Borato Ligand Research Articles

HERFD-XANES and RIXS Study on the Electronic Structure of Trivalent Lanthanides across a Series of Isostructural Compounds.

We performed a systematic study of the complexes of trivalent lanthanide cations with the hydridotris(1-pyrazolyl)borato (Tp) ligand (LnTp3; Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu) using both high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) and resonant inelastic X-ray scattering (RIXS) at the lanthanide L3 absorption edge. Here, we report the results obtained and we discuss them against calculations performed using density functional theory (DFT) and atomic multiplet theory. The spectral shape and the elemental trends observed in the experimental HERFD-XANES spectra are well reproduced by DFT calculations, while the pre-edge energy interval is better described by atomic multiplet theory. The RIXS data show a generally rather complex pattern that originates from the intra-atomic electron–electron interactions in the intermediate and final states, as demonstrated by the good agreement obtained with calculations using an atomic-only model of the absorber. Guided by theoretical predictions, we discuss the possible origins of the observed spectral features and the trends in energy splitting across the series. The insight into the electronic structure of trivalent lanthanide compounds demonstrated here and obtained with advanced X-ray spectroscopies coupled with theoretical calculations can be applied to any lanthanide-bearing compound and be of great interest for all research fields involving lanthanides.

Tris-{Hydridotris(1-pyrazolyl)borato}lanthanide Complexes: Synthesis, Spectroscopy, Crystal Structure and Bonding Properties

Complexes of trivalent lanthanides (Ln) with the hydridotris(1-pyrazolyl)borato (Tp) ligand Ln[η3-HB(N2C3H3)3]3 (LnTp3) were subjected to a joint experimental–theoretical analysis. X-ray diffraction experiments have been performed on CeTp3, NdTp3, SmTp3, GdTp3, and TbTp3 in the nine-fold coordination and on DyTp3, HoTp3, ErTp3, TmTp3, YbTp3, and LuTp3 in the eight-fold coordination form. Density functional theory (DFT) calculations were carried out for all 15 LnTp3 complexes. They extended the X-ray diffraction data available on the LnTp3 compounds and facilitated a straightforward interpretation of trends in the structural parameters. As a result of the joint analysis, significant steric strain in the equatorial coordination sites of the nine-coordinate structures was recognized. Trends in the bonding properties were elucidated by energy decomposition and quantum theory of atoms in molecules (QTAIM) analysis of the electron density distribution. These results revealed the major electrostatic character of the Ln…Tp bonding and fine variation of charge transfer effects across the Ln row.

Tris-{hydridotris(1-pyrazolyl)borato}actinide Complexes: Synthesis, Spectroscopy, Crystal Structure, Bonding Properties and Magnetic Behaviour.

The isostructural compounds of the trivalent actinides uranium, neptunium, plutonium, americium, and curium with the hydridotris(1‐pyrazolyl)borato (Tp) ligand An[η3‐HB(N2C3H3)3]3 (AnTp3) have been obtained through several synthetic routes. Structural, spectroscopic (absorption, infrared, laser fluorescence) and magnetic characterisation of the compounds were performed in combination with crystal field, density functional theory (DFT) and relativistic multiconfigurational calculations. The covalent bonding interactions were analysed in terms of the natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) models.

Potential Precursors for Terminal Methylidene Rare-Earth-Metal Complexes Supported by a Superbulky Tris(pyrazolyl)borato Ligand.

A series of solvent‐free heteroleptic terminal rare‐earth‐metal alkyl complexes stabilized by a superbulky tris(pyrazolyl)borato ligand with the general formula [TptBu,MeLnMeR] have been synthesized and fully characterized. Treatment of the heterobimetallic mixed methyl/tetramethylaluminate compounds [TptBu,MeLnMe(AlMe4)] (Ln=Y, Lu) with two equivalents of the mild halogenido transfer reagents SiMe3X (X=Cl, I) gave [TptBu,MeLnX2] in high yields. The addition of only one equivalent of SiMe3Cl to [TptBu,MeLuMe(AlMe4)] selectively afforded the desired mixed methyl/chloride complex [TptBu,MeLuMeCl]. Further reactivity studies of [TptBu,MeLuMeCl] with LiR or KR (R=CH2Ph, CH2SiMe3) through salt metathesis led to the monomeric mixed‐alkyl derivatives [TptBu,MeLuMe(CH2SiMe3)] and [TptBu,MeLuMe(CH2Ph)], respectively, in good yields. The SiMe4 elimination protocols were also applicable when using SiMe3X featuring more weakly coordinating moieties (here X=OTf, NTf2). X‐ray structure analyses of this diverse set of new [TptBu,MeLnMeR/X] compounds were performed to reveal any electronic and steric effects of the varying monoanionic ligands R and X, including exact cone‐angle calculations of the tridentate tris(pyrazolyl)borato ligand. Deeper insights into the reactivity of these potential precursors for terminal alkylidene rare‐earth‐metal complexes were gained through NMR spectroscopic studies.

Structural characterization and electrochemical properties of nickel (II) complexes bearing sterically bulky hydrotris(3-phenyl)- and hydrotris(3-tert-butylpyrazol-1-yl)borato ligands

Two series of pseudo-tetrahedral nickel (II) complexes bearing the bulky hydrotris(3-phenyl)- or hydrotris(3-tert-butylpyrazol-1-yl)borato ligands, TpPhNiL and TptBuNiL respectively, have been synthesized and characterized with the intent of investigating the affects of substituent size on the redox properties of the nickel center (L=Cl, Br, I, NCS, NO3). X-ray analysis reveals both Tp ligands bind in a κ3 fashion with the R groups pointing out towards the metal producing a pocket in which the 4th ligand, L, resides. The TpPh ligand results in a larger pocket and produces nickel complexes with distorted solid-state geometries, specifically bent B…Ni…L angles, unlike the corresponding TptBu complexes which show much less variation in structure. Cyclic voltammetry experiments indicate all complexes undergo a Ni2+/1+ reduction at large negative potentials vs. ferrocene with varying levels of reversibility. The NCS complexes are the most reversible and the easiest to reduce with an average reduction potential of −1.51V due to the slightly electron withdrawing nature of the thiocyanate ligand. The strong donor properties of the bidentate nitrate ligand result in complexes that are the most difficult to reduce at an average of −1.80V. Overall, the TpPhNiL complexes are easier to reduce than their corresponding TptBuNiL complexes resulting from the weakened donor ability of the TpPh ligand. While the two ligands do produce different structural motifs, the electrochemical trends are more in line with the electronic properties of the complexes than structural differences.

A computational investigation of the hydrogenation of imines catalyzed by rhodium thiolate complexes

The mechanism of imine hydrogenation catalyzed by thiolate complexes of Rh(III) bearing a hydrotris(3,5‐dimethylpyrazolyl)borato ligand has been investigated via the density functional theory calculations. The overall catalytic cycle for heterolytic cleavage of H2 and hydrogenation of N‐benzylidenemethylamine by the model catalyst [TpRh(bdt)MeCN)] is presented in detail. The results show that the reaction proceeds via an ionic mechanism through three steps: formation of dihydrogen complex, protonation of imine and the hydride transfer process. Protonation of imine occurs after the formation of Rh(H)‐S(H) moiety. For the whole catalytic cycle, the heterolytic splitting of dihydrogen is the step with the highest free energy barrier. © 2014 Wiley Periodicals, Inc.

A Family of Four‐Coordinate Iron(II) Complexes Bearing the Sterically Hindered Tris(pyrazolyl)borato Ligand TptBu,Me

A new family of 14-electron, four-coordinate iron(II) complexes of the general formula [Tp(tBu,Me)FeX] (Tp(tBu,Me) is the sterically hindered hydrotris(3-tert-butyl-5-methyl-pyrazolyl) borate ligand and X=Cl (1), Br, I) were synthesized by salt metathesis of FeX(2) with Tp(tBu,Me)K. The related fluoride complex was prepared by reaction of 1 with AgBF(4). Chloride 1 proved to be a good precursor for ligand substitution reactions, generating a series of four-coordinate iron(II) complexes with carbon, oxygen, and sulphur ligands. All of these complexes were fully characterized by conventional spectroscopic methods and most were characterized by single-crystal X-ray crystallographic analysis. Magnetic measurements for all complexes agreed with a high-spin (d(6), S=2) electronic configuration. The halide series enabled the estimation of the covalent radius of iron in these complexes as 1.24 Å.

Heterolytic H2 activation by rhodium thiolato complexes bearing the hydrotris(pyrazolyl)borato ligand and application to catalytic hydrogenation under mild conditions

Thiolato complexes of Rh(III) bearing a hydrotris(3,5-dimethylpyrazolyl)borato ligand (Tp(Me2)) have been prepared, and their reactivity toward H(2) has been investigated. The bis(thiolato) complex [Tp(Me2)Rh(SPh)(2)(MeCN)] (1) reacted with 1 atm H(2) at 20 degrees C to produce the hydrido-thiolato complex [Tp(Me2)RhH(SPh)(MeCN)] (2) and PhSH via heterolytic cleavage of H(2). This process is reversible and in equilibrium in THF and benzene. The bis(selenolato) complex [Tp(Me2)Rh(SePh)(2)(MeCN)] (4) was also converted to [Tp(Me2)RhH(SePh)(MeCN)] and PhSeH under 1 atm H(2), but the equilibrium largely shifted to 4. Reaction of the dithiolato complex [Tp(Me2)Rh(bdt)(MeCN)] (3; bdt = 1,2-C(6)H(4)S(2)) with H(2) occurred in the presence of amine, giving the anionic hydrido complex [Tp(Me2)RhH(bdt)](-) and an equimolar amount of ammonium cations. Catalytic activity for hydrogenation has been examined under 1 atm H(2) at 20-50 degrees C. While 1, 2, and 4 slowly hydrogenated styrene at similar rates at 50 degrees C, activities for the hydrogenation of N-benzylideneaniline increased in the order, 2 < 1 < 4. Complex 3 was found to be the most active and selective catalyst for hydrogenation of imines, and thus a variety of imines were reduced at 20 degrees C under 1 atm H(2), with the C=C and C=O bonds in the substrate molecules completely preserved. An ionic mechanism was involved to explain such high chemoselectivity.

Synthesis and characterization of O-methyldithiocarbonate and triphenylphosphoniodithiocarboxylate complexes containing a tris(pyrazolyl)borato (Tp) ligand

The O-methyldithiocarbonate and triphenylphosphoniodithiocarboxylate complexes having a Tp ligand (Tp = BH(pyrazol-1-yl)3) were prepared. The CS2 insertion of ruthenium chloride complex Tp(PPh3)2Ru–Cl (1) in the presence of CH3OH resulted in the O-methyldithiocarbonate complex Tp(PPh3)Ru(κ2-S2COCH3) (3) and triphenylphosphoniodithiocarboxylate complex [Tp(PPh3)Ru(κ2-S2CPPh3)]Cl (4) with the zwitterion -S2CPPh3+ as a chelating ligand depending on the reaction conditions. Attractively, this outcome contrasts sharply with similar reaction of carbon disulfide with Cp(PPh3)2Ru–Cl, no reaction is observed, even under drastic, vigorous conditions. The structures of 3 and 4 have been determined by X-ray diffraction analysis.

Synthesis and reactivity of ruthenium tetrazolate complexes containing a tris(pyrazolyl)borato (Tp) ligand

Facile ligand substitutions are observed when the neutral ruthenium cyclopropenyl complex (PPh 3)[Ru]–C C(Ph)CHCN ( 1, [Ru] = Tp(PPh 3)Ru) is treated with MeCN and pyrazole yielding the nitrile substituted ruthenium cyclopropenyl complex (MeCN)[Ru]–C C(Ph)CHCN ( 4a) and the ruthenium metallacyclic pyrazole complex (C 3H 3NN)[Ru]–C C(Ph)CH 2CN ( 7a), respectively. The reactions of Me 3SiN 3 with 1, 4a and 7a are investigated. Treatment of 1 with Me 3SiN 3 affords in high yield the cationic N-coordinated nitrile complex {(PPh 3)[Ru]NCCH(Ph)CH 2CN}N 3 ( 3). Interestingly, the reaction of 4a with Me 3SiN 3 in CH 2Cl 2 in the presence of NH 4PF 6 results in an insertion of four nitrogen atoms into the Ru–C α bond to form a diastereomeric mixture of the bright yellow zwitterionic tetrazolate complex (MeCN)[Ru]–N 4CCH(Ph)CH 2CN ( 6a) in a 3:2 ratio. The reaction of 7a with Me 3SiN 3 gives the zwitterionic tetrazolate complex (C 3H 3NNH)[Ru]–N 4CCH(Ph)CH 2CN ( 9a). The two cationic tetrazolate complexes {(C 3H 3NNH)[Ru]–N 4(R)CCH(Ph)CH 2CN} + ( 12a, R = CH 3, 12b, R = C 6H 5CH 2) are prepared by electrophilic addition of organic halides to 9a. All of the complexes are identified by spectroscopic methods as well as elemental analysis. Pathways for the synthesis of these compounds are proposed.

FLUORINATED TRIS(PYRAZOLYL)BORATES AND SILVER(I) COMPLEXES OF GROUP 14 LIGANDS

This review presents an overview of fluorinated tris(pyrazolyl)borate ligands and their role in the development of silver adducts containing group 14 ligands. Tris(pyrazolyl)borates bearing fluorocarbon substituents are sterically somewhat similar but electronically very different from their hydrocarbon counterparts. They have weakly donating nitrogen sites. Fluorinated hydridotris(pyrazolyl)borates also have less reducing B-H groups. These mono-anionic, nitrogen-based donors are ideal supporting ligands to stabilize silver complexes bearing labile donors. For example, fluorinated tris(pyrazolyl)borates have enabled the isolation of thermally stable Ag(I)-CO, Ag(I)-ethylene, and Ag(I)-acetylene adducts. Compounds with unsupported Ag(I)-Ge(II) and Ag(I)-Sn(II) bonds have also been synthesized. Most of these contain easily removable halide groups and silver atoms in the same molecule, but do not show the silver-halide metathesis. Fluorinated tris(pyrazolyl)borate ligands without the problematic B-H moiety have been reported. They afford silver-tris(pyrazolyl) borates with higher solution stability. The κ3-coordination mode is the most common for tris(pyrazolyl)borates but κ2-bonded tris(pyrazolyl)borate silver adducts are also known. Some silver adducts of fluorinated tris(pyrazolyl)borates are excellent tris(pyrazolyl)borato ligand transfer agents, promising homogeneous catalysts and effective antimicrobial agents.

Synthesis and structural characterization of sterically crowded hydridotris(pyrazolyl)borato complexes: Unusual double 1,2-borotropic shift at a titanium centre

The potassium and thallium(I) derivatives of the hydrido-tris(3-Me 2Bz,5-Me-pyrazol-1-yl)borato ligand, K[Tp Me2 Bz,Me] ( 1) and Tl[Tp Me2 Bz,Me] ( 2), are reported. Their reactions with TiCl 4 under mild conditions afforded, after rearrangement of the ligand, recognized as a double 1,2-borotropic shift, the related Ti(IV) complex {hydrido-[bis(3-Me,5-Me 2Bz)(3-Me 2Bz,5-Me)-pyrazol-1-yl]borato}trichlorotitanium(IV), [Tp Me2 Bz,Me∗∗] TiCl 3 ( 3). The 1H- and 13C NMR spectra of the new compounds are discussed, the molecular structure of 3 has been determined by X-ray diffraction methods, the titanium centre has a pseudo-octahedral coordination, with the nitrogen and chloride ligands in a fac geometry. A possible mechanism of formation of 3 is proposed.

Effects of Tris(pyrazolyl)borato Ligand Substituents on Dioxygen Activation and Stabilization by Copper Compounds

Dinuclear [Cu2(mu-O)2(Tp(R,R')2] complexes, analogues of the active site of oxyhemocyanin, are theoretically studied, and the effect of the substituents of the tris(pyrazolyl)borate ligands, Tp(R,R'), is analyzed. Density functional theory calculations reveal that the type of bridging oxygen, peroxo, or bisoxo is strongly influenced by the nature and position of the R substituents because of variable substituent...bridging oxygen interactions, as well as electronic effects. The electronic effects of ligands at the 5 position are not significant, but peroxo complexes are favored by electron-withdrawing groups at the 3 position while bisoxo ones are strongly sterically disfavored.

Comparative Studies with Zwitterionic Platinum(II) Bis(pyrazolyl)borate and 2,2‘-Bipyridylborate Complexes

A comparison between the mononuclear platinum complexes of three structurally different monoanionic borato ligands is presented: [Ph_2B(pyrazolyl)_2]- ([Ph_2B(pz)_2], 1), [4-Ph_3B(2,2‘-bipyridine)]- ([(4-BPh_3)bpy], 2), and [Ph_2B(CH_2PPh_2)_2]- ([Ph_2BP_2], 3). The new bipyridylborate ligand 2 is introduced in this study. The relative trans influence of these ligands has been assessed by comparison of the structural and spectroscopic (NMR) data of the platinum dimethyl complexes [[Ph_2B(pz)_2]Pt(Me)_2][NBu_4] (4), [[(4-BPh_3)bpy]Pt(Me)_2][NBu_4] (5), and [[Ph_2BP_2]Pt(Me)_2][ASN] (6). The neutral complexes [Ph_2B(pz)_2]Pt(Me)(NCCH_3) (7), [Ph_2B(pz)_2]Pt(Me)(CO) (8), [Ph_2B(pz)_2]Pt(Me)(P(C_6F_5)_3) (9), [(4-BPh_3)bpy]Pt(Me)(NCCH_3) (10), [(4-BPh_3)bpy]Pt(Me)(CO) (11), and [(bpy)Pt(Me)(CO)][BPh_4] (12) were prepared, and the carbonyl complexes 8, 11, and 12 provide information pertaining to the relative electron-releasing character of each ligand type. The CO stretching frequencies suggest that the charged borate moiety renders the borato ligands more electron-donating than their neutral analogues. Of the neutral platinum methyl solvento complexes supported by ligands 1, 2, and 3, only those of 1 display very different C−H activation propensities. Upon protonation or methide abstraction in benzene at room temperature, complex 4 rapidly activates two molecules of benzene to generate [[Ph_2B(pz)_2]Pt(Ph)_2][NBu_4] (13). Isotopic scrambling of deuterium into methane in C_6D_6 solvent suggests the intermediacy of a methane σ-adduct in this reaction. The double C−H activation reaction can be halted by addition of acetonitrile to trap the intermediate [Ph_2B(pz)_2]Pt(Ph)(NCCH_3) (14). Complex 3 also displays reactivity toward the benzylic C−H bonds of mesitylene at room temperature to form [Ph_2B(pz)_2]Pt(pzH)(CH_2C_6H_3(CH_3)_2) (15) in modest yield.

Elucidation of a low spin cobalt(II) system in a distorted tetrahedral geometry.

We have prepared a series of divalent cobalt(II) complexes supported by the [PhBP(3)] ligand ([PhBP(3)] = [PhB(CH(2)PPh(2))(3)](-)) to probe certain structural and electronic phenomena that arise from this strong field, anionic tris(phosphine) donor ligand. The solid-state structure of the complex [PhBP(3)]CoI (1), accompanied by SQUID, EPR, and optical data, indicates that it is a pseudotetrahedral cobalt(II) species with a doublet ground state-the first of its type. To our knowledge, all previous examples of 4-coordinate cobalt(II) complexes with doublet ground states have adopted square planar structure types. Complex 1 provided a useful precursor to the corresponding bromide and chloride complexes, ([PhBP(3)]Co(mu-Br))(2), (2), and ([PhBP(3)]Co(mu-Cl))(2), (3). These complexes were similarly characterized and shown to be dimeric in the solid-state. In solution, however, the monomeric low spin form of 2 and 3 dominates at 25 degrees C. There is spectroscopic evidence for a temperature-dependent monomer/dimer equilibrium in solution for complex 3. Furthermore, the dimers 2 and 3 did not display appreciable antiferromagnetic coupling that is typical of halide and oxo-bridged copper(II) and cobalt(II) dimers. Rather, the EPR and SQUID data for solid samples of 2 and 3 suggest that they have triplet ground states. Complexes 1, 2, and 3 are extremely oxygen sensitive. Thus, stoichiometric oxidation of 1 by dioxygen produced the 4-coordinate, high spin complex [PhB(CH(2)P(O)Ph(2))(2)(CH(2)PPh(2))]CoI, (4), in which the [PhBP(3)] ligand had undergone a 4-electron oxidation. Reaction of 1 with TlOAr (Ar = 2,6-Me(2)Ph) afforded an example of a 4-coordinate, high spin complex, [PhBP(3)]Co(O-2,6-Me(2)Ph) (5), with an intact [PhBP(3)] ligand. The latter two complexes were spectroscopically and structurally characterized for comparison to complexes 1, 2, and 3. Our data for these complexes collectively suggest that the [PhBP(3)] ligand provides an unusually strong ligand-field to these divalent cobalt complexes that is chemically distinct from typical tris(phosphine) donor ligand sets, and distinct from tridentate borato ligands that have been previously studied. Coupling this strong ligand-field with a pronounced axial distortion away from tetrahedral symmetry, a geometric consequence that is enforced by the [PhBP(3)] ligand, provides access to monomeric [PhBP(3)]CoX complexes with doublet rather than quartet ground states.

Inorganic Chemistry Based on Tp Ligands —From Dioxygen Complexes to Organometallic Systems—

Abstract Our recent research on transition metal complexes containing hydrotris(pyrazolyl)borato ligands (TpR), which ranges from bioinorganic chemistry of dioxygen complexes to organometallic systems, is reviewed. The TpR ligand turns out to be versatile in a wide variety of inorganic studies, because the coordination properties (both steric and electronic) can be finely tuned in a systematic manner by choosing appropriate substituents on the pyrazolyl rings to serve the purpose of the study (e.g. stabilization, activation, functionalization). For first row transition metal complexes, TpR serves as a tetrahedral enforcer to form a coordinatively unsaturated tetrahedral species, which is interconverted with five- and six-coordinate structures via coordination/dissociation of donor(s). In addition to the traditional view of TpR as a ligand system isoelectronic with cyclopentadienyls (η5-C5R5), the TpR ligand is now recognized as a unique ancillary ligand suitable for bioinorganic studies, because the tripodal ligand can mimic the coordination environment created by three imidazolyl groups from histidine residues, which is frequently found in the active sites of metalloenzymes. Through extension of the metal in TpRM-O2 adducts to those not related to biological systems we have unveiled the following new aspects of the chemistry of transition metal dioxygen complexes: (1) formation of higher valent bis(μ-oxo) species, TpRM(μ-O)2MTpR (M = Co, Ni), via O–O cleavage of TpRM(μ-η2 : η2-O2)MTpR intermediates and their relevance to the active intermediate of methane monooxygenase, (2) formation and full characterization of a variety of peroxo, hydroperoxo (Pd, Rh) and alkylperoxo species (Mn, Co, Ni, Pd), (3) structural evidence for conversion of molecular oxygen into hydroperoxide via protonation of the η2-peroxo intermediate (Rh), and (4) formation of an active species which undergoes oxidative C–C cleavage reaction (Ru). The property of the TpR ligand as a tetrahedral enforcer is best demonstrated in organometallic systems. The hydrocarbyl complexes, TpRM-R′ (M= Fe, Co), are stable with respect to thermal decomposition processes involving β-hydrogen elimination despite their highly coordinatively unsaturated electronic structure [Fe(14e), Co(15e)], when they are kept under inert atmosphere. The stability has been ascribed to a high spin configuration caused by the tetrahedral geometry. All frontier orbitals are occupied by unpaired electrons or electron pairs and no vacant frontier orbital is left for interaction with the electron pairs of a donor. Dinuclear xenophilic complexes, TpRM–M′Ln, with a polar metal–metal bond which bridges a Werner complex type hard open-shell metal center and a coordinatively saturated metal carbonyl fragment are also synthesized and fully characterized.

Synthesis and Characterization of Coordinatively Unsaturated Alkynyl- and Aryl-Cobalt Complexes with 15 Valence Electrons, TpiPr2Co−R, Bearing the Hydrotris(3,5-diisopropylpyrazolyl)borato Ligand (TpiPr2)

Coordinatively unsaturated 15e alkynyl- (TpiPr2Co−C⋮C−R) and aryl-cobalt complexes (TpiPr2Co-aryl) bearing the hydrotris(3,5-diisopropylpyrazolyl)borato ligand (TpiPr2) are prepared by dehydrative condensation of the hydroxo complex [TpiPr2Co(μ-OH)2]2 with 1-alkyne and arylation of the chloro complex TpiPr2Co−Cl with Grignard reagents, respectively. Spectroscopic and crystallographic analyses reveal the apparent C3-symmetrical tetrahedral structures with high-spin electronic configuration (S = 3/2), which should result from the property of the TpiPr2 ligand as a tetrahedral enforcer. The TpiPr2Co and hydrocarbyl fragments are connected dominantly through σ-bonding interaction, and π-interaction including back-donation is not significant as revealed by EHMO calculations. The Co−C bonds are so polarized as to be readily protonated even by moisture to give the corresponding hydrocarbons, but the reactivity toward unsaturated hydrocarbons turns out to be sluggish. TpiPr2Co−C⋮C−COOMe is found to catalyze a rar...

Nickel complexes of bidentate [S2] and [SN] borato ligands.

Nickel(II) complexes of the monoanionic borato ligands [Ph2B(CH2SCH3)2] (abbreviated Ph2Bt), [Ph2B(CH2S(t)Bu)2] (Ph2Bt(tBu)), [Ph2B(1-pyrazolyl)(CH2SCH3)], and [Ph2B(1-pyrazolyl)(CH2S(t)Bu)] have been prepared and characterized. While [Ph2Bt] formed the square planar homoleptic complex, [Ph2Bt]2Ni, the larger [S2] ligand with tert-butyl substituents, [Ph2BttBu], yielded an unexpected organometallic derivative, [Ph2Bt(tBu)]Ni(eta2-CH2SBut), resulting from B-C bond rupture. The analogous thiametallacycle derived from the [S3] ligand, [PhB(CH2S(t)Bu)3] (PhTt(tBu)), has been structurally authenticated (Schebler, P. J.; Mandimutsira, B. S.; Riordan, C. G.; Liable-Sands, L.; Incarvito, C. D.; Rheingold, A. L. J. Am. Chem. Soc. 2001, 123, 331). The [SN] borato ligands formed exclusively the cis stereoisomers upon reaction with Ni(II) sources, [Ph2B(1-pyrazolyl)(CH2SR)]2Ni. Analysis of the Ni(II/I) reduction potentials by cyclic voltammetry revealed a approximately 600 mV anodic shift upon replacement of two thioether donors ([Ph2Bt]2Ni) with two pyrazolyl donors ([Ph2B(1-pyrazolyl)(CH2SCH3)]2Ni) consistent with the all thioether environment stabilizing the lower oxidation state of nickel.

N/O- and C-Bound (Enolato)palladium Complexes with Hydrotris(pyrazolyl)borato Ligands (TpR: R = iPr2, Me2) Obtained via Dehydrative Condensation between the Hydroxo Complexes TpRPd(Py)OH and Active Methylene Compounds: Factors Determining the Isomer Distribution and Dimerization of Cyano Compounds

Reaction of a hydroxopalladium complex bearing the TpiPr2 ligand, (TpiPr2)(py)Pd−OH (1iPr2), with active methylene compounds, X−CH2−Y 2 [dicyanomethane (2a), methyl cyanoacetate (2b), benzoylaceton...

Structural diversity in a family of copper(I) thioether complexes.

Copper(I) complexes of the tridentate thioether ligands [PhB(CH(2)SCH(3))(3)] (abbreviated PhTt), [PhB(CH(2)SPh)(3)] (PhTt(Ph)), [PhB(CH(2)S(t)()Bu)(3)] (PhTt(t)()(Bu)), and [PhB(CH(2)S(p)()Tol)(3)] (PhTt(p)()(Tol)) and bidentate thioether ligands [Ph(2)B(CH(2)SCH(3))(2)] (Ph(2)Bt), [Et(2)B(CH(2)SCH(3))(2)] (Et(2)Bt), and [Ph(2)B(CH(2)SPh)(2)] (Ph(2)Bt(Ph)) have been prepared and characterized. The solution and solid state structures are highly sensitive to the identity of the borato ligand employed. Ligands possessing the smaller (methylthio)methyl donors, [PhTt] and [Ph(2)Bt], yielded tetrameric species, [(PhTt)Cu](4) and [(Ph(2)Bt)Cu](4), containing both terminal and bridging thioether ligation. The ligands containing the larger (arylthio)methyl groups, [PhTt(Ph)] and [PhTt(p)()(Tol)], form monomeric [PhTt(Ar)]Cu(NCCH(3)) in solution and one-dimensional extended structures in the solid state. Each complex type reacted cleanly with acetonitrile, pyridine, or triphenylphosphine generating the corresponding four-coordinate monomer, of which [PhTt(Ph)]Cu(PPh(3)), [PhTt(p)()(Tol)]Cu(PPh(3)), and [Et(2)Bt]Cu(PPh(3))(2) have been structurally characterized.