Monique Rivière-Baudet

Subvalent Group 4B metal alkyls and amides. Part 5. The synthesis and physical properties of thermally stable amides of germanium(II), tin(II), and lead(II)

A series of subvalent Group 4B metal amides of general formula M(NR1R2)2[(i) R1= SiMe3, R2= But; M = Ge, Sn, or Pb; (ii) R1= R2= SiMe3; M = Ge, Sn, or Pb; and (iii) R1= R2= GeMe3, SiEt3, or GePh3; M = Ge or Sn] has been prepared from the appropriate lithium amide and metal(II) halide. Under ambient conditions, the amides are pale yellow to red, thermochromic, diamagnetic, low-melting solids or liquids, and are soluble in hydrocarbons (C6H6 or C6H12) in which they are diamagnetic monomers. The lower homologues give parent molecular ions as the highest m/e species. Infrared spectra show a band at 380–430 cm–1[νasym(MN2)], and 1H or 13C n.m.r. spectra are consistent with the bent-singlet formulation. In the visible region the compounds exhibit a band (364–495 nm) of moderate intensity (Iµ= 600–2 050 dm3 mol–1 cm–1 in n-C6H14) indicative of an allowed electronic transition. Photolysis of each diamide in n-hexane in the cavity of an e.s.r. spectrometer affords (a) the persistent (t½ 5 min—3 months at 25° C) metal-centred radical Ṁ(NR1R2)3[(i) R1= SiMe3, R2= But, M = Ge or Sn; (ii) R1= R2= SiMe3 or GeMe3, M = Ge or Sn; or (iii) R1= R2= GeEt3, M = Sn], (b) a lead mirror (for the lead amides), or (c) no sign of reaction (for the more bulky diamides). E.s.r. parameters have been derived from the isotropic spectra.

Triaryl-silyl, -germyl, and -stannyl radicals .MAr3 (M = Si, Ge, or Sn and Ar = 2,4,6-Me3C6H2) and .Ge(2,6-Me2C6H3)3: Synthesis and ESR studies

Abstract The triarylmetal-centred radicals . MAr 3 (M = Si, Ge, or Sn; Ar = 2,6-Me 2 C 6 H 3 or 2,4,6-Me 3 C 6 H 2 ) have been prepared from the appropriate triarylmetal chloride, MAr 3 Cl, and an electron-rich olefin [R NCH 2 CH 2 NRC ] 2 (R = Me or Et) under UV irradiation in toluene at low temperature. The triarylgermyl radicals are persistent ( t 1 2 > 24 h, 20°C) whilst the analogous tin and silicon radicals are only stable under constant irradiation at temperatures below −20°C; the ESR spectra of the germanium radicals and of . Si(2,4,6-Me 3 C 6 H 2 ) 3 (which is the first triarylsilyl radical to be spectroscopically identified) show coincidental equivalence of all the proton couplings due to twisting of thearomatic rings into a “propeller” arrangement about the metal. The synthesis and characterisation of precursors to these radicals are also reported.

Bis(trimesitylgermylcarbodiimido)germylene, trimesitylgermylcyanamide and trimesitylgermylcarbodiimide

Abstract Bis(trimesitylgermylcarbodiimido)germylene (1), isolated as a white precipitate from the reaction of lithium trimesitylgermylcyanamide with dichlorogermylene, is stable at room temperature in the absence of water and oxygen. The germylene structure is preserved in the reaction with 3,5-di-t-butylcatechol, while subsequent addition to 3,5-di-t-butylorthoquinone gave the corresponding spirogermane. Thermal decomposition of 1 occurs around 50°C leading to bis(trimesitylgermyl)carbodiimide and polycarbodiimidogermylene. Hydrolysis of 1 gave the corresponding monogermylated derivative of cyanamide (3) in two isomeric forms: trimesitylgermylcyanamide (3a) and trimesitylgermylcarbodimide (3b), in equilibrium in solution. Isomer 3b is the first compound to precipitate from a benzene solution. Its structure was established by X-ray diffraction. Compound 3 decomposes on heating to form dicyanamide and bis(trimesitylgermyl)carbodiimide.

Réaction de dérivés à liaison germanium-azote (germylamines, cyclogermazanes et germa-imines transitoires) avec la di-t-butyl-3,5-orthoquinone

Abstract Several germanium-nitrogen compounds were treated with 3,5-di-t-butylorthoquinone ( 1 ). In the case of the germylamines R 3 GeNMe 2 (R = Et, Ph), 1,2 and 1,4 adducts were formed, as shown by 1 H NMR spectroscopy. The thermally unstable 1,4 adduct, decomposes with nitrene elimination to give 2,2-dialkyl or 2,2-diaryl (6,8-di-t-butyl)-4,5-benzo-2-germa-1,3-dioxolane. The 1,2 adduct, through intermolecular redistribution, leads to digermyloxide (R 3 Ge) 2 O and a gem -diamine with partial regeneration of the starting quinone 1 . These addition reactions proceed through a monoelectronic transfer mechanism, with formation of a transient o -semiquinonic radical identified by ESR spectroscopy. This transient radical leads to O -germyl 3,5-di-t-butylcatechol by hydrogen abstraction from the solvent. The proposed mechanism explains the formation of the germylated compounds as well as the organic by-products. Similar reactions were observed between cyclodigermazanes and 1 . The 1,4 cycloaddition generates germadioxolanes with nitrene expulsion, whereas the 1,2-cycloaddition leads to the germoxane and conjugated ketoimine, or diimine. The latter is a good trapping agent for the nitrene formed in the decomposition of the 1,4 adduct. Both the 1,4 and 1,2 cycloadduct decompositions imply transient germaimine formation. The same germaimine, formed at room temperature from intramolecular dehydrohalogenation of the hindered R 2 ClGeNHR′ by 1,8-diaza[5.4.0]bicyclo-7-undecene) gives the same reaction products.

Mesitylpseudohalogermanes Mes2Ge(CN)2 and Mes3GeX (X=CN, NCS, N3, NCO and OH; Mes=2,4,6-trimethylphenyl): syntheses, crystal and molecular structures

Abstract The crystal and molecular structures of the mesitylpseudohalogermanes, Mes2Ge(CN)2 (Mes=2,4,6-trimethylphenyl) and Mes3GeX (X=CN, NCS, N3, NCO, or OH), have been determined by X-ray diffraction methods; the isocyanate and hydroxide crystallise as a 1:1 hydrogen-bonded complex. All are covalent monomers free from pseudohalogen bridging, and all except the cyanides and hydroxide are N-bonded to germanium. Each Ge atom is four-coordinate in a distorted tetrahedral geometry, as evident from (mes)Ge(mes) angles between 112 and 120°, which are attributed to the sterically demanding mesityl groups. The greatest distortion is displayed by Mes2Ge(CN)2, for which the NCGeCN angle of 97.8(3)° and (mes)Ge(mes) angle of 119.8(3)° are also consistent with the bulky mesityl groups and the small steric requirements of the cyano groups. The GeNY angles show a distinctive trend, decreasing from 173.3(5)° for the isothiocyanate (Y=CS), through 153.5(5)° for the isocyanate (Y=CO), to 119.0(7)° for the azide (Y=NN), an effect attributed to differences in electronic structure of the pseudohalo ligands. The geometries of the compounds examined here are compared with those of some other tri- and dimesityl-Group 14 metal derivatives as well as related phenylgermanium compounds.

Synthesis, reactivity and crystal structure of trimesitylgermylamine, Mes3GeNH2

Abstract Trimesitylgermylamine, Mes 3 GeNH 2 , prepared in high yield by the coupling of Mes 3 GeCl (Mes  2,4,6-Me 3 C 6 H 2 ) with NaNH 2 or LiNH 2 , has been fully characterized by 1 H and 13 C NMR, IR and mass spectrometry. It is a rare example of a stable primary germylamine, melting at 166°C, which is only slowly cleaved by H 2 O, CH 3 OH, HCl or phenol, indicating that the central Ge atom is protected from attack by the mesityl groups. Unlike other germylamines, Mes 3 GeNH 2 reacts with t BuCOCl to give the N -substituted amide, Mes 3 GeNHCO t Bu, rather than Mes 3 GeCl. Preliminary X-ray crystallographic analyses reveal that the Ge atom has approximate tetrahedral coordination with an average GeC bond length of 1.978(3) A and a GeN bond length of 1.854(3) A, and crowding around the Ge atom so that it is shielded from attack by approaching reactants.

Stable germa-imines: Synthesis and reactivity of orthosubstituted anilinodimesitylgerma-imines

Abstract The orthosubstituted anilinodimesitylgerma-imines Mes2GeNAA (1) and Mes2GeNAE (2) where NAA is N- (dimethylanthranilamide) and NAE is N-(methylanthranilate) have been prepared by dehydrohalogenation of the corresponding halogenogermylamines. They are rare examples of thermally stable and monomeric germa-imines, probably stabilized by intramolecular CO → Ge coordination. They readily undergo addition reactions with water, ethanol, germanols, phenylacetylene and chloroform to form adducts in which the protonic H is bonded to nitrogen. They also add to 3,5-ditert-butylorthoquinone, forming thermally unstable (2 + 4) and (2 + 2) adducts which rearrange to the expected digermadioxolane and dimesitylgermoxane respectively. By 1–3 cycloaddition, N-tert-butyl-phenylnitrone adds to germa-imines 1 and 2, yielding the first stable 1-oxa-2,4-diaza-5-germolanes.

Sur la stabilisation d'une germa-imine par effet stérique et mésomérie

Abstract Delithiochloration of N -lithio- N -dimesitylchlorogermyl-3-amino-2-methyl-thiophoate at low temperature leads to the corresponding germa-imine, stabilized by the steric effects of mesityl substituents linked to germanium and possibly by mesomeric effects with the thiophoate group. This germa-imine, stable at room temperature was characterized by spectrometry (IR, UV, RMN, DCi mass spectrometry). With specific reagents (MeOH, Et 3 NH + Cl − , etc. ) the reactivity is different from that of cyclodigermazanes, dimers of germa-imines; stoichiometric addition of MeOH and HCl without cleavage of germanium—nitrogen bond is observed. 3,5-Di-t-butylorthoquinone leads to the expected germadioxolane, through decomposition of the transient 1,4-cycloadduct observed in 1 H NMR.

Germa-2 azetidines: precurseurs des premieres germaimines

Abstract N-Methyl-2,2-diphenyl-2-germyl azetidine was prepared by the reaction of MeNLi2 or MeNH2 and 1-chloro-2-diphenylchlorogermylethane. The germylazetidine leads, through a β-elimination process, to the corresponding germaimine which has been characterized by insertion reactions into the GeN bond of both the germylazetidine and dimethyl(triethylgermyl)amine.

Carbonic Anhydrase Inhibitors, Interaction of Boron Derivatives with Isozymes I and II: A New Binding Site for Hydrophobic Inhibitors at the Entrance of the Active Site as shown by Docking Studies

The interaction of human carbonic anhydrase (hCA) isozymes I and II with boron derivatives was investigated by kinetic and spectroscopic studies. These derivatives, tested as new inhibitors of carbonic anhydrase, are sulfonamide and non-sulfonamide boron derivatives and some of them proved to be moderately efficient inhibitors of hCA I and hCA II, their activities being comparable to those of the un-substituted sulfonamides, the classical inhibitors of these zinc enzymes. Ph2BOH, one of the compounds with the highest affinity for hCA II in the present study, has been docked within the active site. After minimisation it was found situated at 7.9 Å from zinc, within the hydrophobic half of the active site, in Van der Waals contacts with the amino acid residues: Val 121, Phe 130, Val 135, Leu 141, Val 143, Val 207 and Pro 201. This is the first time that a CA inhibitor has been found to bind at the edge of the active site cavity, similarly to the CA activator histamine, which binds on the hydrophilic half. This finding may be of importance also for the design of novel types of inhibitors with increased affinity for the different CA isozymes.