CpCo(CO)l2 as Catalyst for Ortho-C,H Activation at Ferrocene: ODG-Dependent preference for 2-Mono- or 2,5-Dialkenylation

• Published in: Organometallics Vol. 37; no. 13; pp. 2095 - 2110
• Main Authors: Schmiel, David, Gathy, Robert, Butenschoen, Holger
• Format: Journal Article
• Language: English
• Published: WASHINGTON Amer Chemical Soc 09.07.2018
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; H BOND ACTIVATION; EFFICIENT ACCESS; OXIDATIVE ALKYLATION; ALLYLIC ALCOHOLS; DIRECTED ORTHO-METALATION; COUPLING REACTION; COMPLEXES; PLANAR CHIRAL FERROCENES; ALKENYLATION; PHOTOREDOX CATALYSIS
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.8b00243

The catalytic ortho-alkenylation at ferrocene has been investigated with C-p*Co(CO)I-2 as the catalyst for some nitrogen ortho-directing groups (ODGs). The reaction conditions were optimized starting from 2-ferrocenylpyridine, and a number of terminal arylethynes gave preferentially the 2,5-dialkenylation products in up to 94% yield. In most cases the 2-monoalkenylation products were not obtained, although there are exceptions with formyl- and thioacetyl-substituted arylethynes and ferrocenylethyne. When 1-phenylpropyne was used, the dialkenylation took place with high selectivity. Use of 1-ferrocenylisoquinoline resulted in moderate yields with poor selectivity for the mono- or dialkenylation. With N,N- dimethylferrocenylcarboxamide, however, very high selectivity for monoalkenylation was observed. Products were obtained in up to 90% yield; in only one case the dialkenylation was product observed in trace amounts. All products were characterized spectroscopically, including four crystal structure analyses. The results are explained by the steric hindrance of the N,N-diemethylcarbamoyl ODG when the conformation necessary for a second alkenylation is adopted. In summary, ODGs for the selective cobalt-catalyzed mono- or dialkenylation have been identified.