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

[RuCp*(η 4 -C 6 H 10 )Cl] (Cp* = C 5 Me 5; 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 CH 2 Cl 2 /MeOH afforded [RuCp*(tmbp)Br] ( 4 ) and [RuCp*(tmbp)CN] ( 5 ), respectively. 3 also reacts in CH 2 Cl 2, in the presence of NH 4 PF 6, with various monodentate ligands to produce a series of stable cationic complexes of the type [RuCp*(tmbp) (L)] + [PF 6 ] - (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 31 P, 1 H, and 13 C 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 [Ru I Cp*(tmbp)] complex with the loss of Cl - . The second reversible reduction wave at −2.24 V was assigned to the formation of the anionic [Ru 0 Cp*(tmbp)] - complex, which is stable within the time scale of the cyclic voltammetry.