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Issue 8, 2012
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Site selectivity and reversibility in the reactions of titanium hydrazides with Si–H, Si–X, C–X and H+ reagents: Ti[double bond, length as m-dash]Nα 1,2-silane addition, Nβ alkylation, Nα protonation and σ-bond metathesis

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Abstract

We report a combined experimental and computational comparative study of the reactions of the homologous titanium dialkyl- and diphenylhydrazido and imido compounds Cp*Ti{MeC(NiPr)2}(NNR2) (R = Me (1) or Ph (2)) and Cp*Ti{MeC(NiPr)2}(NTol) (3) with silanes, halosilanes, alkyl halides and [Et3NH][BPh4]. Compound 1 underwent reversible Si–H 1,2-addition to Ti[double bond, length as m-dash]Nα with RSiH3 (experimental ΔH ca. −17 kcal mol−1), and irreversible addition with PhSiH2X (X = Cl, Br). DFT found that the reaction products and certain intermediates were stabilised by β-NMe2 coordination to titanium. The Ti–D bond in Cp*Ti{MeC(NiPr)2}(D){N(NMe2)SiD2Ph} underwent σ-bond metathesis with BuSiH3 and H2. Compound 1 reacted with RR′SiCl2 at Nα to transfer both Cl atoms to Ti; 2 underwent a similar reaction. Compound 3 did not react with RSiH3 or alkyl halides but formed unstable Ti[double bond, length as m-dash]Nα 1,2-addition or Nα protonation products with PhSiH2X or [Et3NH][BPh4]. Compound 1 underwent exclusive alkylation at Nβ with RCH2X (R = H, Me or Ph; X = Br or I) whereas protonation using [Et3NH][BPh4] occurred at Nα. DFT studies found that in all cases electrophile addition to Nα (with or without NMe2 chelation) was thermodynamically favoured compared to addition to Nβ.

Graphical abstract: Site selectivity and reversibility in the reactions of titanium hydrazides with Si–H, Si–X, C–X and H+ reagents: Ti [[double bond, length as m-dash]] Nα 1,2-silane addition, Nβ alkylation, Nα protonation and σ-bond metathesis

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Publication details

The article was received on 06 Dec 2011, accepted on 09 Dec 2011 and first published on 05 Jan 2012


Article type: Paper
DOI: 10.1039/C2DT12359B
Citation: Dalton Trans., 2012,41, 2277-2288

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    Site selectivity and reversibility in the reactions of titanium hydrazides with Si–H, Si–X, C–X and H+ reagents: Ti[double bond, length as m-dash]Nα 1,2-silane addition, Nβ alkylation, Nα protonation and σ-bond metathesis

    P. J. Tiong, A. Nova, A. D. Schwarz, J. D. Selby, E. Clot and P. Mountford, Dalton Trans., 2012, 41, 2277
    DOI: 10.1039/C2DT12359B

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