Novel bis(β-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 behaviour in solution

New (Q)(2)SnR(2) derivatives (HQ in general; in detail: HQ(CHPh2) = 4-diphenylacetyl-3-methyl-1-phenyl-5-pyrazolone; HQ(Bn) = 3-methyl-1-phenyl-4-phenylacetyl-5-pyrazolone; HQ(naph) = 3-methyl-4-naphthoyl-1-phenyl-5-pyrazolone; R = CH(3), C(2)H(5), C(6)H(11), n- and t-C(4)H(9), C(6)H(5),) have been synthesised and characterised by analytical and spectral techniques. Variable temperature NMR studies of (Q(CHPh2))(2)SnR(2) derivatives (R = CH(3) and C(2)H(5)) 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 (Q(CHPh2))(2)SnMe(2), (Q(CHPh2))(2)SnEt(2), (Q(Bn))(2)SnMe(2) and (Q(naph))(2)SnBu(2)(n), inclusive of a representative of each Q(x) family, show the metal centres in a skewed trans octahedral configuration. The 4-acyl moiety of the beta-diketonate donor exerts a steric effect which is correlated to structural behaviour in the solid and solution state. A solid state (119)Sn CPMAS NMR study of the (Q(Bn))(2)SnR(2) (R = CH(3), C(2)H(5), t-C(4)H(9) and C(6)H(5)) complexes shows a marked deshielding effect and upfield movement of the 119Sn isotropic chemical shift (delta(iso)) through this series. The (119)Sn chemical shift spans (Omega) are the largest reported for directly oxo-coordinated Sn(IV) systems, although the markedly reduced Omega value for the (Q(Bn))(2)SnPh(2) complex may be indicative of a cis octahedral coordination, in contrast to the trans octahedral coordination characterising the other complexes of this suite. (C) 2010 Elsevier B.V. All rights reserved.