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Alkali metal derivatives of octamethyltrisiladiazane. Unusually short NaC contacts in the molecular structure of the disodium salt

Journal of Organometallic Chemistry
Publication Date
DOI: 10.1016/s0022-328x(00)98844-2
  • Chemistry


Abstract Alkali metal derivatives (Me 3SiNM) 2SiMe 2 of octamethyldisilatriazane (I) have been obtained by the reaction of I with mNH 2 (M  Na, K, Cs), or with M in the presence of styrene (M  K, Rb) or with elemental Cs. A monosodium derivative has also been prepared. The dilithium derivative II and the disodium analogue III from stable complexes with ethers. In contrast to the dimeric molecular weights of II and III in benzene solution, an X-ray study of III has revealed trimeric association in the solid state. The crystals belong to the monoclinic space group C2/ c with a 21.725(2), b 18.5012(9), c 12.7867(7) Å, β 103.347(4)°, Z  4 and d c 1.11 g/cm 3. Refinement yielded a conventional R value of 0.045 for 2909 counter-measured observed reflections. The trimers possess a cluster of six Na + which are bridged by the N atoms of the anions. If only nSi and NNa bonds are considered, the N atoms have coordination numbers of 4 and 5 while coordination numbers of 2, 3 and 4 are found for the cations. The NNa distances (2.304(3)-2.601(3) Å) reflect the coordination numbers of both N and Na. Surprisingly, the shortest NaC contact, 2.656(6) Å, is comparable to the longest NNa bond, and the possible chemical consequences of such metal-alkyl interactions are discussed. The SiNSi bond angles vary over a substantial range 122.6(2)–140.0(2)°.

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