Structural and spectroscopic characterization of an Fe(VI) bis(imido) complex
Abstract not provided
Martinez, Jorge L.↗
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1,2-Addition and cycloaddition reactions of niobium bis(imido) and oxo imido complexes
Another slice of pi: the addition of a second π-donor ligand engenders 1,2-addition and [2 + 2] cycloaddition reactivity across Nb-imido and Nb-oxo bonds.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Alkali Metal Ions Dictate the Structure and Reactivity of an Iron(II) Imido Complex
The presence of redox innocent metal ions has been proposed to modulate the reactivity of metal ligand multiple bonds; however, insight from structure/function relationships is limited. Here, alkali metal reduction of the Fe(III) imido complex [Ph 2 B( t BuIm) 2 Fe=NDipp] (1) provides the series of structurally characterized Fe(II) imido complexes [Ph 2 B( t BuIm) 2 Fe=NDippLi(THF) 2 ] (2), [Ph 2 B( t BuIm) 2 Fe=NDippNa(THF) 3 ] (3), and [Ph 2 B( t BuIm) 2 Fe=NDippK] 2 (4), in which the alkali metal cations coordinate the imido ligand. Structural investigations demonstrate that the alkali metal ions modestly lengthen the Fe=N bond distance from that in the charge separated complex [Ph 2 B( t BuIm) 2 Fe=NDipp][K(18-C-6)THF 2 ] (5), with the longest bond observed for the smallest alkali metal ion. In contrast to 5, the imido ligands in 2–4 can be protonated and alkylated to afford Fe(II) amido complexes. Combined experimental and computational studies reveal that the alkali metal polarizes the Fe=N bond, and the basicity of imido ligand increases according to 5 < 4 ≈ 3 < 2. The basicity of the imido ligands influences the relative rates of reaction with 1,4-cyclohexadiene, specifically by gating access to complex 5, which is the species that is active for HAT. All complexes 2–4 react with benzophenone form metastable Fe(II) intermediates that subsequently eliminate the metathesis product Ph 2 C=NDipp, with relative rates dependent on the alkali metal ion. By contrast, the same reaction with 5 does not lead to the formation of Ph 2 C=NDipp. Furthermore, these results demonstrate that the coordination of alkali metal ions dictate both the structure and reactivity of the imido ligand and moreover can direct the reactivity of reaction intermediates.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Transient Triamidoamine Neptunium(V)–Mono(Imido) Complexes: C–H Activations and Hydrogen Atom Transfer Driven by Effective Nuclear Charge
Metal-mono(imido) linkages have been known for seven decades, and they are found in transition metal, main group, lanthanide, thorium, and uranium complexes. However, transuranium-mono(imido) complexes remain unknown in any scenario. Here, we present evidence for transient neptunium(V)–mono(imido) complexes. Treatment of [Np III (Tren TIPS )] (1, Tren TIPS = {N(CH 2 CH 2 NSiPr i 3 ) 3 } 3– ) with N 3 R (R = SiMe 3 ; 1-adamantyl, Ad) results in N 2 evolution and dark purple solutions consistent with the formation of [Np V (Tren TIPS )(NR)] (3NpNR). However, solutions of 3NpNR rapidly turn orange, where for R = SiMe 3 the isolated 1:1 products are [Np IV (Tren TIPS ){N(H)SiMe 3 }] (4a) and [Np IV (Tren TIPS-2H ){N(H)SiMe 3 }] (4b, Tren TIPS-2H = {N(CH 2 CH 2 NS i Pri 3 ) 2 (NCH 2 CH 2 NSiPr i 2 C[Me]=CH 2 )} 3– ). The latter contains a dehydrogenated-Pr i vinyl functionality accounting for the source of the two amido H atoms. The reaction for R = Ad proceeds similarly, but only [Np IV (Tren TIPS ){N(H)Ad}] (5a) could be unequivocally confirmed, though its isolation suggests generality of the imido-to-amido functional group transformation. Complexes 4a/4b exhibit slow relaxation of their magnetization, adding to the small number of transuranium single ion magnets. Experimental and computational analysis suggests that the amido products are formed by C–H activation and two sequential hydrogen atom transfer reactions involving a three-step proton-coupled electron-transfer sequence of H • radical abstraction, electron transfer, then another H • radical abstraction step. In contrast to transient 3NpNR, the 5f 2 uranium(IV)-imido complex [K(2.2.2-cryptand)][U IV (Tren TIPS )(NSiMe 3 )] (8UNSiMe 3 ) is robust, even in boiling THF, suggesting the transience of 5f 2 3NpNR is not due to the 5f n -count but the increased effective nuclear charge of neptunium vs uranium. This work highlights divergence of uranium- and neptunium-imido stabilities, emphasizing that the latter is an inherently challenging synthetic target.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Catalytic Carbodiimide Guanylation by a Nucleophilic, High Spin Iron(II) Imido Complex
Reduction of the three-coordinate iron(III) imido [Ph 2 B( t BuIm) 2 Fe=NDipp] (1) affords [Ph 2 B( t BuIm) 2 Fe=NDipp][K(18-C-6)THF 2 ] (2), a rare example of a high-spin (S = 2) iron(II) imido complex. Unusually for a late metal imido complex, the imido ligand in 2 has nucleophilic character, as demonstrated by the reaction with DippNH 2 , which establishes an equilibrium with the bis(anilido) complex [Ph 2 B( t BuIm) 2 Fe(NHDipp) 2 ][K(18-C-6)THF 2 ] (3). In an unusual transformation, formal insertion of i PrN=C=N i Pr into the Fe=N(imido) bond yields the guanidinate [Ph 2 B( t BuIm) 2 Fe( i PrN) 2 CNDipp][K(18-C-6)THF 2 ] (4). Here, reaction of 4 with excess DippNH 2 provides 3, along with the guanidine ( i PrNH) 2 C=NDipp. As suggested by these stoichiometric reactions, 2 is an efficient catalyst for the guanylation of carbodiimides, converting a wide range of aniline substrates under mild conditions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Iron‐Catalyzed Intermolecular C−H Amination Assisted by an Isolated Iron‐Imido Radical Intermediate
Here we report the use of a base metal complex [( tBu pyrpyrr 2 )Fe(OEt 2 )] (1-OEt 2 ) ( tBu pyrpyrr 2 2− =3,5-tBu 2 -bis(pyrrolyl)pyridine) as a catalyst for intermolecular amination of C sp3 −H bonds of 9,10-dihydroanthracene (2 a) using 2,4,6-trimethyl phenyl azide (3 a) as the nitrene source. The reaction is complete within one hour at 80 °C using as low as 2 mol % 1-OEt 2 with control in selectivity for single C−H amination versus double C−H amination. Catalytic C−H amination reactions can be extended to other substrates such as cyclohexadiene and xanthene derivatives and can tolerate a variety of aryl azides having methyl groups in both ortho positions. Under stoichiometric conditions the imido radical species [( tBu pyrpyrr 2 )Fe{=N(2,6-Me 2 -4-tBu-C 6 H 2 )] (1-imido) can be isolated in 56 % yield, and spectroscopic, magnetometric, and computational studies confirmed it to be an S = 1 Fe IV complex. Complex 1-imido reacts with 2 a to produce the ferrous aniline adduct [( tBu pyrpyrr 2 )Fe{NH(2,6-Me 2 -4-tBu-C 6 H 2 )(C 14 H 11 )}] (1-aniline) in 45 % yield. Lastly, it was found that complexes 1-imido and 1-aniline are both competent intermediates in catalytic intermolecular C−H amination.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Synthesis, Electronic Structure, and Reactivity of a Planar Four–Coordinate, Cobalt–Imido Complex
A four-coordinate cobalt imido complex, ( tBu mPNP)Co=NMes ( tBu mPNP = modified PNP pincer ligand) has been synthesized from addition of 2,4,6-trimethylphenylazide (Mes–N 3 ) to the corresponding dinitrogen complex. The solid-state structure determined by X-ray diffraction established a rare, idealized planar geometry with a Co=N bond distance of 1.716(2) Å. Magnetic measurements revealed an S = 1 ground state with CAS-SCF calculations supporting radical character on the imide nitrogen. Here, thermolysis of the cobalt-imido compound induced selective insertion of the imido group into a Co–P bond and yielded a three-coordinate cobalt complex with a distorted T-shaped geometry. Transition state analysis conducted with DFT calculations established the thermodynamic stability of the P–N coupled product and provided insight into the exclusive selectivity.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Synthesis, Electronic Structure, and Reactivity of a Planar Four‐Coordinate, Cobalt–Imido Complex
Abstract A four‐coordinate cobalt–imido complex, ( t Bu mPNP)Co=NMes ( t Bu mPNP=modified PNP pincer ligand) has been synthesized from addition of 2,4,6‐trimethylphenylazide (Mes–N 3 ) to the corresponding dinitrogen complex. The solid‐state structure determined by X‐ray diffraction established a rare, idealized planar geometry with a Co=N bond distance of 1.716(2) Å. Magnetic measurements revealed an S =1 ground state with CAS‐SCF calculations supporting radical character on the imide nitrogen. Thermolysis of the cobalt–imido compound induced selective insertion of the imido group into a Co−P bond and yielded a three‐coordinate cobalt complex with a distorted T‐shaped geometry. Transition state analysis conducted with DFT calculations established the thermodynamic stability of the P–N coupled product and provided insight into the exclusive selectivity.
Park, Yoonsu↗
Four-Coordinate Fe N 2 and Imido Complexes Supported by a Hemilabile NNC Heteroscorpionate Ligand
Inspired by mechanistic proposals for N 2 reduction at the nitrogenase FeMo cofactor, we report herein a new, strongly σ-donating heteroscorpionate ligand featuring two weak-field pyrazoles and an alkyl donor. This ligand supports four-coordinate Fe(I)-N 2 , Fe(II)-Cl, and Fe(III)-imido complexes, which we have characterized using a variety of spectroscopic and computational methods. Structural and quantum mechanical analysis reveal the nature of the Fe–C bonds to be essentially invariant between the complexes, with conversion between the (formally) low-valent Fe-N 2 and high-valent Fe-imido complexes mediated by pyrazole hemilability. This presents a useful strategy for substrate reduction at such low-coordinate centers and suggests a mechanism by which FeMoco might accommodate the binding of both π-acidic and π-basic nitrogenous substrates.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Insight into geometric preferences in uranium( vi ) mixed tris(imido) systems
Uranium tris(imido) species have been synthesized using different imido groups in the axial and equatorial positions by treating [( Mes PDI Me )U(THF)] 2 ( 1-THF ) – a uranium( iv ) dimer supported by Mes PDI Me tetraanions – with mixed organoazide solutions.
Raghavan, Adharsh↗
Realization of an Elusive U(III) Imido Complex
Abstract Reduction of Cp*( Tripp TerN)UI with KC 8 generates (KCp*( Tripp TerN)UI) 2 , the first example of a trivalent uranium imido, a previously elusive species, which are commonly unstable. Experimental and computational results indicate that the K + coordination is responsible for this isolable U(III) monoimido complex.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Hybrid organic–inorganic two-dimensional metal carbide MXenes with amido- and imido-terminated surfaces
Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) combine the electronic and mechanical properties of 2D inorganic crystals with chemically modifiable surfaces, which provides an ideal platform for both fundamental and applied studies of interfaces. Good progress has been achieved in the functionalization of MXenes with small inorganic ligands, but relatively little work has been reported on the covalent bonding of various organic groups to MXene surfaces. Here we synthesize a family of hybrid MXenes (h-MXenes) that incorporate amido- and imido-bonding between organic and inorganic parts by reacting halogen-terminated MXenes with deprotonated organic amines. The resulting hybrid structures unite tailorability of organic molecules with electronic connectivity and other properties of inorganic 2D materials. Describing the structure of h-MXene necessitates the integration of concepts from coordination chemistry, self-assembled monolayers and surface science. The optical properties of h-MXenes reveal coherent coupling between the organic and inorganic constituents. Further, h-MXenes also exhibit superior stability against hydrolysis.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Syntheses of Tungsten Imido Cyclohexylidene Complexes Using Perfluoro‐ t ‐Butanol or Hexafluoro‐ t ‐Butanol as Acids
Abstract The fluorinated alcohols, (CF 3 ) 3 COH (R F9 OH) and (CF 3 ) 2 MeCOH (R F6 OH), react with W(NR) 2 Cy 2 (Cy=Cyclohexyl; R=2,6‐diisopropylphenyl or 1‐adamantyl) in C 6 D 6 at 55 °C to give cyclohexylidene complexes. Traditional routes to terminal alkylidene complexes (neopentylidene or neophylidene) have used either triflic acid or HCl (rarely), but relatively weak fluorinated acids are sufficient and active bisalkoxide catalysts are therefore prepared directly. An α hydrogen abstraction reaction to give a cyclohexylidene complex from a biscyclohexyl complex appears to be as facile as α hydrogen abstraction to give a neopentylidene or neophylidene ligand, but isomerization of a cyclohexene formed through β hydrogen abstraction is also a possibility. The OR F9 ligands can be replaced readily with dimethylpyrrolide (Me 2 Pyr) or other more basic alkoxides. Single crystal X‐ray studies were carried out on W(NAr) 2 Cy 2 , W(NAr)(OR F9 ) 2 (C 6 H 10 )(ArNH 2 ), W(NAr)(OR F6 ) 2 (C 6 H 10 )(ArNH 2 ), W(NAd)(OR F9 ) 2 (C 6 H 10 )(AdNH 2 ), W(NAr)(O‐ i ‐Pr F6 ) 3 Cy, and W(NAd)(η 1 ‐Me 2 Pyr) 2 (C 6 H 10 ) (C 6 H 10 =cyclohexylidene).
Maji, Milan↗