Sigma/pi Bonding Preferences of Solvated Alkali-Metal Cations to Ditopic Arylmethyl Anions

Harnessing Organopotassium Reagents for Cross-Coupling with YPhos-Pd Catalysts: Opportunities, Applications, and Challenges

With advances in the applications of earth-abundant organopotassium reagents in C-C bond forming processes, this study pioneers Pd-catalyzed cross coupling reactions between aryl halides and a range of aryl and benzylpotassium species generated by direct C-H metalation. Key for the success of this approach is the use of electron-rich ylide-substituted phosphine (YPhos) ligands, which enable fast conversion of the potassium species in solution. This protocol can be carried out in a one-pot manner at room temperature, without the need for purification of the in situ prepared organopotassium compounds or any additional additives, enabling the isolation of a broad scope of coupling products even on a gram-scale.

Diverse Multinuclear Alkali Metallated (Li, Na, K, Rb, Cs) Family of the 1,3,5-tris-2-aminopyridyl-2,4,6-triethylbenzene Framework

Literature on Group One organoelement chemistry is dominated by lithium, though sodium and potassium also feature prominently, whereas rubidium and caesium are rarely mentioned. With recent breakthroughs hinting that organoelement compounds of these two heavier metals can perform better than their lighter congeners in particular applications, important advantages could be missed unless complete sets of alkali metals are included in studies. Here, we report the synthesis and characterisation of a complete set of multi-alkali-metallated molecular compounds of the 1,3,5-tris[(4,6-dimethylpyridin-2-yl)aminomethyl]-2,4,6-triethylbenzene framework. Made by deprotonating the framework N-H bonds by a suitable base, the set comprises six THF-solvated compounds, four of which are homometallic, either containing Li in a trinuclear structure or Na, K, and Rb in hexanuclear structures. Since deprotonation was incomplete with Cs, its homometallic compound is tetranuclear containing two un-metallated N-H bonds. A heterobimetallic trilithium-tricaesium hexanuclear compound was also obtained by using a bimetallic Li-Cs base for deprotonation. Such alkali-metallated frameworks are often precursors to other multimetallic frameworks with unique properties across different fields of science.

Dual Basicity and Nucleophilicity of Organosodium Reagents in Benzylic C-H Additions of Toluenes to Diarylethenes and Ketones

Profiting from the dual high basicity and nucleophilicity of organosodium complexes, here we report the stepwise lateral metalation of a wide range of alkyl arenes (MeAr), mediated by hydrocarbon-soluble NaCH2SiMe3 ⋅ PMDETA (PMDETA=N,N,N',N'',N''-pentamethyldiethylenetriamine), followed by nucleophilic addition to diarylethenes of the newly generated NaCH2Ar ⋅ PMDETA complexes. This method grants access to a range of functionalised hydrocarbons in excellent yields and can be upgraded to catalytic regimes when using trans-stilbene, a 10 mol% of the alkyl sodium base and toluene as a solvent. Extending this approach to aromatic ketones leads to the formation of stilbenes under mild reaction conditions, resulting from the deprotonative coupling of toluenes with ketones. Combining spectroscopic studies with the trapping and characterisation of key reaction intermediates, mechanistic insights have been gained, advancing the understanding of coordination effects in organosodium chemistry, and shedding light on their special reactivity profiles.

Synthesis, characterisation, and catalytic application of a soluble molecular carrier of sodium hydride activated by a substituted 4-(dimethylamino)pyridine

Recently main group compounds have stepped into the territory of precious transition metal compounds with respect to utility in the homogeneous catalysis of fundamentally important organic transformations. Inspired by the need to promote more sustainability in chemistry because of their greater abundance in nature, this change of direction is surprising since main group metals generally do not possess the same breadth of reactivity as precious transition metals. Here, we introduce the dihydropyridylsodium compound, Na-1,2-tBu-DH(DMAP), and its monomeric variant [Na-1,2-tBu-DH(DMAP)]·Me6TREN, and demonstrate their effectiveness in transfer hydrogenation catalysis of the representative alkene 1,1-diphenylethylene to the alkane 1,1-diphenylethane using 1,4-cyclohexadiene as hydrogen source [DMAP = 4-dimethylaminopyridine; Me6TREN = tris(N,N-dimethyl-2-aminoethyl)amine]. Sodium is appealing because of its high abundance in the earth's crust and oceans, but organosodium compounds have been rarely used in homogeneous catalysis. The success of the dihydropyridylsodium compounds can be attributed to their high solubility and reactivity in organic solvents.

Counterion Effect in Cobaltate-Catalyzed Alkene Hydrogenation

We show that countercations exert a remarkable influence on the ability of anionic cobaltate salts to catalyze challenging alkene hydrogenations. An evaluation of the catalytic properties of [Cat][Co(η4 -cod)2 ] (Cat=K (1), Na (2), Li (3), (Dep nacnac)Mg (4), and N(n Bu)4 (5); cod=1,5-cyclooctadiene, Dep nacnac={2,6-Et2 C6 H3 NC(CH3 )}2 CH)]) demonstrated that the lithium salt 3 and magnesium salt 4 drastically outperform the other catalysts. Complex 4 was the most active catalyst, which readily promotes the hydrogenation of highly congested alkenes under mild conditions. A plausible catalytic mechanism is proposed based on density functional theory (DFT) investigations. Furthermore, combined molecular dynamics (MD) simulation and DFT studies were used to examine the turnover-limiting migratory insertion step. The results of these studies suggest an active co-catalytic role of the counterion in the hydrogenation reaction through the coordination to cobalt hydride intermediates.

New Frontiers in Organosodium Chemistry as Sustainable Alternatives to Organolithium Reagents

With their highly reactive respective C-Na and N-Na bonds, organosodium and sodium amide reagents could be viewed as obvious replacements or even superior reagents to the popular, widely utilised organolithiums. However, they have seen very limited applications in synthesis due mainly to poor solubility in common solvents and their limited stability. That notwithstanding in recent years there has been a surge of interest in bringing these sustainable metal reagents into the forefront of organometallics in synthesis. Showcasing the growth in utilisation of organosodium complexes within several areas of synthetic chemistry, this Minireview discusses promising new methods that have been recently reported with the goal of taming these powerful reagents. Special emphasis is placed on coordination and aggregation effects in these reagents which can impart profound changes in their solubility and reactivity. Differences in observed reactivity between more nucleophilic aryl and alkyl sodium reagents and the less nucleophilic but highly basic sodium amides are discussed along with current mechanistic understanding of their reactivities. Overall, this review aims to inspire growth in this exciting field of research to allow for the integration of organosodium complexes within common important synthetic transformations.

Isolable rubidium and caesium derivatives of common organic carbonyl compounds

Light alkali metal (Li, Na, K) amides have a long history of synthetic utility, but heavier (Rb, Cs) congeners have barely been studied. This study reveals remarkable structurally complex outcomes of reacting AM(HMDS) (AM = Rb, Cs; HMDS = hexamethyldisilazide) with benzaldehyde and acetophenone. Though complicated, reactions give a diversity of eye-catching isolated products, an enolate with a hexagonal prismatic network, two dienolates with distinct extended ladder motifs, and two β-imino-alkoxides comprising zig-zag chains of metal-oxygen bonds in infinite cages.

Li vs Na: Divergent Reaction Patterns between Organolithium and Organosodium Complexes and Ligand-Catalyzed Ketone/Aldehyde Methylenation

Organosodium chemistry is underdeveloped compared with organolithium chemistry, and all the reported organosodium complexes exhibit similar, if not identical, reactivity patterns to their lithium counterparts. Herein, we report a rare organosodium monomeric complex, namely, [Na(CH2SiMe3)(Me6Tren)] (1-Na) (Me6Tren: tris[2-(dimethylamino)ethyl]amine) stabilized by a tetra-dentate neutral amine ligand Me6Tren. Employing organo-carbonyl substrates (ketones, aldehydes, amides, ester), we demonstrated that 1-Na features distinct reactivity patterns compared with its lithium counterpart, [Li(CH2SiMe3)(Me6Tren)] (1-Li). Based on this knowledge, we further developed a ligand-catalysis strategy to conduct ketone/aldehyde methylenations, using [NaCH2SiMe3]∞ as the CH2 feedstock, replacing the widely used but hazardous/expensive C═O methylenation methods, such as Wittig, Tebbe, Julia/Julia-Kocieński, Peterson, and so on.

Continuous Flow Preparation of Benzylic Sodium Organometallics

We report a lateral sodiation of alkyl(hetero)arenes using on-demand generated hexane-soluble (2-ethylhexyl)sodium (1) in the presence of TMEDA. (2-Ethylhexyl)sodium (1) is prepared via a sodium packed-bed reactor and used for metalations at ambient temperature in batch as well as in continuous flow. The resulting benzylic sodium species are subsequently trapped with various electrophiles including carbonyl compounds, epoxides, oxetane, allyl/benzyl chlorides, alkyl halides and alkyl tosylates. Wurtz-type couplings with secondary alkyl halides and tosylates proceed under complete inversion of stereochemistry. Furthermore, the utility of this lateral sodiation is demonstrated in the synthesis of pharmaceutical relevant compounds. Thus, fingolimod is prepared from p-xylene applying the lateral sodiation twice. In addition, 7-fold isotopically labeled salmeterol-d7 and fenpiprane as well as precursors to super linear alkylbenzene (SLAB) surfactants are prepared.

Sigma/pi Bonding Preferences of Solvated Alkali-Metal Cations to Ditopic Arylmethyl Anions

Arylmethyl anions allow alkali-metals to bind in a σ-fashion to the lateral carbanionic centre or a π-fashion to the aryl ring or in between these extremities, with the trend towards π bonding increasing on descending group 1. Here we review known alkali metal structures of diphenylmethane, fluorene, 2-benzylpyridine and 4-benzylpyridine. Next, we synthesise Li, Na, K monomers of these diarylmethyls using polydentate donors PMDETA or Me6 TREN to remove competing oligomerizing interactions, studying the effect that two aromatic rings has on negative charge (de)localisation via NMR, X-ray crystallographic and DFT studies. Diphenylmethyl and fluorenyl anions maintain C(H)-M interactions regardless of alkali-metal, although the adjacent arene carbons engage in interactions with larger alkali-metals. Introducing a nitrogen atom into the ring (at the 2- or 4-position) encourages relocalisation of negative charge away from the deprotonated carbon and onto nitrogen. Phenyl(2-pyridyl)methyl moves from an enamide formation at one extremity (lithium) to an aza-allyl formation at the other extremity (potassium), while C- or N-coordination modes become energetically viable for Na and K phenyl(4-pyridyl)methyl complexes.