Molecular and Heterogenized Cp*Ir Water Oxidation Catalysts Bearing Glyphosate and Glyphosine as Ancillary and Anchoring Ligands

Abstract

Two hybrid materials (1_TiO 2 and 2_TiO 2) were designed and prepared by anchoring novel [Cp*Ir(k 3-O,N,O-glyphosate)] (1; glyphosate = N-(phosphonomethyl)glycine) and [Cp*Ir(k 3-O,N,Oglyphosine)] (2; glyphosine = N,N-bis(phosphonomethyl)glycine) complexes onto rutile TiO 2. Characterization in solution (NMR spectroscopy) and solid state (X-Ray diffractometry) indicates that 1 and 2 are stabilized by the two arms of the glycine fragment, whereas they have (2) or can easily generate (1 and 2) a dandling phosphonate arm suitable for their anchoring on TiO 2. As a matter of fact, they exhibit rather elongated Ir-OP (1: 2.1405 Å, 2: 2.142 Å) and short Ir-OC (1: 2.0784 Å, 2: 2.086 Å) and Ir-N (1: 2.155 Å, 2: 2.207 Å) bonds. NMR spectra of 2 show a dynamic process that exchanges the two phosphonate moi-eties, consistently with an easy-OP detachment from Ir. Both molecular and heterogenized species were tested as catalysts in water oxidation (WO) driven by NaIO 4. 1 (TOF up to 96 min À 1) and 2 (26 min À 1) proved to be effective molecular catalysts; more importantly, 1_TiO 2 and 2_TiO 2 showed very high activity (TOF~200 min À 1), which remained rather constant over seven successive runs, even if substantial leaching of the noble metal in solution occurred during the first catalytic tests. TON was very high and limited only by the amount of NaIO 4 used. These results show the potentialities of mixed carboxylate/phosphonate ligands for the development of highly active water oxidation catalysts.

Molecular versus Silica‐Supported Iridium Water Oxidation Catalysts

“…Despite the use of homogeneous catalysts has historically pioneered the field of WO, pointing to an optimization of the recyclability of noble metals, the exploitation of immobilized catalysts turned out to be a successful strategy, too. [7,11,[15][16][17][18][19] Many molecular catalysts have been immobilized onto various supports such as semiconducting titanium oxide (TiO 2 ), [14,18,19,23,24] indium tin oxide (ITO), [25] bismuth vanadate (BiVO 4 ) [21,26,27] or inert porous supports like MOFs [28][29][30] or silica (SiO 2 ). [31,32] For instance, in a recent research, Inagaki reported the use of periodic mesoporous organosilica (PMO) with embedded bipyridine ligands (BPy-PMO) as support for the synthesis of a single site IrÀ Cp* WOC (Ir-BPy-PMOs).…”

Interaction between [(η6-p-cym)M(H2O)3]2+ (MII = Ru, Os) or [(η5-Cp*)M(H2O)3]2+ (MIII = Rh, Ir) and Phosphonate Derivatives of Iminodiacetic Acid: A Solution Equilibrium and DFT Study

“…The retained piano-stool geometry of the complexes was supported by XRD. The hybrid materials that were derived from supporting the above complexes onto rutile TiO 2 were found to be effective molecular catalysts in water oxidation [ 31 ]. In another study, aminophosphonate complexes of [(η 6 - p -cym)Ru] 2+ were used as catalysts to reduce ketones, however, in this case, the phosphonate units were not in the coordination sphere of metal ion [ 32 ].…”

Coating Hollow Carbon Nitride Nanospheres with Porous WO3Shells to Construct Z‐Scheme Heterostructures for Efficient Photocatalytic Water Oxidation

“…Semiconductor photocatalytic water splitting to produce hydrogen directly by solar energy has been regarded as an affordable and sustainable manner to alleviate the two challenges at once. [1][2][3] However, the overall efficiency of water photosplitting is greatly restricted by the sluggish kinetics of H 2 O oxidation half-reaction for O 2 evolution, [4][5][6][7] as it necessitates the transport of four electrons and protons, and the formation of two OÀ O bonds, simultaneously. Therefore, developing efficient and stable water oxidation photocatalysts workable under visible light is highly desirable, toward the production of "green" hydrogen via H 2 O splitting, especially those made from lowcost elements.…”