Derivatives of bivalent germanium, tin, and lead. Part VII. Chromium, molybdenum, and tungsten pentacarbonyl complexes of tin(II) bis(β-ketoenolates)

Abstract

Bis(β-ketoenolato)tin(II)-metal pentacarbonyl complexes, [(O:CR′·CH:CR·O^–)₂SnM(CO)₅](R = R′= Me or CF₃; R = Me, R′= Ph or CF₃; M = Cr, Mo, or W), have been synthesised by photolysis of the Group 6 metal hexacarbonyl and tin(II) bis(β-ketoenolate) in tetrahydrofuran (thf). The i.r. spectra indicate that chelation of the β-ketoenolate residues does not change significantly on complex formation. The complexes exhibit very low isomer shifts (1.80–2.11 mm s^–1), usually assumed to be characteristic of tin(IV) compounds, and demonstrate the invalidity of the use of the isomer shift of β-tin (2.56 mm s^–1) as the arbitrary dividing line between the two oxidation states. The n.m.r. and Mössbauer data have been interpreted in terms of synergic (σ+π) interaction along the tin-transition metal axis.