Synthesis and structure of new oligomethylene-bridged double ladders. How far can the layers be separated?

The synthesis of the α,ω-bis[dichloro(trimethylsilylmethyl)stannyl]alkanes, (Me₃SiCH₂)C1₂Sn(CH₂)_<i>n</i>SnCl₂(CH₂SiMe₃) (<b>13</b>, <i>n</i>=5; <b>14</b>, <i>n</i>=6; <b>15</b>, <i>n</i>=7; <b>16</b>, <i>n</i>=8; <b>17</b>, <i>n</i>=10; <b>18</b>, <i>n</i>=12) and the corresponding oligomethylene-bridged diorganotin oxides [(Me₃SiCH₂)(O)Sn(CH₂)_<i>n</i>Sn(O)(CH₂SiMe₃)]_<i>m</i> (<b>19</b>, <i>n</i>=5; <b>20</b>, <i>n</i>=6; <b>21</b>, <i>n</i>=7; <b>22</b>, <i>n</i>=8; <b>23</b>, <i>n</i>=10; <b>24</b>; <i>n</i>=12) is reported. The reaction of the diorganodichlorostannanes <b>13–18</b> with the corresponding diorganotin oxides <b>19–24</b> provided the spacer-bridged tetraorganodistannoxanes {[(Me₃SiCH₂)ClSn(CH₂)_<i>n</i>SnCl(CH₂SiMe₃)]O}₄ (<b>25</b>, <i>n</i>=5; <b>26</b>, <i>n</i>=6; <b>27</b>, <i>n</i>=7; <b>28</b>, <i>n</i>=8; <b>29</b>, <i>n</i>=10; <b>30</b>, <i>n</i>=12). Compounds <b>13–30</b> have been identified by elemental analyses and multinuclear NMR spectroscopy. Compounds <b>25, 27, 29</b> and <b>30</b> have also been characterised by single crystal X-ray diffraction analysis and electrospray mass spectrometry. For the latter the essential double ladder motif is maintained for all <i>n</i> in the solid state, but subtle changes in alignment of the ladder planes occur. Separation between the two layers of the double ladder ranges from approx. 8.7  Å (for <b>25</b>, <i>n</i>=5) to approx. 15 Å (for <b>30</b>, <i>n</i>=12). In solution there is some dissociation of the double ladders into the corresponding dimers. The degree of dissociation is favoured by increasing oligomethylene chain length <i>n</i>.<br /><br /><br />