Synthesis and structures of the homoleptic cations [M(PMe3)5]+ (M = Rh, Ir)

Capture of mechanically interlocked molecules by rhodium-mediated terminal alkyne dimerisation

The transition metal-mediated dimerisation of terminal alkynes is an attractive and atom-economic method for preparing conjugated 1,3-enynes. Using a phosphine-based macrocyclic pincer ligand, we demonstrate how this transformation can be extended to the synthesis of novel, hydrocarbon-based interlocked molecules: a rotaxane by 'active' metal template synthesis and a catenane by sequential 'active' and 'passive' metal template procedures.

A Stable N-Hetero-Rh-Metallacyclic Silylene

A cyclic (amino)metal-substituted dicoordinated silylene derivative has been synthesized and fully characterized. Of particular interest is that the N-hetero-Rh^I -metallacyclic silylene exhibits a distorted tetrahedral geometry around the rhodium atom and a considerably shortened Si-Rh bond (2.138 Å) compared to classical Si-Rh single bonds (ca. 2.30-2.35 Å). A theoretical investigation reveals that the geometrical deviation around the rhodium center from the classical square-planar to a tetrahedral geometry increases the π-donating and σ-accepting character of the rhodium atom, thereby efficiently stabilizing the silylene moiety.

Pseudo-tetrahedral Rhodium and Iridium Complexes: Catalytic Synthesis of E-Enynes

The reactions of the rhodium(I) and iridium(I) complexes [M(PhBP₃ )(C₂ H₄ )(NCMe)] (PhBP₃ =PhB(CH₂ PPh₂ )₃ ^- ) with alkynes have resulted in the synthesis of a new family of pseudo-tetrahedral complexes, [M(PhBP₃ )(RC≡CR')] (M=Rh, Ir), which contain the alkyne as a four-electron donor. The reactions of these unusual compounds with two-electron donors (L=PMe₃ , CNtBu) produced a change in the "donicity" of the alkyne from a 4e^- to a 2e^- donor to give five-coordinate complexes. These were the final products with the iridium complexes, whereas further reactions took place with the rhodium complexes. In particular, C(sp)-H bond activation of the alkyne occurred leading to hydrido alkynyl complexes. This process is essential for the further reactivity of the alkynes, and if the alkyne itself was used as reagent, E-enyne complexes were obtained. As a consequence of this chemistry, we show that the complex [Rh(PhBP₃ )(C₂ H₄ )(NCMe)] is a very efficient pre-catalyst for the regioselective di- and trimerization of terminal alkynes to E-enynes and benzene derivatives, respectively. Interestingly, acetonitrile significantly enhanced the catalytic activity by facilitating the C(sp)-H bond activation step. A hydrometalation mechanism to account for these experimental observations is proposed.

Triethylsilyl Perfluoro-Tetraphenylborate, [Et(3)Si][F(20)-BPh(4)], a widely used Non-Existent Compound

The commonly used triethylsilyl per-fluoro-tetraphenylborate salt, [Et(3)Si(+)][F(20)-BPh(4) (-)], has been misidentified. As prepared, the cation is a hydride-bridged silane adduct [R(3)Si-H-SiR(3) (+)]. Under favorable circumstances it can be an effective source of the triethylsilylium ion Et(3)Si(+) but in the absence of a stabilizing base the potent electrophilicity of Et(3)Si(+) decomposes the "inert" F(20)-BPh(4) (-) counterion.