Influence of Pnictogen and Ligand Framework on the Lewis Acidity and Steric Environment in Pnictogen Pincer Complexes.

Pnictogen pincer complexes are a fascinating class of compounds due to their dynamic molecular and electronic structures, and valuable stoichiometric or catalytic reactivity. As recognition of their unique chemistry has grown, so too has the library of pincer ligands employed and pnictogen centres engaged to prepare them. Here we computationally study how the choice of pincer ligand framework and pnictogen influence the electronic and steric outcomes within the complexes obtained.

Why Are Some Pnictogen(III) Pincer Complexes Planar and Others Pyramidal?

Geometrically-constrained pnictogen pincer complexes have emerged in recent years as platforms for unique stoichiometric and catalytic chemical transformations. These complexes feature dynamic conformations ranging from fully planar at the pnictogen centre to distorted-pyramidal geometries, as well as variation between phases. Although the valued reactivity of pnictogen pincer complexes is ascribed to their geometries, there is no unified model to explain the observed conformational outcomes across different ligands and pnictogen centres.

Rigid PN cages as 3-dimensional building blocks for crystalline or amorphous networked materials.

Three-dimensional covalent connectors are valuable synthons for accessing crystalline or amorphous networks. Currently, fused polycyclic alkanes are employed as connectors in this context. We debut phosphorus-nitrogen (PN) cages as new 3-dimensional (3-D) inorganic connectors that yield crystalline and amorphous networks, including examples with gas porosity.

Ligand-enforced geometric constraints and associated reactivity in p-block compounds.

The geometry at an element centre can generally be predicted based on the number of electron pairs around it using valence shell electron pair repulsion (VSEPR) theory. Strategies to distort p-block compounds away from these predicted geometries have gained considerable interest due to the unique structural outcomes, spectroscopic properties or reactivity patterns engendered by such distortion. This review presents an up-to-date group-wise summary of this exciting and rapidly growing field with a focus on understanding how the ligand employed unlocks structural features, which in turn influences the associated reactivity.

An Improved Synthesis of PN-adamantanoid Cages P (NR) and a Mechanistic Study of their Fourfold Oxidation.

Phosphorus-nitrogen (PN) adamantanoid cages are valuable precursors for materials chemistry, but their syntheses are based on harsh methods that sometimes require access to restricted reagents. We report a new and scalable synthesis of PN adamantanoid compounds by chlorosilane elimination between bis-silylated amines and phosphorus trichloride. We further study the mechanism of the recently-reported four-fold oxidation of such cages with Me SiN to yield tetravalent tetrahedral connectors for materials chemistry.

A Robust, Divalent, Phosphaza-bicyclo[2.2.2]octane Connector Provides Access to Cage-Dense Inorganic Polymers and Networks.

While polymers containing chain or ring motifs in their backbone are ubiquitous, those containing well-defined molecular cages are very rare and essentially unknown for the inorganic elements. We report that a rigid and dinucleophilic cage (PNSiMe)(NMe), which is chemically robust and accessible on a multi-gram scale from commercial precursors, serves as a linear and divalent connector that forms cage-dense inorganic materials. Reaction of the cage with various ditopic P(III) dihalide comonomers proceeded via MeSiCl elimination to give high molecular weight (30 000-70 000 g mol), solution-processable polymers that form free-standing films.

Ambient Temperature Carbene-Mediated Depolymerization: Stoichiometric and Catalytic Reactions of -Heterocyclic- and Cyclic(Alkyl)Amino Carbenes with Poly(-Methylaminoborane) [MeNH-BH].

The reactions of the -heterocyclic carbenes (NHCs) IDipp and IBu and the cyclic(alkyl)amino carbene (CAAC) CAAC with polyaminoborane [MeNH-BH] were investigated. Stoichiometric quantities of each carbene were found to cause rapid and complete depolymerization, with the major B-N-containing product identified as the NHC-aminoborane adduct, IDipp-BHNMeH (), cyclic borazane [MeNH-BH], or borazine [MeNBH] with IDipp, IBu, and CAAC, respectively. With substoichiometric quantities of IDipp and IBu (down to 10 and 2.

Mesomeric Tuning at Planar Bi centres: Unexpected Dimerization and Benzyl C-H Activation in [CN ]Bi Complexes.

Planar bismuth(III) compounds featuring a N -pincer ligand environment are an unusual class of main group compounds that exhibit Lewis acidity via a 6p orbital. The ability to tune their acidity via Hammett and Coulomb effects has been demonstrated previously. Here we test the ability to tune them via mesomeric effects by replacing the central nitrogen of the [N ] pincer ligand with a less π-donating carbon atom to achieve a [CN ] ligand environment.

An International Study Evaluating Elemental Analysis.

Based on statistical analysis of CHN combustion results of 18 international service providers, it is determined that the ±0.4% deviation most commonly required by chemistry journals is not justified.

(PNSiMe ) (NMe) : A Robust Tetravalent Phosphaza-adamantane Scaffold for Molecular and Macromolecular Construction.

Tetraarylmethanes and adamantanes are important rigid covalent connectors that play a four-way scaffolding role in molecular and materials chemistry. We report the synthesis of a new tetravalent phosphaza-adamantane cage, (PNSiMe ) (NMe) (2), that shows high thermal, air, and redox stability due to its geometry. It nevertheless participates in covalent four-fold functionalization reactions along its periphery.

Hydrostibination of Alkynes: A Radical Mechanism*.

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates.

Squeezing Bi: PNP and PN pincer complexes of bismuth.

We report the first application of a rigid P2N3 pincer ligand in p-block chemistry by preparing its bismuth complex. We also report the first example of bismuth complexes featuring a flexible PNP pincer ligand, which shows phase-dependent structural dynamics. Highly electrophilic, albeit thermally unstable, Bi(iii) complexes of the PNP ligand were also prepared.

Bismuthanylstibanes.

Thermally-robust bismuthanylstibanes are prepared in a one-step, high yield reaction, providing the first examples of neutral Bi-Sb σ-bonds in the solid state. DFT calculations indicate that the bis(silylamino)naphthalene scaffold is well-suited for supporting otherwise labile bonds. The reaction chemistry of the Bi-Sb bond is debuted by showing fission using NHBH and insertion of a sulfur atom, the latter providing the first example of a Bi-S-Sb motif.

Hydrostibination.

A rigid naphthalenediamine framework has been used to prepare antimony hydrides that feature LUMO shapes and energies similar to those found in secondary boranes. By exploiting this feature, we introduce the first examples of uncatalyzed hydrostibination reactions of robust C≡C, C=C, C=O, and N=N bonds as new elementary hydrometalation reactions analogous to hydroboration. These results endorse the notion of a diagonal relationship between the lightest p-block element and the heaviest Group 15 elements and may lead to the conception of novel reaction chemistry.

Photolytic, radical-mediated hydrophosphination: a convenient post-polymerisation modification route to P-di(organosubstituted) polyphosphinoboranes [RR'PBH] .

Polymers with a phosphorus-boron main chain have attracted interest as novel inorganic materials with potentially useful properties since the 1950s. Although examples have recently been shown to be accessible several routes, the materials reported so far have been limited to P-mono(organosubstituted) materials, [RHPBH] , containing P-H groups. Here we report a general route for the post-polymerisation modification of such polyphosphinoboranes giving access to a large range of previously unknown examples featuring P-disubstituted units.

Periodicity in Structure, Bonding, and Reactivity for p-Block Complexes of a Geometry Constraining Triamide Ligand.

The use of pincer ligands to access non-VSEPR geometries at main-group centers is an emerging strategy for eliciting new stoichiometric and catalytic reactivity. As part of this effort, several different tridentate trianionic substituents have to date been employed at a range of different central elements, providing a patchwork dataset that precludes rigorous structure-function correlation. An analysis of periodic trends in structure (solid, solution, and computation), bonding, and reactivity based on systematic variation of the central element (P, As, Sb, or Bi) with retention of a single tridentate triamide substituent is reported herein.

P(v) dications: carbon-based Lewis acid initiators for hydrodefluorination.

The P(iii) dication [(terpy)PPh] is oxidized by reaction with o-chloranil or 9,10-phenanthrenequinone to give the P(v) dications [(terpy)(CClO)PPh] and [(terpy)(CHO)PPh], respectively. These species are coordinatively saturated at phosphorus and yet display the ability to effect Lewis acid initiation of hydrodefluorination of fluoroalkanes. Experimental and computational data support the notion that the P(v) dications are Lewis acidic at the para-carbon of the central ring of the terpy ligand.

Carbonyl and olefin hydrosilylation mediated by an air-stable phosphorus(iii) dication under mild conditions.

The readily-accessible, air-stable Lewis acid [(terpy)PPh][B(C6F5)4]21 is shown to mediate the hydrosilylation of aldehydes, ketones, and olefins. The utility and mechanism of these hydrosilylations are considered.

Synthesis of a Perfluorinated Phenoxyphosphorane and Conversion to Its Hexacoordinate Anions.

We report the synthesis and structural characterization of a neutral P Lewis acid, P(OC F ) , and salts containing the six-coordinate anions [P(OC F ) F] and [P(OC F ) ] . The latter anion exhibits a rare example of F-π interactions in both the solid and the solution phase, which has been quantitatively studied by variable-temperature (VT) NMR spectroscopy. The Lewis acid strength of P(OC F ) has been assessed through experimental fluoride ion competition experiments and quantum-chemical calculations of its fluoride ion affinity (FIA) and global electrophilicity index (GEI).

A Redox-Confused Bismuth(I/III) Triamide with a T-Shaped Planar Ground State.

Reaction of a tethered triamine ligand with Bi(NMe ) gives a Bi triamide, for which a Bi electronic structure is shown to be most appropriate. The T-shaped geometry at bismuth provides the first structural model for edge inversion in bismuthines and the only example of a planar geometry for pnictogen triamides. Analogous phosphorus compounds exhibit a distorted pyramidal geometry because of different Bi-N and P-N bond polarities.

Metal-free dehydropolymerisation of phosphine-boranes using cyclic (alkyl)(amino)carbenes as hydrogen acceptors.

The divalent carbene carbon centre in cyclic (alkyl)(amino)carbenes (CAACs) is known to exhibit transition-metal-like insertion into E-H σ-bonds (E = H, N, Si, B, P, C, O) with formation of new, strong C-E and C-H bonds. Although subsequent transformations of the products represent an attractive strategy for metal-free synthesis, few examples have been reported. Herein we describe the dehydrogenation of phosphine-boranes, RR'PH·BH, using a CAAC, which behaves as a stoichiometric hydrogen acceptor to release monomeric phosphinoboranes, [RR'PBH], under mild conditions.

Synthesis of Urea Derivatives from CO and Silylamines.

A series of thirty-three N,N'-diaryl, dialkyl, and alkyl-aryl ureas have been prepared in pyridine or toluene by reaction of silylamines with CO . This protocol is shown to provide facile access to C-labeled ureas, as well as chiral and macrocyclic ureas. These reactions proceed through initial generation of the corresponding silylcarbamates, which subsequently react with silylamine under thermal conditions to afford the thermodynamically favored urea and disilyl ether.

Interactions of C-F Bonds with Hydridoboranes: Reduction, Borylation and Friedel-Crafts Alkylation.

The stoichiometric reactions of the alkylfluorides 1-fluoroadamantane (Ad-F), fluorocyclohexane (Cy-F), 1-fluoropentane (Pent-F) and benzyl fluorides with secondary boranes pinacolborane (HBpin), catecholborane (HBcat), 9-borabicyclo(3.3.1)nonane (9-BBN) and Piers' borane (HB(C F ) ) are described.

Catalytic Hydrodefluorination of C-F Bonds by an Air-Stable P Lewis Acid.

Catalytic hydrodefluorination (HDF) of unactivated fluoroalkanes or CF -substituted aryl species is performed using the P Lewis acids, [(bipy)PPh] (1 ) and [(terpy)PPh] (2 ) under mild conditions (25 or 50 °C). Mechanistic studies indicate that activation of C-F bond by the P center is key. Particularly noteworthy is that the catalyst 2[B(C F ) ] is air-stable and readily accessible from bench-stable, commercially available reagents in one-step and can be used without isolation.

Non-Metal-Catalyzed Heterodehydrocoupling of Phosphines and Hydrosilanes: Mechanistic Studies of B(CF)-Mediated Formation of P-Si Bonds.

Non-metal-catalyzed heterodehydrocoupling of primary and secondary phosphines (RRPH, R = H or R) with hydrosilanes (RRRSiH, R, R = H or R) to produce synthetically useful silylphosphines (RRP-SiRRR) has been achieved using B(CF) as the catalyst (10 mol %, 100 °C). Kinetic studies demonstrated that the reaction is first-order in hydrosilane and B(CF) but zero-order in phosphine. Control experiments, DFT calculations, and DOSY NMR studies suggest that a RRHP·B(CF) adduct is initially formed and undergoes partial dissociation to form an "encounter complex".