A Crystalline Unsupported Phosphagallene and Phosphaindene.

The synthesis and isolation of TerP═GaTer and TerP═InTer (Ter = 2,6-Dipp-CH; Dipp = 2,6-diisopropylphenyl) is reported. These compounds feature unsupported P═Ga and P═In double bonds and two-coordinate triel element centers. Key to the stabilization of such compounds is the steric bulk of the terphenyl substituents, which serve to shield the highly reactive P═E bonds (E = Ga, In) and prevent further aggregation.

A Transient Iron Carbide Generated by Cyaphide Cleavage.

Despite their potential relevance as molecular models for industrial and biological catalysis, well-defined mononuclear iron carbide complexes are unknown, in part due to the limited number of appropriate C synthons. Here, we show the ability of the cyaphide anion (C≡P) to serve as a C source. The high spin ( = 2) cyaphide complex PhB(BuIm)Fe-C≡P (PhB(BuIm) = phenyl(tris(3--butylimidazol-2-ylidene)borate) is readily accessed using the new cyaphide transfer reagent [Mg(NacNac)(CP)] (NacNac = CH{C(CH)N(Dipp)} and Dipp = 2,6-di(iso-propyl)phenyl).

Supramolecular Control of Helicene Circularly Polarized Luminescence Emitters in Molecular Solids and Bright Nanoparticles.

Circularly polarized luminescence (CPL) from chiral molecules is attracting much attention due to its potential use in optical materials. However, formulation of CPL emitters as molecular solids typically deteriorates photophysical properties in the aggregated state leading to quenching and unpredictable changes in CPL behavior impeding materials development. To circumvent these shortcomings, a supramolecular approach can be used to isolate cationic dyes in a lattice of cyanostar-anion complexes that suppress aggregation-caused quenching and which we hypothesize can preserve the synthetically-crafted chiroptical properties.

Hydrogen atom abstraction by a high spin [Fe=S] complex.

Iron sulfur clusters are critical to a plethora of biological processes; however, little is known about the elementary unit of these clusters, namely the [Fe=S] fragment. Here, we report the synthesis and characterization of a terminal iron sulfido complex. Despite its high spin ( = 5/2) ground state, structural, spectroscopic, and computational characterization provide evidence for iron sulfur multiple bond character.

Isolation and characterization of a two-coordinate phosphinidene oxide.

Nitroso compounds, R-N=O, are common intermediates in organic synthesis, and are typically amenable to storage and manipulation at ambient temperature under aerobic conditions. By contrast, phosphorus-containing analogues, such as R-P=O (R = OH, CH, OCH, Ph), are extremely reactive and need to be studied in inert gas matrices at ultralow temperatures (3-15 K). These species are believed to be key intermediates in the degradation/combustion of organic phosphorus compounds, a class of chemicals that includes chemical warfare agents and flame retardants.

Cone Angles Quantify and Predict the Affinity and Reactivity of Anion Complexes between Trifluoroborates and Rigid Macrocycles.

Steric manipulation is a known concept in molecular recognition but there is currently no linear free energy relationship correlating sterics to the stability of receptor-anion complexes nor to the reactivity of the bound anion. By analogy to Tolman cone angles in cation coordination chemistry, we explore how to define and correlate cone angles of organo-trifluoroborates (R-BF ) to the affinities observed for cyanostar-anion binding. We extend the analogy to a rare investigation of the anion's reactivity and how it changes upon binding.

Trimethylsilyldiazomethane Disassembly at a Three-Fold Symmetric Iron Site.

The reaction of equimolar trimethylsilyldiazomethyllithium (LiTMSD) with high spin ( = 2) PhB(AdIm)FeCl (PhB(AdIm) = tris(3-adamantylimidazol-2-ylidene)phenylborate) affords the corresponding nitrilimido complex PhB(AdIm)Fe-N═N═C(SiMe). This complex can be converted to the thermodynamically more favorable -isocyanoamido isomer PhB(AdIm)Fe-C═N═N(SiMe) by reaction with an additional equivalent of LiTMSD. While the iron(II) complexes are four-coordinate, the diazomethane is bound side-on in the iron(I) congener PhB(AdIm)Fe(,'-κ-NC(H)Si(CH)).

Chiral π-Conjugated Double Helical Aminyl Diradical with the Triplet Ground State.

We report a neutral high-spin diradical of chiral -symmetric bis[5]diazahelicene with Δ ≈ 0.4 kcal mol, as determined by EPR spectroscopy/SQUID magnetometry. The diradical is the most persistent among all high-spin aminyl radicals reported to date by a factor of 20, with a half-life of up to 6 days in 2-MeTHF at room temperature.

A library of vinyl phosphonate anions dimerize with cyanostars, form supramolecular polymers and undergo statistical sorting.

Supramolecular dimers are elementary units allowing the build-up of multi-molecule architectures. New among these are cyanostar-stabilized dimers of phosphate and phosphonate anions. While the anion dimerization at the heart of these assemblies is reliable, the covalent synthesis leading to this class of designer anions serves as a bottleneck in the pathway to supramolecular assemblies.

Solvent Acts as the Referee in a Match-Up Between Charged and Preorganized Receptors.

The prevalence of anion-cation contacts in biomolecular recognition under aqueous conditions suggests that ionic interactions should dominate the binding of anions in solvents across both high and low polarities. Investigations of this idea using titrations in low polarity solvents are impaired by interferences from ion pairing that prevent a clear picture of binding. To address this limitation and test the impact of ion-ion interactions across multiple solvents, we quantified chloride binding to a cationic receptor after accounting for ion pairing.

Thermally Ultrarobust = 1/2 Tetrazolinyl Radicals: Synthesis, Electronic Structure, Magnetism, and Nanoneedle Assemblies on Silicon Surface.

Open-shell organic molecules, including = 1/2 radicals, may provide enhanced properties for several emerging technologies; however, relatively few synthesized to date possess robust thermal stability and processability. We report the synthesis of = 1/2 biphenylene-fused tetrazolinyl radicals and . Both radicals possess near-perfect planar structures based on their X-ray structures and density-functional theory (DFT) computations.

Redox-Neutral Transformations of Carbon Dioxide Using Coordinatively Unsaturated Late Metal Silyl Amide Complexes.

Two-coordinate silylamido complexes of nickel and copper rapidly react with CO to selectively form a new cyanate ligand along with hexamethyldisiloxane byproducts. Mechanistic insight into these reactions was obtained from the synthesis of proposed intermediates, several silyl- and phenyl- substituted amido analogues, and their subsequent reactivity with CO. These studies suggest that a unique intramolecular double silyl transfer step facilitates CO deoxygenation, which likely contributes to the rapid rates of reaction.

Facile Addition of B-H and B-B Bonds to an Iron(IV) Nitride Complex.

The nitride ligand in the iron(IV) complex PhB(PrIm)Fe≡N reacts with boron hydrides to afford PhB(PrIm)FeN()H ( = 9-BBN (), Bpin ()) and with (Bpin) to afford PhB(PrIm)FeN(Bpin) (). The iron(II) borylamido products have all been structurally and spectroscopically characterized, demonstrating facile insertion into B-H and B-B bonds by PhB(PrIm)Fe≡N. Density functional theory (DFT) calculations reveal that the quintet state ( = 2) is significantly lower in energy than the singlet ( = 0) and triplet ( = 1) states for all products.

Defining Stereochemistry in the Polymerization of Lactide by Aluminum Catalysts: Insights into the Dual-Stereocontrol Mechanism.

Aspects of the proposed pathway combining chain-end and enantiomorphic site control for the stereospecific polymerization of lactide (LA) were investigated through studies of aluminum complexes supported by enantiopure and racemic bipyrrolidine-based salan ligands, LigAlOBn and LigAlOBn. Spectroscopic analysis of stoichiometric initiation reactions and the definition of the stereochemistry of the selective formation of the "match" single-insertion products by X-ray crystallography led to key conclusions about the observed stereocontrol. Notably, it was determined to rely heavily on the preference for the trio of stereocenters around the metal to have a "match" formation (-ligand + -polymer), which works synergistically with the enantiomorphic site preference of the catalyst to ring-open next to a stereocenter of a monomer of the same chirality as that of the ligand, resulting in highly heterotactic or syndiotactic PLA from - or -LA, respectively.

High-Spin = 3/2 Ground-State Aminyl Triradicals: Toward High-Spin Oligo-Aza Nanographenes.

We report high-spin aminyl triradicals with near-planar triphenylene backbones. Near-planarity of the fused aminyl radicals and the 2,6,10-triphenylene ferromagnetic coupling unit (FCU), magnetically equivalent to three fused 3,4'-biphenyl FCUs, assures an effective 2p-2p overlap within the cross-conjugated π-system, leading to an = 3/2 (quartet) ground state that is well separated from low-spin excited doublet states. Thermal populations of the low-spin ( = 1/2) excited states are detectable both by SQUID magnetometry and electron paramagnetic resonance (EPR) spectroscopy, providing doublet-quartet energy gaps, Δ, corresponding to >85% population of the quartet ground states at room temperature.

Ene Reactivity of an Fe═NR Bond Enables the Catalytic α-Deuteration of Nitriles and Alkynes.

Herein, we report the reactions of an Fe(II) imido complex [PhB(BuIm)Fe═NDipp] () with internal alkynes and isobutyronitrile, affording the Fe amido allenyl complexes [PhB(BuIm)Fe(NHDipp)((R)C═C═C(R)(H))] (R = Et or Pr; R = Me or Et, ) and the Fe amido keteniminate complex [PhB(BuIm)Fe(NHDipp)(N═C═CMe)K(THF)] (), respectively. These transformations represent the previously unknown ene-like reactivity of a metal-ligand multiple bond. Stoichiometric reactions of and with DippNH lead to the regeneration of 3-hexyne and isobutyronitrile, respectively, with concomitant formation of the bis(anilido) complex [PhB(BuIm)Fe(NHDipp)] ().

High-fidelity Recognition of Organotrifluoroborate Anions (R-BF ) as Designer Guest Molecules.

The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R-BF ). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R-BF , by cyanostar macrocycles that are size-complementary to the inorganic BF progenitors.

Effect of Au/HfS interfacial interactions on properties of HfS-based devices.

X-ray photoemission spectroscopy (XPS) has been used to examine the interaction between Au and HfS at the Au/HfS interface. XPS measurements reveal dissociative chemisorption of O, leading to the formation of an oxide of Hf at the surface of HfS. This surface hafnium oxide, along with the weakly chemisorbed molecular species, such as O and HO, are likely responsible for the observed p-type characteristics of HfS reported elsewhere.

High-Spin ( = 1) Blatter-Based Diradical with Robust Stability and Electrical Conductivity.

Triplet ground-state organic molecules are of interest with respect to several emerging technologies but usually show limited stability, especially as thin films. We report an organic diradical, consisting of two Blatter radicals, that possesses a triplet ground state with a singlet-triplet energy gap, Δ ≈ 0.4-0.

Alkali Metal Ions Dictate the Structure and Reactivity of an Iron(II) Imido Complex.

The presence of redox innocent metal ions has been proposed to modulate the reactivity of metal ligand multiple bonds; however, insight from structure/function relationships is limited. Here, alkali metal reduction of the Fe(III) imido complex [PhB(BuIm)Fe═NDipp] () provides the series of structurally characterized Fe(II) imido complexes [PhB(BuIm)Fe═NDippLi(THF)] (), [PhB(BuIm)Fe═NDippNa(THF)] (), and [PhB(BuIm)Fe═NDippK] (), in which the alkali metal cations coordinate the imido ligand. Structural investigations demonstrate that the alkali metal ions modestly lengthen the Fe═N bond distance from that in the charge separated complex [PhB(BuIm)Fe═NDipp][K(18-C-6)THF] (), with the longest bond observed for the smallest alkali metal ion.

Hydrocarbon Oxidation by an Exposed, Multiply Bonded Iron(III) Oxo Complex.

The iron oxo unit, [Fe=O] is a critical intermediate in biological oxidation reactions. While its higher oxidation states are well studied, relatively little is known about the least-oxidized form [Fe=O]. Here, the thermally stable complex PhB(AdIm)Fe=O has been structurally, spectroscopically, and computationally characterized as a iron(III) oxo.

An Integrated View of Nitrogen Oxyanion Deoxygenation in Solution Chemistry and Electrospray Ion Production.

There has been an increasing interest in chemistry involving nitrogen oxyanions, largely due to the environmental hazards associated with increased concentrations of these anions leading to eutrophication and aquatic "dead zones". Herein, we report the synthesis and characterization of a suite of MNO complexes (M = Co, Zn: = 2, 3). Reductive deoxygenation of cobalt bis(nitrite) complexes with bis(boryl)pyrazine is faster for cobalt than previously reported nickel, and pendant O-bound nitrito ligand is still readily deoxygenated, despite potential implication of an isonitrosyl primary product.