Raymond E. Davis

Crystal and molecular structure of (π-cyclopentadienyl)-(π-cyclobutadiene)cobalt

Abstract The crystal and molecularn structure of (π-cyclopentadienyl)(π-cyclobutadiene)- cobalt (C 5 H 5 )(C 4 H 4 ) has been determined by single crystal X-ray diffraction techniques using three-dimensional data gathered at ca.-35 C by counter methods. Crystals are yellow-orange of irregular shape and og orthorhombic space group Pnma with lattice parameters (at ca.-35 C) α = 10.462(2), b = 9..044(2), and c = 7.672(2) A for a unit cell with four molecules of (C 5 H 5 )(C 4 H 4 )Co. The molecule consist of a Co atom sandwich between the π-bondung cyclopentadienyl and cyclobutadiene ligands. A crystallographic mirror plane passes through the molecule and contains two carbons of the C 4 H 4 moiety resulting in an ordered structure with ? symmetry. Full-matrix least-squares refinement has converged with a R index (on F ) of 0.025 for all 681 symmetry-independent reflections examined within the Mo- K α shell defined by 4 ????.

Crystal structure at −35°C of carboxycobaltocenium hexafluorophosphate

The crystal structure of carboxycobaltocenium hexafluorophosphate has been determined by single crystal X-ray diffraction techniques using three-dimensional data gathered at −35°C by counter methods. Bright yellow prismatic crystals are triclinic, space group P, a 7.7343(8), b 12.294(2), c 7.0316(7) A, α 100.20(1), β 92.92(1), γ 98-91(1)°; dm 1.93 g cm−3, dc 1.938 g cm−3, with two formula weights of [(C5H5)(C5H4COOH)Co]PF6 per unit cell. At convergence of full-matrix least-squares refinement, the conventional R index (on [|F|) is 0.051 for the 3346 symmetry-independent reflections with Io > 2.0σ(Io). The crystal structure consists of hydrogen bonded dimers of [(C5H5)(C5H4COOH)Co]+ ions and discrete PF6− anions. The cobalt ions are sandwiched between pairs of π-bonding carbocycles so as to attain a staggered ring configuration such as that observed for cobaltocene. Both rings are planar, and nearly parallel to one another (dihedral angle, 1.6°). Although the ring CC distances in the [(C5H5)(C5H4COOH)Co]+ species agree with those determined in cobaltocene, the mean CoC(Cp) distance here (2.029(9) A) appears to be shorter than in cobaltocene (2.096(8) A). This difference in metal—Cp distances is rationalized in terms of the concept of imbalance in electronic configuration of the sandwich complexes.

Reactions of copper acetylides. Structure of (π-C5H5)Ru(PPh3)2 (CCPh)CuCl, and new syntheses of transition metal cluster compounds

Abstract In contrast to a related iron—copper compound, the complex (π-C5H5)Ru(PPh3)2(C2Ph)CuCl is shown to be monomeric, and contains linear dicoordinate copper(I); the reactions of this and similar complexes with metal carbonyls are sources of new mixed-metal clusters, such as (π-C5H5)Fe2 Ru(C2Ph)(CO)6 (PPh3).

Synthesis of cyclic hydrocarbons via intramolecular coupling of bis-pentadienyl iron tricarbonyl cations

Abstract A general synthesis for the preparation of medium sized cycloalkanes having 1,2-butadienyl substituents is described. The reaction sequence involved acylation of butadiene-iron tricarbonyl with a diacid chloride, reduction of the resultant diketone to a diol derivative and conversion with HBF 4 to an acyclic bis-pentadienyl Fe(C0) 3 dicationic complex. Upon treatment with zinc the dication undergoes intramolecular ring closure to afford the bis-Fe(C0) 3 complex of the 1,2-dibutadienyl cycloalkane. Five-, six- and ten-membered cyclolalkene derivatives have been prepared in this manner.

Organonitrogen derivatives of metal carbonyls: XIII. Reactions of dialkylaminotrimethylsilylacetylenes with metal carbonyls☆

Abstract Reactions of the dialkylaminotrimethylsilylacetylenes, (CH 3 ) 3 SiCCNR 2 , with Fe(CO) 5 in boiling heptane R = methyl or ethyl or R 2 N = piperidino) or decalin (R = isopropyl) give the yellow air-stable solid cyclobutadiene derivatives [(CH 3 ) 3 Si] 2 (R 2 N) 2 C 4 Fe(CO) 3 as the major organometallic product; in some cases (R = ethyl or R 2 N = piperidino) the dark red tricarbonylferrole-iron tricarbonyl derivatives [(CH 3 ) 3 Si] 2 (R 2 N) 2 C 4 Fe 2 (CO) 6 are also obtained in low yield. The cyclobutadiene complex [(CH 3 ) 3 Si] 2 (C 5 H 10 N) 2 C 4 Fe(CO) 3 crystallizes in the triclinic space group P 1 − with cell constants a 10.602(2), b 14.877(2), c 9.955(2) A, α 96.61(1), β 111.98(1), γ 109.66(1)°, and Z = 2. Solution of the structure using the heavy-atom positions derived from a Patterson map, followed by full-matrix leastsquares refinement of the 4924 observed reflections to a final R value of 0.032, indicate the position of the substituents to be 1,3-[(CH 3 ) 3 Si] 2 -2,4-(C 5 H 10 N) 2 -C 4 Fe(CO) 3 in accord with head-to-tail dimerization of the acetylene. Reactions of (CH 3 ) 3 SiCCNR 2 with Fe 2 (CO) 9 in diethyl ether at room temperature give orange-red (CH 3 ) 3 SiC 2 NR 2 Fe 2 (CO) 6 suggested by their NMR spectra to have the nitrogen atom as well as the two acetylenic carbon atoms involved in the bonding to the diiron unit. Reactions of (CH 3 ) 3 SiCCNR 2 with Co 2 (CO) 8 in diethyl ether at ambient temperature give deep green (CH 3 ) 3 SiC 2 NR 2 Co 2 (CO) 6 apparently analogous to other (alkyne)Co 2 (CO) 6 derivatives except for their unusual colors. Reactions of (CH 3 ) 3 SiCCNR 2 with C 5 H 5 Co(CO) 2 in boiling n-octane give the black trinuclear (CH 3 ) 3 SiC 2 NR 2 Co 3 (C 5 H 5 ) 3 derivatives. Ultraviolet irradiation of (CH 3 ) 3 SiCCNR 2 with Mn 2 (CO) 10 in tetrahydrofuran gives low yields of the red-orange (CH 3 ) 3 SiC 2 NR 2 Mn 2 (CO) 8 .

Crystal structure at −35°C of (2,6-dimethoxyphenyl)(triphenylphosphine)gold(I)

Abstract The crystal structure of (2,6-dimethoxyphenyl)(triphenylphosphine)gold(I) has been determined by single crystal X-ray diffraction techniques using three-dimensional data gathered at −35°C by counter methods. Colorless crystals form as thin plates in the monoclinic space group P21/n, with a 13.040(2), b 19.268(3), c 9.0153(8) », β 96.98(1)°. A measured density (19°C) of 1.73 g cm−3 agrees with the calculated value (−35°C) of 1.769(1) g cm−3, assuming four molecules of (C6H3(OCH3)2)Au(P(C6H5)3) per unit cell. Full-matrix least-squares refinement of the structure has converged with a conventional R index (on ¦F¦) of 0.030 using the 5052 symmetry-independent reflections with 4 2σ(Io). The molecule consists of AuI ion bonded to the P atom of a triphenylphosphine ligand and to the C(1) atom of a 2,6-dimethoxyphenyl group. The PAuC(1) angle of 172.7(1)° is significantly different from linearity, probably as a result of a weak bonding interaction between Au and one of the two methoxy oxygen atoms (Au. … O = 2.961(4) and 3.231(4) »).

Structural studies of enantiomers, racemates, and quasiracemates. 2-(2,4-dichlorophenyl)propanoic acid and 2-(2-chloro-4-nitrophenyl)propanoic acid

Abstract Cocrystallization of a 1:1 solution of (R)-2-(2,4-dichloro)phenoxypropanoic acid and (S)-2-(2-chloro-4-nitro)phenoxypropanoic acid yields quasiracemic crystals. The principal quasiracemate components (sterically similar, differing in chirality and Cl/NO2 substitutions) assemble to form pseudosymmetric heterodimers linked by carboxylic acid O-H⋅⋅⋅O R22(8) interactions. A comparison of the structure of the quasiracemate to the individual enantiomers and the “true” racemates provides a means to probe the influence of molecular topologies on the observed molecular recognition behavior. These results show that the orientation of discrete assemblies for the quasiracemate can be controlled predictably by topological influences. Preferred molecular orientations and key structural features of these systems have been examined in context of the imposed Cl and NO2 structural differences.

Spontaneously resolved chiral arylsulfonamides

Abstract Our recent studies have shown that cocrystallization of 1:1 solutions of (R)-X and (S)-X′ (where X and X′ represent two sterically similar molecules) often form quasiracemic crystals, in which approximately centrosymmetric molecular pairs cocrystallize in an arrangement that resembles a “true” racemic structure. As part of an ongoing study of the influence of molecular shape on crystal packing, the present work centers on the design, synthesis and X-ray structure determination of four homologous N-(α-methylbenzyl)-4-substituted benzenesulfonamides. Crystallization of a solution of these (±)-arylsulfonamides unexpectedly yields enantiomerically pure crystals via a Pasteurian-type resolution process. This mode of crystallization presumably also deters the cocrystallization of different, but structurally similar, arylsulfonamides to form quasiracemates. The X-ray crystal structures of the four sulfonamides reveal the dominance of N–H⋅⋅⋅O–S hydrogen bonds that form infinite helical C(4) molecular chains. For three of the structures this pattern is extended by short inter- and intramolecular π⋅⋅⋅π interactions to form two-dimensional molecular architectures.

A novel ring substitution reaction in a cyclopentadienylruthenium phosphine complex

Abstract The reaction between hexafluoroacetone and Ru(PPh3)2(π-C5H5)[σ-C2(CO2Me)2H] affords a 1 1 adduct, containing a coordinated ester group and an intramolecular hydrogen bond; formal insertion of (CF3)2CO into a CH bond of the cyclopentadienyl group has also occurred.

Crystal and molecular structure at −35°C of (π-cyclobutadiene)dicobalt hexacarbonyl

The structure of cyclobutadienedicobalt hexacarbonyl, (C 4 H 4 )Co 2 (CO) 6 , has been determined by single crystal X-ray diffraction techniques with data gathered at −35°C by counter methods. Crystals form as red prisms in orthorhombic space group Pnma , with lattice parameters (at −35°C) a = 12.916(3), b = 10.353(2) and c = 9.118(3) A for a unit cell with four molecules of (C 4 H 4 )Co 2 (CO) 6 . The molecules have rigorous C s symmetry, with a π-cyclobutadiene ring bound to the Co atom of a Co(CO) 2 moiety which, in turn, is linked to a Co(CO) 4 fragment through the metal atoms. Apparently to decrease repulsion between the cyclobutadiene ring and the bulky Co(CO) 4 group, the four-membered ring is tilted, and as a consequence the CoC 4 H 4 interaction is unsymmetrical (CoC(ring) = 1.980(3) to 2.048(4) A). Full-matrix least-squares refinement of the structure has converged with a R index (on | F |) of 0.027 for 1539 symmetry-independent reflections with I o > 2.0σ( I o ) within the Mo- K α shell defined by 4° < 2θ < 60°.