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Synthesis and π‐Tweezer Properties of tripod Cobalt‐Bisalkynyl Compounds [CH 3 C(CH 2 PPh 2 ) 3 Co(C≡CR) 2 ] − Application to the Oxidative Coupling of Alkynyl Groups
Author(s) -
Rupp Rolf,
Huttner Gottfried,
Lang Heinrich,
Heinze Katja,
Büchner Michael,
Hovestreydt Eric Robert
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200009)2000:9<1953::aid-ejic1953>3.0.co;2-1
Subject(s) - chemistry , electron paramagnetic resonance , ligand (biochemistry) , oxidative addition , medicinal chemistry , stereochemistry , reagent , oxidative coupling of methane , coupling reaction , crystallography , organic chemistry , catalysis , nuclear magnetic resonance , biochemistry , physics , receptor
tripod CoCl 2 [CH 3 C(CH 2 PPh 2 ) 3 CoCl 2 ] ( 1 ) reacts with alkynyllithium reagents RC≡CLi to produce tripod Co(C≡CR) 2 ( 2 ). The neutral paramagnetic Co II species 2 can be reduced to the anionic diamagnetic Co I compounds 2 − , which can also be obtained by treating tripod CoCl ( 3 ) with two equivalents of LiC≡CR. Compounds 2 contain an M(C≡CR) 2 group with the alkynyl substituents in cis ‐positions to each other. The expectation that they might therefore act as π‐tweezer ligands is born out by the characterisation of tripod Co(C≡CR) 2 −NiCO ( 4 ). The cis ‐position of the alkynyl groups in 2 should also facilitate their oxidative coupling. This type of reaction is, in fact, observed when compounds 2 are treated with one‐electron oxidants. Reaction of 2 with Cp 2 Fe + leads to [ tripod Co(η 2 ‐R C ≡ C C≡CR)] + (5) in which one of the triple bonds of the diyne acts as a four‐electron donor ligand while the other one remains uncoordinated. One‐electron oxidation of 2 thus initiates a two‐electron oxidative coupling of the alkynyl groups with concomitant one‐electron reduction of Co II ( 2 ) to Co I ( 5 ). All compounds were characterised by the usual analytical and spectroscopic techniques including EPR spectroscopy. The structure of compounds 5 is exemplified by an X‐ray analysis of [ tripod Co(η 2 ‐ t Bu C ≡ C C≡C t Bu)](PF 6 ) ( 5b ).