Taming Heavier Group 14 Imine Analogues: Accessing Tin Nitrogen [Sn=N] Double Bonds and their Cycloaddition/Metathesis Chemistry

Abstract

A systematic study to access stable stannaimines is reported, by combining different heteroleptic stannylenes with a range of organic azides. The reactions of terphenyl-/hypersilyl-substituted stannylenes yield the putative tin nitrogen double bond, but is directly followed by 1,2-silyl migration to give Sn II systems featuring bulky silylamido ligands. By contrast, the transition from a two σ donor ligand set to a mixed σdonor/π-donor scaffold allows access to three new stannaimines which can be handled at room temperature. The reactivity profile of these Sn=N bonded species is crucially dependent on the substituent at the nitrogen atom. As such, the Sn=NMes (Mes = 2,4,6-Me 3 C 6 H 2 ) system is capable of activating a broad range of substrates under ambient conditions via 1,2-addition reactions, [2+2] and [4+2] cycloaddition reactions. Most interestingly, very rare examples of main group multiple bond metathesis reactions are also found to be viable.

Reactions of main group compounds with azides forming organic nitrogen-containing species

“…In 2022, Fischer, Aldridge and co-workers systematically investigated the reactions of different heteroleptic stannylenes with various azides. 174 Treatment of Sn13 with TMSN 3 or aryl azides (MesN 3 , DipN 3 ) produced the nitrene insertion products Sn13-P1a and Sn13-P2/Sn13-P3 via the Si(TMS) 3 group migration from the Sn centre to the N atom of the stannanimine intermediate (Scheme 106a). Notably, the reaction with TMSN 3 afforded a minor product Sn13-P1b in 33% yield resulting from the intramolecular C-H bond activation in the transient SnQN species.…”

Small molecule activation by well-defined compounds of heavy p-block elements

“…With the heavier heterocumulene CS 2 , a [4+2] cycloaddition occurs to form 67 in which the mesityl substituent is de-aromatized. 84 Compounds based on the heavy group 15 elements antimony and bismuth undergo facile and in some cases reversible reactions with CO 2 . In this context, the insertion of CO 2 into Sb/ Bi-E bonds (E = O, N, C) has been reported.…”

“…With the heavier heterocumulene CS 2 , a [4+2] cycloaddition occurs to form 67 in which the mesityl substituent is de-aromatized. 84…”

Donor‐Acceptor Activation of Carbon Dioxide

“…In the abovementioned zwitterionic compound, CO 2 is trapped intramolecularly in a five‐membered heterocycle [51] . More recently, Aldridge and co‐workers have reported the synthesis of compound 60 by the combination of the stannaimine Mes TerSn(N(SiMe 3 ) 2 )=NMes [ Mes Ter=C 6 H 3 ‐2,6‐(C 6 H 2 ‐2,4,6‐Me 3 ) 2 ] and 1 bar of CO 2 , which represents the first example of [2+2] cycloaddition product derived from Sn=N bond‐based compounds [52] …”

“…[51] More recently, Aldridge and co-workers have reported the synthesis of compound 60 by the combination of the stannaimine Mes TerSn(N(SiMe 3 ) 2 )=NMes [ Mes Ter = C 6 H 3 -2,6-(C 6 H 2 -2,4,6-Me 3 ) 2 ] and 1 bar of CO 2 , which represents the first example of [2 + 2] cycloaddition product derived from Sn=N bond-based compounds. [52] Figure 6. CO 2 activation by other donor-acceptor pairs based on main group elements.…”