Speicherung des labilen Silaethens Me₂Si=C(SiMe₃)₂ mit N-Trimethylsilyl-benzophenonimin Ph₂C=NSiMe₃ / Storing of the Labile Silaethene Me₂Si=C(SiMe₃)₂ with N-Trimethylsilyl-benzophenoneimine Ph₂C=NSiMe₃

Abstract

<jats:p>N-Trimethylsilyl-benzophenoneimine Ph<jats:sub>2</jats:sub>C=NSiMe<jats:sub>3</jats:sub> is able to “store" the silaethene Me<jats:sub>2</jats:sub>Si = C(SiMe<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub> (1). produced from Me<jats:sub>2</jats:sub>SiF-CLi(SiMe<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>, under formation of a [2+4]- and [2+2]-cycloadduct (2, 3), respectively. Above 60 °C (above 120 °C) 2 or 3 by the way of 1 transform into a 1:5 mixture of 2 and 3 (into a 1:1 mixture of the dimer of 1 and the insertion product of 1 into the SiN-bond of Ph<jats:sub>2</jats:sub>C=NSiMe<jats:sub>3</jats:sub>). In the presence of 2,3-dimethyl-1.3-butadiene (dmb), 2 or 3 form by way of the reaction of the intermediate 1 with dmb a [2 + 4]-cycloadduct (75%) and an ene reaction product (25%). The rate constants of the first order decomposition of 2 or 3 in the presence of dmb (80 °C. solvents like Et<jats:sub>2O,</jats:sub> Q<jats:sub>6</jats:sub>H<jats:sub>6</jats:sub> are in the order of 2x10<jats:sup>-4</jats:sup>s<jats:sup>-1</jats:sup> (τ<jats:sub>1/2</jats:sub>ca. 1 h) and 3x10<jats:sub>-</jats:sub><jats:sup>5</jats:sup>s<jats:sup>-1</jats:sup> (τ<jats:sub>1/2</jats:sub> ca. 6 h). respectively. </jats:p>

Diels-Alder and Ene Reactions of the Stannaethene Me2Sn=C(SiMe3)2: Dienophilic and Enophilic Behaviour of Ethenes Me2E=C(SiMe3)2 (E=Si, Ge, Sn)

“…[22] On the basis of electronegativity of Si, Ge and Sn (EN Si/Ge/Sn 1.74/2.02/1.72 [23] ), one expects a similar polarity for Si ± C and Sn ± C but somewhat lower polarity for Ge ± C double bonds. According to this and contrary to experimental results it should apply: (3). However, for the dienophilic versus enophilic character of an unsaturated system not only the polarity of the double bond but the bond strength of the formed E ± C bond in the intermediate stage of Diels ± Alder or ene reaction also plays a role in which strong E ± C bonds favour the ene against the diene reaction (compare formulations 34, 35).…”

“…The above-described studies permit us to state that 3 behaves as dieno-and enophile towards butadiene, propene and their organic derivatives similar to 1 [2][3][4][5][6][7][8] and 2 [9] carbon analogues. Thus the stanna-Diels ± Alder and ene reactions run like the sila-and germa-Diels ± Alder and ene reactions and are concerted as well as HOMO diene ± LUMO dienophile and HOMOene ± LUMO enophile -controlled (normal electron requirement).…”

“…However, for the dienophilic versus enophilic character of an unsaturated system not only the polarity of the double bond but the bond strength of the formed E ± C bond in the intermediate stage of Diels ± Alder or ene reaction also plays a role in which strong E ± C bonds favour the ene against the diene reaction (compare formulations 34, 35). The atomic radius increases for E Si, Ge, Sn and with that the E ± C and E C bond lengths grow strongly for E in the order Si, Ge, Sn (radius Si/Ge/Sn 1.17/1.22/1.40 ; [23] distance Me 3 Si ± Me/ Me 3 Ge ± Me/ Me 3 Sn ± Me 1.87/1.95/2.13 ; [24] distance H 2 SiCH 2 /H 2 GeCH 2 /H 2 SnCH 2 1.69/1.77/1.98 ). Hence, the E ± C bond energy changes in the same direction (dissociation energy Me 3 Si ± Me/Me 3 Ge ± Me/Me 3 Sn ± Me 365/340/290 kJ mol À1 [26] ).…”

“…The subsequent sections describe these results along with our earlier studies on reactions of 1 and 2 with propene, butadiene and their methyl derivatives. [2][3][4][5][6][7][8][9] Results and Discussion Products of reactions of 1 ± 3 with organic dienes and enes Primary products: As evident from Table 1, reactions of 3 with butadiene and propene as well as their methyl and phenyl derivatives occur analogous to similar reactions of 1 and 2 to form Diels ± Alder products (4,5,7,8,11,12,15,16) and ene products (6,9,13,17,18,19,20,22). Anthracene acts as a diene relative to 3 as to 2 or 1.…”

“…Furthermore, Table 2 indicates that the stannaethene 3, similar to the germaethene 2 or the silaethene 1, undergoes cycloaddition to cis-pentadiene substantially slower than to the trans-pentadiene (formation of 11 and 12). Accordingly, Diels ± Alder reactions with stannaethene, like those with silaethenes and germaethenes [2][3][4][5][6][7][8][9] or ethenes, [10] are liable to conformational influences: a reduction in concentration of cisoid diene (29 c) in equilibium with transoid diene (29 a) on the basis of steric interactions in 29 c implying a strong decrease in tendency of [4 2] cycloaddition of dienes. By stronger steric hinderance of isomerisation 29 a > 29 c, it appears quite likely that dienes because of energetically more Table 2.…”