Octahedral alkylbis(phenoxy-imine)tin(IV) complexes: Effect of substituents on the geometry of the complexes and their reactivity toward ionizing species and ethylene

The synthesis and characterization of the organo-tin compounds L 2SnR2 [L = N-(3,5-dichlorosalicylidene)aniline; R = CH3 (1), R = CH2Ph (2)] and L′2SnR 2 [3: L′ = N-(3-tert-butylsalicylidene)aniline, R = CH 2Ph] are described herein. NMR studies showed a highly symmetric structure for complex 1, with the alkyl groups in a trans configuration, and the presence of at least two isomers in fluxional equilibrium for compounds 2 and 3. Single-crystal X-ray characterization for compound 2 showed an octahedral geometry with the alkyl groups in trans relationship. The reactivity of the synthesized compounds toward ionizing agents was studied by NMR spectroscopy. For compounds 1 and 2 formation of cationic species through alkyl abstraction by B(C6F5)3 was observed. For compound 3, a cationic species was obtained by reaction with 1 equiv. of [C(C 6H5)3]+[B(C6F 5]4]-; in this species a ηn coordination of the benzyl group with the metal centre was recognized by NMR solution study. All the obtained cationic species promoted ethylene oligomerization under mild conditions, producing oligomers with saturated end groups and methyl branches. Oligoethylene end-group NMR analysis and deuteriolysis experiments excluded the migratory-insertion mechanism.