Synthesis, structure, and bonding of d${}^3$ molybdenum-oxo complexes

Reduction of d${}^2$ metal-oxo ions of the form [MO(PP)${}_2$Cl]${}^{+}$ (M=Mo, W; PP=chelating diphosphine) produces d${}^3$ MO(PP)${}_2$Cl complexes, which include the first isolated examples in group 6. The stability and reactivity of the MO(PP)${}_2$Cl compounds are found to depend upon the steric bulk of the phosphine ligands: derivatives with bulky phosphines that shield the oxo ligand are stable enough to be isolated, whereas those with phosphines that leave the oxo ligand exposed are more reactive and observed transiently. Magnetic measurements and DFT calculations on MoO(dppe)${}_2$Cl indicate the d${}^3$ compounds are low spin with a ${}^2$[(d${}_{xy}$)${}^2$(π*(MoO))${}^1$] configuration. X-ray crystallographic and vibrational-spectroscopic studies on d${}^2$ and d${}^3$ [MoO(dppe)${}_2$Cl]${}^{0/+}$ establish that the d${}^3$ compound possesses a reduced M-O bond order and significantly longer Mo-O bond, accounting for its greater reactivity. These results indicate that the oxo-centered reactivity of d${}^3$ complexes may be controlled through ligand variation. (© 2020 Wiley‐VCH Verlag GmbH and Co. KGaA, Weinheim)