Disilanes with Pentacoordinate Si Atoms by Carbon Dioxide Insertion into Aminodisilanes: Syntheses, Molecular Structures, and Dynamic Behavior

The insertion of carbon dioxide into the Si-N bonds of aminodisilanes ((RR'N) _n Me_3-n Si)₂ affords carbamoyloxydisilanes ((RR'NC(O)O) _n Me_3-n Si)₂. Some of the obtained insertion products feature pentacoordinate silicon atoms in the solid state and in solution, with two carbamoyloxy moieties bridging the Si-Si bond. The aminodisilanes and their insertion products were extensively analyzed, including single-crystal X-ray structure analyses. The temperature dependence of the higher coordination was investigated using variable temperature NMR experiments.

Trans Element-Hydrogen Bonds: A Distinctive Difference Between Transition Metals and Main Group Elements

The change in sign of the interaction force constant between element-hydrogen stretching modes of trans-dihydrides of the d block and p block elements is analyzed for the first time. As the transition metal M approaches group 12, the higher energy symmetric trans-H-M-H vibration ν_sym approaches the energy of the antisymmetric vibration ν_asym. Crossing to group 13 elements E, the trans-H-E-H vibration ν_sym increasingly drops below ν_asym. This reversal is attributed to the d orbital that participates in the H-M-H bonding but is nonbonding in the H-E-H compounds. DFT calculations are used to probe the energetics of isoelectronic triatomic [H-M-H]ⁿ⁺ and [H-E-H]^n- to reveal this trend and also to demonstrate that the magnitude of these interactions (ν_gap) increases down groups 11, 12, and 14 but remains fairly constant for group 13. They are also used to show that this reversal is seen in the transition state for hydride transfer to CO₂ from the model compounds trans-NiH₂(porphyrin) and trans-EH₂(porphyrin), E = Si and Ge in their singlet states.

(3,5-Dimethyl-1H-pyrazol-1-yl)tri-methyl-silane

The title compound, C8H16N2Si, crystallizes in the the ortho-rhom-bic space group P212121 with one mol-ecule in the asymmetric unit. The Si-N bond is 1.782 (2) Å, which is substanti-ally longer than is found in comparable (3,5-di-methyl-pyrazol-yl)silanes. The tri-methyl-silyl group adopts a staggered conformation with respect to the planar 3,5-di-methyl-pyrazolyl unit. C-H⋯N hydrogen bonds between neighboring mol-ecules form a strand of mol-ecules along the b-axis direction.

Insertion of Ni(0) and Pd(0) precursors into the Si-Si bond of a disilane with two hypercoordinate silicon atoms

The activation of the silicon-silicon bond in disilane Ph2Si(μ-PzMe2)2SiPh2 (1), which possesses two five-coordinate silicon centers, was achieved by a reaction with Pd(0) or Ni(0) precursors of modest steric demand to afford a dinuclear Pd complex (2) or two types of mononuclear Ni complexes (3 and 4), respectively.

Insertion of phenyl isocyanate into mono- and diaminosilanes

The aminosilanes MenSi(NRR′)4−n (n=2,3) with NRR′=ethylamino (NHEt), n-propylamino (NH n Pr), sec-butylamino (NH s Bu), n-octylamino (NH n Oct), n-dodecylamino (NH n Dodec), allylamino (NHAll), tert-butylamino (NH t Bu), diethylamino (NEt2), and anilino (NHPh) were synthesized and their reactions with phenyl isocyanate were studied. In all cases of these silanes Me3SiNRR′ and Me2Si(NRR′)2 formal insertion of the –NCO group into their Si–N bonds was observed, i.e. formation of products with Si–N (rather than Si–O) bonds was found. In some cases, the products could be crystallized and their molecular structures have been elucidated with single-crystal X-ray diffraction analyses.

Hydrosilylation in Aryliminopyrrolide-Substituted Silanes

A range of silanes was synthesized by the reaction of HSiCl3 with iminopyrrole derivatives in the presence of NEt3 . In certain cases, intramolecular hydrosilylation converts the imine ligand into an amino substituent. This reaction is inhibited by factors such as electron-donating substitution on Si and steric bulk. The monosubstituted ((Dipp) IMP)SiHMeCl ((Dipp) IMP=2-[N-(2,6-diisopropylphenyl)iminomethyl]pyrrolide), is stable towards hydrosilylation, but slow hydrosilylation is observed for ((Dipp) IMP)SiHCl2 . Reaction of two equivalents of (Dipp) IMPH with HSiCl3 results in the hydrosilylation product ((Dipp) AMP)((Dipp) IMP)SiCl ((Dipp) AMP=2-[N-(2,6-diisopropylphenyl)aminomethylene]pyrrolide), but the trisubsitituted ((Dipp) IMP)3 SiH is stable. Monitoring the hydrosilylation reaction of ((Dipp) IMP)SiHCl2 reveals a reactive pathway involving ligand redistribution reactions to form the disubstituted ((Dipp) AMP)((Dipp) IMP)SiCl as an intermediate. The reaction is strongly accelerated in the presence of chloride anions.

2-Acylpyrroles as mono-anionic O,N-chelating ligands in silicon coordination chemistry

Kryptopyrrole (2,4-dimethyl-3-ethylpyrrole) was acylated with, for example, benzoyl chloride to afford 2-benzoyl-3,5-dimethyl-4-ethylpyrrole (L(1)H). With SiCl4 this ligand reacts under liberation of HCl and formation of the complex L(1)2SiCl2. In related reactions with HSiCl3 or H2SiCl2, the same chlorosilicon complex is formed under liberation of HCl and H2 or liberation of H2, respectively. The chlorine atoms of L(1)2SiCl2 can be replaced by fluoride and triflate using ZnF2 and Me3Si-OTf, respectively. The use of a supporting base (triethylamine) is required for the complexation of phenyltrichlorosilane and diphenyldichlorosilane. The complexes L(1)2SiCl2, L(1)2SiF2, L(1)2Si(OTf)2, L(1)2SiPhCl, and L(1)2SiPh2 exhibit various configurations of the octahedral silicon coordination spheres (i.e. cis or trans configuration of the monodentate substituents, different orientations of the bidentate chelating ligands relative to each other). Furthermore, cationic silicon complexes L(1)3Si(+) and L(1) SiPh(+) were synthesized by chloride abstraction with GaCl3. In contrast, reaction of L(1)2SiCl2 with a third equivalent of L(1)H in the presence of excess triethylamine produced a charge-neutral hexacoordinate Si complex with a new tetradentate chelating ligand which formed by Si-templated C-C coupling of two ligands L(1).