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

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.