: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Since the latter quarter of the twentieth century, main group chemistry has undergone significant advances. Power's timely review in 2010 highlighted the inherent differences between the lighter and heavier main group elements, and that the heavier analogues resemble transition metals as shown by their reactivity towards small molecules. In this concept article, we present an overview of the last 10 years since Power's seminal review, and the progress made for catalytic application. This examines the use of low oxidation state and/or low coordinate group 13 and 14 complexes towards small molecule activation (oxidative addition step in a redox based cycle) and how ligand design plays a crucial role in influencing subsequent reactivity. The challenge in these redox based catalytic cycles still centres on the main group complexes’ ability to undergo reductive elimination, however considerable progress in this field has been reported via reversible oxidative addition reactions. Within the last 5 years the first examples of well‐defined low valent main group catalysts have begun to emerge, representing a bright future ahead for main group chemistry.

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The Road Travelled: After Main‐Group Elements as Transition Metals

The concerted action of a Lewis acid and base can activate H2 and other small molecules. Such frustrated Lewis pairs (FLPs) have garnered much attention and prompted many investigations into the activation of small molecules and catalysis. Although the nature, mechanism of action, and range of FLP systems continues to expand, this concept has also inspired ever-widening chemistry. Applications in hydrogenation and polymerization catalysis, as well as in synthetic chemistry, have provided selective processes and metal-free protocols. Heterogeneous FLP catalysts are emerging, and polymeric FLPs offer avenues to unique materials and strategies for sensing and carbon capture. The prospects for further impact of this remarkably simple reaction paradigm are considered.

New Directions for Frustrated Lewis Pair Chemistry

The development of new or more sustainable, active, efficient, controlled, and selective polymerization reactions or processes continues to be crucial for the synthesis of important polymers or materials with specific structures or functions. In this context, the newly emerged polymerization technique enabled by main-group Lewis pairs (LPs), termed as Lewis pair polymerization (LPP), exploits the synergy and cooperativity between the Lewis acid (LA) and Lewis base (LB) sites of LPs, which can be employed as frustrated Lewis pairs (FLPs), interacting LPs (ILPs), or classical Lewis adducts (CLAs), to effect cooperative monomer activation as well as chain initiation, propagation, termination, and transfer events. Through balancing the Lewis acidity, Lewis basicity, and steric effects of LPs, LPP has shown several unique advantages or intriguing opportunities compared to other polymerization techniques and demonstrated its broad polar monomer scope, high activity, control or livingness, and complete chemo- or...

Polymerization of Polar Monomers Mediated by Main-Group Lewis Acid-Base Pairs.

Sodium phosphaethynolate, Na(OCP), reacts as a P− transfer reagent with the imidazolium salt [DippNHC–H][Cl] [DippNHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] to give the parent phosphinidene–carbene adduct, DippNHCPH, with the loss of CO. In a less atom economic reaction, the cage compound, P7(TMS)3 (TMS = SiMe3) reacts likewise with the imidazolium salt to yield DippNHCPH thereby giving two entry points into parent phosphinidene-based chemistry. From the building block DippNHCPH, the carbene-supported P3 cation [(DippNHC)2(μ-P3)][Cl] was rationally synthesized using half an equivalent of PCl3 in the presence of DABCO (1,4-diazabicyclo[2.2.2]octane). The corresponding arsenic analogue, [(DippNHC)2(μ-PAsP)][Cl], was synthesized in the same manner using AsCl3. The reduction of both [(DippNHC)2(μ-P3)][Cl] and [(DippNHC)2(μ-PAsP)][Cl] into their corresponding neutral radical species was achieved simply by reducing the compounds with an excess of magnesium. This allowed the electronic structures of the compounds to be investigated using a combination of NMR and EPR spectroscopy, X-ray crystallography, and computational studies. The findings of the investigation into (DippNHC)2(μ-P3) and (DippNHC)2(μ-PAsP) reveal the central pnictogen atom in both cases as the main carrier of the spin density (∼60%), and that they are best described as the P3 or PAsP analogues of the elusive allyl radical dianion. The phosphorus radical was also able to undergo a cycloaddition with an activated acetylene, followed by an electron transfer to give the ion pair [(DippNHC)2(μ-P3)][P3(C(COOMe))2].

Sodium phosphaethynolate, Na(OCP), as a “P” transfer reagent for the synthesis of N-heterocyclic carbene supported P3 and PAsP radicals

There is a clear and pressing need to better manage our planet's resources. Phosphorus is a crucial element for life, but the natural phosphorus cycle has been perturbed to such an extent that humanity faces two dovetailing problems: the dwindling supply of phosphate rock as a resource, and the overabundance of phosphate in water systems leading to eutrophication. This Tutorial Review will explore the current routes to industrial phosphorus compounds, and innovative academic routes towards accessing these same products in a more sustainable manner. It will then describe the many ways that useful phosphate can be recovered from waste streams, and how it can be recycled and used as a resource for new products. Finally, we will briefly discuss the barriers that have thus far prevented the widespread adoption of these technologies, and how we can close the loop to establish a modern phosphorus cycle.

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Phosphorus recovery and recycling - closing the loop.

Hip to be square: Direct carbonylation of solutions of the heptaphosphide trianion (P7(3-)) afforded the phosphaethynolate anion in moderate yields. This species undergoes [2+2] cycloaddition reactions with diphenylketene and bis(2,6-diisopropylphenyl)carbodiimide to yield the anionic four-membered heterocycles P[C(O)]2C(C6H5)2(-) and PC(O)(CNDipp)NDipp(-) .

The 2-Phosphaethynolate Anion: A Convenient Synthesis and [2+2] Cycloaddition Chemistry†

The global electrophilicity index, GEI, is used as a general, quantitative and base-independent metric of Lewis acidity. This parameter has been benchmarked against the established fluoride ion affinity, FIA, for a range of 22 neutral and cationic Lewis acids from across the p-block, including boranes, trityl derivatives, phosphonium cations and sulfoxonium cations. As a demonstration of utility, the GEI is used to catalogue a library of fluoroaryl boranes as it provides a rapid tool for the comparison of a series of Lewis acids featuring peripheral substituent variation.

The global electrophilicity index as a metric for Lewis acidity.

Reactions of the 2-phosphaethynolate anion (PCO–, 1) with ammonium salts quantitatively yielded phosphinecarboxamide (PH2C(O)NH2, 2). The molecular structure and chemical properties of 2 were studied by single-crystal X-ray diffraction and multielement NMR spectroscopy. This phosphorus-containing analogue of urea is a rare example of an air-stable primary phosphine.

Andrew R. Jupp

Papers

New Directions for Frustrated Lewis Pair Chemistry

Phosphorus recovery and recycling - closing the loop.

The 2-Phosphaethynolate Anion: A Convenient Synthesis and [2+2] Cycloaddition Chemistry†

The global electrophilicity index as a metric for Lewis acidity.

Phosphinecarboxamide: a phosphorus-containing analogue of urea and stable primary phosphine.