Bite Angle Effects of κ²<i>P</i>‑dppm vs κ²<i>P</i>‑dppe in Seven-Coordinate Complexes: A DFT Case Study

This paper predicts the effects of replacing dppm (bis­(diphenylphosphino)­methane) with dppe (1,2-bis­(diphenylphosphino)­ethane) in seven-coordinate organometallic complexes by employing density functional theory (DFT) computations for a case example: WI₂(CO)­(κ²P-dppm)­(η²:η²-nbd) (nbd = norbornadiene), an intermediate in the W­(II)-catalyzed ring-opening metathesis polymerization (ROMP) of nbd. Effects on both structure and ligand binding energy (i.e., reactivity) were investigated. For the known W–dppm complex (crystal structure provided here), of 37 energy-distinct stereoisomers found, only one low-energy stereoisomer is predicted, and it agrees with the known X-ray crystal structure, lending faith to the conformer search procedure. For the as yet unknown W–dppe complex, of 31 energy-distinct stereoisomers found, two low-energy stereoisomers are predicted. The computed DFT ligand binding energies {W–P, W–ene, W–CO, W⁺–I^–} are {9, 17, 44, 102} kcal mol^–1 for the W–dppm complex and {3, 15, 37, 95} for the W–dppe complex. The conclusion is that the increased PWP bite angle of dppe vs dppm will reduce <i>all</i> ligand binding energies due to increased interligand steric repulsion

Semicontinuum Solvation Modeling Improves Predictions of Carbamate Stability in the CO₂ + Aqueous Amine Reaction

Quantum chemistry computations with a semicontinuum (cluster + continuum) solvation model have been used to cure long-standing misprediction of aqueous carbamate anion energies in the industrially important CO₂ + aqueous amine reaction. Previous errors of over 10 kcal mol^–1 are revealed. Activation energies were also estimated with semicontinuum modeling, and a refined discussion of the competing hypothetical mechanisms for CO₂ + monoethanolamine (MEA) is presented. Further results are also presented to demonstrate that the basicity of an amine (aqueous proton affinity) correlates only with CO₂ affinity within an amine class: secondary amines have an extra CO₂ affinity that primary amines do not have