A Tin-119 NMR investigation of phosphine and phosphine oxide adducts of organotin chlorides

The stoichiometry and structure of phosphine and phosphine oxide adducts of Ph3SnCl, R2SnCl2 (R=Et, Pr, Bu, t-Bu, and Ph), and RSnCl3 (R=Bu and Ph) were studied with Sn-119 spectroscopy. The shift of the Sn-119 resonance to a lower frequency upon adduct formation, the multiplicity of the resonance, the variation of P-31-Sn-119 coupling with the nature of the substituent, and the change in structure of the peaks with concentration and temperature were all used to determine stoichiometry and structure. The organotin chloride adducts readily exchange with base or with other adducts. The diorganotin dichlorides form only 1:1 adducts with tributylphosphine (TBP), even at high base to acid ratios, but most form 1:2 adducts (as several geometric isomers) with phosphine oxides at mole ratios above 1:1. The lower dialkyltin dichlorides prefer to form 1:1 adducts (at 1:1 mole ratios) with TBP rather than tributylphosphine oxide (TBPO), whereas diphenyltin dichloride and di(t-butyl)tin dichloride prefer TBPO adduct formation. The reactions of the trihalides with TBP and TBPO are complicated by aryl transfer or displacement of chloride by base and consequent ion formation.