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.