Browsing by Author "Verkade, John G."

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    Azasilatrane methanolysis pathways: stereoelectronic influences
    (1990) Gudat, Dietrich; Verkade, John G.
    Trigonal-bipyramidal azasilatranes of the type ZSi(NHCH2CH2)3N (Z = H, Me, OEt) solvolyze in MeOH to give N(CH2CH2NH2)3 (tren) and ZSi(OMe)3. Whereas intermediates in this reaction are not detected, ZSi[N-(SiR3)CH2CH2]3N species afford detectable intermediates of the type ZSi[N(SiR3)CH2CH2]n(NHCH2CH2)3-nN (n = 1, 2) before complete conversion to tren and ZSi(OMe)3 occurs. In cases where steric encumbrances weaken the Si-Nax bond in these molecules, monocyclic intermediates are detected. In contrast, methanolysis of HSi[N(BMe2)CH2CH2]3N gives N(CH2CH2NHBMe2)3 (and HSi-(OMe)3), which in the presence of CD3OD gives (CD3O)nSi(OMe)4-n and the novel adduct N-[CH2CH2NHD·B(OCD3)Me2]3. The possible steric and electronic influences of the equatorial substituents on the solvolysis pathways are discussed.
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    New azasilatranes: bidentate and tridentate coordination modes of the novel ligand EtOSi(Ph2PNCH2CH2)2(HNCH2CH2)N
    (1990) Gudat, Dietrich; Daniels, Lee M.; Verkade, John G.
    The synthesis and characterization of EtOSi(Ph2PNCH2CH)2(HNCH2CH2)N (ethoxy-N,N'·bis(di-phenylphosphino)azasilatrane, the title compound 3b) is reported. Its reactions with sulfur and MeI proceed easily via quaternization at the phosphorus sites to give the bis(phosphonium) salt and the bis(phosphine) sulfide, respectively. Synthesis and characterization of the coordination compounds (3b) Ni(CO)2, (3b) PtCl2, (3b) M(CO)4 (M = Mo, W), and (3b) M(CO)3 (M = Mo, W) give evidence for the existence of two possible coordination modes; one wherein 3b behaves as a bidentate (P,P') ligand and the other as a tridentate (P,P',O) ligand. The latter coordination mode provides a rare example of coordination of a silyl ether to a transition metal. NMR spectroscopic studies in solution and the solid state establish the presence of transannular Si-N bonding and hypercoordination at silicon. Solid-state 31P NMR spectra give direct evidence for the presence of a twisted, helically chiral conformation of the silatranyl cage, which in solution is lost as a consequence of rapid conformational mobility on the NMR time scale. These findings are further corroborated by the results of crystal structure determinations of the bis(phosphine) sulfide and (3b) PtCl2.
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    New azasilatranes: sterically induced transannular bond weakening and cleavage
    (1989) Gudat, Dietrich; Daniels, Lee M.; Verkade, John G.
    Silylation of azasilatrane I (R = R1 = R2 = H) with ClSiMe3/NEt3 gives disilylated I (R = R1 = Me3Si, R2 = H) (II), via the spectroscopically detected monosilylated intermediate. Treatment of II with BuLi gives the stable lithiated deriv. I (R = R1 = Me3Si, R2 = Li) which can be converted to I [R = R1 = Me3Si, R2 = Me, Me3Si (III)], via reaction with MeI or ClSiMe3, resp. The novel structure of III, inferred from NMR data and confirmed by x-ray means, features an Nax nitrogen in a nearly trigonal pyramidal stereochem. with an exceptionally long NaxSi bond [ 2.775(7)?]. Reaction of III with MeOSO2CF3 gives IV, the Nax methylated product.
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    New azasilatranes: synthesis and substitution reactions
    (1989) Gudat, Dietrich; Verkade, John G.
    The syntheses of new azasilatranes XSi(NRCH2CH2)3N (R = H, X = OEt (2f), OPh (2g); R = Me, X = H (8a), OEt (8b); R = SiMe3, X = H (9a)) via condensation reactions of tetraamines N(CH2CH2NHR)3 and substituted tris(dimethylamino)silanes, XSi(NMe2)3, are described. In the case of 2g, the required silane PhOSi(NMe2)3 was generated in situ from the reaction of PhOH and Si(NMe2)4. The chloroazasilatrane, 2h (R = H, X = Cl), whose synthesis was not feasible by the above method, was obtained by reaction of hydroazasilatrane, 2a (R = H, X = H) (V) with CCl4 in the presence of a platinum or palladium catalyst. Reaction of azasilatranes 2a and 2f with ClSiMe2R' (R' = H, Me, Ph) in the presence of triethylamine affords the silyl-substituted azasilatranes XSi(N(SiMe2R')CH2CH2)3N (X = H, R' = H (9b), Me (9a), Ph (9c); X = OEt, R' = H (14a)) and XSi(N(SiMe2R')CH2CH2)2NHCH2CH2N (X = OEt; R' = Me (14b), Ph (14d)), respectively, while no reaction was observed between either 2a or 2f and ClSiMe2-t-Bu. The new azasilatranes are characterized by 1H, 13C, and 29Si NMR spectroscopy, by high-resolution mass spectroscopy, and by an x-ray crystal structure determination in the case of 8b.
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    Novel properties of new phosphatranes and silatranes
    (1989) Gudat, Dietrich; Lensink, Cornelis; Schmidt, Harry; Xi, S.-K.; Verkade, John G.
    The synthesis of the new pro-phosphatranes YP(MeNCH2CH2)3N (Y = lone pair, 0, S, Se, BH3 and CH3+) containing four-coordinate phosphorus, and the tbp phosphatranes YP(MeNCH2CH2)3N (Y = H+, BrCH2 and Cl+) are reported. New azasilatranes of the type YSiRNCH2CH2)3N (R = H, Me, SiMe3; Y = H, OMe, OEt) are also reported and the results of nucleophilic substitution studies of the labile hydrogen on the equatorial nitrogens are given.