Bimetallic systems. Part 9. The synthesis of and nuclear magnetic resonance studies on 10-membered ring complexes of type [(OC)4M1(µ-Ph2PCH2CH2PPh2)2M2(CO)4](M1, M2= Cr, Mo, or W)

Abstract

The Ph₂PCH₂CH₂PPh₂(dppe) bridged, bimetallic 10-membered ring complexes [(OC)₄M¹(µ-dppe)₂-M²(CO)₄] have been synthesised by treating a complex of type cis-[M¹(CO)₄(PPh₂H)₂] with one of type cis-[M²(CO)₄{PPh₂(CHCH₂)}₂] in the presence of potassium t-butoxide as catalyst. The new precursor complexes cis-[M²(CO)₄{PPh₂(CHCH₂)}₂] were prepared by displacement of norbornadiene (nbd) from [M(CO)₄(nbd)]. The fluxional processes in the 10-membered M¹(µ-dppe)₂M² rings have been studied by variable-temperature ³¹P-{¹H} n.m.r. spectroscopy and are characterised by a change from a second-order AA′XX′ system at 20 °C to an essentially first-order AMPX system at –90°C. The spectra have been fully interpreted and values for ²J(cis-PMP) obtained. The ³¹P-{¹H} n.m.r. spectra of the homonuclear M(µ-dppe)₂M systems change from A₄ at 20 °C to AA′BB′ at –90 °C. The low-temperature (–100 °C)¹H and ¹H-{³¹P} spectra were not resolved. These binuclear complexes are remarkably inert towards disproportionation to mononuclear chelate species and to attack by HCl or halogens.