Organosilicon compounds : LI. Further studies of the base-catalysed solvolysis of N-(triorganosilyl)anilines

Relative rates of solvolysis of some N-triorganosilylanilines in mixtures of ethanol and aqueous potassium hydroxide have been determined, with results as follows. (i) For XC₆H₄NHSiEt₃ compounds in MeOH (5 vol) + aq. alkali (2 vol) at 50°: (X =) H, 1.0;p-Me, 0.80;p-OMe, 0.83;m-Me, 0.90; o-Me, 0.87; p-SMe, 1.90; p-F, 1.7; p-Cl, 2.8; o-Cl, 14; m-Cl, 4.2; m-NO₂, 18; p-CN, ca. 43; p-NO₂, ca. 120. (ii) For PhNHSi(C₆H₄Y)₃ compounds in MeOH (10 vol) + aq. alkali (1 vol) at 50°: (Y =) H, 1.0; p-OMe, 0.12; p-Cl, ca. 32; m-Cl, ca. 84. (iii) For PhNHSiR₃ compounds in MeOH (5 vol) + aq. alkali (2 vol) : (R₃ =) Et₃, 1.0; Et₂Me, 18 (at 30°); Me₂-i-Pr, 8 (at 30°);Me₂-t-Bu, 0.012 (at 50°);i-Pr₃, 0.006 (at 50°). In series (i) the relative rates correlate with σ, or where appropriate σ^?-constants, with a ? value of 1.6. It is suggested that in the transition state of the rate-determining step the OSi bond is fully formed, or almost so, the SiN bond approximately 20—50% broken, and the bond between the nitrogen atom and a proton from the solvent ca. 10—30% formed.     

Chemical Research Faculties: An International Directory : Edited by G.L. Pollock. The American Chemical Society, Washington, 1984, xxxv + ca. 530 pages. US $129.95 (U.S.A. and Canada); US $155.95 (elsewhere). ISBN 0-8412-0817-4.

Heterobinuclear complexes of formula [LMCl₂(pz)M′(tfb)] (M = Ru, L = p-cymene, M′ = Rh; M = Ir, L = C₅Me₅, M′ = Rh; M = Rh, L = C₅Me₅, M′ = Ir) and [(C₅Me₅)IrCl(pz)₂Rh(tfb)] (tfb = tetrafluorobenzo[5.6]bicyclo[2.2.2]octan-2,5,7-triene) have been prepared. The molecular structure of [(p-cymene)Ru(μ-Cl)2(μ-pz)Rh(tfb)] has been determined by X-ray diffraction. It consists of two moieties, (p-cymene)Ru and (tfb)Rh, triply-bridged by a pyrazolate group and two chlorine atoms.     

Rates of base-catalysed cleavage of pyridyl-, quinolyl-, picolyl- and (quinolylmethyl)-trimethylsilanes

Rates of cleavage of some picoyl- and (quinolylmethyl)-trimethylsilanes (RSiMe₃, where R = PyCH₂ or QnCH₂SiMe₃) have been measured in “90%” aqueous methanolic sodium methoxide at 50°C. Relative reactivities are: 2-PyCH₂, 1.0; 3-PyCH₂, 0.030; 4-PyCH₂, 8.9; 2-QnCH₂, 41; 3-QnCH₂, 0.161; 4-QnCH₂, 37. The rates correlate well with those for base-catalysed hydrogen-exchange in the parent carbon acids RH. Approximate pK_a's (based on the scale of ion-pair acidities in CsNHC₆H₁₁H₂NC₆H₁₁, with pK_a of 9-phenylfluorene = 18.6) for the carbon acids, RH, can be derived as follows: 2-PyCH₃, 29.5; 3-PyCH₃, 34; 4-PyCH₃, 27; 2-QnCH₃, 25; 3-QnCH₃, 32; 4-QnCH₃, 25.Rates of cleavage of pyridyl- and quinolyl-trimethylsilanes (PySiMe₃ and QnSiMe₃) by sodium hydroxide in 4 : 1 v/v Me₂SO/H₂O at 50°C have also been measured; and the relative reactivities are: 2-Py, 1.0; 3-Py, 2.9; 4-Py, 8.4; 2-Qn, 15.9; 3-Qn, 12.7; 4-Qn, 184. The sequence of reactivity differes from that for base-catalysed hydrogen-exchange at the relevant positions of pyridine and quinoline, indicating that the reactivities are not determined in both cases (if in either) solely by the stabilities of the corresponding carbanions.     

Reactions of alkynes with bis(triphenylphosphine)platinum-ethylene: A P-{H} NMR study

Internally consistent assignments of the ³¹P-{¹H} NMR parameters of the complexes [Pt(RCCR′)(PPh₃)₂] are proposed, based on the premise that the magnitude of ¹J(PtP) depends mainly on the nature of the moiety CR trans to P. For a given R, ²J(PP) correlates with ¹J(PtP) for thebond trans to CR. The alkynes PhCCSnEt₃, PhCCSnPh₃, Me₃SiCCCl, Me₃SiCCBr, Et₃SiCCI and MeCCI undergo oxidative addition reactions with [Pt(C₂H₄)(PPh₃)₂]; the intermediate alkyne complex was detected for PhCCSnEt₃, Me₃SiCCCl and Me₃CCBr. The triyne Me(CC)₃Me forms platinum(0) complexes by coordination with the central or terminal CC bond and appears also to give a platinum(II) complex by oxidative addition.     

Organic Reactions. Vol. 33 : Wiley; New York, etc.; 1985, xx + 347 pages £57.00.

The [CuPPh₃CCPh]₄ tetramer, obtained by treatment of [Cu(PPh₃)₂BH₄] with phenylacetylene and KOH (molar ratio 1/1/1) in 1/1 benzene/benzyl alcohol, consists of a tetrahedral skeleton of metal atoms bonded to four terminal phosphine molecules and to four μ-3 -bridging phenylacetylide ligands which behave essentially as 2e donors.     

Reaction of tris(trimethylsilyl)methylsilicon halides with methanolic sodium methoxide. Probability of sila-olefin intermediates

The compounds TsiSiR₂X [Tsi = Me₃Si)₃C; R = Me, X = Cl, Br, I, or R = Ph, X = F, Cl, Br, I)] react with boiling 2 M MeONa-MeOH to give products of the type (Me₃Si)₂CHSiR₂OMe. It is suggested that the reaction proceeds through an elimination, analogous to E2 eliminations of alkyl halides, involving synchronous attack of MeO^? at an Me₃Si group, liberation of X^?, and formation of (Me₃Si)₂CSiR₂. The compounds TsiSiPhMeF TsiSiPhCl₂ react analogously to give (Me₃Si)₂CHSiPhMe(OMe) and (Me₃Si)₂CHSiPh(OMe)₂ [tha latter presumably by solvolysis of the initially-formed (Me₃Si)₂CHSiPhCl(OMe)]. The compounds TsiSiMe₂OMe and TsiSiMe₃ do not react, while TsiSiMe₂H gives TsiH. The compound TsiSiCl₃ reacts with 0.1 M MeONa-MeOH to give the substitution and elmination products TsiSiCl₂(OMe) and (Me₃Si)₂CHSi(OMe)₃ in ca. $\text{1}\text{2}$ ratio.     

Cleavage of benzyltrimethylstannanes by aqueous methanolic perchloric acid

The rates of cleavage of some XC₆H₄CH₂SnMe₃ bonds by aqueous-methanolic perchloric acid have been measured spectrophotometrically, and the rate of cleavage of the MeSn bonds of PhCH₂SnMe₃ and Me₄Sn by monitoring the methane evolution. The results indicate that for X = H, p-Me, o-Me, p-Bu^t, o-, m- and p-F and -Cl, and o-Br, the cleavage of the CH₂SnMe₃ bond involves attack of the acid at the benzylic atom, and is not much faster than that of the SnMe bonds, but that a mechanism involving ring-protonation is important for X = m-Me, and greatly predominant for X = m-OMe.