Derivatives of bivalent germanium, tin, and lead. Part XI. The interaction of tin(II) halides and bis(β-ketoenolates) with di-iron enneacarbonyl

Abstract

Tin(II) halides and bis(β-ketoenolates) react with di-iron enneacarbonyl to give high yields of complexes [(X₂Sn)-Fe(CO)₄](X = Cl, Br, pd, tbd, bpd, pbd, or dpd). In chloroform solution (osmometry), the pentane-2,4-dionate (pd) is dimeric but the remainder are only partially associated. Nujol mull i.r. spectra of the halide derivatives are consistent with a dimeric structure, but some dissociation is apparent for the β-ketoenolates being essentially complete for the bulky 4-phenylbutane-2,4-and 1,3-diphenylpropane-1,3-dionate ligands. In pyridine solution all the complexes are completely dissociated into pyridine-stabilised monomeric [(X₂Sn)Fe(CO)₄]˙py species. Varying degrees of dissociation occur in less nucleophilic solvents such as tetrahydrofuran and acetonitrile. lron-57 Mössbauer spectra of all the solid complexes demonstrate complete association into dimers at 77 K, but in frozen pyridine solution rehybridisation at iron to give trigonal-bipyramidal geometry occurs. The very low values of the tin-119 isomer shifts in the base-stabilised monomer complexes indicate substantial synergic tin→iron σ and iron→tin (d→d)π bonding.