Bond Stretching and Redox Behavior in Coinage Metal Complexes of the Dichalcogenide Dianions [(SPh2P)2CEEC(PPh2S)2]2− (E=S, Se): Diradical Character of the Dinuclear Copper(I) Complex (E=S)

Synthesis of a labile sulfur-centred ligand, [S(H)C(PPh2S)2](-): structural diversity in lithium(i), zinc(ii) and nickel(ii) complexes

A high-yield synthesis of [Li{S(H)C(PPh2S)2}]2 [Li2·(3)2] was developed and this reagent was used in metathesis with ZnCl2 and NiCl2 to produce homoleptic complexes 4 and 5b in 85 and 93% yields, respectively. The solid-state structure of the octahedral complex [Zn{S(H)C(PPh2S)2}2] (4) reveals notable inequivalence between the Zn-S(C) and Zn-S(P) contacts (2.274(1) Å vs. 2.842(1) and 2.884(1) Å, respectively). Two structural isomers of the homoleptic complex [Ni{S(H)C(PPh2S)2}2] were isolated after prolonged crystallization processes. The octahedral green Ni(ii) isomer 5a exhibits the two monoprotonated ligands bonded in a tridentate (S,S',S'') mode to the Ni(ii) centre with three distinctly different Ni-S bond lengths (2.3487(8), 2.4500(9) and 2.5953(10) Å). By contrast, in the red-brown square-planar complex 5b the two ligands are S,S'-chelated to Ni(ii) (d(Ni-S) = 2.165(2) and 2.195(2) Å) with one pendant PPh2S group. DFT calculations revealed that the energetic difference between singlet and triplet state octahedral and square-planar isomers of the Ni(ii) complex is essentially indistinguishable. Consistently, VT and (31)P CP/MAS NMR spectroscopic investigations indicated that a mixture of isomers exists in solution at room temperature, while the singlet state square-planar isomer 5b becomes favoured at -40 °C.

Homoleptic, heteroleptic and mixed-valent thallium and indium complexes of multidentate chalcogen-centred PCP-bridged ligands

The metathetical reaction of [Li(TMEDA)][HC(PPh(2)Se)(2)] ([Li(TMEDA)]1) with TlOEt in a 1:1 molar ratio afforded a homoleptic Tl(I) complex as an adduct with LiOEt, Tl[HC(PPh(2)Se)(2)]·LiOEt (7), which undergoes selenium-proton exchange upon mild heating (60 °C) to give the mixed-valent Tl(I)/Tl(III) complex {[Tl][Tl{(Se)C(PPh(2)Se)(2)}(2)]}(∞) (8). Treatment of TlOEt with [Li(TMEDA)](2)[(SPh(2)P)(2)CE'E'C(PPh(2)S)(2)] (3b, E' = S; 3c, E' = Se) in a 2:1 molar ratio produced the binuclear Tl(i)/Tl(i) complexes Tl(2)[(SPh(2)P)(2)CE'E'C(PPh(2)S)(2)] (9b, E' = S; 9c, E' = Se), respectively. Selenium-proton exchange also occurred upon addition of [Li(TMEDA)]1 to InCl(3) to yield the heteroleptic complex (TMEDA)InCl[(Se)C(PPh(2)Se)(2)] (10a). Other examples of this class of In(III) complex, (TMEDA)InCl[(E')C(PPh(2)E)(2)] (10b, E = E' = S; 10c, E = S, E' = Se) were obtained via metathesis of InCl(3) with [Li(TMEDA)](2)[(E')C(PPh(2)E)(2)] (2b, E = E' = S; 2c, E = S, E' = Se, respectively). All new compounds have been characterized in solution by (1)H and (31)P NMR spectroscopy and the solid-state structures have been determined for 8, 9c and 10a-c by single-crystal X-ray crystallography. Complex 8 is comprised of Tl(+) ions that are weakly coordinated to octahedral [Tl{(Se)C(PPh(2)Se)(2)}(2)](-) anions to give a one-dimensional polymer. The complex 9c is comprised of two four-coordinate Tl(+) ions that are each S,S',S'',Se bonded to the hexadentate [(SPh(2)P)(2)CSeSeC(PPh(2)S)(2)](2-) ligand in which d(Se-Se) = 2.531(2) Å. The six-coordinate In(III) centres in the distorted octahedral complexes 10a-c are connected to a tridentate [(E')C(PPh(2)E)(2)](2-) dianion, a chloride ion and a neutral bidentate TMEDA ligand.