Understanding the effect of first-row transition metals on the structure and properties of cyclopentadienyl-stabilized 5-metalla-1,3,2,4-dithiadiazoles

The stability in the series of half-sandwich 5-(η⁵-cyclopentadienyl)-5-metalla-1,3,2,4-dithiadiazoles incorporating a first-row transition metal was investigated in function of the electron configuration of the M^III metal centre, at the DFT/B3LYP level of theory. Taking 5-(η⁵-cyclopentadienyl)-5-cobalta-1,3,2,4-dithiadiazole or CpCoS₂N₂, the only known and experimentally available compound in the series, as a reference, calculated electronic, thermodynamic, and geometric properties were combined with molecular orbital (MO) diagrams to investigate the relative stabilities of the systems. The results indicate that the stability of CpCoS₂N₂ is linked to a small (positive or even negative) charge on the metal, the occupation of the bonding MO involved in back donation, and the absence of electrons in high-lying antibonding MOs. Moving away from Co in either direction within the period leads to a decreased stability, except for CpVS₂N₂, which exhibits numerous stabilizing features similar to CpCoS₂N₂.