Disulfur and diselenium complexes of rhodium and iridium

Article abstract of DOI:10.1021/ic00140a016

Coordinatively unsaturated low-valent rhodium and iridium complexes cleave S₈ and Se₈ rings and form complexes with the fragments. With square-planar [M(L-L)₂]Cl (M = Rh, Ir; L-L = (C₆H₅)₂PCH₂CH₂P(C ₆H₅)₂ (dppe), (CH₃)₂PC-H₂CH₂P(CH₃) ₂ (dmpe)) this reaction affords the monomeric electrolytes [M(Y₂)(L-L)₂]Cl (Y₂ = S₂, Se₂). Oligomeric compounds are obtained from the reactions with IrX(CO)(EPh₃)₂ and RhX(EPh₃)₃ (X = Cl, Br; E = P, As); the products are [{Ir(Se₂)X(CO)(PPh₃)}₃], [{Ir(Se₂)Cl(CO)(AsPh₃}₃], [{IrS₆Cl(CO)(PPh₃)₂}_n], [{RhS₃X(PPh₃)₄}], [{RhSe₃Cl(PPh₃)}₄], and [{RhY₂Cl(AsPh₃)}_n] (Y₂ = S₂, Se₂). In the compounds [M(Y₂)(L-L)₂]Cl, disulfur and diselenium are side-on bonded to the metal at equatorial positions of a distorted octahedron. An X-ray structure determination of the diselenium complex [Ir(Se₂)(dppe)₂]Cl·H₂O·0.5C ₆H₆ shows the cation to be very similar to its dioxygen and disulfur analogues. The Se-Se distance is 2.312 (3) A?, about the same as the bond length in Se₈ and 0.16 A? longer than the Se-Se bond in the free Se₂ molecule. [M(Y₂)(L-L)₂]⁺ complexes have ν(S-S) at 510-550 cm^-1 and ν(Se-Se) at 300-310 cm^-1. The lowest energy feature of their electronic absorption spectra is a weak (ε 40-100 M^-1 cm^-1) band assigned as an a₂π_⊥* → b₁ intraligand transition. ¹⁹³Ir(1/2+ → 3/2 +) Mo?ssbauer spectra of [Ir(Y₂)(dppe)₂]Cl give isomer shifts that decrease along the series Y₂ = O₂, S₂, Se₂, in parallel with decreasing Y₂ electronegativity. The disulfur or diselenium group in [M(Y₂)(L-L)₂]⁺ is readily reduced: mercury and tertiary phosphines strip sulfur or selenium from the complex with formation of HgS or HgSe and R₃PS or R₃PSe; the rate is very sensitive to the electronic environment of the disulfur or diselenium group and to the basicity of the phosphine. Low-valent group 8 metal complexes undergo oxidative addition across the S-S or Se-Se bond, allowing synthesis of the heterometallic (μ-S)₂ dimers [(dppe)₂Ir(μ-S)₂PtL₂]X (L = PPh₃, X = Cl; L = PEtPh₂, X = PF₆) and [(dmpe)₂Rh(μ-S)₂Pt(PPh₃)₂]Cl, as well as the asymmetric dimer [(dppe)₂Ir(μ-Se)₂IrCl(CO)(PEt₂Ph) ₂]Cl. Oxidative addition together with displacement of [M(L-L)₂]⁺ by excess of the addend complex also occurs, giving homometallic (μ-S)₂ or (μ-Se)₂ dimers such as [{Ir(μ-Se)Cl(CO)(PEt₂Ph)₂}₂]. Iodine adds across the S-S bond of [Ir(S₂)(dppe)₂]Cl to form the novel cis-octahedral complex [Ir(SI)₂(dppe)₂]Cl.