Synthesis, Structure, Reactivity, and Electrochemical Study of a (2,2‘-Biphosphinine)(η5-pentamethylcyclo- pentadienyl)chlororuthenium(II) Complex

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[RuCp*(η4-C6H10)Cl] (Cp* = C5Me5; 1) reacts with the tmbp ligand (2; tmbp = 4,4‘,5,5‘-tetramethyl-2,2‘-biphosphinine) in THF to afford the [RuCp*(tmbp)Cl] complex 3, which has also been characterized by a single-crystal X-ray diffraction study. Complex 3 crystallizes with one THF molecule. The environment about the Ru atom corresponds to that of a classical three-legged piano-stool structure. Reaction of 3 with LiBr and KCN in CH2Cl2/MeOH afforded [RuCp*(tmbp)Br] (4) and [RuCp*(tmbp)CN] (5), respectively. 3 also reacts in CH2Cl2, in the presence of NH4PF6, with various monodentate ligands to produce a series of stable cationic complexes of the type [RuCp*(tmbp) (L)]+[PF6]- (L = acetonitrile (6), pyridine (7), trimethyl phosphite (8), triphenylphosphine (9), 2-bromo-4,5-dimethylphosphinine (10), tert-butyl isocyanide (11), cis-cyclooctene (12), norbornene (13)). All complexes were obtained in good yields and have been characterized by a combination of elemental analyses and spectroscopic methods (IR and 31P, 1H, and 13C NMR). The redox chemistry of 3 has been investigated by cyclic voltammetry in MeCN. Complex 3 is reversibly oxidized in [RuCp*III(tmbp)Cl] at +0.49 V (vs SCE). The first irreversible monoelectronic reduction wave, which occurs at −1.82 V vs SCE, indicates the formation of the [RuICp*(tmbp)] complex with the loss of Cl-. The second reversible reduction wave at −2.24 V was assigned to the formation of the anionic [Ru0Cp*(tmbp)]- complex, which is stable within the time scale of the cyclic voltammetry.