851267-86-2Relevant academic research and scientific papers
Thermodynamics, kinetics, and mechanism of (silox)3M(olefin) to (silox)3M(alkylidene) rearrangements (silox = tBu 3SiO; M = Nb, Ta)
Hirsekorn, Kurt F.,Veige, Adam S.,Marshak, Michael P.,Koldobskaya, Yelena,Wolczanski, Peter T.,Cundari, Thomas R.,Lobkovsky, Emil B.
, p. 4809 - 4830 (2007/10/03)
Olefin complexes (silox)3M(ole) (silox = tBu 3SiO; M = Nb (1-ole), Ta (2-ole); ole = C2H4, C2H3-Me, C2H3Et, C2H 3C6H4-p-X (X := OMe, H, CF3), C 2H3tBu, cC5H8, cC6H10, cC7H 10 (norbornene)) rearrange to alkylidene isomers (silox) 3M(alk) (M = Nb (1=alk), Ta (2=alk); alk = CHMe, CHEt, CH nPr, CHCH2C6H4-p-X (X = OMe, H, CF3 (Ta only)), CHCH2tBu, cC 5H8, cC6H10, cC7H10 (norbornylidene)). Kinetics and labeling experiments suggest that the rearrangement proceeds via a δ-abstraction on a silox CH bond by the β-olefin carbon to give (silox) 2RM(κ2-O,C-OStBu2CMe 2CH2) (M = Nb (4-R), Ta (6-R); R = Me, Et, nPr, nBu, CH2-CH2C6H4-p-X (X = OMe, H, CF3 (Ta only)), CH2CH2tBu, cC5H9, cC6H 11, cC7H11 (norbomyl)). A subsequent α-abstraction by the cylometalated "arm" of the intermediate on an α-CH bond of R generates the alkylidene 1=alk or 2=alk. Equilibrations of 1-ole with ole′ to give 1-ole′ and ole, and relevant calculations on 1-ole and 2-ole, permit interpretation of all relative ground and transition state energies for the complexes of either metal.
