412351-41-8Relevant academic research and scientific papers
Pyrazolyl-bridged iridium dimers. 18. Influence of metal-metal bonding on the geometry of diiridium(II) adducts and hydrido-diiridium complexes formed from the diiridium(I) prototype [Ir(μ-pz)(PPh3)(CO)]2 (pzH = pyrazole) by dihydrogen addition or protonation
Brost, Ron D.,Bushnell, Gordon W.,Harrison, Daryll G.,Stobart, Stephen R.
, p. 1412 - 1420 (2008/10/08)
Slow uptake of molecular dihydrogen by the diiridium(I) prototype [Ir(μ-pz)(PPh3)(CO)]2 (1: pzH = pyrazole) is accompanied by formation of a 1,2-dihydrido-diiridium(II) adduct [IrH(μ-pz)(PPh3)(CO)]2 (2), for which an X-ray crystal structure determination reveals that (unlike in 1) the PPh3 ligands are axial, with the hydrides occupying trans coequatorial positions across the Ir-Ir bond (2.672 A). Reaction with CCl4 effects hydride replacement in 2, affording the monohydride Ir2H(Cl)(μ-pz)2(PPh3)2(CO) 2 (3) in which Ir-Ir = 2.683 A. At one metal center, H is equatorial and PPh3 is axial, while at the other, Cl is axial as is found in the symmetrically substituted product [Ir(μ-pz)(PPh3)(CO)Cl]2 (4) (Ir-Ir = 2.754 A) that is formed by action of CCl4 on 1. Treatment of 1 with I2 yields the diiodo analogue 5 of 4, which reacts with LiAlH4 to afford the isomorph Ir2H(I)(μ-pz)2(PPh3)2(CO) 2 (6) of 3 (Ir-Ir = 2.684 A). Protonation (using HBF4) of 1 results in formation of the binuclear cation Ir2H(μ-pz)2(PPh3)2(CO) 2+ (7: BF4- salt), which shows definitive evidence (from NMR) for a terminally bound hydride in solution (CH2Cl2 or THF), but 7 crystallizes as an axially symmetric unit in which Ir-Ir = 2.834 A. Reaction of 7 with water or wet methanol leads to isolation of the cationic diiridium(III) products [Ir2H2(μ-OX)(μ-pz)2(PPh3) 2(CO)2]BF4 (8, X = H; 9, X = Me).
