The chemical reduction of π‐conjugated bilayer nanographene
The chemical reduction of π‐conjugated bilayer nanographene
- PAR ID:
- 10364321
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 61
- Issue:
- 10
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 1 (C138H120) with K and Rb in the presence of 18‐crown‐6 affords [K+(18‐crown‐6)(THF)2][{K+(18‐crown‐6)}2(THF)0.5][C138H1223−] (2 ) and [Rb+(18‐crown‐6)2][{Rb+(18‐crown‐6)}2(C138H1223−)] (3 ). Whereas K+cations are fully solvent‐separated from the trianionic core thus affording a “naked”1.3 −anion, Rb+cations are coordinated to the negatively charged layers of1.3 −. According to DFT calculations, the localization of the first two electrons in the helicene moiety leads to an unprecedented site‐specific hydrogenation process at the carbon atoms located on the edge of the helicene backbone. This uncommon reduction‐induced site‐specific hydrogenation provokes dramatic changes in the (electronic) structure of1 as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers. -
Abstract A family of neodymium complexes featuring a redox‐active ligand in three different oxidation states has been synthesized, including the iminoquinone (L0) derivative, (dippiq)2NdI3(
1‐iq ), the iminosemiquinone (L1−) compound, (dippisq)2NdI(THF) (1‐isq ), and the amidophenolate (L2−) [K(THF)2][(dippap)2Nd(THF)2] (1‐ap ) and [K(18‐crown‐6)][(dippap)2Nd(THF)2] (1‐ap crown ) species. Full spectroscopic and structural characterization of each derivative established the +3 neodymium oxidation state with redox chemistry occurring at the ligand rather than the neodymium center. Oxidation with elemental chalcogens showed the reversible nature of the ligand‐mediated reduction process, forming the iminosemiquinone metallocycles, [K(18‐crown‐6)][(dippisq)2Nd(S5)] (2‐isq crown ) and [K(18‐crown‐6)(THF)][(dippisq)2Nd(Se5)] (3‐isq crown ), which are characterized to contain a 6‐membered twist‐boat ring. -
Abstract A family of neodymium complexes featuring a redox‐active ligand in three different oxidation states has been synthesized, including the iminoquinone (L0) derivative, (dippiq)2NdI3(
1‐iq ), the iminosemiquinone (L1−) compound, (dippisq)2NdI(THF) (1‐isq ), and the amidophenolate (L2−) [K(THF)2][(dippap)2Nd(THF)2] (1‐ap ) and [K(18‐crown‐6)][(dippap)2Nd(THF)2] (1‐ap crown ) species. Full spectroscopic and structural characterization of each derivative established the +3 neodymium oxidation state with redox chemistry occurring at the ligand rather than the neodymium center. Oxidation with elemental chalcogens showed the reversible nature of the ligand‐mediated reduction process, forming the iminosemiquinone metallocycles, [K(18‐crown‐6)][(dippisq)2Nd(S5)] (2‐isq crown ) and [K(18‐crown‐6)(THF)][(dippisq)2Nd(Se5)] (3‐isq crown ), which are characterized to contain a 6‐membered twist‐boat ring. -
The use of 18-crown-6 (18-c-6) in place of 2.2.2-cryptand (crypt) in rare earth amide reduction reactions involving potassium has proven to be crucial in the synthesis of Ln( ii ) complexes and isolation of their CO reduction products. The faster speed of crystallization with 18-c-6 appears to be important. Previous studies have shown that reduction of the trivalent amide complexes Ln(NR 2 ) 3 (R = SiMe 3 ) with potassium in the presence of 2.2.2-cryptand (crypt) forms the divalent [K(crypt)][Ln II (NR 2 ) 3 ] complexes for Ln = Gd, Tb, Dy, and Tm. However, for Ho and Er, the [Ln(NR 2 ) 3 ] 1− anions were only isolable with [Rb(crypt)] 1+ counter-cations and isolation of the [Y II (NR 2 ) 3 ] 1− anion was not possible under any of these conditions. We now report that by changing the potassium chelator from crypt to 18-crown-6 (18-c-6), the [Ln(NR 2 ) 3 ] 1− anions can be isolated not only for Ln = Gd, Tb, Dy, and Tm, but also for Ho, Er, and Y. Specifically, these anions are isolated as salts of a 1 : 2 potassium : crown sandwich cation, [K(18-c-6) 2 ] 1+ , i.e. [K(18-c-6) 2 ][Ln(NR 2 ) 3 ]. The [K(18-c-6) 2 ] 1+ counter-cation was superior not only in the synthesis, but it also allowed the isolation of crystallographically-characterizable products from reactions of CO with the [Ln(NR 2 ) 3 ] 1− anions that were not obtainable from the [K(crypt)] 1+ analogs. Reaction of CO with [K(18-c-6) 2 ][Ln(NR 2 ) 3 ], generated in situ , yielded crystals of the ynediolate products, {[(R 2 N) 3 Ln] 2 (μ-OCCO)} 2− , which crystallized with counter-cations possessing 2 : 3 potassium : crown ratios, i.e. {[K 2 (18-c-6) 3 ]} 2+ , for Gd, Dy, Ho. In contrast, reaction of CO with a solution of isolated [K(18-c-6) 2 ][Gd(NR 2 ) 3 ], produced crystals of an enediolate complex isolated with a counter-cation with a 2 : 2 potassium : crown ratio namely [K(18-c-6)] 2 2+ in the complex [K(18-c-6)] 2 {[(R 2 N) 2 Gd 2 (μ-OCHCHO) 2 ]}.more » « less
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Abstract Chemical reduction of a benzo‐fused double [7]helicene (
1 ) with two alkali metals, K and Rb, provided access to three different reduced states of1 . The doubly‐reduced helicene1 2−has been characterized by single‐crystal X‐ray diffraction as a solvent‐separated ion triplet with two potassium counterions. The triply‐ and tetra‐reduced helicenes,1 3−and1 4−, have been crystallized together in an equimolar ratio and both form the contact‐ion complexes with two Rb+ions each, leaving three remaining Rb+ions wrapped by crown ether and THF molecules. As structural consequence of the stepwise reduction of1 , the central axis of helicene becomes more compressed upon electron addition (1.42 Å in1 4−vs. 2.09 Å in1 ). This is accompanied by an extra core twist, as the peripheral dihedral angle increases from 16.5° in1 to 20.7° in1 4−. Theoretical calculations provided the pattern of negative charge build‐up and distribution over the contorted helicene framework upon each electron addition, and the results are consistent with the X‐ray crystallographic and NMR spectroscopic data.