New tridentate phosphine rhodium and iridium complexes, including a stable rhodium(I) silyl. Si-S activation and a strong effect of X in (PP2)M-X (X = H, Cl, Me) on Si-H activation

Article abstract of DOI:10.1021/om020120a

Rhodium and iridium complexes of the general formula (PP₂)MX bearing the new triphosphine ligand ⁱPr₂P(CH₂)₃P(Ph)(CH₂) ₃PⁱPr₂ (PP₂) have been synthesized. Reactivity of the PP₂MX complexes toward HSi(SEt)₃ was studied. Whereas (PP₂)RhCl and (PP₂)IrCl do not react with HSi(SEt)₃, (PP₂)RhH gives rise to the Rh(III) adduct [(PP₂)Rh(H)₂Si(SEt)₃], and (PP₂)RhMe (3) activates both the Si-H and the Si-S bonds of HSi(SEt)₃, affording the Rh(I) complexes (PP₂)RhSi(SEt)₃ (5) and (PP₂)RhSEt (6). Only a few stable Rh(I) silyl complexes are known, and Si-S bond activation by transition-metal complexes has been rarely observed. The X-ray crystal structure of 5 exhibits a considerable distortion from square-planar geometry, the average angle between the trans-disposed ligands being 152.5°. In contrast to 3, (PP₂)IrMe (8) forms a stable Ir(III) adduct with HSi(SEt)₃, fac-[(PP₂)Ir-(Me)(H)(Si(SEt)₃)] (9). No Si-S activation was observed with 8. Thus, the reactivity of (PP₂)-MX complexes toward HSi(SEt)₃ strongly depends on the nature of M and X.