Understanding the Impact of Group 14 Elements on the Reactivity of [1 + 2] Cycloaddition Reaction between a Cyclic (Alkyl)(amino)carbene Analogue with a Group 14 Element and a Heavy Acetylene Molecule

Computational exploration using the density functional theory framework (M06-2X-D3/def2-TZVP) was undertaken to investigate the [1 + 2] cycloaddition reaction between a five-membered-ring heterocyclic carbene analogue (G14-Rea; G14 = group 14 element) and a heavy acetylene molecule (G14G14-Rea). It was theoretically observed that exclusively Si-Rea, Ge-Rea, and Sn-Rea demonstrate the capacity to participate in the [1 + 2] cycloaddition reaction with the triply bonded SiSi-Rea. In addition, only three heavy acetylenes (SiSi-Rea, GeGe-Rea, and SnSn-Rea) can catalyze the [1 + 2] cycloaddition reaction with Si-Rea. Our theoretical findings elucidated that the reactivity trend observed in these [1 + 2] cycloaddition reactions primarily arise from the deformation energies of the distorted G14G14-Rea. Also, our study reveals that the bonding characteristics of their respective transition states are controlled by the singlet-singlet interaction (donor-acceptor interaction), rather than the triplet-triplet interaction (electron-sharing interaction). Additionally, our work demonstrates that the bonding behavior between G14-Rea and G14G14-Rea is predominantly determined by the filled p-π orbital of G14G14-Rea (HOMO) → the empty perpendicular p-π orbital of G14-Rea (LUMO), rather than the vacant p-π* orbital of G14G14-Rea (LUMO) ← the filled sp2 orbital of G14-Rea (HOMO).

Reactions of an Isolable Dialkylsilylene with Aroyl Chlorides. A New Route to Aroylsilanes

The reactions of isolable dialkylsilylene 1 with aromatic acyl chlorides afforded aroylsilanes 3a–3c exclusively. Aroylsilanes 3a–3c were characterized by ¹H-, ¹³C-, and ²⁹Si-NMR spectroscopy, high-resolution mass spectrometry (HRMS), and single-crystal molecular structure analysis. The reaction mechanisms are discussed in comparison with related reaction of 1 with chloroalkanes and chlorosilanes.

1,3-Diazasilabicyclo[1.1.0]butane with a Long Bridging N-N Bond

A 1,3-diazasilabicyclo[1.1.0]butane (1) is synthesized as thermally stable crystals by using the cycloaddition reaction of an isolable dialkylsilylene with aziadamantane. The bridge N-N bond length of 1 (1.70 Å) is the longest among those of known N-N singly-bonded compounds, including side-on bridged transition-metal dinitrogen complexes. The compound 1 is intact in air but moisture sensitive. No reaction occurs with hydrogen, even under pressure at 0.5 MPa. Irradiation of 1 with light gives an isomer quantitatively by N-N and adamantyl C-C bond cleavage. The origin of the remarkable N-N bond elongation is ascribed to significant interaction between a Si-C σ* and Ν-Ν π and σ orbitals as determined by DFT calculations of model compounds.