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Reactivity Diversification – Synthesis and Exchange Reactions of Cobalt and Iron 2‐Alkenylpyridine/‐pyrazine Complexes Obtained by Vinylic C(sp 2 )–H Activation
Author(s) -
Beck Robert,
Camadanli Sebnem,
Flörke Ulrich,
Klein HansFriedrich
Publication year - 2015
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/ejic.201500225
Subject(s) - chemistry , metallacycle , reactivity (psychology) , pyridine , pyrazine , cobalt , moiety , medicinal chemistry , adduct , stereochemistry , x ray crystallography , organic chemistry , medicine , physics , alternative medicine , pathology , diffraction , optics
The reactivity of 2‐alkenylpyridine derivatives with trimethylphosphane‐supported iron– and cobalt–methyl adducts were investigated and provided a series of C , N ‐cyclometalated complexes through smooth vinyl C(sp 2 )–H activation. The reactions of Co(CH 3 )(PMe 3 ) 4 with 2‐vinylpyridine, 2‐(1‐phenylvinyl)pyridine, and 2‐vinylpyrazine provided dark green crystals of the five‐membered metallacycles (κ 2 ‐ C , N ‐R 1 R 2 C=CH)Co(PMe 3 ) 3 ( 1 : R 1 = C 5 H 4 N, R 2 = H; 2 : R 1 = C 5 H 4 N, R 2 = Ph; 3 : R 1 = C 4 H 3 N 2 ,R 2 = H). The oxidative addition of 1 – 3 with iodomethane afforded the mer‐trans trivalent cobalt complexes (κ 2 ‐ C , N ‐R 1 R 2 C=CH)Co(CH 3 )I(PMe 3 ) 2 ( 4 : R 1 = C 5 H 4 N, R 2 = H; 5 : R 1 = C 5 H 4 N, R 2 = Ph; 6 : R 1 = C 4 H 3 N 2 , R 2 = H) in modest yields. The reaction of 2 with an additional equivalent of 2‐(1‐phenylvinyl)pyridine incorporated a second C,N metallacycle with an η 2 ‐bonded alkenyl moiety to provide (κ 2 ‐ C , N ‐C 5 H 4 N–CH=CH)(κ 3 ,η 2 ‐ C , C , N ‐C 5 H 4 N–CH=CH 2 )Co(PMe 3 ) ( 7 ). No cyclometalation was observed with 8‐vinylquinoline and Co(CH 3 )(PMe 3 ) 4 , which afforded (κ 3 ,η 2 ‐ C , C , N ‐C 9 H 6 N–CH=CH 2 )Co(CH 3 )(PMe 3 ) 2 ( 8 ) with retention of the Co–CH 3 group; therefore, a suitable bite angle is required for C–H activation. No N coordination was observed with Fe(CH 3 ) 2 (PMe 3 ) 4 and 8‐vinylquinoline (reductive elimination of C 2 H 6 ), which afforded a low‐valent Fe(PMe 3 ) 3 moiety bound in an η 4 ‐fashion with the exocyclic vinyl group and the ortho ‐carbon atoms to give (κ 4 ,η 4 ‐ C , C , C , C ‐C 9 H 6 N–CH=CH 2 )Fe(PMe 3 ) 3 ( 9 ). In polar solvents, an equilibrium of cyclometalated 7,8‐benzoquinoline exists between the mer ‐ trans (90 %) and mer ‐ cis (10 %) configurations of (κ 2 ‐ C , N ‐C 13 H 6 N)Fe(CH 3 )(PMe 3 ) 3 ( 10 ). At variance with the previously reported bicyclometalation of 2‐(2‐naphthalene‐1‐ylvinyl)pyridine with iron adducts, similar reactions with methylcobalt species provided the monocyclometalated η 2 ,σ 1 ‐bound coordination motif (κ 3 ,η 2 ‐ C , C , N ‐C 5 H 4 N–CH=CH–C 10 H 6 )Co(PMe 3 ) 2 ( 11 ). The reaction of 11 with carbon monoxide provided the monocarbonyl complex (κ 3 ,η 2 ‐ C , C , C ‐C 5 H 4 N–CH=CH–C 10 H 6 )Co(CO)(PMe 3 ) 2 ( 12 ), accompanied by the release of the N‐coordination site. The carbonylation of (κ 3 ‐ C , C , N ‐C 5 H 4 N–CH=C–C 10 H 6 )Fe(PMe 3 ) 3 resulted in the exchange of one PMe 3 ligand with the retention of the coordination sites to generate (κ 3 ‐ C , C , N ‐C 5 H 4 N–CH=C–C 10 H 6 )Fe(CO)(PMe 3 ) 2 ( 13 ). All new compounds were identified by NMR spectroscopy and structurally characterized by single‐crystal X‐ray crystallography (with the exception of 10 and 13 ).