SYNTHESIS OF DPPM-STABILIZED SI-FE-M (M = ZN, CD, HG OR TL) COMPLEXES AND CRYSTAL-STRUCTURE OF A HETEROTETRANUCLEAR FE2CD2 COMPLEX (DPPM = PH2PCH2PPH2)

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 activated Fe(mu-dppm)Cd(mu-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)3a-{Ph2PCH2C(O)Ph}] with CdCl2 in a 1:1 ratio similarly afforded mer-[{[(MeO)3Si](OC)2 activated Fe[mu-Ph2PCH2C(O(Ph]Cd(mu-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 activated Fe(mu-dppm)HgX] (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 activated Fe(mu-dppm)CdCl{Ph2PCH2C(O)Ph}] and mer-[{(MeO)3Si}(OC)3 activated Fe(mu-dppm)HgCl-{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 activated Fe(mu-dppm)Tl(C6F5)2] 9 is also described. The P-31-{H-1} NMR resonance due to the phosphorus bound to thallium consists of a doublet of doublets at delta - 14.0 with 1J(P-Tl-203/Tl-205) 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) angstrom, 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) angstrom, 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.