Cu(dppf) complexes can be synthesized from Cu-exchanged solids and enable a quantification of the Cu-accessibility by 31P MAS NMR spectroscopy

Abstract

Herein, we apply three different copper-exchanged materials (Na–[Al]SBA-15, silica, Na–MCM-22) as hosts for a direct synthesis of Cu^I(1,1′-bis(diphenylphosphino)ferrocene = dppf) complexes in cationic ion exchange position. Using ³¹P MAS NMR spectroscopy, we show that identical complexes as after ion exchange are generated if the solids are applied as reactants directly. The homogeneity of copper exchanges is evaluated by EDX spectroscopy. Both Cu^I and Cu^II result in the formation of complexes, thereby oxidizing dppf. Cu-particles were not reactive. Optimized conditions for a maximized complex formation are identified applying quantitative ³¹P MAS NMR spectroscopy and ICP-OES. Only accessible copper in cationic position of the solids forms the complexes. This enables a quantification of the amount of copper in mesopores vs. the total copper amount. Thus, besides a new synthesis of the complex a suitable method for quantitative elucidation of the location of copper cations is demonstrated herein.