Ytterbium(II) Complex-Catalyzed Selective Single and Double Hydrophosphination of 1,3-Enynes

1,3-Enynes with conjugated alkene and alkyne moieties are attractive building blocks in synthetic chemistry. However, neither 4,1-hydrophosphination nor dihydrophosphination of 1,3-enynes has been reported. In this paper, the divalent ytterbium and calcium amide complexes supported by silaimine-functionalized cyclopentadienyl ligands (C5Me4-Si(L)=NR) were developed, which successfully catalyzed the efficient single and double hydrophosphination of 1,3-enynes with diarylphosphines. The hydrophosphination reactions selectively produced homoallenyl phosphines and (E)-propenylene diphosphines, respectively. This work demonstrated the potential of hemilabile silaimine-Cp ligands in the supporting the efficient and selective rare- and alkaline-earth catalysts.

Fluorenyl-tethered N-heterocyclic carbene (NHC): an exclusive C-donor ligand for heteroleptic calcium and strontium chemistry

Exclusive C-donating ligands are rarely used with kinetically labile heavier alkaline earths (Ca, Sr, Ba). We report herein the aptitude of a combination of NHC with fluorenyl connected by a flexible -(CH2)2- linker as a ligand support for heteroleptic Ca- and Sr-N(SiMe3)2 and iodides. The Ca-N(SiMe3)2 complex even catalyzes the intramolecular hydroamination of aminoalkenes to showcase the effectiveness of this ligand framework.

Cyclopentadienyl Complexes of the Alkaline Earths in Light of the Periodic Trends

The electron-rich cyclopentadienyl and the analogous indenyl and fluorenyl ligands (collectively denoted here as Cp') have been impactful in stabilizing electron-deficient metal centers including the highly electropositive alkaline earths. Being in the s-block, the group 2 metals follow a major periodic variation in their atomic and ionic properties which is reflected in those Cp' compounds. This article presents an overview of this class of compounds for all the five metals from beryllium to barium (radium is excluded for its radioactivity), highlighting their systematic variation.

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

Integration of oxygen vacancies into BiOI via a facile alkaline earth ion-doping strategy for the enhanced photocatalytic performance toward indometacin remediation

Bismuth oxyiodide (BiOI) has garnered intense attention in the field of photocatalysis for environmental remediation; however, it suffers from a high electron-hole recombination rate. In this study, for the first time, we report on a facile strategy for the creation of oxygen vacancies in BiOI via strontium (Sr²⁺) doping. The as-prepared 0.45-SrBiOI demonstrated significantly enhanced photocatalytic degradation of indometacin under visible light exposure, which was almost 10 folds higher than pristine BiOI. This augmented photocatalytic performance was ascribed to the accelerated separation of charge carriers by oxygen vacancies, as well as Sr ion trapping electrons. Reactive species determination experiments revealed that O₂^▪-, ¹O₂, and h⁺ were the dominant active species. Finally, potential indometacin degradation pathways were proposed based on the identification of degradation by-products and theoretical calculations. This study offers new perspectives for the synthesis of highly efficient and cost effective BiOI-based photocatalysts, and provides a promising strategy toward advanced environmental remediation.

Expected and Unexpected Reactivities of Homoleptic LiNacNac and Heteroleptic NacNacMg(TMP) β-Diketiminates toward Various Small Unsaturated Organic Molecules

Homoleptic LiNacNac forms simple donor-acceptor complexes with N,N'-dicyclohexylcarbodiimide (CyN═C═NCy), triphenylphosphine oxide (Ph₃P═O), and benzophenone (Ph₂CO). These crystallographically characterized compounds could be regarded as model intermediates en route to reducing the N═C, P═O, and C═O bonds of unsaturated substrates. Heteroleptic NacNacMg(TMP) intriguingly functions as a TMP nucleophile both with t-BuNCO and t-BuNCS, producing a urea or thiourea derivative respectively attached to Mg, though the NacNac ligand in the former reaction also engages noninnocently with a second t-BuNCO molecule via insertion at the reactive NacNac backbone γ-carbon site.

Calcium and Magnesium Bis(β-diketiminate) Complexes: Impact of the Alkylene Bridge on Schlenk-Type Rearrangements

Dinuclear heteroleptic alkaline-earth-metal complexes are interesting synthetic targets because the close proximity of two metals allows for cooperative effects. However, these complexes are also prone to undergoing Schlenk-type rearrangements, affording less-active homoleptic complexes. Here we present the metalation of bis(β-diketimine) ligands possessing flexible bridging groups, i.e., 1,2-ethylene, 1,3-propylene, and trans-1,2-cyclohexylene, using calcium and magnesium precursors. Four mononuclear homoleptic calcium complexes were obtained, highlighting the pronounced tendency of calcium to undergo Schlenk-like redistributions. In the case of magnesium, however, the bridging group plays a crucial role, yielding seven dinuclear heteroleptic complexes but also one mononuclear and one dinuclear homoleptic complexes. In addition, a trinuclear mixed heteroleptic-homoleptic magnesium complex, which is a rare example of an intermediate of the Schlenk equilibrium, was isolated.

Writing Your Next Medicinal Chemistry Article: Journal Bibliometrics and Guiding Principles for Industrial Authors

Writing scientific articles is immensely rewarding but challenging. This Perspective provides the medicinal chemist with background and advice on the art and process of writing manuscripts and complements the instructions to authors provided by journals. Included are many tips that we wish we had known when we first started writing. Bibliometric data from seven medicinal chemistry journals between 2000 and 2019 are collated including Bioorganic and Medicinal Chemistry Letters and the Journal of Medicinal Chemistry. Although the overall number of articles has doubled, the output from 23 large pharma companies in the past decade has dropped significantly. Commentary is given on the entire process of writing original scientific articles, opinion articles, and reviews. Examples from our own papers and experience are shared including what typically motivates the writer, challenges commonly encountered, and how we find time to write. Finally, the benefits derived from much wider publishing of industrial medicinal chemistry are described.

Main group bimetallic partnerships for cooperative catalysis

Over the past decade s-block metal catalysis has undergone a transformation from being an esoteric curiosity to a well-established and consolidated field towards sustainable synthesis. Earth-abundant metals such as Ca, Mg, and Al have shown eye-opening catalytic performances in key catalytic processes such as hydrosilylation, hydroamination or alkene polymerization. In parallel to these studies, s-block mixed-metal reagents have also been attracting widespread interest from scientists. These bimetallic reagents effect many cornerstone organic transformations, often providing enhanced reactivities and better chemo- and regioselectivities than conventional monometallic reagents. Despite a significant number of synthetic advances to date, most efforts have focused primarily on stoichiometric transformations. Merging these two exciting areas of research, this Perspective Article provides an overview on the emerging concept of s/p-block cooperative catalysis. Showcasing recent contributions from several research groups across the world, the untapped potential that these systems can offer in catalytic transformations is discussed with special emphasis placed on how synergistic effects can operate and the special roles played by each metal in these transformations. Advancing the understanding of the ground rules of s-block cooperative catalysis, the application of these bimetalic systems in a critical selection of catalytic transformations encompassing hydroamination, cyclisation, hydroboration to C-C bond forming processes are presented as well as their uses in important polymerization reactions.

Bismuth as Smart Material and Its Application in the Ninth Principle of Sustainable Chemistry

This paper reports an overview of Green Chemistry and the concept of its twelve principles. This study focusses on the ninth principle of Green Chemistry, that is, catalysis. A report on catalysis, in line with its definition, background, classification, properties, and applications, is provided. The study also entails a green element called bismuth. Bismuth’s low toxicity and low cost have made researchers focus on its wide applications in catalysis. It exhibits smartness in all the catalytic activities with the highest catalytic performance among other metals.

A Stable Calcium Alumanyl

A seven-membered N,N'-heterocyclic potassium alumanyl nucleophile is introduced and utilised in the metathetical synthesis of Mg-Al and Ca-Al bonded derivatives. Both species have been characterised by experimental and theoretical means, allowing a rationalisation of the greater reactivity of the heavier group 2 species implied by an initial assay of their reactivity.

A Stable Calcium Alumanyl

A seven‐membered N,N′‐heterocyclic potassium alumanyl nucleophile is introduced and utilised in the metathetical synthesis of Mg−Al and Ca−Al bonded derivatives. Both species have been characterised by experimental and theoretical means, allowing a rationalisation of the greater reactivity of the heavier group 2 species implied by an initial assay of their reactivity.

A versatile nitrogen ligand for alkaline-earth chemistry

A readily available and versatile bis(imino)carbazolate ligand is shown to allow for the synthesis of a broad range of solution stable heteroleptic complexes of the alkaline-earth metals Mg, Ca, Sr and Ba.

Recent advances in alkaline earth metal-enabled syntheses of heterocyclic compounds

This review summarizes recent progress in alkaline earth metal enabled syntheses of heterocyclic compounds.

Stepwise Reduction at Magnesium and Beryllium: Cooperative Effects of Carbenes with Redox Non-Innocent α-Diimines

In the past two decades, the organometallic chemistry of the alkaline earth elements has experienced a renaissance due in part to developments in ligand stabilization strategies. In order to expand the scope of redox chemistry known for magnesium and beryllium, we have synthesized a set of reduced magnesium and beryllium complexes and compared their resulting structural and electronic properties. The carbene-coordinated alkaline earth-halides, (^Et2CAAC)MgBr₂ (1), (SIPr)MgBr₂ (2), (^Et2CAAC)BeCl₂ (3), and (SIPr)BeCl₂ (4) [^Et2CAAC = diethyl cyclic(alkyl)(amino) carbene; SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazole-2-ylidene] were combined with an α-diimine [2,2-bipyridine (bpy) or bis(2,6-diisopropylphenyl)-1,4-diazabutadiene (^DippDAB)] and the appropriate stoichiometric amount of potassium graphite to form singly- and doubly-reduced compounds (^Et2CAAC)MgBr(^DippDAB) (5), (^Et2CAAC)MgBr(bpy) (6), (^Et2CAAC)Mg(^DippDAB) (7), (^Et2CAAC)Be(bpy) (8), and (SIPr)Be(bpy) (9). The doubly-reduced compounds 7-9 exhibit substantial π-bonding interactions across the diimine core, metal center, and π-acidic carbene. Each complex was fully characterized by UV-vis, FT-IR, X-ray crystallography, ¹H, ¹³C, and ⁹Be NMR, or EPR where applicable. We use these compounds to highlight the differences in the organometallic chemistry of the lightest alkaline earth metals, magnesium and beryllium, in an otherwise identical chemical environment.

Rare-Earth-Metal-Catalyzed Kinetic Resolution of Chiral Aminoalkenes via Hydroamination: The Effect of the Silyl Substituent of the Binaphtholate Ligand on Resolution Efficiency

The kinetic resolution of α-substituted aminopentenes via intramolecular hydroamination was investigated using various 3,3'-silyl-substituted binaphtholate yttrium catalysts. High efficiencies in the kinetic resolution were observed for methyl-, benzyl-, and phenyl-substituted substrates utilizing the cyclohexyldiphenylsilyl-substituted catalyst 2c with resolution factors reaching as high as 90(5) for hex-5-en-2-amine (3a). Kinetic analysis of the enantioenriched substrates with the matching and mismatching catalyst revealed that the efficiency of catalyst 2c benefits significantly from a favorable Curtin-Hammett pre-equilibrium and by a large kfast/kslow ratio. Other binaphtholate catalysts were less efficient due to a less favorable Curtin-Hammett pre-equilibrium, which often favored the mismatching substrate-catalyst combination. Cyclization of the matched substrate proceeds generally with large trans-selectivity, whereas the trans/cis-ratio for mismatched substrates is significantly diminished, favoring the cis-cyclization product isomer in some instances.

Calcium stannyl formation by organostannane dehydrogenation

Reaction of the dimeric calcium hydride, [(BDI)CaH]₂ (1), with Ph₃SnH ensues with elimination of H₂ to provide [(BDI)Ca-μ₂-H-(SnPh₃)Ca(BDI)] (3) and [(BDI)Ca(SnPh₃)]₂ (4) alongside dismutation to Ph₄Sn, H₂ and Sn(0).

Reduction of 1,3,5,7-cyclooctatetraene by a molecular calcium hydride: an even electron polarised insertion/deprotonation mechanism

The reductive aromatisation of 1,3,5,7-cyclooctatetraene by a dimeric calcium hydride occurs via two electron steps and does not necessitate the formation of radical intermediates.

Bis(trimethylsilyl)amide complexes of s-block metals with bidentate ether and amine ligands

The synthesis of the bis(trimethylsilyl)amide complexes of alkali and alkaline-earth metals with bidentate ether and amine bases 1,2-bis(dimethylamino)ethane (tmeda), dimethyl-methoxyethylamine (dmmea), and 1,2-dimethoxyethane (dme) succeedsviaaddition of these bases to coligand-free complexes orvialigand exchange of thf adducts.

Synthesis and catalytic activity of tridentate N-(2-pyridylethyl)-substituted bulky amidinates of calcium and strontium

Sterically protected tridentate amidinates of calcium have been prepared to study the intramolecular hydroamination of an aminoalkene.

Low-valent group 14 element hydride chemistry: towards catalysis

The chemistry of group 14 element(ii) hydride complexes has rapidly expanded since the first stable example of such a compound was reported in 2000. Since that time it has become apparent that these systems display remarkable reactivity patterns, in some cases mimicking those of late transition-metal (TM) hydride compounds. This is especially so for the hydroelementation of unsaturated organic substrates. Recently, this aspect of their reactivity has been extended to the use of group 14 element(ii) hydrides as efficient, "TM-like" catalysts in organic synthesis. This review will detail how the chemistry of these hydride compounds has advanced since their early development. Throughout, there is a focus on the importance of ligand effects in these systems, and how ligand design can greatly modify a coordinated complex's electronic structure, reactivity, and catalytic efficiency.

Amido Ca and Yb(II) Complexes Coordinated by Amidine-Amidopyridinate Ligands for Catalytic Intermolecular Olefin Hydrophosphination

A series of amido Ca and Yb(II) complexes LM[N(SiMe₃)₂](THF) (1Yb, 1-4Ca) coordinated by amidine-amidopyridinate ligands L^1-4 were synthesized via a transamination reaction between proligands L^1-4H and bisamido complexes M[N(SiMe₃)₂]₂(THF)₂ (M = Yb, Ca). The reactions of Yb[N(SiMe₃)₂]₂(THF)₂ with proligands L²H-L⁴H containing CF₃ and C₆H₄F fragments do not allow for preparing the target Yb(II) complexes, while the Ca analogues were synthesized in good yields. Complexes 1Yb and 1-4Ca were evaluated as precatalysts for hydrophosphination of styrene, p-substituted styrenes, α-Me-styrene, and 2,3-dimethylbutadiene with various primary and secondary phosphines (PhPH₂, 2,4,6-Me₃C₆H₂PH₂, 2-C₅NH₄PH₂, Ph₂PH, Cy₂PH). Complexes 1Yb, 1-4Ca performed high catalytic activities in styrene hydrophosphination with PhPH₂ and Ph₂PH and demonstrated high regioselectivity affording exclusively the anti-Markovnikov addition products. For primary PhPH₂ the reactions (1:1 molar ratio of substrates) catalyzed by 1Yb, 1Ca, and 2Ca proved to be highly chemoselective affording the secondary phosphine Ph(PhCH₂CH₂)PH; however, complexes 3Ca and 4Ca led to the formation of both secondary and tertiary phosphines in 80:20 and 86:14 ratios. Styrene hydrophosphinations with 2,4,6-Me₃C₆H₂PH₂ and 2-pyridylphosphine for all complexes 1Yb and 1-4Ca proceeded much more slowly compared to PhPH₂. Addition of 2-C₅NH₄PH₂ to styrene catalyzed by complex 1Yb turned out to be non-regioselective and led to the formation of a mixture of Markovnikov and anti-Markovnikov addition products, while all Ca complexes enabled regioselective anti-Markovnikov addition. Complexes 1Ca and 1Yb containing catalytic centers featuring similar ionic radii performed different catalytic activity: the ytterbium analogue proved to be a more active catalyst for intermolecular hydrophosphination of styrene with Cy₂PH, 2-C₅NH₄PH₂, and PhPH₂, but less active with sterically demanding 2,4,6-Me₃C₆H₂PH₂. Styrenes containing in p-position electron-donating groups (Me, tBu, OMe) performed with noticeably lower rates in the reactions with PhPH₂ compared to styrene. Complexes 1Yb, 1Ca, 2Ca, 3Ca, and 4Ca enabled addition of PhPH₂ toward the double C═C bond of α-Me-styrene, and the reaction rate for this substrate is noticeably lower; however quantitative conversions were reached in ∼40 h. Complexes 1Ca and 2Ca promoted 1,2-addition of PhPH₂ to 2,3-dimethyl butadiene with excellent regio- and chemoselectivity to afford linear secondary phosphines. Hydrophosphination of inert 1-nonene with Ph₂PH with 40% conversion becomes possible due to the application of complex 2Ca (40 h, 70 °C). The rate law for the hydrophosphination of styrene with Ph₂PH catalyzed by 1Ca was found to agree with the idealized equation: v = k[styrene]¹[1Ca]¹.

Influence of 18-Crown-6 Ether Coordination on the Catalytic Activity of Potassium and Calcium Diarylphosphinites in Hydrophosphorylation Reactions

The addition of 18-crown-6 ether (1,4,7,10,13,16-hexaoxacyclooctadecane) to tetranuclear [(thf)K(OPAryl₂)]₄ and [(thf)₄Ca(OPAryl₂)₂] yields the corresponding mononuclear complexes [(18C6)K(OPAryl₂)] [Aryl = Ph (1a), Mes (1b)] and [(18C6)Ca(OPAryl₂)₂] [Aryl = Ph (2a), Mes (2b)]. The metathesis reaction of [(thf)K(OPAryl₂)]₄ with CaI₂ yields the calciate [K₂Ca(thf)_x{OPMes₂}₄]. The addition of dimesitylphosphane oxide and crystallization from a hexane solution gives [K₂Ca{OPMes₂}₄{Mes₂P(O)H}] (3). The complexes [(thf)K(OPMes₂)]₄, [(thf)₄Ca(OPMes₂)₂], 1b, 2b, and the calciate 3 are tested as catalysts in the hydrophosphorylation of isopropylisocyanate with dimesitylphosphane oxide, quantitatively yielding N-isopropyl(dimesitylphosphoryl)formamide. The potassium complexes are more efficient catalysts than the calcium congeners, and coordination of 18-crown-6 decelerates the catalytic conversion.

Group 2 metal (Mg, Ca, Sr) silylamides supported by a cyclen-derived macrocyclic polyamine

Heteroleptic bis(silyl)amides of magnesium and calcium [(L)M{N(SiMe₃)₂}] [M = Mg, Ca; LH = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane; (Me₃TACD)H] were previously synthesized from LH and [M{N(SiMe₃)₂}₂]. Strontium bis(silyl)amides [Sr{N(SiMe₃)₂}₂(thf)₂] and [Sr{N(SiHMe₂)₂}₂(thf)_2/3] reacted with LH to give different types of products, depending on the presence of the β-SiH function. While the former underwent protonolysis to give the amido-bridged dimer [(L)Sr{N(SiMe₃)₂}]₂ (1), the latter gave the adduct [(LH)Sr{N(SiHMe₂)₂}₂] (2) as a stable solid. 2 slowly underwent an intramolecular Si-H/H-N dehydrocoupling in solution to give [{(L)SiMe₂N(SiHMe₂)}Sr{N(SiHMe₂)₂}] (3) by liberating H₂. The results of transamination of 1 with HN(SiHMe₂)₂ depended on the relative stoichiometric ratio. A 1 : 1 mixture in n-pentane gave [{(L)SiMe₂N(SiHMe₂)}Sr{N(SiMe₃)₂}] (4) and H₂, while excess HN(SiHMe₂)₂ gave the adduct 2 under similar conditions. Compounds 2 and 3 exhibit Sr↼H-Si interactions according to X-ray crystallography, NMR, and IR spectroscopy. Lighter congeners of elusive [(L)Sr{N(SiHMe₂)₂}] were isolable for Mg (5) and Ca (6).

Hydrodeoxygenation of isocyanates: snapshots of a magnesium-mediated C[double bond, length as m-dash]O bond cleavage

Organic isocyanates are readily converted to methyl amine products through their hydroboration with HBpin in the presence of a β-diketiminato magnesium catalyst.

Organic isocyanates are readily converted to methyl amine products through their hydroboration with HBpin in the presence of a β-diketiminato magnesium catalyst. Although borylated amide and N-,O-bis(boryl)hemiaminal species have been identified as intermediates during the reductive catalysis, the overall reduction and C–O activation is metal-mediated and proposed to occur through the further intermediacy of well-defined magnesium formamidato, formamidatoborate and magnesium boryloxide derivatives. Examples of all these species have been identified and fully characterised through stoichiometric reactivity studies and the stability of the borate species leads us to suggest that, under catalytic conditions, the onward progress of the deoxygenation reaction is crucially dependent on the further activation provided by the Lewis acidic HBpin substrate. These deductions have been explored and ratified through a DFT study.