TY - JOUR
T1 - Transition-metal complexes of tetrylones [(CO) 5W-E(PPh 3) 2] and tetrylenes [(CO) 5W-NHE] (E=C-Pb)
T2 - A theoretical study
AU - Nguyen, Thi Ai Nhung
AU - Frenking, Gernot
PY - 2012/10/1
Y1 - 2012/10/1
N2 - Quantum chemical calculations at the BP86/TZVPP//BP86/SVP level are performed for the tetrylone complexes [W(CO) 5-E(PPh 3) 2] (W-1 E) and the tetrylene complexes [W(CO) 5-NHE] (W-2 E) with E=C-Pb. The bonding is analyzed using charge and energy decomposition methods. The carbone ligand C(PPh 3) is bonded head-on to the metal in W-1 C, but the tetrylone ligands E(PPh 3) 2 are bonded side-on in the heavier homologues W-1 Si to W-1 Pb. The W-E bond dissociation energies (BDEs) increase from the lighter to the heavier homologues (W-1 C: D e=25.1 kcal mol -1; W-1 Pb: D e=44.6 kcal mol -1). The W(CO) 5←C(PPh 3) 2 donation in W-1 C comes from the σ lone-pair orbital of C(PPh 3) 2, whereas the W(CO) 5←E(PPh 3) 2 donation in the side-on bonded complexes with E=Si-Pb arises from the π lone-pair orbital of E(PPh 3) 2 (the HOMO of the free ligand). The π-HOMO energy level rises continuously for the heavier homologues, and the hybridization has greater p character, making the heavier tetrylones stronger donors than the lighter systems, because tetrylones have two lone-pair orbitals available for donation. Energy decomposition analysis (EDA) in conjunction with natural orbital for chemical valence (NOCV) suggests that the W-E BDE trend in W-1 E comes from the increase in W(CO) 5←E(PPh 3) 2 donation and from stronger electrostatic attraction, and that the E(PPh 3) 2 ligands are strong σ-donors and weak π-donors. The NHE ligands in the W-2 E complexes are bonded end-on for E=C, Si, and Ge, but side-on for E=Sn and Pb. The W-E BDE trend is opposite to that of the W-1 E complexes. The NHE ligands are strong σ-donors and weak π-acceptors. The observed trend arises because the hybridization of the donor orbital at atom E in W-2 E has much greater s character than that in W-1 E, and even increases for heavier atoms, because the tetrylenes have only one lone-pair orbital available for donation. In addition, the W-E bonds of the heavier systems W-2 E are strongly polarized toward atom E, so the electrostatic attraction with the tungsten atom is weak. The BDEs calculated for the W-E bonds in W-1 E, W-2 E and the less bulky tetrylone complexes [W(CO) 5-E(PH 3) 2] (W-3 E) show that the effect of bulky ligands may obscure the intrinsic W-E bond strength. Opposite bonding trends: Quantum chemical calculations suggest that the bond strength of W-E (E=C-Pb) in the experimentally yet unknown tetrylone complexes W-1 E increases for the heavier Group 14 elements from carbon to lead, whereas the W-E bond in the tetrylene complexes W-2 E becomes weaker for the heavier atoms. The heavier ligands prefer a side-on bonding mode in both series of compounds.
AB - Quantum chemical calculations at the BP86/TZVPP//BP86/SVP level are performed for the tetrylone complexes [W(CO) 5-E(PPh 3) 2] (W-1 E) and the tetrylene complexes [W(CO) 5-NHE] (W-2 E) with E=C-Pb. The bonding is analyzed using charge and energy decomposition methods. The carbone ligand C(PPh 3) is bonded head-on to the metal in W-1 C, but the tetrylone ligands E(PPh 3) 2 are bonded side-on in the heavier homologues W-1 Si to W-1 Pb. The W-E bond dissociation energies (BDEs) increase from the lighter to the heavier homologues (W-1 C: D e=25.1 kcal mol -1; W-1 Pb: D e=44.6 kcal mol -1). The W(CO) 5←C(PPh 3) 2 donation in W-1 C comes from the σ lone-pair orbital of C(PPh 3) 2, whereas the W(CO) 5←E(PPh 3) 2 donation in the side-on bonded complexes with E=Si-Pb arises from the π lone-pair orbital of E(PPh 3) 2 (the HOMO of the free ligand). The π-HOMO energy level rises continuously for the heavier homologues, and the hybridization has greater p character, making the heavier tetrylones stronger donors than the lighter systems, because tetrylones have two lone-pair orbitals available for donation. Energy decomposition analysis (EDA) in conjunction with natural orbital for chemical valence (NOCV) suggests that the W-E BDE trend in W-1 E comes from the increase in W(CO) 5←E(PPh 3) 2 donation and from stronger electrostatic attraction, and that the E(PPh 3) 2 ligands are strong σ-donors and weak π-donors. The NHE ligands in the W-2 E complexes are bonded end-on for E=C, Si, and Ge, but side-on for E=Sn and Pb. The W-E BDE trend is opposite to that of the W-1 E complexes. The NHE ligands are strong σ-donors and weak π-acceptors. The observed trend arises because the hybridization of the donor orbital at atom E in W-2 E has much greater s character than that in W-1 E, and even increases for heavier atoms, because the tetrylenes have only one lone-pair orbital available for donation. In addition, the W-E bonds of the heavier systems W-2 E are strongly polarized toward atom E, so the electrostatic attraction with the tungsten atom is weak. The BDEs calculated for the W-E bonds in W-1 E, W-2 E and the less bulky tetrylone complexes [W(CO) 5-E(PH 3) 2] (W-3 E) show that the effect of bulky ligands may obscure the intrinsic W-E bond strength. Opposite bonding trends: Quantum chemical calculations suggest that the bond strength of W-E (E=C-Pb) in the experimentally yet unknown tetrylone complexes W-1 E increases for the heavier Group 14 elements from carbon to lead, whereas the W-E bond in the tetrylene complexes W-2 E becomes weaker for the heavier atoms. The heavier ligands prefer a side-on bonding mode in both series of compounds.
KW - bonding analysis
KW - density functional calculations
KW - donor-acceptor systems
KW - energy decomposition analysis
KW - tetrylene
KW - tetrylone
UR - http://www.scopus.com/inward/record.url?scp=84867059671&partnerID=8YFLogxK
U2 - 10.1002/chem.201200741
DO - 10.1002/chem.201200741
M3 - 文章
AN - SCOPUS:84867059671
SN - 0947-6539
VL - 18
SP - 12733
EP - 12748
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 40
ER -