Af. Heyduk et Dg. Nocera, Hydride, halo, and hydride-halo complexes of two-electron mixed-valence diiridium cores, J AM CHEM S, 122(39), 2000, pp. 9415-9426
Two-electron mixed-valence bimetallic cores of iridium are stabilized in a
diphosphazane, MeN-[P(OCH2CF3)(2)](2) (bis(bis(trifluoroethoxy)phosphino)me
thylamine, tfepma) coordination sphere. Treatment of [Ir(cod)Cl](2) with tf
epma affords the Ir-2(0,II) complex, Ir-2(tfepma)(3)Cl-2 (1), in which the
Ir-0 and Ir-II centers assume trigonal bipyramidal and square pyramidal coo
rdination geometries, respectively. The coordinatively unsaturated two-elec
tron mixed-valence core of 1 supports an extensive acid-base and oxidation-
reduction chemistry. As established by single crystal X-ray analysis, two-e
lectron donor ligands are readily received at the Ir-II center of 1 to comp
lete the octahedral coordination environment that is preferred by a d(7) me
tal-metal bonded center. Alternatively, redox-active substrates rapidly add
across the single metal-metal bond of 1 to form Ir-2(I,III) mixed-valence
complexes; the chlorine and hydrochloric acid adducts, Ir-2(tfepma)(3)Cl-4
(5) and Ir-2(tfepma)(3)-HCl3 (7b), respectively, have been characterized by
NMR spectroscopy and X-ray crystallography. Likewise, H-2 reacts with 1 to
afford an Ir-2(I,III) dihydride complex, Ir-2(tfepma)(3)H2Cl2 (8). Single-
crystal X-ray and NMR analyses of 8 reveal that a single hydride ligand is
coordinated at each iridium center of the bimetallic core. Hydrogen is read
ily removed from the complex in solution and the solid state, providing the
first example of the reversible addition of dihydrogen across a single met
al-metal bond.