Bis(phosphine)hydridorhodacarborane Derivatives of 1,1′-Bis(ortho-carborane) and Their Catalysis of Alkene Isomerization and the Hydrosilylation of Acetophenone

Abstract

Deprotonation of [7-(1′-closo-1′,2′-C2B10H11)-nido-7,8-C2B9H11]− and reaction with [Rh­(PPh3)3Cl] results in isomerization of the metalated cage and the formation of [8-(1′-closo-1′,2′-C2B10H11)-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (1). Similarly, deprotonation/metalation of [8′-(7-nido-7,8-C2B9H11)-2′-(p-cymene)-closo-2′,1′,8′-RuC2B9H10]− and [8′-(7-nido-7,8-C2B9H11)-2′-Cp*-closo-2′,1′,8′-CoC2B9H10]− affords [8-{8′-2′-(p-cymene)-closo-2′,1′,8′-RuC2B9H10}-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (2) and [8-(8′-2′-Cp*-closo-2′,1′,8′-CoC2B9H10)-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (3), respectively, as diastereoisomeric mixtures. The performances of compounds 1–3 as catalysts in the isomerization of 1-hexene and in the hydrosilylation of acetophenone are compared with those of the known single-cage species [3-H-3,3-(PPh3)2-closo-3,1,2-RhC2B9H11] (I) and [2-H-2,2-(PPh3)2-closo-2,1,12-RhC2B9H11] (V), the last two compounds also being the subjects of 103Rh NMR spectroscopic studies, the first such investigations of rhodacarboranes. In alkene isomerization all the 2,1,8- or 2,1,12-RhC2B9 species (1–3, V) outperform the 3,1,2-RhC2B9 compound I, while for hydrosilylation the single-cage compounds I and V are better catalysts than the double-cage species 1–3.

Exopolyhedral Ligand Orientation Controls Diastereoisomer in Mixed-Metal Bis(Carboranes)

“…These results are consistent with a p-cymene ligand locked in conformation and a PPh 3 ligand in which one ring is in a unique environment. Two C cage H resonances are present, one at δ 2.68 ppm assigned to the ruthenacarborane cage by analogy with the resonance in IV Ru [8], and the other at much higher frequency, δ 5.02 ppm, consistent with a non-isomerised 3,1,2-RhC 2 B 9 rhodacarborane cage.…”

“…Recent years have witnessed a significant amount of interest in the chemistry of bis(carboranes) [1][2][3][4], particularly 1,1 -bis(ortho-carborane), formally [1-(1 -closo-1 ,2 -C 2 B 10 H 11 )-closo-1,2-C 2 B 10 H 11 ] (I), Scheme 1. This species offers a versatile scaffold for derivatisation and, amongst other studies, we have reported the single deboronation/metalation [5], double deboronation/homometalation [6] and stepwise deboronation/metalation-deboronation/heterometalation [7] of I, the latter including the use of {Rh(H)(PPh 3 ) 2 } fragments to afford homogeneous catalyst precursors [8].…”

“…Repeating this reaction at room temperature, after workup involving preparative thin-layer chromatography (TLC), resulted in the isolation of a new species 1 as the main product, albeit with a modest yield (11%). Also isolated were trace amounts (<1%) of both diastereoisomers of the known species IV Ru , identified by multinuclear NMR spectroscopy [8].…”

“…Although deprotonation of III CoCp* with n BuLi followed by treatment with [Rh(PPh 3 ) 3 Cl] leads to the heterobimetallic IV CoCp* as a mixture of diastereoisomers [8], the same approach cannot be used with the Cp analog III CoCp because of the attack on the Cp ring by n BuLi. Accordingly, we have reverted to direct reaction between [HNMe 3 ][8- The presence of two diastereoisomers is evident from the observation of two Cp and two high-frequency C cage H resonances in the 1 H NMR spectrum, the latter assigned to the cobaltacarborane cage, and the diastereoisomeric ratio is approximately 1:1.5.…”

“…Deprotonation of the endo H atom and reaction with [Rh(PPh 3 ) 3 Cl] led to isomerisation of the primed cage and the isolation of the product [8-{8 -2 -H-2 ,2 -(PPh 3 ) 2 -closo-2 ,1 ,8 -RhC 2 B 9 H 11 }-2-L-closo-2,1,8-MC 2 B 9 H 10 ] (IV) as a diastereoisomeric mixture [8]. Compounds of type IV were found to be active catalyst precursors for alkene isomerisation and the hydrosilylation of acetophenone.…”