Reaction of molecular hydrogen (H2) with chlorohydridoiridium phosphines IrHCl2P2 (P = PPr-iso3 or PBu-tert2Ph): stereoelectronic control of the stability of molecular H2 transition metal complexes

Abstract

IrHCl2P2 (P = P'Pr3) reacts rapidly with H2 at 25 °C to set up an equilibrium where H2 binds trans to the original hydride ligand (trans-2). A second slower reaction forms IrH(H2)Cl2P2 (cis-2), where the cis disposition of the chlorides, and also H cis to H2, was established by neutron diffraction. This molecule (unlike trans-2), shows rapid site exchange between coordinated H and H2. cis-2 can be induced to lose HC1 to form Ir(H)2ClP2 (3). The structure of Ir(H)2Cl(PlBu2Ph)2, an analog of 3, was shown by neutron diffraction to have a planar H2IrCl in a Y shape, with Cl at the base of the Y and a H-Ir-H angle of only 73°. ECP ab initio calculations of IrH2Cl(PH3)2 show that the

Halide Effects in Transition Metal Catalysis

“…This reaction has been studied computationally 33. To accommodate H 2 binding, distortion of the Ir trigonal‐bipyramidal complex 8 towards the T H ‐shaped (a square pyramid with an H atom at the apex) transition state 10 was proposed 34. While halide to metal π donation can occur in 8 , this interaction is either partially or completely disrupted in the T‐shaped transition state 35.…”

Learning from the Neighbors: Improving Homogeneous Catalysts with Functional Ligands Motivated by Heterogeneous and Biocatalysis

“…Many active catalyst species for outer‐sphere H 2 ‐transfer to the substrate carry strong σ‐donor ligands particularly in trans ‐position to the transferred hydride which labilize MH bonding 26a. 53 For example, out of the possible stereoisomers for [Ru(H) 2 (PPh 3 ) 2 (1,2‐( R , R )‐diaminocyclohexane)] ( 8 ) the trans ‐dihydride complex was shown to be the catalytically active isomer 47. This trend was further demonstrated in a DFT examination of ketone DH with model catalysts [Ru‐ trans ‐(HX)(H 2 NCMe 2 CMe 2 NH 2 )‐ cis ‐(PH 3 ) 2 ] n + ( n =0: X=H, Cl, OR; n =1: CO, NCMe) 54.…”

A Neutron Diffraction Study of [OsClH3(PPh3)3]: A Complex Containing a Highly “Stretched” Dihydrogen Ligand

“…The terminal hydride is located trans to a phosphane ligand (H1‐Os1‐P3 172.5(6)°) while the dihydrogen ligand sits essentially trans to the chloride ligand (X‐Os1‐Cl1 171.4(3)°, where X represents the center of the dihydrogen ligand). The dihydrogen, hydride, and chloride ligands lie in the same plane (Figure 1), which is similar to the atomic arrangement in [IrCl 2 H(H⋅⋅⋅H)(P i Pr 3 ) 2 ] 4e. Two other stretched dihydrogen moieties previously studied by neutron diffraction, in which the dihydrogen ligands were also located trans to negatively charged ligands, were also found in six‐coordinate osmium complexes 4b,c…”