Versatility of nido-Monophosphinocarboranes as Ligands. Tricoordination via PPh₂ and BH in Rhodium(I) Complexes

Abstract

Reaction of [NMe4][7-PPh2-8-R-7,8-C2B9H10] (R = H, Me) with [Rh2(μ-Cl)2(cod)2] in dichloromethane yielded [Rh(7-PPh2-8-R-7,8-C2B9H10)(cod)] (R = H, Me). The carborane ligand coordinates the Rh through Cc−PPh2, B(11)−H, and B(2)−H. The Rh(I) atom is pentacoordinated, assuming that cod is bidentate. The B−H→Rh resonances in the 1H NMR spectra appear in the interval between +1 and +3 ppm, as a consequence of the trans influence generated by cod. The structure was fully elucidated by a crystal diffraction analysis of [Rh(7-PPh2-8-Me-7,8-C2B9H10)(cod)]. The B−H→Rh agostic bonds exist both in the solid state and in solution, as was proven by 11B NMR.

Chelating Monoborane Phosphines: Rational and High-Yield Synthesis of [(COD)Rh{(η2-BH3)Ph2PCH2PPh2}][PF6] (COD = 1,5-cyclooctadiene)

“…This η 2 -coordination motif of the borane was initially unexpected, as the formally d 8 Rh(I) metal center requires only one B−H−Rh interaction to attain a 16-electron count. However, similar pentacoordination has been observed previously in Rh(7-PPh 2 -8-Me-7,8-C 2 B 9 H 10 )(COD) . All hydrogen atoms on the borane were located and freely refined in the crystal structure.…”

Formation of B−P Bonds through the Reaction of nido-Monophosphinocarboranes with Palladium(II) Complexes. The First Example of a Chelating R2P−C−B−PR2 Diphosphine

“…This may be the necessary result to complex Pd(II). In effect, as we have indicated earlier, either the mono- or disubstituted derivatives of [C 2 B 9 H 12 ] - with electron-rich elements are always di- or tricoordinating, depending on the geometrical requirements of the transition-metal ion. − If only one lone-pair-containing group (e.g. −SR or −PR 2 ) is available, the carborane cluster provides one or two extra B−H's to coordinate the metal.…”

“…−SR or −PR 2 ) is available, the carborane cluster provides one or two extra B−H's to coordinate the metal. The first B−H involved is the one corresponding to B(11), − the same boron atom that has formed the B(11)−P bond. Thus, it was not necessary to form a B−P bond to render the [C 2 B 9 H 12 ] - derivatives chelating; they already had this possibility via the Ph 2 P−C−B−H moiety.…”

“…The influence of 7,8-dicarba- nido -undecaborate(1−) on the coordinating behavior of electron-rich elements such as sulfur and phosphorus has been reported. Previously, we have described the syntheses of metallacarboranes based on nido -monothiocarboranes [7-SR-8-R‘-7,8-C 2 B 9 H 10 ] - with Ru(II), Rh(I), and Pd(II) and nido -monophosphinocarboranes [7-PR 2 -8-R‘-7,8-C 2 B 9 H 10 ] - , as special tertiary phosphines, with Ru(II) and Rh(I). 4b, These monosubstituted ligands provide one strong coordinating element, either SR or PR 2 , and require one or two B−H groups, depending on the coordinating metal's demand. Although nido -monothio- and nido -monophosphinocarboranes have shown similar reactivities toward Rh(I),4b some differences have been found for Ru(II) 6a.…”

exo-nido-Cyclooctadienerhodacarboranes: Synthesis, Reactivity, and Catalytic Properties in Alkene Hydrogenation

“…Hawthorne and co-workers first applied this method to a closo -rhodacarborane catalyst and enhanced rates were obtained . However, we are not aware of the existence of exo-nido -rhodacarboranes in which B−H−Rh interactions and Rh-alkene bonds coexist in the same molecule other than our recent report on [Rh(7-PPh 2 -8-Me-7,8-C 2 B 9 H 10 )(cod)] . These considerations led us to explore the possibility of obtaining exo-nido -monothiorhodacarboranes which incorporates ancillary alkene ligands.…”