CU-63 NMR-STUDY OF COPPER(I) CARBONYL-COMPLEXES WITH VARIOUS HYDROTRIS(PYRAZOLYL)BORATES - CORRELATION BETWEEN CU-63 CHEMICAL-SHIFTS AND COSTRETCHING VIBRATIONS
S. Imai et al., CU-63 NMR-STUDY OF COPPER(I) CARBONYL-COMPLEXES WITH VARIOUS HYDROTRIS(PYRAZOLYL)BORATES - CORRELATION BETWEEN CU-63 CHEMICAL-SHIFTS AND COSTRETCHING VIBRATIONS, Inorganic chemistry, 37(12), 1998, pp. 3066-3070
Copper(I) carbonyl complexes with a series of hindered L-R1,L-R2 ligan
ds (L: hydrotris(pyrazolyl)borate, R1 and R2 are substituents at the 3
- and 5-positions of the pyrazole ring, respectively), (LCuCO)-Cu-R1,R
2 [R1, R2 = Me, Me (1), i-Pr, i-Pr (2), t-Bu, Me (3), t-Bu, i-Pr (4),
Ph, i-Pr (5), Ph, Ph (6)1 have been synthesized and characterized by]H
NMR and IR spectroscopy and elemental analysis. The molecular structu
res of 3 and 6 have been determined by X-ray crystallography. The elec
tronic structures of copper(I) sites are characterized by means of Cu-
63 NMR spectroscopy and by the C=O stretching vibration. The sharp Cu-
63 NMR signals are observed for (LCuCO)-Cu-R1,R2 complexes in toluene
at room temperature. The Cu-63 NMR Signals of copper(I) complexes with
alkyl-substituted ligands (1-4) are observed in lower field than thos
e of the phenyl derivatives (5, 6) correlating with the electron-densi
ty at the copper center. This argument is supported by the good correl
ation between the delta((CU)-C-63) value and C=O stretching vibration
which is a sensitive indicator of the extent of back-donation of the C
u d electrons to the antibonding C=O orbitals.