Novel bis(beta-diketonato)diorganotin(IV) derivatives containing bulky 4-acyl-5-pyrazolonato ligands. Influence of the steric hindrance of the acyl moiety on the solid state structures of tin complexes and their behavior in solution

New (Q)2SnR2 derivatives (HQ in general; in detail: HQCHPh2 = 4-diphenylacetyl-3-methyl-1-phenyl-5-pyrazolone; HQBn = 3-methyl-1-phenyl-4-phenylacetyl-5-pyrazolone; HQnaph = 3-methyl-4-naphthoyl-1-phenyl-5-pyrazolone; R = CH3, C 2H5, C6H11, n- and t-C 4H9, C6H5,) have been synthesised and characterised by analytical and spectral techniques. Variable temperature NMR studies of (QCHPh2)2SnR2 derivatives (R = CH3 and C 2H5) in chlorohydrocarbon solvents indicate a fluxional behaviour, with rapid interconversion between six- and five-coordinate species, the latter containing a bidentate acylpyrazolonate and a monodentate one. The X-ray crystal structures of the diorganotin(IV) derivatives (QCHPh2)2SnMe2, (QCHPh2)2SnEt2, (QBn)2SnMe2 and (Qnaph)2SnBun2, inclusive of a representative of each Qx family, show the metal centres in a skewed trans octahedral configuration. The 4-acyl moiety of the β-diketonate donor exerts a steric effect which is correlated to structural behaviour in the solid and solution state. A solid state 119Sn CPMAS NMR study of the (QBn)2SnR2 (R = CH 3, C2H5, t-C4H9 and C6H5) complexes shows a marked deshielding effect and upfield movement of the 119Sn isotropic chemical shift (δiso) through this series. The 119Sn chemical shift spans (Ω) are the largest reported for directly oxo-coordinated Sn(IV) systems, although the markedly reduced Ω value for the (Q Bn)2SnPh2 complex may be indicative of a cis octahedral coordination, in contrast to the trans octahedral coordination characterising the other complexes of this suite. © 2010 Elsevier B.V. All rights reserved.