Nitrogen-15 nuclear magnetic resonance spectroscopy and electronic effects in dinitrogen complexes of molybdenum and tungsten with trans nitrile and diphosphine ligands

Abstract

Nitrogen-15 chemical shifts and oxidation potentials are reported for the complexes trans-[M(¹⁵N₂)(NCR)(P–P)₂](A)[M = Mo or W; R = Me, Prⁿ, or 4-XC₆H₄(X = H, MeO, MeCO, or F); P–P = Ph₂PCH₂CH₂PPh₂ or Et₂PCH₂CH₂PEt₂]. Linear correlations are observed for values of δ(¹⁵N), E_½^ox, and Hammett σ_p parameters for the X substituent of the benzonitrile. The shielding of both nitrogens in the ¹⁵N₂ ligand decreases with increase of (σ+π) electron-releasing properties of the trans ligand on replacement of one N₂ in the complexes trans-[M(¹⁵N₂)₂(P–P)₂](B) by NCR. The shielding of (only) the ligating nitrogen of ¹⁵N₂ in (A) increases with increase of the σ-donor ability of the trans nitrile ligand as the R group is varied.