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.