Darstellung und Charakterisierung neuer niedrigkoordinierter ...

It is interesting to note that in the presence of Me 3Si–N 3 the Lewis
acid GaCl 3 facilitates a methyl/azide exchange even at low
temperatures (T always below –30 °C). Without GaCl3 no
reaction was observed between 5 and Me 3Si–N 3.
Interestingly, the novel azidodimethylsilyl(mterphenyl)amino(chloro)methylarsane
(7) represents one of the
rare example of structurally characterized neutral azidosilanes. 13
Compound 7 is thermally stable up to over 149 °C, is neither heat
nor shock sensitive. Moreover, 7 is extremely air and moisture
sensitive, but under argon it is stable over a long period in solid at
ambient temperatures and in common organic solvents (e.g.
toluene, CH2Cl2, ether etc.) at low temperatures (T < –40 °C). It is
interesting to mention, that, when an excess of Me 3Si–N 3 was
used, a Me 3Si–N 3·GaCl 3 adduct crystallizes together with 7. This
adduct was first described by Kouvetakis et al. 14
Azidosilanes are frequently used for the introduction of azide
groups, for the generation of silylenes and the synthesis of silyliminophosphoranes
via Staudinger reaction. 12b,15,16,17,18,19,20
Figure 4. ORTEP drawing of the molecular structure of 7 in the crystal.
Thermal ellipsoids with 50% probability at 173 K (hydrogen atoms
omitted for clarity).
Ter
AgOTf
Ter
Me
Si
N
As
Cl
-AgCl
Toluen
Me
Si
N
As
Cl
Me Me
Cl
-40°
TfO Me
Me
(5) (8)
Scheme 6. Methyl/triflate exchange in trimethylsilyl(mterphenyl)amino(dichloro)arsane
(5), yielding N-(trifluoromethylsulfonatodimethylsilyl)-N-(m-terphenyl)amino(methyl)chloroarsane
(8)
(utilization of 1 eq AgOTf).
Methyl/triflate-exchange reactions in trimethylsilyl(mterphenyl)aminodichloroarsane.
In a second series of
experiments we studied the reaction of silver triflate, AgOTf (OTf
= SO 3CF 3 = trifluoromethylsulfonate = triflate), with 5, again
observing interesting methyl exchange reactions, this time
triggered by the action of the Lewis acid Ag + (Scheme 6 and 7).
First, one eq. of AgOTf was added to a solution of 5 in CH 2Cl 2 at
–30 °C under exclusion of light, resulting in the formation of N-
(trifluoromethylsulfonatodimethylsilyl)-N-(m-terphenyl)amino-
(methyl)chloroarsane (9) (Mp = 163 °C) in high yields (98 %)
(Scheme 6, Figure 5). Usage of 2 eq. of AgOTf led to the
formation of N-(trifluoromethylsulfonatodimethylsilyl)-N-(m-
terphenyl)amino-trifluoromethylsulfonatomethylarsane (10) (yield
= 96%, Mp = 186 °C). Both compounds (9 and 10) have been
fully characterized. As expected, when one eq. AgOTf was added
a methyl/triflate exchange occurs at the silicon center (Scheme 6).
However, when 2 eq. of AgOTf are used, again only one
methyl/triflate exchange was observed. The second eq. of AgOTf
attacks the arsenic center finally forming an As–OTf bond
(Scheme 7).
Figure 5. ORTEP drawing of the molecular structure of 8 in the crystal.
Thermal ellipsoids with 50% probability at 173 K (hydrogen atoms
omitted for clarity).
Ter
2 AgOTf
Ter
Me
Me
N
Si
Me
As
Cl
Cl
-2 AgCl
Toluen
-40°
Me
TfO
N
Si
Me
OTf
As
Me
(5) (9)
Scheme 7. Methyl/triflate exchange in trimethylsilyl(mterphenyl)amino(dichloro)arsane
(5), yielding N-(trifluoromethylsulfonatodimethylsilyl)-N-(m-terphenyl)amino-trifluoromethylsulfonatomethylarsane
(9) (utilization of 2 eq AgOTf).
Figure 6. ORTEP drawing of the molecular structure of 9 in the crystal.
Thermal ellipsoids with 50% probability at 173 K (hydrogen atoms
omitted for clarity).