Protonation and Hydrogenation Experiments with Iridium(0) and Iridium(−1) tropp Complexes: Formation of Hydrides

The reactions of three different tetracoordinated Ir complexes, [Ir(tropp^ph)₂]ⁿ (n=+1, 0, −1), which differ in the formal oxidation state of the metal from +1 to −1, with proton sources and dihydrogen were investigated (tropp=5‐(diphenylphosphanyl)dibenzo[a,d]cycloheptene). It was found that the cationic 16‐electron complex [Ir(tropp^ph)₂]⁺ ( 2 ) cannot be protonated but reacts with NaBH₄ to the very stable 18‐electron Ir^I hydride [IrH(tropp^ph)₂] ( 5 ), which is further protonated with medium strong acids to give the 18‐electron Ir^III dihydride [IrH₂(tropp^ph)₂]⁺ ( 6 ; pK_s in CH₂Cl₂/THF/H₂O 1 : 1 : 2 ca. 2.2). Both, the neutral 17‐electron Ir⁰ complex [Ir(tropp^ph)₂] ( 3 ) and the anionic 18‐electron complex [Ir(tropp^ph)₂]⁻ ( 4 ) react rapidly with H₂O to give the monohydride 5 . In reactions of 3 with H₂O, the terminal Ir^I hydroxide [Ir(OH)(tropp^ph)₂] ( 8 ) is formed in equal amounts. All these complexes, apart from 5 , which is inert, do react rapidly with dihydrogen. The complex 2 gives the dihydride 6 in an oxidative addition reaction, while 3 , 4 , and 8 give the monohydride 5 . Interestingly, a salt‐type hydride (i.e., LiH) is formed as further product in the unexpected reaction with [Li(thf)_x]⁺[Ir(tropp^ph)₂]⁻ ( 4 ). Because 3 undergoes disproportionation into 2 and 4 according to 2 3 ⇄ 2 + 4 (K_disp=2.7⋅10⁻⁵), it is likely that actually the diamagnetic species and not the odd‐electron complex 3 is involved in the reactions studied here, and possible mechanisms for these are discussed.     

Synthesis and Characterization of Chiral Bis(aminato)iridate(I) and Aminato‐Bridged Iridium(I) Complexes

The two dinuclear Ir^I complexes [Ir₂(μ‐Cl)₂ {(R)‐(S)‐PPF‐PPh₂}₂] ( 1 ; (R)‐(S)‐PPF‐PPh₂=(S)‐1‐(diphenylphosphino)‐2‐[(R)‐1‐(diphenylphosphino)ethyl]ferrocene and [Ir₂(μ‐Cl)₂{(R)‐binap}₂] ( 3 ; (R)‐binap=(R)‐[1,1′‐binaphthalene]‐2,2′‐diylbis[diphenylphosphine]) smoothly react with 4 equiv. of the lithium salt of aniline to afford the new bis(anilido)iridate(I) (=bis(benzenaminato)iridate(1‐)) complexes Li[Ir(NHPh)₂{(R)‐(S)‐PPF‐PPh₂}] ( 4 ) and Li[Ir(NHPh)₂{(R)‐binap}] ( 5 ), respectively. The anionic complexes 4 and 5 react upon protonolysis to give the dinuclear aminato‐bridged derivatives [Ir₂(μ‐NHPh)₂{(R)‐(S)‐PPF‐PPh₂}₂] ( 6 ) and [Ir₂(μ‐NHPh)₂{(R)‐binap}₂] ( 7 ), which were characterized by X‐ray crystallography. None of the new complexes 4 – 7 shows catalytic activity in the hydroamination of olefins.     

A Mixed‐Valence Tri‐Zinc Complex, [LZnZnZnL] (L=Bulky Amide), Bearing a Linear Chain of Two‐Coordinate Zinc Atoms

Reduction of a variety of extremely bulky amido Group 12 metal halide complexes, [LMX(THF)_0,1] (L=amide; M=Zn, Cd, or Hg; X=halide) with a magnesium(I) dimer gave a homologous series of two‐coordinate metal(I) dimers, [L′MML′] (L′=N(Ar^?)(SiMe₃), Ar^?=C₆H₂{C(H)Ph₂}₂Prⁱ‐2,6,4); and the formally zinc(0) complex, [L*ZnMg(^MesNacnac)] (L*=N(Ar*)(SiPrⁱ₃); Ar*=C₆H₂{C(H)Ph₂}₂Me‐2,6,4; ^MesNacnac=[(MesNCMe)₂CH]^?, Mes=mesityl), which contains the first unsupported Zn? Mg bond. Two equivalents of [L*ZnMg(^MesNacnac)] react with ZnBr₂ or ZnBr₂(tmeda) to give the mixed valence, two‐coordinate, linear tri‐zinc complex, [L*Zn^IZn⁰Zn^IL*], and the first zinc(I) halide complex, [L*ZnZnBr(tmeda)], respectively. The analogues [L*ZnMZnL*] (M=Cd or Hg), were also prepared, the Cd species contains the first Zn? Cd bond in a molecular compound. Metal–metal bonding was studied by DFT calculations.     

Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part IV. Derivatives with monodentate ligands and edge-bridging bidentate ligands

The fluxionality of [Ir₄(CO)₈(μ₂-CO)₃L] (L = Br^?, I^?, SCN^?, NO₂^?, P(4-ClC₆H₄)₃, PPh₃, P(4-MeOC₆H₄)₃, P(4-Me₂NC₆H₄)₃), as studied by 2D-¹³C-NMR in solution, is due to two successive scrambling processes: the merry-go-round of six basal CO's and CO bridging to alternative faces of the Ir₄ tetrahedron. The basicity of the ligand L has no significant effect on the activation parameters. The scrambling process of lowest activation energy in [Ir₄(CO)₇(μ₂-CO)₃(PMePh₂)₂] correspond to the two possible synchronous CO bridging about a unique face of the metal tetrahedron swapping the relative axial and radial positions of the ligands L. The disubstituted clusters [Ir₄(CO)₁₀(μ₂-L? L)] with one edge-bridging ligand have a ground-state geometry with three edge-bridging CO's (L? L = bis(diphenylphosphino)methane, bis(diphenylarsino)methane, bis(diphenylphosphino)propane) or with all terminal CO's (L? L = CH₃SCH₂SCH₃). In all cases, the fluxional process of lowest activation energy in the merry-go-round of six CO's about a unique triangular face. For the P and As donor ligands, this process is followed by the rotation of terminal CO's bonded to two Ir-atoms residing on the mirror plane of the unbridged intermediate.     

Controlled Formation of Thiol‐Thiolate Hydrogen versus Disulfide Bonds between Two Iridium(III) Centers

Here, we report an iridium(III) coordination system with 2‐aminoethanethiolate (aet), which shows the formation of S?H???S hydrogen and S?S disulfide bonds in a controlled manner. Treatment of fac‐[Ir(aet)₃] with aqueous HBF₄ under aerobic conditions gave dinuclear [Ir₂(aet)₄(cysta)]²⁺ ([ 1 ]²⁺; cysta=cystamine) with a single S?S disulfide bond, while dimeric [Ir₂(aet)₃(Haet)₃](BF₄)₃ ([ 2 ](BF₄)₃) with a triple S?H???S hydrogen bond was formed by similar treatment under anaerobic conditions. Upon exposure to air, [ 2 ]³⁺ was converted to dinuclear [Ir₂(aet)₂(Haet)₂(cysta)]⁴⁺ ([ 3 ]⁴⁺), in which two Ir^III centers are spanned by a double S?H???S hydrogen bond and a single S?S disulfide bond. Complex [ 3 ]⁴⁺ was interconvertible with [ 1 ]²⁺ via the removal/addition of protons on S donors, accompanied by the intermolecular exchange of the fac‐[Ir(aet)₃] units. Complexes [ 1 ]²⁺, [ 2 ]³⁺, and [ 3 ]⁴⁺, isolated as BF₄^? salts, were fully characterized by single‐crystal X‐ray crystallography.     

Synthesis and Characterization of Iridium(V) Coordination Complexes With an N,O‐Donor Organic Ligand

We have prepared and fully characterized two isomers of [Ir^IV(dpyp)₂] (dpyp=meso‐2,4‐di(2‐pyridinyl)‐2,4‐pentanediolate). These complexes can cleanly oxidize to [Ir^V(dpyp)₂]⁺, which to our knowledge represent the first mononuclear coordination complexes of Ir^V in an N,O‐donor environment. One isomer has been fully characterized in the Ir^V state, including by X‐ray crystallography, XPS, and DFT calculations, all of which confirm metal‐centered oxidation. The unprecedented stability of these Ir^V complexes is ascribed to the exceptional donor strength of the ligands, their resistance to oxidative degradation, and the presence of four highly donor alkoxide groups in a plane, which breaks the degeneracy of the d‐orbitals and favors oxidation.     

Coordination Chemistry of Diiodine and Implications for the Oxidation Capacity of the Synergistic Ag+/X2 (X=Cl,Br, I) System

The synergistic Ag⁺/X₂ system (X=Cl, Br, I) is a very strong, but ill‐defined oxidant—more powerful than X₂ or Ag⁺ alone. Intermediates for its action may include [Ag_m(X₂)_n]^m+ complexes. Here, we report on an unexpectedly variable coordination chemistry of diiodine towards this direction: ( A )Ag‐I₂‐Ag( A ), [Ag₂(I₂)₄]²⁺( A ^?)₂ and [Ag₂(I₂)₆]²⁺( A ^?)₂?(I₂)_x≈0.65 form by reaction of Ag( A ) ( A =Al(OR^F)₄; R^F=C(CF₃)₃) with diiodine (single crystal/powder XRD, Raman spectra and quantum‐mechanical calculations). The molecular ( A )Ag‐I₂‐Ag( A ) is ideally set up to act as a 2 e^? oxidant with stoichiometric formation of 2 AgI and 2 A ^?. Preliminary reactivity tests proved this ( A )Ag‐I₂‐Ag( A ) starting material to oxidize n‐C₅H₁₂, C₃H₈, CH₂Cl₂, P₄ or S₈ at room temperature. A rough estimate of its electron affinity places it amongst very strong oxidizers like MF₆ (M=4d metals). This suggests that ( A )Ag‐I₂‐Ag( A ) will serve as an easily in bulk accessible, well‐defined, and very potent oxidant with multiple applications.     

Halide Abstraction from Organic Solvents in Reactions of a Copper(I) Alkoxide: Synthesis and Crystal Structures of [Cu5(dppm)(dppm−)2(OtBu)Cl2] and [Cu3(dppm)3Br2][CuBr2]

The synthesis and structures of the two Cu^I halide complexes [Cu₅(dppm)(dppm^?)₂(O^tBu)Cl₂] and [Cu₃(dppm)₃Br₂][CuBr₂] (dppm = Ph₂PCH₂PPh₂, dppm^? = [Ph₂PCHPPh₂]^?) are reported. The compounds were obtained by treating reaction mixtures of [CuO^tBu] and dppm with dichloromethane or dibromomethane.     

Coordination Adducts of Niobium(V) and Tantalum(V) Azide M(N3)5 (M=Nb,Ta) with Nitrogen Donor Ligands and their Self‐Ionization

Several new donor–acceptor adducts of niobium and tantalum pentaazide with N‐donor ligands have been prepared from the pentafluorides by fluoride–azide exchange with Me₃SiN₃ in the presence of the corresponding donor ligand. With 2,2′‐bipyridine and 1,10‐phenanthroline, the self‐ionization products [MF₄(2,2′‐bipy)₂]⁺[M(N₃)₆]^?, [M(N₃)₄(2,2′‐bipy)₂]⁺[M(N₃)₆]^? and [M(N₃)₄(1,10‐phen)₂]⁺[M(N₃)₆]^? were obtained. With the donor ligands 3,3′‐bipyridine and 4,4′‐bipyridine the neutral pentaazide adducts (M(N₃)₅)₂?L (M=Nb, Ta; L=3,3′‐bipy, 4,4′‐bipy) were formed.     

Nickel(II) Complexes of 1‐Alkyl‐1‐azonia‐3,5‐diaza‐7‐phosphatricyclo[3.3.1.13,7]decane – Synthesis and Solid‐State Structures

Complexes [NiI₃(mpta)₂]I ( 1 ) and [NiI₃(ppta)₂]I ( 2 ) have been synthesized by reaction of nickel(II) halide salts with ‐1‐methyl‐1‐azonia‐3,5‐diaza‐7‐phosphatricyclo[3.3.1.1^3,7]decane iodide (mpta⁺I^?) and 1‐(n‐propyl)‐1‐azonia‐3,5‐diaza‐7‐phosphatricyclo[3.3.1.1^3,7]decane bromide (ppta⁺Br^?) respectively. The crystal structures of compounds 1 and 2 are described and are similar, with both compounds crystallizing in monoclinic space groups. The geometry about both nickel atoms is that of a trigonal bipyramid with the cationic phosphine ligands found in the axial positions and the iodide ligands arranged in the equatorial plane.     

Reaction of [M(CO)4] (M = Ir, Rh) with cyclopropenyl tetrafluoroborate - Ring opening and coupling of cyclopropenyl ligands to form dinuclear metal complexes

Reaction of the iridium tetracarbonylate [PPN][Ir(CO)₄] (1a) with triphenylcyclopropenyl tetrafluoroborate [C₃Ph₃][BF₄] afforded two dinuclear species Ir₂(CO)₄(μ,η¹:η²-C₃Ph₃)(μ,η²:η³-C₃Ph₃) (2) and Ir₂(CO)₄(μ,η⁴:η⁴-C₆Ph₆) (3a) resulting from the ring opening and in the latter case, coupling of the resulting acyclic, propenyl ligands. The analogous reaction with [PPN][Rh(CO)₄] (1b) afforded only the rhodium analogue for 3a.     

New rhodium(I) water‐soluble complexes with 1‐alkyl‐1‐azonia‐3,5‐diaza‐7‐phospha‐adamantane iodides and their catalytic activity

The water‐soluble phosphine ligands, 1,3,5‐triaza‐7‐phosphatricyclo[3.3.1.1^3,7]decane (tpa) and 1‐alkyl‐1‐azonia‐3,5‐diaza‐7‐phosphatricyclo[3.3.1.1^3,7]decane iodides (Rtpa⁺I⁻), with alkyl=methyl(mtpa⁺I⁻), ethyl (etpa⁺I⁻) and n‐propyl, (ptpa⁺I⁻), and mtpa⁺Cl⁻ react with [Rh₂Cl₂(CO)₄] giving the rhodium(I) complexes [RhCl(CO)(tpa)₂], [RhI(CO)(Rtpa⁺I⁻)₂], [RhCl‐­(CO)(mtpa⁺Cl⁻)₃] and [RhI(CO)(Rtpa⁺I⁻)₃]. The properties and reactivities of the complexes have been investigated using ¹H and ³¹PNMR and IR spectroscopies. The five‐coordinate complexes in solutions show dynamic properties. The complexes are catalysts of the water‐gas shift reaction, the hydrogenation of CC and CO bonds, the hydroformylation of alkenes and the isomerization of unsaturated compounds. Copyright © 1999 John Wiley & Sons, Ltd.     

Homo‐ and Heterodinuclear Ir and Rh Imine‐functionalized Protic NHC Complexes: Synthetic,Structural Studies,and Tautomerization/Metallotropism Insights

The influence of the potentially chelating imino group of imine‐functionalized Ir and Rh imidazole complexes on the formation of functionalized protic N‐heterocyclic carbene (pNHC) complexes by tautomerization/metallotropism sequences was investigated. Chloride abstraction in [Ir(cod)Cl{C₃H₃N₂(DippN=CMe)‐κN3}] ( 1 a ) (cod=1,5‐cyclooctadiene, Dipp=2,6‐diisopropylphenyl) with TlPF₆ gave [Ir(cod){C₃H₃N₂(DippN=CMe)‐κ²(C2,N_imine)}]⁺[PF₆]^? ( 3 a ⁺[PF₆]^?). Plausible mechanisms for the tautomerization of complex 1 a to 3 a ⁺[PF₆]^? involving C2?H bond activation either in 1 a or in [Ir(cod){C₃H₃N₂(DippN=CMe)‐κN3}₂]⁺[PF₆]^? ( 6 a ⁺[PF₆]^?) were postulated. Addition of PR₃ to complex 3 a ⁺[PF₆]^? afforded the eighteen‐valence‐electron complexes [Ir(cod)(PR₃){C₃H₃N₂(DippN=CMe)‐κ²(C2,N_imine)}]⁺[PF₆]^? ( 7 a ⁺[PF₆]^? (R=Ph) and 7 b ⁺[PF₆]^? (R=Me)). In contrast to Ir, chloride abstraction from [Rh(cod)Cl{C₃H₃N₂(DippN=CMe)‐κN3}] ( 1 b ) at room temperature afforded [Rh(cod){C₃H₃N₂(DippN=CMe)‐κN3}₂]⁺[PF₆]^? ( 6 b ⁺[PF₆]^?) and [Rh(cod){C₃H₃N₂(DippN=CMe)‐κ²(C2,N_imine)}]⁺[PF₆]^? ( 3 b ⁺[PF₆]^?) (minor); the reaction yielded exclusively the latter product in toluene at 110 °C. Double metallation of the azole ring (at both the C2 and the N3 atom) was also achieved: [Ir₂(cod)₂Cl{μ‐C₃H₂N₂(DippN=CMe)‐κ²(C2,N_imine),κN3}] ( 10 ) and the heterodinuclear complex [IrRh(cod)₂Cl{μ‐C₃H₂N₂(DippN=CMe)‐κ²(C2,N_imine),κN3}] ( 12 ) were fully characterized. The structures of complexes 1 b , 3 b ⁺[PF₆]^?, 6 a ⁺[PF₆]^?, 7 a ⁺[PF₆]^?, [Ir(cod){C₃HN₂(DippN=CMe)(DippN=CH)(Me)‐κ²(N3,N_imine)}]⁺[PF₆]^? ( 9 ⁺[PF₆]^?), 10? Et₂O ? toluene, [Ir₂(CO)₄Cl{μ‐C₃H₂N₂(DippN=CMe)‐κ²(C2,N_imine),κN3}] ( 11 ), and 12? 2 THF were determined by X‐ray diffraction.     

Synthesis, 119Sn, 13C and 195Pt NMR studies of five-coordinate rhodium(I), iridium(I) and platinum(II) complexes containing three trichlorostannate ligands

The synthesis and ¹¹⁹Sn NMR characteristics of new five-coordinate tris(trichlorostannato) complexes of Rh^I, Ir^I and Pt^II are reported. The Rh^I and Ir^I complexes are complex dianions of the form (PPN)₂[M(SnCl₃)₃L₂] where L can be CO, CN (cyclohexyl) or L₂, a diolefin such as 1,5-COD or NBD (norbornadiene). The anionic platinum complexes (PPN)[Pt(SnCl₃)₃L₂] contain similar L ligands. A number of neutral monotrichlorostannato complexes of type [M(SnCl₃)L₄] including [Ir(SnCl₃)(NBD)(1,5-COD)] have been prepared and characterized. Their δ(¹¹⁹Sn), δ(¹³C), δ(¹⁹⁵Pt) as well as ¹J(¹⁰³Rh, ¹¹⁹Sn), ¹J(¹⁹⁵Pt, ¹¹⁹Sn), ²J(¹¹⁹Sn, ¹¹⁷Sn) and ²J(¹¹⁹Sn, ¹³C) data are given. A trans influence series, based on ¹J(¹⁹⁵Pt, ¹¹⁹Sn), reveals the following sequence: H^? > PR₃ > AsR₃ > SnCl₃^? > olefin > Cl^?.     

Gold(I) and Gold(III) Trifluoromethyl Derivatives

Trifluoromethylation of AuCl₃ by using the Me₃SiCF₃/CsF system in THF and in the presence of [PPh₄]Br proceeds with partial reduction, yielding a mixture of [PPh₄][Au^I(CF₃)₂] ( 1′ ) and [PPh₄][Au^III(CF₃)₄] ( 2′ ) that can be adequately separated. An efficient method for the high‐yield synthesis of 1′ is also described. The molecular geometries of the homoleptic anions [Au^I(CF₃)₂]^? and [Au^III(CF₃)₄]^? in their salts 1′ and [NBu₄][Au^III(CF₃)₄] ( 2 ) have been established by X‐ray diffraction methods. Compound 1′ oxidatively adds halogens, X₂, furnishing [PPh₄][Au^III(CF₃)₂X₂] (X=Cl ( 3 ), Br ( 4 ), I ( 5 )), which are assigned a trans stereochemistry. Attempts to activate C? F bonds in the gold(III) derivative 2′ by reaction with Lewis acids under different conditions either failed or only gave complex mixtures. On the other hand, treatment of the gold(I) derivative 1′ with BF₃?OEt₂ under mild conditions cleanly afforded the carbonyl derivative [Au^I(CF₃)(CO)] ( 6 ), which can be isolated as an extremely moisture‐sensitive light yellow crystalline solid. In the solid state, each linear F₃C‐Au‐CO molecule weakly interacts with three symmetry‐related neighbors yielding an extended 3D network of aurophilic interactions (Au???Au=345.9(1) pm). The high $\tilde \nu $ _CO value (2194 cm^?1 in the solid state and 2180 cm^?1 in CH₂Cl₂ solution) denotes that CO is acting as a mainly σ‐donor ligand and confirms the role of the CF₃ group as an electron‐withdrawing ligand in organometallic chemistry. Compound 6 can be considered as a convenient synthon of the “Au^I(CF₃)” fragment, as it reacts with a number of neutral ligands L, giving rise to the corresponding [Au^I(CF₃)(L)] compounds (L=CNtBu ( 7 ), NCMe ( 8 ), py ( 9 ), tht ( 10 )).     

Highly Effective Water Oxidation Catalysis with Iridium Complexes through the Use of NaIO4

Exceptional water oxidation (WO) turnover frequencies (TOF=17 000 h^?1), and turnover numbers (TONs) close to 400 000, the largest ever reported for a metal‐catalyzed WO reaction, have been found by using [Cp*Ir^III(NHC)Cl₂] (in which NHC=3‐methyl‐1‐(1‐phenylethyl)‐imidazoline‐2‐ylidene) as the pre‐catalyst and NaIO₄ as oxidant in water at 40 °C. The apparent TOF for [Cp*Ir^III(NHC)X₂] ( 1 X , in which X stands for I ( 1 I ), Cl ( 1 Cl ), or triflate anion ( 1 OTf )) and [(Cp*‐NHCMe)Ir^IIII₂] ( 2 ) complexes, is kept constant during almost all of the O₂ evolution reaction when using NaIO₄ as oxidant. The TOF was found to be dependent on the ligand and on the anion (TOF ranging from ≈600 to ≈1100 h^?1 at 25 °C). Degradation of the complexes by oxidation of the organic ligands upon reaction with NaIO₄ has been investigated. ¹H NMR, ESI‐MS, and dynamic light‐scattering measurements (DLS) of the reaction medium indicated that the complex undergoes rapid degradation, even at low equivalents of oxidant, but this process takes place without formation of nanoparticles. Remarkably, three‐month‐old solution samples of oxidized pre‐catalysts remain equally as active as freshly prepared solutions. A UV/Vis feature band at λ_max=405 nm is observed in catalytic reaction solutions only when O₂ evolves, which may be attributed to a resting state iridium speciation, most probably Ir–oxo species with an oxidation state higher than IV.     

Fine‐Tuning of Lewis Acidity: The Case of Borenium Hydride Complexes Derived from Bis(phosphinimino)amide Boron Precursors

Reactions of bis(phosphinimino)amines LH and L′H with Me₂S ? BH₂Cl afforded chloroborane complexes LBHCl ( 1 ) and L′BHCl ( 2 ), and the reaction of L′H with BH₃ ? Me₂S gave a dihydridoborane complex L′BH₂ ( 3 ) (LH=[{(2,4,6‐Me₃C₆H₂N)P(Ph₂)}₂N]H and L′H=[{(2,6‐iPr₂C₆H₃N)P(Ph₂)}₂N]H). Furthermore, abstraction of a hydride ion from L′BH₂ ( 3 ) and LBH₂ ( 4 ) mediated by Lewis acid B(C₆F₅)₃ or the weakly coordinating ion pair [Ph₃C][B(C₆F₅)₄] smoothly yielded a series of borenium hydride cations: [L′BH]⁺[HB(C₆F₅)₃]^? ( 5 ), [L′BH]⁺[B(C₆F₅)₄]^? ( 6 ), [LBH]⁺[HB(C₆F₅)₃]^? ( 7 ), and [LBH]⁺[B(C₆F₅)₄]^? ( 8 ). Synthesis of a chloroborenium species [LBCl]⁺[BCl₄]^? ( 9 ) without involvement of a weakly coordinating anion was also demonstrated from a reaction of LBH₂ ( 4 ) with three equivalents of BCl₃. It is clear from this study that the sterically bulky strong donor bis(phosphinimino)amide ligand plays a crucial role in facilitating the synthesis and stabilization of these three‐coordinated cationic species of boron. Therefore, the present synthetic approach is not dependent on the requirement of weakly coordinating anions; even simple BCl₄^? can act as a counteranion with borenium cations. The high Lewis acidity of the boron atom in complex 8 enables the formation of an adduct with 4‐dimethylaminopyridine (DMAP), [LBH ? (DMAP)]⁺[B(C₆F₅)₄]^? ( 10 ). The solid‐state structures of complexes 1 , 5 , and 9 were investigated by means of single‐crystal X‐ray structural analysis.     

Darstellung,spektroskopische Charakterisierung und Normalkoordinatenanalyse von Nonabromoditechnetat(IV), [Tc2Br9]−

Preparation, Spectroscopic Characterization and Normal Coordinate Analysis of Nonabromoditechnetate(IV), [Tc₂Br₉]^? . On heating the tetraethylammonium salt (TEA)₂[Tc₂Br₆] with trifluoroacetic acid the face-sharing bioctahedral anion [Tc₂Br₉]^? is formed, which vibronic spectrum is assigned according to point group D_3h. Normal coordinate analysis, based on a general valence force field has been performed, resulting in a good agreement of calculated frequencies with the observed IR and Raman bands. Due to stronger bonding of the terminal as compared to the bridging ligands, the valence force constant f_d(TcBr_t) = 1.045 is significantly higher than f_d(TcBr_b) = 0.80 mdyn/Å.     

Synthesis,Coordination Behavior,and Reduction Chemistry of Cymantrenyl‐1,3‐bis(2,3,4,5‐tetraphenyl)borole

We describe the synthesis of base‐free bisborole [Cym^?(BC₄Ph₄)₂]—Cym^?=(OC)₃Mn(η⁵‐C₅H₃)—and its transformation into two fully characterized Lewis acid–base adducts with pyridine bases of the type 4‐R? NC₅H₄ (R=tBu, NMe₂). The results of electrochemical, as well as NMR and UV/Vis spectroscopic studies on [Cym^?(BC₄Ph₄)₂] and the related monoborole derivative [Cym(BC₄Ph₄)]—Cym=(OC)₃Mn(η⁵‐C₅H₄)—provided conclusive evidence for 1) the enhanced Lewis acidity of the two boron centers that result from conjugation of two borole fragments, and 2) the fact that Mn? B bonding interactions between the Lewis acidic borole moieties and the Mn center are considerably less pronounced for bisborole [Cym^?(BC₄Ph₄)₂]. In addition, the reduction chemistry of [Cym^?(BC₄Ph₄)₂] has been studied in detail, both electrochemically and chemically. Accordingly, chemical reduction of [Cym^?(BC₄Ph₄)₂] with magnesium anthracene afforded the corresponding tetraanion, which features a rare Mg? OC bonding mode in the solid state.     

Nitridorhenium(V) Complexes with 1,3,4‐Triphenyl‐1,2,4‐triazol‐5‐ylidene

[ReNCl₂(PPh₃)₂] and [ReNCl₂(PMe₂Ph)₃] react with the N‐heterocyclic carbene (NHC) 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (HL^Ph) under formation of the stable rhenium(V) nitrido complex [ReNCl(HL^Ph)(L^Ph)], which contains one of the two NHC ligands with an additional orthometallation. The rhenium atom in the product is five‐coordinate with a distorted square‐pyramidal coordination sphere. The position trans to the nitrido ligand is blocked by one phenyl ring of the monodentate HL^Ph ligand. The Re–C(carbene) bond lengths of 2.072(6) and 2.074(6) Å are comparably long and indicate mainly σ‐bonding between the NHC ligand and the electron deficient d² metal atom. The chloro ligand in [ReNCl(HL^Ph)(L^Ph)] is labile and can be replaced by ligands such as pseudohalides or monoanionic thiolates such as diphenyldithiophosphinate (Ph₂PS₂^?) or pyridine‐2‐thiolate (pyS^?). X‐ray structure analyses of [ReN(CN)(HL^Ph)(L^Ph)] and [ReN(pyS)(HL^Ph)(L^Ph)] show that the bonding situation of the NHC ligands (Re–C(carbene) distances between 2.086(3) and 2.130(3) Å) in the product is not significantly influenced by the ligand exchange. The potentially bidentate pyS^? ligand is solely coordinated via its thiolato functionality. Hydrogen atoms of each one of the phenyl rings come close to the unoccupied sixth coordination positions of the rhenium atoms in the solid state structures of all complexes. Re–H distances between 2.620 and 2.712Å do not allow to discuss bonding, but with respect to the strong trans labilising influence of “N^3?”, weak interactions are indicated.