Synthesis,Characterization, and Reactivity of a Uranium(VI) Carbene Imido Oxo Complex

We report the uranium(VI) carbene imido oxo complex [U(BIPM^TMS)(NMes)(O)(DMAP)₂] ( 5 , BIPM^TMS=C(PPh₂NSiMe₃)₂; Mes=2,4,6‐Me₃C₆H₂; DMAP=4‐(dimethylamino)pyridine) which exhibits the unprecedented arrangement of three formal multiply bonded ligands to one metal center where the coordinated heteroatoms derive from different element groups. This complex was prepared by incorporation of carbene, imido, and then oxo groups at the uranium center by salt elimination, protonolysis, and two‐electron oxidation, respectively. The oxo and imido groups adopt axial positions in a T‐shaped motif with respect to the carbene, which is consistent with an inverse trans‐influence. Complex 5 reacts with tert‐butylisocyanate at the imido rather than carbene group to afford the uranyl(VI) carbene complex [U(BIPM^TMS)(O)₂(DMAP)₂] ( 6 ).     

Silyl‐Phosphino‐Carbene Complexes of Uranium(IV)

Unprecedented silyl‐phosphino‐carbene complexes of uranium(IV) are presented, where before all covalent actinide–carbon double bonds were stabilised by phosphorus(V) substituents or restricted to matrix isolation experiments. Conversion of [U(BIPM^TMS)(Cl)(μ‐Cl)₂Li(THF)₂] ( 1 , BIPM^TMS=C(PPh₂NSiMe₃)₂) into [U(BIPM^TMS)(Cl){CH(Ph)(SiMe₃)}] ( 2 ), and addition of [Li{CH(SiMe₃)(PPh₂)}(THF)]/Me₂NCH₂CH₂NMe₂ (TMEDA) gave [U{C(SiMe₃)(PPh₂)}(BIPM^TMS)(μ‐Cl)Li(TMEDA)(μ‐TMEDA)_0.5]₂ ( 3 ) by α‐hydrogen abstraction. Addition of 2,2,2‐cryptand or two equivalents of 4‐N,N‐dimethylaminopyridine (DMAP) to 3 gave [U{C(SiMe₃)(PPh₂)}(BIPM^TMS)(Cl)][Li(2,2,2‐cryptand)] ( 4 ) or [U{C(SiMe₃)(PPh₂)}(BIPM^TMS)(DMAP)₂] ( 5 ). The characterisation data for 3 – 5 suggest that whilst there is evidence for 3‐centre P?C?U π‐bonding character, the U=C double bond component is dominant in each case. These U=C bonds are the closest to a true uranium alkylidene yet outside of matrix isolation experiments.     

Uranium–Carbene–Imido Metalla‐Allenes: Ancillary‐Ligand‐Controlled cis‐/trans‐Isomerisation and Assessment of trans Influence in the R2C=UIV=NR′ Unit (R=Ph2PNSiMe3; R′=CPh3)

Uranium(IV)–carbene–imido complexes [U(BIPM^TMS)(NCPh₃)(κ²‐N,N′‐BIPY)] ( 2 ; BIPM^TMS=C(PPh₂NSiMe₃)₂; BIPY=2,2‐bipyridine) and [U(BIPM^TMS)(NCPh₃)(DMAP)₂] ( 3 ; DMAP=4‐dimethylamino‐pyridine) that contain unprecedented, discrete R₂C=U=NR′ units are reported. These complexes complete the family of E=U=E (E=CR₂, NR, O) metalla‐allenes with feasible first‐row hetero‐element combinations. Intriguingly, 2 and 3 contain cis‐ and trans‐C=U=N units, respectively, representing rare examples of controllable cis/trans isomerisation in f‐block chemistry. This work reveals a clear‐cut example of the trans influence in a mid‐valent uranium system, and thus a strong preference for the cis isomer, which is computed in a co‐ligand‐free truncated model—to isolate the electronic trans influence from steric contributions—to be more stable than the trans isomer by approximately 12 kJ mol^?1 with an isomerisation barrier of approximately 14 kJ mol^?1.     

Uranium Metalla‐Allenes with Carbene Imido R2C=UIV=NR′ Units (R=Ph2PNSiMe3; R′=CPh3): Alkali‐Metal‐Mediated Push–Pull Effects with an Amido Auxiliary

We report uranium(IV)‐carbene‐imido‐amide metalla‐allene complexes [U(BIPM^TMS)(NCPh₃)(NHCPh₃)(M)] (BIPM^TMS=C(PPh₂NSiMe₃)₂; M=Li or K) that can be described as R₂C=U=NR′ push–pull metalla‐allene units, as organometallic counterparts of the well‐known push–pull organic allenes. The solid‐state structures reveal that the R₂C=U=NR′ units adopt highly unusual cis‐arrangements, which are also reproduced by gas‐phase theoretical studies conducted without the alkali metals to remove their potential structure‐directing roles. Computational studies confirm the double‐bond nature of the U=NR′ and U=CR₂ interactions, the latter increasingly attenuated by potassium then lithium when compared to the hypothetical alkali‐metal‐free anion. Combined experimental and theoretical data show that the push–pull effect induced by the alkali metal cations and amide auxiliary gives a fundamental and tunable structural influence over the C=U^IV=N units.     

The Nature of the UC Double Bond: Pushing the Stability of High‐Oxidation‐State Uranium Carbenes to the Limit

Treatment of [K(BIPM^MesH)] (BIPM^Mes={C(PPh₂NMes)₂}^2?; Mes=C₆H₂‐2,4,6‐Me₃) with [UCl₄(thf)₃] (1 equiv) afforded [U(BIPM^MesH)(Cl)₃(thf)] ( 1 ), which generated [U(BIPM^Mes)(Cl)₂(thf)₂] ( 2 ), following treatment with benzyl potassium. Attempts to oxidise 2 resulted in intractable mixtures, ligand scrambling to give [U(BIPM^Mes)₂] or the formation of [U(BIPM^MesH)(O)₂(Cl)(thf)] ( 3 ). The complex [U(BIPM^Dipp)(μ‐Cl)₄(Li)₂(OEt₂)(tmeda)] ( 4 ) (BIPM^Dipp={C(PPh₂NDipp)₂}^2?; Dipp=C₆H₃‐2,6‐iPr₂; tmeda=N,N,N′,N′‐tetramethylethylenediamine) was prepared from [Li₂(BIPM^Dipp)(tmeda)] and [UCl₄(thf)₃] and, following reflux in toluene, could be isolated as [U(BIPM^Dipp)(Cl)₂(thf)₂] ( 5 ). Treatment of 4 with iodine (0.5 equiv) afforded [U(BIPM^Dipp)(Cl)₂(μ‐Cl)₂(Li)(thf)₂] ( 6 ). Complex 6 resists oxidation, and treating 4 or 5 with N‐oxides gives [{U(BIPM^DippH)(O)₂‐ (μ‐Cl)₂Li(tmeda)] ( 7 ) and [{U(BIPM^DippH)(O)₂(μ‐Cl)}₂] ( 8 ). Treatment of 4 with tBuOLi (3 equiv) and I₂ (1 equiv) gives [U(BIPM^Dipp)(OtBu)₃(I)] ( 9 ), which represents an exceptionally rare example of a crystallographically authenticated uranium(VI)–carbon σ bond. Although 9 appears sterically saturated, it decomposes over time to give [U(BIPM^Dipp)(OtBu)₃]. Complex 4 reacts with PhCOtBu and Ph₂CO to form [U(BIPM^Dipp)(μ‐Cl)₄(Li)₂(tmeda)(OCPhtBu)] ( 10 ) and [U(BIPM^Dipp)(Cl)(μ‐Cl)₂(Li)(tmeda)(OCPh₂)] ( 11 ). In contrast, complex 5 does not react with PhCOtBu and Ph₂CO, which we attribute to steric blocking. However, complexes 5 and 6 react with PhCHO to afford (DippNPPh₂)₂C?C(H)Ph ( 12 ). Complex 9 does not react with PhCOtBu, Ph₂CO or PhCHO; this is attributed to steric blocking. Theoretical calculations have enabled a qualitative bracketing of the extent of covalency in early‐metal carbenes as a function of metal, oxidation state and the number of phosphanyl substituents, revealing modest covalent contributions to U?C double bonds.     

Oxo–Group‐14‐Element Bond Formation in Binuclear Uranium(V) Pacman Complexes

Simple and versatile routes to the functionalization of uranyl‐derived U^V–oxo groups are presented. The oxo‐lithiated, binuclear uranium(V)–oxo complexes [{(py)₃LiOUO}₂(L)] and [{(py)₃LiOUO}(OUOSiMe₃)(L)] were prepared by the direct combination of the uranyl(VI) silylamide “ate” complex [Li(py)₂][(OUO)(N”)₃] (N”=N(SiMe₃)₂) with the polypyrrolic macrocycle H₄L or the mononuclear uranyl (VI) Pacman complex [UO₂(py)(H₂L)], respectively. These oxo‐metalated complexes display distinct U? O single and multiple bonding patterns and an axial/equatorial arrangement of oxo ligands. Their ready availability allows the direct functionalization of the uranyl oxo group leading to the binuclear uranium(V) oxo–stannylated complexes [{(R₃Sn)OUO}₂(L)] (R=nBu, Ph), which represent rare examples of mixed uranium/tin complexes. Also, uranium–oxo‐group exchange occurred in reactions with [TiCl(OiPr)₃] to form U‐O? C bonds [{(py)₃LiOUO}(OUOiPr)(L)] and [(iPrOUO)₂(L)]. Overall, these represent the first family of uranium(V) complexes that are oxo‐functionalised by Group 14 elements.     

Catalytic Oxo/Imido Heterometathesis by a Well‐Defined Silica‐Supported Titanium Imido Complex

Grafting Ti(=NtBu)(Me₂Pyr)₂(py)₂ (Me₂Pyr= 2,5‐dimethylpyrrolyl, py=pyridine) onto the surface of silica partially dehydroxylated at 700 °C gives the well‐defined silica‐supported Ti imido complex (≡SiO)Ti(=NtBu)(Me₂Pyr)(py)₂, which is fully characterized by IR and solid‐state NMR spectroscopy as well as elemental and mass balance analyses. While stoichiometric imido‐transfer reactivity is typical for Ti imides, the obtained surface complex is unique in that it enables catalytic transformations involving Ti imido and oxo intermediates. In particular, it efficiently catalyzes imidation of carbonyl compounds with N‐sulfinylamines by oxo/imido heterometathesis.     

Subtle Interactions and Electron Transfer between UIII,NpIII, or PuIII and Uranyl Mediated by the Oxo Group

A dramatic difference in the ability of the reducing An^III center in AnCp₃ (An=U, Np, Pu; Cp=C₅H₅) to oxo‐bind and reduce the uranyl(VI) dication in the complex [(UO₂)(THF)(H₂L)] (L=“Pacman” Schiff‐base polypyrrolic macrocycle), is found and explained. These are the first selective functionalizations of the uranyl oxo by another actinide cation. At‐first contradictory electronic structural data are explained by combining theory and experiment. Complete one‐electron transfer from Cp₃U forms the U^IV‐uranyl(V) compound that behaves as a U^V‐localized single molecule magnet below 4 K. The extent of reduction by the Cp₃Np group upon oxo‐coordination is much less, with a Np^III‐uranyl(VI) dative bond assigned. Solution NMR and NIR spectroscopy suggest Np^IVU^V but single‐crystal X‐ray diffraction and SQUID magnetometry suggest a Np^III‐U^VI assignment. DFT‐calculated Hirshfeld charge and spin density analyses suggest half an electron has transferred, and these explain the strongly shifted NMR spectra by spin density contributions at the hydrogen nuclei. The Pu^III–U^VI interaction is too weak to be observed in THF solvent, in agreement with calculated predictions.     

Silylene–Nickel Promoted Cleavage of B−O Bonds: From Catechol Borane to the Hydroborylene Ligand

The first 16 valence electron [bis(NHC)](silylene)Ni⁰ complex 1 , [(^TMSL)ClSi:→Ni(NHC)₂], bearing the acyclic amido‐chlorosilylene (^TMSL)ClSi: (^TMSL=N(SiMe₃)Dipp; Dipp=2,6‐Prⁱ₂C₆H₄) and two NHC ligands (N‐heterocyclic carbene=:C[(Prⁱ)NC(Me)]₂) was synthesized in high yield and structurally characterized. Compound 1 is capable of facile dihydrogen activation under ambient conditions to give the corresponding HSi‐NiH complex 2 . Most notably, 1 reacts with catechol borane to afford the unprecedented hydroborylene‐coordinated (chloro)(silyl)nickel(II) complex 3 , {[cat(^TMSL)Si](Cl)Ni←:BH(NHC)₂}, via the cleavage of two B−O bonds and simultaneous formation of two Si−O bonds. The mechanism for the formation of 3 was rationalized by means of DFT calculations, which highlight the powerful synergistic effects of the Si:→Ni moiety in the breaking of incredibly strong B−O bonds.     

1,2-Addition and cycloaddition reactions of niobium bis(imido) and oxo imido complexes

The bis(imido) complexes (BDI)Nb(N^tBu)₂ and (BDI)Nb(N^tBu)(NAr) (BDI = N,N′-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate; Ar = 2,6-diisopropylphenyl) were shown to engage in 1,2-addition and [2 + 2] cycloaddition reactions with a wide variety of substrates. Reaction of the bis(imido) complexes with dihydrogen, silanes, and boranes yielded hydrido-amido-imido complexes via 1,2-addition across Nb-imido π-bonds; some of these complexes were shown to further react via insertion of carbon dioxide to give formate-amido-imido products. Similarly, reaction of (BDI)Nb(N^tBu)₂ with tert-butylacetylene yielded an acetylide-amido-imido complex. In contrast to these results, many related mono(imido) Nb BDI complexes do not exhibit 1,2-addition reactivity, suggesting that π-loading plays an important role in activating the Nb–N π-bonds toward addition. The same bis(imido) complexes were also shown to engage in [2 + 2] cycloaddition reactions with oxygen- and sulfur-containing heteroallenes to give carbamate- and thiocarbamate-imido complexes: some of these complexes readily dimerized to give bis-μ-sulfido, bis-μ-iminodicarboxylate, and bis-μ-carbonate complexes. The mononuclear carbamate imido complex (BDI)Nb(NAr)(N(^tBu)CO₂) (12) could be induced to eject tert-butylisocyanate to generate a four-coordinate terminal oxo imido intermediate, which could be trapped as the five-coordinate pyridine or DMAP adduct. The DMAP adducted oxo imido complex (BDI)NbO(NAr)(DMAP) (16) was shown to engage in 1,2-addition of silanes across the Nb-oxo π-bond; this represents a new reaction pathway in group 5 chemistry.

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.     

Cation–Cation Interactions,Magnetic Communication,and Reactivity of the Pentavalent Uranium Ion [U(NtBu)2]+

Communication is important : The dimeric bis(imido) uranium complex [{U(NtBu)₂(I)(tBu₂bpy)}₂] (see picture; U green, N blue, I red) has cation–cation interactions between [U(NR)₂]⁺ ions. This f¹–f¹ system also displays f orbital communication between uranium(V) centers at low temperatures, and can be oxidized to generate uranium(VI) bis(imido) complexes.

     

Subtle Interactions and Electron Transfer between UIII,NpIII, or PuIII and Uranyl Mediated by the Oxo Group

A dramatic difference in the ability of the reducing An^III center in AnCp₃ (An=U, Np, Pu; Cp=C₅H₅) to oxo‐bind and reduce the uranyl(VI) dication in the complex [(UO₂)(THF)(H₂L)] (L=“Pacman” Schiff‐base polypyrrolic macrocycle), is found and explained. These are the first selective functionalizations of the uranyl oxo by another actinide cation. At‐first contradictory electronic structural data are explained by combining theory and experiment. Complete one‐electron transfer from Cp₃U forms the U^IV‐uranyl(V) compound that behaves as a U^V‐localized single molecule magnet below 4 K. The extent of reduction by the Cp₃Np group upon oxo‐coordination is much less, with a Np^III‐uranyl(VI) dative bond assigned. Solution NMR and NIR spectroscopy suggest Np^IVU^V but single‐crystal X‐ray diffraction and SQUID magnetometry suggest a Np^III‐U^VI assignment. DFT‐calculated Hirshfeld charge and spin density analyses suggest half an electron has transferred, and these explain the strongly shifted NMR spectra by spin density contributions at the hydrogen nuclei. The Pu^III–U^VI interaction is too weak to be observed in THF solvent, in agreement with calculated predictions.     

Cycloaddition Chemistry of a Silylene-Nickel Complex toward Organic π-Systems: From Reversibility to C−H Activation

The versatile cycloaddition chemistry of the Si−Ni multiple bond in the acyclic (amido)(chloro)silylene→Ni⁰ complex 1 , [(^TMSL)ClSi→Ni(NHC)₂] (^TMSL=N(SiMe₃)Dipp; Dipp=2,6-iPr₂C₆H₄; NHC=C[(iPr)NC(Me)]₂), toward unsaturated organic substrates is reported, which is both reminiscent of and expanding on the reactivity patterns of classical Fischer and Schrock carbene–metal complexes. Thus, 1:1 reaction of 1 with aldehydes, imines, alkynes, and even alkenes proceed to yield [2+2] cycloaddition products, leading to a range of four-membered metallasilacycles. This cycloaddition is in fact reversible for ethylene, whereas addition of an excess of this olefin leads to quantitative sp²-CH bond activation, via a 1-nickela-4-silacyclohexane intermediate. These results have been supported by DFT calculations giving insights into key mechanistic aspects.     

Synthesis,Structures and DFT Studies of Imido‐bridged and (Bis)ligand‐coordinated Titanium Complexes

Syntheses and structures of five imido‐bridged dinuclear titanium complexes and two (bis)ligand‐coordinated mononuclear titanium complexes are reported. Addition of 1 or 2 equiv. of Schiff base ligand (((1H‐pyrrol‐2‐yl)methylene)amino)‐2,3‐dihydro‐1H‐inden‐2‐ol (H₂L) to Ti(NMe₂)₄ resulted in transamination with 4 equiv. of dimethylamides generating a (bis)ligand‐coordinated complex Ti(L)₂ ( 1 ). Treatment of Ti(NMe₂)₄ with 1 equiv. of ^tBuNH₂ followed by addition of 1 equiv. of H₂L afforded an imido‐bridged complex [Ti(L)(N^tBu)]₂ ( 2 ). 1:1:1:1 reaction of Ti(NMe₂)₄/RNH₂/H₂L/py(or phen) produced imido‐bridgedcomplexes [Ti(L)(NPh)(py)]₂ ( 3 ), [Ti(L)(4‐F‐PhN)(py)]₂·Tol ( 4 ·Tol), [Ti(L)(4‐Cl‐PhN)(py)]₂·Tol·THF ( 5 ·Tol·THF), [Ti(L)(4‐Br‐PhN)(py)]₂·Tol ( 6 ·Tol) and a (bis)ligand‐coordinated complex Ti(L)₂·phen ( 7 ) (py = pyridine, phen = 1,10‐phenanthroline). Attempts to prepare the monomeric titianium imido complexes were unsuccessful. DFT studies show that the assumed compound which contains Ti = N species is less stable than imido‐bridged Ti‐N(R)‐Ti complexes, providing the better understanding of the experimental results.     

Two‐Electron Reductive Carbonylation of Terminal Uranium(V) and Uranium(VI) Nitrides to Cyanate by Carbon Monoxide

Two‐electron reductive carbonylation of the uranium(VI) nitride [U(Tren^TIPS)(N)] ( 2 , Tren^TIPS=N(CH₂CH₂NSiiPr₃)₃) with CO gave the uranium(IV) cyanate [U(Tren^TIPS)(NCO)] ( 3 ). KC₈ reduction of 3 resulted in cyanate dissociation to give [U(Tren^TIPS)] ( 4 ) and KNCO, or cyanate retention in [U(Tren^TIPS)(NCO)][K(B15C5)₂] ( 5 , B15C5=benzo‐15‐crown‐5 ether) with B15C5. Complexes 5 and 4 and KNCO were also prepared from CO and the uranium(V) nitride [{U(Tren^TIPS)(N)K}₂] ( 6 ), with or without B15C5, respectively. Complex 5 can be prepared directly from CO and [U(Tren^TIPS)(N)][K(B15C5)₂] ( 7 ). Notably, 7 reacts with CO much faster than 2 . This unprecedented f‐block reactivity was modeled theoretically, revealing nucleophilic attack of the π* orbital of CO by the nitride with activation energy barriers of 24.7 and 11.3 kcal mol^?1 for uranium(VI) and uranium(V), respectively. A remarkably simple two‐step, two‐electron cycle for the conversion of azide to nitride to cyanate using 4 , NaN₃ and CO is presented.     

Facile Conversion of syn‐[FeIV(O)(TMC)]2+ into the anti Isomer via Meunier's Oxo–Hydroxo Tautomerism Mechanism

The syn and anti isomers of [Fe^IV(O)(TMC)]²⁺ (TMC=tetramethylcyclam) represent the first isolated pair of synthetic non‐heme oxoiron(IV) complexes with identical ligand topology, differing only in the position of the oxo unit bound to the iron center. Both isomers have previously been characterized. Reported here is that the syn isomer [Fe^IV(O_syn)(TMC)(NCMe)]²⁺ ( 2 ) converts into its anti form [Fe^IV(O_anti)(TMC)(NCMe)]²⁺ ( 1 ) in MeCN, an isomerization facilitated by water and monitored most readily by ¹H NMR and Raman spectroscopy. Indeed, when H₂¹⁸O is introduced to 2 , the nascent 1 becomes ¹⁸O‐labeled. These results provide compelling evidence for a mechanism involving direct binding of a water molecule trans to the oxo atom in 2 with subsequent oxo–hydroxo tautomerism for its incorporation as the oxo atom of 1 . The nonplanar nature of the TMC supporting ligand makes this isomerization an irreversible transformation, unlike for their planar heme counterparts.     

The Ketimide Ligand is Not Just an Inert Spectator: Heteroallene Insertion Reactivity of an Actinide–Ketimide Linkage in a Thorium Carbene Amide Ketimide Complex

The ketimide anion R₂C?N^? is an important class of chemically robust ligand that binds strongly to metal ions and is considered ideal for supporting reactive metal fragments due to its inert spectator nature; this contrasts with R₂N^? amides that exhibit a wide range of reactivities. Here, we report the synthesis and characterization of a rare example of an actinide ketimide complex [Th(BIPM^TMS){N(SiMe₃)₂}(N?CPh₂)] [ 2 , BIPM^TMS=C(PPh₂NSiMe₃)₂]. Complex 2 contains Th?C_carbene, Th? N_amide and Th? N_ketimide linkages, thereby presenting the opportunity to probe the preferential reactivity of these linkages. Importantly, reactivity studies of 2 with unsaturated substrates shows that insertion reactions occur preferentially at the Th? N_ketimide bond rather than at the Th?C_carbene or Th? N_amide bonds. This overturns the established view that metal‐ketimide linkages are purely inert spectators.     

The trans influence of the pyridine ligand on ruthenium(II)–porphyrin–carbene complexes

In the two ruthenium(II)–porphyrin–carbene complexes ­(di­benzoyl­carbenyl‐κC)(pyridine‐κN)(5,10,15,20‐tetra‐p‐tolyl­porphyrinato‐κ⁴N)­ruthenium(II), [Ru(C₁₅H₁₀O₂)(C₅H₅N)(C₄₈H₃₆N₄)], (I), and (pyridine‐κN)(5,10,15,20‐tetra‐p‐tolyl­porphyrinato‐κ⁴N)[bis(3‐tri­fluoro­methyl­phenyl)­carbenyl‐κC]­ruthenium(II), [Ru(C₁₅H₈F₆)(C₅H₅N)(C₄₈H₃₆N₄)], (II), the pyridine ligand coordinates to the octahedral Ru atom trans with respect to the carbene ligand. The C(carbene)—Ru—N(pyridine) bonds in (I) coincide with a crystallographic twofold axis. The Ru—C bond lengths of 1.877 (8) and 1.868 (3) Å in (I) and (II), respectively, are slightly longer than those of other ruthenium(II)–porphyrin–carbene complexes, owing to the trans influence of the pyridine ligands.     

A ruthenium(II)–porphyrin–carbene complex with a weakly bonded methanol ligand

The title di­phenyl­carbene porphyrin complex (di­phenyl­carbenyl‐κC)(methanol‐κO)(5,10,15,20‐tetra‐p‐tolyl­por­phy­rin­ato‐κ⁴N)ruthenium(II) methanol solvate, [Ru­(C₁₃H₁₀)(C₄₈H₃₆N₄)(CH₄O)]·CH₄O, has a six‐coordinate Ru atom with a methanol mol­ecule as the second axial ligand. The carbene fragment is slightly distorted from an ideal sp² configuration, with a C(phenyl)—C(carbene)—C(phenyl) angle of 112.2 (3)°. The Ru—C bond length of 1.845 (3) Å is comparable with other carbene complexes. The two phenyl rings of the carbene ligand are perpendicular to the carbene plane. Methanol solvate mol­ecules link the methanol ligands of adjacent porphyrin complexes via hydrogen bonds.     

Ligand‐Supported Facile Conversion of Uranyl(VI) into Uranium(IV) in Organic and Aqueous Media

Reduction of uranyl(VI) to U^V and to U^IV is important in uranium environmental migration and remediation processes. The anaerobic reduction of a uranyl U^VI complex supported by a picolinate ligand in both organic and aqueous media is presented. The [U^VIO₂(dpaea)] complex is readily converted into the cis‐boroxide U^IV species via diborane‐mediated reductive functionalization in organic media. Remarkably, in aqueous media the uranyl(VI) complex is rapidly converted, by Na₂S₂O₄, a reductant relevant for chemical remediation processes, into the stable uranyl(V) analogue, which is then slowly reduced to yield a water‐insoluble trinuclear U^IV oxo‐hydroxo cluster. This report provides the first example of direct conversion of a uranyl(VI) compound into a well‐defined molecular U^IV species in aqueous conditions.