173977-35-0Relevant academic research and scientific papers
Erzeugung, nachweis und stabilisierung isomerer silaethene R2Si=C(SiR3) 2 mit jeweils sechs Me-und zwei Ph-substituenten R
Wiberg, Nils,Joo,Polborn
, p. 147 - 161 (2007/10/03)
Bromotrisilylmethanes Me2SiBr-CBrRR2 (2b), PhMeSiBr-CBrRR1 (3b, two diastereomers) and Me2SiBr-CBrR12 (4b) (R = SiMe3, R1 = SiMe2Ph, R2 = SiMePh2) - sources of silaethenes Me2Si=CRR2 (2), PhMeSi=CRR1 (3, two isomers), and Me2Si=CR22 (4) - are formed by bromination of Me2SiH-CBrRR2 (2a), PhMeSiH-CBrRR1 (3a, two diastereomers; bromination takes place stereospecifically), and Me2SiH-CBrR22 (4a), which themselves are formed from CBr4 by introducing three silyl groups step by step according to: ->C-Br + R′Li + ->SiCl → ->C-Si-nBu, (Me3Si)2CH). The structure of one of the two diastereomeric compounds, 3a, has been solved by X-ray analysis. PhLi converts 2b-4b by Br/Li-exchange to lithium organyls Me2SiBr-CLiRR2 (2c). PhMeSiBr-CLiRR1 (3b, two diastereomers), and Me2SiBr-CLiR12 (4c), which in Et2O at - 78°C are in equilibrium with silaethenes 2, 3 and 4 in very low concentrations. The intermediacy of the silaethenes has been established chemically by trapping 2, 3 and 4 with 2,3-dimethyl-1,3-butadiene (DMB): formation of [4 + 2] cycloadducts 2d, 3d (two diastereomers) and 4d, of ene reaction products 2e, 3e (two diastereomers), and 4e as well as of [4 + 2] cycloadducts 2f (diastereomers), 3f (diastereomers), and 4f of the formed ene reaction products. The structure of one of the two diastereomeric compounds, 3d, has been solved by X-ray analysis. By warming the etheral solutions of 2c, 3c and 4c, [2 + 2] cycloadducts 2 X 2, 2 X 4 and 4 X 4 of silaethenes 2 and 4 are found. Considering the types and yields of the products of silaethenes - including Ph2Si=CR2 (1) - in the absence and the presence of DMB, the following is concluded: (i) silaethenes 1, 2, 3, 4 are in equilibrium by methyl and phenyl group migrations; (ii) the relative thermodynamic silaethene stability increases in the order 1 2Si=C(SiMe3)2 (as a consequence of steric effects of phenyl); (iv) the rate of methyl and phenyl group migration is equal; (v) substitution of methyl groups at unsaturated silicon (saturated silicons) in Me2Si=C(SiMe3)2 increases (does not increase) the SiC double bond polarity.
Thermal Stabilization of the Silaethene Ph2Si=C(SiMe3)2
Wiberg, Nils,Link, Matthias
, p. 1241 - 1250 (2007/10/03)
Silaethene Ph2Si=C(SiMe3)2 (3) (generated from Ph2SiBr-CLi(SiMe3)2 = 3*LiBr in Et2O at -78 deg C) reversibly isomerizes fast by methyl migration, then a bit slower by phenyl migration, and finally fast by methyl migration into thermodynamically more stable Me2Si=C(SiMePh2)(SiMe3) (3a), then into medium stable PhMeSi=C(SiMe2Ph)(SiMe3) (3b), and finally into most stable Me2Si=C(SiMe2Ph)2 (3c) (cf.Schemes 1 and 2; Figure 1).Simultaneously with isomerization 3a -> 3c cycloadditions (dimerizations) of 3a and 3c occur (formation of 3a * 3a, 3a * 3c, 3c * 3c; cf.Scheme 2).Over and above that, silaethenes 3a and 3c irreversibly isomerize into disilaindanes 4a, 4b, and 4c (cf.Scheme 6).Certainly, the latter reactions are even slow at 100 deg C.Thermolysis of 3a * 3a, 3a * 3c, 3c * 3c at 340 deg C, on the other hand, leads by way of cycloreversion and the intermediate formation of an equilibrium mixture of 3, 3a, 3b, 3c almost quantitatively to 4.In addition to the thermolysis products mentioned above, products of 3 and its isomers 3a, 3b, 3c with the solvents (for example Et2O; cf.Scheme 7), with the silaethene sources (for example 3 * LiBr; cf.Scheme 8), or with products formed from sources besides silaethene 3 (for example Ph2C=N-SiMe3; cf.Scheme 4) are observed. - Keywords: Methyl and phenyl group migrations in Ph2Si=C(SiMe3)2 ; Silaethenes Me2Si=C(SiMePh2)(SiMe3), PhMeSi=(SiMe2Ph)(SiMe3), Me2Si=C(SiMe2Ph)2 ; Silaethene dimers ; Disilaindanes ; Silaethene reactions with Et2O and with Ph2SiBr-CLi(SiMe3)2 ; Insertions of silaethenes into SiN bond of Ph2C=N-SiMe3
