Oligostannanes cyclic

A process which involves the formation of SnSn bonds by both the reduction of an SnX bond by SnH, and by stannylene insertion into SnH, is illustrated in equation 18-47. It is assumed that the terminal tin hydride is formed by repeated insertion of dibutyl-stannylene into SnH this tin hydride is then coupled with the aminotin compound to give the symmetrical oligostannanes EtOCH2CH2(Bu2Sn)nCH2CH20Et.69 

The various oligomers can be separated by reverse phase HPLC the main products have n = 3, 4, or 5, but higher oligomers with n 15 can be separated. As n increases, the value of /.max increases from /,max 254 nm, v 39,370 cm-1 when n = 3, to Xmax 362 nm, v 27,548 cm 1 when n = 15. This is in accord with the predictions of the San-dorfy modification of the Hiickel MO approximation which takes into account weak vicinal and strong geminal interactions between tin atoms, and implies that the electrons are highly delocalised along the o backbone.69 

Dialkyltin dichlorides, R2SnCl2 (R = Me, Et, or C6H13), react with samarium iodide or with magnesium or calcium vapour to give polystannanes with M u/ 103 and a narrow molecular weight distribution (e.g. equation 18-48). 

The polymers show UV absorption at 285-368 nm, and laser flash photolysis gives chain scission with the formation of the corresponding transient stannyl radicals with absorption at 400 nm (R = Me). They react with oxygen with a pseudo-first order rate constant of ca. 105 s 1 70 

Poly(dialkylstannanes), (Bu2Sn) and (Oct2Sn) , with Mw up to ca. 10,000,71 and the corresponding Bu2Sn/Bu2Si and BioSn/BioGe copolymers,72 have been prepared by electrolysis of the appropriate dichlorides in DME in a one-compartment cell fitted with a Pt cathode and Ag anode. The polystannanes appear to be stable to oxygen, but sensitive to moisture in the air, and the sensitivity of the Sn/Si or Sn/Ge copolymers increases with increase in the content of tin. 

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With the simple triorganotin hydrides, reaction 15-31 occurs only in the presence of a Lewis base such as an amine, or of a transition metal catalyst. The amine-catalysed reaction has been used for preparing catenary and cyclic oligostannanes (e.g. equations 15-33 and 15-34 and Section 18.2.1.3).92... 

Examples of acyclic and cyclic oligostannanes are given in Table 18-1 some di- and tri-stannaferrocenophanes are described in Section 9.3.4... 

The cyclic oligostannanes are an important class of compounds, synthesized in a similar manner to the Snj units above [53], Larger R groups lead to lower degrees of association and the formation of isolated of RjSn stannylene units and doubly bonded dimers discussed below. In terms of reaction chemistry, the principtil modes of reactivity of oligo- and polystannanes are through oxidative or reductive cleavage of Sn-Sn bonds [37]. 

Several cyclic and polycyclic oligostannanes with a rich structural diversity have been reported in the literature16,21 83 and it was concluded by Sita21 that the concepts and strategies established in organic chemistry can successfully be applied for the construction of polystannane frameworks as well. The polycyclic oligostannanes 16-19 are representative examples for this class of compounds. 

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