Polystannanes are main group polymers with a conjugated backbone of tin atoms prepared from the reductive coupling of dihalido-or dihydrido-diorganostannane monomers. Sodium (Wurtz) or electrochemical coupling of X2SnRR' leads directly to the desired materials, while conversion of such materials to diorganostannanes, H2SnRR' followed by transition metal catalyzed dehydropolymerization affords the target polystannanes. Key to both approaches is access to both homo-and hetero-diorganostannanes. This is traditionally achieved by the Kocheshkov reaction, a solventless redistribution of organo and halogen substituents at tetracoordinated tin centers to afford the required organohalo (R4-nSnCln) tin species. Experimentally, alkyl substituents have been more difficult to selectively interchange than aryl ones (n-Bu < Me < Ph < Mes). Interestingly, an increase of coordination number at tin from four to six has a notable impact on these redistribution reactions. Utilizing van Koten's N,C,N pincer ligand, (2,6-(Me2NCH2)C6H3)-, Růžička and coworkers reported a partial redistribution at RT of an intramolecularly bound monochlorostannane (Figure , 1) in solvent to the dichlorostannane and the triphenylstannane after a 2 week time period. Nechaev and co-workers later detailed the high yield redistribution reaction of six coordinate PhSn(κ 2 -O, N-OCH2CH2NMe2)2Cl (Figure , 2) with PhSnCl3 to the symmetrical dialkoxydichlorostannane and Ph2SnCl2 species. In both examples, the presence of hypercoordinating interactions from the tethered donor side chains lead to a "reversed" redistribution of these organotin compounds. Functionalization of stannanes from chlorido or hydrido triorganostannanes has been demonstrated by the teams of Pace and Molloy, respectively. Tandem homogolation of triorganohalostannanes with modified methyl lithium reagents (e.g. LiCH2Cl) yielded α-functionalized monohalomethyl stannanes (3) in good yields (> 80%). Molloy reported the preparation of dihalidodiorganostannanes 4 (Figure ) from an initial hydrostannylation of triphenylstannane with an allyl ether or allyl alcohol substituents, followed by stoichiometric bromination. Our research has demonstrated displacement reactions of the tosyl substituent in 5 (Figure ) with 4-hydroxyazobenzene under Williamson ether-like conditions. This approach may be an effective general method to prepare a variety of hypercoordinating stannane monomers for moisture and light stable polystannanes. Access to a wide variety of functional organic polymers from a single sacrificial macromolecular intermediate has been a successful strategy for the last three decades. Post-polymerization modification of an intermediate using comparatively mild transformations enables the preparation of polymers that are otherwise hard to access, or sensitive to the polymerization conditions. Additionally, new polymers derived from a single, high yielding, low-cost macromolecular intermediate provides an opportunity to probe structure-property relationships between materials built from a common modular structural platform. Post-polymerization of main group and organometallic polymers is relatively unexplored with a few notable exceptions. Modification of poly(methylhydrosiloxanes), 6 (Figure ), with vinylsiloxanes via transition metal-catalyzed hydrosilylation and the nucleophilic substitution of the halo substituents of thermally ring-opened hexachloropolyphosphazene 18 (7) or the closely related polythionylphosphazene (8) with alkoxy, amino or organo substituents has been established. In the mid 1990's, Manners and coworkers also demonstrated the tunable nature of thermally or transition metal-catalyzed ring-opened chlorinated sila [1]ferrocenophanes (9a, b) and were able to prepare substituted poly(ferrocenylsilanes) with sp, sp 2 and sp 3 moieties. In 2017, this same group was able to demonstrate an "inorganic click" reaction with the cycloaddition of cyclophosphines to a polymeric styrene nitrile to yield 10. This approach provides access to a host of tailored polymers bearing inorganic moieties. To gain access to a broader selection of hypercoordinated stannanes and polystannanes, we have carried out a three-part study. First, we have investigated the substitution chemistry of a model tosylstannane with three nucleophiles, preparing a library of small molecules using reactions potentially extensible to post-polymerization modifications. Second, we have estimated the extent of hypercoordination in solution for a subset of these small molecules using DFT calculations of geometries and 119 Sn NMR chemical shifts, with comparison to experimental values. Finally, we disclose our first efforts to prepare tunable hypercoordinated polystannanes by post-polymerization modification of a previously known tosyl-containing polystannane. Functionally similar polymeric materials were also prepared by dehydrocoupling, where appropriate, for comparison. The tosylstannane 4, was prepared in two high yield steps following Yoshida's procedure without the need for column chromatography. This air-and moisture-stable tosyl intermediate is also tolerant to acidic conditions, while substitutionally reactive under basic conditions. Conditions favourable for substitution at 4 (Figure ) with the methoxy, thioacetyl and biphenyloxy nucleophiles were explored. Williamson ether and Williamson ether-like conditions (Scheme 1) in acetone (Method A) were initially used to prepare compounds 11 and 13 in low yields (< 40%) but was unsuccessful in the case of 12. Higher yields of both 11 and 13 were obtained (> 75%) when the reaction was carried out in MeCN (Method B). High purity materials were isolated after extraction (without column chromatography) as determined by NMR spectroscopy ( 1 H, C, 119 Sn), and for 11 was identical to material previously prepared by hydrostannylation protocols. Compound 13 was recovered as a yellow-coloured clear oil, in contrast to solid 11. Compound 12 was readily prepared in good yield as a white coloured solid using NaOMe/MeOH in MeCN under mild conditions (< 2 h: Method C). As MeCN was also found to be preferable for substitutions of both the model stannanes and the tosyl polystannane, it was used exclusively thereafter. Compound 12 was recrystallized from DCM/hexanes and its solid-state structure established by X-ray crystallography (Figure : top left). This model triphenylstannane assumes a distorted tetrahedral geometry (τ4 = 0.52) around the Sn centre. The new model stannanes 22 and 23 were prepared using established protocols. The three step process involved sequential chlorination of the model tristannanes (12, 13) to monochlorides (14, 15), then dichlorides (18, 19) and finally, reduction to the dihydrido (22, 23) compounds with a mild hydride source (Scheme 2).