David J. Brauer

The three-dimensional structure of trans.trans,trans-1,5,9-cyclododecatrienenickel

Abstract The crystal structure of all-trans-1,5,9-cyclododecatrienenickel, C12H18Ni, has been determined from three-dimensional X-ray data collected at room temperature by counter methods. The compound crystallizes in the space group C62h-C2/c with four molecules in a unit cell with the dimensions: a = 14.409(4) A, b = 8.473(1) A, c = 9.001(2)A, β = 108.66(3)°. The calculated density is 1.41 g/cm3. Full-matrix least-squares refinement yielded a conventional R value of 0.039 based on 581 reflections above background. If one assigns one coordination position to each olefinic double bond, the coordination about the Ni atom is trigonal. The molecule possesses rigorous C2 crystallographic symmetry; in addition, the molecular dimensions do not deviate significantly from D3 symmetry. The NiC(sp2) bond lengths average 2.024(2)A, and the C(sp2)C(sp2) bond lengths average 1.372(5)A. The fragments are not planar, the C(1)[C(2)] H groups being bent 8(2)° away from the Ni atom. The twelve membered ring shows some signs of angular strain; in particular, the C(1′)C(1)C(2) angles average 127.5(3)°. The C(1′)C(1) vector forms a 32(1)° angle with the Ni coordination plane.

The stereochemistry of transition metal cyclooctatetraenyl complexes: di-h3,h3′ cyclooctatetraenedinickel, a sandwich compound with two enveloped nickel atoms

Abstract The crystal structure of dicyclooctatetraenedinickel, [(COT)Ni] 2 , has been determined from three-dimensional, single crystal X-ray data collected by counter methods. Crystals of [(COT)Ni] 2 , belong to the monoclinic system with a = 8.2906(3), b = 11.4185(5), c = 7.2340(3) A, β = 115.978(2)°, d (calc) = 1.757 gcm −3 , Z = 2. The space group is C 2 2h - P 2 1 / a . The structure was refined anisotropically (hydrogen atoms and a nickel atom fragment isotropically) by fullmatrix least-squares techniques. Final values of R and R w were 0.046 and 0.079, respectively, for the 1055 unique, absorption and extinction corrected reflections with I > 2σ( I ). Crystals of [(COT)Ni] 2 consists of discrete molecules with crystallographic C i ( 1 ) symmetry. The compound possesses a sandwich structure with both metal atoms between the COT rings. Each nickel atom forms π-allyl type bonds to three carbon atoms of each COT ring. The nickel atoms are disordered over three sites. The effect of this disorder on the interpretation of the derived structural parameters is discussed.

Structural investigations of mixed metal compounds; the stereochemistry of two dilithium-tris(olefin)nickel(0) complexes

Abstract The structures of bis(lithium-N,N,N′,N′-tetramethylethylenediamine) (all-trans-1,5,9-cyclododecatrienenickel) (I) and tris(N,N,N′,N′,-tetramethyl-2-butene-1,4-diamine)dilithiumnickel (II) have been determined from single cyrstal X-ray data measured by counter methods. Crystals of I belong to the orthorhombic space group Pbca with a 13.776(2), b 14.090(2), c 58.374(6) », Z = 16 and dc 1.10 g cm-3. Compound II crystallizes in the monoclinic space group C2/c with a 22.960(2), b 8.9860(3), c 15.1984(6) », β 109.015(5)°, Z = 4 and dc 1.12 g cm-3. Refinement of I (II) coverged with R = 0.097 (0.037) for the 4281 (2424) reflections with I > 2σ(I). Two unique and essentially identical molecules not having crystallographic symmetry were found for I while molecules of II possess crystallographic C2 symmetry, the two fold axis passing through the Ni atom and bisecting one olefinic CC bond. The trigonal bipyramidal geometry of the Ni atoms, the centers of three olefinic double bonds in the trigonal plane and Li atoms in apical positions, is distorted in I but nearly exact in II. The NiC (olefinic) bond lengths average 1.99(3) and 2.000(3) » in I and II respectively. The shorter bond distances to the Ni a toms formed by the three-coordinate Li atoms in I, average 2.400(6) », compared to those formed by the four-coordinate Li atoms in II, 2.561(3) », may be due to Ni → Li dπ → pπ backbonding in I. The LiNiLi angles are (average) 164(2)° in I and 178.9(1)° in II. The strength of the Ni olefin interactions in these compounds is most clearly shown by the long mean CC distances (1.452(9) ») and 40(2)° bending back of the olefinic substituents from the Ni atom in II.

Stereochemistry and bonding in nickel olefin complexes. The structure of t etramethylethylenenickel 1,2-bis (dicyclohexylphosphino)ethane

Abstract The structure of tetramethylethylenenickel 1,2-bis(dicyclohexylphosphino) ethane, (CH 3 ) 2 C 2 (CH 3 ) 2 Ni[(C 6 H 11 ) 2 PCH 2 CH 2 P(C 6 H 11 ) 2 ], has been determined from 4995 observed, absorption-corrected reflections collected by counter methods. The compound crystallizes in the monoclinic space group C 5 2 h  P 2 1 / n with cell dimensions a 17.1306(7), b 16.9016(7), c 11.4899(8)» and > 100.082(5)°. The calculated density is 1.147 g/cm 3 for Z =4. Least-square refinement yielded a final conventional R value of 0.036. If one coordination site is assigned to the olefin, the nickel atom is three-coordinate. Although no crystallographic symmetry is required, the molecule posses idealized C 2 symmetry. The average NiC and NiP bond lenghts are 1.981(2) and 2.156(6)», respectively. The central bond of the olefin has beenlengthened upon coordination to 1.421(3) ». The tetramethylethylene moiety is distorted from planarity with the C(CH 3 ) 2 planes bent away from the nickel atom 27.2(6)°. The nickel atom and four atoms bonded to it are not coplanar, the central bond of the tetramethylethylene species forming a 16.5° angle with the Ni,P(1),P(2) plane. A segmented rigid-body analysis of the thermal motion of the molecule indicates that the barrier to rotation of the olefin is 18 kcal/mole.

Chemical synthesis with metal atoms. The preparation and structure of cyclo-octadiene trifluorophosphine complexes of chromium. The crystal structure of (η5-cyclo-octa-1,3-dienyl)hydridotris(trifluorophosphine) chromium

The reaction of cyclo-octa-1,5-diene (1,5-cod), PF3, and chromium atoms produces [Cr(1,5-cod)(PF3)4](1) and [Cr(C8H11)(PF3)3H](2). The use of 1,3- rather than 1,5-cod produces only (2) under the same conditions. Complex (1) is readily converted into (2) by heating (90 °C, in toluene). The preparation of [Cr(1,5-cod)(CO)4](3) from 1,3- or 1,5-cod is also described. The structure of (2) was determined by X-ray crystallography. The compound crystallizes in the orthorhombic space group Pbca with a= 13.452(3), b= 14.419(4), c= 15.268(3)A, and Z= 8. The final R value was 0.065 9 for 1 699 observed reflections. The structure is retained in solution below –80 °C, but is shown by 13C and 1H n.m.r. spectroscopy to become fluxional upon warming. There are two distinct exchange processes; one results in pairwise coalescence of the 13C and 1H resonances; the other finally leads to a set of only two 1H signals with an intensity ratio of 8 : 4, thus indicating equivalence of the eight ring positions.

Crystal and molecular structures of methyl 2α,3α;4α,5α-diepoxy-cis-(1αH,2αH)-bicyclo[4.1.0]heptane-7α-carboxylate and methyl 2,5-dihydroxybicyclo[4.1.0]heptane-7-carboxylate

X-Ray crystal analysis has been used to identify one isomer (III) of the two products C9H10O4{methyl 2,5-epidioxybicyclo[4.1.0]hept-3-ene-7-carboxylate (II) and methyl 2α,3α:4α,5α-diepoxy-cis(1αH,2αH)-bicyclo[4.1.0]heptane-7α-carboxylate (III)} produced by the photosensitized oxygenation of methyl cyclohepta-2,4,6-trienecarboxylate (I). Crystals of (III) are orthorhombic, space group P212121, with a= 19.548(1), b= 6.0101 (5), and c= 7.3944(4)A and Z= 4. By hydrogenation of (II), methyl 2,5-dihydroxybicyclo[4.1.0]heptane-7carboxylate (V) is formed which also crystallizes in space group P212121 with Z= 4, and cell dimensions a= 18.192(1), b= 7.7284(5), and c= 6.7139(3)A. The structures were solved by the tangent formula phasing method and refined by full-matrix least-squares to R 0.055 (962 observed reflections) and 0.044 (1 028 observed reflections) respectively.Compound (III) contains a six-membered ring consisting two planar fragments oriented at 3.4° to each other. The epoxide groups are tilted 108.0 and 105.6° from the plane through the four carbon atoms they include. In compound (V), two C–O bonds are broken, allowing the six-membered ring to assume the half-chair conformation. The cyclopropyl ring is inclined at 107.1 (III) and 109.0°(V) to the best plane through the two included and two adjacent carbon atoms. In both compounds, the carbonyl oxygen is located directly behind the cyclopropyl ring.

Structure of the 1-Ethyl-3-methyl-1-alumina-indane Dimer, [C2H5(O-C6H4CH(CH3)CH2)Al]2

Abstract The molecular structure of the 1-ethyl-3-methyl-1-alumina-indane dimer has been determined from single crystal X-ray data collected by counter methods. The compound crystallizes in the monoclinic space group C2h5-P21/c with a = 14.621(2), b = 8.3967(3), c = 8.7516(5) Å, β = 107.998(4)°, Z = 2 and dc = 1.15 gem-3 . Refinement converged with an R value of 0.037 for the 1836 reflections with I > 3 σ (I). The crystals are composed of discrete dimeric molecules possessing crystallographic 1̄ (Ci) symmetry. Each Al atom bonds to an ethyl C atom, 1.964(2) Å, as well as to alkyl 1.974(2) and aryl 2.168(1) Å C atoms of one monomer and, surprisingly, to the aryl C atom 2.104(1) Å, of the inversion related monomer. The Al-Al′ distance in the dimers is 2.6639(7) Å.