A Choise of Recent Publications 2015 - 2017

Dalton Trans. 46, 13628-13659 (2017), Issue 40, 2017

DOI: 10.1039/C7DT01297G

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

Reinhold Tacke and Tatjana Ribeck

This article deals with the synthesis and reactivity of the bis(amidinato)silylene [iPrNC(Ph)NiPr]₂Si (5), the bis(guanidinato)silylene [iPrNC(NiPr₂)NiPr]₂Si (6), the mono(amidinato)silylene [DippNC(Ph)NDipp]SiNMe₂ (Dipp = 2,6-diisopropylphenyl) (8) and the mono(guanidinato)silylene [DippNC(NMe₂)NDipp]SiN(SiMe₃)₂ (9). The reactions studied include (i) nucleophilic substitutions, (ii) Lewis acid/base reactions, (iii) Brønsted acid/base reactions, (iv) oxidative additions (bond activations, small-molecule activations), (v) cycloaddition reactions with unsaturated organic substrates, (vi) reductions and (vii) radical formation by muonium addition. Silylenes 5, 6, 8 and 9 have been demonstrated to display unique reactivity profiles and to be versatile precursors for the synthesis of novel four- or five-coordinate silicon(II) and four-, five- or six-coordinate silicon(IV) complexes with unprecedented structural motifs. This article also deals with the structural characterisation of all the new silicon(II) and silicon(IV) compounds synthesised. Crystal structure analyses and ²⁹Si NMR spectroscopic studies in the solid state and in solution were used to characterise the silicon coordination polyhedra of these compounds.

J. A. Baus, R. Tacke, Neutral six-xoordinate bis(dithiocarbamato)-silicon(IV) complexes with an SiCl₂S₄ skeleton, Dalton Trans., in print (2017.) http://dx.doi.org/10.1002/ejic.201600982more ... 

Abstract

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.

J. A. Baus, F. M. Mück, H. Schneider, R. Tacke, Iron(II), cobalt(II), and zinc(II) silylene complexes: reaction of the silylene [i(PrNC(NiPr₂)NiPr₂]Si with FeBr₂, CoBr₂, NiBe₂ • MeOCH₂CH₂OMe, ZnCl₂, and ZnBr₂, Chem. Eur. J. 23, 296-303 (2017). http://dx.doi.org/10.1002/ejic.201600982more ... 

 Abstract

  Donor-Stabilized Silylenes The chemistry of donor-stabilized silylenes has developed into one of the most actively studied research areas in molecular silicon chemistry. In their Full Paper on page 296 ff., R. Tacke et al report on the synthesis and characterization of novel transition-metal silylene complexes of FeBr₂, CoBr₂, NiBr₂, ZnBr₂, and ZnCl₂ with the bis(guanidinato)silicon(II) complex [iPrNC(NiPr₂)NiPr]₂Si. These compounds represent very rare examples of carbonyl-free silylene complexes of 3d transition metals in the formal oxidation state +2.

J. A. Baus, J. Poater, F. M. Bickelhaupt, R. Tacke, Silylene-induced reduction of [Mn₂(CO)₁₀]: formation of a five-coordinate silicon(IV) complex with an O-bound [(OC)₄Mn=Mn)CO)₄]^2- ligand, Eur. J. Inorg. Chem. 186-191 (2017). http://dx.doi.org/10.1002/ejic.201600982more ... 

Abstract:

M. Geyer, J. A. Baus, O. Fjellström, E. Wellner, L. Gustafsson, R. Tacke, Synthesis and pharmacological properties of silicon-sontaining GPR81 and GPR109A agonists, ChemMedChem 10, 2063-2070 (2015). more ...

F. M. Mück, D. Kloß, J. A. Baus, C. Burschka, R. Bertermann, J. Poater, C. Fonseca Guerra, F. M. Bickelhaupt, R. Tacke, Stable four-coordinate guanidinatosilicon(IV) complexes with SiN₃El skeletons (El = S, Se, Te) and Si=El double bonds, Chem. Eur. J. 21, 14011-14021(2015). more ...

R. Tacke, C. Kobelt, J. A. Baus, R. Bertermann, C. Burschka, Synthesis, structure and reactivity of a donor-stabilised silylene with a bulky bidentate benzamidinato ligand, Dalton Trans. 44, 1459-14974 (2015). more ...

The novel donor-stabilised silylene 5 was prepared in a four-step synthesis, starting from bis(2,6-diisopropylphenyl)carbodiimide (Dipp–NCN–Dipp), and its reactivity was studied in a series of oxidative addition reactions and a nucleophilic substitution reaction. The three-coordinate silicon(II) complex 5 contains the bulky bidentate amidinato ligand Dipp–NC(Ph)N–Dipp⁻ and a dimethylamido ligand. Treatment of 5 with N₂O afforded the dinuclear five-coordinate silicon(IV) complex 6 (SiO₂N₃ skeletons), and the reaction with S₈ yielded the dinuclear four-coordinate silicon(IV) complex 7 (SiS₂N₂ skeletons). Treatment of 5 with Se and Te afforded the respective four-coordinate silicon(IV) complexes 8 (SiSeN₃ skeleton) and 9 (SiTeN₃ skeleton), which contain an SiSe and SiTe double bond, respectively. The reaction of 5 with the silyl azide Me₃SiN₃ yielded the four-coordinate silicon(IV) complex 10 (SiN₄ skeleton) with an SiN double bond, whereas the reaction with the alkyl azide PhSCH₂N₃ gave the four-coordinate silicon(IV) complex 11 (SiSN₃ skeleton), the first silicon(IV) complex with an unsubstituted methyleneamido ligand. The reaction of 5 with [Fe(CO)₅] afforded the four-coordinate silicon(II) complex 12 (SiFeN₃ skeleton) with an Si–Fe bond. Compounds 5–12 (and the precursors 14 and 15 (five-coordinate silicon(IV) complexes with an SiCl₃N₂ and SiCl₂N₃ skeleton, respectively) in the synthesis of 5) were characterised by elemental analyses, crystal structure analyses and multinuclear NMR spectroscopic studies in the solid state and in solution.

P. Luger, B. Dittrich, R. Tacke, Invariom based electron density studies on the C/Si analogues haloperidol/sila-haloperidol and venlafaxine/sila-venlafaxine, Org. Biomol. Chem. 13, 9093-9106 (2015). more ...

Hirshfeld surfaces of haloperidol hydropicrate (left) and sila-haloperidol hydrochloride (right) show comparable sites of ED concentrations due to comparable intermolecular environments.

M. Geyer, O. Karlsson, J. A. Baus, E. Wellner, R. Tacke, Si- and C-functional organosilicon building blocks for synthesis based on 4-silacyclohexan-1-ones containing the silicon protecting groups MOP (4-methoxyphenyl), DMOP (2,6-dimethoxyphenyl), or TMOP (2,4,6-trimethoxyphenyl), J. Org. Chem. 80, 5804-5811 (2015). more ...

M. Geyer, E. Wellner, U. Jurva, S. Saloman, D. Amstrong, R. Tacke, Can silicon make an excellent drug even better? An in vitro and in vivo head-to-head comparison between loperamide and its silicon analogue sila-loperamide, ChemMedChem 10, 911-924 (2015). more ...

Carbon/silicon switch: Sila-loperamide (1b), a silicon analogue of the opioid receptor agonist loperamide (1a), was synthesized. A head-to-head comparison of the in vitro pharmacodynamics and pharmacokinetics and the in vivo pharmacokinetics of 1a and 1b revealed that the C/Si switch strategy is a smart choice to modulate potency, efficacy, stability, and metabolic fate.