Extending the coordination capabilities of tertiary phosphines and arsines: preparation, molecular structure, and reactivity of dinuclear rhodium complexes with PR3 and AsR3 in a doubly bridging coordination mode

Abstract

The reactions of [Rh₂(κ²-acac)₂(μ-CPh₂)₂(μ-PR₃)] (PR₃ = PMe₃4, PMe₂Ph 7, PEt₃8) with an equimolar amount of Me₃SiX (X = Cl, Br, I) afforded the unsymmetrical complexes [Rh₂X(κ²-acac)(μ-CPh₂)₂(μ-PR₃)] 5, 9–12, which contain the phosphine in a semi-bridging coordination mode. From 4 and excess Me₃SiCl, the tetranuclear complex [{Rh₂Cl(μ-Cl)(μ-CPh₂)₂(μ-PMe₃)}₂] 6 was obtained. In contrast, the reaction of 4 with an excess of Me₃SiX (X = Br, I) yielded the dinuclear complexes [Rh₂X₂(μ-CPh₂)₂(μ-PMe₃)] 13, 14 in which, as shown by the X-ray crystal structure analysis of 14, the bridging phosphine is coordinated in a truly symmetrical bonding mode. While related compounds with PEt₃ and PMe₂Ph as bridging ligands were prepared on a similar route, the complex [Rh₂Cl₂(μ-CPh₂)₂(μ-PiPr₃)] 19 was obtained from the mixed-valence species [(PiPr₃)Rh(μ-CPh₂)₂Rh(κ²-acac)₂] 17 and HCl. The reaction of [Rh₂(κ²-acac)₂(μ-CPh₂)₂(μ-SbiPr₃)] 3 with AsMe₃ gave the related Rh(μ-AsMe₃)Rh compound 21. With Me₃SiCl, the acac ligands of 21 can be replaced stepwise by chloride to give [Rh₂Cl(κ²-acac)(μ-CPh₂)₂(μ-AsMe₃)] 23 and [{Rh₂Cl(μ-Cl)(μ-CPh₂)₂(μ-AsMe₃)}₂] 24, the latter being isomorphous to the phosphine-bridged dimer 6.