(Eta5-pentamethylcyclopentadienyl)rhodium and -iridium complexes with weakly and strongly coordinating anions: isolation and first X-ray molecular structures of the tris(solvent) complexes [(C5Me5)M(acetone)2(H2O)][BF4]2 (M = Rh, Ir)

Several novel pentamethylcyclopentadienyl complexes of general formula [(C5Me5)IrL3][BF4]2 were prepared including the tris(solvent) precursors [(C5Me5)M(acetone)2(H2O)][BF4]2 (M = Rh, Ir) (1a,b). The X-ray molecular structures of 1a,b were determined at low temperature. Complexes 1a,b are isostructural, and both compounds crystallize in the monoclinic space group P2(1)/c with a = 10.157(3) A, b = 14.038(9) A, c = 16.335(2) A, beta = 99.73(2) degrees, and Z = 4 for 1a and with a = 10.107(9) A, b = 13.994(16) A, c = 15.996(34) A, beta = 99.61(12) degrees, and Z = 4 for 1b. The coordinated water molecule is hydrogen bonded to both BF4(-) anions. Reaction of 1a,b with pyridine (py) afforded the related tris(pyridine) complexes [(C5Me5)M(eta1-(N)-py)3][BF4]2 (M = Rh, Ir) (2a,b). Complex 2b was characterized by X-ray crystallography, monoclinic space group P2(1)/c with a = 8.665(3) A, b = 19.687(7) A, c = 18.408(5) A, beta = 94.17(3) degrees, and Z = 4. Moreover, we prepared the novel neutral compounds (C5Me5)M(eta2-NO3)(eta1-NO3) (M = Rh, Ir) (4a,b) where the anions are bonded to the metal center instead of a coordinating solvent as confirmed by X-ray study on the iridium complex 4b. The latter crystallizes in the orthorhombic space group Pcab with a = 13.032(4) A, b = 14.370(11) A, c = 14.839(18) A, and Z = 8.     

General access to iminosugar C-glycoside building blocks by means of cross-metathesis: a gateway to glycoconjugate mimetics

[reaction: see text] Cross-metathesis reactions of alpha-1-C-allyl-1-deoxynojirimycin derivatives 7a,b and various functionalized alkenes mediated by Grubbs's catalyst 3 are reported. The reactions showed reasonable to very good yields and excellent E/Z selectivity. This methodology allows the efficient and convergent synthesis of iminosugar C-glycosides with a great degree of structural diversity in the aglycone, opening the way to a variety of new glycoconjugate mimetics of biological interest.     

Hexacyanometalate molecular chemistry: di-, tri-, tetra-, hexa- and heptanuclear heterobimetallic complexes; control of nuclearity and structural anisotropy

Following a bottom-up approach to nanomaterials, we present a rational synthetic route to high-spin and anisotropic molecules based on hexacyanometalate [M(CN)(6)](3-) cores. Part 1 of this series was devoted to isotropic heptanuclear clusters; herein, we discuss the nuclearity and the structural anisotropy of nickel(II) derivatives. By changing either the stoichiometry, the nature of the terminal ligand, or the counterion, it is possible to tune the nuclearity of the polynuclear compounds and therefore to control the structural anisotropy. We present the synthesis and the characterisation by mass spectrometry, X-ray crystallography and magnetic susceptibility of bi-, tri-, tetra-, hexa- and heptanuclear species [M(CN)(n)(CN-M'L)(6-n)](m+) (with n=0-5; M=Cr(III), Co(III), M'=Ni(II); L=pentadentate ligand). Thus, with M=Cr(III), d(3), S=3/2, a dinuclear complex [Cr(III)(CN)(5)(CN-NiL(n))](9+), (L(n)=polydentate ligand) was built and characterised, showing a spin ground state, S(G)=5/2, with a ferromagnetic interaction J(Cr,Cu)=+18.5 cm(-1). With M=Co(III) (d(6), S=0) were built di-, tri-, tetra-, hexa and hepanuclear CoNi species: CoNi, CoNi(2), CoNi(3), CoNi(5) and CoNi(6). By a first approximation, they behave as one, two, three, five and six isolated nickel(II) complexes, respectively, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'.     

Ultrasoft pseudopotentials for lanthanide solvation complexes: core or valence character of the 4f electrons

The 4f electrons of lanthanides, because of their strong localization in the region around the nucleus, are traditionally included in a pseudopotential core. This approximation is scrutinized by optimizing the structures and calculating the interaction energies of Gd(3+)(H(2)O) and Gd(3+)(NH(3)) microsolvation complexes within plane wave Perdew-Burke-Ernzerhof calculations using ultrasoft pseudopotentials where the 4f electrons are included either in the core or in the valence space. Upon comparison to quantum chemical MP2 and CCSD(T) reference calculations it is found that the explicit treatment of the 4f electrons in the valence shell yields quite accurate results including the required small spin polarization due to ligand charge transfer with only modest computational overhead.     

Design of neutral, mono- or di-cationic water-soluble trihydrazidophosphoradamantanes

The versatile behavior of a trihydrazidophosphoradamantane allowing the synthesis of a variety of neutral, mono- or di-cationic water-soluble molecules of potential interest for biphasic catalysis is reported.     

Production and reactions of organic-soluble lanthanide complexes of the monolacunary Dawson [alpha1-P2W17O61]10- polyoxotungstate

The incorporation of lanthanides into polyoxometalates provides entry to new classes of potentially useful materials that combine the intrinsic properties of both constituents. To utilize the [alpha1-Ln(H2O)4P2W17O61]7- species in applications of catalysis and development of luminescent materials, the chemistry of this family of lanthanide polyoxometalates in organic solvents has been developed. Organic-soluble polyoxometalate-lanthanide complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] (Ln = La(III), Sm(III), Eu(III), Yb(III)) were prepared and characterized by elemental analysis, acid-base titration, IR, 31P NMR, and mass spectrometry. The synthetic procedure involves a cation metathesis reaction in aqueous solution under strict pH control. A solid-liquid-phase transfer protocol yielded a unique species (TBA)8K3[Yb(alpha1-YbP2W17O61)2] with three ytterbium ions and two [alpha1-P2W17O61]10- polyoxotungstates. A centrosymmetric dimeric complex [{alpha1-La(H2O)4P2W17O61}2]14- was crystallized from aqueous solution and characterized by X-ray diffraction. ESI mass spectral analysis of the complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] shows that similar dimers exist in organic solution, in particular for the early lanthanides. Fragmentation in the mass spectrometer of the complexes from dry acetonitrile solution involves double protonation of an oxo ligand and loss of one water molecule. Low mass tungstate fragments combine into [(WO3)n]2- (n = 1-5) ions and their condensation products with phosphate. Reaction of TBA5H2[alpha1-Eu(H2O)4P2W17O61] with 1,10-phenanthroline or 2,2'-bipyridine showed an increase of the europium luminescence. This result is explained by the formation of a ternary complex of [alpha1-Eu(H2O)4P2W17O61]7- and two sensitizing ligands.     

Excited-state hydrogen-atom transfer along solvent wires: water molecules stop the transfer

Excited-state hydrogen-atom transfer (ESHAT) along a hydrogen-bonded solvent wire occurs for the supersonically cooled n = 3 ammonia-wire cluster attached to the scaffold molecule 7-hydroxyquinoline (7HQ) [Tanner, C.; et al. Science 2003, 302, 1736]. Here, we study the analogous three-membered solvent-wire clusters 7HQ.(NH3)n.(H2O)m, n + m = 3, using resonant two-photon ionization (R2PI) and UV-UV hole-burning spectroscopies. Substitution of H2O for NH3 has a dramatic effect on the excited-state H-atom transfer: The threshold for the ESHAT reaction is approximately 200 cm(-1) for 7HQ.(NH3)3, approximately 350 cm(-1) for both isomers of the 7HQ.(NH3)2.H2O cluster, and approximately 600 cm(-1) for 7HQ.NH3.(H2O)2 but increases to approximately 2000 cm(-1) for the pure 7HQ.(H2O)3 water-wire cluster. To understand the effect of the chemical composition of the solvent wire on the H-atom transfer, the reaction profiles of the low-lying electronic excited states of the n = 3 pure and mixed solvent-wire clusters are calculated with the configuration interaction singles (CIS) method. For those solvent wires with an NH3 molecule at the first position, injection of the H atom into the wire can occur by tunneling. However, further H-atom transfer is blocked by a high barrier at the first (and second) H2O molecule along the solvent wire. H-atom transfer along the entire length of the solvent wire, leading to formation of the 7-ketoquinoline (7KQ) tautomer, cannot occur for any of the H2O-containing clusters, in agreement with experimentally observed absence of 7KQ fluorescence.