Insights into the Metal–CO Bond in O₂M(η¹-CO) (M = Cr, Mo, W, Nd, and U) Complexes

Abstract

Investigations on the structures and bonding properties of metal carbonyl compounds provide fundamental understandings on the origin of small-molecule activations. Herein, the geometry and bonding trends of a series of isovalent metal oxocarbonyl complexes O 2 M(η 1 -CO) (M = Cr, Mo, W, Nd, and U) were studied by combined matrix-isolation infrared spectroscopy and advanced quantum chemical calculations. The title complexes present red shift of C−O stretching bands in the range from 122 to 244 cm −1 , indicating the difference of CO activation ability for the series of isovalent metal dioxides. Density functional theory calculations predict T-shaped structures with a C 2v symmetry for all the title molecules. O 2 Nd(η 1 -CO) bears little resemblance to the other complexes in bonding characters because of the weak interactions between the NdO 2 and CO moiety. For the other complexes, natural localized molecular orbital analysis reveals a gradual increase of covalent character in M−CO bonds along the metal series Cr → Mo → W→ U. Energy decomposition analysis with natural orbitals for chemical valence calculations demonstrates that the M−CO bonding patterns conform to the conventional Dewar−Chatt−Duncanson motif. The contributions from orbital interactions in total attractions increase from Cr (41.7%) to U (52.7%). The breakdown of the orbital term into pairwise interactions shows that contributions of the M ← CO σ donation decrease from Cr (59.2%) to U (28.4%), while the M → CO π* backdonation increases significantly from Cr (23.8%) to U (67.3%). The more effective overlap and the better energy matching of U 5f and U 6d valence orbitals with CO π* orbitals result in much stronger U → CO π backdonation than the other metal elements.

CO Oxidation to CO2 on Uranium Dioxide Molecules through Intermediate O2U(η1-CO)

“…The singly occupied NO with b 1 irreducible representation exhibits the overlap of the π* CO orbital with the hybrid U-5f/U-6d orbitals, which actually consist of 31.3% C-2p, 12.5% O L -2p, 44.9% U-6d π , 6.6% U-5f π , and 4.0% U-6p. This π bonding orbital indicates a typical U → CO π back-donation in the classical Dewar-Chatt-Duncanson (DCD) model. − The bonding patterns between the UO 2 fragment and CO ligand in O 2 U­(η 1 -CO) have been investigated previously by a combined energy decomposition analysis (EDA) , with the natural orbital chemical valence (NOCV) , method. Briefly, the orbital mixing Δ E orb (51.8%) makes a slightly larger contribution to the total interaction Δ E int between UO 2 and CO moieties than the electrostatic interaction Δ E elstat (45.9%).…”

“…The experimental details for investigating CO reactions with laser-ablated UO 2 molecules in solid argon matrices are similar to those in our previous works. 27,29 An Nd:YAG laser fundamental beam (1064 nm wavelength, <10 ns pulse width, and 10 Hz repetition rate) was focused onto a rotating ceramic UO 2 disc target (Φ10 mm*2 mm), which was fabricated by powder sintering for 6.5 h at 1700 K. 30 The typical laser power was 15−20 mJ/pulse. Notice that UO, UO 2 , and UO 3 molecules were produced simultaneously at varying concentrations during laser ablation.…”

“…For U oxocarbonyls, in particular, OU­(η 1 -CO) and O 2 U­(η 1 -CO) serve as the simplest prototypes for reacting on uranium oxide surfaces. Their spectra in solid matrices, geometries, and U–CO bonding patterns have been reported, − Nevertheless, the possibilities of catalytic CO oxidations in these oxocarbonyls are still under exploration.…”

Matrix-Isolation Infrared Spectra and Electronic Structure Calculations for Dinitrogen Complexes with Uranium Trioxide Molecules UO3(η1-NN)1–4

“…The UO 2 disc target with a size of Φ 10 mm × 2 mm was prepared by powder sintering at 1700 K for 6.5 h . The experimental details have been described previously. , A Nd:YAG laser fundamental beam (1064 nm, 10 Hz repetition rate, and 10 ns pulse width) with a typical laser power of 10–20 mJ/pulse was focused on the rotating uranium metal or UO 2 ceramic target. The laser-ablated U atoms or UO 3 molecules were co-deposited with an O 2 /N 2 (>99.99%, Messer Inc.) mixture or N 2 , respectively, in excess argon onto a 9 K KBr window for 40–60 min.…”

Biomimetic Frustrated Lewis Pair Catalysts for Hydrogenation of CO to Methanol at Low Temperatures

“…The activation of CO by metal complexes is a highly important field in chemistry, and it has been explained in terms of the Dewar−Chatt−Duncanson model, which involves the σdonation and dπ-back-donation interactions (Figure 5a). 79 In contrast, the CO activation by organic catalysts does not involve dπ-back-donation, and it is still unclear. In order to unveil the reasons for CO activation by the bioinspired FLP, the unusual 1,1-addition of CO was simulated.…”