Cationic Five-Coordinate Bis(guanidinato)silicon(IV) Complexes with SiN4 El Skeletons (El=S, Se): "Heterolytic Activation" of S-S and Se-Se Bonds

Synthesis, Reactivity, and Complexation with Fe(0) of a Tight-bite Bis(N-heterocyclic silylene)

The synthesis, reactivity, and complexation with Fe(0) precursor of a tight-bite bis(N-heterocyclic silylene) (bis(NHSi)) ligand 1 are reported. The reaction of 1 with p-toluidine led to the activation of both N-H bonds across Si(II) atoms to afford a four-membered heterocyclic cyclodisilazane 2, with hydride substituents attached to five-coordinate Si atoms. A 1 : 2 reaction of 1 with Fe(CO)5 led to an intriguing dinuclear complex 3 featuring a five-membered (N-Si-Fe-Fe-Si) ring with a Fe-Fe bond distance of 2.6892(13) Å. All compounds (1-3) were thoroughly characterized by various spectroscopic methods and X-ray diffraction studies conclusively established their molecular structures. DFT calculations were carried out to shed light on bonding and energetic aspects in 1-3.

Chalcogen-atom transfer and exchange reactions of NHC-stabilized heavier silaacylium ions

Heavier analogues of silaacylium ions 2-4 ([m-TerSiE(NHC)₂]Cl; m-Ter = 2,6-Mes₂C₆H₃; Mes = 2,4,6-Me₃C₆H₂; 2 (E = S), 3 (E = Se), 4 (E = Te)) were synthesized by the reaction of the NHC-stabilized silyliumylidene cation 1 with elemental chalcogens. Fascinating regeneration of 1 from the reaction of 2-4 with AuI was achieved, as successful recovery of a parent Si(ii) species from a silachalcogen Si(iv) compound. Furthermore, unique chalcogen exchange reactions from 4 → 3 → 2 were observed in line with the calculated silicon-chalcogen bond energies.

Neutral six-coordinate bis(dithiocarbamato)silicon(iv) complexes with an SiCl2S4 skeleton

Treatment of SiCl₄ with lithium dithiocarbamates of the formula type Li[R₂NCS₂] (R = Ph, iPr) in a molar ratio of 1 : 2 afforded the respective six-coordinate silicon(iv) complexes [Ph₂NCS₂]₂SiCl₂ (3) and [iPr₂NCS₂]₂SiCl₂ (4), which were isolated as the solvates 3·MeCN and 4·MeCN. Compounds 3·MeCN and 4·MeCN were structurally characterised by single-crystal X-ray diffraction and multinuclear NMR spectroscopic studies in the solid state and in solution. In this study, dithiocarbamato ligands were implemented in silicon coordination chemistry for the first time. Compounds 3 and 4 represent the first six-coordinate silicon(iv) complexes with an SiCl₂S₄ skeleton.

First Insertions of Carbene Ligands into Ge-N and Si-N Bonds

The insertion of carbene ligands into Ge-N (three examples) and Si-N (one example) bonds has been achieved for the first time by treating Fischer carbene complexes (M=W, Cr) with bulky amidinatotetrylenes (E=Ge, Si). These reactions, which start with a nucleophilic attack of the amidinatotetrylene heavier group 14 atom to the carbene C atom, proceed through a stereoselective insertion of the carbene fragment into an E-N bond of the amidinatotetrylene ENCN four-membered ring, leading to [M(CO)₅ L] derivatives in which L belongs to a novel family of tetrylene ligands comprising an ECNCN five-membered ring.

Iron(II), Cobalt(II), Nickel(II), and Zinc(II) Silylene Complexes: Reaction of the Silylene [iPrNC(NiPr2 )NiPr]2 Si with FeBr2 , CoBr2 , NiBr2 ⋅MeOCH2 CH2 OMe, ZnCl2 , and ZnBr2

Reaction of the donor-stabilized silylene [iPrNC(NiPr₂ )NiPr]₂ Si (1) with FeBr₂ , CoBr₂ , NiBr₂ ⋅MeOCH₂ CH₂ OMe, ZnCl₂ , and ZnBr₂ afforded the respective transition-metal silylene complexes 4-8, the formation of which can be described in terms of a Lewis acid/base reaction (4, 5, 7, 8) or a nucleophilic substitution reaction (6). However, the reactivity profile of silylene 1 is not only based on its strong Lewis base character; the different coordination modes of the two guanidinato ligands (4-6 vs. 7 and 8) add an additional reactivity facet. The paramagnetic compounds 4 and 5 and the diamagnetic compounds 6⋅THF, 7, and 8⋅0.5 Et₂ O were structurally characterized by single-crystal X-ray diffraction. In addition, compound 6⋅THF was studied by ¹⁵ N and ²⁹ Si solid-state NMR spectroscopy, and 7 and 8 were characterized by NMR spectroscopic studies in the solid state (¹⁵ N, ²⁹ Si) and in solution (¹ H, ¹³ C, ²⁹ Si). Compounds 4-8 represent very rare examples of Fe^II , Co^II , Ni^II , and Zn^II silylene complexes. Four-coordinate silicon(II) compounds with an SiN₃ M skeleton (M=Fe, Co, Ni) and M in the formal oxidation state +2 (4-6) have not yet been reported, and five-coordinate silicon(II) compounds with an SiN₄ Zn skeleton (7, 8) are also unprecedented.

Bis(amidinato)- and bis(guanidinato)silylenes and silylenes with one sterically demanding amidinato or guanidinato ligand: synthesis and reactivity

Silylenes 1–4 have great synthetic potential for the synthesis of higher coordinate silicon(ii) and silicon(iv) complexes with unprecedented structural motifs.