1,6-Diazabicyclo[4.4.4]tetradecane and its lnside-protonated lon: Changes in Space Groups

The crystal structures of 1,6-diazabicyclo[4.4.4]tetradecane (1) and of its inside-protonated ion (2), which were originally described in space group C2/c, should be described instead in trigonal space groups, (1) in R3c and (2) in P31c; both moieties have crystallographically imposed point symmetry D_3 rather than C_2

The Snub Cube in the Glanville Courtyard of the Beckman Institute at the California Institute of Technology

In the central (Glanville) courtyard of the recently constructed Beckman Institute building at the California Institute of Technology is a fountain, placed there by the architect, Mr. Tim Vreeland, to create some “white noise” and thus separate acoustically four areas of the courtyard designed for conversational groups. The architect asked for help from the future occupants of the building in designing the fountain itself; several suggestions were made and rejected by the Caltech administration as not having any relationship to the purpose of the building. Arnold O. Beckman, the donor of the building, had specified that he wanted this Institute to develop new methods and instruments that would advance research in the fields of biology and chemistry, including their interface. After our latest suggestion had been rejected, Harry B. Gray, then the Director-designate of the Beckman Institute (now Director), recalled a paper [1] describing the tertiary structure of the iron-containing protein ferritin; the molecule of ferritin was found to have 432 (read as four, three, two) symmetry; i.e., it has fourfold axes, threefold axes, and twofold axes relating the 24 subunits of the protein

Structure of a Permethylcyclopentadienyl-μ-tetramethylcyclopentadienylmethylene Scandium Dimer

Bis(η^5-pentamethylcyclopentadienyl)-bis[μ-2,3,4,5-tetramethyl-1-methylene-ScC^1:Sc'(η^5)-cyclopentadienyl]-discandium(III), [Sc_2(C_(10)H_(15))_2-(C_(10)H_(14)_2], M_r = 628.90, triclinic, Pl, ɑ = 8.641 (5), b= 9.478 (2), c = 12.338 (5) Å, ɑ = 75.58 (3), β = 80.39 (4), y = 63.75 (3)º, V = 875.8 (7) Å^3, Z = 1, D_x = 1.19 g cm^(-3), λ(Mo Kɑ}=0.71073 Å, μ = 4.11 cm^(-1), F(000) = 340, room temperature, R (on F) = 0.046 for 2241 reflections with F_o^2 > 3σ(F_o^2). Two bis(pentamethylcyclopentadienyl)scandium molecules are joined across a center of symmetry. One of the Cp^* methyl groups has lost an H atom and that methylene group bonds to the symmetry-related Sc atom: Sc-C6' = 2.282 (5) Å. Other aspects of the bis-Cp^*Sc geometry are normal

Structures of Two Diastereomeric Aldol Products from a New Silicon-Directed Condensation

Hexahydro-3,3,6-trimethyl-5-phenyl- 1 H,7H-pyrrolo[2,1-e][1,3,6,2]dioxazasilonin-7-one, C17H25NO3Si, Mr=319.48. (2S,3R)-anti-Diastereomer (I), orthorhombic, P212121, a= 8-716(4), b=11-677(3), c=17.161(6)A, V=1746(1)A3, Z=4, Dx=1.22 g cm-3, wavelength(Mo Kce) = 0.71073 A, u=1.50 cm-1 F(000)=688, room temperature, final R=0.040 for 1683 reflections with Fo2 greater than 0. (2S,3S)-syn- Diastereomer (II), monoclinic, P21, a=6.633(2), b=14.645(3), c=9.630(2) A, Beta=109.96(2)o, V=879.3(4) A3, Z=2, Dx=1.21 g cm-3, wavelength(Mo Ka)=0.71073 A,u = 1-49 cm-1, F(000)=344, room temperature, final R = 0.042 for 2537 reflections with F2o greater than 0. The compounds have a nine-membered hetero-cyclic ring containing the Si atom, the N atom of the pyrrolidine ring, two O atoms bonded to silicon and a carbonyl C atom. Bond distances in the molecules are normal and equivalent bonds are equal within three times their e.s.d.'s. Isomer (I) shows a disorder in the pyrrolidine ring that is absent in isomer (II).Chemistry and Chemical Biolog

The Snub Cube in the Glanville Courtyard of the Beckman Institute at the California Institute of Technology

In the central (Glanville) courtyard of the recently constructed Beckman Institute building at the California Institute of Technology is a fountain, placed there by the architect, Mr. Tim Vreeland, to create some “white noise” and thus separate acoustically four areas of the courtyard designed for conversational groups. The architect asked for help from the future occupants of the building in designing the fountain itself; several suggestions were made and rejected by the Caltech administration as not having any relationship to the purpose of the building. Arnold O. Beckman, the donor of the building, had specified that he wanted this Institute to develop new methods and instruments that would advance research in the fields of biology and chemistry, including their interface. After our latest suggestion had been rejected, Harry B. Gray, then the Director-designate of the Beckman Institute (now Director), recalled a paper [1] describing the tertiary structure of the iron-containing protein ferritin; the molecule of ferritin was found to have 432 (read as four, three, two) symmetry; i.e., it has fourfold axes, threefold axes, and twofold axes relating the 24 subunits of the protein

Cp,Cp*-Dimethyltantalum Triflate

(η^5-Cyclopentadienyl)(dimethyl)(η^5-pentamethylcyclopentadienyl)tantalum trifluoromethylsulfonate, [Ta(C_5H_5)(C_(10)H_(15)CH_3)_2]CF_3S0_3, M_r = 560.41, orthorhombic, Pbca, ɑ = 14.230 (4), b = 19.283 (4), c = 14.628 (4) Å, v = 4014 (2) Å^3, z = 8, D_x = 1.855 g cm^(-3), λ(Mo Kɑ)= 0.71073 Å, μ = 55.3 cm^(-1), F(000) = 2192, room temperature, R(F) = 0.038 for 1882 reflections with F_o^2 > 3σ(F_o^2). The Ta-C(methyl)Å distances are virtually equal at 2.171 (12) Å, with a C-Ta-C angle of 95.8 (5)º. The coordination of the two η^5 ligands is normal; the Cp(centroid}-Ta-Cp^*(centroid) angle is 136.2°. Intermolecular contacts are all approximately at van der Waals distances, with indications of CH···O hydrogen bonding between methyl groups and the triflate anion

Structure of a scandium-(silicon-bridged Cp, Cp^*) complex

({η^5-3-[2-(Di-tert-butylphosphino)ethyl]-cyclopentadienyl} (dimethyl)(η^5-tetramethylcyclopentadienyl)silane)bis(trimethylsilyl)methylscandium, C_(33)H_(62)PScSi_3, M_r = 595.04, monoclinic, P2_1/n, ɑ = 14.449 (3), b = 12.807 (5), c = 20.848 (5) Å, β = 99.52 (2)º, V = 3804.8 (18) Å^3, Z = 4, D_x = 1.04 g cm^(-3), λ(Mo Kɑ)= 0.71073 Å,μ = 3.18 cm^(-1)F(000) = 1352, T = 296 K, final R = 0.108 for 3100 reflections with F_o^2 > 0, 0.054 for 1766 reflections with F_o^2 > 3σ(F_o^2). The Sc-C(l) bond [2.253 (8) Å] is insignificantly shorter than the 2.271 (7) Å found in a similar compound; the geometry about C(l) is nearly trigonal, with angles 118.5 (5), 116.0 (5) and 119.4(6)º

Pentamethylcyclopentadienyl-dicarbollide derivatives of scandium

The reactions of [Cp*ScCl_2]_x (Cp* = (η^5-C_5Me_5)) with Na_2[C_2B_9H_(11) or [Cp*ScMe_2]_x, with C_2B_9H_(13), followed by treatment with THF yield Cp*(C_2B_9H_(11))Sc(THF)_3. Alkylation of Cp*-(C_2 B_9 H_(11)) with LiCH(SiMe_3)_2 yields Cp(C_2B_9H_(11))ScCH(SiMe_3)_2Li(THF)_3, and {[Cp*(C_2B_9H_(11))ScCH(SiMe_3)_2]_2Li}-Li(THF)_3, which is obtained by its recrystallization from pentane/toluene, has been characterized structurally. This alkyl derivative reacts slowly with H_2 to yield [Cp*(C_2B_9H_(11))SCH]_2[LiTHF)_n]_2, a surprisingly reactive scandium hydride dimer. Once again, recrystallization from toluene affords a crystalline form with less coordinated THF, [Cp*(C_2B_9H_(11))ScH]_2[Li(THF)_2•(3/2)(C_6H_5CH_)3, whose structure reveals that the two anionic [Cp*(C_2B_9H_(11))ScH]^- fragments are held together by reciprocal B-H dative bonding from the dicarbollide ligand to the electron deficient scandium. The potential of pentamethylcyclopentadienyl-dicarbollide derivatives of scandium to serve as efficient a olefin polymerization catalysts is discussed