No abstract

The silane [ 2-(MezNCHz)C&] ZSiClz (7) shows a new dynamic N**&-N "flip-flop" coordination mode below T, = 233 K (AG* = 46.5 (f0.5) kJ mol-l) with both amine donors displacing each other. 7 is pentacoordinated in the solid state; crystal data: orthorhombic, Paca, a = 13.802(1) A, b = 17.908(1) A, c = 15.544(2) A, Z = 8. Reaction of the silanes C~H~[~-(M~ZNCHZ)C~H~]S~C~P (61, 7, and [~-( M~Z N C H Z ) -~-(~-C~H~) C~H~~Z S~C~Z (8) with chromiumpentacarbonylmetallate yields the silanediyl complexes [~-(M~zNCHZ)C~H~IC~H~S~=C~(CO)B (111, [2-(Mez-N C H Z ) C~H~] zSi=Cr(CO)5 (12), and 12-(M~zNCHZ)-~-(~-C~H~)C~H~I zSi=Cr(CO)s (13); 12-(Mez-N C H Z ) C~H~] H S~= C~( C O )~ (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, AG* = 80.4 (*0.5) kJ mol-'). A single crystal X-ray structure determination of 11 reveals a CrSi bond distance of 2.409(1) A and a N-Si bond length of 1.991(2) A. Crystal data: triclinic, Pi, a = 9.401(1) A, b = 10.207(1) A, c = 11.586(1) A, Z = 2. Silanediyl complexes with two intramolecular donor functions feature a dynamic "flip-flop" coordination of the amine groups to silicon. Both (dimethy1amino)phenyl groups in 12 and 13 can be detached from silicon under liberation of a three-coordinate silicon atom at T, = 58 'C (VTJH-NMR), AG* = 67.1 (f0.5) kJ mol-l for 12 and T, = 61 'C, AG* = 70.1 (k0.5) kJ mol-' for 13. A single crystal X-ray structure determination of 12 gives 2.408(1) A for the Si-Cr bond length and 2.046(2) A for the N1-Si dative bond (the second contact N2-Si has a nonbonding distance of 3.309 A; the sum of bond angles at silicon amounts to 351.3'). Crystal data: triclinic, Pi, a = 9.531(1) A, b = 10.339(1) A, c = 11.676(1) A, 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 [2-(Me~NCHz)c6H31 [2-(MezrjCHz)C6H3] Si=Cr(CO)r (20) has been characterized by a single crystal X-ray structure determination and has a bond distance Cr-Si 2.3610(4) A and N1-Si 1.981(1) A. Crystal data: monoclinic, P21/c, a = 10.344(5) A, b = 11.761(3) A, c = 18.96(1) A, 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 (silica-0-) [~-(HNM~zCHZ)C~H~~[~-(M~ZNCHZ)C~H~~ Si=Cr(CO)s (22) to the surface via the silicon atom. Reaction of 13 with HzO leads to (HO) [~-( H N M~z C H Z ) C~H~I [~-( M~Z N C H Z ) C~H~I S~-Cr(CO)5 (23) which has a structure similar to 22 with a Cr-Si bond length of 2.469(2) A. The dimethylamino or dimethylammonium substituent is pointing away from the silicon atom forming hydrogen bridges between Nl-*HO*-HN2; crystal data: monoclinic, P&/n, a = 13.198(2) A, b = 17.017(2) A, c = 17.066(1) A, Z = 4.

New stereoregular cyclic polysilanols of the general formula [PhSi(O)OH]n (n = 6 and 12) have been selectively obtained in high yields by the reaction of cagelike oligophenylmetallasiloxanes with dilute solutions of hydrochloric acid at low temperatures. An alternative method was used to prepare cis-[PhSi(O)OH](4) from sodium phenylsiloxanolate, cis-[(Na(+))(4)[PhSi(O)O(-)](4)].(1-butanol)(x). All compounds were fully characterized by NMR and IR spectroscopy and molecular weight determinations. The structure of cis-[PhSi(O)OH](6) was confirmed by single-crystal X-ray analysis. Furthermore, a series of stereoregular cyclosiloxanes containing triorganylsiloxy groups at each silicon atom was prepared by the reactions of the cyclic polysilanols with triorganylchlorosilanes Me(3)SiCl, Me(2)ViSiCl, and Me(2)(CH(2)Cl)SiCl.