Diimine−Acetylide Compounds of Ruthenium: The Structural and Spectroscopic Effects of Oxidation

The reaction of Ru(Me2bipy)(PPh3)2Cl2 1 with terminal alkynes HCCR in the presence of TlPF6 leads to the formation
of the vinylidene compounds [Ru(Me2bipy)(PPh3)2Cl(CCHR)][PF6] (2) (2a, R = But; 2b, R = p-C6H4−Me; 2c,
R = Ph). These compounds decompose in oxygenated solution to form the carbonyl compound [Ru(Me2bipy)(PPh3)2Cl(CO)][PF6] (3), and may be deprotonated by K2CO3 to give the ruthenium(II) terminal acetylide compounds
Ru(Me2bipy)(PPh3)2Cl(C⋮C−R) (4) (4a, R = But; 4b, R = p-C6H4−Me; 4c, R = Ph). Cyclic voltammetry shows
that 2a−c may also be reductively dehydrogenated to form 4a−c. 4a−c are readily oxidized to their ruthenium(III)
analogues [4a]+−[4c]+, and the changes seen in their UV/visible spectra upon performing this oxidation are analyzed.
These show that whereas the UV/visible spectra of 4a−c show MLCT bands from the ruthenium atom to the
bipyridyl ligand, those of [4a]+−[4c]+ contain LMCT bands originating on the acetylide ligands. This is in agreement
with the IR and ESR spectra of [4a]+−[4c]+. The X-ray crystal structures of the redox pair 4a and [4a][PF6] have
been determined, allowing the bonding within the metal−acetylide unit to be analyzed, and an attempt is made to
determine Lever electrochemical parameters (EL) for the vinylidene and acetylide ligands seen herein. Room
temperature luminescence measurements on 4a−c show that the compounds are not strongly emissive.