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

Abstract The stability in the series of half-sandwich 5-(η 5 -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-(η 5 -cyclopentadienyl)-5-cobalta-1,3,2,4-dithiadiazole or CpCoS 2 N 2 , 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 CpCoS 2 N 2 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 CpVS 2 N 2 , which exhibits numerous stabilizing features similar to CpCoS 2 N 2 .