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.
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).
Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, UK OX1 3TA.
Pei Jen
PJ
Tiong
Ainara
A
Nova
Andrew D
AD
Schwarz
Jonathan D
JD
Selby
Eric
E
Clot
Philip
P
Mountford
D000478:Alkylation; D001665:Binding Sites; D007202:Indicators and Reagents / Q000737:chemistry; D008024:Ligands; D009584:Nitrogen / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D012821:Silanes / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry*; D013379:Substrate Specificity; D014025:Titanium / Q000737:chemistry*
D007202:Indicators and Reagents; D008024:Ligands; D011522:Protons; D012821:Silanes; D014025:Titanium; D009584:Nitrogen; D012825:Silicon