F. Van Meurs

The molecular structure of π-(tricarbonylchromium)-toluene

The molecular structure of π-(tricarbonylchromium)toluene, CrC 10 H 8 O 3 , has been determined from three-dimensional X-ray data. The orthorhombic unit-cell, P 2 1 2 1 2 1 with a = 11.109(4), b = 7.231(3) and c = 12.206(4)A, contains four molecules. Refinement converged to a final weighted R -index of 4.1% for 1163 observed reflexions. The orientation of the tricarbonylchromium group is nearly eclipsed with respect to the carbon atoms C(1), C(3) and C(5).

The molecular structure of 4-tert-butyl-π-(tricarbonylchromium)benzoic acid

Abstract The molecular structure of 4-tert-butyl-π-(tricarbonylchromium)benzoic acid, CrC 14 O 5 H 14 , has been determined from three-dimensional X-ray data. The crystals are monoclinic, space group P 2 1 / c . The unit-cell, of dimensions a = 12.230(5), b = 7.509(3), c = 18.099(6) A and β = 117.91(4)°, contains four molecules. The structure has been solved using the heavy-atom method. Refinement by the least-squares method converged to a final R index of 4.8% for 1717 independent non-zero reflexions. 4-tert-Butyl-π-(tricarbonylchromium)benzoic acid adopts a conformation which departs from perfect staggering by about seven degrees.

The molecular structure of (1′-t-butl-2′,2′-dimethylpropyl)-π-(tricarbonylchromium)benzene

Abstract The molecular structure of (1′-t-butyl-2′,2′-dimetnylpropyl)-π-(tricarbonylchromium)benzene, CrC 18 H 24 O 3 , has been determined from three-dimensional X-ray data. The crystals are monoclinic, space group P2 1/ c . The unit-cell, of dimensions a 8.321(3), b 14.741(5), c 14.369(5) A and β 98.85(3)°, contains four molecules. The structure has been solved using the heavy-atom method. Least-squares refinement converged to a final R index of 3.2% for 2738 independent non-zero reflexions. The molecular strain is relieved by a deviation of the CH-t-Bu 2 group and the Cr(CO) 3 group from their usual position. The α-carbon atom is forced out of the arene ring plane by 0.41 A. The dihedral angle between the aromatic plane and the plane through the oxygen atoms is 8.0°. The octahedral symmetry around the chromium atom is almost maintained. The average twist of the Cr(CO) 3 group from the electronically favoured conformation (i.c. eclipsed with respect to the alkyl group) is 44.4°.

Substituent effects in π-(Tricarbonylchromium) arenes

Abstract The thermodynamic dissociation constants of a series of 38 substituted π-(tricarbonylchromium)benzoic acids in 50% aqueous ethanol at 25°C have been determined. The results require revision of some literature values. The p K a * -values of the π-(tricarbonylchromium)benzoic acids were correlated with the electronic substituent parameters in terms of the Yukawa-Tsuno equation. The reaction constant (ρ) decreases from 1.4 for the benzoic acids to 0.8 for the π-(tricarbonylchromium)benzoic acids, reflecting the decreased ability of the complexed aromatic system to transmit electronic substituent effects. For the alkylsubstituted π-(tricarbonylchromium)benzoic acids, conformational effects of the Cr(CO) 3 group can account for some of the anomalies observed. The substituent parameters, σ meta and σ para , of the π-(Cr(CO) 3 )phenyl group as a substituent were derived from the dissociation constants of the complexed phenylbenzoic acids.

Substituent effects in π-(tricarbonylchromium)arenes : III. an ir study of the co-stretching vibrations in substituted methyl π-(Tricarbonylchromium)benzoates

Abstract The preparation and the IR spectra (2050–1650 cm -1 ) of some forty substituted methyl π-(tricarbonylchromium)benzoates and the corresponding free aromatic ligands are reported. The ester carbonyl wavenumbers of the tricarbonylchromium complexes correlate only poorly with electronic substituent parameters, whereas a fair correlation is obtained for the free aromatic ligands. This is explained in terms of conformational preference. The metal carbonyl stretching frequencies were assigned on the basis of local C 3 v symmetry (A 1 + E ). The force constants, obtained from the metal CO-modes, correlate satisfactorily with substituent constants in terms of the Yukawa-Tsuno equation. Mono- and bi-nuclear tricarbonylchromium complexes of some biphenyl systems have been prepared. The data for these complexes permit computation of the σ meta and σ para constants for the π-(Cr(CO) 3 )phenyl group as a substituent.

An unusual vinylidene complex from hydride addition to the aromatic ring of the tolyl—carbyne ligand in a cationic osmium carbyne complex

Abstract The cationic osmium carbyne complex [Os(CR)(CO)2(PPh3)2]+ (R = p-tolyl) reacts with Li(Et3BH) with hydride addition to the para-position of the aromatic ring of the carbyne ligand giving an unusual vinylidene complex. This formulation of the product, which was suggested by the 1H NMR data, was confirmed by an X-ray crystal structure determination.

Substituent effects in π-(tricarbonylchromium)arenes : IV. 1H NMR Spectroscopy of substituted methyl π-(tricarbonylchromium)benzoates

Abstract The 1 H NMR spectra of a series of thirty substituted methyl π-(tricarbonyl-chromium)benzoates (and the corresponding free ligands) have been recorded and analysed. A comparison of the chemical shifts of the aromatic protons in the complex and ligand often allows conclusions regarding the preferred orientation of the tricarbonylchromium group in the complexes studied.

The molecular structure of 2,2,4,4-tetramethyl-3-(3,4,5-trimethoxyphenyl)pentan-3-ol

Abstract The molecular structure of 2,2,4,4-tetramethyl-3-(3,4,5-trimethoxyphenyl)pentan-3-ol, C18H30O4, has been determined from 3-dimensional X-ray data. The monoclinic unit-cell, P21/c with a = 14.420(6), b = 8.629(4) and c = 15.003(6) A and β = 109.45(3)°, contains four molecules. Refinement converged to a final conventional R-index 4.6% for 2662 observed reflexions. The orientation of the C(OH)-t-Bu2 group and the OMe groups with respect to the benzene nucleus is discussed and compared with the orientations found in related compounds.

Dynamic behaviour in (1′-t-butyl-2′,2′-dimethylpropyl)-π- (tricarbonylchromium)benzene

The temperature dependence of the 1H NMR spectrum of the title compound was studied over the temperature range 0–115° C. Two conformers were detected. The conformational isomerism is caused by a restricted rotation about the bond between the alkyl group and the complexed aromatic ring. The gDG≠ value for the interconversion amounts to 16.9 kcal mol−1, which is substantially smaller than the corresponding ΔG≠ value for the free ligand. This decrease is ascribed to additional steric strain between the alkyl and the tricarbonylchromium groups in the conformers of the complex.

Hydrogenation of ferrocene

Abstract Ferrocene and derivatives can be hydrogenated in acidic medium at ambien temperature and atmospheric hydrogen pressure using supported palladium as the catalyst.