Recent developments in the chemistry of stable doubly bonded germanium compounds

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.     

SYNTHESIS OF TWO STABLE DIPHOSPHENES WITH A NEW STABILIZING SUBSTITUENT

Abstract

Two new diphosphenes 7 and 10 have been synthesized by action of DBU on trichlorogermylphosphines 4 and 8; this route involves the intermediate formation of chlorophosphines 5 and 9. Diphosphenes 7 and 10 are stabilized by the 2,6-bis(trifuoromethyl)phenyl group which presents both steric and electronic effects and is used for the first time in phosphorus chemistry.     

METALLAPHOSPHENES AND DIPHOSPHENES

Abstract

Transient metallaphosphenes (rbnd2;M[dbnd]P[sbnd]) have been obtained by exchange reactions between disilylphosphines and organometaldihalides (M = Ge, Sn), or by thermolysis of 2-metallaphosphetanes (M = Si, Ge). They are characterized by trapping reactions with strained heterocycles. The first stable germaphosphene 12 has been synthesized by dehydrohalogenation from the parent halogermylphosphine and isolated in form of orange crystals. It is very reactive toward compounds with active hydrogen.

Transient diphosphenes ([sbnd]P[dbnd]P[sbnd]) have been prepared by the same type of exchange reactions between disilylphosphines and dichlorophosphines and characterized by trapping reactions on dienes. The second stable diphosphene 18 has been obtained by addition of t-BuLi on trisyldichlorophosphine. Its structure has been determined by X-ray diffraction and some aspects of its reactivity are described. The reaction of bisyltrichlorogermylphosphine with DBU affords the new stable and potentially reactive diphosphene 30.     

A stable distannirane

The first three-membered ring compound containing two tin and one carbon atoms, 1,1,2,2-tetra(2,4,6-triisopropylphenyl)-3-fluorenylidene-1,2-distannirane, has been synthesized in a two-step procedure from the 9-[bis(2,4,6-triisopropylphenyl)fluorostannyl]chloromethylenefluorene.     

The use of a germene for the synthesis of esters of alpha-germyl-substituted alpha-amino acid and alpha-aminophosphonic acid

The first alpha-germyl-substituted alpha-amino ester and alpha-germyl-substituted alpha-aminophosphonic ester have been synthesized by a one-pot reaction between the germene Mes2Ge=CR2 (CR2 = fluorenylidene) and the iminoester or iminophosphonate Ph(H)C=NCH2-Y (Y = COOMe, P(O)(OEt)2).     

Methyl 3‐para‐anisyl‐4‐(2‐hydroxy­benzoyl)­isoxazole‐5‐carboxyl­ate

The title compound, C₁₉H₁₅NO₆, contains a planar isoxazole ring. An intramolecular hydrogen bond is formed between the OH group attached to a phenyl ring and a carbonyl O atom.     

Phosphasila-, phosphagerma-, and phosphaarsaallenes --P=C=E (E = Si,Ge, As) and arsa- and diarsaallenes --As=C=E" (E" = C,As)

The paper reviews the contribution from our group to the studies of heteroallenes. The transient 1,3-phosphasilaallene ArP=C=Si(Ph)Tip (Ar = 2,4,6-tri-tert-butylphenyl, Tip = 2,4,6-triisopropylphenyl) and 1,3-phosphagermaallene ArP=C=GeMes₂ (Mes = 2,4,6-trimethylphenyl) were characterized below –40 °C by NMR spectroscopy and chemical trapping. These compounds dimerize above –40 °C through two routes. With increased steric hindrance on germanium, the phosphagermaallene ArP=C=Ge(Bu^t)Tip was stabilized as monomer at room temperature. 3-Chloro-2-lithio-1,3-phosphasilapropene ArP=C(Li)Si(Cl)CMeR₂ (CMeR₂ = 9-methylfluorenyl) behaves, at least in some cases, as a synthetic equivalent of the functionalizable allene ArP=C=Si(Cl)CMeR₂. Arsaallene ArAs=C=CR₂, phosphaarsaallenes ArP=C=AsAr and ArP=C=AsDmt (Dmt = 2,6-dimesityl-4-methylphenyl), and diarsaallene ArAs=C=AsAr exhibit a higher thermal, air, and moisture stability than the above phosphasilaallenes and phosphagermaallenes. The physicochemical data for the arsaallenes and diarsaallenes, particularly, their X-ray structural parameters, display a bonding system close to allenes. On going down the Periodic table, the stabilization becomes more difficult. For this reason, tin allenic derivatives are very rare and antimony allenic compounds have not yet been isolated.     

Reaction of stannenes and phosphastannenes with aldehydes and ketones: New tin four-membered ring derivatives

Stannene Tip₂Sn=CR₂ 1 (Tip=2,4,6-triisopropylphenyl, CR₂=fluorenylidene) enters a [2+2] cycloaddition reaction with benzophenone to afford the four-membered ring derivative2. This stannaoxetane undergoes a [2+2] decomposition with formation of the corresponding stannanone8 and alkene9 and an easy hydrolysis by initial cleavage of the Sn–C bond. Diphenylacetaldehyde also gives with1 a stannaoxetane, which has been characterized by its hydrolysis products. Phosphastannene Tip₂Sn=PAr13 (Ar=2,4,6-tri-tert-butylphenyl) reacts with benzaldehyde according to a [2+2] cycloaddition pattern leading to stannaphosphaoxetane14, whereas ene-products19–21 were obtained with acetaldehyde, acetone, and acetophenone.Hétérochimie Fondamentale et Appliquée, UPRES A 5069, Université Paul Sabatier, 31062 Toulouse cedex 04, France. Faculté des Sciences et Techniques, Route d'Immouzzer, BP 2022, Fs-Saiss, Fs, Maroc. Laboratoire de Synthse Organique, Faculté des Sciences, 40 Avenue du Recteur Pineau, 86022 Poitiers, France. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp 1098–1106, August, 1999.     

New Stable Diphosphenes

Abstract

Since the isolation of the first stable diphosphene by YOSHIFUJI, some other diphosphenes have been prepared and stabilized by very bulky substituents. We have recently described the synthesis, via a germylated way, of the bis [bis (trimethylsilyl)methyl]diphosphene 1, one of the least crowded stable diphosphenes: