Structural and electronic analysis of bimetallic thiolate complexes of group-5 transition metal ions

Abstract

The chemistry of group-5 transition metals, namely vanadium, niobium, and tantalum supported by thiolate ligand framework, has been described. Special emphasis has been given to the electronic and structural properties of binuclear thiolate complexes of group-5 metals exhibiting interesting coordination modes of the chelating thiolate ligands. The mild thermolysis of [(CH2S2)4B]Na5 with [Cp*VCl2]3 afforded the divanadium trithiocarbonate complex, [(Cp*V)2(μ-CS3-κ2S,S')(μ-H2CS2-κ2S'',S''')] (1) along with [{S(CH2S)2}VOCp*] (2). The single crystal X-ray structure of 1 illustrates that the trithiocarbonate and methanedithiolate ligands are symmetrically coordinated to two {Cp*V} units. However, reaction of the heavier group-5 metal precursor, [Cp*NbCl4] with [(CH2S2)4B]Na5 at 60 °C in toluene produced a bimetallic trithiolate complex [(Cp*Nb)2(μ-SCS2-κ1S:κ3C,S',S'')(μ-S)2] (3) along with [(Cp*Nb)2(μ,η2:η2-SH3B)(μ-S)(μ-H2CS2-κ2S,S')]. In a similar manner, [Cp*TaCl4] led to the formation of ditantalum thiolate complexes [(Cp*Ta)2(μ-S)(μ-S2CH2CHS2-κ2S:κ2S',S'')(μ-H)(μ-S2CH2-κ2S''',S'''')] (4) and [Cl(Cp*Ta)2(μ-H)(μ-S2CH2-κ2S,S')(μ-S)(μ-S2CH2-κ2S'':κ1S''')] (5) along with [(Cp*Ta)2(μ-S){μ-(BH2S)(CH2S)2(BS3)-κ2B:κ2S:κ4S',S'',S''',S''''}]. However, the reaction of LiBH4·THF with [Cp*TaCl4] followed by the thermolysis in the presence of S2C·PPh3 led to the formation of [(Cp*Ta)2(μ-S)(μ-S2CH2-κ2S,S')(μ-H)(μ-CHS3-κ2S'':κ2S''',S'''')] (6) along with [(Cp*Ta)2(μ-S2CH2-κ2S,S')2(μ-H)(μ,η2:η2-B2H5)] (I) and [(Cp*Ta)2(μ,η2:η2-B2H6)2] (II). Complex 3 is an example of trithiolate {CS3} stabilized bimetallic niobium complex. The (dimercaptomethyl)-methanedithiolate ligand (C2H3S4) in 4 is coordinated to both the tantalum centres via three sulfur donors and displayed exclusive bonding mode (μ,κ2S:κ2S',S''). Complex 5 consists of two methanedithiolate ligands (S2CH2) with different coordination towards the metal centres, whereas methanetrithiolate (HCS3) and methanedithiolate (S2CH2) units are symmetrically coordinated to both the tantalum centres in complex 6. This study demonstrates that the electronic properties of these complexes vary depending on the metal centres and thiolate ligands. This is reflected in the paramagnetic behaviour of the vanadium complex 1. In contrast, the niobium and tantalum thiolate complexes 3, 4, 5 and 6 are diamagnetic. Further, theoretical investigations provided the insights into the electronic structures and bonding of these group-5 metal thiolate complexes.