Chemistry of [1-Cp*-<i>arachno</i>-1-IrB<sub>4</sub>H<sub>10</sub>] and [1-Cp*-<i>arachno</i>-1-IrB<sub>3</sub>H<sub>9</sub>]: Synthesis and Characterization of the New Substituted Iridaboranes [1-Cp*-<i>arachno</i>-1-IrB<sub>3</sub>H<sub>7</sub>-2-L], [1-Cp*-<i>arachno</i>-1-IrB<sub>2</sub>H<sub>6</sub>-2-L], and [1-Cp*-<i>arachno</i>-1-IrB<sub>4</sub>H<sub>8</sub>-2,5-(Br)<sub>2</sub>] (L = PMe<sub>3</sub>, PMe<sub>2</sub>Ph, PMePh<sub>2</sub>, py, NEt<sub>3</sub>)
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The treatment of [Cp*IrB4H10] (1) and [Cp*IrB3H9] (2) with typical Lewis bases afforded the new substituted iridatetra- and iridatriboranes [Cp*IrB3H7L] (L = PMe3 (3), PMe2Ph (5), PMePh2 (7), PPh3 (10), py (12), NEt3 (14)) and [Cp*IrB2H6L] (L = PMe3 (4), PMe2Ph (6), PMePh2 (8), PPh3 (11), py (13), NEt3 (15)), respectively, plus the adduct BH3L as coproduct. With PPh3, py, and NEt3, the formation of the iridapentaborane [1-Cp*-nido-1-IrB4H8] (9) was also observed. The molecular structure of [Cp*IrB2H6L] was confirmed by X-ray diffraction analysis on compounds 4, 8, and 13. The substituted iridatetraboranes were found to decompose in solution and in the solid state with decomposition pathways that depend on the nature of the L−B bond and the concentration of the free Lewis bases. Two routes involving the apparent disproportionation of iridaborane−base adducts were found to compete with the loss of a {BH} unit. A reaction cycle driven by the Lewis acid/base chemistry of BH3 was constructed from these reactions. The P−B bond is labile, leading to ligand exchange with free Lewis bases. For compound 3, the equilibrium constant for the exchange with PMe2Ph, PMePh2, and py was measured. In contrast to reaction with nucleophiles, treatment of 1 with bromine and N-bromosuccinimide led to the formation of the dibromo- and monobromo derivatives [1-Cp*-1-H-2,5-(Br)2-arachno-1-IrB4H7] (16) and[1-Cp*-1-H-2-Br-arachno-1-IrB4H8] (17), respectively. The molecular structure of 16 was confirmed by X-ray diffraction analysis.
