| Summary: | Proceeding our initial studies of compounds with formally dative TM→Si bonds (TM = Ni, Pd, Pt), which feature a paddlewheel arrangement of four (<i>N</i>,<i>S</i>) or (<i>N</i>,<i>N</i>) bridging ligands around the TM⁻Si axis, the current study shows that the (<i>N</i>,<i>O</i>)-bidentate ligand 2-pyridyloxy (pyO) is also capable of bridging systems with TM→Si bonds (shown for TM = Pd, Cu). Reactions of MeSi(pyO)<sub>3</sub> with [PdCl<sub>2</sub>(NCMe)<sub>2</sub>] and CuCl afforded the compounds MeSi(µ-pyO)<sub>4</sub>PdCl (<b>1</b>) and MeSi(µ-pyO)<sub>3</sub>CuCl (<b>2</b>), respectively. In the latter case, some crystals of the Cu(II) compound MeSi(µ-pyO)<sub>4</sub>CuCl (<b>3</b>) were obtained as a byproduct. Analogous reactions of Si(pyO)<sub>4</sub>, in the presence of HpyO, with [PdCl<sub>2</sub>(NCMe)<sub>2</sub>] and CuCl<sub>2</sub>, afforded the compounds [(HpyO)Si(µ-pyO)<sub>4</sub>PdCl]Cl (<b>4</b>), (HpyO)<sub>2</sub>Si[(µ-pyO)<sub>2</sub>PdCl<sub>2</sub>]<sub>2</sub> (<b>5</b>), and (HpyO)<sub>2</sub>Si[(µ-pyO)<sub>2</sub>CuCl<sub>2</sub>]<sub>2</sub> (<b>6</b>), respectively. Compounds <b>1</b>⁻<b>6</b> and the starting silanes MeSi(pyO)<sub>3</sub> and Si(pyO)<sub>4</sub> were characterized by single-crystal X-ray diffraction analyses and, with exception of the paramagnetic compounds <b>3</b> and <b>6</b>, with NMR spectroscopy. Compound <b>2</b> features a pentacoordinate Si atom, the Si atoms of the other complexes are hexacoordinate. Whereas compounds <b>1</b>⁻<b>4</b> feature a TM→Si bond each, the Si atoms of compounds <b>5</b> and <b>6</b> are situated in an O<sub>6</sub> coordination sphere, while the TMCl<sub>2</sub> groups are coordinated to pyridine moieties in the periphery of the molecule. The TM⁻Si interatomic distances in compounds <b>1</b>⁻<b>4</b> are close to the sum of the covalent radii (<b>1</b> and <b>4</b>) or at least significantly shorter than the sum of the van-der-Waals radii (<b>2</b> and <b>3</b>). The latter indicates a noticeably weaker interaction for TM = Cu. For the series <b>1</b>, <b>2</b>, and <b>3</b>, all of which feature the Me⁻Si motif <i>trans</i>-disposed to the TM→Si bond, the dependence of the TM→Si interaction on the nature of TM (Pd(II), Cu(I), and Cu(II)) was analyzed using quantum chemical calculations, that is, the natural localized molecular orbitals (NLMO) analyses, the non-covalent interaction (NCI) descriptor, Wiberg bond order (WBO), and topological characteristics of the bond critical points using the atoms in molecules (AIM) approach.
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