Cyano(triphenylsilyl)phosphanide as a Building Block for P,C,N Conjugated Molecules.

The cyano(triphenylsilyl)phosphanide anion was prepared as a sodium salt from 2-phosphaethynolate. The electronic structure of this new cyano(silyl)phosphanide was studied via computational methods and its reactivity investigated using various electrophiles and Lewis acids, demonstrating its P- and N-nucleophilicity. The ambident reactivity is in agreement with computations. The silyl group also shows lability and therefore the cyano(silyl)phosphanide can be considered as a phosphacyanamide synthon, [PCN]2- , and serves as building block for the transfer of a PCN moiety.

Reduction of Nitrogen Oxides by Hydrogen with Rhodium(I)-Platinum(II) Olefin Complexes as Catalysts.

The nitrogen oxides NO2 , NO, and N2 O are among the most potent air pollutants of the 21st century. A bimetallic RhI -PtII complex containing an especially designed multidentate phosphine olefin ligand is capable of catalytically detoxifying these nitrogen oxides in the presence of hydrogen to form water and dinitrogen as benign products. The catalytic reactions were performed at room temperature and low pressures (3-4 bar for combined nitrogen oxides and hydrogen gases). A turnover number (TON) of 587 for the reduction of nitrous oxide (N2 O) to water and N2 was recorded, making these RhI -PtII complexes the best homogeneous catalysts for this reaction to date. Lower TONs were achieved in the conversion of nitric oxide (NO, TON=38) or nitrogen dioxide (NO2 , TON of 8). These unprecedented homogeneously catalyzed hydrogenation reactions of NOx were investigated by a combination of multinuclear NMR techniques and DFT calculations, which provide insight into a possible reaction mechanism. The hydrogenation of NO2 proceeds stepwise, to first give NO and H2 O, followed by the generation of N2 O and H2 O, which is then further converted to N2 and H2 O. The nitrogen-nitrogen bond-forming step takes place in the conversion from NO to N2 O and involves reductive dimerization of NO at a rhodium center to give a hyponitrite (N2 O2 2- ) complex, which was detected as an intermediate.

The Underlying Chemistry to the Formation of PO2 Radicals from Organophosphorus Compounds: A Missing Puzzle Piece in Flame Chemistry.

Reactive species, such as . PO2 and HOPO, are considered of upmost importance in flame inhibition and catalytic combustion processes of fuels. However, the underlying chemistry of their formation remains speculative due to the unavailability of suitable analytical techniques that can be used to identify the transient species which lead to their formation. This study elucidates the reaction mechanisms of the formation of phosphoryl species from dimethyl methyl phosphonate (DMMP) and dimethyl methyl phosphoramidate (DMPR) under well-defined oxidative conditions. Photoelectron photoion coincidence techniques that utilized vacuum ultraviolet synchrotron radiation were applied to isomer-selectively detect the elusive key intermediates and stable products. With the help of in situ recorded spectral fingerprints, different transient species, such as PO2 and triplet O radicals, have been exclusively identified from their isomeric components, which has helped to piece together the formation mechanisms of phosphoryl species under various conditions. It was found that . PO2 formation required oxidative conditions above 1070 K. The combined presence of O2 and H2 led to significant changes in the decomposition chemistry of both model phosphorus compounds, leading to the formation of . PO2 . The reaction . PO+O2 →. PO2 +O: was identified as the key step in the formation of . PO2 . Interestingly, the presence of O2 in DMPR thermolysis suppresses the formation of PN-containing species. In a previous study, PN species were identified as the major species formed during the pyrolysis of DMPR. Thus, the findings of this study has shed light onto the decomposition pathways of organophosphorus compounds, which are beneficial for their fuel additive and fire suppressant applications.

Isomerism and Biradical Character of Tetrapnictide Dianions: A Computational Study.

We present a computational study on tetrapnictide dianions Pn 4 2- (Pn = P, As, Sb, Bi), using density functional theory (DFT), coupled-cluster [DLPNO-CCSD(T)] and complete active space self-consistent field (CASSCF) methods. Environmental effects such as solvation and coordination of counterions are included. The calculations reveal that out of three isomers (square-planar, butterfly and capped-triangle), the square planar isomers are generally the most stable. The counterion (Li+ and Mg2+) used in the calculations have a substantial effect on the relative stabilities. The square planar isomers show considerable biradical character. Calculated reactions toward alkenes indicate that this unusual electronic structure has significant implications on the reactivity of the Pn 4 2- dianions.

Synthesis and Characterization of Ion Pairs between Alkaline Metal Ions and Anionic Anti-Aromatic and Aromatic Hydrocarbons with π-Conjugated Central Seven- and Eight-Membered Rings.

The synthesis, isolation and full characterization of ion pairs between alkaline metal ions (Li+, Na+, K+) and mono-anions and dianions obtained from 5H-dibenzo[a,d]cycloheptenyl (C15H11 = trop) is reported. According to Nuclear Magnetic Resonance (NMR) spectroscopy, single crystal X-ray analysis and Density Functional Theory (DFT) calculations, the trop‒ and trop2-• anions show anti-aromatic properties which are dependent on the counter cation M+ and solvent molecules serving as co-ligands. For comparison, the disodium and dipotassium salt of the dianion of dibenzo[a,e]cyclooctatetraene (C16H12 = dbcot) were prepared, which show classical aromatic character. A d8-Rh(I) complex of trop- was prepared and the structure shows a distortion of the C15H11 ligand into a conjugated 10π -benzo pentadienide unit-to which the Rh(I) center is coordinated-and an aromatic 6π electron benzo group which is non-coordinated. Electron transfer reactions between neutral and anionic trop and dbcot species show that the anti-aromatic compounds obtained from trop are significantly stronger reductants.

A Room-Temperature Stable Distonic Radical Cation.

Distonic radical cations (DRCs) with spatially separated charge and radical sites have, so far, largely been observed by gas-phase mass spectrometry and/or matrix isolation spectroscopy work. Herein, we disclose the isolation of a crystalline dicarbondiphosphide-based ß-distonic radical cation salt 3.+ (BARF) (BARF=[B(3,5-(CF3 )2 C6 H3 )4 )]- ) stable at room temperature and formed by a one-electron-oxidation-induced intramolecular skeletal rearrangement reaction. Such a species has been validated by electron paramagnetic resonance (EPR) spectroscopy, single-crystal X-ray diffraction, UV/Vis spectroscopy and density functional theory (DFT) calculations. Compound 3.+ (BARF) exhibits a large majority of spin density at a two-coordinate phosphorus atom (0.74 a.u.) and a cationic charge located predominantly at the four-coordinate phosphorus atom (1.53 a.u.), which are separated by one carbon atom. This species represents an isolable entity of a phosphorus radical cation that is the closest to a genuine phosphorus DRC to date.

N-Heterocyclic Carbene Stabilized Dicarbondiphosphides: Strong Neutral Four-Membered Heterocyclic 6π-Electron Donors.

In contrast to cyclic π-conjugated hydrocarbons, the coordination chemistry of inorganic heterocycles is less developed. Dicarbondiphosphides stabilized by N-heterocyclic carbenes (NHCs) NHC→C2 P2 ←NHC (1 a,b) (NHC=IPr or SIPr) contain a four-membered C2 P2 ring with an aromatic 6π-electron configuration. These heterocycles coordinate to a variety of complex fragments with metals from groups 6, 9, and 10, namely [M0 (CO)3 ] (M=Cr, Mo), [CoI (CO)2 ]+ , or [NiII Br2 ], through an η4 -coordination mode, leading to complexes 2 a,b, 3 a,b, 5 a,b, and 6 a,b, respectively. These complexes were characterized by X-ray diffraction methods using single crystals, IR spectroscopy, and DFT calculations. In combination these methods indicate that 1 a,b behave as exceptionally strong 6π-electron donors.