Redox chemistry, acid reactivity, and hydrogenation reactions of two-electron mixed valence diiridium and dirhodium complexes

The syntheses and reaction chemistry of two electron mixed-valence diphosphazane- bridged dirhodium and diiridium complexes M² _0,II(tfepma)₂(CN^tBu)₂Cl₂ [M = Rh (1), Ir (2); tfepma = MeN[P(OCH₂CF₃) ₂]₂, CN^tBu = tert-butyl isocyanide] are described. 1 and 2 undergo addition and two-electron oxidation and reduction chemistries. In the presence of CN^tBu, the addition product with the stoichiometry M²_0,II(tfepma)_2- (CN ^tBu)₃Cl₂ [M = Rh (3), Ir (3)] is generated; in the presence of 1 equiv of CN^tBu and 2 equiv of bis(pentamethyl- cyclopentadienyl)cobalt(II), 1 and 2 are reduced to furnish M₂ ^0,0(tfepma)₂(CN^tBu)₃ [M=Rh (5), Ir (6)], which feature both four- and five-coordinate M⁰ centers. Complexes 1, 2, 5, and 6 all possess coordinatively unsaturated square planarM⁰ centers that are reactive: (1) 2 reacts with PhICl ₂ to produce Ir₂^II,^II(tfepma) ₂(CN^tBu)₂Cl₄ (7); (2) protonation of 2 with HX yields Ir₂^II,^II(tfepma) ₂(CN^tBu)₂Cl₂HX [X = Cl^- (8), OTs^- (9)]; (3) protonation of 5 with HOTs produces [Rh ₂ ^I,I(tfepma)₂(CN^tBu) ₃(μ- H)](OTs); and (4) the reversible hydrogenation of 2 proceeds smoothly, furnishing the cisdihydride complex Ir₂^II, ^II(tfepma)₂(CN^tBu)₂(H) ₂Cl₂ (11). Substitution of tfepma in 2 with bis(diphenylphsophino)methane (dppm) yields the orthometalated complex Ir ₂^II,^II(dppm)(PPh(o-C₆H ₄)CH₂PPh₂)(CN^tBu)₂Cl ₂H (12). The X-ray crystal structures of 11 compounds are presented and discussed, and spectroscopic characterization by multinuclear and variable temperature NMR provides details about solution structures and in some cases the formation of isomeric products. The electronic spectra of the new complexes are also described briefly, with absorption and emission features derived from the bimetallic core.