From a P-Bridging Phosphaketene to μ-Phosphinidenide and μ-Diphosphaurea Units at a Dinickel Core.

Salt metathesis of dinickel(II) complex LNiBr (1; L is a dinucleating pyrazolate ligand with two β-diketiminato chelate arms) with Na(OCP) ⋅ (dioxane) yielded LNi(PCO) (2) with a P-bridging phosphaethynolate. Further reaction of 2 with benzyl isocyanide or with an N-heterocyclic carbene (NHC) triggered decarbonylation and gave LNi(PCN-CHPh) (3) and LNiP(NHC) (4) with P-bridging cyanophosphide and NHC-phosphinidenide, respectively. Electronic structure analysis indicated a μ-η : η binding mode of the PCO anion between the two Ni ions in 2, which is even more pronounced for the [PCN(-CHPh)] anion in 3.

Structural Snapshots, Trajectory and Thermodynamics of the Reversible μ-1,2-Peroxo/μ-1,1-Hydroperoxo Dicopper(II) Interconversion.

Hydrogen bonds involving the oxygen atoms of intermediates that result from copper-mediated O activation play a key role for controlling the reactivity of Cu/O active sites in metalloenzymes and synthetic model complexes. However, structural insight into H-bonding in such transient species as well as thermodynamic information about proton transfer to or from the O-derived ligands is scarce. Here we present a detailed study of the reversible interconversion of a μ-peroxodicopper(II) complex ([1]) and its μ-hydroperoxo congener ([2]) via (de)protonation, including the isolation and structural characterization of several H-bond donor (HBD) adducts of [1] and the determination of binding constants.

C=C Dissociative Imination of Styrenes by a Photogenerated Metallonitrene.

Photolysis of a platinum(II) azide complex in the presence of styrenes enables C=C double bond cleavage upon dissociative olefin imination to aldimido (Pt-N=CHPh) and formimido (Pt-N=CH) complexes as the main products. Spectroscopic and quantum chemical examinations support a mechanism that commences with the decay of the metallonitrene photoproduct (Pt-N) via bimolecular coupling and nitrogen loss as N. The resulting platinum(I) complex initiates a radical chain mechanism via a dinuclear radical-bridged species (Pt-CHCHPhN-Pt) as a direct precursor to C-C scission.

Expanding the Clip-and-Cleave Concept: Approaching Enantioselective C-H Hydroxylations by Copper Imine Complexes Using O and HO as Oxidants.

Copper-mediated aromatic and aliphatic C-H hydroxylations using benign oxidants (O and HO) have been studied intensively in recent years to meet the growing demand for efficient and green C-H functionalizations. Herein, we report an enantioselective variant of the so-called clip-and-cleave concept for intramolecular ligand hydroxylations by the application of chiral diamines as directing groups. We tested the hydroxylation of cyclohexanone and 1-acetyladamantane under different oxidative conditions (Cu/O; Cu/HO; Cu/HO) in various solvents.

Triplet carbenes with transition-metal substituents.

The extraordinary advances in carbene (R-C-R) chemistry have been fuelled by strategies to stabilize the electronic singlet state via π interactions. In contrast, the lack of similarly efficient approaches to obtain authentic triplet carbenes with appreciable lifetimes beyond cryogenic temperatures hampers their exploitation in synthesis and catalysis. Transition-metal substitution represents a potential strategy, but metallocarbenes (M-C-R) usually represent high-lying excited electronic configurations of the well-established carbyne complexes (M≡C-R).

Trapping of a Terminal Intermediate in the Boron-Mediated Dinitrogen Reduction: Mono-, Tri-, and Tetrafunctionalized Hydrazines in Two Steps from N.

The addition of chlorotrimethylsilane to a boron-mediated, transition-metal-free N activation reaction leads to the isolation of multiple potassium boryl(silyl)hydrazido species, likely trapping products of a terminal dinitrogen complex of boron. One of these silylated N species can be protonated or methylated, providing access to mono- to tetrafunctionalized hydrazines in two steps from N and in the absence of transition metals.

C-H Bond Activation by Iridium(III) and Iridium(IV) Oxo Complexes.

Oxidation of an iridium(III) oxo precursor enabled the structural, spectroscopic, and quantum-chemical characterization of the first well-defined iridium(IV) oxo complex. Side-by-side examination of the proton-coupled electron transfer thermochemistry revealed similar driving forces for the isostructural oxo complexes in two redox states due to compensating contributions from H and e transfer. However, C-H activation of dihydroanthracene revealed significant hydrogen tunneling for the distinctly more basic iridium(III) oxo complex.

Experimental and Computational Study of a Confirmed Borylene-to-Diborene Dimerization.

While the dimerization of heavier group 13 carbene analogues to the corresponding alkene analogues is known and relatively well understood, the dimerization of dicoordinate borylenes (LRB:, L = neutral donor; R = anionic substituent) to the corresponding diborenes (LRB═BRL) has never been directly observed. In this study we present the first example of a formal borylene-to-diborene dimerization through abstraction of a labile phosphine ligand from the tricoordinate hydroborylene precursor (CAAC)(MeP)BH (CAAC = cyclic alkyl(amino)carbene) by bulky Lewis-acidic dihaloboranes (BXY, X = Cl, Br, Y = aryl, boryl), generating the corresponding dihydrodiborene (CAAC)HB═BH(CAAC) and (MeP)BXY as the byproduct. An in-depth experimental and computational mechanistic analysis shows that this seemingly simple process (2 LL'BH + 2 BXY → LHB═BHL + 2 L'BXY) is in fact based on a complex sequence of finely tuned processes, involving the one-electron oxidation of and PMe abstraction from the borylene precursor by BXY, multiple halide transfers between (di)boron intermediates and BXY/[BXY], and multiple one-electron redox processes between diboron intermediates and the borylene precursor, which make the reaction ultimately autocatalytic in [(CAAC)(MeP)BH].

Ferrocene-Based N-Heterocyclic Plumbylenes [Fe{(η -C H )NSiMe R} Pb:]: Influence of the Steric Demand of the N-Substituents on Their Dimerization via C-H Activation with Pb.

Ferrocene-based N-heterocyclic plumbylenes fc[(NSiMe R) Pb:] (1; fc=1,1'-ferrocenylene) are easily accessible by transamination from [(Me Si) N] Pb and the corresponding 1,1'-diaminoferrocene derivatives fc(NHSiMe R) . They may form unconventional dimers 2 by a process, which causes the cleavage of a cyclopentadienyl C-H bond and the formation of a Pb-C and an N-H bond. The monomer-dimer equilibrium (2 1⇆2) has been addressed experimentally and computationally.

Achieving Control over the Reduction/Coupling Dichotomy of N by Boron Metallomimetics.

We report a detailed computational and experimental study of the fixation and reductive coupling of dinitrogen with low-valent boron compounds. Consistent with our mechanistic findings, the selectivity toward nitrogen fixation or coupling can be controlled through either steric bulk or the reaction conditions, allowing for the on-demand synthesis of nitrogen chains. The electronic structure and intriguing magnetic properties of intermediates and products of the reaction of dinitrogen with borylenes are also elucidated using high-level computational approaches.

Siemens Reloaded: Chloride-Assisted Selective Hydrodechlorination of SiCl to HSiCl.

Trichlorosilane is the key intermediate for the large-scale production of polycrystalline silicon in the Siemens and Union Carbide processes. Both processes, however, are highly inefficient, and over two thirds of the trichlorosilane employed is converted to unwanted silicon tetrachloride accumulating in millions of tons per year on a global scale. In this combined experimental and theoretical study we report an energetically and environmentally benign synthetic protocol for the highly selective conversion of SiCl to HSiCl using organohydridosilanes as recyclable hydrogen transfer reagents in combination with onium chlorides as efficient catalysts.

Stabilizing Doubly Deprotonated Diazomethane: Isolable Complexes with CN and CN Radical Ligands.

Transition metal complexes with a doubly deprotonated diazomethane (CNN) ligand have been proposed as fleeting intermediates in nitrogen transfer reactions. However, in contrast to isoelectronic azide (N), well-defined examples are unknown. We here report the synthesis and characterization of isolable complexes with terminal and bridging CNN ligands, stabilized by platinum(II) pincer fragments.

A crystalline cyclic (alkyl)(amino)carbene with a 1,1'-ferrocenylene backbone.

Cyclic (alkyl)(amino)carbenes with a 1,1'-ferrocenylene backbone (fcCAACs) are established as an original family by the preparation of a crystalline congener. The C bond angle is unprecedentedly wide for a CAAC, causing an exceptionally pronounced ambiphilicity. The redox-active backbone opens the door to unconventional metalloradicals and oligoradicals.

Nitrogen Atom Transfer Catalysis by Metallonitrene C-H Insertion: Photocatalytic Amidation of Aldehydes.

C-H amination and amidation by catalytic nitrene transfer are well-established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) terminal nitride ligands into C-H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium.

Rhenium-Mediated Conversion of Dinitrogen and Nitric Oxide to Nitrous Oxide.

Reductive splitting of N is an attractive strategy towards nitrogen fixation beyond ammonia at ambient conditions. However, the resulting nitride complexes often suffer from thermodynamic overstabilization hampering functionalization. Furthermore, oxidative nitrogen atom transfer of N derived nitrides remains unknown.

Probing the Boundaries between Lewis-Basic and Redox Behavior of a Parent Borylene.

The parent borylene (CAAC)(Me P)BH, 1 (CAAC=cyclic alkyl(amino)carbene), acts both as a Lewis base and one-electron reducing agent towards group 13 trichlorides (ECl , E=B, Al, Ga, In), yielding the adducts 1-ECl and increasing proportions of the radical cation [1] for the heavier group 13 analogues. With boron trihalides (BX , X=F, Cl, Br, I) 1 undergoes sequential adduct formation and halide abstraction reactions to yield borylboronium cations and shows an increasing tendency towards redox processes for the heavier halides. Calculations confirm that 1 acts as a strong Lewis base towards EX and show a marked increase in the B-E bond dissociation energies down both group 13 and the halide group.

Reactivity of an N-heterocyclic silylene with a 1,1'-ferrocenediyl backbone towards carbonyl compounds, including carbon suboxide.

Reactions of a silylene with a ketene and with carbon suboxide are reported, respectively leading to the first silaallene oxide and to a silylketene, whose reaction with water affords the first structurally characterised stable methyleneketene and constitutes a unique type of single-crystal-to-single-crystal transformation of a molecular solid by a stoichiometric gas-solid chemical reaction.

Selective Route to Stable Silicon-Boron Radicals and Their Corresponding Cations.

Herein, we report on a facile and selective one-pot synthetic route to silicon-boron radicals. Reduction of BrBTip (Tip = 2,4,6-PrCH) with KC in the presence of LSi-R affords LSi(Bu)-B(Br)Tip () and LSi(N(TMS))-B(Br)Tip () [L = PhC(NBu)]. These first examples of silicon-boron isolated radical species feature spin density on the silicon and boron atoms.

Coligand role in the NHC nickel catalyzed C-F bond activation: investigations on the insertion of bis(NHC) nickel into the C-F bond of hexafluorobenzene.

The reaction of [Ni(MesIm)] () (MesIm = 1,3-dimesityl-imidazolin-2-ylidene) with polyfluorinated arenes as well as mechanistic investigations concerning the insertion of and [Ni(PrIm)] () (PrIm = 1,3-diisopropyl-imidazolin-2-ylidene) into the C-F bond of CF is reported. The reaction of with different fluoroaromatics leads to formation of the nickel fluoroaryl fluoride complexes -[Ni(MesIm)(F)(Ar)] (Ar = 4-CF-CF , CF , 2,3,5,6-CFN , 2,3,5,6-CFH , 2,3,5-CFH , 3,5-CFH ) in fair to good yields with the exception of the formation of the pentafluorophenyl complex (less than 20%). Radical species and other diamagnetic side products were detected for the reaction of with CF, in line with a radical pathway for the C-F bond activation step using .

Imino(silyl)disilenes: application in versatile bond activation, reversible oxidation and thermal isomerization.

Two novel disilenes of type ABSi[double bond, length as m-dash]SiAB bearing N-heterocyclic imino (A = NItBu) and trialkylsilyl (B = SitBu31, B = SitBu2Me 2) groups are reported. The reduced steric demand in 2 results in a highly stable, nonetheless flexible system, wherefore (E/Z) isomerization is observed from room temperature up to 90 °C. The proposed isomerization mechanism proceeds via monomeric silylenes in line with experimental results.

1-Aza-2,4-disilabicyclo[1.1.0]butanes with Superelongated C-N σ-Bonds.

Two silylene molecules oxidatively react under formal [1 + 2 + 1]-cycloaddition to the C≡N bond of nitriles to yield 1-aza-2,4-disilabicyclo[1.1.0]butanes (L)(Cl)Si[μ-η-NC(-RCH)]Si(Cl)(L) (L = PhC(NBu), R = CF (), F (), Cl (), Br ()).

A Stable N-Heterocyclic Silylene with a 1,1'-Ferrocenediyl Backbone.

The N-heterocyclic silylene [{Fe(η -C H -NDipp) }Si] (1DippSi, Dipp=2,6-diisopropylphenyl) shows an excellent combination of pronounced thermal stability and high reactivity towards small molecules. It reacts readily with CO and N O, respectively affording (1DippSiO ) C and (1DippSiO) as follow-up products of the silanone 1DippSiO. Its reactions with H O, NH , and FcPH (Fc=ferrocenyl) furnish the respective oxidative addition products 1DippSi(H)X (X=OH, NH , PHFc).