Dinitrogen, carbonyl complexes

It appears that the metal-ligand bonds in carbonyl and dinitrogen complexes are similar but somewhat weaker in the dinitrogen complexes. Carbon monoxide is no only a better cr donor but also a better ir acceptor. This is 10 be expected on the basis of whatever polarity exists in the CO molecule (see Fig. 5.18) and the fact that the ir antibonding orbital is concentrated on the carbon atom (see Fig. 5.20), which favors overlap with the metal orbital. The superior r accepting ability of CO also accounts for the instability of carbonyl dinitrogen complexes. Both Cr(CO)sN2 and cis-... 

In 1982, a most remarkable reaction was discovered by Bercaw et al. which involved the reductive coupling of the terminal carbonyl ligands of [CpFe(CO)2]2- When 1 equivalent of the permethylated zirconocene dinitrogen complex [(rj-CsMe Zr k (29) was treated with 2 equivalents of [CpFe(CO)2]2 in toluene above -20°C, 3 equivalents of N2 evolved... 

Increased-valence formulae have been drawn up for some dinitrogen complexes and, in the most stable state, the bonding is considerably different from that in carbonyl complexes. ... 

A number of (CO)2(L)2Fe(j7 -carbonyl) complexes have been isolated (113) rf--C=0). These have been prepared by replacement of N2 from /r-dinitrogen complexes (112) by the aldehyde in question. Two phosphine or phosphite ligands appear to be necessary for satisfactory stability of these complexes. This is in apparent agreement with the results of both ab initio see Ab Initio Calculations) and EHMO calculations and emphasizes the importance of d tt back-donation to the overall bonding in these complexes. The EHMO calculations also emphasize the role of the repulsive fom-electron ligand-ligand interactions in determining the likelihood of rf-coordination. 

The 18-Electron Rule 624 Metal Carbonyl Complexes 630 Nitrceyl Complexes 650 Dinitrogen Complexes 653... 

Dinitrogen complexes of titanocene and zirconocene are excellent sources for generating metallocene species in situ, which are highly active and are readily trapped by organic and inorganic unsaturated compounds. Eq (13) is an example that involves carbonyl coupling in iron-carbonyl to give the metallacyclic compound [118]. 

The dinitrogen complexes are very reactive, undergoing facile ligand substitution reactions with a variety of added Lewis bases. For example, exposure to carbon monoxide gas produced the carbonyl complexes Tp °Co-CO in quantitative yield. 

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