Synthesis and Structural Characterization of Several Ytterbium Bis(trimethylsilyl)amides Including Base‐free [Yb{N(SiMe3)2}2(μ‐Cl)]2 — A Coordinatively Unsaturated Complex with Additional Agostic Yb···(H3C—Si) Interactions

The reaction of YbCl₃ with two equivalents of NaN‐(SiMe₃)₂ has afforded a mixture of several ytterbium bis(trimethylsilyl) amides with the known complexes [Yb{N(SiMe₃)₂}2(μ‐Cl)(thf)]₂ ( 1 ) and [Yb{N(SiMe₃)₂}₃]( 4 ) as the main products and the cluster compound [Yb₃Cl₄O{N(SiMe₃)₂}₃(thf)₃]( 2 ) as a minor product. Treatment of 1 and 2 with hot n‐heptane gave the basefree complex [Yb{N(SiMe₃)₂}₂(μ‐Cl)]₂ ( 3 ) in small yield. The structures of compounds 1—4 and the related peroxo complex [Yb₂{N(SiMe₃)₂}₄(μ‐O₂)(thf)₂]( 5 ) have been investigated by single crystal X‐ray diffraction. In the solid‐state, 3 shows chlorobridged dimers with terminal amido ligands (av. Yb—Cl = 262.3 pm, av. Yb—N = 214.4 pm). Additional agostic interactions are observed from the ytterbium atoms to four methyl carbon atoms of the bis(trimethylsilyl)amido groups (Yb···C = 284—320 pm). DFT calculations have been performed on suitable model systems ([Yb₂(NH₂)₄(μ‐Cl)₂(OMe₂)₂]( 1m ), [Yb₂(NH₂)₄(μ‐Cl)₂]( 3m ), [Yb‐(NH₂)₃]( 4m ), [Yb₂(NH2₄(μ‐O₂)(OMe₂)₂]( 5m ), [Yb{N‐(SiMe₃)₂}₂Cl] ( 3m/2 ) and Ln(NH₂)₂NHSiMe₃ (Ln = Yb ( 6m ), Y ( 7m )) in order to rationalize the different experimentally observed Yb—N distances, to support the assignment of the O—O stretching vibration (775 cm ^‐1) in the Raman spectrum of complex 5 and to examine the nature of the agostic‐type interactions in σ‐donorfree 3 .     

Two‐Coordinate Iron(I) Complex [Fe{N(SiMe3)2}2]−: Synthesis,Properties, and Redox Activity

First‐row two‐coordinate complexes are attracting much interest. Herein, we report the high‐yield isolation of the linear two‐coordinate iron(I) complex salt [K(L)][Fe{N(SiMe₃)₂}₂] (L=18‐crown‐6 or crypt‐222) through the reduction of either [Fe{N(SiMe₃)₂}₂] or its three‐coordinate phosphine adduct [Fe{N(SiMe₃)₂}₂(PCy₃)]. Detailed characterization is gained through X‐ray diffraction, variable‐temperature NMR spectroscopy, and magnetic susceptibility studies. One‐ and two‐electron oxidation through reaction with I₂ is further found to afford the corresponding iodo iron(II) and diiodo iron(III) complexes.     

Amidometallate von Seltenerdelementen. Synthese und Kristallstrukturen von [Na(12-Krone-4)2][M{N(SiMe3)2}3(OSiMe3)] (M = Sm,Yb), [Na(THF)3Sm{N(SiMe3)2}3(C≡C–Ph)], [Na(THF)6][Lu2(μ-NH2)(μ-NSiMe3){N(SiMe3)2}4] sowie von [NaN(SiMe3)2(THF)]2. Anwendungen der Seltenerdkomplexe als Polymerisationskatalysatoren

Amido Metalates of Rare Earth Elements. Syntheses and Crystal Structures of [Na(12-crown-4)₂][M{N(SiMe₃)₂}₃(OSiMe₃)] (M = Sm, Yb), [Na(THF)₃Sm{N(SiMe₃)₂}₃(C≡C–Ph)], [Na(THF)₆][Lu₂(μ-NH₂)(μ-NSiMe₃){N(SiMe₃)₂}₄], and of [NaN(SiMe₃)₂(THF)]₂. Applications of Rare Earth Metal Complexes as Polymerization Catalysts The amido silyloxy complexes [Na(12-crown-4)₂][M{N(SiMe₃)₂}₃(OSiMe₃)] with M = Sm ( 1 a ), Eu ( 1 b ), Yb ( 1 c ), and Lu ( 1 d ) were obtained from the trisamides M[N(SiMe₃)₃]₃ and NaOSiMe₃ in n-hexane in the presence of 12-crown-4; they form yellow to orange-red crystals, of which 1 a and 1 c were characterized crystallographically. The complexes crystallize isotypically with one another in the monoclinic space group I2/a with eight formula units per unit cell. The metal atoms of the complex anions are tetrahedrally coordinated by the three nitrogen atoms of the N(SiMe₃)₂^– ligands and by the oxygen atom of the OSiMe₃^– ligand. With 172.4° for 1 a and 179.3° for 1 c the bond angles M–O–Si are practically linear. With ethynylbenzene in the presence of NaN(SiMe₃)₂ in tetrahydrofuran the trisamides M[N(SiMe₃)₂]₃ react under formation of the complexes [Na(THF)₃M{N(SiMe₃)₂}₃ · (C≡C–Ph)] with M = Ce ( 2 a ), Sm ( 2 b ), and Eu ( 2 c ), of which 2 b was characterized crystallographically (monoclinic, space group P2₁/n, Z = 4). 2 b forms an ion pair in which the terminal carbon atom of the C≡C–Ph^– ligand is connected with the samarium atom of the Sm[N(SiMe₃)₂]₃ group and the sodium ion is side-on connected with the acetylido group. According to the crystal structure determination (space group P2₁2₁2₁, Z = 4) [Na(THF)₆][Lu₂(μ-NH₂)(μ-NSiMe₃) · {N(SiMe₃)₂}₄] ( 3 ), which is formed as a by-product, consists of [Na(THF)₆]⁺ ions and dimeric anions, in which the lutetium atoms are connected to form a planar Lu₂N₂ four-membered ring via a μ-NH₂ bridge with average Lu–N distances of 227.2 pm and via a μ-NSiMe₃ bridge of average Lu–N distances of 218.5 pm. According to the crystal structure determination (space group P 1, Z = 1) [NaN(SiMe₃)₂(THF)]₂ ( 4 ) forms centrosymmetric dimeric molecules with Na–N distances of the Na₂N₂ four-membered ring of 239.9 pm and distances Na–O of the terminally bonded THF molecules which are 226.7 pm. The vinylic polymerization of methylmethacrylate (MMA) catalyzed by 1 c resulted in high molecular weight polymethylmethacrylate (PMMA) with moderate yields. The reaction of 1 a or 2 b with MMA did not give PMMA. Insoluble polynorbornene was obtained in low yields by reaction of norbornene/methylaluminoxane (MAO) with 1 a , 1 c , or 2 b . The ring opening polymerization of ϵ-caprolacton or δ-valerolacton catalyzed by 2 b resulted in corresponding polylactones in quantitative yields.     

Two‐Coordinate Iron(I) Complex [Fe{N(SiMe3)2}2]−: Synthesis,Properties, and Redox Activity

First‐row two‐coordinate complexes are attracting much interest. Herein, we report the high‐yield isolation of the linear two‐coordinate iron(I) complex salt [K(L)][Fe{N(SiMe₃)₂}₂] (L=18‐crown‐6 or crypt‐222) through the reduction of either [Fe{N(SiMe₃)₂}₂] or its three‐coordinate phosphine adduct [Fe{N(SiMe₃)₂}₂(PCy₃)]. Detailed characterization is gained through X‐ray diffraction, variable‐temperature NMR spectroscopy, and magnetic susceptibility studies. One‐ and two‐electron oxidation through reaction with I₂ is further found to afford the corresponding iodo iron(II) and diiodo iron(III) complexes.     

Komplexchemie P‐reicher Phosphane und Silylphosphane. XXII. Die Bildung von [η2‐{tBu–P=P–SiMe3}Pt(PR3)2]aus (Me3Si)tBuP–P=P(Me)tBu2 und [η2‐{C2H4}Pt(PR3)2]

Coordination Chemistry of P‐rich Phosphanes and Silylphosphanes. XXII. The Formation of [η²‐{^tBu–P=P–SiMe₃}Pt(PR₃)₂] from (Me₃Si)^tBuP–P=P(Me)^tBu₂ and [η²‐{C₂H₄}Pt(PR₃)₂] (Me₃Si)^tBuP–P = P(Me)^tBu₂ reacts with [η²‐{C₂H₄}Pt(PR₃)₂] yielding [η²‐{^tBu–P=P–SiMe₃}Pt(PR₃)₂]. However, there is no indication for an isomer which would be the analogue to the well known [η²‐{^tBu₂P–P}Pt(PPh₃)₂]. The syntheses and NMR data of [η²‐{^tBu–P=P–SiMe₃}Pt(PPh₃)₂] and [η²‐{^tBu–P=P–SiMe₃}Pt(PMe₃)₂] as well as the results of the single crystal structure determination of [η²‐{^tBu–P=P–SiMe₃}Pt(PPh₃)₂] are reported.     

Iron‐ and Cobalt‐Catalyzed Synthesis of Carbene Phosphinidenes

In the presence of stoichiometric or catalytic amounts of [M{N(SiMe₃)₂}₂] (M=Fe, Co), N‐heterocyclic carbenes (NHCs) react with primary phosphines to give a series of carbene phosphinidenes of the type (NHC)?PAr. The formation of (IMe₄)?PMes (Mes=mesityl) is also catalyzed by the phosphinidene‐bridged complex [(IMe₄)₂Fe(μ‐PMes)]₂, which provides evidence for metal‐catalyzed phosphinidene transfer.     

Dinuclear Rare‐Earth Metal Alkyl Complexes Supported by Indolyl Ligands in μ‐η2:η1:η1 Hapticities and their High Catalytic Activity for Isoprene 1,4‐cis‐Polymerization

Two series of new dinuclear rare‐earth metal alkyl complexes supported by indolyl ligands in novel μ‐η²:η¹:η¹ hapticities are synthesized and characterized. Treatment of [RE(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of 3‐(tBuN?CH)C₈H₅NH ( L₁ ) in THF gives the dinuclear rare‐earth metal alkyl complexes trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH(CH₂SiMe₃)}Ind)RE(thf)(CH₂SiMe₃)]₂ (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L₁ is deprotonated by the metal alkyl species and the imino C?N group is transferred to the amido group by alkyl CH₂SiMe₃ insertion, affording a new dianionic ligand that bridges two metal alkyl units in μ‐η²:η¹:η¹ bonding modes, forming the dinuclear rare‐earth metal alkyl complexes. When L₁ is reduced to 3‐(tBuNHCH₂)C₈H₅NH ( L₂ ), the reaction of [Yb(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of L₂ in THF, interestingly, generated the trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (major) and cis‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (minor) complexes. The catalytic activities of these dinuclear rare‐earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio‐ and stereoselectivities for isoprene 1,4‐cis‐polymerization.     

Low‐Coordinate Barium Boryloxides: Synthesis and Dehydrocoupling Catalysis for the Production of Borasiloxanes

The first soluble barium boryloxides [Ba]– OB{CH(SiMe₃)₂} are presented. These mono‐ or dinuclear complexes feature low coordination numbers, as low as two for [Ba(OB{CH(SiMe₃)₂}₂)₂], which is further stabilized by intra‐ and intermolecular Ba???H₃C agostic interactions. Barium boryloxides and the parent [Ba{N(SiMe₃)₂}₂?(thf)₂] catalyze the dehydrocoupling of borinic acids with hydrosilanes, providing borasiloxanes under mild conditions.     

Barium‐Mediated Cross‐Dehydrocoupling of Hydrosilanes with Amines: A Theoretical and Experimental Approach

Alkaline‐earth (most prominently barium) complexes of the type [Ae{N(SiMe₃)₂}₂?(THF)_x] and [{N^N}Ae{N(SiMe₃)₂}?(THF)_x] are very active and productive precatalysts (TON=396, TOF up to 3600 h^?1; Ca相似文献   

Dinuclear Dysprosium and Ytterbium Complexes Incorporating N,N‐Bis(pyrrolyl‐α‐methyl)‐N‐methylamine Ligand: Syntheses and Structures

Reaction of DyCl₃ with two equivalents of NaN(SiMe₃)₂ in THF yielded {Dy(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 1 ). X‐ray crystal structure analysis revealed that 1 is a centrosymmetric dimer with asymmetrically bridging chloride ligands. The metal coordination arrangement can be best described as distorted trigonal bipyramid. The bond lengths of Ln–Cl and Ln–N showed a decreasing trend with the contraction of the size of Ln³⁺. Treatment of N,N‐bis(pyrrolyl‐α‐methyl)‐N‐methylamine (H₂dpma) with 1 and known compound {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂, respectively, led to the formations of [Dy(μ‐Cl)(dpma)(THF)₂]₂ ( 2 ) and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 3 ). Compounds 2 and 3 were fully characterized by single‐crystal X‐ray crystallography, elemental analysis, and ¹H NMR spectroscopy. Structure determination indicated that 2 and 3 exhibit as centrosymmetric dimers with asymmetrically bridging chloride ligands. One pot reactions involving LnCl₃ (Ln = Dy and Yb), LiN(SiMe₃)₂, and H₂dpma were explored and desired products 2 and 3 were not yielded, which indicated that 1 and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ are the demanding precursors to synthesize Dysprosium and Ytterbium complexes supported by dpma^2– ligand. Compounds 2 and 3 are the first reported lanthanide complexes chelated by dpma^2– ligand.     

The [Zr(N{SiMe3}2)3]+ cation as a novel initiator for carbocationic isobutene homo- and isobutene/isoprene co-polymerisations

Methyl abstraction of ZrMe{N(SiMe₃)₂}₃ with B(C₆F₅)₃ gives the cationic zirconium amide complex [Zr{N(SiMe₃)₂}₃]⁺ which acts as an initiator for the carbocationic polymerisation of isobutene and for isobutene-isoprene copolymerisations. High molecular weight homo- and co-polymers are obtained at temperatures up to −30°C. Molecular weights are less temperature dependent than in metal halide initiated systems.     

Tris(3,5‐dimethylpyrazolyl)methane‐Based Heterobimetallic Complexes that Contain Zn and CdTransition‐Metal Bonds: Synthesis,Structures, and Quantum Chemical Calculations

Reactions of the tris(3,5‐dimethylpyrazolyl)methanide amido complexes [M′{C(3,5‐Me₂pz)₃}{N(SiMe₃)₂}] (M′=Mg ( 1 a ), Zn ( 1 b ), Cd ( 1 c ); 3,5‐Me₂pz=3,5‐dimethylpyrazolyl) with two equivalents of the acidic Group 6 cyclopentadienyl (Cp) tricarbonyl hydrides [MCp(CO)₃H] (M=Cr ( 2 a ), Mo ( 2 b )) gave different types of heterobimetallic complex. In each case, two reactions took place, namely the conversion of the tris(3,5‐dimethylpyrazolyl)methanide ligand (Tpmd*) into the ‐methane derivative (Tpm*) and the reaction of the acidic hydride M?H bond with the M′?N(SiMe₃)₂ moiety. The latter produces HN(SiMe₃)₂ as a byproduct. The Group 2 representatives [Mg(Tpm*){MCp(CO)₃}₂(thf)] ( 3 a / b ) form isocarbonyl bridges between the magnesium and chromium/molybdenum centres, whereas direct metal–metal bonds are formed in the case of the ions [Zn(Tpm*){MCp(CO)₃}]⁺ ( 4 a / b ; [MCp(CO)₃]^? as the counteranion) and [Cd(Tpm*){MCp(CO)₃}(thf)]⁺ ( 5 a / b ; [Cd{MCp(CO)₃}₃]^? as the counteranion). Complexes 4 a and 5 a / b are the first complexes that contain Zn?Cr, Cd?Cr, and Cd?Mo bonds (bond lengths 251.6, 269.8, and 278.9 pm, respectively). Quantum chemical calculations on 4 a / b* (and also on 5 a / b* ) provide evidence for an interaction between the metal atoms.     

Structural and Magnetic Diversity in Alkali‐Metal Manganate Chemistry: Evaluating Donor and Alkali‐Metal Effects in Co‐complexation Processes

By exploring co‐complexation reactions between the manganese alkyl Mn(CH₂SiMe₃)₂ and the heavier alkali‐metal alkyls M(CH₂SiMe₃) (M=Na, K) in a benzene/hexane solvent mixture and in some cases adding Lewis donors (bidentate TMEDA, 1,4‐dioxane, and 1,4‐diazabicyclo[2,2,2] octane (DABCO)) has produced a new family of alkali‐metal tris(alkyl) manganates. The influences that the alkali metal and the donor solvent impose on the structures and magnetic properties of these ates have been assessed by a combination of X‐ray, SQUID magnetization measurements, and EPR spectroscopy. These studies uncover a diverse structural chemistry ranging from discrete monomers [(TMEDA)₂MMn(CH₂SiMe₃)₃] (M=Na, 3 ; M=K, 4 ) to dimers [{KMn(CH₂SiMe₃)₃?C₆H₆}₂] ( 2 ) and [{NaMn(CH₂SiMe₃)₃}₂(dioxane)₇] ( 5 ); and to more complex supramolecular networks [{NaMn(CH₂SiMe₃)₃}_∞] ( 1 ) and [{Na₂Mn₂(CH₂SiMe₃)₆(DABCO)₂}_∞] ( 7 )). Interestingly, the identity of the alkali metal exerts a significant effect in the reactions of 1 and 2 with 1,4‐dioxane, as 1 produces coordination adduct 5 , while 2 forms heteroleptic [{(dioxane)₆K₂Mn₂(CH₂SiMe₃)₄(O(CH₂)₂OCH=CH₂)₂}_∞] ( 6 ) containing two alkoxide–vinyl anions resulting from α‐metalation and ring opening of dioxane. Compounds 6 and 7 , containing two spin carriers, exhibit antiferromagnetic coupling of their S=5/2 moments with varying intensity depending on the nature of the exchange pathways.     

Synthese und Insertionsreaktionen von Cp2′HfCl{As(SiMe3)2} (Cp′ = C5H4Me)

Synthesis and Insertion Reactions of Cp₂′HfCl{As(SiMe₃)₂} (Cp′ = C₅H₄Me) The reaction of Cp₂′HfCl₂ (Cp′ = C₅H₄Me) with Li(THF)_2,5As(SiMe₃)₂ (1 : 1) at room temperature gives the terminal hafnocene arsenido complex Cp₂′HfCl{As(SiMe₃)₂} ( 1 ) in high yield. 1 inserts CS₂ and PhNC into the Hf? As bond yielding Cp₂′HfCl{η²-S₂CAs(SiMe₃)₂} ( 2 ) and Cp₂′HfCl{η²-N(Ph)CAs(SiMe₃)₂} ( 3 ). The thermally sensitive complexes 1–3 were characterised spectroscopically and crystal structure determinations were carried out on 1 and 3 which shows the η² bonding mode of the N(Ph)CAs(SiMe₃)₂ ligand in the latter.     

1‐Azaallyl Complexes of NiII,PdII, and TiIII

The metal complexes [Ni{N(Ar)C(R)C(H)Ph}₂) ( 2 ) (Ar = 2,6‐Me₂C₆H₃, R = SiMe₃), [Ti(Cp₂){N(R)C(Bu^t)C(H)R}] ( 3 ), M{N(R)C(Bu^t)C(H)R}I [M = Ni ( 4 a ) or Pd ( 4 b )] and [M{N(R)C(Bu^t)C(H)R}I(PPh₃)] [M = Ni ( 5 a ) or Pd ( 5 b )] have been prepared from a suitable metal halide and lithium precursor of ( 2 ) or ( 3 ) or, alternatively from [M(LL)₂] (M = Ni, LL = cod; M = Pd, LL = dba) and the ketimine RN = C(Bu^t)CH(I)R ( 1 ). All compounds, except 4 were fully characterised, including the provision of X‐ray crystallographic data for complex 5 a .     

Synthese,Struktur und Reaktivität von η3‐1,2‐Diphosphaallylkomplexen sowie von [{(η5‐C5H5)(CO)2W–Co(CO)3}{μ‐AsCH(SiMe3)2}(μ‐CO)]

Syntheses, Structure and Reactivity of η³‐1,2‐Diphosphaallyl Complexes and [{(η⁵‐C₅H₅)(CO)₂W–Co(CO)₃}{μ‐AsCH(SiMe₃)₂}(μ‐CO)] Reaction of ClP=C(SiMe₂iPr)₂ ( 3 ) with Na[Mo(CO)₃(η⁵‐C₅H₅)] afforded the phosphavinylidene complex [(η⁵‐C₅H₅)(CO)₂Mo=P=C(SiMe₂iPr)₂] ( 4 ) which in situ was converted into the η¹‐1,2‐diphosphaallyl complex [η⁵‐(C₅H₅)(CO)₂Mo{η³‐tBuPPC(SiMe₂iPr)₂] ( 6 ) by treatment with the phosphaalkene tBuP=C(NMe₂)₂. The chloroarsanyl complexes [(η⁵‐C₅H₅)(CO)₃M–As(Cl)CH(SiMe₃)₂] [where M = Mo ( 9 ); M = W ( 10 )] resulted from the reaction of Na[M(CO)₃(η⁵‐C₅H₅)] (M = Mo, W) with Cl₂AsCH(SiMe₃)₂. The tungsten derivative 10 and Na[Co(CO)₄] underwent reaction to give the dinuclear μ‐arsinidene complex [(η⁵‐C₅H₅)(CO)₂W–Co(CO)₃{μ‐AsCH(SiMe₃)₂}(μ‐CO)] ( 11 ). Treatment of [(η⁵‐C₅H₅)(CO)₂Mo{η³‐tBuPPC(SiMe₃)₂}] ( 1 ) with an equimolar amount of ethereal HBF₄ gave rise to a 85/15 mixture of the saline complexes [(η⁵‐C₅H₅)(CO)₂Mo{η²‐tBu(H)P–P(F)CH(SiMe₃)₂}]BF₄ ( 18 ) and [Cp(CO)₂Mo{F₂PCH(SiMe₃)₂}(tBuPH₂)]BF₄ ( 19 ) by HF‐addition to the PC bond of the η³‐diphosphaallyl ligand and subsequent protonation ( 18 ) and/or scission of the PP bond by the acid ( 19 ). Consistently 19 was the sole product when 1 was allowed to react with an excess of ethereal HBF₄. The products 6 , 9 , 10 , 11 , 18 and 19 were characterized by means of spectroscopy (IR, ¹H‐, ¹³C{¹H}‐, ³¹P{¹H}‐NMR, MS). Moreover, the molecular structures of 6 , 11 and 18 were determined by X‐ray diffraction analysis.     

[Cs(Toluol)3(FIn{N(SiMe3)2}3)], ein Fluoroindat mit gestreckter Cs–F–In-Achse

[Cs(toluene)₃(FIn{N(SiMe₃)₂}₃)], a Fluoroindate with Rectified Cs–F–In Axis The metalate [Cs(FIn{N(SiMe₃)₂}₃)] has been prepared by the reaction of In[N(SiMe₃)₂]₃ with CsF in THF: The title compound 1 can be obtained by recrystallization from toluene as colorless airsensitive needles. 1 has been characterized by NMR-, IR-, and MS-techniques as well as by an X-ray structure determination. The result of the structure analysis shows an prolated molecule with an almost linear Cs–F–In axis [174.7(1)°]. The Cs⁺ center is surrounded by the indate ion and three toluene molecules in a distorted tetrahedral fashion.     

The Instability of Ni{N(SiMe3)2}2: A Fifty Year Old Transition Metal Silylamide Mystery

The characterization of the unstable Ni^II bis(silylamide) Ni{N(SiMe₃)₂}₂ ( 1 ), its THF complex Ni{N(SiMe₃)₂}₂(THF) ( 2 ), and the stable bis(pyridine) derivative trans‐Ni{N(SiMe₃)₂}₂(py)₂ ( 3 ), is described. Both 1 and 2 decompose at ca. 25 °C to a tetrameric Ni^I species, [Ni{N(SiMe₃)₂}]₄ ( 4 ), also obtainable from LiN(SiMe₃)₂ and NiCl₂(DME). Experimental and computational data indicate that the instability of 1 is likely due to ease of reduction of Ni^II to Ni^I and the stabilization of 4 through dispersion forces.     

Synthese,NMR‐Spektren und Molekülstruktur von [(CH3)2Ga{μ‐P(H)Si(CH3)3}2Ga(CH3)2{μ‐P(Si(CH3)3)2}Ga(CH3)2]

Synthesis, NMR Spectra and Structure of [(CH₃)₂Ga{μ‐P(H)Si(CH₃)₃}₂Ga(CH₃)₂{μ‐P(Si(CH₃)₃)₂}Ga(CH₃)₂] The title compound has been prepared in good yield by the reaction of [Me₂GaOMe]₃ (Me = CH₃) with HP(SiMe₃)₂ in toluene (ratio 1 : 1,1) and purified by crystallization from pentane or toluene, respectively. This organogallium compound forms (Ga–P)₃ ring skeletons with one Ga–P(SiMe₃)₂–Ga and two Ga–P(H)SiMe₃–Ga bridges and crystallizes in the monoclinic space group C2/c. The known homologous Al‐compound is isotypic, both (M^III–P)₃ heterocycles have twist‐conformations, the ligands of the monophosphane bridges have trans arrangements.     

Single metal four-electron reduction by U(ii) and masked “U(ii)” compounds

The redox chemistry of uranium is dominated by single electron transfer reactions while single metal four-electron transfers remain unknown in f-element chemistry. Here we show that the oxo bridged diuranium(iii) complex [K(2.2.2-cryptand)]₂[{((Me₃Si)₂N)₃U}₂(μ-O)], 1, effects the two-electron reduction of diphenylacetylene and the four-electron reduction of azobenzene through a masked U(ii) intermediate affording a stable metallacyclopropene complex of uranium(iv), [K(2.2.2-cryptand)][U(η²-C₂Ph₂){N(SiMe₃)₂}₃], 3, and a bis(imido)uranium(vi) complex [K(2.2.2-cryptand)][U(NPh)₂{N(SiMe₃)₂}₃], 4, respectively. The same reactivity is observed for the previously reported U(ii) complex [K(2.2.2-cryptand)][U{N(SiMe₃)₂}₃], 2. Computational studies indicate that the four-electron reduction of azobenzene occurs at a single U(ii) centre via two consecutive two-electron transfers and involves the formation of a U(iv) hydrazide intermediate. The isolation of the cis-hydrazide intermediate [K(2.2.2-cryptand)][U(N₂Ph₂){N(SiMe₃)₂}₃], 5, corroborated the mechanism proposed for the formation of the U(vi) bis(imido) complex. The reduction of azobenzene by U(ii) provided the first example of a “clear-cut” single metal four-electron transfer in f-element chemistry.

Both a masked and the actual complex [U(ii){N(SiMe₃)₂}₃]⁺ effect the reduction of azobenzene to yield a U(vi) bis-imido species providing the first example of a “clear-cut” metal centred four-electron reduction in f-element chemistry.