Synthesis of dppm-stabilized Si–Fe–M (M = Zn, Cd, Hg or Tl) complexes and crystal structure of a heterotetranuclear Fe2Cd2 complex (dppm = Ph2PCH2PPh2)

Abstract

Treatment of K[Fe(CO)₃{Si(OMe)₃}(dppm-P)](dppm = Ph₂PCH₂PPh₂) with CdX₂(X = Cl or Br) in tetrahydrofuran (thf) in a 1 : 1 ratio afforded the tetranuclear iron–cadmium complexes mer-[{[(MeO)₃Si](OC)₃[graphic omitted](µ-X)}₂]2a(X = Cl) and 2b(X = Br) in 78 and 65% isolated yield, respectively. Each Fe–Cd bond is supported by a dppm ligand. The reaction of the ketophosphine-substituted metalate K[Fe(CO)₃{Si(OMe)₃}{Ph₂PCH₂C(O)Ph}] with CdCl₂ in a 1 : 1 ratio similarly afforded mer-[{[(MeO)₃Si](OC)₃[graphic omitted](µ-Cl)}₂]2c, in which a bridging mode for the functional (P,O) ligand is assumed for the first time. Reaction of K[Fe(CO)₃{Si(OMe)₃}(dppm-P)] with ZnCl₂ afforded the Fe–Zn analogue 3, which is very labile. Similarly, Fe–Hg complexes of the type mer-[{(MeO)₃Si}(OC)₃[graphic omitted]X](R = Et, X = Ph; R = Me, X = C₆Cl₅ or Cl) were prepared. The chloride bridges of 2a are easily split by nucleophiles. Using Ph₂PCH₂C(O)Ph, mer-[{(MeO)₃Si}(OC)₃[graphic omitted]Cl{Ph₂PCH₂C(O)Ph}] and mer-[{(MeO)₃Si}(OC)₃[graphic omitted]gCl{Ph₂PCH₂C(O)Ph}] were obtained. They reacted with Tl[PF₆] to yield cationic complexes in which the ketophosphine acts as a chelating ligand. The synthesis of the Fe–Tl^III complex mer-[{(MeO)₃Si}(OC)₃[graphic omitted](lC₆F₅)₂]9 is also described. The ³¹P-{¹H} NMR resonance due to the phosphorus bound to thallium consists of a doublet of doublets at δ–14.0 with ¹J(P–²⁰³Tl/²⁰⁵Tl)= 6765 Hz. The molecular structure of complex 2a was determined by X-ray diffraction. Crystals of the hexane solvate are orthorhombic, space group Pbcn, with a= 23.498(9), b= 16.856(8), c= 18.220(8)Å, and Z= 4. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.0653 for 2906 observed reflections. In the dimeric complex, having an imposed C₂ symmetry, the two Fe–Cd distances, 2.624(2)Å, are indicative of metal–metal bonds and the two Cd atoms are joined by a double nearly symmetrical chloride bridge. A phosphorus atom of the dppm ligand completes the co-ordination of the Cd atom. Each Fe atom is octahedrally co-ordinated by three carbonyl groups in a meridional arrangement, by a phosphorus atom of the dppm ligand, by the Si atom of the Si(OMe)₃ ligand and by the Cd atom.