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  • Magnesium, N,N′-Bis(trimethylsi yl)benzamidinate  (1)
  • spectroelectrochemistry  (1)
  • 1
    ISSN: 0044-2313
    Keywords: Magnesium, N,N′-Bis(trimethylsi yl)benzamidinate ; synthesis ; spectroscopic data ; structure of magnesium bis[N,N′-bis(trimethylsilyl)benzamidinate] ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis of Magnesium Bis[N,N′ -bis(trimethylsilyl)benzamidinate] as both Bis(THF) and Benzonitrile AdductMagnesium bis[bis(trimethylsilyl)amide] 1, reacts with benzonitrile in toluene at room temperature to yield magnesium bis[N,N′-bis(trimethylsilyl)benzamidinate]-benzonitrile(1/1) 2. Addition of THF leads to a quantitative substitution of the benzonitrile ligand by two THF molecules. The performance of the addition reaction in THF yields magnesium bis[N,N′-bis(trimethylsilyl)benzamidinate] · THF(1/2) 3. The upper benzonitrile complex 2, crystallizes in the orthorhombic space group Pbcn with {a = 1383.2(2); b = 2589.1(4); c = 1133.7(1) pm; Z = 4}. The magnesium atom is coordinated distorted trigonal-bipyramidal, where the benzonitrile ligand lies within the equatorial plane. The axial bound nitrogen atom of the benzamidinate substitution shows with a value of 213 pm a slightly longer bond distance to the metal center than the one in the equatorial plane (210 pm). The steric strain within the benzamidinate ligand leads to an elongation of the silicon atoms out of the 1,3-diazaallylic moiety under an enlargement of the C—N—Si angle to 131°.
    Notes: Magnesium-bis[bis(trimethylsilyl)amid] 1, reagiert mit Benzonitril in Toluol bei Zimmertemperatur zu Magnesium-bis[N,N′-bis(trimethylsilyl)benzamidinat]-Benzonitril(1/1) 2. Der Benzonitriligand läßt sich durch Zugabe von THF quantitativ durch zwei Ethermoleküle ersetzen. Auch die Durchführung der Additionsreaktion in THF führt zum Magnesium-bis [N,N′ -bis(trimethylsilyl)benzaminidat]-THF(1/2) 3. Der erstgenannte Benzonitril-Komplex 2, kristallisiert in der orthorhombischen Raumgruppe Pbcn mit {a = 1383,2(2); b = 2589,1(4); c = 1133,7(1) pm; Z = 4}. Das Magnesiumatom weist verzerrt trigonal-bi-pyramidale Umgebung auf, wobei sich der Benzonitrilligand in der äquatorialen Ebene anordnet. Das in der axialen Position befindliche Stickstoffatom des Benzamidinat-Substituenten weist mit 213 pm einen um etwa 3 pm größeren Abstand zum Metallzentrum auf als dasjenige in der äquatorialen Ebene. Die sterischen Spannungen innerhalb des Benzamidinat-Liganden führen zur Auslenkung der Siliciumatome aus der 1,3-Diazaallylebene unter gleichzeitiger C—N—Si-Winkelaufweitung auf 131°.
    Additional Material: 3 Ill.
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  • 2
    ISSN: 0947-6539
    Keywords: charge transfer ; EPR spectroscopy ; organometallic compounds ; platinum compounds ; spectroelectrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In spite of their very similar cyclic voltammograms, absorption spectra, and solvatochromic behavior, the two 1,4-diazabutadiene title complexes exhibit markedly different photoreactivities and underlying electronic structures, as evident from absorption and EPR spectra of the persistent anion radical forms. The lowest excited state of the nonphotoreactive PtII system [(CyN=CH—CH=NCy)-PtMe2] has MLCT (metal-to-ligand charge-transfer, 5d → π*) character, and the EPR spectrum of the corresponding anion radical at 〈g〉 = 2.016 exhibits sizable metal/ligand orbital mixing. On the other hand, the structurally characterized PtIV complex [(CyN=CH—CH=NCy)-PtMe4] (C2/c; a = 2021.6(2), b = 805.3(1), c = 1254.2(1) pm; β = 111.05(1)°; V = 1905.7(4) × 106 pm3; Z = 4) has a lowlying photoreactive LLCT (ligand-to-ligand charge-transfer, σPt—C → π*) excited state in which the axial Pt—C bonds are activated, as already suggested by the longer Pt—C(ax) bonds (214.0(8) pm) relative to Pt—C(eq) in the ground state (204.5(5) pm). The anion radical of the PtIV complex has lost the long-wavelength absorption band in the visible; it shows a well-resolved EPR spectrum at 〈g〉 = 1.9945 with π-ligand and 195Pt hyperfine structure and a small g anisotropy. A qualitative MO scheme is presented to account for the similar frontier-orbital energy differences despite dissimilar underlying electronic structures.
    Additional Material: 7 Ill.
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