Synthesis of main group, rare-earth, and d{sup 0} metal complexes containing beta-hydrogen

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A series of organometallic compounds containing the tris(dimethylsilyl)methyl ligand are described. The potassium carbanions KC(SiHMe{sub 2}){sub 3} and KC(SiHMe{sub 2}){sub 3}TMEDA are synthesized by deprotonation of the hydrocarbon HC(SiHMe{sub 2}){sub 3} with potassium benzyl. KC(SiHMe{sub 2}){sub 3}TMEDA crystallizes as a dimer with two types of three-center-two-electron KH- Si interactions. Homoleptic Ln(III) tris(silylalkyl) complexes containing β-SiH groups M{C(SiHMe{sub 2}){sub 3}}{sub 3} (Ln = Y, Lu, La) are synthesized from salt elimination of the corresponding lanthanide halide and 3 equiv. of KC(SiHMe{sub 2}){sub 3}. The related reactions with Sc yield bis(silylalkyl) ate-complexes containing either LiCl or KCl. The divalent calcium and ytterbium ... continued below

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Yan, Ka King May 2, 2013.

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  • Ames Laboratory
    Publisher Info: Ames Laboratory (AMES), Ames, IA (United States)
    Place of Publication: Ames, Iowa

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A series of organometallic compounds containing the tris(dimethylsilyl)methyl ligand are described. The potassium carbanions KC(SiHMe{sub 2}){sub 3} and KC(SiHMe{sub 2}){sub 3}TMEDA are synthesized by deprotonation of the hydrocarbon HC(SiHMe{sub 2}){sub 3} with potassium benzyl. KC(SiHMe{sub 2}){sub 3}TMEDA crystallizes as a dimer with two types of three-center-two-electron KH- Si interactions. Homoleptic Ln(III) tris(silylalkyl) complexes containing β-SiH groups M{C(SiHMe{sub 2}){sub 3}}{sub 3} (Ln = Y, Lu, La) are synthesized from salt elimination of the corresponding lanthanide halide and 3 equiv. of KC(SiHMe{sub 2}){sub 3}. The related reactions with Sc yield bis(silylalkyl) ate-complexes containing either LiCl or KCl. The divalent calcium and ytterbium compounds M{C(SiHMe{sub 2}){sub 3}}{sub 2}L (M = Ca, Yb; L = THF{sub 2} or TMEDA) are prepared from MI{sub 2} and 2 equiv of KC(SiHMe{sub 2}){sub 3}. The compounds M{C(SiHMe{sub 2}){sub 3}}{sub 2}L (M = Ca, Yb; L = THF{sub 2} or TMEDA) and La{C(SiHMe{sub 2}){sub 3}}{sub 3} react with 1 equiv of B(C{sub 6}F{sub 5}){sub 3} to give 1,3- disilacyclobutane {Me2Si-C(SiHMe2)2}2 and MC(SiHMe2)3HB(C6F5)3L, and La{C(SiHMe{sub 2}){sub 3}}{sub 2}HB(C{sub 6}F{sub 5}){sub 3}, respectively. The corresponding reactions of Ln{C(SiHMe{sub 2}){sub 3}}{sub 3} (Ln = Y, Lu) give the β-SiH abstraction product [{(Me{sub 2}HSi){sub 3}C}{sub 2}LnC(SiHMe{sub 2}){sub 2}SiMe{sub 2}][HB(C{sub 6}F{sub 5}){sub 3}] (Ln = Y, Lu), but the silene remains associated with the Y or Lu center. The abstraction reactions of M{C(SiHMe{sub 2}){sub 3}}{sub 2}L (M = Ca, Yb; L = THF{sub 2 }or TMEDA) and Ln{C(SiHMe{sub 2}){sub 3}}{sub 3} (Ln = Y, Lu, La) and 2 equiv of B(C{sub 6}F{sub 5}){sub 3} give the expected dicationic M{HB(C{sub 6}F{sub 5}){sub 3}}{sub 2}L (M = Ca, Yb; L = THF{sub 2} or TMEDA) and dicationic mono(silylalkyl) LnC(SiHMe{sub 2}){sub 3}{HB(C{sub 6}F{sub 5}){sub 3}}{sub 2} (Ln = Y, Lu, La), respectively. Salt metathesis reactions of Cp{sub 2}(NR{sub 2})ZrX (X = Cl, I, OTf; R = t-Bu, SiHMe{sub 2}) and lithium hydrosilazide ultimately afford hydride products Cp{sub 2}(NR{sub 2})ZrH that suggest unusual β-hydrogen elimination processes. A likely intermediate in one of these reactions, Cp{sub 2}Zr[N(SiHMe{sub 2})t-Bu][N(SiHMe{sub 2}){sub 2}], is isolated under controlled synthetic conditions. Addition of alkali metal salts to this zirconium hydrosilazide compound produces the corresponding zirconium hydride. However as conditions are varied, a number of other pathways are also accessible, including C-H/Si-H dehydrocoupling, γ-abstraction of a CH, and β-abstraction of a SiH. Our observations suggest that the conversion of (hydrosilazido)zirconocene to zirconium hydride does not follow the classical four-center β- elimination mechanism. Elimination and abstraction reactions dominate the chemistry of ligands containing β- hydrogen. In contrast, Cp{sub 2}Zr{N(SiHMe{sub 2}){sub 2}}H and Cp{sub 2}Zr{N(SiHMe{sub 2}){sub 2}}Me undergo selective γ-CH bond activation to yield the azasilazirconacycle Cp{sub 2Zr}{κ{sup 2}-N(SiHMe{sub 2})SiHMeCH{sub 2}}, even though there are reactive β-hydrogen available for abstraction. The β-SiH groups in metallacycle provide access to new pathways for sixteen-electron zirconium alkyl compounds, in which Cp{sub 2}Zr{κ{sup 2}-N(SiHMe{sub 2})SiHMeCH{sub 2}} undergoes a rare σ-bond metathesis reaction with ethylene. The resulting vinyl intermediate undergoes β-hydrogen abstraction to reform ethylene and a silanimine zirconium species that reacts with ethylene to give a metallacyclopentane as the isolated product. The pendent β-SiH in metallocycle also reacts with paraformaldehyde through an uncatalyzed hydrosilylation to form an exocyclic methoxysilyl moiety, while the zirconium-carbon bond in metallocycle is surprisingly inert toward formaldehyde. Still, the Zr-C moiety in metallocycle is available for chemistry, and it interacts with the carbon monoxide and strong electrophile B(C{sub 6}F{sub 5}){sub 3} to provide Cp{sub 2}Zr[κ{sup 2}- OC(=CH{sub 2})SiMeHN(SiHMe{sub 2})] and Cp{sub 2}Zr[N(SiHMe{sub 2})SiHMeCH{sub 2}B(C{sub 6}F{sub 5}){sub 3}]. Finally, the frustrated Lewis-pair 2,6-lutidine-B(C{sub 6}F{sub 5}){sub 3} adduct reacts with the intra-cyclic SiH to give a transient 2,6-lutidine-stabilized silicon cation [Cp{sub 2}ZrCH{sub 2}SiMe(2,6-Me{sub 2 }- NC{sub 6}H{sub 3})N(SiMe{sub 2}H)][HB(C{sub 6}F{sub 5}){sub 3}] that slowly rearranges to give Cp{sub 2}Zr[N(SiHMe{sub 2})SiHMeCH{sub 2}B(C{sub 6}F{sub 5}){sub 3}] and free 2,6-lutidine. Finally, we also demonstrated a β-elimination of a cationic zirconocene disilazide compound [Cp{sub 2}ZrN(SiHMe{sub 2}){sub 2}]{sup +} that is facilitated by DMAP (4-N,N-dimethylaminopyridine) to give [Cp{sub 2}ZrH{N(SiHMe{sub 2})(SiMe{sub 2DMAP})}]{sup +}. A formal insertion reaction of a Zr-R group of Cp{sub 2}ZrN(SiHMe{sub 2}){sub 2}R (R = H, alkyl, halide, alkoxide) into a silaimine, formed by reaction of the zirconocene silazide and B(C{sub 6}F{sub 5}){sub 3}, to give [Cp{sub 2}Zr{N(SiHMe{sub 2})(SiRMe{sub 2})]{sup +}. Thus, we also show the application of the β-elimination reaction in hydrosilylation of ketones and aldehydes.

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  • Report No.: IS-T 3091
  • Grant Number: DE-AC02-07CH11358
  • DOI: 10.2172/1082979 | External Link
  • Office of Scientific & Technical Information Report Number: 1082979
  • Archival Resource Key: ark:/67531/metadc828403

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  • May 2, 2013

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  • May 19, 2016, 9:45 a.m.

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  • Aug. 3, 2016, 6:47 p.m.

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Yan, Ka King. Synthesis of main group, rare-earth, and d{sup 0} metal complexes containing beta-hydrogen, thesis or dissertation, May 2, 2013; Ames, Iowa. (digital.library.unt.edu/ark:/67531/metadc828403/: accessed January 15, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.