Transition‐Metal Complexes of Tetrylones [(CO)₅W‐E(PPh₃)₂] and Tetrylenes [(CO)₅W‐NHE] (E=C–Pb): A Theoretical Study

Abstract

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.

Structures, Energies, and Bonding Analysis of Monoaurated Complexes with N-Heterocyclic Carbene and Analogues

“…The calculated partial charges showed that the metal fragment AuCl in the complexes carried always a negative charge which increases from Au1-NHC (-0.31 e) to Au1-NHPb (-0.53 e). The amount of charge donation to the AuCl fragment is always smaller than the donation to other transition metal moieties such as W(CO) 5 and Mo(CO) 4 that carry the similar NHE Me ligands in the complexes which have been calculated in the previous papers (Nguyen & Frenking 2012;Nguyen et al 2014a;Nguyen et al 2014b) in which the more negative charges in transition metal fragments W(CO) 5 and Mo(CO) 4 are between -0.47 and -0.77 e from the lighter to the heavier homologues.…”

“…Figure 3 also shows that the energy level of the π orbital increased, whereas that of the σ orbital decreased as atom E became heavier. The trend of the energy levels of the energetically highest-lying σ and π orbitals of NHE ligand rationalize the preference of the heavier ligands NHSn to NHPb for side-on co-ordination to the metal, in which the σ-donation takes place through the π orbital of the ligand (Nguyen & Frenking 2012). The end-on coordination of the lighter homologues NHC to NHGe could be explained by various factors that also influence the bending angle α of the ligands ( Table 1).…”

“…There was a significant decrease from the carbene complex Au1-NHC (D e = 79.2 kcal/mol) to the silylene Au1-NHSi complex (D e = 67.0 kcal/mol) and continuous decrease for the BDEs of the heavier group-14 ligands (51.9 -42.7 kcal/mol). The calculations suggest that the NHC Me ligand in Au1-NHC is the strongest bonded while the heavier homologues Au1-NHE where E = Si, Ge, Sn, Pb have weaker bonds which are not much different compared with the BDEs of the complexes in the previous studies (Boehme & Frenking 1998;Nguyen & Frenking 2012). The trend of the theoretically predicted AuCl-carbene and analogues bond energy in this study was significantly higher than the calculated values for the borane-NHE Me complexes (D e = 59.8 -13.8 kcal/mol) (Nguyen et al 2015), the classical Fischer complex (CO) 5 W-CH(OH) (D e = 75.0 kcal/ mol) (Vyboishchikov & Frenking 1998) as well as the (CO) 5 W-carbene (D e = 54.4 kcal/ mol) and analogues (D e = 44.3 -25.5 kcal/mol) {(CO) 5 W-NHE with E = C -Pb} (Nguyen & Frenking 2012).…”

“…Note that the most important information which was provided by the EDA-NOCV calculations concerned the strength of the σ and π bonding. (Nguyen & Frenking 2012). Thus, the EDA-NOCV calculations showed that the Au-E bonding in the complexes Au1-NHC-Au1-NHPb had a small contribution which might come from NHE Me →AuCl π-donation and NHE Me →AuCl π-back-donation.…”

[MnBrL(CO)4] (L = Amidinatogermylene): Reductive Dimerization, Carbonyl Substitution, and Hydrolysis Reactions

“…XRD molecular structure of 5 (35% displacement ellipsoids; H atoms omitted for clarity). Selected bond lengths (Å) and angles (deg): Mn1−Mn2 2.8690(7), Mn1−Ge1 2.3271(6), Ge1−C14 1.999(4), Ge1−N1 1.998(2), Ge1−N2 1.982(3), N1−C2 1.474(4), N1−C4 1.324(4), N2−C4 1.328(4), N2−C11 1.465(4), C4−C5 1.488(4), Mn2−Ge2 2.3222(6); Mn1−Ge1−N1 116.97 (8), Mn1−Ge1−N2 121.23 (9), C14−Ge1−Mn1 127.2(1), C14−Ge1−N1 103.6(1), C14−Ge1−N2 105.0(1), N1−Ge1−N2 65.9(1), Ge1−N1−C4 92.0(2), Ge1−N2−C4 92.6(2), N1−C4−N2 109.5(3), Ge1−Mn1−Mn2 169.87(2), Ge2−Mn2− Mn1 172.48(2). 4 ] have not been experimentally observed for X = Ph and t Bu (in these cases eq.…”