Lanthanide/group 3 complexes

Different main-group-, transition- and lanthanide-metal complexes can catalyze the cycloaddition reaction of activated aldehydes with activated and non-activated dienes. The chiral metal complexes which can catalyze these reactions include complexes which enable substrates to coordinate in a mono- or bidentate fashion. 

To date, the only organometallic lanthanide porphyrin complexes to be reported contain yttrium and lutetium, and they will be considered in the section on scandium. Representative structural types of porphyrin complexes containing groups 3 and 4 metals are shown in Fig. 3 and selected data for all the structurally characterized complexes are given in Table 11. 

Biuret (bu) co-ordinates transition metals in both neutral and anionic forms. Compounds containing neutral bu include both bis- and tetrakis-complexes. The latter are limited to the larger cations of the group II [e.g., [Sr(bu)4]2+ [9] and lanthanide groups e.g., [Sm(bu)4]2+ [ 10,11]. Only the former are considered in detail in this review, together with bis-complexes containing anionic bu as they have the greater potential for formation of 1-D chains and 2-D sheets. 

Substitution at the 2-position of the pyridine ring in PyO introduces steric hindrance to coordination as is evident from the formation of Heptakis-2-MePyO complexes with lanthanide perchlorates (167) and pentakis-2-MePyO complexes with the corresponding bromides (168), iodides (162) and chlorides (169). The lanthanide nitrate complexes prepared by Ramakrishnan and Soundararajan (170) have the formula Ln(2-MePy0)3(N03)3 -xH20in which all the nitrate groups are bidentate. 

Viewed as a group, aU of the lanthanide cyclopentadienyl complexes show the behavior expected if the metal-ring interaction were purely electrostatic in nature. 

Another lanthanide carboxylate complex that also contains nonacoordinated lanthanide ion in a monocapped square antiprismatic arrangement of nine oxygens is the erbium oxalate trihydrate with the composition Er(OOCCOO) (HOOCCOO) (OH2)3. This complex crystaUizes (767) in space group P4/ with 0 = 8.664, c =6.4209 A and Z=2, when the precipitate of erbium oxalate, ob-... 

Table 12.7 Ethylene polymerization based on supported group 3 and lanthanide metallocene complexes-examples from relevant patents.

MtfBy, M Bg, M B10, 3, 165 Group 10 complexes, 3, 167 lanthanide and actinide complexes, 3, 137 macropolyhedral metallaboranes, 3, 168 main group complexes, 3, 139 main group and lanthanide metal complexes, 3, 139 monoboron clusters, 3, 146... 

Pyrrole ligands can form both Ln-N or-bonds and tjs-n-Ln bonds. complexes with sterically less crowded pyrrole ligands [195]. The introduction of sterically demanding groups in a-position as in 2,5-di-fert-butylpyrrole led to a shielding of the nitrogen and subsequent -coordination to the lanthanide center [196]. Additionally, rj1-coordination to a sodium atom is observed in the obtained ate complex. 

Interaction of the nitrate ion with lanthanide(III) in acetonitrile solution was studied by conductivity, vibrational spectroscopy and luminescence spectroscopy. Bidentate nitrate with approximate C2V local symmetry was detected. FT-IR spectral evidence for the formation of [La(N03)5]2, where La = Nd, Eu, Tb and Er with coordination number 9.9 has been obtained [128]. Two inequivalent nitrate ions bound to lanthanides were detected by vibrational spectroscopy. The inequivalent nature varied with different lanthanides. For example three equivalent nitrate groups for La and Yb, one nitrate different from the other two for Eu ion were detected. Vibrational spectral data point towards strong La-NC>3 interaction in acetonitrile [129]. Stability constants for lanthanide nitrate complexes are given in Table 4.10. 

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