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), E½ox, and Hammett σp 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.