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.

Bis(acyl)phosphide - Ambidentate Ligands for the Synthesis of Group 14 and 15 Main Group Element Compounds.

The reactivity of the bis(acyl)phosphide ion [P(COR)2 ]- (BAP- , R=Ph, Mes) with silicon halides SiX4 (X=Cl, Br) and pnictogen chlorides ECl3 (E=As, Sb and Bi) was investigated. The reaction with SiX4 leads to the hexacoordinate silanes SiX2 (BAP)2 in which BAP- is coordinated in the chelating κ2 -O,O' mode, analogously to acac- . Unexpectedly, the coordination behaviour of BAP- differs from the one of acac- in the interpnictogen compounds E(BAP)3 (E=As, Sb) in which the formation of E-P bonds is favoured over κ2 -O,O' chelation via the oxygen centres. Finally, the reaction of BiCl3 with three equivalents of Na(BAP) leads to the formation of red, crystalline Bi2 (BAP)4 , an air stable dibismuthine, as product of a redox reaction.

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.

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.

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.

Polycationic Redox-Active Cyclophanes with Integrated Electron-Rich Diboron Units.

Cationic cyclophanes are widely used in a variety of applications in supramolecular chemistry and materials science. In this work the authors systematically study the integration of electron-rich diboron units with BII atoms into polycationic cyclophanes with viologen-like electron-acceptor units. They also report a first hexacationic cage-compound in which three diboron units connect two tris(4-pyridyl)triazine acceptor units. Moreover, di- and tetracationic open-structure compounds, in which one diboron unit connects two bispyridyl groups, were synthesized and the properties compared to those of the corresponding closed structures (cyclophanes). The combination of diboron electron-donor units and bi- or oligopyridyl electron-acceptor units leads to intriguing optical and redox properties.

Electron-Rich, Lewis Acidic Diborane Meets N-Heterocyclic Aromatics: Formation and Electron Transfer in Cyclophane Boranes.

Herein reported are the reactions of an electron-rich, Lewis acidic diborane with N-heterocyclic aromatics to give first members of an unprecedented family of highly charged cationic cyclophanes with diboranyl units. Tetracationic cyclophanes with 4,4'-bipyridine/ 1,2-bis(4-pyridyl)ethylene and diboranyl units were synthesized and their redox chemistry was studied. Cyclisation of two diboranyl and two pyrazine units is accompanied by electron transfer from the diboranyl unit to the pyrazine. Our results pave the way for the integration of redox-active diboranyl units into cyclophanes and supramolecular structures.

Four Boron Atoms, Four Positive Charges, and Four Skeletal Electrons: A Fluorescent σ-Aromatic Tetraborane(4).

Reaction of a ditriflatodiborane compound with the Lewis acids AlCl3 or GaCl3 leads to abstraction of the two triflate substituents and dimerization of the resulting dicationic diborane to give a σ-aromatic tetracationic tetraborane with a planar, rhomboid B4 core. The compound exhibits four skeletal σ-electrons involved in two (3c,2e) bonds and represents the first stable fourfold base-stabilized [B4 H4 ]4+ analogue. The product is isolated from the reaction mixture in the form of bright orange crystals that display fluorescence. Further analysis shows that the new tetraborane(4) is stabilized in the solid state by the lattice energy. It exhibits an extremely high electron affinity and is only stable in solution after one-electron reduction to the radical cation.

Boron(II) Cations: Interplay between Lewis-Pair-Acceptor and Electron-Donor Properties.

Boron(III) cations are widely used as highly Lewis acidic reagents in synthetic chemistry. In contrast, boron(II) cations are extremely rare and their chemistry almost completely unknown. They are both Lewis acids and electron donors, properties that are commonly associated with catalytically active late-transition-metal complexes. This double reactivity pattern ensures a rich and diverse chemistry. Herein we report the facile synthesis of several new boron(II) cations starting with a special diborane with two easily exchangeable triflate substituents. By increasing the π-acceptor character of the neutral σ-donor reaction partners, first reactions were developed in which the combined Lewis acidity and electron-donor properties of boron(II) cations are applied for the reduction of organic molecules. The results of our study pave the way for applications of these unusual compounds in synthetic chemistry.

Tuning the nucleophilicity of electron-rich diborane(4) compounds with bridging guanidinate substituents by substitution.

Diborane(4) compounds are versatile reagents in synthetic chemistry. Generally, diboranes(4) with sp2-hybridized boron atoms react as electrophiles. By contrast, the chemistry of nucleophilic diborane(4) compounds with two sp3-hybridized boron atoms is very much underdeveloped. In this work, we systematically vary the substituents of electron-rich diborane(4) compounds with bridging guanidinate substituents. In this way, five new diboranes are synthesized and fully characterized. Using quantum chemical computations, we show that the electronic properties and reactivity of these compounds can be rationally varied by the choice of substituents. The HOMO energies, adiabatic ionization energies and proton affinities are considered as parameters to compare the chemical properties of these unusual compounds.

Synthesis and Properties of Tetranitro-Substituted Adamantane Derivatives.

Several new nitro-substituted adamantane compounds based on adamantane-1,3,5,7-tetrol were synthesized and the previously only briefly reported tetranitrate was reinvestigated. The materials were completely characterized by spectroscopic methods including some by X-ray diffraction. The energetic properties, thermal stabilities, and sensitivities of the nitrocarbamate, nitrocarbamate salt, and nitrate were determined and compared to current composites in terms of potential high-energy dense oxidizers (HEDOs). Furthermore, the enthalpies of all compounds were calculated, and their energetic performances investigated by using the EXPLO5 code.

On the Dual Reactivity of a Nucleophilic Dihydrido-Diborane: Reaction at the B-B Bond and/or the B-H Bond.

The electron-rich, double-base stabilized dihydrido-diborane(4) [HB(hpp)]2 (hpp=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate) combines two different, easily accessible reactive sites: the B-B and B-H bond. Herein, we report two basically similar reactions of [HB(hpp)]2 with catecholborane and B-chlorocatecholborane unsuspectedly resulting in two different reactivities. While reaction of the diborane with two equivalents of HB(cat) proceeded with formation of a cationic triborane with a (3c2e) bond, [{HB(µ-hpp)}2 (µ-BH2 )]+ , reaction with ClB(cat) led to hydride-chloride substitution yielding [ClB(hpp)]2 . The cationic triborane was also obtained by the addition of BH3 to the in situ generated [HB(hpp)2 B]+ . Proceeding from the new compound [ClB(hpp)]2 , we investigated its reactivity towards chloride abstraction with AlCl3 and GaCl3 . Irrespectively of the salt chosen, the reaction led to formation of a radical tricationic tetraborane [{B(hpp)}4 ].3+ with a (4c,5e) bond. Moreover, the dichloro-diborane proves as a versatile reagent for further substitution cleanly reacting with the strong nucleophile nBuLi to a new dibutyl-diborane [nBuB(hpp)]2 .