ISSN:
1434-1948
Keywords:
Tripod ligands
;
Dienes
;
Heterodienes
;
η4-Coordination
;
Hindered rotation
;
Line-shape analysis
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 [tripodCoI-(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 [tripodCoI-(CO)2]+ (4). Reaction of [tripodCoaq](BF4)2 with allyl mercaptan produces [tripodCoI-(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 {tripodCoIII-[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.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
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