Building up Strain in One Step: Synthesis of an Edge‐Fused Double Silacyclobutene from an Extensively Trichlorosilylated Butadiene Dianion

The exhaustive trichlorosilylation of hexachloro‐1,3‐butadiene was achieved in one step by using a mixture of Si₂Cl₆ and [nBu₄N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu₄N]₂[ 1 ] was isolated in 36 % yield after recrystallization. The negative charges of [ 1 ]^2? are mainly delocalized across its two carbanionic (Cl₃Si)₂C termini (α‐effect of silicon) such that the central bond possesses largely C=C double‐bond character. Upon treatment with 4 equiv of HCl, [ 1 ]^2? is converted into neutral 1,2,3,4‐tetrakis(trichlorosilyl)but‐2‐ene, 3 . The Cl^? acceptor AlCl₃, induces a twofold ring‐closure reaction of [ 1 ]^2? to form a six‐membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4 , which was structurally characterized by X‐ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C.     

Transfer hydrogenation of ketones catalyzed by nickel complexes bearing an NHC [CNN] pincer ligand

Four NHC [CNN] pincer nickel (II) complexes, [^iPrCNN (CH₂)₄‐Ni‐Br] ( 5a ), [^nBuCNN (CH₂)₄‐Ni‐Br] ( 5b ), [^iPrCNN (Me)₂‐Ni‐Br] ( 6a ) and [^nBuCNN (Me)₂‐Ni‐Br] ( 6b ), bearing unsymmetrical [C (carbene)N (amino)N (amine)] ligands were synthesized by the reactions of [CNN] pincer ligand precursors 4 with Ni (DME)Cl₂ in the presence of Et₃N. Complexes 5a and 5b are new and were completely characterized. The transfer hydrogenation of ketones catalyzed by the four pincer nickel complexes were explored. Complexes 5a and 6a have better catalytic activity than 5b and 6b . With a combination of NaO^tBu/ⁱPrOH/80 °C and 2% catalyst loading of 5a , 77–98% yields of aromatic alcohols could be obtained.     

Catalytic Ammonia Oxidation to Dinitrogen by a Nickel Complex

We report a nickel complex for catalytic oxidation of ammonia to dinitrogen under ambient conditions. Using the aryloxyl radical 2,4,6-tri-tert-butylphenoxyl (^tBu₃ArO⋅) as a H atom acceptor to cleave the N−H bond of a coordinated NH₃ ligand up to 56 equiv of N₂ per Ni center can be generated. Employing the N-oxyl radical 2,2,6,6-(tetramethylpiperidin-1-yl)oxyl (TEMPO⋅) as the H-atom acceptor, up to 15 equiv of N₂ per Ni center are formed. A bridging Ni-hydrazine product identified by isotopic nitrogen (¹⁵N) studies and supported by computational models indicates the N−N bond forming step occurs by bimetallic homocoupling of two paramagnetic [Ni]−NH₂ fragments. Ni-mediated hydrazine disproportionation to N₂ and NH₃ completes the catalytic cycle.     

Living cationic isomerization polymerization of β-pinene. III. Synthesis of end-functionalized polymers and graft copolymers

α-End-functionalized polymers and macromonomers of β-pinene were synthesized by living cationic isomerization polymerization in CH₂Cl₂ at −40°C initiated with the HCl adducts [ 1; CH₃CH(OCH₂CH₂X)Cl; X = chloride ( 1a ), acetate ( 1b ), and methacrylate ( 1c )] of vinyl ethers carrying pendant substituents X that serve as terminal functionalities. In conjunction with TiCl₃(OiPr) and nBu₄NCl, these functionalized initiators led to living β-pinene polymerization where the carbon–chlorine bond of 1 was activated by TiCl₃(OiPr). Similarly, end-functionalized poly(p-methylstyrene)-block-poly(β-pinene) were also obtained. ¹H-NMR analysis showed that the polymers possess controlled molecular weights (DP _n = [M]₀/[ 1 ]₀) and number-average end functionalities close to unity. The end-functionalized methacrylate-capped macromonomers form 1c were radically copolymerized with methyl methacrylate (MMA) to give graft copolymers carrying poly(β-pinene) or poly(p-methylstyrene)-block-poly(β-pinene) as graft chains attached to a PMMA backbone. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1423–1430, 1997     

Hexanuclear Niobium Cluster Complex Anions with Acetato Ligands on Intramolecular Bridging Sites: [Nb6Cli4(OAc)i8Cla6]2– and [Nb6(OAc)i12Cla6]2–

From the reaction of [Nb₆Cl₁₄(H₂O)₄] · 4H₂O with acetic anhydride in the presence of an excess of (nBu₄N)F the novel cluster compounds (nBu₄N)₂[Nb₆Clⁱ₄(OAc)ⁱ₈Cl^a₆] ( 1 ) and (nBu₄N)₂[Nb₆(OAc)ⁱ₁₂Cl^a₆] ( 2 ) (OAc = acetato ligand) are obtained. They are the first examples of hexanuclear niobium cluster compounds with acetato ligands on the inner sites of the metal atom octahedron. The crucial role of the presence of fluoride ions in the synthesis is discussed. Each acetato ligand bridges in a μ₂-η¹-fashion with one O atom an edge of the metal atom octahedron. The monoclinic crystals of 1 consist of discrete (nBu₄N)⁺ cations and [Nb₆Clⁱ₄(OAc)ⁱ₈Cl^a₆]^2– cluster anions. They are oxidized by two electrons with respect to the cluster starting material. Besides the syntheses of 1 and 2 , the structure of 1 and spectral properties of both compounds are reported.     

Gallium “Shears” for C=N and C=O Bonds of Isocyanates

Digallane [L¹Ga−GaL¹] ( 1 , L¹=dpp-bian=1,2-[(2,6-iPr₂C₆H₃)NC]₂C₁₂H₆) reacts with RN=C=O (R=Ph or Tos) by [2+4] cycloaddition of the isocyanate C=N bonds across both of its C=C−N−Ga fragments to afford [L¹(O=C−NR)Ga−Ga(RN−C=O)L¹] (R=Ph, 3 ; R=Tos, 4 ). The reactions with both isocyanates result in new C−C and N−Ga single bonds. In the case of allyl isocyanate, the [2+4] cycloaddition across one C=C−N−Ga fragment of 1 is accompanied by insertion of a second allyl isocyanate molecule into the Ga−N bond of the same fragment to afford compound [L¹Ga−Ga(AllN− C=O)₂L¹] ( 5 ) (All=allyl). In the presence of Na metal, the related digallane [L²Ga−GaL²] ( 2 ; L²=dpp-dad=[(2,6-iPr₂C₆H₃)NC(CH₃)]₂) is converted into the gallium(I) carbene analogue [L²Ga:]⁻ ( 2 A ), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na₂(THF)₅]{L²Ga[EtN−C(O)]₂GaL²} ( 6 ), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF)₂]₂[L²Ga(p-MeC₆H₄)(N−C(O))₂−N(p-MeC₆H₄)]₂ ( 7 ), cleavage of the C=O bond to yield the di-O-bridged digallium compound [Na(THF)₃]₂[L²Ga-(μ-O)₂-GaL²] ( 8 ), and generation of the further addition product [Na₂(THF)₅][L²Ga(CyNCO₂)]₂ ( 9 ). Complexes 3 – 9 have been characterized by NMR (¹H, ¹³C), IR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their electronic structures have been examined by DFT calculations.     

Titanium-based lewis acids for living cationic polymerizations of vinyl ethers and styrene: Control of lewis acidity in design of initiating systems

This brief account discusses the development of HCl/TiCl_4-n(OR)_n (n = 1–4), the titanium-based new initiating systems for living cationic polymerizations of vinyl ethers and styrene. The focus of this development is controlling the Lewis acidity of the metal halide components [TiCl_4-n(OR)_n] or “activators” in relation to the structure of the monomers. Thus, for vinyl ethers, relatively mild Lewis acids such as TiCl(OiPr)₃ and TiCl₂(OiPr)₂ are effective, whereas for styrene, a stronger Lewis acid such as TiCl₃(OiPr) is employed along with an added salt (nBu₄N⁺Cl⁻). In both cases, living polymers of controlled molecular weights can be obtained in methylene chloride solvent at −15°C.     

Reversible Oxidative Addition of Zinc Hydride at a Gallium(I)-Centre: Labile Mono- and Bis(hydridogallyl)zinc Complexes

In the presence of TMEDA (N,N,N’,N’-tetramethylethylenediamine), partially deaggregated zinc dihydride as hydrocarbon suspensions react with the gallium(I) compound [(BDI)Ga] ( I , BDI={HC(C(CH₃)N(2,6-iPr₂-C₆H₃))₂}⁻) by formal oxidative addition of a Zn−H bond to the gallium(I) centre. Dissociation of the labile TMEDA ligand in the resulting complex [(BDI)Ga(H)−(H)Zn(tmeda)] ( 1 ) facilitates insertion of a second equiv. of I into the remaining Zn−H to form a thermally sensitive trinuclear species [{(BDI)Ga(H)}₂Zn] ( 2 ). Compound 1 exchanges with polymeric zinc dideuteride [ZnD₂]_n in the presence of TMEDA, and with compounds I and 2 via sequential and reversible ligand dissociation and gallium(I) insertion. Spectroscopic and computational studies demonstrate the reversibility of oxidative addition of each Zn−H bond to the gallium(I) centres.     

Synthesis and Complexation Study of New Aminoalkynyl−amidinate Ligands

The current library of amidinate ligands has been extended by the synthesis of two novel dimethylamino-substituted alkynylamidinate anions of the composition [Me₂N−CH₂−C≡C−C(NR)₂]⁻ (R = ⁱPr, cyclohexyl (Cy)). The unsolvated lithium derivatives Li[Me₂N−CH₂−C≡C−C(NR)₂] ( 1 : R = ⁱPr, 2 : R = Cy) were obtained in good yields by treatment of in situ-prepared Me₂N−CH₂−C≡C−Li with the respective carbodiimides, R−N=C=N−R. Recrystallization of 1 and 2 from THF afforded the crystalline THF adducts Li[Me₂N−CH₂−C≡C−C(NR)₂] ⋅ nTHF ( 1 a : R = ⁱPr, n=1; 2 a : R = Cy, n=1.5). Precursor 2 was subsequently used to study initial complexation reactions with selected di- and trivalent transition metals. The dark red homoleptic vanadium(III) tris(alkynylamidinate) complex V[Me₂N−CH₂−C≡C−C(NCy)₂]₃ ( 3 ) was prepared by reaction of VCl₃(THF)₃ with 3 equiv. of 2 (75 % yield). A salt-metathesis reaction of 2 with anhydrous FeCl₂ in a molar ratio of 2 : 1 afforded the dinuclear homoleptic iron(II) alkynylamidinate complex Fe₂[Me₂N−CH₂−C≡C−C(NCy)₂]₄ ( 4 ) in 69 % isolated yield. Similarly, treatment of Mo₂(OAc)₄ with 3 or 4 equiv. of 2 provided the dinuclear, heteroleptic molybdenum(II) amidinate complex Mo₂(OAc)[Me₂N−CH₂−C≡C−C(NCy)₂]₃ ( 5 ; yellow crystals, 50 % isolated yield). The cyclohexyl-substituted title compounds 2 a , 4 , and 5 were structurally characterized through single-crystal X-ray diffraction studies.     

Nitrene Insertion into C?C and C?H Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron

The impact of redox non‐innocence (RNI) on chemical reactivity is a forefront theme in coordination chemistry. A diamide diimine ligand, [{‐CHN(1,2‐C₆H₄)NH(2,6‐iPr₂C₆H₃)}₂]ⁿ (n=0 to −4), (dadi)ⁿ, chelates Cr and Fe to give [(dadi)M] ([ 1 Cr(thf)] and [ 1 Fe]). Calculations show [ 1 Cr(thf)] (and [ 1 Cr]) to have a d⁴ Cr configuration antiferromagnetically coupled to (dadi)²⁻*, and [ 1 Fe] to be S=2. Treatment with RN₃ provides products where RN is formally inserted into the C C bond of the diimine or into a C H bond of the diimine. Calculations on the process support a mechanism in which a transient imide (imidyl) aziridinates the diimine, which subsequently ring opens.     

Isolation and Characterization,Including by X‐ray Crystallography,of Contact and Solvent‐Separated Ion Pairs of Silenyl Lithium Species

Reaction of bromoacylsilane 1 (pink solution) with tBu₂MeSiLi (3.5 equiv) in a 4:1 hexane:THF solvent mixture at −78 °C to room temperature yields the solvent separated ion pair (SSIP) of silenyl lithium E‐[(tBuMe₂Si)(tBu₂MeSi)C=Si(SiMetBu₂)]⁻ [Li⋅4THF]⁺ 2 a (green–blue solution). Removal of the solvent and addition of benzene converts 2 a into the corresponding contact ion pair (CIP) 2 b (violet–red solution) with two THF molecules bonded to the lithium atom. The 2 a ⇌ 2 b interconversion is reversible upon THF⇌ benzene solvent change. Both 2 a and 2 b were characterized by X‐ray crystallography, NMR and UV/Vis spectroscopy, and theoretical calculations. The degree of dissociation of the Si−Li bond has a large effect on the visible spectrum (and thus color) and on the silenylic ²⁹Si NMR chemical shift, but a small effect on the molecular structure. This is the first report of the X‐ray molecular structure of both the SSIP and the CIP of any R₂E=E′RM species (E=C, Si; E′=C, Si; M=metal).     

Darstellung,Kristallstrukturen und Schwingungsspektren von [Pt(N3)6]2– und [Pt(N3)Cl5]2–, 195Pt‐ und 15N‐NMR‐Spektren von [Pt(N3)nCl6–n]2– und [Pt(15NN2)n(N215N)6–n]2–, n = 0–6

Synthesis, Crystal Structures, and Vibrational Spectra of [Pt(N₃)₆]^2– and [Pt(N₃)Cl₅]^2–, ¹⁹⁵Pt and ¹⁵N NMR Spectra of [Pt(N₃)_nCl_6–n]^2– and [Pt(¹⁵NN₂)_n(N₂¹⁵N)_6–n]^2–, n = 0–6 By ligand exchange of [PtCl₆]^2– with sodium azide mixed complexes of the series [Pt(N₃)_nCl_6–n]^2– and with ¹⁵N‐labelled sodium azide (Na¹⁵NN₂) mixtures of the isotopomeres [Pt(¹⁵NN₂)_n(N₂¹⁵N)_6–n]^2–, n = 0–6 and the pair [Pt(¹⁵NN₂)Cl₅]^2–/[Pt(N₂¹⁵N)Cl₅]^2– are formed. X‐ray structure determinations on single crystals of (Ph₄P)₂[Pt(N₃)₆] ( 1 ) (triclinic, space group P1, a = 10.175(1), b = 10.516(1), c = 12.380(2) Å, α = 87.822(9), β = 73.822(9), γ = 67.987(8)°, Z = 1) and (Ph₄As)₂[Pt(N₃)Cl₅] · HCON(CH₃)₂ ( 2 ) (triclinic, space group P1, a = 10.068(2), b = 11.001(2), c = 23.658(5) Å, α = 101.196(14), β = 93.977(15), γ = 101.484(13)°, Z = 2) have been performed. The bond lengths are Pt–N = 2.088 ( 1 ), 2.105 ( 2 ) and Pt–Cl = 2.318 Å ( 2 ). The approximate linear azido ligands with N^α–N^β–N^γ‐angles = 173.5–174.6° are bonded with Pt–N^α–N^β‐angles = 116.4–121.0°. In the vibrational spectra the PtCl stretching vibrations of (n‐Bu₄N)₂[Pt(N₃)Cl₅] are observed at 318–345, the PtN stretching modes of (n‐Bu₄N)₂[Pt(N₃)₆] at 401–428 and of (n‐Bu₄N)₂[Pt(N₃)Cl₅] at 408–413 cm^–1. The mixtures (n‐Bu₄N)₂[Pt(¹⁵NN₂)_n(N₂¹⁵N)_6–n], n = 0–6 and (n‐Bu₄N)₂[Pt(¹⁵NN₂)Cl₅]/(n‐Bu₄N)₂[Pt(N₂¹⁵N)Cl₅] exhibit ¹⁵N‐isotopic shifts up to 20 cm^–1. Based on the molecular parameters of the X‐ray determinations the vibrational spectra are assigned by normal coordinate analysis. The average valence force constants are f_d(PtCl) = 1.93, f_d(PtN^α) = 2.38 and f_d(N^αN^β, N^βN^γ) = 12.39 mdyn/Å. In the ¹⁹⁵Pt NMR spectrum of [Pt(N₃)_nCl_6–n]^2–, n = 0–6 downfield shifts with the increasing number of azido ligands are observed in the range 4766–5067 ppm. The ¹⁵N NMR spectrum of (n‐Bu₄N)₂[Pt(¹⁵NN₂)_n(N₂¹⁵N)_6–n], n = 0–6 exhibits by ¹⁵N–¹⁹⁵Pt coupling a pseudotriplett at –307.5 ppm. Due to the isotopomeres n = 0–5 for terminal ¹⁵N six well‐resolved signals with distances of 0.03 ppm are observed in the low field region at –201 to –199 ppm.     

Tetrabutylammonium Salts of Aluminum(III) and Gallium(III) Phthalocyanine Radical Anions Bonded with Fluoren‐9‐olato− Anions and Indium(III) Phthalocyanine Bromide Radical Anions

Reduction of aluminum(III), gallium(III), and indium(III) phthalocyanine chlorides by sodium fluorenone ketyl in the presence of tetrabutylammonium cations yielded crystalline salts of the type (Bu₄N⁺)₂[M^III(HFl−O⁻)(Pc^.3−)]^.−(Br⁻) ⋅ 1.5 C₆H₄Cl₂ [M=Al ( 1 ), Ga ( 2 ); HFl−O⁻=fluoren‐9‐olato⁻ anion; Pc=phthalocyanine] and (Bu₄N⁺) [In^IIIBr(Pc^.3−)]^.− ⋅ 0.875 C₆H₄Cl₂ ⋅ 0.125 C₆H₁₄ ( 3 ). The salts were found to contain Pc^.3− radical anions with negatively charged phthalocyanine macrocycles, as evidenced by the presence of intense bands of Pc^.3− in the near‐IR region and a noticeable blueshift in both the Q and Soret bands of phthalocyanine. The metal(III) atoms coordinate HFl−O⁻ anions in 1 and 2 with short Al−O and Ga−O bond lengths of 1.749(2) and 1.836(6) Å, respectively. The C−O bonds [1.402(3) and 1.391(11) Å in 1 and 2 , respectively] in the HFl−O⁻ anions are longer than the same bond in the fluorenone ketyl (1.27–1.31 Å). Salts 1 – 3 show effective magnetic moments of 1.72, 1.66, and 1.79 μ_B at 300 K, respectively, owing to the presence of unpaired S= 1/2 spins on Pc^.3−. These spins are coupled antiferromagnetically with Weiss temperatures of −22, −14, and −30 K for 1 – 3 , respectively. Coupling can occur in the corrugated two‐dimensional phthalocyanine layers of 1 and 2 with an exchange interaction of J /k _B=−0.9 and −1.1 K, respectively, and in the π‐stacking {[In^IIIBr(Pc^.3−)]^.−}₂ dimers of 3 with an exchange interaction of J /k _B=−10.8 K. The salts show intense electron paramagnetic resonance (EPR) signals attributed to Pc^.3−. It was found that increasing the size of the central metal atom strongly broadened these EPR signals.     

Synthesis and X-ray structure of a complex containing the trisimido borate trianion—the imido analogue of the orthoborate trianion

Reaction of BCl₃ with 2-methoxyaniline (1:6 equiv.) in toluene, and subsequent metallation with ⁿBuLi (3 equiv.) produces {[Li₄B(NR)₃·THF]⁺[BⁿBu₄]⁻·toluene}₂ (R=2-methoxyphenyl), which contains the first example of a trisimido borate trianion—the imido analogue of the orthoborate trianion, [BO₃]³⁻.     

Synthesen und NMR‐Untersuchungen von Salzen mit den neuen Anionen [PtXn(CF3)6‐n]2— (n = 0 ‐ 5, X = F,OH, Cl,CN) und die Kristallstrukturanalyse von K2[(CF3)2F2Pt(μ‐OH)2PtF2(CF3)2]·2H2O

Syntheses and NMR Spectroscopic Ivestigations of Salts containing the Novel Anions [PtX_n(CF₃)_6‐n]^2— (n = 0 ‐ 5, X = F, OH, Cl, CN) and Crystal Structure of K₂[(CF₃)₂F₂Pt(μ‐OH)₂PtF₂(CF₃)₂]·2H₂O The first syntheses of trifluoromethyl‐complexes of platinum through fluorination of cyanoplatinates are reported. The fluorination of tetracyanoplatinates(II), K₂[Pt(CN)₄], and hexacyanoplatinates(IV), K₂[Pt(CN)₆], with ClF in anhydrous HF leads after working up of the products to K₂[(CF₃)₂F₂Pt(μ‐OH)₂PtF₂(CF₃)₂]·2H₂O. The structure of the salt is determined by a X‐ray structure analysis, P2₁/c (Nr. 14), a = 11.391(2), b = 11.565(2), c = 13.391(3)Å, β = 90.32(3)°, Z = 4, R₁ = 0.0326 (I > 2σ(I)). The reaction of [Bu₄N]₂[Pt(CN)₄] with ClF in CH₂Cl₂ generates mainly cis‐[Bu₄N]₂[PtCl₂(CF₃)₄] and fac‐[Bu₄N]₂[PtCl₃(CF₃)₃], but in contrast that of [Bu₄N]₂[Pt(CN)₆] with ClF in CH₂Cl₂ results cis‐[Bu₄N]₂[PtX₂(CF₃)₄], [Bu₄N]₂[PtX(CF₃)₅] (X = F, Cl) and [Bu₄N]₂[Pt(CF₃)₆]. In the products [Bu₄N]₂[PtX_n(CF₃)_6‐n] (X = F, Cl, n = 0—3) it is possibel to exchange the fluoro‐ligands into chloro‐ and cyano‐ligands by treatment with (CH₃)₃SiCl und (CH₃)₃SiCN at 50 °C. With continuing warming the trifluoromethyl‐ligands are exchanged by chloro‐ and cyano‐ligands, while as intermediates CF₂Cl and CF₂CN ligands are formed. The identity of the new trifluoromethyl‐platinates is proved by ¹⁹⁵Pt‐ and ¹⁹F‐NMR‐spectroscopy.     

Air‐Stable,Well‐Soluble AI2[Nb6Cl18] Cluster Compounds (AI = Organic Cation): A New Route for Preparation,Single‐Crystal Structures,Properties, and ESI‐Mass Spectra

Five niobium cluster compounds of the A^I₂[Nb₆Cl₁₈] type (A^I = organic cation: [nPr₄N]⁺, [nBu₄N]⁺, [BMIm]⁺, [Ph₄P]⁺, and [PPN]⁺) are obtained through treatment of [Nb₆Cl₁₄(H₂O)₄] · 4H₂O with excess of thionyl chloride in the presence of an organic chloride, A^ICl. Single‐crystal structure studies show that the compounds consist of discrete cations and cluster [Nb₆Cl₁₈]^2– anions. The cluster unit of the hydrated cluster starting material is oxidized by two electrons. Powder diffraction studies and NMR spectroscopic measurements show all compounds to crystallize without co‐crystallized solvent molecules. They are air and water stable. The solubility in organic solvents changes to a great extent on changing the type of cation. The ESI‐MS spectra of [nPr₄N]₂[Nb₆Cl₁₈] and [Ph₄P]₂[Nb₆Cl₁₈] show the pseudomolecular peak of the anionic cluster as well as additional signals, which involve simultaneously chloride mass loss and reduction processes.     

Mixed-ligand complexes of paddlewheel dinuclear molybdenum as hydrodehalogenation catalysts for polyhaloalkanes

We developed a hydrodehalogenation reaction of polyhaloalkanes catalyzed by paddlewheel dimolybdenum complexes in combination with 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (MBTCD) as a non-toxic H-atom source as well as a salt-free reductant. A mixed-ligated dimolybdenum complex Mo₂(OAc)₂[CH(NAr)₂]₂ (3a, Ar = 4-MeOC₆H₄) having two acetates and two amidinates exhibited high catalytic activity in the presence of ⁿBu₄NCl, in which [ⁿBu₄N]₂[Mo₂{CH(NAr)₂}₂Cl₄] (9a), derived by treating 3a with ClSiMe₃ and ⁿBu₄NCl, was generated as a catalytically-active species in the hydrodehalogenation. All reaction processes, oxidation and reduction of the dimolybdenum complex, were clarified by control experiments, and the oxidized product, [ⁿBu₄N][Mo₂{CH(NAr)₂}₂Cl₄] (10a), was characterized by EPR and X-ray diffraction studies. Kinetic analysis of the hydrodehalogenation reaction as well as a deuterium-labelling experiment using MBTCD-d₈ suggested that the H-abstraction was the rate-determining step for the catalytic reaction.     

Vibrational spectroscopic studies of uranyl complexes in aqueous and non-aqueous solutions

Vibrational spectra have been obtained for aqueous solution of uranyl-perchlorates, -fluorides, -chlorides, -acetates and -sulphates over a range of solution composition with added anions. We have prepared [Buⁿ₄N][UO₂Cl₄], [Me₄N][UO₂Cl₄], [Prⁿ₄N][[UO₂(NO₃)₃], [Buⁿ₄N][UO₂(NO₃)₃], with the expectation that the large cation would give a better approximation to vibrational frequencies of the free anion and would allow measurements in non-coordinating solvents. As the perchlorate is not coordinated to [UO₂]²⁺ in aqueous solution the expected structure is a solvated cation [UO₂(OH₂)₅]²⁺ with characteristic infrared 962.5, 253 and 160 cm⁻¹ and Raman 874 and 198 cm⁻¹ bands. The formation of weak, solvated [UO₂X]⁺ complexes (X=F, Cl) has been established with frequencies at 908, 827, 254, 380 cm⁻¹ and 956, 871, 254 and 222 cm⁻¹ for [UO₂F]⁺ and [UO₂Cl]⁺, respectively. Bidentate NO₃ coordination has been established for solid and dissolved (in CH₂Cl₂) [R₄N][UO₂(NO₃)₃] (R=Prⁿ, Buⁿ). Aqueous solutions of UO₂(NO₃)₂ and Cs[UO₂(NO₃)₃] show no clear evidence that bidentate or monodentate nitrate is present. Both unidentate and bidentate linkage of acetate-uranyl were established for acetate complexes in aqueous solutions. For the uranyl sulphate system, monodentate sulphate coordination is the major mode at low SO₄:U ratios, and even at a ratio of 3:1 there is very little free sulphate.     

Organophosphonate derivatives of titanium and niobium alkoxoanions

The organophosphonate-substituted alkoxides [Bu₄ⁿN]₂[{Ti(OMe)₃(O₃PPh)}₂] (1) and [Bu₄ⁿN]₂[{Nb(OMe)₃(O₃PPh)}₂(μ-O)] (2) have been prepared from [Bu₄ⁿN][PhPO₃H] and the metal alkoxides Ti(OMe)₄ or Nb(OMe)₅ respectively. In 1, the bridging phenylphosphonates occupy trans coordination sites, whereas in 2, a cis–bridging geometry is adopted.     

Neutral and Anionic Monomeric Zirconium Imides Prepared via Selective C=N Bond Cleavage of a Multidentate and Sterically Demanding β‐Diketiminato Ligand

A sterically encumbering multidentate β‐diketiminato ligand, ^tBuL2 (^tBuL2=[ArNC(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂NMe₂]^?, Ar=2,6‐iPr₂C₆H₃), is reported in this study along with its coordination chemistry to zirconium(IV). Using the lithio salt of this ligand, Li(^tBuL2) ( 4 ), the zirconium(IV) precursor (^tBuL2)ZrCl₃ ( 6 ) could be readily prepared in 85 % yield and structurally characterized. Reduction of 6 with 2 equiv of KC₈ resulted in formation of the terminal and mononuclear zirconium imide‐chloride [C(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂NMe₂]Zr(=NAr)(Cl) ( 7 ) as the result of reductive C=N cleavage of the imino fragment in the multidentate ligand ^tBuL2 by an elusive Zr^II species (^tBuL2)ZrCl ( A ). The azabutadienyl ligand in 7 can be further reduced by 2 e^? with KC₈ to afford the anionic imide [K(THF)₂]{[CH(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂N(Me)CH₂]Zr=NAr} ( 8‐2THF ) in 42 % isolated yield. Complex 8‐2THF results from the oxidative addition of an amine C?H bond followed by migration to the vinylic group of the formal [C(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂NMe₂]^? ligand in 7 . All halides in 6 can be replaced with azides to afford (^tBuL2)Zr(N₃)₃ ( 9 ) which was structurally characterized, and reduction with two equiv of KC₈ also results in C=N bond cleavage of ^tBuL2 to form [C(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂NMe₂]Zr(=NAr)(N₃) ( 10 ), instead of the expected azide disproportionation to N^3? and N₂. Solid‐state single crystal structural studies confirm the formation of mononuclear and terminal zirconium imido groups in 7 , 8‐Et₂O , and 10 with Zr=NAr distances being 1.8776(10), 1.9505(15), and 1.881(3) Å, respectively.