Taming phosphorus mononitride

Pnictogen-Rich Heterocycles Derived from a Phosphadiazonium Cation

Heterocycles that pair main group elements and nitrogen are extremely important within the π-conjugated heterocycles research community. Compared to the vast number of boron-nitrogen heterocycles, those that include phosphorus are less common. Furthermore, the use of phosphorus-nitrogen triple bonds of any type to prepare such compounds is unprecedented. Here, we pair pyridyl hydrazonide ligands with phosphadiazonium cations and demonstrate that the chelated Mes*NP group is directly implicated in the photophysical and redox properties observed for the resulting heterocycles. In doing so, we introduce a novel building block for the production of phosphorus-containing heterocycles that could find use in small molecule activation and catalysis or as the functional component of emerging organic electronics.

Chemoselective Staudinger Reactivity of Bis(azido)phosphines Supported with a π-Donating Imidazolin-2-iminato Ligand

Synthesis and characterization of new P(III) and P(V) bis(azido)phosphines/phosphoranes supported by an N,N'-bis(2,6-diisopropylphenyl) imidazolin-2-iminato (IPrN) ligand and their reactivity with various secondary and tertiary phosphines result in the formation of chiral and/or asymmetric mono(phosphinimino)azidophosphines via the Staudinger reaction. The reaction of IPrNP(N3)2 (2) or IPrNP(S)(N3)2 (4S) with an excess of tertiary phosphine resulted in the chemoselective formation of IPrNP(N3)(NPMe3) (7) or IPrNP(S)N3(NPR3) (5R), respectively. The chemoselective Staudinger reactivity was also observed in reactions using a secondary phosphine (HPCy2) to produce IPrNP(S)N3[NP(H)Cy2] (6a), which exists in equilibrium with a tautomeric IPrNP(S)N3[N(H)PCy2] form (6b), as confirmed by 31P-31P nuclear Overhauser effect spectroscopy (NOESY). Density functional theory (DFT) calculations point to a combination of energetically unfavorable lowest unoccupied molecular orbitals (LUMOs) and the accumulation of increasing negative charge at the terminal azido-nitrogen upon a single azide-to-phosphinimine conversion that gave rise to the observed chemoselectivity.

Synthesis of Carbene-Stabilized PNPN Fragments and Their Carbene-Dependent Redox Properties

Herein, we report the synthesis of carbene-stabilized 1,3-diaza-2,4-diphosphabutenes CAACMePNPNCAACMe 4CAAC (CAACMe = 1-[2,6-bis(isopropyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene) and IPrPNPNIPr 4NHC (IPr = 1,3-Bis(2,6-diisopropylphenyl)-imidazol-2-ylidene). The bonding in both systems is defined by a delocalized polar covalent π-system, with 4NHC exhibiting increased conjugation relative to 4CAAC. The nature of the stabilizing carbene also influences the redox properties of the compound, with 4CAAC undergoing potassium-mediated reduction to the closed-shell P-P bonded dimer K252, which upon treatment with Kryptofix-2,2,2 converts to the transient radical anion [Kcrypt][5], the formal one-electron reduction product of 4CAAC. In contrast, 4NHC undergoes reversible one-electron oxidation to the stable radical cation [6NHC][SbF6]. Computational and spectroscopic analyses of both radical species are suggestive of unevenly delocalized spin, with the bulk of the spin density residing on phosphorus in both cases.

A Ruthenophosphanorcaradiene as a Synthon for an Ambiphilic Metallophosphinidene

Reaction of the ruthenium carbene complex Cp*(IPr)RuCl (1) (IPr = 1,3-bis(Dipp)imidazol-2-ylidene; Dipp = 2,6-diisopropylphenyl) with sodium phosphaethynolate (NaOCP) led to intramolecular dearomatization of one of the Dipp substituents on the Ru-bound carbene to afford a Ru-bound phosphanorcaradiene, 2. Computations by DFT reveal a transition state characterized by a concerted process whereby CO migrates to the Ru center as the P atom adds to the π system of the aryl group. The phosphanorcaradiene possesses ambiphilic properties and reacts with both nucleophilic and electrophilic substrates, resulting in rearomatization of the ligand aryl group with net P atom transfer to give several unusual metal-bound, P-containing main-group moieties. These new complexes include a metallo-1-phospha-3-azaallene (Ru─P═C═NR), a metalloiminophosphanide (Ru─P═N─R), and a metallophosphaformazan (Ru─P(═N─N═CPh2)2). Reaction of 2 with the carbene 2,3,4,5-tetramethylimidazol-2-ylidene (IMe4) produced the corresponding phosphaalkene DippP═IMe4.

Prediction of vibrational spectrum and thermodynamic properties for phosphorus mononitride

In this work, an accurate potential energy curve (PEC) for the ground electronic state of phosphorus mononitride (PN) molecule has been determined from a variationally improved Hulburt-Hirschfelder (VIHH) oscillator model in conjunction with the experimental spectral constants (De,ωe,ωexe,Be,αe,re). We have numerically solved the Schrödinger equation for the VIHH potential using the LEVEL program, obtaining the pure vibrational spectrum that converges to the dissociation limit. In addition, the partition functions of PN molecule are calculated using the full rovibrational energies. Ultimately, thermodynamic properties like molar heat capacity, entropy, enthalpy, and Gibbs free energy were calculated for the PN molecule and show good agreement with those data from the NIST (National Institute of Standards and Technology) database.

Synthesis and Reactivity of Hetero-Pnictogen Diazonium Analogs Stabilized by Transition Metal Units

The reactivity of the mixed dipnictogen complexes [{CpMo(CO)2 }2 (μ,η2 : 2 -PE)] (E=P, As, Sb) towards different group 14 electrophiles is reported. The resulting library of cationic compounds [{CpMo(CO)2 }2 (μ,η2 : 2 -EPR)]+ (R=Mes (2,4,6-C6 H2 Me3 ), CH3 , CPh3 , SnMe3 ) represents formally inorganic diazonium homologs which are stabilized by transition metal units. Modifying the steric and electronic properties of the electrophile drastically impacts the respective P-R bond lengths and is accompanied by increasing (SnMe3 >CPh3 >CH3 ) dynamic behavior in solution. In contrast to the well-studied organic analogs, the prepared compounds are stable at room temperature. The subsequent reaction of the model substrate [{CpMo(CO)2 }2 (μ,η2 : 2 -P2 Me)][OTf] ([OTf]- =[CF3 SO3 ]- ) with different N-heterocyclic carbenes (NHCs) leads to an addition at the unsubstituted P atom which is also predicted by computational methods. NMR spectroscopy confirms the formation of two isomers sync/gauche-[{CpMo(CO)2 }(μ,η2 : 1 -P(NHC)PMe){CpMo(CO)2 }][OTf]. X-ray crystallographic characterization and additional DFT calculations shed light on the spatial arrangement as well as on the possible formation pathways of the isomers.

Cooperative bond activations by a tucked-in iron complex

Herein, we report the first example of a 'tucked-in' iron diphosphine complex, formed through deprotonation of a Cp*-(CH̲3) (Cp* = C5Me5-) group by n-butyllithium. The reactivity of this complex was demonstrated by activation of organic and metal-containing substates, including CO2, benzaldehyde, Br-AuI-PPh3, B(C6F5)3, and HBCy2 (Cy = cyclohexyl).

Reactions of main group compounds with azides forming organic nitrogen-containing species

Since the seminal discovery of phenyl azide by Grieß in 1864, a variety of organic azides (R-N3) have been developed and extensively studied. The amenability of azides to a number of reactions has expanded their utility as building blocks not only in organic synthesis but also in bioorthogonal chemistry and materials science. Over the decades, it has been demonstrated that the reactions of main group compounds with azides lead to diverse N-containing main group molecules. In view of the pronounced progress in this area, this review summarizes the reactions of main group compounds with azides, emphatically introducing their reaction patterns and mechanisms. The reactions of forming inorganic nitrogen species are not included in this review.

Uranium-Mediated Peroxide Activation and a Precursor toward an Elusive Uranium cis-Dioxo Fleeting Intermediate

The activation of chalcogen-chalcogen bonds using organometallic uranium complexes has been well documented for S-S, Se-Se, and Te-Te bonds. In stark contrast, reports concerning the ability of a uranium complex to activate the O-O bond of an organic peroxide are exceedingly rare. Herein, we describe the peroxide O-O bond cleavage of 9,10-diphenylanthracene-9,10-endoperoxide in nonaqueous media, mediated by a uranium(III) precursor [((^Me,AdArO)₃N)U^III(dme)] to generate a stable uranium(V) bis-alkoxide complex, namely, [((^Me,AdArO)₃N)U^V(DPAP)]. This reaction proceeds via an isolable, alkoxide-bridged diuranium(IV/IV) species, implying that the oxidative addition occurs in two sequential, single-electron oxidations of the metal center, including rebound of a terminal oxygen radical. This uranium(V) bis-alkoxide can then be reduced with KC₈ to form a uranium(IV) complex, which upon exposure to UV light, in solution, releases 9,10-diphenylanthracene to generate a cyclic uranyl trimer through formal two-electron photooxidation. Analysis of the mechanism of this photochemical oxidation via density functional theory (DFT) calculations indicates that the formation of this uranyl trimer occurs through a fleeting uranium cis-dioxo intermediate. At room temperature, this cis-configured dioxo species rapidly isomerizes to a more stable trans configuration through the release of one of the alkoxide ligands from the complex, which then goes on to form the isolated uranyl trimer complex.

Frustrated Lewis Pair Adduct of Atomic P(-1) as a Source of Phosphinidenes (PR), Diphosphorus (P2 ), and Indium Phosphide

We report phosphinidenes (PR) stabilized by an intramolecular frustrated Lewis pair (FLP) chelate. These adducts include the parent phosphinidene, PH, which is accessed via thermolysis of coordinated HPCO. The reported FLP-PH species acts as a springboard to other phosphorus-containing compounds, such as FLP-adducts of diphosphorus (P₂ ) and InP₃ . Our new adducts participate in thermal- or light-induced phosphinidene elimination (of both PH and PR, R=organic group), transfer P₂ units to an organic substrate, and yield the useful semiconductor InP at only 110 °C from solution.

Synthesis of phosphiranes via organoiron-catalyzed phosphinidene transfer to electron-deficient olefins

Herein is reported the structural characterization and scalable preparation of the elusive iron-phosphido complex FpP( t Bu)(F) (2-F, Fp = (Fe(η5-C5H5)(CO)2)) and its precursor FpP( t Bu)(Cl) (2-Cl) in 51% and 71% yields, respectively. These phosphide complexes are proposed to be relevant to an organoiron catalytic cycle for phosphinidene transfer to electron-deficient alkenes. Examination of their properties led to the discovery of a more efficient catalytic system involving the simple, commercially available organoiron catalyst Fp2. This improved catalysis also enabled the preparation of new phosphiranes with high yields ( t BuPCH2CHR; R = CO2Me, 41%; R = CN, 83%; R = 4-biphenyl, 73%; R = SO2Ph, 71%; R = POPh2, 70%; R = 4-pyridyl, 82%; R = 2-pyridyl, 67%; R = PPh3 +, 64%) and good diastereoselectivity, demonstrating the feasibility of the phosphinidene group-transfer strategy in synthetic chemistry. Experimental and theoretical studies suggest that the original catalysis involves 2-X as the nucleophile, while for the new Fp2-catalyzed reaction they implicate a diiron-phosphido complex Fp2(P t Bu), 4, as the nucleophile which attacks the electron-deficient olefin in the key first P-C bond-forming step. In both systems, the initial nucleophilic attack may be accompanied by favorable five-membered ring formation involving a carbonyl ligand, a (reversible) pathway competitive with formation of the three-membered ring found in the phosphirane product. A novel radical mechanism is suggested for the new Fp2-catalyzed system.

Ligand-stabilized heteronuclear diatomics of group 13 and 15

A theoretical investigation of ligand-stabilized MX diatomics (M = group 13, X = group 15 element) with N-heterocyclic carbene (NHC) ligands has been carried out to assess bonding and electronic structure. Binding of two ligands in the form L-MX-L is generally preferred over binding of a single ligand as L-MX or MX-L. Binding of carbene donor ligands is predicted to be thermodynamically favorable for all the systems, and is very favorable for the lighter group 15 systems (nitrogen and phosphorus). Detailed analysis of the bonding in these complexes has been carried out with energy decomposition analysis (EDA). In all cases, the carbene to boron and carbene to nitrogen bonding is described as an electron-sharing double bond with both σ and π bonding interactions. For the heavier elements, bonding to C (except for PC interactions) is best described as a donor-acceptor σ single bond.