Oligostannanes

Each of the discrete oligomers was characterized by single-crystal X-ray diffraction, and the structures are shown in Fig. 6.1. The Sn-Sn bond lengths varied in the range 2.80-2.97 A, and each oligomer was shown to possess a trans-planar conformation. 

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Polystannanes would be expected to possess even more o-delocalised structures, as suggested by studies of linear oligostannanes with up to six tin... 

C5Me5)2SmCH(SiMe3)2 was recently found to catalyze the formation of low molecular weight oligostannanes from nBu2SnH2 [93],... 

SCHEME 10. Synthesis of oligostannanes via metal-halogen exchange... 

SCHEME 12. Synthetic strategy to prepare oligostannanes with up to 15 tin atoms in the linear chain... 

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. 

Currently, there is growing interest in polymers the frameworks of which are constructed from the Group 14 elements silicon, germanium and tin. Several reviews on polysilanes have appeared in the literature . In the first section of this article we focus on recent developments in the chemistry of polygermanes and polystannanes. The chemistry and structure-property relationship of oligostannanes and low molecular weight polystannanes was the subject of earlier reviews . ... 

This early work is summarised in Krause and von Grosse s Organometallische Che-mie which was published first in 1937,11 and which described examples of tetraalkyl-and tetraaryl-stannanes, and of the organotin halides, hydrides, carboxylates, hydroxides, oxides, alkoxides, phenoxides, R2Sn(II) compounds (incorrectly), distannanes (R3SnSnR3), and oligostannanes (RiSn) . 

The third class of compounds that are not prone to increase their coordination numbers are the hexaalkyldistannanes, R3SnSnR3, and the related oligostannanes. The Sn-Sn stretch is infrared inactive, but Raman active, and Me3SnSnMe3 shows v(SnSn) 192 cm-1. If the phenyl groups in hexaphenylditin are alkylated in the ortho positions, steric hindrance weakens the Sn-Sn bond, and the vibration frequency and force constant are reduced (see Table 18-2). 

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... 

The SnSn bond in distannanes and oligostannanes can be formed in a number of different reactions, and these compounds are sometimes isolated adventitiously as byproducts from reactions aimed at other compounds. The principal ways of forming the SnSn bond are as follows. 

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

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