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Electrochemistry and Reactivity of Cobaltadithiolene Complexes Having Sulfilimine Structures:  Effect of Phosphorus Ligand Basicity and Cone Angle on the Electrochemical Behavior and on the Imido Migration to the Cp Ring

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posted on 15.03.2004, 00:00 by Mitsushiro Nomura, Chikako Takayama, Toru Sugiyama, Yasuo Yokoyama, Masatsugu Kajitani
Various types of cobaltadithiolene complexes having the sulfilimine structure CpCo[S(NTs)SC2(COOMe)2](PR3) were newly synthesized. The lifetimes of the sulfilimine complexes are influenced by the basicities and by the cone angles of PR3 ligands used. Some of the sulfilimine complexes rapidly eliminate PR3 ligands by a one-electron reduction (PR3 = PPh3, P(OPh)3, P(p-C6H4Me)3, P(p-C6H4Cl)3, PCy3, P(p-C6H4OMe)3) to give the precursor of the sulfilimine complex, the imido-bridged cobaltadithiolene adduct [CpCo{S2C2(COOMe)2}(NTs)]. On the other hand, the complexes of PBu3 and P(OMe)3 were stable during a one-electron reduction. The elimination of the imido group (NTs) by a second reduction was confirmed in all of the sulfilimine complexes. The investigation of the reactivity of the sulfilimine complexes showed that some of the sulfilimine complexes were the intermediates in the imido migration to the Cp ring (PR3 = PPh3, P(OPh)3, P(p-C6H4Me)3, P(p-C6H4Cl)3). The basicities (or nucleophilicities) of PR3 were important parameters for the imido migration. Sulfilimine complexes containing strongly nucleophilic PR3 ligands (PR3 = P(p-C6H4OMe)3, PBu3, P(OMe)3) did not undergo migration of the imido group. In the formation of the disubstituted Cp complex [{C5H3(NTs)(PR3)}Co{S2C2(COOMe)2}], the basicity (or nucleophilicity) of PR3 ligands is also an important parameter (PR3 = PPh3, P(p-C6H4Me)3).