Structural and electronic effects on one-bond spin-spin coupling constants 1J(B-N), 1J(B-H), and 1J(B-F) for complexes of nitrogen bases with BH3 and its fluoro-substituted derivatives

Ab initio equation-of-motion coupled cluster (EOM-CCSD) one-bond spin-spin coupling constants (1)J(B-N), (1)J(B-H), and (1)J(B-F) have been evaluated for complexes X:BH(n)F(3-n) with X = N(2), NCH, NCLi, H(2)CNH, NF(3), and NH(3), for n = 0-3. These complexes can be classified as either covalent or van der Waals complexes, on the basis of their binding energies and B-N distances. (1)J(B-N) for covalent complexes varies significantly from -19 to +9 Hz, whereas (1)J(B-N) is less than 2 Hz for van der Waals complexes. An absolute value of (1)J(B-N) of 3 Hz or greater indicates that the complex is covalently bonded, but a small value of this coupling constant does not necessarily mean that it is a van der Waals complex, in view of the variation among these complexes found for (1)J(B-N) as a function of the B-N distance. Deformation of the boron acid upon complex formation and electron donation by the nitrogen base has opposing effects on both (1)J(B-H) and (1)J(B-F). These effects are relatively small in van der Waals complexes. In covalent complexes, electron donation has the dominant effect on (1)J(B-H), and on (1)J(B-F) in complexes with BH(2)F and BHF(2), but acid deformation has the dominant effect on (1)J(B-F) in complexes with BF(3). Values of both (1)J(B-H) and (1)J(B-F) reflect the van der Waals or covalent nature of the B-N bond.     

Low-valent group-13 chemistry. Theoretical investigation of the structures and relative stabilities of donor-acceptor complexes R(3)E[bond]E'R' and their isomers R(2)E[bond]E'RR'

The results of quantum chemical calculations at the gradient-corrected density functional theory (DFT) level with the B3LYP functional of the donor-acceptor complexes R(3)E[bond]E'R' and their isomers R(2)E[bond]E'RR', where E, E' = B[bond]Tl and R, R' = H, Cl, or CH(3), are reported. The theoretically predicted energy differences between the donor-acceptor form R(3)E[bond]E'R' and the classical isomer R(2)E[bond]E'RR' and the bond dissociation energies of the E[bond]E' bonds are given. The results are discussed in order to show which factors stabilize the isomers R(3)E[bond]E'R'. There is no simple correlation of the nature of the group-13 elements E, E' and the substituents R, R' with the stability of the complexes. The isomers R(3)E[bond]'R' come stabilized by pi donor groups R', while the substituents R may either be sigma- or pi-bonded groups. Calculations of Cl(3)B[bond]BR' [R' = Cl, cyclopentadienyl (Cp), or Cp*] indicate that the Cp* group has a particularly strong effect on the complex form. The calculations show that the experimentally known complex Cl(3)B[bond]BCp* is the strongest bonded donor-acceptor complex of main-group elements that has been synthesized until now. The theoretically predicted B[bond]B bond energy is D(o) = 50.6 kcal/mol. However, the calculations indicate that it should also be possible to isolate donor-acceptor complexes R(3)E[bond]E'R' where R' is a sigma-bonded bulky substituent. Possible candidates that are suggested for synthetic work are the borane complexes (C(6)F(5))(3)B[bond]E'R' and (t)Bu(3)B[bond]E'R' (E' = Al[bond]Tl) and the alane complexes Cl(3)Al[bond]E'R' (E' = Ga[bond]Tl).     

Synthesis,crystal structure,and in vitro antitumor activities of copper(II) complexes containing tetradentate pyridine-based ligands

Several new Cu(II) complexes of Schiff bases obtained by condensation of 2-[N-(α-picolyl)-amino]-benzophenone with different chiral amino acids were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structure of one of the complexes was determined using single crystal X-ray diffraction. The ligands were coordinated to the metal atom in a tetradentate manner with ONNN donor sets using the carboxyl oxygen, azomethine nitrogen, CON⁻, and pyridine nitrogen. The cytotoxicities of the complexes were evaluated against human cancer cells. The substituents on the aromatic rings strongly influenced the cytotoxicities of the complexes. The complex with bromine substituents on the pyridine rings showed the highest cytotoxicity. The antitumor activities against tumor cell lines were assayed in vitro, and the complexes were found to be highly effective, with six of the nine complexes having inhibition ratios better than that of 5-Fluorouracil. This behavior is indicative of a high ability to circumvent the cellular drug resistance mechanisms.     

Bridging fluorides and hard/soft mismatch in d6 and d8 complexes: the case of [Tl(mu-F)3Ru(PPh3)3

[RuCl2(PPh3)3] reacts with thallium(I) fluoride to give either [Tl(mu-F)3Ru(PPh3)3] (1) or [Tl(mu3-F)(mu2-Cl)2Ru2(mu2-Cl)(mu2-F)(PPh3)4] (2) depending on the excess of TlF used. Both 1 and 2 were fully characterized, including X-ray structure determinations. Complex 1 reacts with dihydrogen to form the known ruthenium hydride complex [Ru(H)2(H2)(PPh3)3] upon hydrogenolysis of the Ru-F bond. The reaction of 1 with activated alkyl bromides (R-Br) gives the corresponding alkyl fluorides and the trinuclear complex [Tl(mu3-F)(mu2-F)(mu2-X)Ru2(mu2-Br)(mu2-F)(PPh3)4] (X=Br, F) (3), whose structure closely resembles that of 2. However, 1 is not active as catalyst for the nucleophilic fluorination of R-Br in the presence of thallium fluoride. The effect of the bridging coordination mode of fluoride on the Ru-F bond is discussed in terms of the HSAB principle, which suggests a more general model for predicting the stability of d6 and d8 complexes containing hard ligands (such as fluoro, oxo, and amido).     

Synthesis and structure of isomeric palladium(II)-pyrazole chelate complexes with and without an N-H group as hydrogen bond donor

Four new ligands containing a pyrazole ring and either a phosphine or thioether were prepared and converted to their cis-dichloropalladium(II) complexes. Two of the ligands are especially notable for the attachment of a side chain at pyrazole carbon, rather than at nitrogen. The new metal complexes include dichloro[3-(diphenylphosphinomethyl)pyrazole]palladium(II) (1-PdCl2) and dichloro[3-(methylthiomethyl)pyrazole]palladium(II) (2-PdCl2), which both feature an N-H group as a potential proton or hydrogen bond donor. For comparison, isomeric complexes lacking an NH group were prepared: dichloro[1-(diphenylphosphinomethyl)pyrazole]palladium(II) (3-PdCl2) and dichloro[1-(methylthiomethyl)pyrazole]palladium(II) (4-PdCl2). As determined by X-ray crystallography, all four complexes were found to have slightly distorted square planar geometry. Complexes 1-PdCl2 and 2-PdCl2, which contain an NH group, exhibit both intermolecular and intramolecular hydrogen bonding, whereas isomers 3-PdCl2 and 4-PdCl2 do not. Single-crystal X-ray structure determinations on the following compounds are reported: 1-PdCl2, space group P1, a = 8.4488(9) A, b = 8.9175(13) A, c = 12.731(2) A, Z = 2, V = 871.8(2) A3; 2-PdCl2, space group Pbca, a = 10.8827(10) A, b = 11.7721(7) A, c = 14.874(2) A, Z = 8, V = 1905.6 A3; 3-PdCl2, space group P2(1)/c, a = 20.520(2) A, b = 12.549(2) A, c = 13.9784(13) A, Z = 8, V = 3401.1(6) A3; 4-PdCl2, space group Pbca, a = 10.6545(10) A, b = 12.0205(11) A, c = 14.6474(14) A, Z = 8, V = 1875.9(3) A3.     

单电子卤键复合体系H3C···Br-Y(Y=H, CN, NC, CCH, C2H3)的作用机制

对单电子溴键复合物H₃C···Br—Y(Y=H, CCH, CN, NC, C2H3)的结构与性质进行了理论研究. 在B3LYP/6-311++G**水平上计算了稳定构型并做了频率分析. BSSE矫正的相互作用能(E^BSSE)和NBO及AIM分析输入的波函数在MP2/6-311++G**水平下完成. 复合物H₃C···Br—Y中, CH₃(供电子体)自由基均提供一未成对电子与Br—Y中Br(受电子体)形成了单电子溴键, 此单电子溴键也具有“三电子”键的特征. 单电子溴键的形成导致甲基H的背向Y弯曲和Br—Y键的拉长及红移单电子溴键复合物的产生. 考察了电子受体中不同取代基, C(spⁿ)-Br杂化及溶剂的存在对复合物作用的影响, 将单电子氢键, 单电子卤键和单电子锂键的作用强度做了对比, 进一步对Popelier提出的氢键体系中的前三个重要拓扑指标在单电子溴键体系中的重现性进行了探讨.     

Isomerism in rhodium(I) N,S-donor heteroscorpionates: ring substituent and ancillary ligand effects

The heteroscorpionate ligands [HB(taz)(2)(pz(R))](-) (pz(R) = pz, pz(Me2), pz(Ph)) and [HB(taz)(pz)(2)](-), synthesised from the appropriate potassium hydrotris(pyrazolyl)borate salt and 4-ethyl-3-methyl-5-thioxo-1,2,4-triazole (Htaz), react with [{Rh(cod)(μ-Cl)}(2)] to give [Rh(cod)Tx] {Tx = HB(taz)(2)(pz), HB(taz)(2)(pz(Me2)), HB(taz)(2)(pz(Ph)), HB(taz)(pz)(2)}; the heteroscorpionate rhodaboratrane [Rh{B(taz)(2)(pz(Me2))}{HB(taz)(2)(pz(Me2))}] is the only isolable product from the reaction of [{Rh(nbd)(μ-Cl)}(2)] with K[HB(taz)(2)(pz(Me2))]. Carbonylation of the cod complexes gave a mixture of [Rh(CO)(2)Tx] and [(RhTx)(2)(μ-CO)(3)] which reacts with PR(3) to give [Rh(CO)(PR(3))Tx] (R = Cy, NMe(2), Ph, OPh). In the solid state the complexes are square planar with the particular structure dependent on the steric and/or electronic properties of the scorpionate and ancillary ligands. The complex [Rh(cod){HB(taz)(pz)(2)}] has the heteroscorpionate κ(2)[N(2)]-coordinated to rhodium with the B-H bond directed away from the rhodium square plane while [Rh(cod){HB(taz)(2)(pz(Me2))}] is κ(2)[SN]-coordinated, with the B-H bond directed towards the metal. The complexes [Rh(CO)(PPh(3)){HB(taz)(2)(pz)}] and [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Me2))}] are also κ(2)[SN]-coordinated but with the pyrazolyl ring cis to PPh(3); in the former the B-H bond is directed towards rhodium while in the latter the ring is pseudo-parallel to the rhodium square plane, as also found for [Rh(CO)(2){HB(taz)(2)(pz(Me2))}]. The analogues [Rh(CO)(PR(3)){HB(taz)(2)(pz(Me2))}] (R = Cy, NMe(2)) have the phosphines trans to the pyrazolyl ring. Uniquely, [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Ph))}] is κ(2)[S(2)]-coordinated. A qualitative mechanism is given for the rapid ring-exchange, and hence isomerisation, observed in solution.     

What is the best bonding model of the (σ-H-BR) species bound to a transition metal? Bonding analysis in complexes [(H)2Cl(PMe3)2M(σ-H-BR)] (M = Fe, Ru, Os)

Density Functional Theory calculations have been performed for the σ-hydroboryl complexes of iron, ruthenium and osmium [(H)(2)Cl(PMe(3))(2)M(σ-H-BR)] (M = Fe, Ru, Os; R = OMe, NMe(2), Ph) at the BP86/TZ2P/ZORA level of theory in order to understand the interactions between metal and HBR ligands. The calculated geometries of the complexes [(H)(2)Cl(PMe(3))(2)Ru(HBNMe(2))], [(H)(2)Cl(PMe(3))(2)Os(HBR)] (R = OMe, NMe(2)) are in excellent agreement with structurally characterized complexes [(H)(2)Cl(P(i)Pr(3))(2)Os(σ-H-BNMe(2))], [(H)(2)Cl(P(i)Pr(3))(2)Os{σ-H-BOCH(2)CH(2)OB(O(2)CH(2)CH(2))}] and [(H)(2)Cl(P(i)Pr(3))(2)Os(σ-H-BNMe(2))]. The longer calculated M-B bond distance in complex [(H)(2)Cl(PMe(3))(2)M(σ-H-BNMe(2))] are due to greater B-N π bonding and as a result, a weaker M-B π-back-bonding. The B-H2 bond distances reveal that (i) iron complexes contain bis(σ-borane) ligand, (ii) ruthenium complexes contain (σ-H-BR) ligands with a stretched B-H2 bond, and (iii) osmium complexes contain hydride (H2) and (σ-H-BR) ligands. The H-BR ligands in osmium complexes are a better trans-directing ligand than the Cl ligand. Values of interaction energy, electrostatic interaction, orbital interaction, and bond dissociation energy for interactions between ionic fragments are very large and may not be consistent with M-(σ-H-BR) bonding. The EDA as well as NBO and AIM analysis suggest that the best bonding model for the M-σ-H-BR interactions in the complexes [(H)(2)Cl(PMe(3))(2)M(σ-H-BR)] is the interaction between neutral fragments [(H)(2)Cl(PMe(3))(2)M] and [σ-H-BR]. This becomes evident from the calculated values for the orbital interactions. The electron configuration of the fragments which is shown for C in Fig. 1 experiences the smallest change upon the M-σ-H-BR bond formation. Since model C also requires the least amount of electronic excitation and geometry changes of all models given by the ΔE(prep) values, it is clearly the most appropriate choice of interacting fragments. The π-bonding contribution is 14-22% of the total orbital contribution.     

Theoretical study of the interaction mechanism of single-electron halogen bond complexes H3C⋯Br-Y (Y = H, CN, NC, CCH, C2H3)

The characteristics and structures of single-electron halogen bond complexes [H₃C?Br-Y (Y = H, CCH, CN, NC, C₂H₃)] have been investigated by theoretical calculation methods. The geometries were optimized and frequencies calculated at the B3LYP/6-311++G** level. The interaction energies were corrected for basis set superposition error (BSSE) and the wavefunctions obtained by the natural bond orbital (NBO) and atom in molecule (AIM) analyses at the MP2/6-311++G** level. For each H₃C?Br-Y complex, a single-electron Br bond is formed between the unpaired electron of the CH₃ (electron donor) radical and the Br atom of Br-Y (electron acceptor); this kind of single-electron bromine bond also possesses the character of a “three-electron bond”. Due to the formation of the single-electron Br bond, the C-H bonds of the CH₃ radical bend away from the Br-Y moiety and the Br-Y bond elongates, giving red-shifted single-electron Br bond complexes. The effects of substituents, hybridization of the carbon atom, and solvent on the properties of the complexes have been investigated. The strengths of single-electron hydrogen bonds, single-electron halogen bonds and single-electron lithium bonds have been compared. In addition, the single-electron halogen bond system is discussed in the light of the first three criteria for hydrogen bonding proposed by Popelier.     

Synthesis, characterization and antioxidant activity of new copper(I) complexes of scorpionate and water soluble phosphane ligands

New copper(I) complexes have been synthesised from the reaction of CuCl with potassium hydrotris(4-bromo-1H-pyrazol-1-yl)borate, KTp4Br or lithium bis(3,5-dimethylpyrazol-1-yl)acetate, Li[L2CO2] ligands and 4- or 2-(diphenylphosphane)benzoic acid or tris(m-sulfonatophenyl)posphine trisodium salt (TPPTS) coligands. The complexes obtained have been characterized by elemental analyses and FT-IR in the solid state, and by NMR (1H and 31P[1H]) and electrospray mass spectrometry (ESI-MS) in solution. Single crystal structural characterisation was undertaken for the [Cu[PPh2(4-C6H4COOH)](Tp4Br)] derivative, an interesting dimeric supramolecular assembly. A chemiluminescence study has demonstrated the superoxide scavenging activity of these new copper complexes. The Comet assay was used to evaluate the impairment of DNA in rat epithelial cells exposed to different reactive nitrogen species. In addition, the same complexes were included in this study to determine their efficacy as antioxidants in mitigating oxidative DNA damage. The parameter tail moment, used as an index of DNA damage, showed that the complex [Cu[PPh2(4-C6H4COOH)](Tp4Br)] remarkably inhibited DNA strand breaks induced by the different nitrogen oxide species. The other copper complexes under study showed a different ability to reduce tail moment values depending on the type of RNOS donor used.     

Steric Effects on the Structures,Reactivity, and Coordination Chemistry of Tris(2‐pyridyl)aluminates

Introducing substituents in the 6‐position of the 2‐pyridyl rings of tris(pyridyl)aluminate anions, of the type [EtAl(2‐py′)₃]^? (py′=a substituted 2‐pyridyl group), has a large impact on their metal coordination characteristics. This is seen most remarkably in the desolvation of the THF solvate [EtAl(6‐Me‐2‐py)₃Li?THF] to give the monomer [EtAl(6‐Me‐2‐py)₃Li] ( 1 ), containing a pyramidal, three‐coordinate Li⁺ cation. Similar monomeric complexes are observed for [EtAl(6‐CF₃‐2‐py)₃Li] ( 2 ) and [EtAl(6‐Br‐2‐py)₃Li] ( 3 ), which contain CF₃ and Br substituents (R). This steric influence can be exploited in the synthesis of a new class of terminal Al?OH complexes, as is seen in the controlled hydrolysis of 2 and 3 to give [EtAl(OH)(6‐R‐2‐py)₂]^? anions, as in the dimer [EtAl(OH)(6‐Br‐2‐py)₂Li]₂ ( 5 ). Attempts to deprotonate the Al?OH group of 5 using Et₂Zn led only to the formation of the zincate complex [LiZn(6‐Br‐py)₃]₂ ( 6 ), while reactions of the 6‐Br substituted 3 and the unsubstituted complex [EtAl(2‐py)₃Li] with MeOH give [EtAl(OMe)(6‐Br‐2‐py)₂Li]₂ ( 7 ) and [EtAl(OMe)(2‐py)₂Li]₂ ( 8 ), respectively, having similar dimeric arrangements to 5 . The combined studies presented provide key synthetic methods for the functionalization and elaboration of tris(pyridyl)aluminate ligands.     

Bonding trends of thiosemicarbazones in mononuclear and dinuclear copper(I) complexes: syntheses, structures, and theoretical aspects

Reactions of copper(I) halides with a series of thiosemicarbazone ligands (Htsc) in the presence of triphenylphosphine (Ph(3)P) in acetonitrile have yielded three types of complexes: (i) monomers, [CuX(eta1-S-Htsc)(Ph3P)2] [X, Htsc = I (1), Br (2), benzaldehyde thiosemicarbazone (Hbtsc); I (5), Br (6), Cl (7), pyridine-2-carbaldehyde thiosemicarbazone (Hpytsc)], (ii) halogen-bridged dimers, [Cu2(mu2-X)2(eta1-S-Htsc)2(Ph3P)2] [X, Htsc = Br (3), Hbtsc; I (8), furan-2-carbaldehyde thiosemicarbazone (Hftsc); I (11), thiophene-2-carbaldehyde thiosemicarbazone (Httsc)], and (iii) sulfur-bridged dimers, [Cu2X2(mu2-S-Htsc)2(Ph3P)2] [X, Htsc = Cl (4), Hbtsc; Br (9), Cl (10), pyrrole-2-carbaldehyde thiosemicarbazone (Hptsc); Br (12), Httsc]. All of these complexes have been characterized with the help of elemental analysis, IR, 1H, 13C, or 31P NMR spectroscopy, and X-ray crystallography (1-12). In all of the complexes, thiosemicarbazones are acting as neutral S-donor ligands in eta()S or mu2-S bonding modes. The Cu...Cu separations in the Cu(mu2-X)2Cu and Cu(mu2-S)2Cu cores lie in the ranges 2.981(1)-3.2247(6) and 2.813(1)-3.2329(8) Angstroms, respectively. The geometry around each Cu center in monomers and dimers may be treated as distorted tetrahedral. Ab initio density functional theory calculations on model monomeric and dimeric complexes of the simplest thiosemicarbazone [H2C=N-NH-C(S)-NH2, Htsc] have revealed that monomers and halogen-bridged dimers have similar stability and that sulfur-bridged dimers are stable only when halogen atoms are engaged in hydrogen bonding with the solvent of crystallization or H2O molecules.     

Double-strand DNA cleavage by copper complexes of 2,2'-dipyridyl with electropositive pendants

Two highly charged cationic copper(II) complexes have been synthesized and characterized structurally and spectroscopically: [Cu(L1)2(Br)](ClO4)5 (1) and [Cu(L2)2(Br)](ClO4)5 (2) (L1= 5,5'-di(1-(triethylammonio)methyl)-2,2'-dipyridyl cation and L2= 5,5'-di(1-(tributylammonio)methyl)-2,2'-dipyridyl cation bidentate ligands). X-Ray structures show that Cu(II) ions in both complexes have a trigonal-bipyramidal CuN4Br-configuration. Two nitrogen atoms of the electropositive pendants and coordinated bromine atom basically array in a straight line. Their close distances of N[dot dot dot]Br atoms are 5.772 and 5.594 A, respectively, which is comparable to that of adjacent phosphodiesters in B-form DNA (ca. 6 A). In the absence of reducing agent, supercoiled plasmid DNA cleavage by the complexes has been performed and their hydrolytic mechanisms have been investigated. The pseudo-Michaelis-Menten kinetic parameters (kcat), 4.15 h(-1) for 1, 0.43 h(-1) for 2 and 0.61 h(-1) for [Cu(bipy)(NO3)2], were obtained. This result indicates that 1 exhibits markedly higher nuclease activity than its corresponding analogues. The high ability of DNA cleavage for 1 is attributed to the effective cooperation of the metal moiety and two positive pendants since the array of linear tri-binding sites matches with one of three phosphodiester backbones of nucleic acid.     

New class of oligonuclear platinum-thallium compounds with a direct metal-metal bond. 5. Structure determination of heterodimetallic cyano complexes in aqueous solution by EXAFS and vibrational spectroscopy

The structures of three closely related heterodimetallic cyano complexes, [(NC)(5)Pt-Tl(CN)(n)()](n)()(-) (n = 1-3), formed in reactions between [Pt(II)(CN)(4)](2)(-) and Tl(III) cyano complexes, have been studied in aqueous solution. Multinuclear NMR data ((205)Tl, (195)Pt, and (13)C) were used for identification and quantitative analysis. X-ray absorption spectra were recorded at the Pt and Tl L(III) edges. The EXAFS data show, after developing a model describing the extensive multiple scattering within the linearly coordinated cyano ligands, short Pt-Tl bond distances in the [(NC)(5)Pt-Tl(CN)(n)()](n)()(-) complexes: 2.60(1), 2.62(1), and 2.64(1) A for n = 1-3, respectively. Thus, the Pt-Tl bond distance increases with increasing number of cyano ligands on the thallium atom. In all three complexes the thallium atom and five cyano ligands, with a mean Pt-C distance of 2.00-2.01 A, octahedrally coordinate the platinum atom. In the hydrated [(NC)(5)Pt-Tl(CN)(H(2)O)(4)](-) species the thallium atom coordinates one cyano ligand, probably as a linear Pt-Tl-CN entity with a Tl-C bond distance of 2.13(1) A, and possibly four loosely bound water molecules with a mean Tl-O bond distance of about 2.51 A. In the [(NC)(5)Pt-Tl(CN)(2)](2)(-) species, the thallium atom probably coordinates the cyano ligands trigonally with two Tl-C bond distances at 2.20(2) A, and in [(NC)(5)Pt-Tl(CN)(3)](3)(-) Tl coordinates tetrahedrally with three Tl-C distances at 2.22(2) A. EXAFS data were reevaluated for previously studied mononuclear thallium(III)-cyano complexes in aqueous solution, [Tl(CN)(2)(H(2)O)(4)](+), [Tl(CN)(3)(H(2)O)], and [Tl(CN)(4)](-), and also for the solid K[Tl(CN)(4)] compound. A comparison shows that the Tl-C bond distances are longer in the dinuclear complexes [(NC)(5)Pt-Tl(CN)(n)()](n)()(-) (n = 1-3) for the same coordination number. Relative oxidation states of the metal atoms were estimated from their (195)Pt and (205)Tl chemical shifts, confirming that the [(NC)(5)Pt-Tl(CN)(n)()](n)()(-) complexes can be considered as metastable intermediates in a two-electron-transfer redox reaction from platinum(II) to thallium(III). Vibrational spectra were recorded and force constants from normal-coordinate analyses are used for discussing the delocalized bonding in these species.     

Synthesis and reactivity of (C6F5)3B-N-heterocycle complexes. 1. Generation of highly acidic sp3 carbons in pyrroles and indoles

The reaction of pyrroles and indoles with B(C(6)F(5))(3) and BCl(3) produces 1:1 B-N complexes containing highly acidic sp(3) carbons, for example, N-[tris(pentafluorophenyl)borane]-5H-pyrrole (1) and N-[tris(pentafluorophenyl)borane]-3H-indole (2), that are formed by a new formal N-to-C hydrogen shift, the mechanism of which is discussed. With some derivatives, restricted rotation around the B-N bond and/or the B-C bonds was observed by NMR techniques, and some rotational barriers were calculated from experimental data. The acidity of the sp(3) carbons in these complexes is shown by their ability to protonate NEt(3), with formation of pyrrolyl- and indolyl-borate ammonium salts. The driving force for this reaction is given by the restoration of the aromaticity of the heterocycle.     

Cluster core controlled reactions of substitution of terminal bromide ligands by triphenylphosphine in octahedral rhenium chalcobromide complexes

Reactions of rhenium chalcobromides Cs4[{Re6(mu3-S)8}Br6].2H2O, Cs3[{Re6(mu3-Se)8}Br6].2H2O, Cs3[{Re6(mu3-Q)7(mu3-Br)}Br6].H2O (Q = S, Se), and K2[{Re6(mu3-S)6(mu3-Br)2}Br6] with molten triphenylphosphine (PPh3) have resulted in a family of novel molecular hybrid inorganic-organic cluster compounds. Six octahedral rhenium cluster complexes containing PPh3 ligands with general formula [{Re6(mu3-Q)8-n(mu3-Br)n}(PPh3)4-nBrn+2] (Q = S, n = 0, 1, 2; Q = Se, n = 0, 1) have been synthesized and characterized by X-ray single-crystal diffraction and elemental analyses, 31P{1H} NMR, luminescent measurements, and quantum-chemical calculations. It was found that the number of terminal PPh3 ligands in the complexes is controlled by the composition and consequently by the charge of the cluster core {Re6Q8-nBrn}n+2. In crystal structures of the complexes with mixed chalcogen/bromine ligands in the cluster core all positions of a cube [Q8-nBrn] are ordered and occupied exclusively by Q or Br atoms. Luminescence characteristics of the compounds trans-[{Re6Q8}(PPh3)4Br2] and fac-[{Re6Se7Br}(PPh3)3Br3] (Q = S, Se) have been investigated in CH2Cl2 solution and the broad emission spectra in the range of 600-850 nm were observed.     

Synthesis and luminescence behaviour of novel heterodecanuclear silver(I)-rhenium(I) alkynyl complexes. X-ray crystal structures of [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Me2bpy)(CO)3]4](PF6)2 and [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Br2phen)(CO)3]4](PF6)2

A novel series of luminescent heterodecanuclear mixed-metal alkynyl complexes, [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(N--N)(CO)3]4](PF6)2, (N--N = tBu2bpy, Me2bpy, phen, Br2phen), have been successfully synthesized; the X-ray crystal structures of [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Me2bpy)(CO)3]4](PF6)2 and [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Br2phen)(CO)3]4](PF6)2 have also been determined.     

High-valent imido complexes of manganese and chromium corroles

The oxidation reaction of M(tpfc) [M = Mn or Cr and tpfc = tris(pentafluorophenyl)corrole] with aryl azides under photolytic or thermal conditions gives the first examples of mononuclear imido complexes of manganese(V) and chromium(V). These complexes have been characterized by NMR, mass spectrometry, UV-vis, EPR, elemental analysis, and cyclic voltammetry. Two X-ray structures have been obtained for Mn(tpfc)(NMes) and Cr(tpfc)(NMes) [Mes = 2,4,6-(CH(3))(3)C(6)H(2)]. Short metal-imido bonds (1.610 and 1.635 Angstroms) as well as nearly linear M-N-C angles are consistent with triple M triple-bond NR bond formation. The kinetics of nitrene [NR] group transfer from manganese(V) corroles to various organic phosphines have been defined. Reduction of the manganese(V) corrolato complex affords phosphine imine and Mn(III) with reaction rates that are sensitive to steric and electronic elements of the phosphine substrate. An analogous manganese complex with a variant corrole ligand containing bromine atoms in the beta-pyrrole positions, Mn(Br(8)tpfc)(NAr), has been prepared and studied. Its reaction with PEt(3) is 250x faster than that of the parent tpfc complex, and its Mn(V/IV) couple is shifted by 370 mV to a more positive potential. The EPR spectra of chromium(V) imido corroles reveal a rich signal at ambient temperature consistent with Cr(V) triple-bond NR (d(1), S = 1/2) containing a localized spin density in the d(xy) orbital, and an anisotropic signal at liquid nitrogen temperature. Our results demonstrate the synthetic utility of organic aryl azides in the preparation of mononuclear metal imido complexes previously considered elusive, and suggest strong sigma-donation as the underlying factor in stabilizing high-valent metals by corrole ligands.     

New bis-, tris- and tetrakis(pyrazolyl)borate ligands with 3-pyridyl and 4-pyridyl substituents: synthesis and coordination chemistry

The new ligands dihydrobis[3-(4-pyridyl)pyrazol-1-yl]borate [Bp(4py)]-, hydrotris[3-(4-pyridyl)pyrazol-1-yl]borate [Tp(4py)]-, tetrakis[3-(4-pyridyl)pyrazol-1-yl]borate [Tkp(4py)]-, dihydrobis[3-(3-pyridyl)pyrazol-1-yl]borate [Bp(3py)]-, hydrotris[3-(3-pyridyl)pyrazol-1-yl]borate [Tp(3py)]- and tetrakis[3-(3-pyridyl)pyrazol-1-yl]borate [Tkp(4py)]- are derivatives of the well known bis-, tris- and tetrakis-(pyrazolyl)borate cores, bearing 4-pyridyl or 3-pyridyl substituents attached to the pyrazolyl C3 positions. These pyridyl groups cannot chelate to the metal ions in the poly(pyrazolyl) cavity but are externally directed. Structural studies on a range of metal complexes show how, in many cases, coordination of these pendant pyridyl groups to the M(pyrazolyl)n core of an adjacent metal complex fragment results in formation of coordination oligomers or polymeric networks. [Tl(Bp(3py))], [Tl(Bp(4py))] and [Tl(Tp(4py))] form one-dimensional polymeric chains via coordination of one of their pendant pyridyl units to the Tl(I) centre of an adjacent complex fragment; in contrast, in [Tl(Tp(3py))] coordination of all three pendant pyridyl units to separate Tl(I) neighbours results in formation of a two-dimensional polymeric sheet. In [Tl(Tkp(3py))] and [Tl(Tkp(4py))] the Tl(I) is coordinated by two or three of the four pyrazolyl arms, respectively; bridging interactions of pendant 4-pyridyl groups with adjacent Tl(I) centres result in a two-dimensional sheet forming in each case. In Ag(Tkp(4py)) each Ag(I) ion is coordinated by two pyrazolyl rings, and two bridging pyridyl ligands from other complex units, resulting in a one-dimensional chain consisting of pairs of cross-linked zigzag chains. In contrast to these polymeric coordination networks, the structures of [Cu(Tp(4py))] and [(Tp(3py))Cd(CH3CO2)] are dimers, with a pendant pyridyl residue from the first metal centre attaching to a vacant coordination site on the second, and vice versa; these dimers are stabilised by pi-stacking interactions between sections of the two ligands. [Ni(Tp(3py))2] is monomeric, with an octahedral coordination geometry arising from two tris(pyrazolyl)borate chelates; the array of pendant 3-pyridyl groups is involved only in intramolecular hydrogen-bonding. [(Tp(4py))Re(CO)3] is also monomeric, with a facial arrangement of three pyrazolyl ligands and three carbonyls, with the pendant 4-pyridyl groups not further coordinated. [(Tp(2py))Re(CO)3], based on the related ligand hydrotris[3-(2-pyridyl)pyrazol-1-yl]borate, has a similar fac-(CO)3(pyrazolyl)3 coordination geometry.     

A hardwon dirhodium paddlewheel with guanidinate type (hpp) bridging ligands

We report a dirhodium paddlewheel compound which has an Rh2(5+) core enveloped by four guanidinate ligands and an axially coordinated bromine atom; Rh2(hpp)4Br crystallizes as a 1-D chain with a Rh-Rh distance of 2.430(3) è and a Rh-Rh bond order of 1.5 (hpp = the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2a]pyrimidine).