Xiao Xu-Qiong

An unusual germole-to-silole transformation is described. As key intermediates hetero-fulvenes are formed which rearrange to more stable bicyclic carbene analogues. The so-formed germylenes undergo a reductive elimination yielding elemental germanium and siloles. In contrast, the analogous silylenes are stable at ambient conditions and were identified by MS spectrometry and NMR spectroscopy supported by the results of quantum mechanical calculations. These bicyclic silylenes are stable derivatives of the global minimum of the C₄Si₂H₆ potential energy surface.

Always expect the unexpected: An unprecedented germole to silole transformation opened the way for the synthesis of novel bicyclic silylenes that are stable derivatives of the global minimum on the C₄Si₂H₆ potential energy surface.

We have prepared and fully characterized two isomers of [Ir^IV(dpyp)₂] (dpyp=meso-2,4-di(2-pyridinyl)-2,4-pentanediolate). These complexes can cleanly oxidize to [Ir^V(dpyp)₂]⁺, which to our knowledge represent the first mononuclear coordination complexes of Ir^V in an N,O-donor environment. One isomer has been fully characterized in the Ir^V state, including by X-ray crystallography, XPS, and DFT calculations, all of which confirm metal-centered oxidation. The unprecedented stability of these Ir^V complexes is ascribed to the exceptional donor strength of the ligands, their resistance to oxidative degradation, and the presence of four highly donor alkoxide groups in a plane, which breaks the degeneracy of the d-orbitals and favors oxidation.

A robust ligand and a rare oxidation state: [Ir^IV(dpyp)₂] cleanly oxidizes to [Ir^V(dpyp)₂]⁺, the first mononuclear example of Ir^V in an N,O-donor environment. Full characterization of the Ir^V species, including by X-ray crystallography in one case, allows exploration of this rare oxidation state.

A 1,3-digerma-2-silacyclopenta-1,2-diene, that is, a 1,3-digerma-2-silaallene incorporated into a five-membered ring system, was synthesized and obtained as a stable orange solid. Owing to incorporation into a cyclic framework, the 1,3-digerma-2-silaallene moiety is highly bent, exhibiting a Si⁰ character for the central silicon moiety.

The bends: A 1,3-digerma-2-silacyclopenta-1,2-diene, that is, a 1,3-digerma-2-silaallene incorporated into a five-membered ring system, was synthesized and obtained as a stable orange solid. Owing to incorporation into a cyclic framework, the 1,3-digerma-2-silaallene moiety is highly bent, exhibiting a Si⁰ character for the central silicon moiety.

Manganese and hydrogen are two key elements used by D. J. H. Emslie et al. in their Communication (DOI: 10.1002/anie.201700863). The reactions described sequentially introduce silicon and carbon into the core of the molecule, which is represented by an inukshuk, a stone landmark used by peoples of the Arctic region, including northern Canada. On the left-hand side, the climb of two silylene hydride molecules towards the core of the final product, represented by “Hounds Tooth” in British Columbia (Canada), is shown.

Reaction of the ethylene hydride complex trans-[(dmpe)₂MnH(C₂H₄)] (1) with Et₂SiH₂ at 20 °C afforded the silylene hydride [(dmpe)₂MnH(=SiEt₂)] (2 a) as the trans-isomer. By contrast, reaction of 1 with Ph₂SiH₂ at 60 °C afforded [(dmpe)₂MnH(=SiPh₂)] (2 b) as a mixture of the cis (major) and trans (minor) isomers, featuring a Mn-H-Si interaction in the former. The reaction to form 2 b also yielded [(dmpe)₂MnH₂(SiHPh₂)] (3 b); [(dmpe)₂MnH₂(SiHR₂)] (R=Et (3 a) and Ph (3 b)) were accessed cleanly by reaction of 2 a and 2 b with H₂, and the analogous reactions with D₂ afforded [(dmpe)₂MnD₂(SiHR₂)] exclusively. Both 2 a and 2 b engaged in unique reactivity with ethylene, generating the silene hydride complexes cis-[(dmpe)₂MnH(R₂Si=CHMe)] (R=Et (4 a), Ph (4 b)). Compounds trans-2 a, cis-2 b, 3 b, and 4 b were crystallographically characterized, and bonding in 2 a, 2 b, 4 a, and 4 b was probed computationally.

Alkene hydride complex trans-[(dmpe)₂MnH(C₂H₄)] eliminates ethane upon reaction with secondary silanes, yielding cis- and trans-isomers of the silylene hydride complexes [(dmpe)₂MnH(=SiR₂)]. Reaction with ethylene yields silene hydride complexes [(dmpe)₂MnH(R₂Si=CHMe)]—most likely via a low-coordinate silyl isomer [(dmpe)₂Mn(SiHR₂)] that is in equilibrium with the silylene hydrides.