Hydrido, Halo, and Hydrido-Halo Complexes of Two-Electron Mixed-Valence Diiridium Cores

Abstract

Two-electron mixed-valence bimetallic cores of iridium are stabilized in a diphosphazane, MeN[P(OCH2CF3)2]2 (bis(bis(trifluoroethoxy)phosphino)methylamine, tfepma) coordination sphere. Treatment of [Ir(cod)Cl]2 with tfepma affords the Ir2 0,II complex, Ir2(tfepma)3Cl2 (1), in which the Ir0 and IrII centers assume trigonal bipyramidal and square pyramidal coordination geometries, respectively. The coordinatively unsaturated two-electron mixed-valence core of 1 supports an extensive acid−base and oxidation−reduction chemistry. As established by single crystal X-ray analysis, two-electron donor ligands are readily received at the IrII center of 1 to complete the octahedral coordination environment that is preferred by a d7 metal−metal bonded center. Alternatively, redox-active substrates rapidly add across the single metal−metal bond of 1 to form Ir2 I,III mixed-valence complexes; the chlorine and hydrochloric acid adducts, Ir2(tfepma)3Cl4 (5) and Ir2(tfepma)3HCl3 (7b), respectively, have been characterized by NMR spectroscopy and X-ray crystallography. Likewise, H2 reacts with 1 to afford an Ir2 I,III dihydride complex, Ir2(tfepma)3H2Cl2 (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 readily removed from the complex in solution and the solid state, providing the first example of the reversible addition of dihydrogen across a single metal−metal bond.

Reversible Binding of Dihydrogen in Multimetallic Complexes

“…[44] Nocera has reported that the mixed-valence, unsaturated, 32-electron, Ir 2 dimer 18 reversibly adds H 2 across the IrIr bond to form saturated dihydride 19. [45] Purging with N 2 recovers 18. The mechanism is suggested to proceed by addition of H 2 to one metal centre and then hydride migration rather than the symmetry-forbidden concerted 1,2 addition.…”

Chemistry of Personalized Solar Energy

“…The A–D–A ligands, bis(difluorophosphino)methylamine (dfpma, CH 3 N(PF 2 ) 2 ) and bis(bistrifluoroethoxyphosphino)methylamine (tfepma, CH 3 N[P(OCH 2 CF 3 ) 2 ] 2 ) shown in Chart 1, exhibit a particular proclivity for promoting the internal disproportionation of binuclear M 2 I,I cores to M 2 0,II cores 65 for the metals of rhodium 57,58 and iridium. 59–61,66 X-ray crystal structures reveal a pronounced asymmetry in the diphosphazane framework upon ligation to a bimetallic core derived from the asymmetric stabilization of metals that differ by two in their formal oxidation. The result is consistent with π-donation of the amine bridgehead lone pair to the PR F 2 bonded to M II .…”

“…Our success in using M n ⋯M n+2 species to drive two- and four-electron transformations along ground and excited state pathways 57–59 established two-electron mixed valency as a useful design concept for the development of multielectron reaction schemes. The two-electron mixed valence core is particularly effective in hydrogen management and production.…”

Metal–Metal Interactions in Heterobimetallic Complexes with Dinucleating Redox‐Active Ligands

“…Redox-active ligands have initially been utilized primarily to induce two-electron transformations at metal centers that are redox-inert, prone to undergo one-electron processes,o r that are lacking delectrons to induce two-electron bond activation processes. [6] Alternatively,e lectron repulsion between two electron-rich elements can destabilize ar educed state, thereby inducing reactivity. [4] Synthetic systems featuring metal-metal interactions have successfully been exploited to facilitate (multi-electron) chemical transformations.…”