CHAIN CORE ISOMERISM IN DPPM-BRIDGED POLYMETALLIC COMPLEXES - SYNTHESIS, REACTIVITY, AND STRUCTURE OF FE-HG-PT, FE-SN-PT, AND FE-PD-SN ARRAYS (DPPM=PH2PCH2PPH2)

The 14-electron fragment Pt(PPh3)2, delivered by [Pt(PPh3)2(C2H4)], se lectively inserts into the Hg-C bond of the bimetallic complex [(OC)3{ (MeO)3Si}Fe(mu-dppm)Hg(C6Cl5)] (2) (dppm = Ph2PCH2PPh2) and quantitati vely forms a 1:1 mixture of the isomeric complexes -Si(OMe)2(OMe)}(mu- dppm)(mu-Hg)Pt(C6Cl5)(PPh3)](3) and mu-Si-(OMe)2(OMe)}(mu-dppm)(mu-Hg) Pt(C6Cl5)(PPh3)] (4) (in which the PPh3 ligand is cis or trans relativ e to the Pt-bound phosphorus atom of the dppm ligand, respectively). C omplex 3 was also obtained, selectively and in high yields, upon react ion of K[Fe{Si(OMe)3}(CO)3-(dppm-P)] with trans-[PtCl{Hg(C6Cl5)}(PPh3) 2]. It readily isomerizes when heated in solution to quantitatively yi eld the thermodynamically more stable isomer 4. The geometry of 3 and 4 has been deduced from their reactivity and spectroscopic data. React ion Of [(OC)3-{(MeO)}3Si}Fe(mu-dppm)PtH(PPh3)] (5) with [Hg(C6Cl5)]PF6 afforded the chloride-bridged cationic complex [(OC)3Fe(mu-dppm)(mu-C I)Pt(PPh3)]PF6 (6) and a small amount of 4. Two-electron donor ligands like isonitriles or CO displace the P(dppm) --> Pt bond of 3, but not of 4, and selectively give chain complexes of the type [(OC)3{(MeO)3S i}Fe(mu-dppm)HgPt(C6-Cl5)(L)(PPh3)] [L = (t-Bu)NC (7), (2,6-xylyl)NC ( 8), CO (9)]. Reaction of K[FetSi(OMe)3}-(CO)3(dppm-P)] with trans-[PtC l(SnCl3)(PEt3)2] led to the stannylene-bridged complex [(OC)3{(MeO)3Si }Fe(mu-dppm)(mu-SnCl2)PtCl(PEt3)] (10) in high yields. Possible molecu lar rearrangements leading to the Fe-Sn-Pt sequence of 10 are discusse d. Stirring a solution Of [(OC)3Fe{mu-Si(OMe)2(OMe)}(mu-dppm)PdCl] wit h SnCl2 yielded [(OC)3Fe{mu-Si(OMe)2(OMe)}-(mu-dppm)PdSnCl3] (11) Whic h contains a terminal SnCl3 group, whereas the Pt analog could not be isolated. The solid state structures of 2, 7-CH2Cl2, and 10-CH2Cl2 hav e been determined by X-ray diffraction. 2 crystallizes in the monoclin ic space group P2(1)/a with Z = 4 in a unit cell of dimensions a = 20. 943(8) angstrom, b = 16.612(7) angstrom, c = 11.837(5) angstrom, and b eta = 95.02(2)-degrees. 7-CH2Cl2 crystallizes in the monoclinic space group P2(1)/c with Z = 4 in a unit cell of dimensions a = 14.212(4) an gstrom, b = 26.717(8) angstrom, c = 19.318(6) angstrom, and beta = 117 .58(2)-degrees. 10-CH2-Cl2 crystallizes in the triclinic space group P l with Z = 2 in a unit cell of dimensions a = 17.882(8) angstrom, b = 11.443(6) angstrom, c = 12.457(6) angstrom, alpha = 79.79(2), beta = 8 8.18(2), and gamma = 72.25(2)-degrees. The structures have been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares on the basis of 5363 (2), 2696 (7.CH2Cl2 ), and 10 339 (10-CH2Cl2) observed reflections to R and R' values of 0 .0400 and 0.0464 (2), 0.0550 and 0.0357 (7.CH2Cl2), and 0.0494 and 0.0 653 (10.CH2Cl2), respectively.