Zwitterionic Cobalt(I)–NHC Complexes with Tetraphenylborate Ligation: Synthesis, Characterization, and Reactivity

Abstract

Zwitterionic metal complexes of Rh and Ru featuring a tetraphenylborate ancillary ligand have been explored widely in organometallic chemistry. Analogous 3d metal complexes, however, are rarely known. From the oxidation reaction of cobalt( 02) in good yields. Characterization data and computational studies revealed the S = 1 ground spin state for 1 and 2. These zwitterionic cobalt(I) complexes can act as cobalt(I) synthons to prepare cobalt(I)−NHC complexes bearing other ancillary ligands. Their reactions to CO and CNBu t form the zwitterionic cobalt(I) complexes [(IMes)Co((η 6 -C 6 H 5 )BPh 3 )(CO)] (3), [(IPr)Co((η 6 -C 6 H 5 )BPh 3 )(CO)] (4), and [(IMes)Co((η 6 -C 6 H 5 )BPh 3 )(CNBu t )] ( 5) and the ionic cobalt(I) complex [(IMes)Co(CNBu t ) 4 ]-[BPh 4 ] (6). In the reactions of 2 with pyridine, IPr, and IMes, the ionic cobalt(I)−NHC complexes [(IPr)Co(py) 3 ][BPh 4 ] (7), [(IPr) 2 Co][BPh 4 ] (8) and [(IPr)Co(IMes)][BPh 4 ] (9) were formed. The structures of these complexes were established by singlecrystal X-ray diffraction studies.