| Summary: | Chapter 1 begins with a brief introduction to the structural characteristics of cyclopentadienyl complexes and carbametallaboranes derived from [7,8-<i>nido</i>-C<SUB>2</SUB>B<SUB>9</SUB>H<SUB>11</SUB>]<SUP>2-</SUP>. This is followed by a discussion of the chemistry of monoanionic <i>nido</i>-icosahedral carbaboranes, paying particular attention to compounds containing the ligand [9-SMe<SUB>2</SUB>-7,8-<i>nido</i>-C<SUB>2</SUB>B<SUB>9</SUB>H<SUB>10</SUB>]<SUP>-</SUP>. The chapter ends with a survey of compounds involving the sterically demanding species [7,8-Ph<SUB>2</SUB>-7,8-<i>nido</i>-C<SUB>2</SUB>B<SUB>9</SUB>H<SUB>9</SUB>]<SUP>2-</SUP>. Chapter 2 describes the synthesis and spectroscopic and structural characterisation of three [ML<SUB>2</SUB>] derivatives of [9-SMe<SUB>2</SUB>-7,8-<i>nido</i>-C<SUB>2</SUB>B<SUB>9</SUB>H<SUB>10</SUB>]<SUP>-</SUP>. The crystallographically observed cornformations of the [ML<SUB>2</SUB>] fragments with respect to the carbaborane ligand in 3,3-(CO)<SUB>2</SUB>-4-SMe<SUB>2</SUB>-4-SMe<SUB>2</SUB>-3,1,2-<i>closo</i>-RhC<SUB>2</SUB>B<SUB>9</SUB>H<SUB>10</SUB>, 1, and 3-(η2,η2-C<SUB>8</SUB>H<SUB>12</SUB>)-4-SMe<SUB>2</SUB>-3,1,2-<i>closo</i>-3,1,2-RhC<SUB>2</SUB>B<SUB>9</SUB>H<SUB>10</SUB>, 2, differ significantly from those adopted by (ML<SUB>2</SUB>) complexes of the unsubstituted ligand [7,8-<i>nido</i>-C<SUB>2</SUB>B<SUB>9</SUB>H<SUB>11</SUB>]<SUP>2-</SUP>. This has been traced to differences in the π frontier molecular orbitals of the carbaborane fragments, the observed orientations being consistent with the results of extended Hükel molecular orbital (EHMO) calculations. The conformation adopted in [3-(η2,η2-C_8H_12)-4-SMe_2-3,1,2-<i>closo</i>-PdC_2B_9H_10]BF_4, 4.BF_4, is strongly influenced by electrostatic interactions both within and between ion pairs within the crystal. 4^+ is a rare example of a cationic heteroborane, analogous to compound 2 except in the notional replacement of Rh^+ by Pd^2+ . Comparative EHMO calculations show that the additional charge in 4^+ is delocalised over the entire icosahedral framework and is not localised either at the metal vertex or at the pendant, cage-bound sulphur atom. Chapter 3 presents a series of palladium allyl derivatives of [9-SMe_2-7,8-<i>nido</i>-C_2B_9H_10]^- of the general formula 3-(C_3H_4R)-4-SMe_2-3,1,2-<i>closo</i>PdC_2B_9H_10, all of which have been characterised by ^1H and ^11B n.m.r. spectroscopy. and three of which have been structurally characterised.
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