New Hypercoordinating Organostannanes for the Modular Functionalization of Mono‐ and Polystannanes: Synthetic and Computational Studies**

Jeffrey Pau,Robert A Gossage,Mokhamed Ranne,R Stephen Wylie,Daniel A Foucher,Jung‐Won Choi,Kaitlyn Silverthorne,Alan J Lough

doi:10.1002/ejic.202100937

Abstract

AbstractA series of potentially hypercoordinate tin compounds derived from a substitutionally labile tosyl stannane (5) was produced to gain access to a library of propyloxybiphenyl (11), propylmethoxy (12, 14, 18, 22) or propylthioester (13, 15, 19, 23) stannanes for structure/property/polymerization investigations. Structural characterizations by single crystal X‐ray diffraction of 12, 14, 18 and 19 were also undertaken. The relative energies of hypercoordinate conformers for the propylmethoxystannanes 12, 14, 18, and 22 were determined with DFT methods and the fractional abundance of conformers in the gas and solution (CHCl3) phase were estimated. Relativistic DFT calculations of 119Sn NMR chemical shifts were carried out for a series of non‐hypercoordinate reference compounds and the conformers, allowing the estimation of Boltzmann‐averaged chemical shifts of the hypercoordinate propylmethoxystannanes. A semi‐crystalline homopolymer (25) was isolated from the dehydropolymerization of 22 using Wilkinson's catalyst. Conversion of the liable tosylated polystannane (24) to a new partially substituted polystannane (28) via nucleophile displacement reactions was achieved.

Highlights

Polystannanes are main group polymers with a conjugated backbone of tin atoms prepared from the reductive coupling of dihalido- or dihydrido- diorganostannane monomers.[1,2] Sodium (Wurtz)[3,4,5] or electrochemical coupling[6,7] of X2SnRR’ leads directly to the desired materials, while conversion of such materials to diorganostannanes, H2SnRR’ followed by transition metal catalyzed dehydropolymerization[8,9,10] affords the target polystannanes
Relativistic calculations using the zeroth order regular approximation with spin-orbit coupling (ZORA-SO) give very good agreement with experimental results, even for Sn compounds with heavy atoms such as Br or I.37
DFT optimization of individual molecules using the PBE0-GD3BJ method generally provided the best predictions of solid-state molecular properties

Summary

Introduction

Polystannanes are main group polymers with a conjugated backbone of tin atoms prepared from the reductive coupling of dihalido- or dihydrido- diorganostannane monomers.[1,2] Sodium (Wurtz)[3,4,5] or electrochemical coupling[6,7] of X2SnRR’ leads directly to the desired materials, while conversion of such materials to diorganostannanes, H2SnRR’ followed by transition metal catalyzed dehydropolymerization[8,9,10] affords the target polystannanes. We have estimated the extent of hypercoordination in solution for a subset of these small molecules using DFT calculations of geometries and 119Sn NMR chemical shifts, with comparison to experimental values.

Results

Conclusion