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Bis(4-benzhydryl-benzoxazol-2-yl)methane - from a Bulky NacNac Alternative to a Trianion in Alkali Metal Complexes.

ABSTRACT: A novel sterically demanding bis(4-benzhydryl-benzoxazol-2-yl)methane ligand 6 (^4-BzhH2 BoxCH₂ ) was gained in a straightforward six-step synthesis. Starting from this ligand monomeric [M(^4-BzhH2 BoxCH)] (M=Na (7), K (8₁ )) and dimeric [{M(^4-BzhH2 BoxCH)}₂ ] (M=K (8₂ ), Rb (9), Cs (10)) alkali metal complexes were synthesised by deprotonation. Abstraction of the potassium ion of 8 by reaction with 18-crown-6 resulted in the solvent separated ion pair [{(THF)₂ K@(18-crown-6)}{bis(4-benzhydryl-benzoxazol-2-yl)methanide}] (11), including the energetically favoured monoanionic (E,E)-(^4-BzhH2 BoxCH) ligand. Further reaction of ^4-BzhH2 BoxCH₂ with three equivalents KH and two equivalents 18-crown-6 yielded polymeric [{(THF)₂ K@(18-crown-6)}{K@(18-crown-6)K(^4-Bzh BoxCH)}]_n (n→∞) (12) containing a trianionic ligand. The neutral ligand and herein reported alkali complexes were characterised by single X-ray analyses identifying the latter as a promising precursor for low-valent main group complexes.

SUBMITTER: Kretsch J

PROVIDER: S-EPMC8361911 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Alkali Metal Complexes of a Bis(diphenylphosphino)methane Functionalized Amidinate Ligand: Synthesis and Luminescence.

Project description:A novel bis(diphenylphosphino)methane (DPPM) functionalized amidine ligand (DPPM-C(N-Dipp)2 H) (Dipp=2,6-diisopropylphenyl) was synthesized. Subsequent deprotonation with suitable alkali metal bases resulted in the corresponding complexes [M{DPPM-C(N-Dipp)2 }(Ln )] (M=Li, Na, K, Rb, Cs; L=thf, Et2 O). The alkali metal complexes form monomeric species in the solid state, exhibiting intramolecular metal-π-interactions. In addition, a caesium derivative [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 was obtained by cleavage of a diphenylphosphino moiety, forming an unusual six-membered ring structure in the solid state. All complexes were fully characterized by single crystal X-ray diffraction, NMR spectroscopy, IR spectroscopy as well as elemental analysis. Furthermore, the photoluminescent properties of the complexes were thoroughly investigated, revealing differences in emission with regards to the respective alkali metal. Interestingly, the hexanuclear [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 metallocycle exhibits a blue emission in the solid state, which is significantly red-shifted at low temperatures. The bifunctional design of the ligand, featuring orthogonal donor atoms (N vs. P) and a high steric demand, is highly promising for the construction of advanced metal and main group complexes.

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Project description:Alkali metal amides are vital reagents in synthetic chemistry and the bis(silyl)amide {N(SiMe?)?} (N′′) is one of the most widely-utilized examples. Given that N′′ has provided landmark complexes, we have investigated synthetic routes to lithium and sodium bis(silyl)amides with increased steric bulk to analyse the effects of R-group substitution on structural features. To perform this study, the bulky bis(silyl)amines {HN(SitBuMe?)(SiMe?)}, {HN(SiiPr?)(SiMe?)}, {HN(SitBuMe?)?}, {HN(SiiPr?)(SitBuMe?)} and {HN(SiiPr?)?} (1) were prepared by literature procedures as colourless oils; on one occasion crystals of 1 were obtained. These were treated separately with nBuLi to afford the respective lithium bis(silyl)amides [Li{μ-N(SitBuMe?)(SiMe?)}]? (2), [Li{μ-N(SiiPr?)(SiMe?)}]? (3), [Li{N(SitBuMe?)?}{μ-N(SitBuMe?)?}Li(THF)] (4), [Li{N(SiiPr?)(SitBuMe?)}(DME)] (6) and [Li{N(SiiPr?)?}(THF)] (7) following workup and recrystallization. On one occasion during the synthesis of 4 several crystals of the ‘ate’ complex [Li?{μ-N(SitBuMe?)?}(μ-nBu)]? (5) formed and a trace amount of [Li{N(SiiPr?)?}(THF)?] (8) was identified during the recrystallization of 7. The reaction of {HN(SitBuMe?)?} with NaH in the presence of 2 mol % of NaOtBu gave crystals of [Na{μ-N(SitBuMe?)?}(THF)]? (9-THF), whilst [Na{N(SiiPr?)?}(C?H?)] (10) was prepared by deprotonation of 1 with nBuNa. The solid-state structures of 1?10 were determined by single crystal X-ray crystallography, whilst 2?4, 7, 9 and 10 were additionally characterized by NMR and FTIR spectroscopy and elemental microanalysis.

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Alkali metal complexes of an enantiopure iminophosphonamide ligand with bright delayed fluorescence.

Project description:The enantiomerically pure ligand P,P-diphenyl-N,N'-bis((R)-1-phenylethyl)phosphinimidic amide (1; (R)-HPEPIA) was synthesized and subsequently deprotonated with alkali metal precursors to yield dimeric complexes [M2{(R)-PEPIA}2] (M = Li (2), Na (3), K (4), Rb (5)). The cesium compound [M{(R)-PEPIA}] (6) crystallized as a cocrystal composed of dimeric ([Cs2{(R)-PEPIA}2] (6d ) and 1D-polymeric ([Cs{(R)-PEPIA}] n ) (6p ) species in a 1 : 1 ratio. The coordination polymer 6p features a unique sinus-shaped configuration of repeating -Cs-N-P-N-Cs-N-P-N- units. Unusual photoluminescence (PL) properties were found for solid 1-6: in contrast to the fluorescent ligand 1, the alkali metal complexes show phosphorescence at low temperatures (<100 K) and thermally activated delayed fluorescence (TADF) above ∼150 K. The latter provides for PL quantum yields up to 36% (3) at ambient temperature. DFT calculations support that both 1 and 2-6d have similar singlet and triplet excited states with energy separations of a few tens of meV. The strongly enhanced intersystem crossing (ISC) in the metal complexes, resulting in TADF, is attributed to their dimeric structure. This suggests that the fluorophore dimerization may serve as a tool to effect ISC for the design of TADF emitters.

| S-EPMC6510313 | biostudies-literature

Alkali Metal Variation and Twisting of the FeNNFe Core in Bridging Diiron Dinitrogen Complexes.

Project description:Alkali metal cations can interact with Fe-N2 complexes, potentially enhancing back-bonding or influencing the geometry of the iron atom. These influences are relevant to large-scale N2 reduction by iron, such as in the FeMoco of nitrogenase and the alkali-promoted Haber-Bosch process. However, to our knowledge there have been no systematic studies of a large range of alkali metals regarding their influence on transition metal-dinitrogen complexes. In this work, we varied the alkali metal in [alkali cation]2[LFeNNFeL] complexes (L = bulky ?-diketiminate ligand) through the size range from Na(+) to K(+), Rb(+), and Cs(+). The FeNNFe cores have similar Fe-N and N-N distances and N-N stretching frequencies despite the drastic change in alkali metal cation size. The two diketiminates twist relative to one another, with larger dihedral angles accommodating the larger cations. In order to explain why the twisting has so little influence on the core, we performed density functional theory calculations on a simplified LFeNNFeL model, which show that the two metals surprisingly do not compete for back-bonding to the same ?* orbital of N2, even when the ligand planes are parallel. This diiron system can tolerate distortion of the ligand planes through compensating orbital energy changes, and thus, a range of ligand orientations can give very similar energies.

| S-EPMC4856002 | biostudies-literature

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Project description:Determining the electronic structure of actinide complexes is intrinsically challenging because inter-electronic repulsion, crystal field, and spin-orbit coupling effects can be of similar magnitude. Moreover, such efforts have been hampered by the lack of structurally analogous families of complexes to study. Here we report an improved method to U≡N triple bonds, and assemble a family of uranium(V) nitrides. Along with an isoelectronic oxo, we quantify the electronic structure of this 5f1 family by magnetometry, optical and electron paramagnetic resonance (EPR) spectroscopies and modelling. Thus, we define the relative importance of the spin-orbit and crystal field interactions, and explain the experimentally observed different ground states. We find optical absorption linewidths give a potential tool to identify spin-orbit coupled states, and show measurement of UV···UV super-exchange coupling in dimers by EPR. We show that observed slow magnetic relaxation occurs via two-phonon processes, with no obvious correlation to the crystal field.

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