| Sumario: | The [8,8,8-(H)(PPh 3) 2-9-(Py)-nido-8,7-RhSB 9H 9] (2)/[1,1-(PPh 3) 2-3-(Py)-closo- 1,2-RhSB 9H 8] (3) pair catalyzes the hydrogenation of olefins through nido-to-closo transformations. Substitution of the phosphine ligands can lead to an improvement of the catalytic activity of this system. Therefore, the substitutional chemistry of 2 with PMePh 2, PMe 2Ph, and PMe 3 has been studied, leading to the formation of [8,8,8-(H)(PPh 3)(PR 3)-9-(Py)-nido-8,7-RhSB 9H 9], where R 3 = Me 2Ph (5) or Me 3 (6), and [8,8,8-(H)(PR 3) 2-9-(Py)-nido-8,7- RhSB 9H 9], where R 3 = MePh 2 (4) or Me 2Ph (7). Kinetic studies on the reaction of PMe 2Ph with 2 indicate that the substitutions follow a dissociative mechanism. The thermal dehydrogenation of 5-7 affords the corresponding closo-derivatives [1,1-(L)(PPh 3)-3-(Py)-closo-1,2-RhSB 9H 8], where L = PMe 2Ph (9) or PMe 3 (10), and [1,1-(L) 2-3-(Py)-closo-1,2-RhSB 9H 8], where L = PMe 2Ph (11) or PMe 3 (12). The substitution of PPh 3 by the more basic, less bulky phosphines facilitates hydrogen loss and consequent nido-to-closo transformations. The reaction of 5 and 6 with C 2H 4 promotes a nido-to-closo cluster change and the consequent formation of 10 and 11 together with small amounts of C 2H 4-ligated [1,1-(η 2-C 2H 4)(L)-3-(Py)-closo-1,2-RhSB 9H 8], where L = PPh 3 (13) or PMe 3 (15), characterized in situ by 1H NMR spectroscopy. In the reactions with ethylene, ethane is detected in situ, indicating that the olefin is hydrogenated. The reactions of 5 and 6 with CO afford the CO-ligated [1,1-(CO)(L)-3-(Py)-closo-1,2-RhSB 9H 8], where L = PMe 2Ph (16) or PMe 3 (17). The reactivity of the new PR 3-ligated nido-clusters versus H 2, C 2H 4, and CO is not improved with the phosphines studied in this work; however, the changes found in the chemical beahavior of this system are dramatic, confirming the tailorability of these 11-vertex rhodathiaboranes and the potential optimization of their catalytic activity by the judicious choice of the exo-polyhedral ligands. © 2012 American Chemical Society.
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