Preparation of RSn(I)–Sn(I)R with Two Unsymmetrically Coordinated Sn(I) Atoms and Subsequent Gentle Activation of P4

This article reports the reduction of [{2,6-iPr2C6H3NC(CH3)}2C6H3SnCl] (1) with potassium graphite to afford a new distannyne [{2,6-iPr2C6H3NC(CH3)}2C6H3Sn]2 (2) with a Sn–Sn bond. The most striking phenomenon of 2 is the presence of two differently coordinated Sn atoms (one is three-coordinated, the other is four-coordinated). The Sn–Sn bond length in 2 is 2.8981(9) Å, which is very close to that of a Sn–Sn single bond (2.97–3.06 Å). To elucidate the nature of the Sn–Sn bond, DFT calculation is carried out that shows there is no multiple bond character in 2. Furthermore, the reaction of 2 with white P4 affords the tetraphosphabicylobutane derivative 3. This is the first example of gentle activation of white phosphorus by a compound with low valent Sn atoms. Note that, unlike 2, in 3 both Sn atoms are four-coordinated.