Metal-ligand bond strength trends

The trend in bond strengths for the T-metals is opposite to that which is found for the main group elements for example, the metal-ligand bond strength is ordered by 3d 4d < 5d. 

The data for the 1,2-diaminoethane complexes now parallels the trends in ionic radius and LFSE rather closely, except for the iron case, to which we return shortly. What is happening Copper(ii) ions possess a configuration, and you will recall that we expect such a configuration to exhibit a Jahn-Teller distortion - the six metal-ligand bonds in octahedral copper(ii) complexes are not all of equal strength. The typical pattern of Jahn-Teller distortions observed in copper(ii) complexes involves the formation of four short and two long metal-ligand bonds. 

In 2001, Schumann and co-workers reported a similar set of metallocene complexes with l,3-di- o-propyl-4,5-dimethylimidazoly-2-ylidene.22 X-ray crystallography and NMR studies confirmed a similar trend between metal-carbene bond strength and alkaline earth metal as that found by Arduengo and co-workers. Additionally they showed that as the steric bulk of the cyclopentadienyl ligand increases the metal-carbene bond distance is elongated. 

In this contribution we shall present several applications of the new method, which we shall refer to as LSD/NL, to the calculation of bond energies of transition metal complexes. We shall focus on trends along a transition period and/or down a transition triad. The following subjects will be discussed a) metal-metal bonds in dimers of the group 6 transition metals b) metal-ligand bonds in early and late transition metal complexes c) the relative strength of metal-hydrogen and metal-methyl bond in transition metal complexes d) the metal-carbonyl bond in hexa- penta-and tetra-carbonyl complexes. 

The dependence of the observed rate constant on the identity of the departing ligand tends to be less than the dependence on the property of the incoming nucleophile, but is large enough to be easily detected. This dependence correlates with the strength of the metal-ligand bond. For the reaction of Pt(dien)X with pyridine in Table 5.4, this dependence follows the trend X = NOj > H,0 > CP > Br > P > Nj > SCN > NO/ > CN. " Since these substitutions are associative, this trend reflects the extent to which the M-X... 

In a dissociative process the reaction rate is expected to decrease as the strength of the metal to leaving ligand bond increases. This trend is generally observed in Co(III) ammine complexes. As can be seen in Table 2, a partial leaving group order is... 

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