TY - JOUR
T1 - Donor-acceptor properties of bidentate phosphines. DFT study of nickel carbonyls and molecular dihydrogen complexes
AU - Flener Lovitt, Charity
AU - Frenking, Gernot
AU - Girolami, Gregory S.
PY - 2012/6/11
Y1 - 2012/6/11
N2 - Density functional theory (DFT) is used to investigate the geometries and metal-ligand bonding in nickel complexes of bidentate phosphines, NiX 2(R 2P(CH 2) nPR 2), where X = H, CO, n = 1-3, and R = H, Me, CF 3, Et, i-Pr, t-Bu, Ph, OMe, F. The net donor-acceptor properties of the phosphine ligands can be deduced from the computed frequency of the symmetric CO stretch of the Ni(CO) 2(R 2P(CH 2) nPR 2) carbonyl complexes. This frequency (in cm -1) can be estimated from the empirical expression ν(CO) = 1988 + -π B - 4n, where the sum is over the four substituents on the bidentate phosphine, π B is a substituent-dependent parameter, and n is the number of carbon atoms in the backbone (1 ≥ n ≥ 3). The deduced values of π B (in units of cm -1)-t-Bu (0.0), i-Pr (0.8), Et (3.0), Me (4.0), Ph (4.3), H (6.3), OMe (10.8), CF 3 (17.8), and F (18.3)-are generally similar to Tolman's electronic parameter π derived from nickel complexes of unidentate phosphines. For the NiH 2(R 2P(CH 2) nPR 2) hydride complexes, the global minimum is a nonclassical dihydrogen structure, irrespective of the nature of the phosphine. For bidentate phosphines that are strongly donating, a classical cis-dihydride structure lies higher in energy (in some cases, by only 0.4 kcal mol -1 above the global minimum). For phosphines that are less electron donating, the dihydride structure is no longer a local minimum but instead is an inflection point on the potential energy surface. Atoms in molecules (AIM) and natural bond order (NBO) analyses confirm that the nickel-dihydrogen interaction involves a three-center-two-electron bond. The Kohn-Sham molecular orbital diagram and energy decomposition analysis of these complexes show that metal to H 2 π back-donation is the dominant orbital component for phosphines with electron-donating substituents, whereas H 2 to metal σ donation is dominant for phosphines with electron-withdrawing substituents. The EDA results clearly indicate that long H-H distances are seen when the metal to H 2 π back-donation dominates over H 2 to M σ donation.
AB - Density functional theory (DFT) is used to investigate the geometries and metal-ligand bonding in nickel complexes of bidentate phosphines, NiX 2(R 2P(CH 2) nPR 2), where X = H, CO, n = 1-3, and R = H, Me, CF 3, Et, i-Pr, t-Bu, Ph, OMe, F. The net donor-acceptor properties of the phosphine ligands can be deduced from the computed frequency of the symmetric CO stretch of the Ni(CO) 2(R 2P(CH 2) nPR 2) carbonyl complexes. This frequency (in cm -1) can be estimated from the empirical expression ν(CO) = 1988 + -π B - 4n, where the sum is over the four substituents on the bidentate phosphine, π B is a substituent-dependent parameter, and n is the number of carbon atoms in the backbone (1 ≥ n ≥ 3). The deduced values of π B (in units of cm -1)-t-Bu (0.0), i-Pr (0.8), Et (3.0), Me (4.0), Ph (4.3), H (6.3), OMe (10.8), CF 3 (17.8), and F (18.3)-are generally similar to Tolman's electronic parameter π derived from nickel complexes of unidentate phosphines. For the NiH 2(R 2P(CH 2) nPR 2) hydride complexes, the global minimum is a nonclassical dihydrogen structure, irrespective of the nature of the phosphine. For bidentate phosphines that are strongly donating, a classical cis-dihydride structure lies higher in energy (in some cases, by only 0.4 kcal mol -1 above the global minimum). For phosphines that are less electron donating, the dihydride structure is no longer a local minimum but instead is an inflection point on the potential energy surface. Atoms in molecules (AIM) and natural bond order (NBO) analyses confirm that the nickel-dihydrogen interaction involves a three-center-two-electron bond. The Kohn-Sham molecular orbital diagram and energy decomposition analysis of these complexes show that metal to H 2 π back-donation is the dominant orbital component for phosphines with electron-donating substituents, whereas H 2 to metal σ donation is dominant for phosphines with electron-withdrawing substituents. The EDA results clearly indicate that long H-H distances are seen when the metal to H 2 π back-donation dominates over H 2 to M σ donation.
UR - http://www.scopus.com/inward/record.url?scp=84862152711&partnerID=8YFLogxK
U2 - 10.1021/om200456j
DO - 10.1021/om200456j
M3 - 文章
AN - SCOPUS:84862152711
SN - 0276-7333
VL - 31
SP - 4122
EP - 4132
JO - Organometallics
JF - Organometallics
IS - 11
ER -