A pi-basic rhenium center that effects cyclohexene isomerization to a beta-agostic carbene ligand.
The molecule (PNPR)Re(H)4 (PNPR = (R2PCH2SiMe2)2N, R = iPr or cyclohexyl) reacts at 20 degrees C with 2 mol of cyclohexene to form equimolar cyclohexane and (PNPR)Re(H)2[=C(CH2)5]. This product is characterized by 1H, 13C, and 31P NMR and by X-ray diffraction as having one CH2 hydrogen (from a carbon located beta to Re) donating to the metal ("agostic CH"). This interaction occurs in preference to PNPR amide nitrogen pi-donation. DFT calculations confirm this agostic interaction, and show that the (PNPR)Re(H)2 fragment indeed reverses the greater stability of free olefin vs free carbene.
Ozerov
Oleg V
OV
Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA.
Watson
Lori A
LA
Pink
Maren
M
Caulton
Kenneth G
KG