Bite Angle Effects of κ<sup>2</sup><i>P</i>‑dppm vs κ<sup>2</sup><i>P</i>‑dppe
in Seven-Coordinate Complexes: A DFT Case Study
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Abstract
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: WI<sub>2</sub>(CO)(κ<sup>2</sup>P-dppm)(η<sup>2</sup>:η<sup>2</sup>-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<sup>+</sup>–I<sup>–</sup>} are {9, 17, 44, 102} kcal mol<sup>–1</sup> 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