114763-05-2Relevant academic research and scientific papers
Hindered rotation about the palladium-aryl bonds in [Pd(C6H4-2-N=NPh)(η5-C5H 5)(PR3)] and related molecules: X-ray crystal structure of (η5-cyclopentadienyl)[2-(phenylazo)phenyl-C1] (tricyclohexylphosphine) palladium
Anderson, Gordon K.,Cross, Ronald J.,Manojlovi?-Muir, Ljubica,Muir, Kenneth W.,Rocamora, Mercè
, p. 1520 - 1525 (2008/10/08)
The compound [Pd(C6H4-2-N=NPh)(η5-C5H 5)(PCy3)] has been isolated from the reaction of [Pd-(C6H4-2-N=NPh)(η5-C5H 5)] with PCy3. It crystallizes in space group Pbca with a = 11.958 (1) A?, b = 19.079 (2) A?, c = 28.247 (3) A?, V = 6444.5 (12) A?3, and Z = 8. The structure was refined by using 3252 reflections to R = 0.029. There are no significant intermolecular interactions. The PPdC(aryl) bond angle is 92.4 (2)°, and the 2-(phenylazo)phenyl group is constrained nearly perpendicular to the plane defined by these three atoms. Calculations indicate a considerable barrier to rotation about the Pd-C(aryl) bond even with phosphines less bulky than PCy3. The retention of this conformation in solution at low temperatures is revealed by 1H and 13C{1H} NMR studies of the related complexes [Pd(Ar)(η5-C5H5)(PR2Ph)] (Ar = 2-(phenylazo)phenyl or 2-[(methylimino)methyl]phenyl; R = Me or Et), in which the phosphine methyl or ethyl groups are magnetically nonequivalent. The observations of four nonequivalent hydrogens and five nonequivalent carbons in the analogous C5H4Me and C5H4SiMe3 complexes, typical of η5-C5H4R rings attached to chiral metal centers, are also compatible with significant barriers to Pd-C (aryl) rotation and allow detection of this phenomenon in complexes of the more symmetrical phosphines PEt3 and PCy3. Raising the solution temperatures causes coalescence of the 1H NMR signals due to the methyl or ethyl groups of the PMe2Ph or PEt2Ph complexes, and merging of the 1H and 13C resonances of the C5H4R rings, in keeping with the onset of rapid rotation about the Pd-aryl bonds in the PEt3, PMe2Ph, and PEt2Ph complexes. The NMR spectra of the more crowded [Pd(C6H4-2-N=NPh)(η5-C5H 4Me)(PCy3)] retain their static pattern above room temperature to the onset of decomposition.
