Group 4-organometallic Reagents - A H-1, C-13, and Sn-119 Nuclear Magnetic-resonance Study On 2,2-dibutyl-1,3,2-dioxastannolane Structure In Solution

The behaviour of 2,2-dibutyl-1,3,2-dioxastannolane (DOS) in chloroform solution has been investigated by concerted 1H, 13C, and 119Sn n.m.r. spectroscopy at variable temperatures; the results are compared with previous reports. A complex pattern of association equilibria involving the five-membered DOS is evident. The controversy about the dimeric structure of the title compound has been composed assigning to the dimer a 'fluxional type' structure in which a fast intramolecular shift with inversion at tin is responsible for the apparent high symmetry features of the molecule. The energy barrier relative to fluxional exchange is of the order of 42 kJ mol-1. The interconversion of four-, five-, and six-co-ordinate tin species represents a new example of configurational instability of the organotin compounds.