Abstract
The influence of the hydrotris(pyrazolyl)borate (tpzb) ligand substituents on the electron delocalization of the copper(I) center with carbon monoxide and triphenylphosphine, i.e. the copper(I) carbonyl complexes, [Cu{HB(3,5- iPr 2pz) 3}(CO)] ( 1), [Cu{HB(3,5-Me 2pz) 3}(CO)] ( 2), [Cu{HB(pz) 3}(CO)] ( 3), [Cu{HB(3-CF 3-5-Mepz) 3}(CO)] ( 4), and the copper(I) triphenylphosphine complexes [Cu{HB(3,5- iPr 2pz) 3}(PPh 3)] ( 5), [Cu{HB(3-CF 3-5-Mepz) 3}(PPh 3)] ( 6), are studied by using paired interacting orbitals (PIO) analysis. Carbon monoxide is a weak σ-donor and strong π-acceptor ligand. The Cu(I)–CO interaction is entirely dominated by π back bonding between the two degenerate π∗ orbitals of carbon monoxide and two t 2 type d orbitals of copper(I) ion. This interaction is clearly expressed by two PIOs, PIO-2 and PIO-3, and the strength of this π-acceptability is estimated by the summation of their overlap populations (ΣOP). On the other hand, triphenylphosphine is a strong σ-donor ligand. The Cu(I)–P interaction is dominated by donation from the P atom to the copper(I) ion and expressed by PIO-1, and the strength of this donative interaction ( σ-donationability) is estimated by the overlap population of PIO-1. These results are consistent with experimental data of the C O stretching frequencies by IR spectroscopy and of 13C chemical shifts of 13C O and the broadness of the 31P signals of PPh 3 by 13C and 31P NMR spectroscopy.
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