Oxygen-bridged borate anions from tris(pentafluorophenyl)borane: synthesis, NMR characterization, and reactivity

The previously known anion [(C6F5)3B(mu-OH)B(C6F5)3]- (2) has been prepared by a two-step procedure, involving deprotonation of (C6F5)3BOH2 to give [B(C6F5)3OH]- (1), followed by addition of B(C6F5)3. The solution structure and the dynamics of 2 have been investigated by 1H and 19F NMR spectroscopy. The reaction of [NHEt3]2 with NEt3 resulted in the formation of [NHEt3]+ [(C6F5)3BOH]-, [NHEt3]+ [(C6F5)3BH]-, and (C6F5)3B- (CH2CH=N+ Et2). This indicates that in the presence of a nucleophile anion 2 can dissociate to B(C6F5)3 and 1. The reaction of [HDMAN]2 with 1,8-bis(dimethylamino)naphthalene (DMAN) confirmed this trend. In the presence of water, 2 transformed into the adduct [(C6F5)3BO(H)H...O(H)B(C6F5)3]- (3), containing the borate 1 hydrogen-bonded to a water molecule coordinated to B(C6F5)3. The same compound is formed by treating (C6F5)3BOH2 with 0.5 equiv of a base. A competition study established that for 1 the Lewis acid-base interaction with B(C6F5)3 is about 5 times preferred over H-bonding to (C6F5)3BOH2. The X-ray single-crystal analysis of [2-methyl-3H-indolium]3 provided the first experimental observation of an asymmetric H-bond in the [H3O2]- moiety, the measured O-H and H...O bond distances being significantly different [1.14(2) vs 1.26(2) A]. The reaction of NEt3 with an equimolar mixture of B(C6F5)3 and bis(pentafluorophenyl)borinic acid, (C6F5)2BOH, afforded the novel borinatoborate salt [NHEt3]+ [(C6F5)3BOB(C6F5)2]- ([NHEt3]4). X-ray diffraction showed that the B-O bond distances are significantly shorter than in [(C6F5)3B(mu-OH)B(C6F5)3]-. Variable-temperature 19F NMR revealed high mobility of the five aryl rings, at variance with the more crowded anion 2. 2D NMR correlation experiments showed that in CD2Cl2 the two anions [(C6F5)3BOH]- and [(C6F5)3BH]- form tight ion pairs with [NHEt3]+, in which the NH proton establishes a conventional (BO...HN) or an unconventional (BH...HN), respectively, hydrogen bond with the anion. The diborate anions 2-4, on the contrary, gave loose ion pairs with the ammonium cation, due both to the delocalized anionic charge and to the more sterically encumbered position of the oxygen atoms that should act as H-bond acceptors.     

Fluorotris(trifluoromethylsulfonyl)methane: synthesis, characterization and reactivity

The hitherto elusive title compound was synthesized and characterized with the aim to study its potential as a carbon-based (“CF-type”) electrophilic fluorination reagent. A detailed discussion of its structure, properties and reactivity is based on experimental studies as well as on molecular modeling.     

Two tetrakis(benzoylacetonato)lanthanide species: synthesis,characterization and structures of tetrakis(benzoylacetonato)cerium(IV) and triethylammonium tetrakis(benzoylacetonato)lanthanate(III) tetrahydrate

Tetrakis(benzoylacetonato)cerium(IV), [Ce(bzac)₄] and triethylammonium tetrakis(benzoylacetonato)lanthanate(III) tetrahydrate, [Et₃NH][La(bzac)₄] · 4H₂O were prepared and characterized by TG and DCS measurements, IR spectroscopy, and X-ray structure analysis. The coordination polyhedron of cerium is a trigonal dodecahedron, while that of lanthanum is a distorted square antiprism. Thermal and spectroscopic measurements indicate that bonding of the ligand to metal is stronger in [Ce(bzac)₄] than in [La(bzac)₄]^?.     

Tris(allyl) indium compounds: synthesis and structural characterization

Allyl and 2-methylallyl indium compounds were prepared by salt metathesis starting from indium trichloride and a Grignard reagent. They are highly fluxional in solution and reveal coordination numbers of the indium atoms of four and five in the solid state.     

Bis[(18-crown-6)potassium] tetrakis(isothiocyanato)zinc(II): synthesis and crystal structure

A new complex, bis[(18-crown-6)potassium] tetrakis(isothiocyanato)zinc(II) [[K(18-crown-6)₂] [Zn(NCS)₄]] (I), is synthesized. Its crystal structure is studied using X-ray diffraction analysis (space group Pna2₁, a = 17.604 Å, b = 14.190 Å, c = 17.625 Å, Z = 4) by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.099 for all 3994 measured independent reflections (CAD4 automated diffractiometer, λMoK _α radiation).     

Oxo-molybdenum(VI,V,IV) complexes of the facially coordinating tris(mercaptoimidazolyl)borate ligand: synthesis, characterization, and oxygen atom transfer reactivity

A series of monooxo-Mo(IV,V) and dioxo-Mo(VI) complexes of the "soft" tripodal ligand, sodium tris(mercaptoimidazolyl)borate (NaTm(Me)), have been synthesized as potential oxygen atom transfer (OAT) models for sulfite oxidase. Complexes have been characterized by X-ray crystallography, cyclic voltammetry, and EPR, where appropriate. Oxygen atom transfer kinetics of Tm(Me)MoO(2)Cl, both stoichiometric and catalytic, have been studied by a combination of UV-vis and (31)P NMR spectroscopies under a variety of conditions. OAT rates are consistent with previously established relationships between redox potential/reactivity and mechanistic studies. The analysis of these complexes as potential structural and functional analogues of relevance to molybdoenzymes is further discussed.     

Unprecedented copper(I) bifluoride complexes: synthesis, characterization and reactivity

To be or not to bifluoride: Two synthetic pathways to unprecedented N-heterocyclic carbene copper(I) bifluoride complexes have been developed. Catalytic tests demonstrated that copper(I) bifluorides are very efficient catalysts, which do not require any additional activating agent. The first Cu-catalyzed diastereoselective allylation of (R)-N-tert-butanesulfinyl aldimines was also established. The method enables efficient, simple and general synthesis of enantiomerically enriched homoallylic amines at room temperature in high yields.     

Bis(allyl)zinc revisited: sigma versus pi bonding of allyl coordination

The reinvestigation of two allyl zinc compounds, parent bis(allyl)zinc [Zn(C(3)H(5))(2)] (1) and 2-methallyl chloro zinc [Zn(C(4)H(7))Cl] (2), revealed two new coordination modes in the solid state for the allyl ligand, viz cis- and trans-μ(2)-η(1):η(1). These results call for modification of the conventional interpretation of zinc-allyl interactions. Computational results indicate that the classical η(3)-bonding mode of the allyl ligand is not favored in zinc compounds. A rare case of a zinc-olefin interaction in the dimer of [Zn(η(1)-C(3)H(5))(OC(C(3)H(5))Ph(2))] was found in the monoinsertion product of 1 with benzophenone.     

Bis(diphenylphosphino)ethane nickel polychloridophenylthiolate complexes: synthesis and characterization

Transition Metal Chemistry - Reactions of (dppe)NiCl2 (dppe?=?1,2-bis(diphenylphosphino)ethane) with chlorido-substituted phenyl thiolates (RClS?) produced the corresponding...     

Synthesis of tris(cyclopentadienyl)zirconium tetrakis(pentafluorophenyl)borate

Russian Chemical Bulletin - An efficient procedure for the synthesis of tris(cyclopentadienyl)zirconium tetrakis-(pentafluorophenyl)borate [Cp3Zr][B(C6F5)4] was suggested based on the reaction of...     

Chromium(II) and chromium(III) complexes supported by tris(2-pyridylmethyl)amine: synthesis, structures, and reactivity

This report describes the synthesis, structural characterization, and polymerization behavior of a series of chromium(II) and chromium(III) complexes ligated by tris(2-pyridylmethyl)amine (TPA), including chromium(III) organometallic derivatives. For instance, the combination of TPA with CrCl(2) yields monomeric (TPA)CrCl(2) (1). A similar reaction of CrCl(2) with TPA, followed by chloride abstraction with NaBPh(4) or NaBAr(F)(4) (Ar(F) = 3,5-(CF(3))(2)C(6)H(3)), provides the weakly associated cationic dimers [(TPA)CrCl](2)[BPh(4)](2) (2A) and [(TPA)CrCl](2)[BAr(F)(4)](2) (2B), respectively. X-ray crystallographic analysis reveals that each chromium(II) center in 1, 2A, and 2B is a tetragonally elongated octahedron; such Jahn-Teller distortions are consistent with the observed high spin (S = 2) electronic configurations for these chromium(II) complexes. Likewise, reaction of CrCl(3)(THF)(3) with TPA, followed by anion metathesis with NaBPh(4) or NaBAr(F)(4), yields the monomeric, cationic chromium(III) complexes [(TPA)CrCl(2)][BPh(4)] (4A) and [(TPA)CrCl(2)][BAr(F)(4)] (4B), respectively. Treatment of 4A with methyl and phenyl Grignard reagents produces the cationic chromium(III) organometallic derivatives [(TPA)Cr(CH(3))(2)][BPh(4)] (5) and [(TPA)CrPh(2)][BPh(4)] (6), respectively. Similar reactions of 4A with organolithium reagents leads to intractable solids, presumably due to overreduction of the chromium(III) center. X-ray crystallographic analysis of 4A, 5, and 6 confirms that each possesses a largely undistorted octahedral chromium center, consistent with the observed S = (3)/(2) electronic ground states. Compounds 1, 2A, 2B, 4A, 4B, 5, and 6 are all active polymerization catalysts in the presence of methylalumoxane, producing low to moderate molecular weight high-density polyethylene.     

Tetrahedranyllithium: synthesis, characterization, and reactivity

The first representative of stable tetrahedranyl anion, tris(trimethylsilyl)tetrahedranyllithium (3), has been synthesized by the reaction of tetrakis(trimethylsilyl)tetrahedrane (2) with methyllithium in tetrahydrofuran. The structural characterization of the tetrahedranyllithium has been achieved by X-ray crystallography, showing that the structure of 3.(TMEDA)1.5 represents a stretched tetrahedron. The endocyclic C(Li)-C(SiMe3) bond lengths range from 1.5408(15) to 1.5441(15) A (av 1.5425(15) A), and are longer than the endocyclic C(SiMe3)-C(SiMe3) bond lengths, which range from 1.4961(15) to 1.5009(15) A (av 1.4986(15) A). Methyl- and hydrogen-substituted tetrahedranes have also been prepared by the reaction of 3 with dimethyl sulfate and cyclopentadiene, respectively.     

The synthesis and characterization of some titanium (III) tris N,N-dialkyldithiocarbamates

It has been demonstrated that the reaction of sodium salts of dialkyldithiocarbamates with titanium trichloride in ethanol gives a yellow-green solid, which shows a three to one stoichiometry indicating a tris coordination. Infrared spectral data indicate the complexes to be approximately of D₃h symmetry, bonded through the sulfur atoms as chelates. Magnetic data show that the d¹ state is retained.     

Some reactions of tris(trimethylstannyl)- and tetrakis(trimethylstannyl)-methane

With a variety of electrophilic reagents reaction occurs exclusively at the CH₃Sn bonds of [(CH₃)₃Sn]₄C and [(CH₃)₃Sn]₃CH. While the inner SnC bonds remain intact, methyl groups may be progressively cleaved off, one from each of the trimethylstannyl groups; in the case of bromine a second Me group may be cleaved from each of the SnMe₂Br groups. The various products were identified by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy.     

Synthesis of tris(trifluoromethyl)gallium and its adducts

Tris(trifluoromethyl)gallium and its trimethylphosphine and trimethylarsine complexes have been synthesized using the Morrison reagent. Several new materials of potential importance to the microelectronic industry have been produced.     

Homoleptic tris(dithiolene) and tetrakis(dithiolene) complexes of uranium(IV)

Reaction of UCl4 with 3 or 4 mol equiv of Na2dddt (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) in THF afforded the first example of a tetrakis(dithiolene) metal compound, [Na4(THF)8U(dddt)4](infinity) (1). The red crystals of 1 are composed of infinite zigzag chains in which Na2(micro-THF)3 fragments ensure the linking of Na2(THF)5U(dddt)4 moieties; the uranium atom is in a dodecahedral environment of eight sulfur atoms. Treatment of UCl4 with 3 mol equiv of Na2dddt in pyridine gave a mixture of tris- and tetrakis(dithiolene) compounds. After addition of 18c6 (18-crown-6), only the tris(dithiolene) complex was obtained and crystallized as orange crystals of [Na(18c6)(py)2]2[U(dddt)3].2py (2.2py) in which the isolated [U(dddt)3]2- anion adopts a slightly distorted trigonal prismatic configuration. A few red crystals of the unsolvated complex 2 and the trinuclear anionic compound [Na(18c6)(py)2]3[Na{U(dddt)3}2] (3) were also obtained along with orange crystals of 2.2py. All the tris(dithiolene) compounds exhibit large folding of the dddt ligand and significant interaction between the C=C double bond and the metal center.     

Imidomolybdenum(IV) porphyrin complexes: synthesis, characterization, and intermetal imido transfer reactivity

The imido(meso-tetra-p-tolylporphyrinato)molybdenum(IV) complexes, (TTP)Mo=NR, where R = C6H5 (1a), p-CH3C6H4 (1b), 2,4,6-(CH3)3C6H2 (1c), and 2,6-(i-Pr)2C6H4 (1d), can be prepared by the reaction of (TTP)MoCl2 with 2 equiv of LiNHR in toluene. Upon treatment of the imido complexes with pyridine derivatives, NC5H4-p-X (X = CH3, CH(CH3)2, C[triple bond]N), new six-coordinate complexes, (TTP)Mo=NR.NC5H4-p-X, were observed. The reaction between the molybdenum imido complexes, (TTP)Mo=NC6H5 or (TTP)Mo=NC6H4CH3, and (TTP)Ti(eta2-PhC[triple bond]CPh) resulted in complete imido group transfer and two-electron redox of the metal centers to give (TTP)Mo(eta2-PhC[triple bond]CPh) and (TTP)Ti=NC6H5 or (TTP)Ti=NC6H4CH3.