A one-pot synthetic procedure for a series of bimetallic Nb/M complexes, Cl−Nb( i PrNPPh 2 ) 3 M−X (M = Fe (2), Ni (4), Cu (5)), is described. A similar procedure aimed at synthesizing a Nb/Co analogue instead affords i PrNNb( i PrNPPh 2 ) 2 (μ-PPh 2 )Co−I (3) through cleavage of one phosphinoamide P−N bond under reducing conditions. Complexes 4 and 5 are found to have short Nb-M distances, corresponding to unusual metal−metal bonds between Nb and these first row transition metals. For comparison, a series of heterobimetallic ONb( i PrNPPh 2 ) 3 M−X complexes (M = Fe (7), Co (8), Ni (9), Cu ( 10)) was synthesized. In these complexes, the Nb V center is engaged in sufficient π-bonding to the terminal oxo ligand to remove the driving force for direct metal−metal interactions. A comparison of the cyclic voltammograms of 2 and 4−10 reveals that the presence of a second metal shifts the redox potentials of both Nb and the late metal center anodically, even when direct metal−metal interactions are not present.
A series of Fe(iii) complexes was recently reported that are active for photocatalytic hydrogen generation when paired with fluorescein and triethylamine. Herein we report an Fe(iii) complex immobilized on TiO2 and SrTiO3 that is significantly more active than the homogeneous system, achieving up to 7800 turnovers in 31 hours.
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