Syntheses and Structures of Buta-1,3-Diynyl Complexes from "on Complex" Cross-Coupling Reactions

© 2015 American Chemical Society. The Pd(PPh3)4/CuI-cocatalyzed reaction of Ru(C≡CC≡CH)(PPh3)2Cp (2) with aryl iodides, Ar-I (3, Ar = C6H4CN-4 (a); C6H4Me-4 (b); C6H4OMe-4 (c); 2,3-dihydrobenzo[b]thiophene (d); C5H4N (e)) proceeds smoothly in diisopropylamine and under an inert atmosphere to give the substituted buta-1,3-diynyl complexes Ru(C≡CC≡CAr)(PPh3)2Cp (4a-e) in moderate to good yield. The procedure allows the rapid preparation of a range of metal complexes of arylbuta-1,3-diynyl ligands without necessitating the prior synthesis of the individual buta-1,3-diynes as ligand precursors. Similar reaction of 2 with half an equivalent of 1,4-diiodobenzene affords the bimetallic derivative {Ru(PPh3)2Cp}2(μ-C≡CC≡C-1,4-C6H4-C≡CC≡C) (5). In the presence of atmospheric oxygen, homocoupling of the diynyl reagent 2 takes place to provide the octa-1,3,5,7-tetrayndiyl complex {Ru(PPh3)2Cp}2(μ-C≡CC≡CC≡CC≡C) (6). Crystallographically determined molecular structures are reported for five complexes (4a, 4b, 4d, 5, and 6). Quantum chemical calculations indicate that the HOMOs are mainly located on the C4-C6H4-C4 and C8 bridges for 5 and 6, respectively, while spectroelectrochemical (UV-vis-NIR and IR) studies on 6 establish that oxidation takes place at the C8 bridge, likely followed by cyclodimerization reactions of the bridging ligand.