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

Reaction of (C5Me5)2Th(CH3)2 with 2 equiv of NC-ArF gives the corresponding fluorinated thorium(IV) bis(ketimide) complexes (C5Me5)2Th[-N=C(CH3)(ArF)]2 (where ArF = 3-F-C6H4 (4), 4-F-C6H4 (5), 2-F-C6H4 (6), 3,5-F2-C6H3 (7), 3,4,5-F3-C6H2 (8), 2,6-F2-C6H3 (9), 2,4,6-F3-C6H2 (10), and C6F5 (11)). The complexes have been characterized by a combination of single-crystal X-ray diffraction, cyclic voltammetry and NMR, and UV-visible absorption and low-temperature luminescence spectroscopies. Density functional theory (DFT) and time-dependent DFT (TD-DFT) results are reported for complexes 5, 11, and (C5Me5)2Th[-N=C(Ph)2]2 (1) for comparison with experimental data and to guide in the interpretation of the spectroscopic results. The most significant structural perturbation imparted by the fluorine substitution in these complexes is a rotation of the fluorophenyl group (ArF) out of the plane defined by the N=C(CMe)(Cipso) fragment in complexes 9-11 when the ArF group possesses two ortho fluorine atoms. Excellent agreement is obtained between the optimized ground state DFT calculated structures and crystal structures for 11, which displays the distortion, as well as 5, which does not. In complexes 9-11, the out-of-plane rotation results in large interplanar angles (phi) between the planes formed by ketimide atoms N=C(CMe)(Cipso) and the ketimide aryl groups in the range phi = 49.1-88.8 degrees , while in complexes 5, 7, and 8, phi = 5.7-34.9 degrees . The large distortions in 9-11 are a consequence of an unfavorable steric interaction between one of the two ortho fluorine atoms and the methyl group [-N=C(CH3)] on the ketimide ligand. Excellent agreement is also observed between the experimental electronic spectroscopic data and the TD-DFT predictions that the two lowest lying singlet states are principally of nonbonding nitrogen p orbital to antibonding C=N pi* orbital (pN-->pi*C=N or npi*) character, giving rise to moderately intense transitions in the mid-visible spectral region that are separated in energy by less than 0.1 eV. Low-temperature (77 K) luminescence from both singlet and triplet excited states are also observed for these complexes. Emission lifetime data at 77 K for the triplet states are in the range 50-400 mus. These emission spectral data also exhibit vibronic structure indicative of a small Franck-Condon distortion in the ketimide M-N=C(R1)(R2) linkage. Consistent with this vibronic structure, resonance enhanced Raman vibrational scattering is also observed for (C5Me5)2Th[-N=C(Ph)(CH2Ph)]2 (2) when exciting into the visible excited states. These systems represent rare examples of Th(IV) complexes that engender luminescence and resonance Raman spectral signatures.     

Substituent effects in formally quintuple-bonded ArCrCrAr compounds (Ar = terphenyl) and related species

The effects of different terphenyl ligand substituents on the quintuple Cr-Cr bonding in arylchromium(I) dimers stabilized by bulky terphenyl ligands (Ar) were investigated. A series of complexes, ArCrCrAr (1-4; Ar = C6H2-2,6-(C6H3-2,6-iPr2)2-4-X, where X = H, SiMe3, OMe, and F), was synthesized and structurally characterized. Their X-ray crystal structures display similar trans-bent C(ipso)CrCrC(ipso) cores with short Cr-Cr distances that range from 1.8077(7) to 1.8351(4) A. There also weaker Cr-C interactions [2.294(1)-2.322(2) A] involving an C(ipso) of one of the flanking aryl rings. The data show that the changes induced in the Cr-Cr bond length by the different substituents X in the para positions of the central aryl ring of the terphenyl ligand are probably a result of packing rather than electronic effects. This is in agreement with density functional theory (DFT) calculations, which predict that the model compounds (4-XC6H4)CrCr(C6H4-4-X) (X = H, SiMe3, OMe, and F) have similar geometries in the gas phase. Magnetic measurements in the temperature range of 2-300 K revealed temperature-independent paramagnetism in 1-4. UV-visible and NMR spectroscopic data indicated that the metal-metal-bonded solid-state structures of 1-4 are retained in solution. Reduction of (4-F3CAr')CrCl (4-F3CAr' = C6H2-2,6-(C6H3-2,6-iPr2)2-4-CF3) with KC8 gave non-Cr-Cr-bonded fluorine-bridged dimer {(4-F3CAr')Cr(mu-F)(THF)}2 (5) as a result of activation of the CF3 moiety. The monomeric, two-coordinate complexes [(3,5-iPr2Ar*)Cr(L)] (6, L = THF; 7, L = PMe3; 3,5-iPr2Ar* = C6H1-2,6-(C6H-2,4,6-iPr3)2-3,5-iPr2) were obtained with use of the larger 3,5-Pri2-Ar* ligand, which prevents Cr-Cr bond formation. Their structures contain almost linearly coordinated CrI atoms, with high-spin 3d5 configurations. The addition of toluene to a mixture of (3,5-iPr2Ar*)CrCl and KC8 gave the unusual dinuclear benzyl complex [(3,5-iPr2Ar*)Cr(eta3:eta6-CH2Ph)Cr(Ar*-1-H-3,5-iPr2)] (8), in which a C-H bond from a toluene methyl group was activated. The electronic structures of 5-8 have been analyzed with the aid of DFT calculations.     

Synthesis and characterization of thermally robust amidinato group 13 hydride complexes

The reactivity of two sterically bulky amidines, ArNC(R)N(H)Ar (Ar=2,6-diisopropylphenyl; R=H (HFiso); tBu, (HPiso)) towards LiMH4, M=Al or Ga, [AlH3(NMe3)], and [GaH3(quin)] (quin=quinuclidine) has been examined. This has given rise to a variety of very thermally stable aluminum and gallium hydride complexes. The structural motif adopted by the prepared complexes has been found to be dependent upon both the amidinate ligand and the metal involved. The 1:1 reaction of HFiso with LiAlH4 yielded dimeric [{AlH3(mu-Fiso)Li(OEt2)}2]. Amidine HFiso reacts in a 1:1 ratio with [AlH3(NMe3)] to give the unusual hydride-bridging dimeric complex, [{AlH2(Fiso)}2], in which the Fiso- ligand is nonchelating. The equivalent reaction with the bulkier amidine, HPiso, yielded a related hydride-bridging complex, [{AlH2(Piso)}2], in which the Piso- ligand is chelating. In contrast, the treatment of [GaH3(quin)] with one equivalent of HFiso afforded the four-coordinate complex [GaH2(quin)(Fiso)], in which the Fiso- ligand acts as a localized monodentate amido-imine ligand. The 2:1 reactions of HFiso with [AlH3(NMe3)] or [GaH3(quin)] gave the monomeric complexes [MH(Fiso)2], which are thermally robust and which exhibit chelating amidinate ligands. In contrast, HPiso did not give 2:1 complexes in its reactions with either of the Group 13 trihydride precursors. For sake of comparison, the reactions of [AlH3(NMe3)] and [GaH3(quin)] with the bulky carbodiimide ArN=C=NAr and the thiourea Ar(H)NC(=S)N(H)Ar were examined. These last reactions afforded the five-coordinate thioureido complexes, [MH{N(Ar)C[N(H)(Ar)]S}2], M=Al or Ga.     

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.     

Synthesis,Characterization, Luminescence,and Electrochemistry of the Tetranuclear Gold(I) Amidinate Clusters,Precursors to CO Oxidation Catalysts: Au4[(ArNC(H)NAr)]4, Au4[(PhNC(Ph)NPh)]4 and Au4[PhNC(CH3)NPh)4]

A summary of the chemistry of the tetranuclear Au(I) amidinate complexes is presented. Tetranuclear Au(I) amidinate clusters are produced by the reaction of the sodium salt of a amidine ligand with the gold precursor Au(THT)Cl in a (1:1) stoichiometry. The structures of the tetranuclear Au₄[ArNC(H)NAr]₄, Ar = C₆H₄‐4‐OMe, C₆H₃‐3,5‐Cl, C₆H₄‐4‐Me, C₆H₄‐3‐CF₃, C₆F₅, C₁₀H₇ and the tetranuclear Au₄[(PhNC(Ph)NPh]₄ and Au₄[PhNC(CH₃)NPh]₄ have been characterized by X‐ray crystallography. The average Au···Au distance between adjacent Au(I) atoms is ?3.0 Å, typical of compounds having an aurophilic interaction. The four gold atoms are located at the corner of a rhomboid with the amidinate ligands bridged above and below the near plane of the four Au(I) atoms. The angles at Au···Au···Au in the cyclic units are between 70° and 116°. The tetranuclear gold(I) amidinate clusters each show different luminescence behavior. The tetranuclear clusters Au₄[(ArNC(H)NAr]₄, Ar = C₆H₄‐4‐OMe, Ar = C₆H₄‐3‐CF₃, Ar = C₆H₄‐4‐Me and Ar = C₆H₄‐3,5‐Cl are the first tetranuclear gold(I) cluster species from group 11 elements that show fluorescence at room temperature. The tetranuclear naphthyl derivative Ar = C₁₀H₇ is luminescent only at 77 K. The pentafluorophenyl derivative Ar = C₆F₅ does not show any photoluminescence in the solid state nor in the solution. The lifetimes of the naphthyl and trifluoromethylphenyl complexes are in the millisecond range indicating phosphorescent processes. Electrochemical and chemical oxidation studies of the tetranuclear Au(I) amidinate clusters are presented. The tetranuclear complexes Au₄[ArNC(H)NAr]₄, Ar = C₆H₄‐4‐OMe, Ar = C₆H₄‐4‐Me, and Ar = C₆H₃‐3,5‐Cl, show three reversible waves at 0.75, 0.95, 1.09 V vs. Ag/AgCl at a scan rate of 500 mV/s in 0.1 M Bu₄NPF₆/CH₂Cl₂ at a Pt working electrode in CH₂Cl₂. Three reversible waves at 0.87, 1.19, 1.42 V vs. Ag/AgCl at a scan rate of 100 mV/s are also observed for the tetranuclear complex Au₄[PhNC(Ph)NPh]₄ in CH₂Cl₂. The pentafluorophenyl amidinate derivative, Au₄[ArNC(H)NAr]₄, Ar = C₆F₅ shows no oxidation wave below 1.8 V. Recently it has been shown that Au₄[ArNC(H)NAr]₄ is a very effective catalyst precursor for room temperature CO oxidation.     

Flexible coordination of bulky amidinates and guanidinates towards rhodium(I): conversion of kinetic to thermodymanic isomers

Reactions of the bulky amidinate and guanidinate salts K[(ArN)(2)CR] (R = Bu(t), NPr(i)(2) or N(C(6)H(11))(2); Ar = 2,6-diisopropylphenyl) with [{RhCl(eta(4)-COD)}(2)] (COD = 1,5-cyclooctadiene) lead to KCl elimination and the formation of the complexes, [Rh{(eta(5)-ArN)(ArN)CR}(COD)], in which the anionic ligand coordinates the rhodium centre in an unprecedented eta(5)-cyclohexadienyl mode. The thermal conversions of these complexes to their N,N'-chelated isomers, [Rh{kappa(2)-N,N'-(ArN)(2)CR}(COD)], were carried out and the kinetics of these processes have been shown to be first order. The rates of the isomerisations are inversely proportional to the size of the amidinate or guanidinate backbone substituent. Analogies between the ligating properties of the bulky amidinates and guanidinates used in the study, and those of beta-diketiminates are discussed.     

Ni(II) and Fe(II) complexes based on bis(imino)aryl pincer ligands: synthesis, structural characterization and catalytic activities

Bis(imino)aryl NCN pincer Ni(II) complexes 2,6-(ArN=CH)(2)C(6)H(3)NiBr (1: Ar = 2,6-Me(2)C(6)H(3); 2: Ar = 2,6-Et(2)C(6)H(3); 3: Ar = 2,6-(i)Pr(2)C(6)H(3)) were prepared via the oxidative-addition of Ni(0)(Ph(3)P)(4) with bis(N-aryl)-2-bromoisophthalaldimine. These nickel complexes were characterized by NMR and elemental analyses. Their solid molecular structures were established by X-ray diffraction analyses. The nickel metal centers adopt distorted square planar geometries with the bromine atoms acting as one coordinate ligands. The NCN pincer Fe(II) complexes 2,6-(ArN=CH)(2)C(6)H(3)Fe(μ-Cl)(2)Li(THF)(2) (4: Ar = 2,6-Me(2)C(6)H(3); 5: Ar = 2,6-Et(2)C(6)H(3); 6: Ar = 2,6-(i)Pr(2)C(6)H(3)) were synthesized by lithium salt metathesis reactions of the ligand lithium salts with FeCl(2). X-ray structure analyses of 4 and 5 revealed that the Fe(II) complexes are hetero-dinuclear with the iron atoms in trigonal bipyramidal environments. When activated with MAO, the nickel complexes are active for norbornene vinyl polymerization but are inert for butadiene polymerization. The Fe(II) complexes show moderate activities in butadiene polymerization when activated with alkylaluminium, affording the cis-1,4 enriched polymer.     

Synthesis, characterization of bridged bis(amidinate) lanthanide amides and their application as catalysts for addition of amines to nitriles for monosubstituted N-arylamidines

A series of lanthanide amide complexes supported by bridged bis(amidinate) ligand L, LLnNHAr(1)(DME) (L = [Me(3)SiNC(Ph)N(CH(2))(3)NC(Ph)NSiMe(3)], Ar(1) = 2,6-(i)Pr(2)C(6)H(3), DME = dimethoxyethane, Ln = Y (1), Pr (2), Nd (3), Gd (4), Yb (5)), [Yb(μ(2)-NHPh)](2)(μ(2)-L)(2) (6) and [LYb](2)(μ(2)-NHAr(2))(2) (7) (Ar(2) = (o-OMe)C(6)H(4)), were synthesized by reaction of LLnCl(THF)(2) with the corresponding lithium amide in good yields and structurally characterized by X-ray crystal structure analyses. All complexes were found to be precatalysts for the catalytic addition of aromatic amines to aromatic nitriles to give monosubstituted N-arylamidines. The catalytic activity was influenced by lanthanide metals and the amido groups with the active sequence of Y (1) < Gd (4) < Nd (3) < Pr (2) ～ Yb (5) for the lanthanide metals and -NHAr(2) < -NHPh < -NHAr(1) for the amido groups. The catalytic addition reaction with complex 5 showed a good scope of aromatic amines. Some key reaction intermediates were isolated and structurally characterized, including the amidinate complexes LLn[NPhCNAr(1)](PhCN) (Ln = Y (8), Ln = Yb (9)), LYb[NAr(2)CNAr(1)](Ar(2)CN) (10), and amide complex 5 prepared by protonation of 9 by Ar(1)NH(2). Reactivity studies of these complexes suggest that the present catalytic formation of monosubstituted N-arylamidines proceeds through nucleophilic addition of an amido species to a nitrile, followed by amine protonolysis of the resultant amidinate species.     

Remarkable reactions of cyclooctatetraene diiron-bridging carbyne complexes with amino and amido compounds: nucleophilic addition to and breaking of the cyclooctatetraene ring

The reactions of the cationic, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(8)-C(8)H(8))]BF(4) (1, Ar=C(6)H(5); 2, Ar=p-CH(3)C(6)H(4); 3, Ar=p-CF(3)C(6)H(4)) with LiN(C(6)H(5))(2) in THF at low temperature gave novel N-nucleophilic-addition products, namely, the neutral, diiron-bridging carbyne complexes [Fe(2)(mu-CAr)(CO)(4)(eta(7)-C(8)H(8)N(C(6)H(5))(2))] (4, Ar=C(6)H(5); 5, Ar=p-CH(3)C(6)H(4); 6, Ar=p-CF(3)C(6)H(4))). Cationic bridging carbyne complexes 1-3 react with (C(2)H(5))(2)NH, (iC(3)H(7))(2)NH, and (C(6)H(11))(2)NH under the same conditions with ring cleavage of the COT ligand to produce the novel diiron-bridging carbene inner salts [Fe(2)[mu-C(Ar)C(8)H(8)NR(2)](CO)(4)] (7, Ar=C(6)H(5), R=C(2)H(5); 8, Ar=p-CH(3)C(6)H(4), R=C(2)H(5); 9, Ar=p-CF(3)C(6)H(4), R=C(2)H(5); 10, Ar=C(6)H(5), R=iC(3)H(7); 11, Ar=p-CH(3)C(6)H(4), R=iC(3)H(7); 12, Ar=p-CF(3)C(6)H(4), R=iC(3)H(7); 13, Ar=C(6)H(5), R=C(6)H(11); 14, Ar=p-CH(3)C(6)H(4), R=C(6)H(11), 15, Ar=p-CF(3)C(6)H(4), R=C(6)H(11)). Piperidine reacts similarly with cationic carbyne complex 3 to afford the corresponding bridging carbene inner salt [Fe(2)[mu-C(Ar)C(8)H(8)N(CH(2))(5)](CO)(4)] (16). Compound 9 was transformed into a new diiron-bridging carbene inner salt 17, the trans isomer of 9, by heating in benzene. Unexpectedly, the reaction of C(6)H(5)NH(2) with 2 gave a novel COT iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NHC(6)H(5)](mu-CO)(CO)(3)(eta(8)-C(8)H(8))] (18). However, the analogous reactions of 2-naphthylamine with 2 and of p-CF(3)C(6)H(4)NH(2) with 3 produce novel chelated iron-carbene complexes [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(10)H(7)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (19) and [Fe(2)[=C(C(6)H(4)CF(3)-p)NC(6)H(4)CF(3)-p](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (20), respectively. Compound 18 can also be transformed into the analogous chelated iron-carbene complex [Fe(2)[=C(C(6)H(4)CH(3)-p)NC(6)H(5)](CO)(4)(eta(2):eta(3):eta(2)-C(8)H(9))] (21). The structures of complexes 6, 9, 15, 17, 18, and 21 have been established by X-ray diffraction studies.     

Lithium fluoroarylamidinates: syntheses, structures, and reactions

Lithium fluoroarylamidinates [(Ar(F)C(NSiMe(3))(2)Li)(n).xD] (Ar(F) = 4-CF(3)C(6)H(4), n = 2, D = OEt(2), x = 1 (2a); n = 1, D = TMEDA, x = 1 (4a); Ar(F) = 2-FC(6)H(4), n = 2, D = OEt(2), x = 1 (2b); Ar(F) = 4-FC(6)H(4), n = 2, D = OEt(2), x = 2 (2c); Ar(F) = 2,6-F(2)C(6)H(3), n = 2, D = OEt(2), x = 1 (2d); n = 2, D = 2,6-F(2)C(6)H(3)CN, x = 2 (3d); Ar(F) = C(6)F(5), n= 2, D = OEt(2), x = 1 (2e), n = 1, D = TMEDA, x = 1 (4e); n = 1, x = 2, D = OEt(2) (5e); D = THF (6e)) were prepared by the well-known method from LiN(SiMe(3))(2) and the corresponding nitrile in diethyl ether or by addition of the appropriate donor D to the respective diethyl ether complexes. Depending on the substituents at the aryl group and on the donors D, three different types of structures were confirmed by X-ray crystallography. Hydrolysis of 2e gave C(6)F(5)C(NSiMe(3))N(H)SiMe(3) (7e) and C(6)F(5)C(NH)N(H)SiMe(3) (8e). The lithium fluoroarylamidinates 2a-2d react with Me(3)SiCl to give the corresponding tris(trimethylsilyl)fluoroarylamidines Ar(F)C(NSiMe(3))N(SiMe(3))(2) (9a-9d). Attempts to prepare C(6)F(5)C(NSiMe(3))N(SiMe(3))(2) from 2e and Me(3)SiCl failed; however, the unprecedented cage [[C(6)F(5)C(NSiMe(3))(2)Li](4)LiF] (10e) in which a fluoride center is surrounded by a distorted trigonal bipyramid of five Li atoms was obtained from this reaction.     

Synthesis, characterisation and theoretical studies of amidinato-indium(I) and thallium(I) complexes: isomers of neutral group 13 metal(I) carbene analogues

The synthesis and characterisation of the monomeric amidinato-indium(I) and thallium(I) complexes, [M(Piso)].PisoH, M = In or Tl, Piso- = [ArNC(Bu(t))NAr]-, Ar = C6H3Pr(i)2-2,6, are reported. These complexes, in which the metal centre is chelated by the amidinate ligand in an N,eta3-arene-fashion, can be considered as isomers of four-membered group 13 metal(I) carbene analogues. Theoretical studies have compared the relative energies of both isomeric forms of a model complex, [In{PhNC(H)NPh}].     

Syntheses of highly fluorinated 1,3,5-triazapentadienyl ligands and their use in the isolation of copper(I)-carbonyl and copper(I)-ethylene complexes

Fully fluorinated triazapentadienyl ligand [N{(C3F7)C(C6F5)N}2]- and the related [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]- have been synthesized in good yield via a convenient route and used in the isolation of three- and four-coordinate copper(I)-carbon monoxide complexes. They show fairly high nu(CO) values (>2100 cm(-1)), indicating the presence of electron-poor Cu sites. The copper(I)-ethylene adduct [N{(C3F7)C(C6F5)N}2]Cu(C2H4), featuring a three-coordinate Cu site, has also been synthesized using [N{(C3F7)C(C6F5)N}2]CuNCCH3 and C2H4.     

Reversible oxidative addition and reductive elimination of fluorinated disulfides at gold(I) thiolate complexes: a new ligand exchange mechanism

Reaction of HAuCl4 x 3 H2O with excess HSAr (Ar = C6F5 or C6F4H) in ethanol, followed by addition of [Et4N]Cl, produced [Et4N][Au(SAr)4] (Ar = C6F5 (1a) or C6F4H (1b)) as red crystalline solids in high yield. These complexes are rare examples of homoleptic gold(III) thiolate complexes. The crystal structures 1 show square planar geometry at the gold center with elongated Au-S bonds. Both complexes undergo reversible reductive elimination/oxidative addition processes in solution via thermal and photochemical pathways. Equilibrium constant and photostationary state measurements indicate that the relative importance of the two pathways depends on the nature of the aromatic groups. The metal-containing reductive elimination products, [Et4N][Au(SAr)2] (Ar = C6F5 (2a) or C6F4H (2b)), were confirmed by both independent synthesis and crystallographic characterization. Cross-reactions between either 1 or 2 and various disulfides led to ligand exchange via an addition-elimination process, a previously unknown reaction pathway for ligand exchange at gold(I) centers.     

Chromium complexes supported by phenanthrene-imine derivative ligands: synthesis, characterization and catalysis on isoprene cis-1,4 polymerization

Reactions of CrCl(2)(THF)(2) with N-aryl-9,10-iminophenanthraquinone in CH(2)Cl(2) give the monoimine chromium complexes (Ar)IPQCrCl(2)(THF)(2) (1, Ar = 2,6-Me(2)C(6)H(3); 2, Ar = 2,6-Et(2)C(6)H(3); 3, Ar = 2,6-(i)Pr(2)C(6)H(3)). Molecular structures of 1 and 3 were revealed to be monomeric with the chromium atoms in distorted octahedral geometries. Similar reactions of CrCl(2)(THF)(2) with N,N-bis(arylimino)phenanthrene ligands afford the diimine complexes (Ar1,Ar2)BIPCrCl(μ-Cl)(3)Cr(THF)(Ar1,Ar2)BIP (4, Ar(1) = Ar(2) = 2,6-Me(2)C(6)H(3); 5, Ar(1) = Ar(2) = 2,6-Et(2)C(6)H(3); 6, Ar(1) = Ar(2) = 2,6-(i)Pr(2)C(6)H(3); 7, Ar(1) = 2,6-Me(2)C(6)H(3), Ar(2) = 2,6-(i)Pr(2)C(6)H(3)). The X-ray diffraction analysis shows that 4, 5, and 7 are chlorine-bridged dimers with each chromium atom in a distorted octahedral geometry. Upon activation with MAO, all these complexes exhibit good catalytic activities for isoprene polymerization affording polyisoprene with predominantly a cis-1,4 unit.     

Synthesis and reactivity of cationic niobium and tantalum methyl complexes supported by imido and β-diketiminato ligands

The synthesis and reactivity of the cationic niobium and tantalum monomethyl complexes [(BDI)MeM(N(t)Bu)][X] (BDI = [Ar]NC(CH(3))CHC(CH(3))N[Ar], Ar = 2,6-(i)Pr(2)C(6)H(3); M = Nb, Ta; X = MeB(C(6)F(5))(3), B(C(6)F(5))(4)] was investigated. The cationic alkyl complexes failed to irreversibly bind CO but formed phosphine-trapped acyl complexes [(BDI)(R(3)PC(O)Me)M(N(t)Bu)][B(C(6)F(5))(4)] (R = Et, Cy) in the presence of a combination of trialkylphosphines and CO. Treatment of the monoalkyl cationic Nb complex with XylNC (Xyl = 2,6-Me(2)-C(6)H(3)) resulted in irreversible formation of the iminoacyl complex [(BDI)(XylN[double bond, length as m-dash]C(Me))Nb(N(t)Bu)][B(C(6)F(5))(4)], which did not bind phosphines but would add a methide group to the iminoacyl carbon to provide the known ketimine complex (BDI)(XylNCMe(2))Nb(N(t)Bu). Further stoichiometric chemistry explored i) migratory insertion reactions to form new alkoxide, amidinate, and ketimide complexes; ii) protonolysis reactions with Ph(3)SiOH to form thermally robust cationic siloxide complexes; and iii) catalytic high-density polyethylene formation mediated by the cationic Nb methyl complex.     

Pi-bonding encapsulation in aryl-substituted lanthanide selenolates: monomeric compounds with apparent low-coordinate metal atoms

Reaction of LnCl3 with KSeAr* in thf afforded the unsolvated, alkane-soluble complexes LnCl(SeAr*)2 (Ln = Nd, Pr; Ar* = 2,6-Trip(2)C(6)H(3); Trip = 2,4,6-iPr(3)C(6)H(2)) in which the rare-earth metal cations show additional eta6-pi-coordination by two flanking arene rings.     

Syntheses, structures, and reactivities of mono- and dinuclear iridium thiolato complexes containing nitrosyl ligands

Reactions of the iridium(III) nitrosyl complex [Ir(NO)Cl2(PPh3)2] (1) with hydrosulfide and arenethiolate anions afforded the square-pyramidal iridium(III) complex [Ir(NO)(SH)2(PPh3)2] (2) with a bent nitrosyl ligand and a series of the square-planar iridium(I) complexes [Ir(NO)(SAr)2(PPh3)] (3a, Ar = C6H2Me3-2,4,6 (Mes); 3b, Ar = C6H3Me2-2,6 (Xy); 3c, Ar = C6H2Pri3-2,4,6) containing a linear nitrosyl ligand, respectively. Complex 1 also reacted with alkanethiolate anions or alkanethiols to give the thiolato-bridged diiridium complexes [Ir(NO)(mu-SPri)(SPri)(PPh3)]2 (4) and [Ir(NO)(mu-SBut)(PPh3)]2 (5). Complex 4 contains two square-pyramidal iridium(III) centers with a bent nitrosyl ligand, whereas 5 contains two tetrahedral iridium(0) centers with a linear nitrosyl ligand and has an Ir-Ir bond. Upon treatment with benzoyl chloride, 3a and 3b were converted into the (diaryl disulfide)- and thiolato-bridged dichlorodiiridium(III) complexes [[IrCl(mu-SC6HnMe4-nCH2)(PPh3)]2(mu-ArSSAr)] (6a, Ar = Mes, n = 2; 6b, Ar = Xy, n = 3) accompanied by a loss of the nitrosyl ligands and cleavage of a C-H bond in an ortho methyl group of the thiolato ligands. Similar treatment of 4 gave the dichlorodiiridium complex [Ir(NO)(PPh3)(mu-SPri)3IrCl2(PPh3)] (7), which has an octahedral dichloroiridium(III) center and a distorted trigonal-bipyramidal Ir(I) atom with a linear nitrosyl ligand. The detailed structures of 3a, 4, 5, 6a, and 7 have been determined by X-ray crystallography.     

Electronic perturbations of iron dipyrrinato complexes via ligand β-halogenation and meso-fluoroarylation

Systematic electronic variations were introduced into the monoanionic dipyrrinato ligand scaffold via halogenation of the pyrrolic β-positions and/or via the use of fluorinated aryl substituents in the ligand bridgehead position in order to synthesize proligands of the type 1,9-dimesityl-β-R(4)-5-Ar-dipyrrin [R = H, Cl, Br, I; Ar = mesityl, 3,5-(F(3)C)(2)C(6)H(3), C(6)F(5) in ligand 5-position; β = 2,3,7,8 ligand substitution; abbreviated ((β,Ar)L)H]. The electronic perturbations were probed using standard electronic absorption and electrochemical techniques on the different ligand variations and their divalent iron complexes. The free-ligand variations cause modest shifts in the electronic absorption maxima (λ(max): 464-499 nm) and more pronounced shifts in the electrochemical redox potentials for one-electron proligand reductions (E(1/2): -1.25 to -1.99 V) and oxidations (E(1/2): +0.52 to +1.14 V vs [Cp(2)Fe](+/0)). Installation of iron into the dipyrrinato scaffolds was effected via deprotonation of the proligands followed by treatment with FeCl(2) and excess pyridine in tetrahydrofuran to afford complexes of the type ((β,Ar)L)FeCl(py) (py = pyridine). The electrochemical and spectroscopic behavior of these complexes varies significantly across the series: the redox potential of the fully reversible Fe(III/II) couple spans more than 400 mV (E(1/2): -0.34 to +0.50 V vs [Cp(2)Fe](+/0)); λ(max) spans more than 40 nm (506-548 nm); and the (57)Fe M?ssbauer quadrupole splitting (|ΔE(Q)|) spans nearly 2.0 mm/s while the isomer shift (δ) remains essentially constant (0.86-0.89 mm/s) across the series. These effects demonstrate how peripheral variation of the dipyrrinato ligand scaffold can allow systematic variation of the chemical and physical properties of iron dipyrrinato complexes.     

Rare earth metal bis(amide) complexes bearing amidinate ancillary ligands: synthesis, characterization, and performance as catalyst precursors for cis-1,4 selective polymerization of isoprene

A family of rare earth metal bis(amide) complexes bearing monoanionic amidinate [RC(N-2,6-Me(2)C(6)H(3))(2)](-) (R = cyclohexyl (Cy), phenyl (Ph)) as ancillary ligands were synthesized and characterized. One-pot salt metathesis reaction of anhydrous LnCl(3) with one equivalent of amidinate lithium [RC(N-2,6-Me(2)C(6)H(3))(2)]Li, following the introduction of two equivalents of NaN(SiMe(3))(2) in THF at room temperature afforded the neutral and unsolvated mono(amidinate) rare earth metal bis(amide) complexes [RC(N-2,6-Me(2)C(6)H(3))(2)]Y[N(SiMe(3))(2)](2) (R = Cy (1); R = Ph (2)), and the "ate" mono(amidinate) rare earth metal bis(amide) complex [CyC(N-2,6-Me(2)C(6)H(3))(2)]Lu[N(SiMe(3))(2)](2)(μ-Cl)Li(THF)(3) (3) in 61-72% isolated yields. These complexes were characterized by elemental analysis, NMR spectroscopy, FT-IR spectroscopy, and X-ray single crystal diffraction. Single crystal structural determination revealed that the central metal in complexes 1 and 2 adopts a distorted tetrahedral geometry, and in complex 3 forms a distorted trigonal bipyramidal geometry. In the presence of AlMe(3), and in combination with one equimolar amount of [Ph(3)C][B(C(6)F(5))(4)], complexes 1 and 2 showed high activity towards isoprene polymerization to give high molecular weight polyisoprene (M(n) > 10(4)) with good cis-1,4 selectivity (>90%).     

Ytterbium amides of linked bis(amidinate): synthesis, molecular structures, and reactivity for the polymerization of L-lactide

The steric effect of an amide group on the synthesis, molecular structures and reactivity of ytterbium amides supported by linked bis(amidinate) L (L = [Me3SiNC(Ph)N(CH2)3NC(Ph)NSiMe3]) is reported. Reaction of LYbCl(THF)2 with equimolar NaNHAr' and NaNHAr (Ar' = 2,6-Me2C6H3; Ar = 2,6-iPr2C6H3), respectively, gave the corresponding monometallic amide complexes LYb(NHAr')(DME) 1 and LYb(NHAr)(DME) 2, in which the linked bis(amidinate) is coordinated to the metal center as a chelating ligand. The similar reaction with NaN(SiMe3)2 afforded a bimetallic amide complex (TMS)2NYb(L)2YbN(TMS)2 3 formed through the rearrangement reaction of L induced by the bulky N(SiMe3)2 group. In complex 3 the two linked bis(amidinate)s act as bridging ancillary ligands to link two YbN(TMS)2 species in one molecule. The definite molecular structures of 1-3 were provided by single-crystal X-ray analysis. Complexes 1-3 are efficient initiators for the polymerization of L-lactide, and their catalytic performance is highly dependent on the amido groups and molecular structures. The polymerizations initiated by complexes 1 and 2 proceeded in a living fashion as evidenced by the narrow polydispersities of the resulting polymers, together with the linear natures of the number average molecular weight versus conversion plots, while the polymerization system with complex 3 provided polymers with rather broad molecular weight distributions.