Naked (C5Me5)2M cations (M = Sc, Ti, and V) and their fluoroarene complexes

The ionic metallocene complexes [Cp*(2)M][BPh(4)] (Cp* = C(5)Me(5)) of the trivalent 3d metals Sc, Ti, and V were synthesized and structurally characterized. For M = Sc, the anion interacts weakly with the metal center through one of the phenyl groups, but for M = Ti and V, the cations are naked. They each contain one strongly distorted Cp* ligand, with one (V) or two (Ti) agostic C-H...M interactions involving the Cp*Me groups. For Sc and Ti, these Lewis acidic species react with fluorobenzene and 1,2-difluorobenzene to yield [Cp*(2)M(kappaF-FC(6)H(5))(n)][BPh(4)] (M = Sc, n = 2; M = Ti, n = 1) and [Cp*(2)M(kappa(2)F-1,2-F(2)C(6)H(4))][BPh(4)], the first examples of kappaF-fluorobenzene and kappa(2)F-1,2-difluorobenzene adducts of transition metals. With the perfluorinated anion [B(C(6)F(5))(4)](-), both Sc and Ti form [Cp*(2)M(kappa(2)F-C(6)F(5))B(C(6)F(5))(3)] contact ion pairs. The nature of the metal-fluoroarene interaction was studied by density functional theory (DFT) calculations and by comparison with the corresponding tetrahydrofuran (THF) adducts and was found to be predominantly electrostatic for all metals studied.     

Novel H2 activation by a tris[3,5-bis(trifluoromethyl)phenyl]borane frustrated Lewis pair

Tris[3,5-bis(trifluoromethyl)phenyl]borane (1, BArF(18)), has been synthesised on a practical scale for the first time. According to the Gutmann-Beckett method it is a more powerful Lewis acid than B(C(6)F(5))(3). It forms a 'frustrated Lewis pair' with 2,2,6,6-tetramethylpiperidine which cleaves H(2) to form a salt containing the novel anion [μ-H(BArF(18))(2)](-).     

Frustrated Lewis pairs beyond the main group: cationic zirconocene-phosphinoaryloxide complexes and their application in catalytic dehydrogenation of amine boranes

The cationic zirconocene-phosphinoaryloxide complexes [Cp(2)ZrOC(6)H(4)P(t-Bu)(2)][B(C(6)F(5))(4)] (3) and [Cp*(2)ZrOC(6)H(4)P(t-Bu)(2)][B(C(6)F(5))(4)] (4) were synthesized by the reaction of Cp(2)ZrMe(2) or Cp*(2)ZrMe(2) with 2-(diphenylphosphino)phenol followed by protonation with [2,6-di-tert-butylpyridinium][B(C(6)F(5))(4)]. Compound 3 exhibits a Zr-P bond, whereas the bulkier Cp* derivative 4 was isolated as a chlorobenzene adduct without this Zr-P interaction. These compounds can be described as transition-metal-containing versions of linked frustrated Lewis pairs (FLPs), and treatment of 4 with H(2) under mild conditions cleaved H(2) in a fashion analogous to that for main-group FLPs. Their reactivity in amine borane dehydrogenation also mimics that of main-group FLPs, and they dehydrogenate a range of amine borane adducts. However, in contrast to main-group FLPs, 3 and 4 achieve this transformation in a catalytic rather than stoichiometric sense, with rates superior to those for previous high-valent catalysts.     

Heterolytic activation of hydrogen using frustrated Lewis pairs containing tris(2,2',2'-perfluorobiphenyl)borane

The extremely sterically hindered borane tris(2,2',2'-perfluorobiphenyl)borane (PBB) has been structurally characterised. In combination with bulky nitrogen bases, it forms the 'frustrated Lewis pairs' (FLPs) PBB/2,2,6,6-tetramethylpiperidine (TMP) (1), PBB/1,4-diazobicyclo[2.2.2]-octane (DABCO) (2) and PBB/2,6-lutidine (lut) (3). These novel, unquenched acid-base pairs have been shown to effect facile room temperature heterolytic cleavage of dihydrogen to form the ammonium borate salts [2,2,6,6-Me(4)C(5)H(6)NH(2)][HB(C(12)F(9))(3)] (4) and [N(C(2)H(4))(3)NH][HB(C(12)F(9))(3)] (5), and lutidinium borate [2,6-Me(2)C(5)H(3)NH][HB(C(12)F(9))(3)] (6). Although these reactions are equilibria, the reverse reaction and release of hydrogen gas was not apparent at temperatures up to 120 °C. The relative Lewis acidity of PBB has been determined using the Gutmann-Beckett method.     

Synthesis and structure of amido- and imido(pentafluorophenyl)borane zirconocene and hafnocene complexes: N-H and B-H activation

Treatment of Me(2)S·B(C(6)F(5))(n) H(3-n) (n=1 or 2) with ammonia yields the corresponding adducts. H(3)N·B(C(6)F(5))H(2) dimerises in the solid state through N-H···H-B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH(2)B(C(6)F(5))(n)H(3-n)]. Reaction of the n=2 reagent with [Cp(2)ZrCl(2)] leads to disubstitution, but [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)] is in equilibrium with the product of β-hydride elimination [Cp(2)Zr(H){NH(2)B(C(6)F(5))(2)H}], which proves to be the major isolated solid. The analogous reaction with [Cp(2)HfCl(2)] gives a mixture of [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)] and the N-H activation product [Cp(2)Hf{NHB(C(6)F(5 )(2)H}]. [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)]·PhMe and [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]·4(thf) exhibit β-B-agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]?PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp(2)Hf{NHB(C(6)F(5))(2)H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond-length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp(2)MMe(μ-Me)B(C(6)F(5))(3)] (M=Zr, Hf) with Li[NH(2)B(C(6)F(5))(n)H(3-n)] (n=2) results in [Cp(2) MMe{NH(2)B(C(6)F(5))(2)H}] complexes, for which the spectroscopic data, particularly (1)J(B,H), again suggest β-B-agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp'(2)ZrMe(μ-Me)B(C(6)F(5))(3)] precursor (Cp'=1,3-C(5)H(3)(SiMe(3))(2) , n=1 or 2) to give [Cp'(2)ZrMe{NH(2)B(C(6)F(5))(n)H(3-n)}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp'(2)HfMe(2)] and the formation of Li[HB(C(6)F(5))(3)] through hydride abstraction.     

(N-pyrrolyl)B(C6F5)2--a new organometallic Lewis acid for the generation of group 4 metallocene cation complexes

Treatment of the (C6F5)2BF x OEt2 (3) complex with N-pyrrolyl lithium gives bis(pentafluorophenyl)(N-pyrrolyl)borane (2), a strong organometallic Lewis acid, which was characterized by X-ray diffraction (B-N bond length: 1.401(5) A). It exhibits a columnar superstructure in the crystal and contains pi-stacks of pyrrolyl units. Compound 2 readily abstracts alkyl anions from a variety of alkyl Group 4 metallocene-type complexes and leads to the clean formation of the respective metallocene ions or ion pairs. For example, the treatment of Cp3ZrCH3 (9) with 2 transfers a methyl anion to yield the ion pair [Cp3Zr]+[(C4H4N)B(CH3)(C6F5)2]- (12). The X-ray crystal structure analysis of 12 shows a close contact between zirconium and the pyrrolyl-beta-carbon (2.641(2) A). The borane 2 adds to (butadiene)zirconocene (13) to yield the betaine system [Cp2Zr]+[(C4H6)B- (NC4H4)(C6F)2]- (15). Complex 15 contains a distorted eta3-allyl moiety inside the metallacyclic framework and it features an internal Zr+...(pyrrolyl)B- ion pair interaction with a Zr...pyrrolyl-alphacarbon separation of 2.723(3) A (determined by X-ray diffraction). From the dynamic NMR spectra of 15 the bond strength of the internal ion pair interaction was estimated to be deltaGdiss (223 K) approximately = to15 kcalmol(-1). Treatment of dimethylzirconocene (16) with 2 yields the metallocene borate salt [Cp2ZrCH3]+[(C4H4N)B(CH3)(C6F5)2]- (17), which is an active catalyst for the polymerization of ethene.     

Intra- and intermolecular N-H...F-C hydrogen-bonding interactions in amine adducts of tris(pentafluorophenyl)borane and -alane

The reaction between B(C(6)F(5))(3) and NH(3)(g) in light petroleum yielded the solvated adduct H(3)N.B(C(6)F(5))(3).NH(3). Treatment with a second equivalent of B(C(6)F(5))(3) afforded H(3)N.B(C(6)F(5))(3). Attempts to prepare the analogous alane adduct were unsuccessful and resulted in protolysis. Related compounds of the form R'R' 'N(H).M(C(6)F(5))(3) were synthesized from M(C(6)F(5))(3) and the corresponding primary and secondary amines (M = B, Al; R' = H, Me, CH(2)Ph; R' ' = Me, CH(2)Ph, CH(Me)(Ph); R'R' ' = cyclo-C(5)H(10)). The solid-state structures of 13 new compounds have been elucidated by single-crystal X-ray diffraction and are discussed. Each of the borane adducts has a significant bifurcated intramolecular hydrogen bond between an amino hydrogen and two o-fluorines, while N-H...F-C interactions in the alane adducts are weaker and more variable. (19)F NMR studies demonstrate that the borane adducts retain the bifurcated C-F...H...F-C hydrogen bond in solution. Compounds of the type R'R' 'N(H).M(C(6)F(5))(3) conform to Etter's rules for the prediction of hydrogen-bonding interactions.     

New cationic and zwitterionic Cp*M(kappa2-P,S) complexes (M = Rh, Ir): divergent reactivity pathways arising from alternative modes of ancillary ligand participation in substrate activation

Treatment of 0.5 equiv of [Cp*IrCl(2)](2) with 1/3-P(i)Pr(2)-2-S(t)Bu-indene afforded Cp*Ir(Cl)(kappa(2)-3-P(i)Pr(2)-2-S-indene) (1) in 95% yield (Cp* = eta(5)-C(5)Me(5)). Addition of AgOTf or LiB(C(6)F(5))(4) x 2.5 OEt(2) to 1 gave [Cp*Ir(kappa(2)-3-P(i)Pr(2)-2-S-indene)](+)X(-) ([2](+)X(-); X = OTf, 78%; X = B(C(6)F(5))(4), 82%), which represent the first examples of isolable coordinatively unsaturated [Cp'Ir(kappa(2)-P,S)](+)X(-) complexes. Exposure of [2](+)OTf(-) to CO afforded [2 x CO](+)OTf(-) in 91% yield, while treatment of [2](+)B(C(6)F(5))(4)(-) with PMe(3) generated [2 x PMe(3)](+)B(C(6)F(5))(4)(-) in 94% yield. Treatment of 1 with K(2)CO(3) in CH(3)CN allowed for the isolation of the unusual adduct 3 x CH(3)CN (41% isolated yield), in which the CH(3)CN bridges the Lewis acidic Cp*Ir and Lewis basic indenide fragments of the targeted coordinatively unsaturated zwitterion Cp*Ir(kappa(2)-3-P(i)Pr(2)-2-S-indenide) (3). In contrast to the formation of [2 x CO](+)OTf(-), exposure of 3 x CH(3)CN to CO did not afford 3 x CO; instead, a clean 1:1 mixture of (kappa(2)-3-P(i)Pr(2)-2-S-indene)Ir(CO)(2) (4) and 1,2,3,4-tetramethylfulvene was generated. Treatment of [2](+)OTf(-) with Ph(2)SiH(2) resulted in the net loss of Ph(2)Si(OTf)H to give Cp*Ir(H)(kappa(2)-3-P(i)Pr(2)-2-S-indene) (5) in 44% yield. In contrast, treatment of [2](+)B(C(6)F(5))(4)(-) with Ph(2)SiH(2) or PhSiH(3) proceeded via H-Si addition across Ir-S to give the corresponding [Cp*Ir(H)(kappa(2)-3-P(i)Pr(2)-2-S(SiHPhX)-indene)](+)B(C(6)F(5))(4)(-) complexes 6a (X = Ph, 68%) or 6b (X = H, 77%), which feature a newly established S-Si linkage. Compound 6a was observed to effect net C-O bond cleavage in diethyl ether with net loss of Ph(2)Si(OEt)H, affording [Cp*Ir(H)(kappa(2)-3-P(i)Pr(2)-2-SEt-indene)](+)B(C(6)F(5))(4)(-) (7) in 77% yield. Furthermore, 6a proved capable of transferring Ph(2)SiH(2) to acetophenone, with concomitant regeneration of [2](+)B(C(6)F(5))(4)(-); however, [2](+)X(-) did not prove to be effective ketone hydrosilylation catalysts. Treatment of 1/3-P(i)Pr(2)-2-S(t)Bu-indene with 0.5 equiv of [Cp*RhCl(2)](2) gave Cp*Rh(Cl)(kappa(2)-3-P(i)Pr(2)-2-S-indene) (8) in 94% yield. Combination of 8 and LiB(C(6)F(5))(4) x 2.5 Et(2)O produced the coordinatively unsaturated cation [Cp*Rh(kappa(2)-3-P(i)Pr(2)-2-S-indene)](+)B(C(6)F(5))(4)(-) ([9](+)B(C(6)F(5))(4)(-)), which was transformed into [Cp*Rh(H)(kappa(2)-3-P(i)Pr(2)-2-S(SiHPh(2))-indene)](+)B(C(6)F(5))(4)(-) (10) via net H-Si addition of Ph(2)SiH(2) to Rh-S. Unlike [2](+)X(-), complex [9](+)B(C(6)F(5))(4)(-) was shown to be an effective catalyst for ketone hydrosilylation. Treatment of 3 x CH(3)CN with Ph(2)SiH(2) resulted in the loss of CH(3)CN, along with the formation of Cp*Ir(H)(kappa(2)-3-P(i)Pr(2)-2-S-(1-diphenylsilylindene)) (11) (64% isolated yield) as a mixture of diastereomers. The formation of 11 corresponds to heterolytic H-Si bond activation, involving net addition of H(-) and Ph(2)HSi(+) fragments to Ir and indenide in the unobserved zwitterion 3. Crystallographic data are provided for 1, [2 x CO](+)OTf(-), 3 x CH(3)CN, 7, and 11. Collectively, these results demonstrate the versatility of donor-functionalized indene ancillary ligands in allowing for the selection of divergent metal-ligand cooperativity pathways (simply by ancillary ligand deprotonation) in the activation of small molecule substrates.     

Transition metal complexes of the chelating phosphine borane ligand Ph2PCH2Ph2P.BH3

Chromium and ruthenium complexes of the chelating phosphine borane H(3)B.dppm are reported. Addition of H(3)B.dppm to [Cr(CO)(4)(nbd)](nbd = norbornadiene) affords [Cr(CO)(4)(eta1-H(3)B.dppm)] in which the borane is linked to the metal through a single B-H-Cr interaction. Addition of H(3)B.dppm to [CpRu(PR(3))(NCMe)(2)](+)(Cp =eta5)-C(5)H(5)) results in [CpRu(PR(3))(eta1-H(3)B.dppm)][PF(6)](R = Me, OMe) which also show a single B-H-Ru interaction. Reaction with [CpRu(NCMe)(3)](+) only resulted in a mixture of products. In contrast, with [Cp*Ru(NCMe)(3)](+)(Cp*=eta5)-C(5)Me(5)) a single product is isolated in high yield: [Cp*Ru(eta2-H(3)B.dppm)][PF(6)]. This complex shows two B-H-Ru interactions. Reaction with L = PMe(3) or CO breaks one of these and the complexes [Cp*Ru(L)(eta1-H(3)B.dppm)][PF(6)] are formed in good yield. With L = MeCN an equilibrium is established between [Cp*Ru(eta2-H(3)B.dppm)][PF(6)] and the acetonitrile adduct. [Cp*Ru (eta2-H(3)B.dppm)][PF(6)] can be considered as being "operationally unsaturated", effectively acting as a source of 16-electron [Cp*Ru (eta1-H(3)B.dppm)][PF(6)]. All the new compounds (apart from the CO and MeCN adducts) have been characterised by X-ray crystallography. The solid-state structure of H(3)B.dppm is also reported.     

Alkyne and alkene complexes of a d(0) zirconocene aryl cation

The generation and properties of nonchelated Zr-aryl-alkyne and Zr-aryl-alkene complexes that are stabilized by the presence of beta-Si-substituents in the alkyne and alkene ligands and fluorination of the aryl ligand are described. Reaction of [Cp'2Zr(OtBu)(ClCD2Cl)][B(C6F5)4] (1, Cp' = C5H4Me) with alkyne and alkene substrates (L) generates Cp'2Zr(OtBu)(L)+ adducts (L = HCCCH2SiMe3 (2); H2C=CHCH2SiMe3 (3); HCCMe (4); H2C=CHCH2CMe3 (5)). Equilibrium constants for substrate binding (Keq = [Zr-L][1]-1[L]-1; CD2Cl2, -89 degrees C) are much larger for the beta-Si-substituted compounds 2 (1.0(2) x 105 M-1) and 3 (1.7(4) x 103 M-1) than for hydrocarbon analogues 4 (3.6(7) x 102 M-1) and 5 (1.9(1) M-1), which is ascribed to beta-Si stabilization of the partial positive charge on Cint of the bound substrate. [Cp2Zr(C6F5)][B(C6F5)4] (7, Cp = C5H5) was generated by the reaction of Cp2Zr(C6F5)Me with [Ph3C][B(C6F5)4] in C6D5Cl. Reaction of 7 with alkyne and alkene substrates (L) generates Cp2Zr(C6F5)(L)+ adducts (L = HCCCH2SiMe3 (8); H2C=CHCH2SiMe3 (10)). No insertion of the substrate into the Zr-C6F5 bond is observed in 8 (at -38 degrees C) or 10 (up to 22 degrees C). The allyltrimethylsilane ligand in 10 undergoes nondissociative alkene face exchange ("alkene flipping", i.e., exchange of the Cp2Zr(C6F5)+ unit between the two alkene enantiofaces without alkene dissociation), with a first-order rate constant kflip = 23(1) s-1 (C6D5Cl, -38 degrees C). 10 also undergoes slower reversible decomplexation of the alkene (kdissoc = 5.0(8) s-1; C6D5Cl, -38 degrees C).     

Mononuclear and polynuclear copper(I) complexes with a new N,N',S-donor ligand and with structural analogies to the copper thionein core

The N,N',S-donor ligand 4-methoxy-3,5-dimethyl-2-((3-(2-(methylthio)phenyl)-1H-pyrazol-1-yl)methyl)pyridine (L) was prepared from 2-(chloromethyl)-4-methoxy-3,5-dimethylpyridine hydrochloride and 3-(2-(methylthio)phenyl)-1H-pyrazole. The Cu(I) complexes [Cu2(L)2CH3CN][Cu(L)CH3CN](BF4)3 (1), [Cu(L)PPh3]BF4 (2), and [Cu6(L)2(C6F5S)6] (3) were prepared and characterized by X-ray crystallography (PPh3=triphenylphosphine, C6F5S-=pentafluorothiophenolate). The unit cell of compound 1 consists of cocrystallized mononuclear and dinuclear entities in which all of the copper atoms exhibit distorted tetrahedral coordination. Compound 2 is monomeric with L bound in the kappa3-N,N',S mode and a PPh3 molecule that completes the coordination environment. Compound 2 presents a fluxional behavior in CDCl3 solution due to the boat inversion of the six-membered N,N' chelate ring (DeltaH=+43.6(3) kJ mol(-1), DeltaS=-16(1) J mol(-1) K(-1)). Crystallization of 3 in acetonitrile leads to a polynuclear structure that contains a CH3CN molecule coordinated to one of the copper atoms: [Cu6(L)2(C6F5S)6CH3CN] (3a). The core of 3a partially resembles a {Cu4S6} adamantane-like moiety, the only difference being that the Cu-NCCH3 interaction leads to the opening of the cluster by disrupting a Cu-Cu interaction. Part of this assembly is found in the yeast metallothionein copper(I)-cysteinate core whose crystal structure has recently been reported. Two additional [Cu(L)]+ peripheral moieties interact with the cluster by means of bridging thiolates. ESI-mass spectrometry, conductivity measurements, and 1H/19F pulsed gradient spin echo (PGSE) NMR experiments suggest that 3a dissociates in acetonitrile solution: 3a+CH3CN-->[Cu4(C6F5S)6]2-+2[Cu(L)CH3CN]+. The stability of the cluster with respect to the hypothetical mononuclear species, [Cu(L)(C6F5S)], is confirmed by DFT calculations (B3LYP), which illustrate the exergonic character of the reaction: 6[Cu(L')(C6H5S)]-->[Cu6(L')2(C6H5S)6]+4L' (DeltaG298=-58.6 kJ mol(-1), where L' and C6H5S- are simplified models for L and C6F5S-, respectively). The energetics pertinent to the ionic dissociation of the cluster in acetonitrile is computed using the polarizable continuum model (PCM) approach.     

2,6-吡啶二亚胺基锰(Ⅲ)配合物的合成、晶体结构及催化性能

由三齿含氮配体2,6-二[1-(2,6-二甲基苯基亚胺)乙基]吡啶(L1)、2,6-二[1-(2,6-二乙基苯基亚胺)乙基]吡啶(L2)和2,6-二[1-(2,4,6-三甲基苯基亚胺)乙基]吡啶(L3)分别与MnCl2·4H2O在乙腈中反应,合成了3个新的具有较大空间位阻的2,6-吡啶二亚胺基氯化锰配合物L1Mn(Ⅱ)...     

Reduction of Dioxygen by Radical/B(p‐C6F4X)3 Pairs to Give Isolable Bis(borane)superoxide Compounds

Triplet dioxygen was reduced by TEMPO or trityl radicals in the presence of two molar equivalents of the strong B(p ‐C₆F₄X)₃ (X: F or H) boron Lewis acids under mild conditions to give the bis(borane)superoxide systems 2 . The sensitive radical anion species were isolated and characterized by methods including X‐ray crystal structure analysis and EPR spectroscopy.     

Systematic studies of early actinide complexes: uranium(IV) fluoroketimides

The reaction of (C5Me5)2U(CH3)2 with 2 equiv of N[triple bond]C-ArF gives the fluorinated uranium(IV) bis(ketimide) complexes (C5Me5)2U[-N=C(CH3)(ArF)]2 [where ArF=2-F-C6H4 (4), 3-F-C6H4 (5), 4-F-C6H4 (6), 2,6-F2-C6H3 (7), 3,5-F2-C6H3 (8), 2,4,6-F3-C6H2 (9), 3,4,5-F3-C6H2 (10), and C6F5 (11)]. These have been characterized by single-crystal X-ray diffraction, 1H and 19F NMR, cyclic voltammetry, UV-visible-near-IR absorption spectroscopy, and variable-temperature magnetic susceptibility. Density functional theory (DFT) results are reported for complexes 6 and 11 for comparison with experimental data. The most significant structural perturbation imparted by the F substitution in these complexes is a rotation of the fluorinated aryl (ArF) group out of the plane defined by the N=C(CMe)(Cipso) fragment in complexes 7, 9, and 11 when the ArF group possesses two o-fluorine atoms. Excellent agreement is obtained between the DFT-calculated and experimental crystal structures for 11, which displays the distortion, as well as for 6, which does not. In 7, 9, and 11, the out-of-plane rotation results in large angles (phi=53.7-89.4 degrees) between the planes formed by ketimide atoms N=C(CMe)(Cipso) and the ketimide aryl groups. Complexes 6 and 10 do not contain o-fluorine atoms and display interplanar angles in the range of phi=7-26.8 degrees. Complex 4 with a single o-fluorine substituent has intermediate values of phi=20.4 and 49.5 degrees. The distortions in 7, 9, and 11 result from an unfavorable steric interaction between one of the two o-fluorine atoms and the methyl group [-N=C(CH3)] on the ketimide ligand. All complexes exhibit UV/UIV and UIV/UIII redox couples, although the distortion in 7, 9, and 11 appears to be a factor in rendering the UIV/UIII couple irreversible. The potential separation between these couples remains constant at 2.15+/-0.03 V. The electronic spectra are dominated by unusually intense f-f transitions in the near-IR that retain nearly identical band energies but vary in intensity as a function of the fluorinated ketimide ligand, and visible and near-UV bands assigned to metal (5f)-to-ligand (pi*) charge-transfer and interconfiguration (5f2-->5f16d1) transitions, respectively. Variable-temperature magnetic susceptibility data for these complexes indicate a temperature-independent paramagnetism (TIP) below approximately 50 K that results from admixing of low-lying crystal-field excited states derived from the symmetry-split 3H4 5f2 manifold into the ground state. The magnitude of the TIP is smaller for the complexes possessing two o-fluorine atoms (7, 9, and 11), indicating that the energy separation between ground and TIP-admixed excited states is larger as a consequence of the greater basicity of these ligands.     

Mononuclear Ni(III) complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]0/1- (L = thiolate, selenolate, CH2CN, Cl, PPh3): relevance to the nickel site of [NiFe] hydrogenases

The stable mononuclear Ni(III)-thiolate complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]- (L = SePh (2), Cl (3), SEt (4), 2-S-C4H3S (5), CH2CN (7)) were isolated and characterized by UV-vis, EPR, IR, SQUID, CV, 1H NMR, and single-crystal X-ray diffraction. The increased basicity (electronic density) of the nickel center of complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]- modulated by the monodentate ligand L and the substituted groups of the phenylthiolate rings promotes the stability and reactivity. In contrast to the irreversible reduction at -1.17 V (vs Cp2Fe/Cp2Fe+) for complex 3, the cyclic voltammograms of complexes [NiIII(SePh)(P(o-C6H4S)3)]-, 2, 4, and 7 display reversible NiIII/II redox processes with E(1/2) = -1.20, -1.26, -1.32, and -1.34 V (vs Cp2Fe/Cp2Fe+), respectively. Compared to complex 2 containing a phenylselenolate-coordinated ligand, complex 4 with a stronger electron-donating ethylthiolate coordinated to the Ni(III) promotes dechlorination of CH2Cl2 to yield complex 3 (kobs = (6.01 +/- 0.03) x 10-4 s-1 for conversion of complex 4 into 3 vs kobs = (4.78 +/- 0.02) x 10-5 s-1 for conversion of complex 2 into 3). Interestingly, addition of CH3CN into complex 3 in the presence of sodium hydride yielded the stable Ni(III)-cyanomethanide complex 7 with a NiIII-CH2CN bond distance of 2.037(3) A. The NiIII-SEt bond length of 2.273(1) A in complex 4 is at the upper end of the 2.12-2.28 A range for the NiIII-S bond lengths of the oxidized-form [NiFe] hydrogenases. In contrast to the inertness of complexes 3 and 7 under CO atmosphere, carbon monoxide triggers the reductive elimination of the monodentate chalcogenolate ligand of complexes 2, 4, and 5 to produce the trigonal bipyramidal complex [NiII(CO)(P(C6H3-3-SiMe3-2-S)3]- (6).     

Relative stabilities of weakly coordinating anions: a computational study

This article describes BP86/SV(P) (DFT) calculations on a representative set of weakly coordinating anions (WCAs) of type [M(L)n]-, their parent neutral Lewis acids M(L)(n-1) and their ate complexes with fluoride, that is, [FM(L)(n)](n-1) (M=B, L=F, OTeF5, C6H5, C6F5, C6H3(CF3)2, CF3; M=P, As, Sb, L=F, OTeF5; M=Al, L=OC(CF3)3). Compounds with fluoride bridges, that is, Sb(n)F(5n) and [Sb(n)F(5n+1)]- (n=2, 3, 4), Al2(L)5F and [(L)3Al-F-Al(L)3]- (L=OC(CF3)3), (F4C6[1,2-B(L)2]2, [F4C6[1,2-B(L)2]2F]-, [F4C6[1,2-B(L)2]2OMe]- (L=C6F5) were also calculated. Based on these BP86/SV(P) and auxiliary MP2/TZVPP, G2, and CBS-Q calculations the relative stabilities and coordinating abilities of these WCAs were established with regard to the fluoride ion affinities (FIA) of the parent Lewis acids, the ligand affinity (LA) of the WCAs, the decomposition of a given WCA in the presence of a hard (H+, proton decomposition PD) and a soft electrophile (Cu+, copper decomposition CuD), the position of the HOMO, the HOMO-LUMO gap, and population analyses of the anions providing partial charges for all atoms. To obtain data that is more reliable, the assessed quantities were calculated through isodesmic reactions. If parts of the calculations could not be done isodesmically, higher levels such as MP2/TZVPP, G2, and CBS-Q were used to obtain reliable values for these reactions. Although the obtained results can not be taken as absolute, the relative ordering of the stabilities of all WCAs will undoubtedly be correct, since a single methodology was chosen for the investigation. To include media effects the decomposition reactions of a subset of 14 WCAs with the SiMe3+ and [Cp2ZrMe]+ ions were also calculated in PhCl and 1,2-F2C6H4 (COSMO solvation model). We found that in most cases gas-phase calculations and solution calculations give comparable results for the stability of the anion. Applications of the LA and FIA that allow one to decide, on thermodynamic grounds, which WCA or Lewis acid is the most suitable for a given problem are sketched.     

Tris(pentafluorophenyl)borane: a special boron Lewis acid for special reactions

Tris(pentafluorophenyl)borane is best known for its role as an excellent activator component in homogeneous Ziegler-Natta chemistry. However, the special properties of B(C6F5)3 have made this strong boron Lewis acid an increasingly used catalyst or stoichiometric reagent in organic and organometallic chemistry. This includes catalytic hydrometallation reactions, alkylations and catalyzed aldol-type reactions. B(C6F5)3 catalyzes tautomerizations and can sometimes stabilize less favoured tautomeric forms by adduct formation. It induces some rather unusual reactions of early metal acetylide complexes and can help in stabilizing uncommon coordination geometries of carbon. The growing number of such examples indicates an increasing application potential of the useful Lewis acid B(C6F5)3 aside from its established role in olefin polymerization catalysis.     

Fluoride ion capture from water with a cationic borane

The reaction of the [Li(THF)4]+ salt of dimesityl-1,8-naphthalenediylborate with [Me2NCH2]I affords a borane (1-(Mes2B)-8-(Me2NCH2)-C10H6) which can be converted into a cationic borane [3]+ ([1-(Mes2B)-8-(Me3NCH2)-C10H6]+) by methylation with MeOTf. This cationic borane promptly complexes fluoride to afford the corresponding zwitterionic ammonium/fluoroborate 3-F (1-(Mes2FB)-8-(Me3NCH2)-C10H6). Cation [3]+ fails to react with chloride, bromide, and iodide indicating that fluoride complexation is selective. Structural, spectroscopic, and computational studies carried out on 3-F show the existence of an unusual C-H...F-B hydrogen bond. Remarkably, [3]+ captures fluoride from water under biphasic conditions (H2O/CHCl3) to form 3-F. The high fluoride affinity of [3]+ can be correlated to the Coulombic forces which stabilize the B-F bond against heterolysis.     

Novel micro3-oxo complexes prepared from Cp*Zr(B(3R)3 (R = H, CH3) and B(C6F5)3 in diethyl ether

From the reactions of Cp*ZrCl(3) with 3 equiv. of LiBH(3)R (R = CH(3), Ph), the organotrihydroborate complexes, Cp*Zr(BH(3)CH(3))(3), 1, and Cp*Zr(BH(3)Ph)(3), 2, were isolated. One of the Zr-H-B bonding interactions in 2 could be described as an intermediate case between the bidentate and tridentate modes. Reactions of and Cp*Zr(BH(4))(3), 3, with Lewis acid B(C(6)F(5))(3) in diethyl ether produced the novel 14-electron ionic compounds [(micro(3)-O)(micro(2)-OC(2)H(5))(3){(Cp*Zr(OC(2)H(5)))(2)(BCH(3))}][HB(C(6)F(5))(3)], 4, and [(micro(3)-O)(micro(2)-OC(2)H(5))(3){(Cp*Zr(OC(2)H(5)))(2)(BOC(2)H(5))}][HB(C(6)F(5))(3)], 5, respectively. These two unique compounds resulted from a sequential cleavage of Zr-H-B bonds of 1 and 3 and C-O bonds of ether followed by the formation of O-B bonds. The solid state single crystal X-ray analyses revealed that both compounds have similar structures. A micro(3)-oxygen bridges two zirconiums and a boron atom. The latter three atoms are further connected by three micro(2)-bridging ethoxy groups giving rise to three four-membered metallacycles within the structure of each cation.     

Quasi-octahedral complexes of pentamethylcyclopentadienyliridium(III) bearing bis(diphenylphosphinomethyl)phenylphosphine (dpmp)

Reaction of [Cp*IrCl2]2 (1) with dpmp in the presence of KPF6 afforded a binuclear complex [Cp*IrCl(dpmp-P1,P2;P3)IrCl2Cp*](PF6) (2) (dpmp =(Ph2PCH2)2PPh). The mononuclear complex [Cp*IrCl(dpmp-P1,P2)](PF6) (4) was generated by the reaction of [Cp*IrCl2(BDMPP)](BDMPP =PPh[2,6-(MeO)2C6H3]2) with dpmp in the presence of KPF6. These mono- and binuclear complexes have four-membered ring structures with a terminal and a central P atom of the dpmp ligand coordinated to an iridium atom as a bidentate ligand. Since there are two chiral centers at the Ir atom and a central P2 atom, there are two diastereomers that were characterized by spectrometry. Complexes anti-4 and syn-4 reacted with [Cp*RhCl2]2 or [(C6Me6)RuCl2]2, giving the corresponding mixed-metal complexes, anti- and syn- [Cp*IrCl(dppm-P1,P2;P3)MCl2L](PF6) (6: M = Rh, L = Cp*; 7: M = Ru, L = C6Me6). Treatment with AuCl(SC4H8) gave tetranuclear complexes, anti- and syn-8 [[Cp*IrCl(dppm-P1,P2;P3)AuCl]2](PF6)2 bearing an Au-Au bond. Reaction of anti- with PtCl2(cod) generated the trinuclear complex anti-9, anti-[[Cp*IrCl(dppm-P1,P2;P3)]2PtCl2](PF6)2. These reactions proceeded stereospecifically. The P,O-chelated complex syn-[Cp*IrCl(BDMPP-P,O)] (syn-10)(BDMPP-P,O = PPh[2,6-(MeO)2C6H3][2-O-6-(MeO)C6H3]2) reacted with dpmp in the presence of KPF6, generating the corresponding anti-complex as a main product as well as a small amount of syn-complex, [Cp*Ir(BDMPP-P,O)(dppm-P1)](PF6) (11). The reaction proceeded preferentially with inversion. The reaction processes were investigated by PM3 calculation. anti- was treated with MCl2(cod), giving anti-[Cp*Ir(BDMPP-P,O)(dppm-P1;P2,P3)MCl2](PF6)(14: M = Pt; 15: M = Pd), in which the MCl2 moiety coordinated to the two free P atoms of anti-11. The X-ray analyses of syn-2, anti-2, anti-4, anti-8 and anti-11 were performed.