<jats:title>Abstract</jats:title><jats:p>Novel neutral and cationic Rh<jats:sup>I</jats:sup> and Ir<jats:sup>I</jats:sup> complexes that contain only DMSO molecules as dative ligands with S‐, O‐, and bridging S,O‐binding modes were isolated and characterized. The neutral derivatives [RhCl(DM<jats:italic>S</jats:italic>O)<jats:sub>3</jats:sub>] (<jats:bold>1</jats:bold>) and [IrCl(DM<jats:italic>S</jats:italic>O)<jats:sub>3</jats:sub>] (<jats:bold>2</jats:bold>) were synthesized from the dimeric precursors [M<jats:sub>2</jats:sub>Cl<jats:sub>2</jats:sub>(coe)<jats:sub>4</jats:sub>] (M=Rh, Ir; COE=cyclooctene). The dimeric Ir<jats:sup>I</jats:sup> compound [Ir<jats:sub>2</jats:sub>Cl<jats:sub>2</jats:sub>(DM<jats:italic>S</jats:italic>O)<jats:sub>4</jats:sub>] (<jats:bold>3</jats:bold>) was obtained from <jats:bold>2</jats:bold>. The first example of a square‐planar complex with a bidentate S,O‐bridging DMSO ligand, [(coe)(DM<jats:italic>S</jats:italic>O)Rh(μ‐Cl)(μ‐DM<jats:italic>SO</jats:italic>)RhCl(DM<jats:italic>S</jats:italic>O)] (<jats:bold>4</jats:bold>), was obtained by treating [Rh<jats:sub>2</jats:sub>Cl<jats:sub>2</jats:sub>(coe)<jats:sub>4</jats:sub>] with three equivalents of DMSO. The mixed DMSO–olefin complex [IrCl(cod)(DM<jats:italic>S</jats:italic>O)] (<jats:bold>5</jats:bold>, COD=cyclooctadiene) was generated from [Ir<jats:sub>2</jats:sub>Cl<jats:sub>2</jats:sub>(cod)<jats:sub>2</jats:sub>]. Substitution reactions of these neutral systems afforded the complexes [RhCl(py)(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>] (<jats:bold>6</jats:bold>), [IrCl(py)(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>] (<jats:bold>7</jats:bold>), [IrCl(<jats:italic>i</jats:italic>Pr<jats:sub>3</jats:sub>P)(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>] (<jats:bold>8</jats:bold>), [RhCl(dmbpy)(DM<jats:italic>S</jats:italic>O)] (<jats:bold>9</jats:bold>, dmbpy=4,4′‐dimethyl‐2,2′‐bipyridine), and [IrCl(dmbpy)(DM<jats:italic>S</jats:italic>O)] (<jats:bold>10</jats:bold>). The cationic O‐bound complex [Rh(cod)(DMS<jats:italic>O</jats:italic>)<jats:sub>2</jats:sub>]BF<jats:sub>4</jats:sub> (<jats:bold>11</jats:bold>) was synthesized from [Rh(cod)<jats:sub>2</jats:sub>]BF<jats:sub>4</jats:sub>. Treatment of the cationic complexes [M(coe)<jats:sub>2</jats:sub>(OCMe<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>]PF<jats:sub>6</jats:sub> (M=Rh, Ir) with DMSO gave the mixed S‐ and O‐bound DMSO complexes [M(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>(DMS<jats:italic>O</jats:italic>)<jats:sub>2</jats:sub>]PF<jats:sub>6</jats:sub> (Rh=<jats:bold>12</jats:bold>; Ir=in situ characterization). Substitution of the O‐bound DMSO ligands with dmbpy or pyridine resulted in the isolation of [Rh(dmbpy)(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>]PF<jats:sub>6</jats:sub> (<jats:bold>13</jats:bold>) and [Ir(py)<jats:sub>2</jats:sub>(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>]PF<jats:sub>6</jats:sub> (<jats:bold>14</jats:bold>). Oxidative addition of hydrogen to [IrCl(DM<jats:italic>S</jats:italic>O)<jats:sub>3</jats:sub>] (<jats:bold>2</jats:bold>) gave the kinetic product <jats:italic>fac</jats:italic>‐[Ir(H)<jats:sub>2</jats:sub>Cl(DM<jats:italic>S</jats:italic>O)<jats:sub>3</jats:sub>] (<jats:bold>15</jats:bold>) which was then easily converted to the more thermodynamically stable product <jats:italic>mer</jats:italic>‐[Ir(H)<jats:sub>2</jats:sub>Cl(DM<jats:italic>S</jats:italic>O)<jats:sub>3</jats:sub>] (<jats:bold>16</jats:bold>). Oxidative addition of water to both neutral and cationic Ir<jats:sup>I</jats:sup> DMSO complexes gave the corresponding hydrido–hydroxo addition products <jats:italic>syn</jats:italic>‐[(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>HIr(μ‐OH)<jats:sub>2</jats:sub>(μ‐Cl)IrH(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>][IrCl<jats:sub>2</jats:sub>(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>] (<jats:bold>17</jats:bold>) and <jats:italic>anti</jats:italic>‐[(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>(DMS<jats:italic>O</jats:italic>)HIr(μ‐OH)<jats:sub>2</jats:sub>IrH(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>(DMS<jats:italic>O</jats:italic>)][PF<jats:sub>6</jats:sub>]<jats:sub>2</jats:sub> (<jats:bold>18</jats:bold>). The cationic [Ir(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>(DMS<jats:italic>O</jats:italic>)<jats:sub>2</jats:sub>]PF<jats:sub>6</jats:sub> complex (formed in situ from [Ir(coe)<jats:sub>2</jats:sub>(OCMe<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>]PF<jats:sub>6</jats:sub>) also reacts with methanol to give the hydrido–alkoxo complex <jats:italic>syn</jats:italic>‐[(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>HIr(μ‐OCH<jats:sub>3</jats:sub>)<jats:sub>3</jats:sub>IrH(DM<jats:italic>S</jats:italic>O)<jats:sub>2</jats:sub>]PF<jats:sub>6</jats:sub> (<jats:bold>19</jats:bold>). Complexes <jats:bold>1, 2, 4, 5, 11, 12, 14, 17, 18</jats:bold>, and <jats:bold>19</jats:bold> were characterized by crystallography.</jats:p>