Revealing redox isomerism in trichromium imides by anomalous diffraction

In polynuclear biological active sites, multiple electrons are needed for turnover, and the distribution of these electrons among the metal sites is affected by the structure of the active site. However, the study of the interplay between structure and redox distribution is difficult not only in biological systems but also in synthetic polynuclear clusters since most redox changes produce only one thermodynamically stable product. Here, the unusual chemistry of a sterically hindered trichromium complex allowed us to probe the relationship between structural and redox isomerism. Two structurally isomeric trichromium imides were isolated: asymmetric terminal imide (^tbsL)Cr₃(NDipp) and symmetric, μ³-bridging imide (^tbsL)Cr₃(μ³–NBn) ((^tbsL)⁶⁻ = (1,3,5-C₆H₉(NC₆H₄-o-NSi^tBuMe₂)₃)⁶⁻). Along with the homovalent isocyanide adduct (^tbsL)Cr₃(CNBn) and the bisimide (^tbsL)Cr₃(μ³–NPh)(NPh), both imide isomers were examined by multiple-wavelength anomalous diffraction (MAD) to determine the redox load distribution by the free refinement of atomic scattering factors. Despite their compositional similarities, the bridging imide shows uniform oxidation of all three Cr sites while the terminal imide shows oxidation at only two Cr sites. Further oxidation from the bridging imide to the bisimide is only borne at the Cr site bound to the second, terminal imido fragment. Thus, depending on the structural motifs present in each [Cr₃] complex, MAD revealed complete localization of oxidation, partial localization, and complete delocalization, all supported by the same hexadentate ligand scaffold.

Application of high-resolution Multiwavelength Anomalous Diffraction (MAD) allows the assignment of localized, partly delocalized, and fully delocalized oxidation in a series of trichromium imide isomers.     

Lewis Acid Supported Nickel Nitrenoids

Metalation of the polynucleating ligand ^F,tbsLH₆ (1,3,5-C₆H₉(NC₆H₃−4-F−2-NSiMe₂^tBu)₃) with two equivalents of Zn(N(SiMe₃)₂)₂ affords the dinuclear product (^F,tbsLH₂)Zn₂ ( 1 ), which can be further deprotonated to yield (^F,tbsL)Zn₂Li₂(OEt₂)₄ ( 2 ). Transmetalation of 2 with NiCl₂(py)₂ yields the heterometallic, trinuclear cluster (^F,tbsL)Zn₂Ni(py) ( 3 ). Reduction of 3 with KC₈ affords [KC₂₂₂][(^F,tbsL)Zn₂Ni] ( 4 ) which features a monovalent Ni centre. Addition of 1-adamantyl azide to 4 generates the bridging μ³-nitrenoid adduct [K(THF)₃][(^F,tbsL)Zn₂Ni(μ³-NAd)] ( 5 ). EPR spectroscopy reveals that the anionic cluster possesses a doublet ground state (S = ). Cyclic voltammetry of 5 reveals two fully reversible redox events. The dianionic nitrenoid [K₂(THF)₉][(^F,tbsL)Zn₂Ni(μ³-NAd)] ( 6 ) was isolated and characterized while the neutral redox isomer was observed to undergo both intra- and intermolecular H-atom abstraction processes. Ni K-edge XAS studies suggest a divalent oxidation state for the Ni centres in both the monoanionic and dianionic [Zn₂Ni] nitrenoid complexes. However, DFT analysis suggests Ni-borne oxidation for 5 .     

Organo‐Palladium(II)‐Verbindungen mit PdC4‐Koordination: Phenylethinyl‐ und Methylphenylethinylkomplexe

Tetrakis(p‐tolyl)oxalamidinato‐bis[acetylacetonatopalladium(II)] ([Pd₂(acac)₂(oxam)]) reacted with Li–C≡C–C₆H₅ in THF with formation of [Pd(C≡C–C₆H₅)₄Li₂(thf)₄] ( 1a ). Reaction of [Pd₂(acac)₂(oxam)] with a mixture of 6 equiv. Li–C≡C–C₆H₅ and 2 equiv. LiCH₃ resulted in the formation of [Pd(CH₃)(C≡C–C₆H₅)₃Li₂(thf)₄] ( 2 ), and the dimeric complex [Pd₂(CH₃)₄(C≡C–C₆H₅)₄Li₄(thf)₆] ( 3 ) was isolated upon reaction of [Pd₂(acac)₂(oxam)] with a mixture of 4 equiv. Li–C≡C–C₆H₅ and 4 equiv. LiCH₃. 1 – 3 are extremely reactive compounds, which were isolated as white needles in good yields (60–90%). They were fully characterized by IR, ¹H‐, ¹³C‐, ⁷Li‐NMR spectroscopy, and by X‐ray crystallography of single crystals. In these compounds Li ions are bonded to the two carbon atoms of the alkinyl ligand. 1a reacted with Pd(PPh₃)₄ in the presence of oxygen to form the already known complexes trans‐[Pd(C≡C–C₆H₅)₂(PPh₃)₂] and [Pd(η²‐O₂)(PPh₃)₂]. In addition, 1a is an active catalyst for the Heck coupling reaction, but less active in the catalytic Sonogashira reaction.     

Novel dinuclear and trinuclear ruthenium clusters derived from 2‐aryl‐substituted indenylphosphines via C─H bond cleavage

Treatment of Ru₃(CO)₁₂ with an equivalent of (2‐phenyl‐1H ‐inden‐3‐yl)dicyclohexylphosphine ( 1 ) and (2‐pyridyl‐1H ‐inden‐1‐yl)dicyclohexylphosphine ( 4 ) in refluxing heptane gave the novel trinuclear ruthenium clusters (μ₃‐η¹:η²:η⁵–2‐phenyl‐3‐Cy₂PC₉H₄)Ru₃(CO)₈ ( 1c ) and [μ₂‐η¹–2‐(pyridin‐2‐yl)‐3‐Cy₂PC₉H₆]Ru₃(CO)₉ ( 4a ), respectively, via C ─ H bond cleavage. (2‐Mesityl‐1H ‐inden‐3‐yl)dicyclohexylphosphine ( 2 ) reacted with Ru₃(CO)₁₂ in refluxing heptane to give the trinuclear ruthenium cluster [μ‐2‐mesityl‐(3‐Cy₂PC₉H₅)](μ₂‐CO)Ru₃(CO)₉ ( 2c ) via C ─ H bond cleavage and carbonyl insertion. 2‐(Anthracen‐9‐yl)‐1H –inden‐3‐yldicyclohexylphosphine ( 3 ) reacted with Ru₃(CO)₁₂ in refluxing heptane to give the dinuclear ruthenium cluster [μ₂‐η³:η³–2‐(anthracen‐9‐yl)‐3‐Cy₂PC₉H₆]Ru₂(CO)₅ ( 3a ). The structures of 1c , 2c , 3a and 4a were fully characterized using IR and NMR spectroscopy, elemental analysis and single‐crystal X‐ray diffraction. These results suggest that the 2‐aryl substituent on the indenyl ring has a pronounced effect on the reaction and coordination modes of Ru₃(CO)₁₂.     

Synthese,Struktur und Reaktivität von Tris‐, Bis‐ und Mono(2,4‐dimethylpentadienyl)‐Komplexen des Neodyms,Lanthans und des Yttriums

The tris(2,4‐dimethylpentadienyl) complexes [Ln(η⁵‐Me₂C₅H₅)₃] (Ln = Nd, La, Y) are obtained analytically pure by reaction of the tribromides LnBr₃·nTHF with the potassium compound K(Me₂C₅H₅)(thf)_n in THF in good yields. The structural characterization is carried out by X‐ray crystal structure analysis and NMR‐spectroscopically. The tris complexes can be transformed into the dimeric bis(2,4‐dimethylpentadienyl) complexes [Ln₂(η⁵‐Me₂C₅H₅)₄X₂] (Ln, X: Nd, Cl, Br, I; La, Br, I; Y, Br) by reaction with the trihalides THF solvates in the molar ratio 2:1 in toluene. Structure and bonding conditions are determined for selected compounds by X‐ray crystal structure analysis and NMR‐spectroscopically in general. The dimer‐monomer equilibrium existing in solution was investigated NMR‐spectroscopically in dependence of the donor strength of the solvent and could be established also by preparation of the corresponding monomer neutral ligand complexes [Ln(η⁵‐Me₂C₅H₅)₂X(L)] (Ln, X, L: Nd, Br, py; La, Cl, thf; Br, py; Y, Br, thf). Finally the possibilities for preparation of mono(2,4‐dimethylpentadienyl)lanthanoid(III)‐dibromid complexes are shown and the hexameric structure of the lanthanum complex [La₆(η⁵‐Me₂C₅H₅)₆Br₁₂(thf)₄] is proved by X‐ray crystal structure analysis.     

Reactivity of an All‐Ferrous Iron–Nitrogen Heterocubane under Reductive and Oxidative Conditions

The reactivity of the all‐ferrous FeN heterocubane [Fe₄(Ntrop)₄] ( 1 ) with i) Brønsted acids, ii) σ‐donors, iii) σ‐donors/π‐acceptors, and iv) one‐electron oxidants has been investigated (trop = 5H‐dibenzo[a,d]cyclo‐hepten‐5‐yl). 1 showed self‐re‐assembling after reactions with i) and proved surprisingly inert in reactions with ii) and iii), with the exception of CO. Reductive and oxidative cluster degradation was observed in reactions with CO and TEMPO, respectively. These reactions yielded new cluster compounds, namely a trinuclear bis(μ₃‐imido) 48 electron complex in the former case and a tetranuclear all ferric μ‐oxo‐μ‐imido species in the latter case. Characterization techniques include NMR and in situ IR spectroscopy, single crystal X‐ray analysis, Mössbauer spectroscopy, cyclic voltammetry, magnetic susceptibility measurements, and DFT calculations.     

Phosphorus‐Stabilized Titanium Carbene Complexes: Synthesis,Reactivity and DFT Studies

The synthesis of two novel titanium carbene complexes from the bis(thiophosphinoyl)methanediide geminal dianion 1 (SCS^2?) is described. Dianion 1 reacts cleanly with 0.5 equivalents of [TiCl₄(thf)₂] to afford the bis‐carbene complex [(SCS)₂Ti] ( 2 ) in 86 % yield. The mono‐carbene complex [(SCS)TiCl₂(thf)] ( 3 ) can also be obtained by using an excess of [TiCl₄(thf)₂]. The structures of 2 and 3 are confirmed by X‐ray crystallography. A strong nucleophilic reactivity towards various electrophiles (ketones and aldehydes) is observed. The reaction of 3 with N,N′‐dicyclohexylcarbodiimide (DCC) and phenyl isocyanate leads to the formation of two novel diphosphinoketenimines 8 a and 8 b . The bis‐titanium guanidinate complex 9 is trapped as the by‐product of the reaction with DCC. The X‐ray crystal structures of 8 a and 9 are presented. The mechanism of the reaction between complex 3 and DCC is rationalized by DFT studies.     

Kinetics and Mechanism of Oxidation of Chromium(III)‐guanosine 5‐Monophosphate Complex by Periodate

The kinetics of oxidation of the chromium(III)‐guanosine 5‐monophosphate complex, [Cr^III(L)(H₂O)₄]³⁺(L = guanosine 5‐monophosphate) by periodate in aqueous solution to Cr^VI have been studied spectrophotometrically over the 25–45 °C range. The reaction is first order with respect to both [IO₄^?] and [Cr^III], and increases with pH over the 2.38–3.68 range. Thermodynamic activation parameters have been calculated. It is proposed that electron transfer proceeds through an inner‐sphere mechanism via coordination of IO₄^? to chromium(III).     

A Water Stable CdII‐based Metal‐Organic Framework as a Multifunctional Sensor for Selective Detection of Cu2+ and Cr2O72– Ions

A water stable tetrazolate‐containing metal‐organic framework, [Cd₂(L)(OH)(H₂O)₂]_n ( 1 ) [H₃L = 5‐(4‐(tetrazol‐5‐yl)phenyl)isophthalic acid], was synthesized under solvothermal conditions and structurally characterized. Compound 1 displays a three dimensional porous network with one dimensional tubular channels based on trinuclear cluster [Cd₃(μ₃‐OH)N₄C] units. Notably, 1 exhibits highly sensitive response to Cu²⁺ and Cr₂O₇^2– through luminescence quenching effects with the detection limit of 0.666 ppm for Cu²⁺ and 0.846 ppm for Cr₂O₇^2–, respectively. The possible mechanism of the luminescence quenching was discussed in detail.     

An azide‐bridged copper(II) complex: poly[piperazine‐1,4‐dium [tetra‐μ3‐azido‐κ12N1:N1:N1‐hexa‐μ2‐azido‐κ12N1:N1‐di‐μ2‐azido‐κ4N1:N3‐pentacopper(II)] tetrahydrate]

A new Cu^II–azide complex, {(C₄H₁₂N₂)[Cu₅(N₃)₁₂]·4H₂O}_n, has been synthesized by the reaction of piperazine, Cu(OAc)₂·2H₂O (OAc is acetate) and NaN₃. In the structure, μ₂‐1,1‐ and μ₃‐1,1,1‐azide anions bridge five Cu^II cations to form a linear pentanuclear cluster unit, which is further linked by μ₂‐1,1‐ and μ₂‐1,3‐azide anions to form a two‐dimensional condensed [Cu₅(N₃)₁₂]_n layer. The diprotonated piperazine and the solvent water molecules are hydrogen bonded to the coordination layers to form a three‐dimensional supramolecular network.     

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.     

Y,Lu, and Gd Complexes of NCO/NCS Pincer Ligands: Synthesis,Characterization, and Catalysis in the cis‐1,4‐Selective Polymerization of Isoprene

A series of NCO/NCS pincer precursors, 3‐(Ar²OCH₂)‐2‐Br‐(Ar¹N?CH)C₆H₃ ((^Ar1NCO^Ar2)Br, 3a , 3b , 3c , 3d ) and 3‐(2,6‐Me₂C₆H₃SCH₂)‐2‐Br‐(Ar¹N?CH)C₆H₃ ((^Ar1NCS^Me)Br, 4a and 4b ) were synthesized and characterized. The reactions of [^Ar1NCO^Ar2]Br/ [^Ar1NCS^Me]Br with nBuLi and the subsequent addition of the rare‐earth‐metal chlorides afforded their corresponding rare‐earth‐metal–pincer complexes, that is, [(^Ar1NCO^Ar2)YCl₂(thf)₂] ( 5a , 5b , 5c , 5d ), [(^Ar1NCO^Ar2)LuCl₂(thf)₂] ( 6a , 6d ), [(^Ar1NCO^Ar2)GdCl₂(thf)₂] ( 7 ), [{(^Ar1NCS^Me)Y(μ‐Cl)}₂{(μ‐Cl)Li(thf)₂(μ‐Cl)}₂] ( 8 , 9 ), and [{(^Ar1NCS^Me)Gd(μ‐Cl)}₂{(μ‐Cl)Li(thf)₂(μ‐Cl)}₂] ( 10 , 11 ). These diamagnetic complexes were characterized by ¹H and ¹³C NMR spectroscopy and the molecular structures of compounds 5a , 6a , 7 , and 10 were well‐established by X‐ray diffraction analysis. In compounds 5a , 6a , and 7 , all of the metal centers adopted distorted pentagonal bipyramidal geometries with the NCO donors and two oxygen atoms from the coordinated THF molecules in equatorial positions and the two chlorine atoms in apical positions. Complex 10 is a dimer in which the two equal moieties are linked by two chlorine atoms and two Cl? Li? Cl bridges. In each part, the gadolinium atom adopts a distorted pentagonal bipyramidal geometry. Activated with alkylaluminum and borate, the gadolinium and yttrium complexes showed various activities towards the polymerization of isoprene, thereby affording highly cis‐1,4‐selective polyisoprene, whilst the NCO? lutetium complexes were inert under the same conditions.     

A new double‐cube nitride complex containing titanium and potassium

The reaction of the imide–nitride complex [{Ti(η⁵‐C₅Me₅)(μ‐NH)}₃(μ₃‐N)] with potassium iodide in pyridine at room temperature affords the adduct di‐μ‐iodido‐1:1′κ⁴I‐bis{tri‐μ₃‐imido‐1:2:3κ³N;1:2:4κ³N;1:3:4κ³N‐μ₃‐nitrido‐2:3:4κ³N‐tris[2,3,4(η⁵)‐pentamethylcyclopentadienyl](pyridine‐1κN)‐tetrahedro‐potassiumtrititanium(IV)}, [K₂Ti₆(C₁₀H₁₅)₆I₂N₂(NH)₆(C₅H₅N)₂] or [(C₅H₅N)(μ‐I)K{(μ₃‐NH)₃Ti₃(η⁵‐C₅Me₅)₃(μ₃‐N)}]₂. The crystal structure contains two [KTi₃N₄] cube‐type units held together by two bridging I atoms. There is a centre of inversion located in the middle of this unprecedented discrete K₂I₂ unit. The geometry around K is best described as distorted trigonal prismatic, with three imide groups, two bridging I atoms and one pyridine ligand.     

Lutetium‐Methanediide‐Alkyl Complexes: Synthesis and Chemistry

The first four‐coordinate methanediide/alkyl lutetium complex (BODDI)Lu₂(CH₂SiMe₃)₂(μ₂‐CHSiMe₃)(THF)₂ (BODDI=ArNC(Me)CHCOCHC(Me)NAr, Ar=2,6‐iPr₂C₆H₃) ( 1 ) was synthesized by a thermolysis methodology through α‐H abstraction from a Lu–CH₂SiMe₃ group. Complex 1 reacted with equimolar 2,6‐iPrC₆H₃NH₂ and Ph₂C?O to give the corresponding lutetium bridging imido and oxo complexes (BODDI)Lu₂(CH₂SiMe₃)₂(μ₂‐N‐2,6‐iPr₂C₆H₃)(THF)₂ ( 2 ) and (BODDI)Lu₂(CH₂SiMe₃)₂(μ₂‐O)(THF)₂ ( 3 ). Treatment of 3 with Ph₂C?O (4 equiv) caused a rare insertion of Lu–μ₂‐O bond into the C?O group to afford a diphenylmethyl diolate complex 4 . Reaction of 1 with PhN=C?O (2 equiv) led to the migration of SiMe₃ to the amido nitrogen atom to give complex (BODDI)Lu₂(CH₂SiMe₃)₂‐μ‐{PhNC(O)CHC(O)NPh(SiMe₃)‐κ³N,O,O}(THF) ( 5 ). Reaction of 1 with tBuN?C formed an unprecedented product (BODDI)Lu₂(CH₂SiMe₃){μ₂‐[η²:η²‐tBuNC(=CH₂)SiMe₂CHC?NtBu‐κ¹N]}(tBuN?C)₂ ( 6 ) through a cascade reaction of N?C bond insertion, sequential cyclometalative γ‐(sp³)‐H activation, C?C bond formation, and rearrangement of the newly formed carbene intermediate. The possible mechanistic pathways between 1 , PhN?C?O, and tBuN?C were elucidated by DFT calculations.     

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.     

Novel bimetallic Cr<Subscript>3</Subscript>Yb<Subscript>3</Subscript> mixed salt containing a 3<Emphasis Type="Italic">d</Emphasis>-4<Emphasis Type="Italic">f</Emphasis> heterometallic Cr<Subscript>2</Subscript>Yb<Subscript>3</Subscript> cluster

A novel bimetallic Cr₃Yb₃ coordination compound containing a 3d-4f heterometallic Cr₂Yb₃ cationic cluster has been synthesized and structurally characterized. The crystal structure was determined by X-ray analysis. Results denote that the complex consists of an original [Cr ₂ ^III Yb ₃ ^III ]³⁺ moiety with a trigonal-bipyramidal topology of the [Cr₂Yb₃(μ-OOCCH₃)₆(μ-OH)₆(H₂O)₆]³⁺ core, an isolated [Cr^III(CN)₆]^3? anion, and four molecular neutral 4,4′-bipyridene (Bipy) ligands, namely, [Cr₂Yb₃(μ-OOCCH₃)₆(μ-OH)₆(H₂O)₆][Cr(CN)₆] · 4Bipy · 13H₂O.     

Structural Diversity of Calcium Organocuprates(I): Synthesis of Mesityl Cuprates via Addition and Transmetalation Reactions of Mesityl Copper(I)

The addition of [(L)₄Ca(I)Mes] (Lewis base L=thf, Et₂O) to mesityl copper(I) and the transmetalation reaction of mesityl copper(I) with activated calcium are suitable pathways for the synthesis of dimesityl cuprates(I) of calcium. However, the structures of the calcium cuprates(I) depend on the preparative procedure. The transmetalation reaction leads to the formation of [Mes‐Cu‐Mes]^? anions whereas the addition yields dinuclear [(Mes‐Cu)₂(μ‐Mes)]^? anions. The solvent‐separated counterions are [Ca(thf)₆]²⁺ and [(thf)₅CaI]⁺, respectively. In contrast to these findings, the addition of [(L)₄Ca(I)Mes] to mesityl copper(I) in an Et₂O/toluene mixture led to formation of tetrameric solvent‐free iodocalcium dimesityl cuprate(I) [ICa(μ‐η¹,η⁶‐Mes₂Cu)]₄, representing a rare example of a heavy Normant‐type organocuprate.     

Bis[trans‐dibromo(2,2‐di­methylpropane‐1,3‐diamine‐κ2N,N′)chromium(III)] dibromide hydrogen perchlorate hexahydrate

In the title compound, [CrBr₂(C₅H₁₄N₂)₂]₂Br₂·HClO₄·6H₂O, there are two independent Cr^III complex cations which are conformational isomers of each other. The Cr atoms lie respectively on a center of symmetry and on a mirror plane and have octahedral environments, coordinated by the N atoms of two 2,2‐di­methylpropane‐1,3‐diamine ligands and by two Br atoms in trans positions. The Cr—N and Cr—Br bond lengths are in the ranges 2.078 (3)–2.089 (3) and 2.4495 (9)–2.5017 (9) Å, respectively. The crystal structure consists of two Cr^III complex cations, two Br^? anions, a (ClO₄)^? anion and an [H₁₃O₆]⁺ hydrogen‐bonded cluster cation.     

Sigma‐ versus Pi‐Koordination in Bis‐indenyl‐ und Bis‐2‐methallyl‐Imidokomplexen des sechswertigen Molybdäns und Wolframs: DF‐Rechnungen und Kristallstrukturanalyse

Sigma‐ versus Pi‐Coordination in Bis‐indenyl‐ and Bis‐2‐methallyl Imido Complexes of Hexavalent Molybdenum and Tungsten: DF‐Calculations and Crystal Structure Analysis Bis‐indenyl and bis‐2‐methallyl imido complexes [(C₉H₇)₂M(NR)₂] (M = Mo, W; R = tert‐butyl, mesityl) 1 — 4 and [(H₃C‐C₃H₄)₂M(NtBu)₂] (M = Mo, W) 6 , 7 have been prepared starting from [Mo(NtBu)₂Cl₂] or [M(NR)₂Cl₂L₂] (M = W, R = tBu, L = py; M = Mo, W, R = Mes, L₂ = dme) and indenyl lithium or 2‐methallyl magnesium bromide, respectively. According to spectroscopic data and the crystal structure of 4 there are two different coordination modes of the indenyl ligands, [(η³‐C₉H₇)M(NR)₂(η¹‐C₉H₇)], in solution as well as in the solid state. These compounds show fluxional rearrangements in solution, namely σ, π‐exchange of η¹‐ and η³‐coordinated ligands. Similar behavior has been observed for the 2‐methallyl complexes 6 and 7 in solution. In agreement with experimental observations, DF calculations on models of 6 strongly suggest a (σ+π)‐coordination mode of the η³‐coordinated ligand.     

Divalent Ytterbium Iodide Supported by β‐Diketiminato Based Tridentate Ligand: Synthesis,Structure and Small Molecule Activation†

Divalent ytterbium iodide [LYb(μ‐I)(THF)]₂ ( 1 ; L = [MeC(NDIPP)CHC(Me)NCH₂CH₂NMe₂]^?, DIPP = 2,6‐(ⁱPr)₂C₆H₃) was synthesized and its reactivity was studied. Complex 1 was synthesized by salt metathesis of YbI₂(THF)₂ with the potassium salt of ligand (KL) in high yield. In the reactions with trimethylsilyl azide, azobenzene, sulfur and diphenyl disulfide, complex 1 acts as a 2e reductant. In the reaction with CO₂, the central carbon atom of β‐diketiminato backbone in 1 nucleophilically attacks the CO₂ molecule to give a divalent ytterbium carboxylate.