Polyhedral Rearrangements in the Complexes of Rhodium and Iridium with Isomeric Carborane Anions [7,8-Me₂‑X-SMe₂‑7,8-<i>nido</i>-C₂B₉H₈]⁻ (X = 9 and 10)

Polyhedral rearrangement of iridacarborane 1,2-Me₂-3,3-(cod)-4-SMe₂-3,1,2<i>-closo</i>-IrC₂B₉H₈ (<b>1</b>) proceeds in a solution at RT and affords a product of 1,2 → 1,7 isomerization 1,8-Me₂-2,2-(cod)-7-SMe₂-2,1,8-<i>closo</i>-IrC₂B₉H₈ (<b>2</b>). Rhodium derivative 1,2-Me₂-3,3-(cod)-4-SMe₂-3,1,2<i>-closo</i>-RhC₂B₉H₈ (<b>3</b>) is significantly more stable toward heating than iridium complex <b>1</b> and isomerizes at 110 °C by 1,2 → 1,2 and 1,2 → 1,7 reaction schemes with 1,2 → 1,2 being the predominant route forming 1,2-Me₂-4,4-(cod)-8-SMe₂-4,1,2-<i>closo-</i>RhC₂B₉H₈ (<b>4</b>) and 1,8-Me₂-2,2-(cod)-7-SMe₂-2,1,8-<i>closo</i>-RhC₂B₉H₈ (<b>5</b>). Complexes <b>4</b> and <b>5</b> were characterized by ¹¹B­{¹H}–¹¹B­{¹H} COSY NMR spectrometry. A mechanism of 1,2 → 1,2 isomerization of <b>3</b> to <b>4</b> was proposed on the basis of DFT calculations. Reaction of the thallium salt Tl­[7,8-Me₂-9-SMe₂-7,8-<i>nido</i>-C₂B₉H₈] (CarbTl) with [Cp*RuCl]₄ in THF furnishes new ruthenacarborane 1,2-Me₂-3-(Cp*)-4-SMe₂-3,1,2<i>-closo</i>-RuC₂B₉H₈ (<b>6</b>). Heating of <b>6</b> at 80 and 144 °C leads to the partial and complete decomposition, respectively. Interaction of CarbTl with [Cp*IrCl₂]₂ in the presence of TlPF₆ provides two new Ir­(III) complexes [1,2-Me₂-3-(Cp*)-4-SMe₂-3,1,2<i>-closo</i>-IrC₂B₉H₈]­PF₆ (<b>7</b>PF₆) and 1,2-Me₂-3-(Cp*)-4-SMe-3,1,2<i>-closo</i>-IrC₂B₉H₈ (<b>8</b>) both stable upon heating in boiling tetrachloroethane (146 °C). A new 10-substituted charge-compensated carborane [7,8-Me₂-10-SMe₂-7,8-<i>nido</i>-C₂B₉H₉] (<b>9</b>) was synthesized via an interaction of dicarbollide dianion [7,8-Me₂-7,8-<i>nido</i>-C₂B₉H₉]^2– with dimethyl sulfide and acetaldehyde in acidic media. Thallium salt of <b>9</b> Tl­[7,8-Me₂-10-SMe₂-7,8-<i>nido</i>-C₂B₉H₈] (<b>10</b>) reacts with [(cod)­IrCl]₂ furnishing positional isomer of <b>1</b> with a symmetrical emplacement of SMe₂ substituent complex 1,2-Me₂-3,3-(cod)-8-SMe₂-3,1,2-<i>closo</i>-IrC₂B₉H₈ (<b>11</b>). Iridacarborane <b>11</b> requires elevated temperatures to undergo cage isomerization and converts upon heating at 110 °C to two new compounds 1,8-Me₂-2,2-(cod)-11-SMe₂-2,1,8-<i>closo</i>-IrC₂B₉H₈ (<b>12</b>) and 1,2-Me₂-4,4-(cod)-9-SMe₂-4,1,2-<i>closo-</i>IrC₂B₉H₈ (<b>13</b>) as a result of 1,2 → 1,7 and 1,2 → 1,2 rearrangements respectively with <b>13</b> being the minor product. The structures of <b>2</b>, <b>6</b>, <b>7</b>PF₆, <b>8</b>, <b>10</b>, <b>12</b>, and <b>13</b> were determined by single-crystal X-ray diffraction

Cyclobutadiene Metal Complexes: A New Class of Highly Selective Catalysts. An Application to Direct Reductive Amination

A catalyst of a new type, cyclobutadiene complex [(C₄Et₄)­Rh­(<i>p</i>-xylene)]­PF₆, was found to promote selective reductive amination in the presence of carbon monoxide under mild conditions (1–3 bar, 90 °C). The reaction demonstrated perfect compatibility with a wide range of functional groups prone to reduction by conventional reducing agents. The developed system represents the first systematic investigation of cyclobutadiene metal complexes as catalysts