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The subjects of this study are the structures and electron densities of the carbon/silicon analogues haloperidol/sila-haloperidol (1a/1b) and venlafaxine/sila-venlafaxine (2a/2b). The parent carbon compounds 1a (an antipsychotic agent) and 2a (an antidepressant) are both in clinical use. For haloperidol/sila-haloperidol, three published structures were studied in more detail: the structures of haloperidol hydrochloride (1a·HCl), haloperidol hydropicrate (1a·HPic) and sila-haloperidol hydrochloride (1b·HCl). For venlafaxine/sila-venlafaxine, the published structures of venlafaxine (2a), venlafaxine hydrochloride (2a·HCl; as orthorhombic (2a·HCl-ortho) and monoclinic polymorph (2a·HCl-mono)) and sila-venlafaxine hydrochloride (2b·HCl) were investigated. Based on these structures, the molecular electron densities were reconstructed by using the invariom formalism. They were further analysed in terms of Bader's quantum theory of atoms in molecules, electrostatic potentials mapped onto electron density isosurfaces and Hirshfeld surfaces. These studies were performed with a special emphasis on the comparison of the corresponding carbon/silicon analogues.

Si-enterobactin (2a), a hexacoordinated complex of the siderophore enterobactin (2b) with silicon as the central atom, was isolated from an endophytic Streptomyces sp. occurring in Piper guinensis roots. The structure and absolute configuration were determined from NMR and MS data, and by X-ray diffraction. The orientation of the molecule along the pseudo-3-fold axis shows that the coordination environment of the silicon atom complexed with three bidentate ligands is Δ. We assume that 2a or related complexes may be involved in the transport of silicon in plants, diatoms, or other silicon-dependent organisms.

Reduction of the neutral carbene tetrachlorosilane adduct (cAAC)SiCl4 (cAAC=cyclic alkyl(amino) carbene :C(CMe2)2(CH2)N(2,6-iPr2C6H3) with potassium graphite produces stable (cAAC)3Si3, a carbene-stabilized triatomic silicon(0) molecule. The Si−Si bond lengths in (cAAC)3Si3 are 2.399(8), 2.369(8) and 2.398(8) Å, which are in the range of Si−Si single bonds. Each trigonal pyramidal silicon atom of the triangular molecule (cAAC)3Si3 possesses a lone pair of electrons. Its bonding, stability, and electron density distributions were studied by quantum chemical calculations. [ABSTRACT FROM AUTHOR]

The reaction of LSi tBu [L = PhC(N tBu)2] ( 1) with 4,4′-bis(dimethylamino)thiobenzophenone resulted in the [1+2]-cycloaddition product silathiacyclopropane 3, bearing a three-membered SiCS ring. The reaction of LSiC(SiMe3)3 ( 2) with 3,5-di- tert-butyl- o-benzoquinone leads to the [1+4]-cycloaddition product 4. In 3 the silicon atom is five- and in 4 it is four-coordinate. Compounds 3 and 4 were characterized by spectroscopic and spectrometric techniques. The molecular structures of 1, 3, and 4 were unequivocally established by single-crystal X-ray structure analysis. [ABSTRACT FROM AUTHOR]

A 1,4-diamino-2,3-disila-1,3-butadiene derivative of composition (Me2-cAAC)2(Si2Cl2) (Me2-cAAC = :C(CMe2)2(CH2)N-2,6-iPr2C6H3) was synthesized by reduction of the Me2-cAAC:SiCl4 adduct with KC8. This compound is stable at 0 °C for 3 months in an inert atmosphere. Theoretical studies reveal that the silicon atoms exhibit pyramidal coordination, where the Cl–Si–Si–Cl dihedral angle is twisted by 43.3° (calcd 45.9°). The two silicon–carbon bonds are intermediates between single and double Si–C bonds due to twisting of the C–Si–Si–C dihedral angle (163.6°). [ABSTRACT FROM AUTHOR]

Pentacoordinate silicon fluorides L1SiF3 (2a), L2SiF3 (2b), and (L3SiF2)2 (2c)2 based on amidinate (L1 = PhC(NtBu)2), guanidinate (L2 = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate), and triazapentadienate (L3 = NC(NMe2)NC(NMe2)NAr; Ar = 2,6-iPr2C6H3) ligands were prepared by fluorination of the corresponding chlorosilanes L1SiCl3 (1a), L2SiCl3 (1b), and L3SiCl2 (1c) with Me3SnF at ambient temperature. Compounds 1b, 1c, 2a, 2b, and (2c)2 were characterized by 1H, 13C, 19F, and 29Si NMR spectroscopic studies. Molecular structures of 1b, 1c, 2a, and (2c)2 were determined by single crystal X-ray structural analysis. Invariom refinement involving non-spherical scattering factors of the Hansen-Coppens multipole model was performed for 1b. Compound L3SiF2 (2c) is dimeric both in the solid state and in solution, whereas its chloro-analogue 1c is monomeric. The attempted synthesis of diamidinatotetrachlorodisilane by reaction of lithium amidinate with Si2Cl6 led to the formation of the silane (1a) and the silylene L1SiCl (3). Reaction of Si2Cl6 with N-heterocyclic carbenes (NHC) afforded NHC adducts of dichlorosilylene and SiCl4. A one pot method for the preparation of base-stabilized silylenes from Si2Cl6 is discussed. [ABSTRACT FROM AUTHOR]

A stable silicon analogue of an acid anhydride {PhC(ButN)2}Si{-O·B(C6F5)3}O-Si(H){-O·B(C6F5)3}{(NBut)(HNBut)CPh} (4) with a O-Si-O-Si-O core has been prepared by treating monochlorosilylene PhC(ButN)2SiCl (1) with H2O·B(C6F5)3 in the presence of NHC (NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Compound 4 has been characterized by elemental analysis and multinuclear NMR spectroscopic investigations. The molecular structure of 4 has been established by single-crystal X-ray diffraction studies, and DFT calculations support the experimental results. [ABSTRACT FROM AUTHOR]