Henri Ranaivonjatovo

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.

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.

A stable compound with a tin–phosphorus double bond: the (2,4,6-triisopropylphenyl)(supermesityl)stannaphosphene

The stable bis(2,4,6-triisopropylphenyl)(supermesityl)stannaphosphene 1(supermesityl : 2,4,6-tri-tert-butylphenyl) has been synthesized by dehydrofluorination of the corresponding fluorostannylphosphine by tert-butyllithium; its structure has been evidenced by NMR spectroscopy and by addition of methanol and water onto the tin–phosphorus double bond.

A Compound With a Tin-carbon Double-bond, Bis(2,4,6-triisopropylphenyl)(fluorenylidene)stannane - Aspects of its Reactivity and X-ray Structure of its Dimer

Bis(2,4,6-triisopropylphenyl)(fluorenylidene)stannane (1) reacts nearly quantitatively with compounds having active hydrogen atoms (alcohols, amines, mineral acids, phenylacetylene) and with lithium aluminium hydride to give the corresponding stannanes. Methyl iodide also adds easily to the tin-carbon double bond. Compound 1 slowly dimerizes at room temperature in solution. The head-to-tail dimer 10 has been structurally characterized by X-ray analysis which reveals long intracyclic Sn-C bonds (2.288(4) to 2.293(5) angstrom) and a planar four-membered ring.

New routes to diarsenes and arsaphosphenes involving fluorinated arsines

Abstract The stable diarsene ArAsAsAr ( 1 ) and arsaphosphene ArAsPAr ( 6 ) (Ar=2,4,6-tri- tert -butylphenyl) have been synthesized in excellent yields from the difluoroarsine ArAsF 2 by reaction with ArAs(Li)SiMe 3 (for 1 ) and with ArP(H)Li followed by t -BuLi (for 6 ). Compound 1 , previously prepared by other routes, as well as the new compound 6 were characterized by single-crystal X-ray diffraction ( d (AsAs) 2.2634(3) A, d (PAs) 2.141(5) A).

The first stable 3,1-germaphosphaallene Tip(t-Bu)GeCPAr

Abstract The first stable heteroallenic derivative with two heavy doubly-bonded Group 14 and 15 elements, the germaphosphaallene Tip( t -Bu)GeCPAr 1 (Tip=2,4,6-triisopropylphenyl, Ar=2,4,6-tri- tert -butylphenyl), has been prepared in a nearly quantitative yield by dechlorofluorination of Tip( t -Bu)Ge(F)C(Cl)PAr (obtained from ArPCCl 2 and successive reaction with n -butyllithium and Tip( t -Bu)GeF 2 ) with tert -butyllithium. 1 gives [2+2] cycloadducts by the GeC double bond with benzaldehyde, benzophenone and fluorenone to afford the corresponding germaoxetanes 11 – 13 . 13 has been structurally characterized showing a long GeO bond (1.821(2) A) and a slightly folded four-membered ring GeOCC (18.8° along C(1)Ge axis).

An isolable o-quinodimethane and its fixation of molecular oxygen to give an endoperoxide.

Addition of the germene Mes2Ge=CR2 to 1,4-naphthoquinone yields a singular o-quinodimethane which gives Diels-Alder reactions at room temperature and reacts cleanly with oxygen to form an endoperoxide.

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(But)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.

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.