265116-95-8Relevant academic research and scientific papers
η4-Coordination of dienes and heterodienes to the tripodcobalt(I) template [CH3C(CH2PPh2)3CO]+: Synthesis, structure, and dynamics
Rupp, Rolf,Frick, Axel,Huttner, Gottfried,Rutsch, Peter,Winterhalter, Ute,Barth, Annette,Kircher, Peter,Zsolnai, Laszlo
, p. 523 - 536 (2007/10/03)
CH3C(CH2PPh2)3CoCl (1) is easily accessible from CH3C(CH2PPh2)3CoCl2 by reduction with activated zinc powder. Upon dehalogenation with TlPF6, 1 reacts with dienes to give [tripodCo(I)-(η4- diene)]+ (2). The heterodienes acrolein and methyl vinyl ketone produce the analogous η4-heterodiene compounds 3. When crotonaldehyde is used as the potential η4-diene ligand, decarbonylation is observed leading to [tripodCo(I)-(CO)2]+ (4). Reaction of [tripodCo(aq)](BF4)2 with allyl mercaptan produces [tripodCO(I)-(η4-thioacrolein)]+ (3a) through dehydrogenation of the ligand precursor. 1,2-Diketones such as benzil and phenanthrenequinone do not coordinate in a η4 fashion but rather generate η2-coordinate enediolato ligands by an electron-transfer process, resulting in compounds of the type {tripodCo(III)-[η2-RC(O)=C(O)R]}+ (5). All the compounds have been characterized by standard analytical and spectroscopic techniques, including X-ray analysis in some cases. Compounds 4 and 5 show trigonal-bipyramidal coordination in the solid state, whereas the coordination polyhedra in compounds 2 and 3 are better described as square- pyramidal. While a minimum of two phosphorus resonances might be expected for each of these coordination geometries, only one time-averaged signal is normally observed, only with the η4-coordinated heterodienes acrolein, methyl vinyl ketone, and thioacrolein present in 3 is there a resolution of the signals of the three chemically distinct phosphorus nuclei at low temperatures. By 31P-NMR line-shape analysis, the activation barriers for the rotational reorientation of the heterodienes are found to be around ΔH(≠)=47 kJmol-1 for all three compounds 3.
