Other Amine Ligands

Co(en)2(/3-AlaOi-Pr)](C104)3 in aqueous solution (49). We add some further information on these two studies here. Both esters are bound via terminal amino-iV as well as carbonyl-O. Such chelation stabilizes carbonyl-0 coordination and the O-donor is not displaced from the metal at any stage. The other amine ligands surrounding Co(III) provide the necessary octahedral ligand field (27), and we have found the... 

IR data supported the formation of rhodium carbonyl anions on addition of amine suggesting a mechanism in which these anions are in equilibrium with the active species, a hydrido rhodium carbonyl containing coordinated amine. Such a mechanism provides an explanation for the variation in catalyst activity with amine concentration and basicity and affords a method for predicting the effect of other amine ligands. 

Most ruthenium catalysts used in epoxidation reactions are based on bulky porphyrins or other amine ligands and require the use of PhIO and Cl2PyNO as oxidants. For examples see the reviews in Refs. [5,6,45] and some recent examples by Liu and coworkers [46,47] and Jitsukawa et al. [48]. Examples for the aerobic epoxidation of alkenes are the ruthenium mesityl porphyrin complex Ru(TMP)(0)2, where TMP is 5,10,15,20-tetramesitylporphyrinato, of Groves and Quinn [12] in 1985 (Eq. 7), the ruthenium dimethylphenanthroline complex, czs-[Ru(2,9-dimethyl-l,10-phenanthroline)(CH3CN)2]2+ published by Goldstein et al. [23] in 1994 (Eq. 8), and the ruthenium POM catalyst [WZnRu2(0H)(H20)](ZnW9034)2 n of Neumann and Dahan [49] in 1997 (Eq. 9). 

For Rh (and also Ir) cationic species with NH3 and other amine ligands are known, generally of the types [ML6]3+, [ML5X]2+, and [ML4X2]+ they are usually made from aqueous solutions of RhClj. 

The II state, d6. An enormous number of Ru and Os complexes with CO, PR3 and similar 7t-acid ligands are known. For other ligands, the main chemistry is that of chloro, ammonia and other amine ligands, and again I large numbers of complexes exist. The aquo ion, [Ru(H20)6]2 + has been prepared, but it is readily oxidized to [Ru(H20)6]3+. For osmium the best characterized complexes are those with aromatic amines. 

AT-heterocyclic carbenes show a pure donor nature. Comparing them to other monodentate ligands such as phosphines and amines on several metal-carbonyl complexes showed the significantly increased donor capacity relative to phosphines, even to trialkylphosphines, while the 7r-acceptor capability of the NHCs is in the order of those of nitriles and pyridine [29]. This was used to synthesize the metathesis catalysts discussed in the next section. Experimental evidence comes from the fact that it has been shown for several metals that an exchange of phosphines versus NHCs proceeds rapidly and without the need of an excess quantity of the NHC. X-ray structures of the NHC complexes show exceptionally long metal-carbon bonds indicating a different type of bond compared to the Schrock-type carbene double bond. As a result, the reactivity of these NHC complexes is also unique. They are relatively resistant towards an attack by nucleophiles and electrophiles at the divalent carbon atom. 

A number of metal carbonyls undergo disproportionation reactions in the presence of other coordinating ligands. For example, in the presence of amines, Fe(CO)5 reacts as follows ... 

Replacement of the NH3 group(s) in ds-DDP with other amines affects only little the hydrolysis rate of the Cl" ligand(s) (Table 1). Accordingly, the rate constant for the hydrolysis of the first Cl" ligand from dj4PtCl2(NH3)(NH2C6Hn)] (Figure 2) is comparable to that of... 

Fig. 5. Ten types of different structures identified by X-ray diffraction, where the abbreviated N-0 is used to express each bridging amidate ligand and X denotes axial donors such as OH2, N03, N02 (nitro), Cl, and Br. For the compounds involving axial ligands (X), the total complex charge is given assuming that X is a monoanion. Note that, in some cases, amine ligand in cis-Pt(NH3)2 will be replaced with other ligands, such as in Pt(en), cis-Pt(NH3)Cl, cis-PtCl2, and Pt(bpy).

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