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The N‐heterocyclic silylene (NHSi) [Ph2P(tBuN)2]SiCl (1), supported by an iminophosphonamide ligand, was obtained from the dehydrochlorination of [Ph2P(tBuN)2]SiHCl2 (2) with LiN(SiMe3)2. NHSi 1 contains an extremely high‐energy HOMO level and consequently displays unique coordination behavior toward RhI complexes. When 1 was treated with 1/4 of an equivalent of [RhCl(cod)]2 (cod=1,5‐cyclooctadiene), the 14‐electron Y‐shaped bis(chlorosilylene) RhI complex 5 was obtained as dark purple crystals. The reaction of 1 with 1/6 of an equivalent of [RhCl(cod)]2 yielded the cationic tris(silylene)‐RhI complex [6]+⋅Cl− as red crystals, wherein a two‐coordinated silylene ligand engages in a Si=Rh double bond. A structural analysis of 5 and [6]+⋅Cl− revealed that the central rhodium atoms adopt trigonal and square‐planar coordination geometries, respectively, with considerably shortened Si‐Rh bonds [5: 2.1605(5) Å; [6]+: 2.133(1) Å]. [ABSTRACT FROM AUTHOR]

A novel N‐hetero‐RhI‐metallacyclic silanone 2 has been synthesized. The silanone 2, showing an extremely large dimerization energy (ΔG=+86.2 kcal mol−1), displays considerable stability and persists in solution up to 60 °C. Above 120 °C, an intramolecular Csp3−H insertion occurs slowly over a period of two weeks leading to the bicyclic silanol 5. The exceptional stability of 2, related to the unusual electronic and steric effects of RhI‐substituent, should allow for a more profound study and understanding of these new species. Furthermore, the metallacyclic silanone 2 presents two reactive centers (Si=O and Rh), which can be involved depending upon the nature of reagents. Of particular interest, the reaction with H2 starts with the hydrogenation of RhI center leading to the corresponding RhIII‐dihydride complex 7 and it undergoes a cis/trans‐isomerization via a particular mechanism, demonstrating that addition‐elimination processes can also happen for silanones just like for their carbon analogues! [ABSTRACT FROM AUTHOR]