Reactivity of the metalloligand [Pt2(µ-S)2(PPh3)4] toward tellurium(II) thiourea complexes: synthesis and structural characterization of the ditellurium(I) derivative [{Pt2(µ-S)2(PPh3)4}2Te2]2+

Abstract

Reaction of the platinum(II) sulfide metalloligand Pt₂(µ-S)₂(PPh₃)₄] with the tellurium(II) source TeCl₂(tu)₂ (tu?=?thiourea) is dependent on reaction conditions employed. In the presence of added acid, the dominant species observed in the electrospray ionization (ESI) mass spectrum is the tetraplatinum species {Pt₂(µ-S)₂(PPh₃)₄}₂Te₂]²⁺. This contains the Te₂²⁺ moiety and is related to the previously reported tellurium(I) dithiophosphinate analog (Ph₂PS₂)₂Te₂]. However, in the absence of acid, considerable degradation of the {Pt₂S₂} metalloligand occurs as evidenced by the formation of the mononuclear complex Pt{SC(NH₂)NH}(PPh₃)₂]⁺ containing a deprotonated thiourea ligand, together with other thiourea-containing ions, identified by ESI MS. Likewise, attempted use of a fully substituted thiourea, viz. Me₂NC(S)NMe₂ (tmtu) in TeCl₂(tmtu)₂, also resulted in degradation of the {Pt₂S₂} core and detection of the known complex (Ph₃P)₂PtCl{SC(NMe₂)₂}]⁺. The {Pt₂(µ-S)₂(PPh₃)₄}₂Te₂]²⁺ cation was isolated with several anions, and unequivocal confirmation of the structure of the complex was obtained by an X-ray structure determination on the BF₄^- salt, which shows the presence of the Te₂²⁺ unit, with the Te–Te bond bridged by two {Pt₂S₂} metalloligands. Density functional theory was used to further probe the Te₂²⁺ bonding interactions in {Pt₂(μ-S)₂(PPh₃)₄}₂Te₂]²⁺ and the previously reported (Ph₂PS₂)₂Te₂].