Molecular and heterogenized dinuclear Ir-Cp^* water oxidation catalysts bearing EDTA or EDTMP as bridging and anchoring ligands

分子和异质化的双核Ir-Cp^*水氧化催化剂含EDTA或EDTMP作为桥接和锚定配体

The development of efficient water oxidation catalysts(WOCs)is of key importance in order to drive sustainable reductive processes aimed at producing renewable fuels.Herein,two novel dinuclear complexes,[(Cp^*Ir)2(μ-κ^3-O,N,O-H4-EDTMP)](Ir-H4-EDTMP,H4-EDTMP^4-=ethylenediamine tetra(methylene phosphonate))and[(Cp^*Ir)2(μ-κ^3-O,N,O-EDTA)](Ir-EDTA,EDTA^4-=ethylenediaminetetraacetate),were synthesized and completely characterized in solution,by multinuclear and multidimensional NMR spectroscopy,and in the solid state,by single crystal X-Ray diffraction.They were supported onto rutile TiO2 nanocrystals obtaining Ir-H4-EDTMP@TiO2 and Ir-EDTA@TiO2 hybrid materials.Both molecular complexes and hybrid materials were found to be efficient catalysts for WO driven by NaIO4,providing almost quantitative yields,and TON values only limited by the amount of NaIO4 used.As for the molecular catalysts,Ir-H4-EDTMP(TOF up to 184 min^-1)exhibited much higher activity than Ir-EDTA(TOF up to 19 min^-1),likely owing to the higher propensity of the former to generate a coordination vacancy through the dissociation of a Ir–OP bond(2.123A,significantly longer than Ir–OC,2.0913A),which is a necessary step to activate these saturated complexes.Ir-H4-EDTMP@TiO2(up to 33 min^-1)and IrEDTA@TiO2(up to 41 min^-1)hybrid materials showed similar activity that was only marginally reduced in the second and third catalytic runs carried out after having separated the supernatant,which did not show any sign of activity,instead.The observed TOF values for hybrid materials are higher than those reported for analogous systems deriving from heterogenized mononuclear complexes.This suggests that supporting dinuclear molecular precursors could be a successful strategy to obtain efficient heterogenized water oxidation catalysts.

开发高效的水氧化催化剂对于推动以生产可再生燃料为目标的可持续还原过程具有重要意义.本文报道了两个新型双核铱配合物(Ir-H4-EDTMP和Ir-EDTA)的合成和广泛表征,其中N,N,N',N'-乙二胺四乙酸(EDTA)及其类似物N,N,N',N'-乙二胺四(亚甲基膦酸)(EDTMP)充当两个片段Ir-Cp^*的κ^3-O,N,O-桥接配体.文章还展示了如何利用它们的羧酸盐和膦酸酯团的锚点在TiO2上异质化这些复合物.由此获得的混合材料(Ir-H4-EDTMP@TiO2和Ir-EDTA@TiO2)代表双核异质水氧化催化剂的罕见例子.由NaIO4引导的水氧化中测试了分子和异质化的催化剂,显示出高效率和活性.特别是,在效率、TOF和可回收性方面,杂化材料的性能明显优于单核配合物的类似材料.