TY - JOUR
T1 - A new look at the ylidic bond in phosphorus ylides and related compounds
T2 - Energy decomposition analysis combined with a domain-averaged fermi hole analysis
AU - Calhorda, Maria José
AU - Krapp, Andreas
AU - Frenking, Gernot
PY - 2007/4/19
Y1 - 2007/4/19
N2 - Geometries and bond dissociation energies of the ylide compounds H 2CPH3, H2CPMe3, H 2CPF3, (BH2)2-CPH3, H2CNH3, H2CAsH3, H 2SiPH3, and (BH2)2SiPH3 have been calculated using ab initio (MP2, CBS-QB3) and DFT (B3LYP, BP86) methods. The nature of the ylidic bond R2E1-E 2X3 was investigated with an energy decomposition analysis and with the domain-averaged Fermi hole (DAFH) analysis. The results of the latter method indicate that the peculiar features of the ylidic bond can be understood in terms of donor -acceptor interactions between closed-shell R 2E1 and E2X3 fragments. The DAFH analysis clearly shows that there are two bonding contributions to the ylidic bond. The strength of the donor and acceptor contributions to the attractive orbital interactions can be estimated from the energy decomposition analysis (EDA) calculations, which give also the contributions of the electrostatic attraction and the Pauli repulsion of the chemical bonding. The EDA and DAFH results clearly show that the orbital interactions take place through the singlet ground state of the R2E1 fragment where the donor orbital of E1 yields π-type back-donation while the E 2X3 lone-pair orbital yields a-type bonding. Both bonds are polarized toward E2X3 when E2 = P, while the σ-type bonding remains more polarized at E2X3 when E2 = N, As. This shows that the phosphorus ylides exhibit a particular bonding situation which is clearly different from that of the nitrogen and arsenic homologues. With ylides built around a P - C linkage, the π-acceptor strength of phosphorus and the σ-acceptor strength at carbon contribute to a double bond which is enhanced by electrostatic contributions. The strength of the σ and π components and the electrostatic attraction are then fine-tuned by the substituents at C and P, which yields a peculiar type of carbon-phosphorus bonding. The EDA data reveal that the relative strength of the ylidic bond may be determined not only by the R 2E1 → E2X3 π back-donation, but also by the electrostatic contribution to the bonding. The calculations of the R2E1-E2X3 bond dissociation energy using ab initio methods predict that the order of the bond strength is H2C-PMe3 > H2C-PF3 > H 2C-PH3 > (BH2)2C-PH3 > H2C-AsH3 > H2C-NH3 ∼ H2Si-PH3 ∼ (BH2)2Si-PH 3. The DFT methods predict a similar trend, but they underestimate the bond strength of (BH2)2CPH3.
AB - Geometries and bond dissociation energies of the ylide compounds H 2CPH3, H2CPMe3, H 2CPF3, (BH2)2-CPH3, H2CNH3, H2CAsH3, H 2SiPH3, and (BH2)2SiPH3 have been calculated using ab initio (MP2, CBS-QB3) and DFT (B3LYP, BP86) methods. The nature of the ylidic bond R2E1-E 2X3 was investigated with an energy decomposition analysis and with the domain-averaged Fermi hole (DAFH) analysis. The results of the latter method indicate that the peculiar features of the ylidic bond can be understood in terms of donor -acceptor interactions between closed-shell R 2E1 and E2X3 fragments. The DAFH analysis clearly shows that there are two bonding contributions to the ylidic bond. The strength of the donor and acceptor contributions to the attractive orbital interactions can be estimated from the energy decomposition analysis (EDA) calculations, which give also the contributions of the electrostatic attraction and the Pauli repulsion of the chemical bonding. The EDA and DAFH results clearly show that the orbital interactions take place through the singlet ground state of the R2E1 fragment where the donor orbital of E1 yields π-type back-donation while the E 2X3 lone-pair orbital yields a-type bonding. Both bonds are polarized toward E2X3 when E2 = P, while the σ-type bonding remains more polarized at E2X3 when E2 = N, As. This shows that the phosphorus ylides exhibit a particular bonding situation which is clearly different from that of the nitrogen and arsenic homologues. With ylides built around a P - C linkage, the π-acceptor strength of phosphorus and the σ-acceptor strength at carbon contribute to a double bond which is enhanced by electrostatic contributions. The strength of the σ and π components and the electrostatic attraction are then fine-tuned by the substituents at C and P, which yields a peculiar type of carbon-phosphorus bonding. The EDA data reveal that the relative strength of the ylidic bond may be determined not only by the R 2E1 → E2X3 π back-donation, but also by the electrostatic contribution to the bonding. The calculations of the R2E1-E2X3 bond dissociation energy using ab initio methods predict that the order of the bond strength is H2C-PMe3 > H2C-PF3 > H 2C-PH3 > (BH2)2C-PH3 > H2C-AsH3 > H2C-NH3 ∼ H2Si-PH3 ∼ (BH2)2Si-PH 3. The DFT methods predict a similar trend, but they underestimate the bond strength of (BH2)2CPH3.
UR - http://www.scopus.com/inward/record.url?scp=34247567056&partnerID=8YFLogxK
U2 - 10.1021/jp057320v
DO - 10.1021/jp057320v
M3 - 文章
AN - SCOPUS:34247567056
SN - 1089-5639
VL - 111
SP - 2859
EP - 2869
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 15
ER -