Pentacoordination of silicon by five different ligand atoms: neutral silicon(IV) complexes with SiClSONC and SiISONC skeletons

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.

On the Potential of Silicon as a Building Block for Life

Despite more than one hundred years of work on organosilicon chemistry, the basis for the plausibility of silicon-based life has never been systematically addressed nor objectively reviewed. We provide a comprehensive assessment of the possibility of silicon-based biochemistry, based on a review of what is known and what has been modeled, even including speculative work. We assess whether or not silicon chemistry meets the requirements for chemical diversity and reactivity as compared to carbon. To expand the possibility of plausible silicon biochemistry, we explore silicon's chemical complexity in diverse solvents found in planetary environments, including water, cryosolvents, and sulfuric acid. In no environment is a life based primarily around silicon chemistry a plausible option. We find that in a water-rich environment silicon's chemical capacity is highly limited due to ubiquitous silica formation; silicon can likely only be used as a rare and specialized heteroatom. Cryosolvents (e.g., liquid N2) provide extremely low solubility of all molecules, including organosilicons. Sulfuric acid, surprisingly, appears to be able to support a much larger diversity of organosilicon chemistry than water.

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

The donor-stabilized silylene [iPrNC(NiPr2 )NiPr]2 Si (2) reacts with PhEl-ElPh (El=S, Se) to form the respective cationic five-coordinate bis(guanidinato)silicon(IV) complexes {[iPrNC(NiPr2 )NiPr]2 SiSPh}(+) PhS(-) (4) and {[iPrNC (NiPr2 )NiPr]2 SiSePh}(+) PhSe(-) (5). Compounds 4 and 5 were characterized by crystal structure analyses and NMR spectroscopic studies in the solid state.

N,N-Bis-(dimethylfluorosilylmethyl)amides of N-organosulfonylproline and sarcosine: synthesis, structure, stereodynamic behaviour and in silico studies

(O→Si)-Chelate difluorides R₃R₂NCH(R₁)C(O)N(CH₂SiMe₂F)₂, were synthesized by silylmethylation of amides R₃R₂NCH(R₁)C(O)NH₂, subsequent hydrolysis of unstable dichlorides into 2,6-disilamorpholines and the reaction of the latter compounds with BF₃·Et₂O.

Integration of benzo[h]quinoline and π-extended dibenzo[b,f]silepins on pentacoordinate silicon

We investigated the relationship between the chemical structure involving the pentacoordinate silicon and the electronic properties of the molecules.

Synthesis of chlorosilicates

Chlorosilicates represent important intermediates in S(N)2 reactions of chlorosilanes. They can be stabilized by the introduction of electron-withdrawing substituents. Salts of various (pentafluoroethyl)chlorosilicates have been isolated and structurally characterized.

Disilicon complexes with two hexacoordinate Si atoms: paddlewheel-shaped isomers with (ClN4 )Si-Si(S4 Cl) and (ClN2 S2 )Si-Si(S2 N2 Cl) skeletons

The reaction of 1-methyl-3-trimethylsilylimidazoline-2-thione with hexachlorodisilane proceeds toward substitution of four of the disilane Cl atoms during the formation of disilicon complexes with two neighboring hexacoordinate Si atoms. The N,S-bidentate methimazolide moieties adopt a buttressing role, thus forming paddlewheel-shaped complexes of the type ClSi(μ-mt)4 SiCl (mt=methimazolyl). Most interestingly, three isomers (i.e., with (ClN4 )SiSi(S4 Cl), (ClN3 S)SiSi(S3 NCl), and (ClN2 S2 )SiSi(S2 N2 Cl) skeletons as so-called (4,0), (3,1), and cis-(2,2) paddlewheels) were detected in solution by using (29) Si NMR spectroscopic analysis. Two of these isomers could be isolated as crystalline solids, thus allowing their molecular structures to be analyzed by using X-ray diffraction studies. In accord with time-dependent NMR spectroscopy, computational analyses proved the cis-(2,2) isomer with a (ClN2 S2 )SiSi(S2 N2 Cl) skeleton to be the most stable. The compounds presented herein are the first examples of crystallographically evidenced disilicon complexes with two SiSi-bonded octahedrally coordinated Si atoms and representatives of the still scarcely explored class of Si coordination compounds with sulfur donor atoms.

Ylenes in the M(II)→Si(IV) (M=Si, Ge, Sn) coordination mode

The reaction of the methimazolyl (mt, i.e., 2-mercapto-1-methylimidazolide) substituted silane Si(mt)(4) with SnCl(2) and GeCl(2) in dioxane affords the paddlewheel-shaped complexes [ClSi(μ-mt)(4)MCl] (M=Sn (1) and Ge (2), respectively). These compounds represent the first crystallographically characterized hexacoordinate silicon complexes comprising a Sn or Ge atom in the Si coordination sphere. An attempt to synthesize the related silicon compound 3 [ClSi(μ-mt)(4)SiCl] instead afforded the trisilane [ClSi(μ-mt)(4)Si-SiCl(3)] (3a), which provides the first crystallographic evidence for the feasibility of oligosilanes with adjacent hexacoordinate Si atoms. One of the hexacoordinate Si atoms of 3a features the unprecedented (Si(2)S(4))Si skeleton. Natural bonding orbital (NBO) analyses of compounds 1, 2, 3a (and the target compound 3) revealed characteristics of M(II)→Si(IV) (for 2 and 3) or M(I)→Si(IV) (for 3a) dative bonding in the systems with M=Si and Ge, whereas compound 1 exhibits a covalent Sn(III)-Si(III) bond.

Optically active zwitterionic lambda(5)Si,lambda(5)Si'-disilicates: syntheses, crystal structures, and behavior in aqueous solution

The zwitterionic lambda(5)Si,lambda(5)Si'-disilicates 1-8 were synthesized and characterized by solid-state and solution NMR spectroscopy. In addition, compounds 26 H(2)O, 32 CH(3)CN, 45/2 CH(3)CN, 6CH(3)OH, 7, and 8CH(3)OHCH(3)CN were studied by single-crystal X-ray diffraction. The optically active (Delta,Delta,R,R,R,R)-configured compounds 1-8 contain two pentacoordinate (formally negatively charged) silicon atoms and two tetracoordinate (formally positively charged) nitrogen atoms. One (ammonio)alkyl group is bound to each of the two silicon centers, and two tetradentate (R,R)-tartrato(4-) ligands bridge the silicon atoms. Although these lambda(5)Si,lambda(5)Si'-disilicates contain SiO(4)C skeletons, some of them display a remarkable stability in aqueous solution as shown by NMR spectroscopy and ESI mass spectrometry.