The crystal and molecular structures of the acaricides chlorotrineophylstannane (ta), chlorotris[( dimethylphenylsilyl)methyl]stannane (tb ), and trineophyl(1,2,4-triazol-1-yl)stannane hemihydrate (2a · 0.5H 2 0), have been determined by single-crystal X-ray diffraction studies. The structure of 2,5-dimethyl-2,5-diphenylhexane (4) was also investigated for comparison.

forms adducts 3 . donor, the stability of which increases in the order of donor = E t 2 0 < Br-< THF < NEtMe, < F-, and combines with the reactants a-b (e.g. R-Li; R = H, Me, nBu, Ph) with insertion into the a-b bond, with a=b-c-H [e.g. O=CtBu-CH,-H; CH2=CR-CH2-H, R = Me, CMe=CH,, CH2SiPhzCH(SiMe3),] according to a n ene reaction, with a = b (e.g. CHz=CHOMe; PhzC=NSiMe3) or a = b = c (e.g. tBuzRSiN3, R = Me, tBu) or a=b-c=d [e.g. may be said that going from Me,Si=C(SiMe& to PhzSi=C-(SiMe,), there is only a gradual but not principal change of silaethene reactivity. This change is due to increasing polarity and overcrowding of the double bond, that is increasing Lewis acidity and steric hindrance of the unsaturated silicon atom. Certainly, the former silaethene stabilizes thermally by dimerization, the latter by isomerization.Der von uns aufgefundene einfache Darstellungsweg zum dimerisierungslabilen Silaethen 1 durch ,,thermische Salzeliminierung" gemaD GI.( 1)F2] ermoglichte, wie wir in der Folgezeit feststellten, auch einen Zugang zu den dimerisierungsstabilen Silaethenen Z13] und 3F41 (das Silaethen 1 dimerisiert in Diethylether selbst bei -100°C, wahrend sich das Siaethen 2 in das bei Raumtemperatur metastabile Silaethen 2a und das Silaethen 3 in Diethylether bei -20°C in das um 0°C zu Folgeprodukten reagierende Silaethen 3ar51 umlagert). 3*L& L 2 , 33 ) P h R2Si-C(SiMe& Me, ,SiMe3Me ' si=c \SiMeRz Die Synthese von 3 interessierte U. a. im Zusammenhang mit der Frage, ob ein Ersatz der beiden Methylsubstituenten am ungesattigten Silicium-Atom in 1 durch aromatische Reste zu einer Stabilisierung der ungesattigten Verbindung fiihrt. Auch sollte geklart werden, welche Anderungen der allgemeinen Reaktivitat mit einem derartigen Substituententausch verbunden sind. Nachdem in einer ersten Mitteilung[4] iiber Erzeugung und Nachweis des Silaethens 3 berichtet worden ist, sol1 nunmehr nachfolgend zur Reaktivitat und in weiteren Mitteilungen ['] zur thermischen Stabilisievung des Silaethens 3 Stellung genommen werden. Donoraddukte von Ph2Si = C(SiMe3)2 als SilaethenquellenNach unseren bisherigen Erkenntnissen vermogen Silaethene R2Si=CR2 und Silanimine R2Si=NR im Unterschied zu Ethenen R2C=CR2 und Ketiminen R,C=NR Reagenzien mit freiem Elektronenpaar wie Ether OR2 oder Amine NR3 am ungesattigten Silicium-Atom unter Bildung stabiler Donor-Akzeptor-Komplexe aufzunehmen und bei erhohter Temperatur wieder abzugebenr61. Da den betreffenden Addukten eine hohere Metastabilitat als den donorfreien ungesattigten Siliciumverbindungen zukommt, wirken die Donoren gewissermaDen als "Silaethen-" bzw. ,,Silanimin-Speicher". Die Metastabilitat der Additionsverbindungen wachst mit der Basizitat der Donoren, welche in Richtung Et20 < Br-< THF < NMe3, NEtMe2 < Fansteigtc61. Fur eine Stabilisierung des auDerst dimerisierungslabilen Silaethens 1 geniigt die Basizitat von EtzO,

Generation and Detection of the Silaetheae Ph2Si= C(SiMe3)z')Bromotrisilylmethanes (Me3Si)2(Ph2XSi)CBr (4-13; Table 1) are formed by the reaction of (Me3Si)2(Ph2HSi)CM (M = Li, Na) with bromine or with bromine/chlorine (X = H, C1, Br) and also by treating (Me3Sik(Ph2BrSi)CBr with KHF2 (X = F), H 2 0 or MeOH (X = OH, OMe), MeLi (X = Me), BuLi/Br2 (X = Bu), PhLi/Brz or PhLi/PhOLi/Brz (X = Ph, OPh). PhLi, BuLi, and tBu3SiNa convert the bromotrisilylmethanes by Br/M exchange into compounds (Me3Si)z(Ph2XSi)CM, which may be protolyzed, alkylated, and brominated [formation of (Me3Si)2(Ph2XSi)CY with Y = H, R, Br; cf. 4-23, Table I]. For X = halogen the equilibrium (Me3Sih(Ph2XSi)CMePh2Si = C(SiMe3h (3) + MX exists. Thereby, silaethene 3 is formed in Et20 at -78°C (X/M = Br/Li) or at room temperature (X/M = F b i , Br/Na), respectively, reversibly in low concentrations and at higher temperatures irreversibly (formation of secondary products of 3). The intermediacy of 3 has been established chemically by trapping 3 with (for example) RLi (formation of insertion products in the R -Li bond), Ph2C = NSiMe3 (formation of a [2 + 41 cycloadduct, which may serve as a source of 3), tBu2MeSiN3 (formation of a [2 + 31 cycloadduct), and particularly 2,3-dimethyl-1,3-butadiene (forrnation of Diels-Alder and ene reaction products). In the last case products and yields are independent of the origin of 3. From Me2Si = C(SiMe& (1) to 3 there is only a gradual (but no principal) change of silaethene reactivity (3 is more Lewis acidic than 1).

A new in situ preparation of trirnethylsilyl tnfluoromethanesulfonate (3) is described: 3 is generated by a thermally induced rearrangement of (dimethylsily1)methyI trifluoromethanesulfonate (2), which can be prepared by reaction of (CH3)&(H)CH20H (1) with (CF3S0&0. Starting with C6H5(CH3)Si(H)CH,0H (5), the derivative (methylphenylsily1)-methyl trifluoromethanesulfonate (6) can be obtained by a similar method. Its thermally induced rearrangement leads to dimethylphenylsilyl trifluoromethanesulfonate (7). The rearrangements 2+3 and 6-7 were found to be first-order reactions with half-lifes at 80°C of 0.75 and 1.7 h, respectively.

Abstract Starting from SnCl4. hexasila-fenbutatinoxide (2b) [a silicon analogue of the acaricide fenbutatinoxide (2b)] and its derivatives lb and 3b were prepared (SnCl4 → 1b → 2b -> 3b). The distannoxanes 2a and 2b were found to react very easily with H2O to give the corresponding stannols 4a and 4b, respectively. In solution (C6D6 or CDCl3) the equilibria 2a/2b + H2O ⇄ 2 4a/4b were observed (1H NMR). With regard to the system 2a/4a/H2O, this observation is at variance with an earlier report in which the sterically bulky neophyl substituents [C6H5(CH3)2CCH2] are said to prevent the condensation of 4a to give 2a. - 1b -3b were found to be potent acaricides showing activities similar to those of their carbon analogues 1a -3a (test organisms: adult females of Tetranychus urticae Koch)