Jean Escudié

Recent developments in the chemistry of stable doubly bonded germanium compounds

Abstract During the last 10 years, several compounds of the type Ge=X (X = C, Ge, N, P, S) have been isolated as monomers. The stabilization of such derivatives, which are generally highly polymerizable, was achieved by using very bulky groups both on the germanium atom and on the heteroelement X. Conjugation (particularly in a few germenes and germaimines) and intramolecular or intermolecular coordination with oxygen or nitrogen, also contributes, in some cases, to the stabilization. The X-ray analyses of such compounds show a significant bond shortening of the double bond (8–10%) relative to the corresponding single bond and a planar or nearly planar germanium. These doubly bonded germanium derivatives are usually thermally stable but must be handled in an inert atmosphere because of their high sensitivity to oxygen and moisture; they are extremely reactive, much more than the corresponding carbon analogues. Nearly quantitative additions on the double bond have been observed with electrophiles and nucleophiles, and various types of cycloadditions also occur. Except in one case, a germylene behavior has not been observed, proving that such compounds retain their structural integrity in solution.

Silenes 〉SiC〈, germenes 〉GeC〈 and stannenes 〉SnC〈: The French contribution

Abstract Various stable silenes 〉SiC〈, germenes 〉GeC〈 and stannenes 〉SnC〈 have been synthesized by reaction of tert-butyllithium with halovinylsilanes and -germanes (addition–elimination reactions) or with halofluorenylgermanes and -stannanes (substitution–elimination reactions). These two routes are among the most often used to synthesize stable organometallic alkenes. These derivatives, easily evidenced by their characteristic physicochemical data, are extremely reactive, much more than their alkene analogues, and appear as fruitful synthons in organic and organometallic chemistry.

Un Nouveau diphosphene stable: Le bis[tris(trimethylsilyl)methyl] diphosphene

Abstract A new stable diphosphene (Me 3 Si) 3 CPPC(SiMe 3 ) 3 has been isolated and characterized particularly by its NMR data; the 31 P NMR chemical shift appears to be the largest ever observed.

Stable N‐Heterocyclic Carbene Complexes of Hypermetallyl Germanium(II) and Tin(II) Compounds

The chemistry of the heavier Group 14 element carbene analogues has received wide interest because of their special properties and reactivity. Recently, an unexpected application of cyclopentadienyl, amido, or alkoxy germylenes and cyclic diazastannylene as precursors of nanomaterials has been described, thus opening a wide and promising field for investigation. Germanium nanowires have also been obtained by decomposition of hexakis(trimethylsilyl)digermane, highlighting the labile character of trimethylsilyl groups. Thus, the hypermetallyl germylenes or stannylenes, which contain both a low-coordinate Group 14 atom and a good leaving substituent, might be suitable candidates for nanomaterial alloys preparations. However, to the best of our knowledge, germylenes or stannylenes having electropositive silyl or germyl substituents have only been postulated as transient species; for example, in the reaction of Cl2Ge·dioxane with (Me3Si)3ELi (E = Si, Ge), chloro(silyl)germylenes rapidly oligomerize with the formation of cyclotetragermanes [(Me3Si)3EGeCl]4 or rearrange leading to cyclotrimetallanes [(Me3Si)2E{Ge(SiMe3)2}E(SiMe3)2]. To date, only one bis(hypersilyl)stannylene has been reported, but in its dimeric form in equilibrium with the monomeric form in solution and as a dimer in the solid state. Recently, a thermally unstable bis(hypergermyl)stannylene was synthesized (requiring preparation and handling below 30 8C), but like its hypersilyl substituted analogue, the X-ray structural analysis revealed the presence of dimers in the solid state. These results show the limitations of the steric shielding of the hypersilyl or hypergermyl ligands for the stabilization of low-coordinate species. Among the stabilization strategies of germylenes or stannylenes, the intermolecular coordination has aroused a great interest in the last decades, particularly with the use of N-heterocyclic carbenes (NHC) as stabilizing co-ligand. The first examples of carbene–germanium(II) adducts were described by Arduengo et al. ((NHC)GeI2) [8] and then by Lappert et al. (NHC–heterocyclic germylene). Later, NHCs were successfully employed for the stabilization of transient germanium(II) species. In contrast, there are few examples of carbene–stannylene adducts. In all of these cases, the carbene coordination is one of the key factors to obtain divalent species in their monomeric state. Herein we describe the synthesis of hypermetallyl germylenes and stannylenes that are stabilized by complexation with carbene units. We investigated the reactivity of the carbene–germylene adduct 1 and of the carbene–stannylene adduct 3, which were obtained as previously reported from the known carbene [DC{N(iPr)C(Me)}2] [13] and Cl2Ge·dioxane or Cl2Sn, respectively, towards various sources of hypermetallyl units. All attempts to displace the chloride from germylenes with hypersilyl salts (Me3Si)3SiLi [14] or (Me3Si)3SiK [15] were unsuccessful and led to complex mixtures in which only some amounts of disilagermirane [(Me3Si)2Si{Ge(SiMe3)2}Si(SiMe3)2] could be identified. [4a] The latter has been previously obtained by mixing (Me3Si)3SiLi and Cl2Ge·dioxane. By contrast, treatment of 1 with one half equivalent of [(Me3Si)3Si]2Mg [16] in THF solution at room temperature gave the complex 2 a as the only product in a good yield (71%) (Scheme 1). Compound 2a is the first example of a donor-stabilized hypersilyl(chloro)germylene that could be isolated by the combination of both steric hindrance of the hypersilyl ligand and strong Lewis base coordination. Similarly, the addition of a stoichiometric amount of digermylmagnesium [(Me3Si)3Ge]2Mg [17] to 1 produces the hypergermyl-

Un derive à double liaison phosphore-arsenic : le premier phospha-arsene stable

Summary The first compound with a phosphorus-arsenic double bond, the phospha-arsene (Me 3 Si) 3 C-P=As-C(SiMe 3 ) 3 5 has been isolated and characterized by its physico-chemical chemical data; it reacts with sulphur leading to a novel heterocycle, the phospharsatiiran Download full-size image 6 .

A new route to bis(2,4,6-tri-tert-butylphenyl)diphosphene via silylated compound

Abstract A new synthesis of stable diphosphene is reported. δ 31 P value is reinvestigated.

ArP=C=Si(Ph)Tip: The first allenic compound with doubly bonded phosphorus and silicon

The first allenic compound with doubly bonded silicon and phosphorus, the 3-phospha-1-silaallene 1, has been obtained by dechlorination of the corresponding (chlorosilyl)chlorophosphaalkene 10 with tert-butyllithium at low temperature. Compound 1 was characterized by C-13 NMR (delta = 269.1 for the allenic carbon), Si-29 NMR (delta=75.7), and P-31 NMR spectroscopy (delta = 288.7), and by addition of methanol to the Si=C double bond. In the absence of a trapping agent, 1 dimerizes above - 30 degrees C to afford two types of dimers: 14, formed over one Si=C and one P=C double bond, and 15, formed over two Si=C double bonds, probably according to a concerted pathway. A thermodynamic equilibrium has been observed between the two stereoisomers 15 and 16 involving an isomerization around the P=C double bond. Compound 16 has been structurally characterized, displaying a nearly planar 1,3-disilacyclobutane ring with the two phenyl (Ph) and the two 2,4,6-tri-tert-butylphenyl (Ar) groups on the same side of this ring and the two 2,4,6-triisopropylphenyl (Tip) groups on the other side.

Bis(amidinato)germylenerhodium complexes: synthesis, structure, and density functional theory calculations.

The first monogermylenerhodium complexes stabilized by bulky amidinato ligands on the divalent germanium center have been synthesized and characterized by NMR spectroscopy and X-ray crystallography. Their stability strongly depends on the steric hindrance of the amidinato ligand. With trimethysilyl groups on the nitrogen atoms of the amidinato ligand, only the germylene oxide rhodium complex could be obtained; by contrast, with t-Bu groups, the germylenerhodium complex was isolated. In both cases, the formation of amidinatorhodium complexes was observed. The donating ability of the germylene ligand has been assessed from the CO stretching frequency of the corresponding dicarbonylrhodium complex and was confirmed by density functional theory calculations.

Les sila-2 phosphetannes precurseurs de sila-phosphimines

Abstract The first 2-silaphosphetane was synthetized by reaction of butyllithium with a β-chlorosilylphosphine, followed by intramolecular cyclisation. Physicochemical data show the existence of an equilibrium between the monomeric form (2-silaphosphetane) and the dimeric form (2,6-disila-1,5-diphosphocane). Thermic decomposition under reduced pressure of the 2-dimethylsila-1-phenylphosphetane, through a β-elimination process, leads to the dimethylsilaphenylphosphimine; this new species with a SiP double bond has been characterized by formation of the dimer (Me 2 SiPPh) 2 and by insertion reaction of the 2-silaphosphetane into the SiP bond.

Addition des germyl- et silylphosphines aux aldehydes et cetones α-ethyleniques

Abstract Germyl- and silyl-phosphines R 3 MPR′ 2 (M = Ge, Si) generally add in 1-4 position to α-ethylenic aldehydes and ketones with formation of phosphorus alkenoxy-germanes or -silanes. The α-ethylenic aldehydes always lead to 1-4 Z and E adducts ( Z preponderant), α-ethylenic ketones exclusively to the Z isomer. This particular stereochemistry is explained by a mechanism involving initial nucleophilic attack of the metal phosphine on carbon 4, steric hindrance of the reaction intermediate and participation of a 6-center pseudo-cyclic complex. On the contrary 1-2 addition on the carbonyl group of the 9-fluorenone is exculsively observed. The orientation of the additions (1–2 or 1–4) is interpreted in terms of Pearson (HSAB) theory.