Homoleptic complexes group

Scheme 8.1 Three key methods of the synthesis of lanthanide(lll) bis(phthalocyanine) complexes. Homoleptic complexes symmetrical (A, B) and unsymmetrical (C1 and C2, D1). Thereby, the thermal fusion group A can be subdivided into (A1) solvent free fusion (A2) refluxing in the mixture of protic solvents in the presence of organic base - DBU and (A3) MW assisted fusion.

Particularly interesting are the homoleptic complexes 46 to 49 (Figure 2.3-7) in which Ni or Pt atoms are tetrahedrally coordinated by four Ga-R or In-R ligands [71, 72]. These compounds are analogues of Ni(CO)4. They have relatively short M-Ga or M-In bond lengths, and quantum-chemical calculations verify an effective 71-back bonding of electron density from the transition metal atom into the empty p-orbitals of the E-R groups. 

Inspection of Table 7.13 leads to the conclusion that the Fe-EMe BDEs of the homoleptic complexes Fe(EMe)5 are higher than their counterparts predicted for the (CO)4Fe-EMe bonds. The homoleptic group-13 complexes M(EMe)4 are also predicted to have high bond energies, except for the Pt-AlCp and Pt-GaCp BDEs in Pt(dhpe) (ECp)2 that are rather low. 

As discussed above, lanthanides and group 3 homoleptic complexes are attractive initiators because of their moderate Lewis acidities, good activities of polymerization, and low toxicity [94, 111, 112, 115-118]. A list of lanthanide initiators and their polymerization activity is listed in Table 5. 

Carboxylic acid amide functionalised imidazolium salts can be reacted with group 10 halides directly in the presence of an inorganic base (e.g. K COj) to form homoleptic complexes (see Figure 4.41) [122]. Interestingly, the carbene units are cis to each other and not trans as would be expected (see Figures 4.30 and 4.38). The cis complexation is not aided by hydrogen bonding as the carboxylic acid amide functionality loses its proton upon complexation to nickel. 

Reaction of the same functionalised imidazolium salt with PdCl produced interesting results [123], In the presence of pyridine as base, the simple palladium(ll) carbene adduct was formed (see Figure 4.42), but when K COj was used as base, activation of the amide functional groups produced the corresponding homoleptic complexes, as a mixture of the cis and trans isomers. 

The reaction between Pd(acac)2 and lithium / -diketiminate, a nitrogen derivative of acac, gives a mixed-ligand and homoleptic complex. Interestingly, these complexes are stable at ambient temperature, but in acetonitrile solution they decompose to elemental Pd presumably due to reaction of Pd(II) and the acac ligand. Fmthermore, in pentane or ether solution the complex can isomerize into the thermodynamically stable form. Both isomers are similar, but their NMR spectra are inequivalent due to an asymmetric structure with nonrotating substituents. Since one of the imine groups is coordinated to the Pd ion, this isomerization results in the formation of a chiral center at the coordinated C atom. 

Complexes in which a metal is bound to only one kind of donor group, e.g. [Co(NH,),], are known as homoleptic Complexes in which a metal is bound to more than one kind of donor group, e.g. [Co(NHd,Ck]. are known as heteroleptic. 

The EDA results for the complexes (CO)4Fe-EMe (Table 13.21) are very similar to those of (CO)4Fe-EPh (Table 13.20). This means that the methyl and phenyl groups behave as weak rr-donor groups. A comparison of the bonding analysis of the homoleptic complexes Fe(EMe)5 (Table 13.22) with the results of the heteroleptic species (CO)4Fe-EMe (Table 13.21) shows that the BDEs of the former are higher than those of the latter. The EDA data suggest that the higher bond strength of... 

The EDA results of the group-10 homoleptic complexes TM(EMe)4 (E = B-Tl, TM = Ni, Pd, Pt) are given in Table 13.23. The data indicate that the statement concerning significant Fe ER Tr-backdonation holds also true for other transition metals. In TM(EMe)4 (TM = Ni, Pd, Pt), the contribution of TM —> EMe ir-backdonation is between 33-49% of the covalent term However, the bonding... 

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