Pd-catalyzed boronations and cross-coupling reactions of aromatic cobaltadithiolene complexes with aryl halides

Abstract

The Pd-catalyzed reaction of [CpCo(S2C2(Ph)(Bpin))] ( 1, Bpin = 4,4,5,5-tetramethyl-1,3,2-dioxaboronate) with 1-iodonaphthalene or 2-bromothiophene gave the cross-coupling product [CpCo(S2C2(Ph)(Ar))] (Ar = 1-Np ( 4) or 2-Th ( 5)), although an early paper described the reaction of 1 with 3-bromopyridine or 9-bromoanthracene (Ar = 3-Py ( 2) or 9-Anth ( 3)). The boronation of the brominated precursor [CpCo(S2C2(p-C6H4Br)(H))] ( 7) with Bpin-H in the presence of Pd catalyst gave the expected boronated product [CpCo(S2C2(p-C6H4Bpin)(H))] ( 8) but also underwent an unexpected direct boronation on the dithiolene carbon to form [CpCo(S2C2(p-C6H4Br)(Bpin))] ( 9). The brominated complex 7 or [CpCo(S2C2(Ph)(p-C6H4Br))] ( 10) was synthesized by thermal reaction and the microwave-enhanced reaction relatively gave better yield with shorter reaction time than that of the conventional heating reaction. The cross-coupling reactions of the boronated or [CpCo(S2C2(Ph)(p-C6H4Bpin))] ( 11) with aryl halides successfully produced the corresponding cross-coupling products such as [CpCo(S2C2(p-C6H4Py)(H))] ( 12) or [CpCo(S2C2(p-C6H4Anth)(H))] ( 13) from 8 and [CpCo(S2C2(Ph)(p-C6H4Py))] ( 14) from 11. The structures of 7, 9, 11, 12, 13 and 14 were determined by X-ray diffraction studies. Electronic absorption maxima ( λ max) due to dithiolene LMCT in dichloromethane solution can be modified in the range of 574–602 nm by a substituent effect on the dithiolene ring. Redox potentials obtained from CV measurement were also reported.