Site Selectivity and Reversibility in the Reactions of Titanium Hydrazides With Si-H, Si-X, C-X and H+ Reagents: Ti=N(α) 1,2-silane Addition, Nβ Alkylation, Nα Protonation and σ-bond Metathesis

Dalton Trans. 2012 Feb 28;41(8):2277-88. doi: 10.1039/c2dt12359b. Epub 2012 Jan 5.

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(N(i)Pr)(2)}(NNR(2)) (R = Me (1) or Ph (2)) and Cp*Ti{MeC(N(i)Pr)(2)}(NTol) (3) with silanes, halosilanes, alkyl halides and [Et(3)NH][BPh(4)]. Compound 1 underwent reversible Si-H 1,2-addition to Ti=N(α) with RSiH(3) (experimental ΔH ca. -17 kcal mol(-1)), and irreversible addition with PhSiH(2)X (X = Cl, Br). DFT found that the reaction products and certain intermediates were stabilised by β-NMe(2) coordination to titanium. The Ti-D bond in Cp*Ti{MeC(N(i)Pr)(2)}(D){N(NMe(2))SiD(2)Ph} underwent σ-bond metathesis with BuSiH(3) and H(2). Compound 1 reacted with RR'SiCl(2) at N(α) to transfer both Cl atoms to Ti; 2 underwent a similar reaction. Compound 3 did not react with RSiH(3) or alkyl halides but formed unstable Ti=N(α) 1,2-addition or N(α) protonation products with PhSiH(2)X or [Et(3)NH][BPh(4)]. Compound 1 underwent exclusive alkylation at N(β) with RCH(2)X (R = H, Me or Ph; X = Br or I) whereas protonation using [Et(3)NH][BPh(4)] occurred at N(α). DFT studies found that in all cases electrophile addition to N(α) (with or without NMe(2) chelation) was thermodynamically favoured compared to addition to N(β).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkylation
  • Binding Sites
  • Indicators and Reagents / chemistry
  • Ligands
  • Nitrogen / chemistry*
  • Protons*
  • Quantum Theory
  • Silanes / chemistry*
  • Silicon / chemistry*
  • Substrate Specificity
  • Titanium / chemistry*

Substances

  • Indicators and Reagents
  • Ligands
  • Protons
  • Silanes
  • Titanium
  • Nitrogen
  • Silicon