A Pair of Cobalt(III/IV) Terminal Imido Complexes Mao, Weiqing; Fehn, Dominik; Heinemann, Frank W. ...
Angewandte Chemie (International ed.),
July 19, 2021, Letnik:
60, Številka:
30
Journal Article
Recenzirano
Odprti dostop
The reaction of the cobalt(I) complex (TIMMNmes)CoI(BPh4) (2) (TIMMNmes=tris‐2‐(3‐mesitylimidazolin‐2‐ylidene)methylamine) with 1‐adamantylazide yields the cobalt(III) imido complex ...(TIMMNmes)CoIII(NAd)(BPh4) (3) with concomitant release of dinitrogen. The N‐anchor in diamagnetic 3 features an unusual, planar tertiary amine, which results from repulsive electrostatic interaction with the filled d(z2)‐orbital of the cobalt ion and negative hyperconjugation with the neighboring methylene groups. One‐electron oxidation of 3 with FeCp2(OTf) provides access to the rare, high‐valent cobalt(IV) imido complex (TIMMNmes)CoIV(NAd)(OTf)2 (4). Despite a half‐life of less than 1 h at room temperature, 4 could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2
, electron configuration. A computational analysis of 4 suggests high covalency within the CoIV=NAd bond with non‐negligible spin density located at the imido moiety, which translates into substantial triplet nitrene character.
Straightforward access to a cobalt(IV) terminal imido complex was provided by one‐electron oxidation of a cobalt(III) terminal imido precursor. The cobalt(IV) monoimido complex could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2
, electron configuration.
We report the synthesis of a unique cubic metal–organic framework (MOF), Fe‐HHTP‐MOF, comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions, arranged in a diamond topology. ...The MOF is synthesized under solvothermal conditions, yielding a highly crystalline, deep black powder, with crystallites of 300–500 nm size and tetrahedral morphology. Nitrogen sorption analysis indicates a highly porous material with a surface area exceeding 1400 m2 g−1. Furthermore, Fe‐HHTP‐MOF shows broadband absorption from 475 up to 1900 nm with excellent absorption capability of 98.5 % of the incoming light over the visible spectral region. Electrical conductivity measurements of pressed pellets reveal a high intrinsic electrical conductivity of up to 10−3 S cm−1. Quantum mechanical calculations predict Fe‐HHTP‐MOF to be an efficient electron conductor, exhibiting continuous charge‐carrier pathways throughout the structure.
Fe‐HHTP‐MOF, a unique cubic metal–organic framework (MOF) comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions arranged in a diamond topology is reported. Fe‐HHTP‐MOF is a highly crystalline, porous and deep black material featuring high electrical conductivity.
We report the synthesis of a unique cubic metal–organic framework (MOF), Fe‐HHTP‐MOF, comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions, arranged in a diamond topology. ...The MOF is synthesized under solvothermal conditions, yielding a highly crystalline, deep black powder, with crystallites of 300–500 nm size and tetrahedral morphology. Nitrogen sorption analysis indicates a highly porous material with a surface area exceeding 1400 m2 g−1. Furthermore, Fe‐HHTP‐MOF shows broadband absorption from 475 up to 1900 nm with excellent absorption capability of 98.5 % of the incoming light over the visible spectral region. Electrical conductivity measurements of pressed pellets reveal a high intrinsic electrical conductivity of up to 10−3 S cm−1. Quantum mechanical calculations predict Fe‐HHTP‐MOF to be an efficient electron conductor, exhibiting continuous charge‐carrier pathways throughout the structure.
Fe‐HHTP‐MOF, a unique cubic metal–organic framework (MOF) comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions arranged in a diamond topology is reported. Fe‐HHTP‐MOF is a highly crystalline, porous and deep black material featuring high electrical conductivity.
Single atom (SA) catalysis, over the last 10 years, has become a forefront in heterogeneous catalysis, electrocatalysis, and most recently also in photocatalysis. Most crucial when engineering a SA ...catalyst/support system is the creation of defined anchoring points on the support surface to stabilize reactive SA sites. Here, a so far unexplored but evidently very effective approach to trap and stabilize SAs on a broadly used photocatalyst platform is introduced. In self‐organized anodic TiO2 nanotubes, a high degree of stress is incorporated in the amorphous oxide during nanotube growth. During crystallization (by thermal annealing), this leads to a high density of Ti3+‐Ov surface defects that are hardly present in other common titania nanostructures (as nanoparticles). These defects are highly effective for SA iridium trapping. Thus a SA‐Ir photocatalyst with a higher photocatalytic activity than for any classic co‐catalyst arrangement on the semiconductive substrate is obtained. Hence, a tool for SA trapping on titania‐based back‐contacted platforms is provided for wide application in electrochemistry and photoelectrochemistry. Moreover, it is shown that stably trapped SAs provide virtually all photocatalytic reactivity, with turnover frequencies in the order of 4 × 106 h−1 in spite of representing only a small fraction of the initially loaded SAs.
Single atoms of Ir can be trapped efficiently on the walls of anodic TiO2 nanotubes‐this is due to the presence of unique surface defects in the annealed nanotubes. This combination (SA Ir@TiO2 NTs) provides a higher activity for photocataltic H2 generation than using classic nanoparticles of Ir as a co‐catalyst.
Lithium trimethylsilyldiazomethanide and a cobalt (II) precursor with an N‐anchored tris‐NHC (TIMENmes) ligand provide access to the cobalt nitrilimide 1. Complex 1 was structurally characterized by ...single‐crystal X‐ray diffractometry (SC‐XRD) and its electronic structure was examined in detail, including EPR spectroscopy, SQUID magnetometry and computational analyses. The desilylation of the C‐(trimethylsilyl)nitrilimide reveals a transient complex with an elusive diazomethanediide ligand, which substitutes one of the mesitylene rings of the ancillary ligand through C−N bond cleavage. This transformation results in the cyclometalated cobalt(II) complex 2, featuring a rare isocyanoamido‐κ‐C ligand.
Trimethylsilylium ion from a cobalt nitrilimide complex generates a transient cobalt diazomethanediide complex, which forms a terminal isocyanoamido ligand through a radical de‐arylation.
The reaction of the cobalt(I) complex (TIMMNmes)CoI(BPh4) (2) (TIMMNmes=tris‐2‐(3‐mesitylimidazolin‐2‐ylidene)methylamine) with 1‐adamantylazide yields the cobalt(III) imido complex ...(TIMMNmes)CoIII(NAd)(BPh4) (3) with concomitant release of dinitrogen. The N‐anchor in diamagnetic 3 features an unusual, planar tertiary amine, which results from repulsive electrostatic interaction with the filled d(z2)‐orbital of the cobalt ion and negative hyperconjugation with the neighboring methylene groups. One‐electron oxidation of 3 with FeCp2(OTf) provides access to the rare, high‐valent cobalt(IV) imido complex (TIMMNmes)CoIV(NAd)(OTf)2 (4). Despite a half‐life of less than 1 h at room temperature, 4 could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2
, electron configuration. A computational analysis of 4 suggests high covalency within the CoIV=NAd bond with non‐negligible spin density located at the imido moiety, which translates into substantial triplet nitrene character.
Straightforward access to a cobalt(IV) terminal imido complex was provided by one‐electron oxidation of a cobalt(III) terminal imido precursor. The cobalt(IV) monoimido complex could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2
, electron configuration.
Abstract
Illumination of anatase in an aqueous methanolic solution leads to the formation of Ti
3+
sites that are catalytically active for the generation of dihydrogen (H
2
). With increasing ...illumination time, a light‐induced self‐amplification of the photocatalytic H
2
production rate can be observed. The effect is characterized by electron paramagnetic resonance (EPR) spectroscopy, reflectivity, and photoelectrochemical techniques. Combined measurements of H
2
generation rates and in situ EPR spectroscopic observation over the illumination time with AM 1.5G or UV light establish that the activation is accompanied by the formation of Ti
3+
states, which is validated through their characteristic EPR resonance at
g
=1.93. This self‐activation and amplification behavior can be observed for anatase nanoparticles and nanotubes.
Abstract The nitrido‐ate complex (PN) 2 Ti(N){μ 2 ‐K(OEt 2 )} 2 ( 1 ) (PN − =(N‐(2‐P i Pr 2 ‐4‐methylphenyl)‐2,4,6‐Me 3 C 6 H 2 ) reductively couples CO and isocyanides in the presence of DME or ...cryptand (Kryptofix222), to form rare, five‐coordinate Ti II complexes having a linear cumulene motif, K(L)(PN) 2 Ti(NCE) (E=O, L=Kryptofix222, ( 2 ); E=NAd, L=3 DME, ( 3 ); E=N t Bu, L=3 DME, ( 4 ); E=NAd, L=Kryptofix222, ( 5 )). Oxidation of 2 – 5 with FcOTf afforded an isostructural Ti III center containing a neutral cumulene, (PN) 2 Ti(NCE) (E=O, ( 6 ); E=NAd ( 7 ), N t Bu ( 8 )) and characterization by CW X‐band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e − reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete Ti II complexes 2 and 5 , which were further characterized by solution magnetization measurements and high‐frequency and ‐field EPR (HFEPR) spectroscopy. Furthermore, oxidation of 7 with Fc*B(C 6 F 5 ) 4 resulted in a ligand disproportionated Ti IV complex having transoid carbodiimides, (PN) 2 Ti(NCNAd) 2 ( 9 ). Comparison of spectroscopic, structural, and computational data for the divalent, trivalent, and tetravalent systems, including their 15 N enriched isotopomers demonstrate these cumulenes to decrease in order of backbonding as Ti II →Ti III →Ti IV and increasing order of π‐donation as Ti II →Ti III →Ti IV , thus displaying more covalency in Ti III species. Lastly, we show a synthetic cycle whereby complex 1 can deliver an N‐atom to CO and CNAd.
Using the potentially tridentate N,N′-bis(N-heterocyclic silylene)pyridine SiNSi pincer-type ligand, 2,6-N,N′-diethyl-bisN,N′-di-tert-butyl(phenylamidinato)silylene diaminopyridine, led to the first ...isolable bis(silylene)pyridine-stabilized manganese(0) complex, {κ3-SiNSiMn(dmpe)} 4 (dmpe = (Me2P)2C2H4), which represents an isolobal 17 VE analogue of the elusive Mn(CO)5 radical. The compound is accessible through the reductive dehalogenation of the corresponding dihalido (SiNSi)Mn(ii) complexes 1 (Cl) and 2 (Br) with potassium graphite. Exposing 4 towards the stronger π-acceptor ligands CO and 2,6-dimethylphenyl isocyanide afforded the related Mn(0) complexes κ2-SiNSiMn(CO)3 (5) and κ3-SiNSiMn(CNXylyl)2(κ1-dmpe) (6), respectively. Remarkably, the stabilization of Mn(0) in the coordination sphere of the SiNSi ligand favors the d7 low-spin electronic configuration, as suggested by EPR spectroscopy, SQUID measurements and DFT calculations. The suitability of 4 acting as a superior pre-catalyst in regioselective hydroboration of quinolines has also been demonstrated.
Reaction of the CoI complex (TIMMNmes)CoI(PF6) (1) (TIMMNmes=tris‐2‐(3‐mesityl‐imidazolin‐2‐ylidene)‐methylamine) with mesityl azide yields the CoIII imide (TIMMNmes)CoIII(NMes)(PF6) (2). Oxidation ...of 2 with FeCp2(PF6) provides access to a rare CoIII imidyl (TIMMNmes)Co(NMes)(PF6)2 (3). Single‐crystal X‐ray diffractometry and EPR spectroscopy confirm the molecular structure of 3 and its S=1/2
ground state. ENDOR, X‐ray absorption spectroscopy and computational analyses indicate a ligand‐based oxidation; thus, an imidyl‐radical electronic structure for 3. Migratory insertion of one ancillary NHC to the imido ligand in 2 gives the CoI N‐heterocyclic imine (4) within 12 h. Conversely, it takes merely 0.5 h for 3 to transform to the CoII congener (5). The migratory insertion in 2 occurs via a nucleophilic attack of the imido ligand at the NHC to give 4, whereas in 3, a nucleophilic attack of the NHC at the electrophilic imidyl ligand yields 5. The reactivity shunt upon oxidation of 2 to 3 confirms an umpolung of the imido ligand.
Straightforward access to a CoIII terminal imidyl radical complex was provided by one‐electron oxidation of a CoIII terminal imido precursor. Oxidation of the CoIII terminal imido to its imidyl redox isomer facilitates intramolecular migratory insertion reactions of the imido with an NHC ligand by a switch of mechanism through umpolung of the imido ligand.
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