TY - JOUR
T1 - Role of coordination geometry in dictating the barrier to hydride migration in d6 square-pyramidal iridium and rhodium pincer complexes
AU - Findlater, Michael
AU - Cartwright-Sykes, Alison
AU - White, Peter S.
AU - Schauer, Cynthia K.
AU - Brookhart, Maurice
PY - 2011/8/10
Y1 - 2011/8/10
N2 - Syntheses of the olefin hydride complexes [(POCOP)M(H)(olefin)][BAr f 4 ] (6a-M, M = Ir or Rh, olefin = C 2 H 4 ; 6b-M, M = Ir or Rh, olefin = C 3 H 6 ; POCOP = 2,6-bis(di-tert-butylphosphinito)benzene; BAr f = tetrakis(3,5- trifluoromethylphenyl)borate) are reported. A single-crystal X-ray structure determination of 6b-Ir shows a square-pyramidal coordination geometry for Ir, with the hydride ligand occupying the apical position. Dynamic NMR techniques were used to characterize these complexes. The rates of site exchange between the hydride and the olefinic hydrogens yielded δG ‡ = 15.6 (6a-Ir), 16.8 (6b-Ir), 12.0 (6a-Rh), and 13.7 (6b-Rh) kcal/mol. The NMR exchange data also established that hydride migration in the propylene complexes yields exclusively the primary alkyl intermediate arising from 1,2-insertion. Unexpectedly, no averaging of the top and bottom faces of the square-pyramidal complexes is observed in the NMR spectra at high temperatures, indicating that the barrier
AB - Syntheses of the olefin hydride complexes [(POCOP)M(H)(olefin)][BAr f 4 ] (6a-M, M = Ir or Rh, olefin = C 2 H 4 ; 6b-M, M = Ir or Rh, olefin = C 3 H 6 ; POCOP = 2,6-bis(di-tert-butylphosphinito)benzene; BAr f = tetrakis(3,5- trifluoromethylphenyl)borate) are reported. A single-crystal X-ray structure determination of 6b-Ir shows a square-pyramidal coordination geometry for Ir, with the hydride ligand occupying the apical position. Dynamic NMR techniques were used to characterize these complexes. The rates of site exchange between the hydride and the olefinic hydrogens yielded δG ‡ = 15.6 (6a-Ir), 16.8 (6b-Ir), 12.0 (6a-Rh), and 13.7 (6b-Rh) kcal/mol. The NMR exchange data also established that hydride migration in the propylene complexes yields exclusively the primary alkyl intermediate arising from 1,2-insertion. Unexpectedly, no averaging of the top and bottom faces of the square-pyramidal complexes is observed in the NMR spectra at high temperatures, indicating that the barrier
M3 - Article
SP - 12274
EP - 12284
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
ER -