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Reaction of the 6π-electron aromatic fourmembered heterocycle (IPr) 2 C 2 P 2 (1) (IPr = 1,3-bis(2,6diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) with [Fe 2 CO 9 ] gives the neutral iron tricarbonyl complex [Fe(CO) 3 -η 3 -{(IPr) 2 C 2 P 2 }] (2). Oxidation with two equivalents of the ferrocenium salt, [Fe(Cp) 2 ](BArF 24 ), affords the dicationic tricarbonyl complex [Fe(CO) 3 -η 4 -{(IPr) 2 C 2 P 2 }](BArF 24 ) 2 (4). The one-electron oxidation proceeds under concomitant loss of one CO ligand to give the paramagnetic dicarbonyl radical cation complex [Fe(CO) 2 -η 4 -{(IPr) 2 C 2 P 2 }](BArF 24 ) (5). Reduction of 5 allows the preparation of the neutral dicarbonyl complex [Fe(CO) 2 -η 4 -{(IPr) 2 C 2 P 2 }] ( 6). An analysis by various spectroscopic techniques ( 57 Fe Mössbauer, EPR) combined with DFT calculations gives insight into differences of the electronic structure within the members of this unique series of iron carbonyl complexes, which can be either described as electron precise or Wade-Mingos clusters.

Supporting two metal binding sites by a tailored polydentate trop-based (trop = 5H-dibenzo[a,d]cyclohepten-5-yl) ligand yields highly unsymmetric homobimetallic rhodium(i) complexes. These were studied as models for Rh/C hydrogenation catalysts.

The nitrogen oxides NO 2 ,NO, and N 2 Oare among the most potent air pollutants of the 21 st century.Abimetallic Rh I -Pt II complex containing an especially designed multidentate phosphine olefin ligand is capable of catalytically detoxifying these nitrogen oxides in the presence of hydrogen to form water and dinitrogen as benign products.The catalytic reactions were performed at room temperature and low pressures (3-4 bar for combined nitrogen oxides and hydrogen gases). Aturnover number (TON) of 587 for the reduction of nitrous oxide (N 2 O) to water and N 2 was recorded, making these Rh I -Pt II complexes the best homogeneous catalysts for this reaction to date.L ower TONs were achieved in the conversion of nitric oxide (NO,TON = 38) or nitrogen dioxide (NO 2 ,T ON of 8). These unprecedented homogeneously catalyzedh ydrogenation reactions of NO x were investigated by ac ombination of multinuclear NMR techniques and DFT calculations,w hich provide insight into ap ossible reaction mechanism. The hydrogenation of NO 2 proceeds stepwise,t o first give NO and H 2 O, followed by the generation of N 2 Oand H 2 O, whichi st hen further converted to N 2 and H 2 O. The nitrogen À nitrogen bond-forming step takes place in the conversion from NO to N 2 Oa nd involves reductive dimerization of NO at ar hodium center to give ah yponitrite (N 2 O 2 2À ) complex, whichw as detected as an intermediate.