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Proof of Concept Studies Directed Towards Designed Molecular Wires: Property‐Driven Synthesis of Air and Moisture‐Stable Polystannanes
Author(s) -
Pau Jeffrey,
Lough Alan J.,
Wylie R. Stephen,
Gossage Robert A.,
Foucher Daniel A.
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201703453
Subject(s) - toluene , moisture , azobenzene , chemistry , solvation , metal , conjugated system , polymer , polymer chemistry , crystallography , materials science , molecule , organic chemistry
Polystannanes with azobenzene moieties designed to protect the Sn–Sn backbone from light‐ and moisture‐induced degradation are described. The azo‐stannyl precursor 3 (70 %) is converted in good yields (88–91 %) to the mono‐ ( 4 ), and dichlorostannanes ( 5 ), by sequential chlorination, followed by further reduction of 5 to the dihydride ( 6 ) using NaBH 4 (78 %). All stannanes were characterised by NMR ( 1 H, 13 C, 119 Sn) spectroscopy and HRMS; in addition, 3 , 4 and 5 were structurally elucidated using X‐ray diffraction analysis. Metal‐free dehydrocoupling of 6 at RT leads exclusively to homopolymer ( 7 ‐ i ) displaying an initial solution 119 Sn NMR signal ( δ =−196 ppm) that migrates to −235 ppm after 10 days ( 7 ‐ f ). In contrast, metal‐catalyzed dehydrocoupling of 6 in toluene at RT leads directly 7 ‐ f . Random co‐polymers formed from 6 and ( n Bu) 2 SnH 2 at 4:1 ( 8 a ) and 1:1 ( 8 b ) ratios were compared to the alternating polystannane ( 9 ) prepared by the reaction of 6 with ( n Bu) 2 Sn(NEt 2 ) 2 . DFT calculations of 3 – 6 indicate that hypercoordination at Sn is influenced by substituents and by solvation. Homopolymer 7 was found to have unprecedented moisture and light stability in the solid state for >6 months.