Reversible intramolecular base-stabilization in silylene (silanediyl) complexes: surprising reactivity for silylene coordination compounds with a dynamic N.cntdot..cntdot..cntdot.Si.cntdot..cntdot..cntdot.N bond
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The silane [2-(Me2NCH2)C6H4]2SiCl2 (7) shows a new dynamic N⋯Si⋯N “flip-flop” coordination mode below Tc = 233 K (ΔGǂ = 46.5 (±0.5) kJ mol−1) with both amine donors displacing each other. 7 is pentacoordinated in the solid state; crystal data: orthorhombiC., Pbca, a = 13.802(1) Å, b = 17.908(1) Å, c = 15.544(2) Å, Z = 8. Reaction of the silanesC6H5[2-(Me2NCH2)C6H4]SiCl2 (6), 7, and [2-(Me2NCH2)-5-(t-C4H9)C6H3]2SiCl2 (8) with chromiumpentacarbonylmetallate yields the silanediyl complexes [2-(Me2NCH2)C6H4]C6H6SiCr(CO)5 (11), [2-(Me2NCH2)C6H4]2SiCr(CO)5 (12), and [2-(Me2NCH2)-5-(t-C4H9)C6H3]2SiCr(CO)5 (13); [2-(Me2NCH2)C6H4]HSiCr(CO)5 (14) was obtained by photolytic methods. Silanediyl complexes with one chelating donor show a rigid coordination of the donor to silicon which can be lifted at higher temperatures (95 °C for 11, ΔGǂ = 80.4 (±0.5) kJ mol−1). A single crystal X-ray structure determination of 11 reveals a CrSi bond distance of 2.409(1) Å and a N→Si bond length of 1.991(2) Å. Crystal data: tricliniC., P1̅, a = 9.401(1) Å, b = 10.207(1) Å, c = 11.586(1) Å, Z = 2. Silanediyl complexes with two intramolecular donor functions feature a dynamic “flip-flop” coordination of the amine groups to silicon. Both (dimethylamino)phenyl groups in 12 and 13 can be detached from silicon under liberation of a three-coordinate silicon atom at Tc = 58 °C (VT-1H-NMR), ΔGǂ = 67.1 (±0.5) kJ mol−1 for 12 and Tc = 61 °C., ΔGǂ = 70.1 (±0.5) kJ mol−1 for 13. A single crystal X-ray structure determination of 12 gives 2.408(1) Å for the SiCr bond length and 2.046(2) Å for the N1Si dative bond (the second contact N2Si has a nonbonding distance of 3.309 Å; the sum of bond angles at silicon amounts to 351.3°). Crystal data: tricliniC., P1̅, a = 9.531(1) Å, b = 10.339(1) Å, c = 11.676(1) Å, Z = 2. The donor in 12 has been functionalized at the nitrogen atom by protonation or complexation with BF3. Photolysis of 12 and 13 leads to a 1,2-amine shift of one donor from silicon to the metal with loss of CO. The product [formula omitted] (20) has been characterized by a single crystal X-ray structure determination and has a bond distance CrSi 2.3610(4) Å and N1Si 1.981(1) Å. Crystal data: monocliniC., P21/C., a = 10.344(5) Å, b = 11.761(3) Å, c = 18.96(1) Å, Z = 4. Furthermore, the silanediyl complex 12 has been immobilized on silica gel. IR and UV spectroscopy and 13C CPMAS NMR provide evidence for the fixation of (silicaO)[2-(HNMe2CH2)C6H4][2-(Me2NCH2)C6H4]SiCr(CO)5 (22) to the surface via the silicon atom. Reaction of 13 with H2O leads to (HO)[2-(HNMe2CH2)C6H4][2-(Me2NCH2)C6H4]SiCr(CO)6 (23) which has a structure similar to 22 with a CrSi bond length of 2.469(2) µ. The dimethylamino or dimethylammonium substituent is pointing away from the silicon atom forming hydrogen bridges between N1⋯HO⋯HN2; crystal data: monocliniC., P21/n, a = 13.198(2) Å, b = 17.017(2) Å, c = 17.066(1) Å, Z = 4. © 1993, American Chemical Society. All rights reserved.
author list (cited authors)
Handwerker, H., Leis, C., Probst, R., Bissinger, P., Grohmann, A., Kiprof, P., ... Zybill, C.