Cationic Triarylchlorostibonium Lewis Acids.

Organopnictogen cations show promise as powerful, tunable main-group Lewis acid catalysts. The synthesis, solid-state structures, and reactivity of a series of weakly coordinated triarylchlorostibonium salts [Ar3SbCl][B(C6F5)4] (Ar = Ph, 3-FC6H4, 4-FC6H4, 3,5-F2C6H3, 2,4,6-F3C6H2) are reported. The cation in each adopts a tetrahedral coordination environment of antimony, with near complete separation from the anion. Structural, computational, and reactivity studies reveal that the Lewis acidity of [Ar3SbCl]+ generally increases with increased fluorination of the Ar substituents, with a secondary quenching effect from para fluorination. [Ar3SbCl]+ is reduced to Ar3Sb in the presence of Et3SiH, and the mechanism of this reaction has been modeled computationally. Preliminary studies demonstrate that they are useful catalysts for the dimerization of 1,1-diphenylethylene and the Friedel-Crafts alkylation of benzene.

Diverse structure and reactivity of pentamethylcyclopentadienyl antimony(iii) cations.

The pentamethylcyclopentadienyl (Cp*) antimony(iii) cations [Cp*2Sb][B(C6F5)4], [Cp2*Sb][OTf], [Cp*SbCl][B(C6F5)4] and [Cp*Sb][OTf]2 have been isolated and structurally characterised. [Cp*SbCl]+ forms dimers in the solid state via an intermolecular Sb-Cl interaction. Initial screening shows that [Cp*SbCl][B(C6F5)4] is significantly Lewis acidic and can catalyse the dimerisation of 1,1-diphenylethylene; [Cp2*Sb][B(C6F5)4] exhibits negligible Lewis acidity. Highly unstable [Cp*SbF][B(C6F5)4] could not be isolated, but stabilisation with the IMes ligand allowed isolation of [Cp*SbF(IMes)][B(C6F5)4]. Fluorodechlorination of CH2Cl2 and PhCCl3 was observed in the presence of crude [Cp*SbF][B(C6F5)4] in solution. A computational mechanistic investigation suggests that the latter proceeds via a carbocation intermediate.

Hyperpolarization of Pyridyl Fentalogues by Signal Amplification By Reversible Exchange (SABRE).

Fentanyl, also known as 'jackpot', is a synthetic opiate that is 50-100 times more potent than morphine. Clandestine laboratories produce analogues of fentanyl, known as fentalogues to circumvent legislation regarding its production. Three pyridyl fentalogues were synthesized and then hyperpolarized by signal amplification by reversible exchange (SABRE) to appraise the forensic potential of the technique. A maximum enhancement of -168-fold at 1.4 T was recorded for the ortho pyridyl 1H nuclei. Studies of the activation parameters for the three fentalogues revealed that the ratio of ligand loss trans to hydride and hydride loss in the complex [Ir(IMes)(L)3(H)2]+ (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazole-2-ylidene) ranged from 0.52 to 1.83. The fentalogue possessing the ratio closest to unity produced the largest enhancement subsequent to performing SABRE at earth's magnetic field. It was possible to hyperpolarize a pyridyl fentalogue selectively from a matrix that consisted largely of heroin (97 : 3 heroin:fentalogue) to validate the use of SABRE as a forensic tool.

Crystal structure of 2,4-di-tert-butyl-6-(hy-droxy-methyl)-phenol.

The title compound, C15H24O2, is an example of a phenol-based pendant-arm precursor. In the mol-ecule, the phenol hy-droxy group participates in an intra-molecular O-H⋯O hydrogen bond with the pendant alcohol group, forming an S(6) ring. This ring adopts a half-chair conformation. In the crystal, O-H⋯O hydrogen bonds connect mol-ecules related by the 31 screw axes, forming chains along the c axis. The C-C-O angles for the hy-droxy groups are different as a result of the type of hybridization for the C atoms that are involved in these angles. The C-C-O angle for the phenol hy-droxy group is 119.21 (13)°, while the angle within the pendant alcohol is 111.99 (13)°. The bond length involving the phenolic oxygen is 1.3820 (19) Å, which contrasts with that of the alcoholic oxygen which is 1.447 (2) Å. The former is conjugated with the aromatic ring and so leads to the observed shorter bond length.

Nanoscale arrays of antimony telluride single crystals by selective chemical vapor deposition.

Arrays of individual single nanocrystals of Sb2Te3 have been formed using selective chemical vapor deposition (CVD) from a single source precursor. Crystals are self-assembled reproducibly in confined spaces of 100 nm diameter with pitch down to 500 nm. The distribution of crystallite sizes across the arrays is very narrow (standard deviation of 15%) and is affected by both the hole diameter and the array pitch. The preferred growth of the crystals in the <1 1 0> orientation along the diagonal of the square holes strongly indicates that the diffusion of adatoms results in a near thermodynamic equilibrium growth mechanism of the nuclei. A clear relationship between electrical resistivity and selectivity is established across a range of metal selenides and tellurides, showing that conductive materials result in more selective growth and suggesting that electron donation is of critical importance for selective deposition.

[Pd4(µ3-SbMe3)4(SbMe3)4]: A Pd(0) Tetrahedron with µ3-Bridging Trimethylantimony Ligands.

The palladium(II) chlorostibine complex [PdCl2(SbMe2Cl)2]2 has a dimeric structure in the solid state, stabilized by hyper-coordination at the Lewis amphoteric Sb centers. Reaction with 8 equiv of MeLi forms [Pd4(µ3-SbMe3)4(SbMe3)4], whose structure comprises a tetrahedral Pd(0) core with four terminal SbMe3 ligands and four µ3-SbMe3 ligands, one capping each triangular Pd3 face. Density functional theory calculations, supported by energy decomposition analysis and the natural orbitals for chemical valence scheme, highlight significant donor and acceptor orbital contributions to the bonding between both the terminal and the bridging SbMe3 ligands and the Pd4 core.

Niobium tetrahalide complexes with neutral diphosphine ligands.

The reactions of NbCl4 with diphosphine ligands o-C6H4(PMe2)2, Me2PCH2CH2PMe2 or Et2PCH2CH2PEt2 in a 1 : 2 molar ratio in MeCN solution produced eight-coordinate [NbCl4(diphosphine)2]. [NbBr4(diphosphine)2] (diphosphine = o-C6H4(PMe2)2 or Me2PCH2CH2PMe2) were made similarly from NbBr4. X-ray crystal structures show that [NbCl4{o-C6H4(PMe2)2}2] has a dodecahedral geometry, but the complexes with dimethylene-backboned diphosphines are distorted square antiprisms. The Nb-P distances and

Niobium(V) and tantalum(V) halide chalcogenoether complexes--towards single source CVD precursors for ME2 thin films.

A series of pentavalent niobium and tantalum halide complexes with thio-, seleno- and telluro-ether ligands, [MCl5(E(n)Bu2)] (M = Nb, Ta; E = S, Se, Te), [TaX5(TeMe2)] (X = Cl, Br, F) and the dinuclear [(MCl5)2{o-C6H4(CH2SEt)2}] (M = Nb, Ta), has been prepared and characterised by IR, (1)H, (13)C{(1)H}, (77)Se, (93)Nb and (125)Te NMR spectroscopy, as appropriate, and microanalyses. Confirmation of the tantalum(V)-telluroether coordination follows from the crystal structure of [TaCl5(TeMe2)], which represents the highest oxidation state transition metal complex with telluroether coordination structurally authenticated. The Ta(V) monotelluroether complexes are much more stable than the Nb(V) analogues. In the presence of TaCl5 the ditelluroether, CH2(CH2Te(t)Bu)2, is decomposed; one of the products is the dealkylated [(t)BuTe(CH2)3Te][TaCl6], whose structure was determined crystallographically. Crystal structures of [(MCl5)2{o-C6H4(CH2SEt)2}] (M = Nb, Ta) show ligand-bridged species. The complexes bearing ß-hydrogen atoms on the terminal alkyl substituents have also been investigated as single source reagents for the deposition of ME2 thin films via low pressure chemical vapour deposition. While the tantalum complexes proved to be unsuitable, the [NbCl5(S(n)Bu2)] and [NbCl5(Se(n)Bu2)] deposit NbS2 and NbSe2 as hexagonal platelets onto SiO2 substrates at 750 °C and 650 °C, respectively. Grazing incidence and in-plane X-ray diffraction confirm both materials adopt the 3R-polytype (R3mh), and the sulfide shows preferred orientation with the crystallites aligned predominantly with the c axis perpendicular to the substrate. Scanning electron microscopy and Raman spectra are consistent with the X-ray data.

Medium and high oxidation state metal/non-metal fluoride and oxide-fluoride complexes with neutral donor ligands.

While most high and medium oxidation state (O.S. ≥ 3) metal and non-metal fluorides and oxide fluorides are strong Lewis acids, exploration of their coordination chemistry with neutral ligands has been limited and mostly non-systematic. This is despite the very different properties conferred on the acceptor centre by the small electronegative fluoride ligands compared to the heavier halides. This article sets out these key differences, discusses possible synthetic routes, the key characterisation techniques, and appropriate bonding models. Current knowledge of the coordination chemistry of d, f and p-block fluorides and oxide fluorides with neutral ligands (with donor atoms drawn from Groups 15 and 16 and including N-heterocyclic carbenes) is then presented and discussed, and the differences in properties compared to complexes containing the heavier halides are illustrated. The emphasis is on work published post 1990, but earlier work is also included as essential background and where no more recent information exists. Attention is drawn to unexplored areas meriting investigation and to possible applications of these complexes.

Area Selective Growth of Titanium Diselenide Thin Films into Micropatterned Substrates by Low-Pressure Chemical Vapor Deposition.

The neutral, distorted octahedral complex [TiCl4(Se n Bu2)2] (1), prepared from the reaction of TiCl4 with the neutral Se n Bu2 in a 1:2 ratio and characterized by IR and multinuclear (1H, 13C{1H}, 77Se{1H}) NMR spectroscopy and microanalysis, serves as an efficient single-source precursor for low-pressure chemical vapor deposition (LPCVD) of titanium diselenide, TiSe2, films onto SiO2 and TiN substrates. X-ray diffraction patterns on the deposited films are consistent with single-phase, hexagonal 1T-TiSe2 (P3̅m1), with evidence of some preferred orientation of the crystallites in thicker films. The composition and structural morphology was confirmed by scanning electron microscopy (SEM), energy dispersive X-ray, and Raman spectroscopy. SEM imaging shows hexagonal plate crystallites growing perpendicular to the substrate, but these tend to align parallel to the surface when the quantity of reagent is reduced. The resistivity of the crystalline TiSe2 films is 3.36 ± 0.05 × 10-3 Ω·cm with a carrier density of 1 × 1022 cm-3. Very highly selective film growth from the reagent was observed onto photolithographically patterned substrates, with film growth strongly preferred onto the conducting TiN surfaces of SiO2/TiN patterned substrates. TiSe2 is selectively deposited within the smallest 2 µm diameter TiN holes of the patterned TiN/SiO2 substrates. The variation in crystallite size with different diameter holes is determined by microfocus X-ray diffraction and SEM, revealing that the dimensions increase with the hole size, but that the thickness of the crystals stops increasing above ∼20 µm hole size, whereas their lengths/widths continue to increase.

Preparation and structures of coordination complexes of the very hard Lewis acids ZrF4 and HfF4.

[MF(4)(dmso)(2)] (M = Zr or Hf) and [MF(4)(dmf)(2)], prepared by dissolving MF(4)·nH(2)O in the appropriate solvent, have been used as synthons for a range of complexes of these otherwise intractable tetrafluorides. These reagents react with OPR(3) (R = Me or Ph) or OAsPh(3) (L) in anhydrous CH(2)Cl(2) to form six-coordinate [MF(4)L(2)] which exist as a mixture of cis (predominant form) and trans isomers in CH(2)Cl(2) solution but which crystallise as trans (OPPh(3), OAsPh(3)) or cis (OPMe(3)) forms. Cis-[ZrF(4)(OAsPh(3))(2)] crystals were obtained from MeCN. Cis-[MF(4)(pyNO)(2)] and eight-coordinate (distorted dodecahedral) [MF(4)(L-L)(2)] (L-L = 2,2'-bipy, or 1,10-phen), and [MF(4)(Me(4)-cyclam)] were also obtained. Attempts to prepare complexes with the N-heterocyclic carbene, 1,3-(2,6-di-isopropylphenyl)imidazol-2-ylidene (IDiPP) or alkyl diphosphines were unsuccessful. Crystal structures are reported for trans-[ZrF(4)(OPPh(3))(2)], cis- and trans-[ZrF(4)(OAsPh(3))(2)], cis-[HfF(4)(OPMe(3))(2)], [ZrF(4)(2,2'-bipy)(2)], cis-[HfF(4)(dmf)(2)], and geometric isomers (both pentagonal bipyramidal) of [(dmso)(2)F(3)M(µ-F)(2)MF(3)(dmso)(2)]. The failed attempts to make IDiPP adducts led to crystals of [IDiPPH](3)[M(3)F(15)] containing discrete anions based upon a triangle of M atoms with single F bridges. The results are compared with previous work on TiF(4) adducts and with complexes of MCl(4), and demonstrate that the MF(4) are very hard Lewis acids, with a marked preference for O- over N-donors.

[Cl5Ta(µ-O)TaCl3{(i)PrS(CH2)2S(i)Pr}] and [(TaCl4)2(µ-O)(µ-Me2Se2)]: two chalcogenoether complexes of Ta2OCl8 with very different geometries.

The title compounds, [1,2-bis(isopropylsulfanyl)ethane-2κ(2)S,S']octachlorido-1κ(5)Cl,2κ(3)Cl-µ-oxido-ditantalum(V), [Ta(2)Cl(8)O(C(8)H(18)S(2))], (I), and µ-dimethyldiselane-κ(2)Se:Se'-µ-oxido-bis[tetrachloridotantalum(V)], [Ta(2)Cl(8)O(C(2)H(6)Se(2))], (II), contain six-coordinate Ta(V) centres linked by a nonlinear oxide bridge. Compound (I) contains one Ta(V) centre bonded to a chelating dithioether and three terminal chloride ligands, with the second Ta(V) centre bonded to five terminal chloride ligands. In (II), two tetrachloridotantalum(V) residues are bridged by the diselenide, giving a puckered five-membered Ta/O/Ta/Se/Se ring. The Ta-O distances in the bridges are short in both compounds, indicating that significant multiple-bond character is retained despite the deviation from linearity, and the bond lengths reveal a clear trans influence order of O > Cl > S > Se on the hard Ta(V) centre. The structures are compared with the [Ta(2)Cl(10)O](2-) anion, which contains a linear oxide bridge.

Hybrid dibismuthines and distibines as ligands towards transition metal carbonyls.

The hybrid dibismuthines O(CH(2)CH(2)BiPh(2))(2) and MeN(CH(2)-2-C(6)H(4)BiPh(2))(2) react with [M(CO)(5)(thf)] (M = Cr or W) to form [{M(CO)(5)}(2){O(CH(2)CH(2)BiPh(2))(2)}] and [{Cr(CO)(5)}(2){MeN(CH(2)-2-C(6)H(4)BiPh(2))(2)}] containing bridging bidentate (Bi(2)) coordination. The unsymmetrical tertiary bismuthine complexes [M(CO)(5){BiPh(2)(o-C(6)H(4)OMe)}] are also described. Depending upon the molar ratio, the hybrid distibines O(CH(2)CH(2)SbMe(2))(2) and MeN(CH(2)-2-C(6)H(4)SbMe(2))(2) react with [M(CO)(5)(thf)] to give the pentacarbonyl complexes [{M(CO)(5)}(2){O(CH(2)CH(2)SbMe(2))(2)}] and [{Cr(CO)(5)}(2){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}] or tetracarbonyls cis-[M(CO)(4){O(CH(2)CH(2)SbMe(2))(2)}] and cis-[M(CO)(4){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}]. The latter can also be obtained from [Cr(CO)(4)(nbd)] or [W(CO)(4)(pip)(2)], and contain chelating bidentates (Sb(2)-coordinated) as determined crystallographically. S(CH(2)-2-C(6)H(4)SbMe(2))(2) coordinates as a tridentate (SSb(2)) in fac-[M(CO)(3){S(CH(2)-2-C(6)H(4)SbMe(2))(2)}] (M = Cr or Mo) and fac-[Mn(CO)(3){S(CH(2)-2-C(6)H(4)SbMe(2))(2)}][CF(3)SO(3)]. Fac-[Mn(CO)(3){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}][CF(3)SO(3)] contains NSb(2)-coordinated ligand in the solid state, but in solution a second species, Sb(2)-coordinated and with a κ(1)-CF(3)SO(3) replacing the coordinated amine is also evident. X-ray crystal structures were also determined for fac-[Cr(CO)(3){S(CH(2)-2-C(6)H(4)SbMe(2))(2)}], fac-[Mn(CO)(3){S(CH(2)-2-C(6)H(4)SbMe(2))(2)}][CF(3)SO(3)] and fac-[Mn(CO)(3){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}] [CF(3)SO(3)]. Hypervalent N···Sb interactions are present in cis-[M(CO)(4){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}] (M = Mo or W), but absent for M = Cr.