- 29Si NMR Spectroscopy as a Probe of s- And f-Block Metal(II)-Silanide Bond Covalency
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We report the use of 29Si NMR spectroscopy and DFT calculations combined to benchmark the covalency in the chemical bonding of s- and f-block metal-silicon bonds. The complexes [M(SitBu3)2(THF)2(THF)x] (1-M: M = Mg, Ca, Yb, x = 0; M = Sm, Eu, x = 1) and [M(SitBu2Me)2(THF)2(THF)x] (2-M: M = Mg, x = 0; M = Ca, Sm, Eu, Yb, x = 1) have been synthesized and characterized. DFT calculations and 29Si NMR spectroscopic analyses of 1-M and 2-M (M = Mg, Ca, Yb, No, the last in silico due to experimental unavailability) together with known {Si(SiMe3)3}-, {Si(SiMe2H)3}-, and {SiPh3}-substituted analogues provide 20 representative examples spanning five silanide ligands and four divalent metals, revealing that the metal-bound 29Si NMR isotropic chemical shifts, ?Si, span a wide (?225 ppm) range when the metal is kept constant, and direct, linear correlations are found between ?Si and computed delocalization indices and quantum chemical topology interatomic exchange-correlation energies that are measures of bond covalency. The calculations reveal dominant s- and d-orbital character in the bonding of these silanide complexes, with no significant f-orbital contributions. The ?Si is determined, relatively, by paramagnetic shielding for a given metal when the silanide is varied but by the spin-orbit shielding term when the metal is varied for a given ligand. The calculations suggest a covalency ordering of No(II) > Yb(II) > Ca(II) ≈ Mg(II), challenging the traditional view of late actinide chemical bonding being equivalent to that of the late lanthanides.
- Basford, Annabel R.,Berryman, Victoria E. J.,Kaltsoyannis, Nikolas,Liddle, Stephen T.,Mills, David P.,Nodaraki, Lydia E.,Réant, Benjamin L. L.,Tuna, Floriana,Wooles, Ashley J.
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- NOVEL PYRIMIDINE NUCLEOSIDE COMPOUND OR ITS SALT
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A novel pyrimidine nucleoside compound represented by the following formula (1) : (wherein one of X and Y represents a cyano group, and the other represents a hydrogen atom; one of R1 and R2 represents a hydrogen atom, a carbonyl group having a C1-C6 alkyl group which has been mono-substituted by an amino group, or a group represented by (R3) (R4) (R5) Si-, and the other represents a silyl group represented by (R6) (R7) (R8) Si-, or R1 and R2 together form a 6-membered cyclic group represented by -Si(R9)(R10)-; R3, R4, R5, R6, R7, and R8 each represent an alkyl group, a cyclic alkyl group, an aryl group, or an alkyl group which has been substituted by one or two aryl groups; and R9 and R10 each represent an alkyl group) or a salt thereof. The novel pyrimidine nucleoside compound exhibits excellent anti-tumor effect as compared with existing pyrimidine nucleoside compounds.
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Page/Page column 21
(2008/06/13)
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- Reactivity of the Germaethene Me2Ge=C(SiMe3)2
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Germaethene Me2Ge=C(SiMe3)2 (2), generated as a reaction intermediate by thermal elimination of LiX from Me2XGe-CLi(SiMe3)2 or by thermal cycloreversion from the adduct 2*Ph2CO, combines with reactants a-b (e. g.MeO-H) under insertion into the a-b bond (formation of 4), with a=b-c-H (e. g.CH2=CR-CH2-H; R = H, Me, CMe=CH2) under ene reaction (formation of 19 - 21), and with ab 3-nMenSi), O=N=N or CH2=CR-CR=CH2 (R = H, Me)> under , , and cycloaddition (formation of 6, 7 or 9 - 14 or 17, 18).By comparison with the silaethene Me2Si=C(SiMe3)2 (1), 2 is less Lewis acidic and its double bond is less polar.
- Wiberg, Nils,Kim, Chung-Kyun
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p. 2980 - 2994
(2007/10/02)
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