T. G. Hewitt

syn- and anti-(1-Alkyl-π-Allyl)palladium chlorides

Abstract π-Allylpalladium chlorides with bulky substituents on the terminal carbon atoms are often formed with these substituents in the less stable anti configuration. The activation energy of the π-σ-π rearrangement to the syn configuration increases with the bulkiness of the substituent. The difference in energy between the anti and syn configurations decreases with increasing size of the substituents on the terminal and meso carbon atoms. The phenomena can best be explained by assuming that there is steric interaction between the substituents on the terminal carbons of the π-allyl ligand and either other ligands on the metal or the substituent on the mso carbon of the π-allyl ligand.

Crystal and molecular structure of the chloroform solvate of bikaverin

The crystal and molecular structure of bikaverin, 7,10-dihydro-6,11-dihydroxy-3,8-dimethoxy-1-methyl-12H-benzo[b]xanthene-7,10,12-trione, has been determined at ca.–90 °C by single-crystal X-ray diffraction and the positions of all non-hydrogen atoms have been unambiguously determined. The space group is P21/c and cell dimensions are a= 9·26(1), b= 27·36(3), c= 10·26(1)A, and β= 109·15(5)°. All bond distances and angles are within the normal ranges. 1267 Independent reflexions were used in the refinement which was terminated at R= 8·4%.

Molecular structure of the co-ordinated allene ligand

The crystal and molecular structures of two transition-metal ion complexes with tetramethylallene have been determined by single-crystal X-ray diffractometry. They are acetylacetonatobis(tetramethylallene)rhodium(I)(C5H7O2)RhI(C7H12)2, and the dimer of dichloro(tetramethylallene)platinum(II)–carbon tetrachloride, [Cl2Pt(C7H12)]2,2CCl4. In both cases the tetramethylallene ligand is perpendicular to the co-ordinating plane and functions as a π-bonded mono-olefin. The co-ordinated allene ligand is not linear and in the rhodium complex the central C–C bonds differ in length. In the platinum complex both C–C bonds are longer than in the free-ligand.