Synthesis of dppm-stabilized Si–Fe–M (M = Zn, Cd, Hg or Tl) complexes and crystal structure of a heterotetranuclear Fe2Cd2complex (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–TlIII 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)A, 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)A, 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.