Thermodynamically Favored Anion Rearrangements in Li and Na Complexes of (S)-N-α-(Methylbenzyl)allylamine

Sodiated Oppolzer Enolates: Solution Structures, Mechanism of Alkylation, and Origin of Stereoselectivity

NMR spectroscopic studies reveal camphorsultam-derived sodium enolates known as Oppolzer enolates reside as monomers in neat THF and THF/HMPA solutions and as dimers in toluene when solvated by N,N,N',N'-tetramethylethylenediamine (TMEDA) and N,N,N',N'',N''-pentamethyldiethylenediamine (PMDTA). Density functional theory (DFT) computations attest to the solvation numbers. Rate studies show analogy with previously studied lithiated Oppolzer enolates in which alkylation occurs through non-chelated solvent-separated ion pairs. The origins of the selectivity trace to transition structures in which the alkylating agent is guided to the exo face of the camphor owing to stereoelectronic preferences imparted by the sultam sulfonyl moiety. Marked secondary-shell solvation effects are gleaned from the rate studies.

Base-Induced Dehydrogenative and Dearomative Transformation of 1-Naphthylmethylamines to 1,4-Dihydronaphthalene-1-carbonitriles

Solvothermal treatment of 1-naphthylmethylamine with potassium hydride (KH) or n-butyllithium (n-BuLi)-potassium t-butoxide (t-BuOK) in THF induces unusual two consecutive β-hydride eliminations to form 1-naphthonitrile and KH. The freshly generated KH is hydridic enough to undergo dearomative hydride addition to the resultant 1-naphthonitrile regioselectively at the C4 position to afford α-cyano benzylic carbanion, which could be functionalized by a series of electrophiles, liberating the corresponding 1,4-dihydronaphthalene-1-carbonitriles having a quaternary carbon center.

Reactions of Sodium Diisopropylamide: Liquid-Phase and Solid-Liquid Phase-Transfer Catalysis by N,N,N',N″,N″-Pentamethyldiethylenetriamine

Sodium diisopropylamide (NaDA) in N,N-dimethylethylamine (DMEA) and DMEA-hydrocarbon mixtures with added N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDTA) reacts with alkyl halides, epoxides, hydrazones, arenes, alkenes, and allyl ethers. Comparisons of PMDTA with N,N,N',N'-tetramethylethylenediamine (TMEDA) accompanied by detailed rate and computational studies reveal the importance of the trifunctionality and κ2-κ3 hemilability. Rate studies show exclusively monomer-based reactions of 2-bromooctane, cyclooctene oxide, and dimethylresorcinol. Catalysis with 10 mol % PMDTA shows up to >30-fold accelerations (kcat > 300) with no evidence of inhibition over 10 turnovers. Solid-liquid phase-transfer catalysis (SLPTC) is explored as a means to optimize the catalysis as well as explore the merits of heterogeneous reaction conditions.

Unique reactivity of an α-ketiminopyridine ligand with metal–alkyls: Synthesis and ROP of ε-caprolactone

The reaction of an α-ketimininopyridine ligand 2-((Me)CN(C₆H₃-2,6-iPr₂))-6-(OMe)C₅H₃N (L¹) with metal–alkyls, such as MeLi, Et₂Zn, Me₃Al and Me₂AlCl, was studied.

Isomers of Alkali Metal (Methylbenzyl)allylamides: A Theoretical Perspective

Recent studies of alkali metal N-(α-methylbenzyl)allylamides containing lithium, sodium, and potassium have shown unique rearrangements in NMR experiments. It was found that lithium isomers favored the formation of aza-allyl and aza-enolate complexes that could exist in a solution for a substantial amount of time. As the radius of the metal ion increases going from lithium to potassium, so does the preference for the formation of the imine structure. For sodium, the aza-allyl complex could still be isolated, whereas the imine structure was only found to be stable on the scale of several hours for potassium. In this work, ab initio calculations were used to shed light on this phenomenon. Decomposition of intermolecular interaction energies of the aza-allyl, aza-enolate, and imine complexes showed that for lithium, the formation of aza-allyl and aza-enolate complexes was driven by electrostatic interactions. For potassium, the dispersion component of the metal interaction with the ligand proved to be more important for the stability of the imine structure. The presence of the imine formation in potassium and partially in sodium was found to be due to the reduced electrostatic nature of these larger metals. The assignment of the experimental NMR spectra was further confirmed with the natural bond order (NBO) analysis as well as the partial charge calculations. Analysis of orbital energies, specifically those of the highest occupied molecular orbitals (HOMOs), as well as the deformation energies of each of the ligands, were also considered. Through these procedures, an understanding of the tendency for each metal to have a unique isomerization pathway was gained.

Sodium Diisopropylamide: Aggregation, Solvation, and Stability

The solution structures, stabilities, physical properties, and reactivities of sodium diisopropylamide (NaDA) in a variety of coordinating solvents are described. NaDA is stable for months as a solid or as a 1.0 M solution in N,N-dimethylethylamine (DMEA) at -20 °C. A combination of NMR spectroscopic and computational studies show that NaDA is a disolvated symmetric dimer in DMEA, N,N-dimethyl-n-butylamine, and N-methylpyrrolidine. Tetrahydrofuran (THF) readily displaces DMEA, affording a tetrasolvated cyclic dimer at all THF concentrations. Dimethoxyethane (DME) and N,N,N',N'-tetramethylethylenediamine quantitatively displace DMEA, affording doubly chelated symmetric dimers. The trifunctional ligands N,N,N',N″,N″-pentamethyldiethylenetriamine and diglyme bind the dimer as bidentate rather than tridentate ligands. Relative rates of solvent decompositions are reported, and rate studies for the decomposition of THF and DME are consistent with monomer-based mechanisms.

Structural Diversity in Alkali Metal and Alkali Metal Magnesiate Chemistry of the Bulky 2,6-Diisopropyl-N-(trimethylsilyl)anilino Ligand

Bulky amido ligands are precious in s-block chemistry, since they can implant complementary strong basic and weak nucleophilic properties within compounds. Recent work has shown the pivotal importance of the base structure with enhancement of basicity and extraordinary regioselectivities possible for cyclic alkali metal magnesiates containing mixed n-butyl/amido ligand sets. This work advances alkali metal and alkali metal magnesiate chemistry of the bulky arylsilyl amido ligand [N(SiMe3 )(Dipp)]- (Dipp=2,6-iPr2 -C6 H3 ). Infinite chain structures of the parent sodium and potassium amides are disclosed, adding to the few known crystallographically characterised unsolvated s-block metal amides. Solvation by N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA) or N,N,N',N'-tetramethylethylenediamine (TMEDA) gives molecular variants of the lithium and sodium amides; whereas for potassium, PMDETA gives a molecular structure, TMEDA affords a novel, hemi-solvated infinite chain. Crystal structures of the first magnesiate examples of this amide in [MMg{N(SiMe3 )(Dipp)}2 (μ-nBu)]∞ (M=Na or K) are also revealed, though these breakdown to their homometallic components in donor solvents as revealed through NMR and DOSY studies.

Simplifying metal-'ate' chemistry: formation and comprehensive characterisation of a homo-metallic amido lithiate complex

Addition of TMEDA to lithium allyl-1-naphthylamide in a 1 : 1 ratio afforded the novel amido lithium/lithiate complex, [Li(TMEDA)2][Li{N(1-naph)(CH2CH[double bond, length as m-dash]CH2)}2]. (7)Li NMR and computational calculations indicate this model to be representative of the solution state, with (1)H and (13)C NMR showing a 1,3-sigmatropic rearrangement. [Li{N(1-naph)(CH2CH[double bond, length as m-dash]CH2)}·Et2O]2, and [Li{N(1-naph) (CH2CH[double bond, length as m-dash]CH2)}·PMDETA] , are presented for comparison.