REVERSIBLE INTRAMOLECULAR BASE STABILIZATION IN SILYLENE (SILANEDIYL)COMPLEXES - SURPRISING REACTIVITY FOR SILYLENE COORDINATION-COMPOUNDSWITH A DYNAMIC N...SI...N BOND

The silane [2-(Me2NCH2)C6H4]2SiCl2 (7) shows a new dynamic N...Si...N ''flip-flop'' coordination mode below T(c) = 233 K (DELTAG(double dagg er) = 46.5 (+/- 0.5) kJ mol-1) with both amine donors displacing each other. 7 is pentacoordinated in the solid state; crystal data: orthorh ombic, P(bca), a = 13.802(1) angstrom, b = 17.908(1) angstrom, c = 15. 544(2)angstrom, Z = 8. Reaction of the silanes C6H5[2-(Me2NCH2)C6H4]Si Cl2 (6), 7, and [2-(Me2NCH2)-5-(t-C4H9)C6H3]2SiCl2 (8) with chromiumpe ntacarbonyl-metallate yields the silanediyl complexes [2-(Me2NCH2)C6H4 ]C6H5Si=Cr(CO)5 (11), [2-(Me2NCH2)C6H4]2Si=Cr(CO)5 (12), and [2-(Me2NC H2)-5-(t-C4H9)C6H3]2Si=Cr(CO)5 (13); [2-(Me2NCH2)C6H4]HSi=Cr(CO)5 (14) was obtained by photolytic methods. Silanediyl complexes with one che lating donor show a rigid coordination of the donor to silicon which c an be lifted at higher temperatures (95-degrees-C for 11, DELTAG(doubl e dagger) = 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) angstrom and a N-->Si bond length of 1.991(2) A. Crystal data: triclinic, P1BAR , a = 9.401(1) angstrom, b = 10.207(1) angstrom, c = 11.586(1) angstro m, Z = 2. Silanediyl complexes with two intramolecular donor functions feature a dynamic ''flip-flop'' coordination of the amine groups to s ilicon. Both (dimethylamino)phenyl groups in 12 and 13 can be detached from silicon under liberation of a three-coordinate silicon atom at T (c) = 58-degrees-C (VT-H-1-NMR), DELTAG(double dagger) = 67.1 (+/-0.5) kJ mol-1 for 12 and T(c) = 61-degrees-C, DELTAG(double dagger) = 70.1 (+/-0.5) kJ mol-1 for 13. A single crystal X-ray structure determinat ion of 12 gives 2.408(1) angstrom for the Si-Cr bond length and 2.046( 2) angstrom for the Nl-Si dative bond (the second contact N2-Si has a nonbonding distance of 3.309 angstrom; the sum of bond angles at silic on amounts to 351.3-degrees). Crystal data: triclinic, P1BAR, a = 9.53 1(1) angstrom, b = 10.339(1) angstrom, c = 11.676(1) angstrom, z = 2. The donor in 12 has been functionalized at the nitrogen atom by proton ation 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. T he product [2-(Me2NCH2)C6H3] (2-(Me2NCH2)C6H3]Si--Cr(CO)4 (20) has bee n characterized by a single crystal X-ray structure determination and has a bond distance Cr-Si 2.3610(4) angstrom and Nl-Si 1.981(1) angstr om. Crystal data: monoclinic, P2(1)/c, a = 10.344(5) angstrom, b = 11. 761(3) angstrom, c = 18.96(1) angstrom, Z = 4. Furthermore, the silane diyl complex 12 has been immobilized on silica gel. IR and UV spectros copy and C-13 CPMAS NMR provide evidence for the fixation of a-O-)[2-( HNMe2CH2)C6H4][2-(Me2NCH2)C6H4]Si=Cr(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)5 (23) which has a structure similar to 22 wit h a Cr-Si bond length of 2.469(2) angstrom. The dimethylamino or dimet hylammonium substituent is pointing away from the silicon atom forming hydrogen bridges between N1...HO...HN2; crystal data: monoclinic, P2( 1)/n, a = 13.198(2) angstrom, b = 17.017(2) angstrom, c = 17.066(1) an gstrom, Z = 4.