TY - JOUR
T1 - Is CO a Special Ligand in Organometallic Chemistry? Theoretical Investigation of AB, Fe(CO)4(AB), and Fe(AB)5 (AB=N2, CO, F, SiO)
AU - Radius, U.
AU - Bickelhaupt, F.M.
AU - Ehlers, A.W.
AU - Goldberg, N.
AU - Hoffmann, R.
PY - 1998
Y1 - 1998
N2 - Carbon monoxide, CO, is a ubiquitous ligand in organometallic and coordination chemistry. In the present paper we investigate the neutral isoelectronic molecules AB = N2, CO, BF, and SiO and their coordination in the model complexes Fe(CO)4AB and Fe(AB)5, using nonlocal density functional theory and a large, polarized STO basis set of triple-ζ quality (NL-SCF/TZ(2P)). Our aim is to get more insight into the ligating properties of SiO and BF in comparison to CO and N2. The computed 298 K Fe(CO)4−AB bond dissociation enthalpies of C3v-symmetric Fe(CO)4AB are 18.1, 42.3, 67.9, and 35.6 kcal/mol for N2, CO, BF, and SiO, respectively; the corresponding values for C2v-symmetric Fe(CO)4AB are comparable: 19.0, 42.3, 66.7, and 39.7 kcal/mol. Good, balanced σ donation (through 5σ) and π acceptance (through 2π) are what makes CO a good donor, of course. The gap between these frontier orbitals (5σ and 2π) becomes even smaller in SiO and BF. The analysis of the bonding mechanism of the Fe−AB bond shows that SiO is a better σ donor but a worse π acceptor ligand than CO and that BF should be superior to CO in terms of both σ donor and π acceptor properties. However, these polar ligands are therefore also more reactive; and more sensitive, e.g. to nucleophilic attack, because of a low-energy 2π LUMO. Our results suggest that BF and SiO should, in principle, be excellent ligands. We also find interesting side-on and O-bound local minima, not very unstable, for SiO bound to an Fe(CO)4 fragment.
AB - Carbon monoxide, CO, is a ubiquitous ligand in organometallic and coordination chemistry. In the present paper we investigate the neutral isoelectronic molecules AB = N2, CO, BF, and SiO and their coordination in the model complexes Fe(CO)4AB and Fe(AB)5, using nonlocal density functional theory and a large, polarized STO basis set of triple-ζ quality (NL-SCF/TZ(2P)). Our aim is to get more insight into the ligating properties of SiO and BF in comparison to CO and N2. The computed 298 K Fe(CO)4−AB bond dissociation enthalpies of C3v-symmetric Fe(CO)4AB are 18.1, 42.3, 67.9, and 35.6 kcal/mol for N2, CO, BF, and SiO, respectively; the corresponding values for C2v-symmetric Fe(CO)4AB are comparable: 19.0, 42.3, 66.7, and 39.7 kcal/mol. Good, balanced σ donation (through 5σ) and π acceptance (through 2π) are what makes CO a good donor, of course. The gap between these frontier orbitals (5σ and 2π) becomes even smaller in SiO and BF. The analysis of the bonding mechanism of the Fe−AB bond shows that SiO is a better σ donor but a worse π acceptor ligand than CO and that BF should be superior to CO in terms of both σ donor and π acceptor properties. However, these polar ligands are therefore also more reactive; and more sensitive, e.g. to nucleophilic attack, because of a low-energy 2π LUMO. Our results suggest that BF and SiO should, in principle, be excellent ligands. We also find interesting side-on and O-bound local minima, not very unstable, for SiO bound to an Fe(CO)4 fragment.
U2 - 10.1021/ic970897+
DO - 10.1021/ic970897+
M3 - Article
SN - 0020-1669
VL - 37
SP - 1080
EP - 1090
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 5
ER -