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F-block metallocene
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F-block metallocene
In organometallic chemistry, f-block metallocenes are a class of sandwich compounds consisting of an f-block metal and a set of electron-rich ligands such as the cyclopentadienyl anion.
The first prepared and well-characterized f-block metallocenes were the tris(cyclopentadienyl) lanthanide complexes, (C5H5)3Ln (Ln = La, Ce, Pr, Nd, Sm and Gd). However, their significance is limited more to their existences and structures than to their reactivity. The cyclopentadienyl ligands of f-block metallocenes were considered as inert ancillary ligands, only capable of enhancing their stability and solubility, but not their reactivity. In addition, only late and small metals in the lanthanide series, i.e., elements from Sm to Lu, are trivalent metallocene complexes, [(C5H5)2LnZ]n In 1980, the pentamethylcyclopentadienyl ligand, C5Me−
5, was introduced to prepare the lanthanide complexes with all metals in the series. Apart from improving the stability and solubility of the complexes, it was demonstrated to participate in organometallic reactions. Subsequently, William J. Evans and his coworkers successfully isolated (C5Me5)2Sm(THF)2 and (C5Me5)2Sm, making a breakthrough in f-block metallocenes, since both of these two organosamarium(II) complexes were unexpectedly found to participate in the coordination, activation and transformation of a variety of unsaturated compounds, including olefins, dinitrogen, internal alkynens, phosphaalkynes, carbon monoxide, carbon dioxide, isonitriles, diazine derivatives, imines and polycyclic aromatic hydrocarbons (PAHs). Moreover, due to its strong reducing potential, it was used to synthesize [(C5Me5)2Sm(μ-H)]2 and other trivalent f-block element complexes. Subsequently, tris(pentamethylcyclopentadienyl) lanthanide complexes, (C5Me5)3Ln, and their relevant complexes were synthesized from Sm2+ complexes. These metallocenes included (C5Me5)3Sm, [(C5H3(SiMe3)2]3Sm, (C5Me5)2Sm(C5H5), [(C5Me5)2Sm]2(μ-C5H5). Later, one tris(pentamethylcyclopentadienyl) f-element halide complex, (C5Me5)3UCl, was successfully isolated as the intermediate of the formation of (C5Me5)2UCl2. It is worthy mentioning that (C5Me5)3UCl has a very similar structure as (C5Me5)3U and its uranium-chloride bond (2.90 Å) is relatively longer than the uranium-chloride bonds of other analogues. Its existence also indicates that the larger f-block elements are capable of accommodating additional ligands in addition to the three cyclopentadienyl ligands resulting in the isolation of the following complexes: (C5Me5)3UF, (C5H3(TMS)2)3Th and (C5Me5)3ThH.
I. the synthesis of the first f-block metallocenes is described by following equation:
II. Preparation of (C5Me5)3Sm:
(i) the first (C5Me5)3Sm was prepared via exploratory Sm2+ chemistry with cyclooctatetraene:
(ii) Similar to method (i), (C5Me5)3Sm can be efficiently synthesized from a Sm2+ precursor and (C5Me5)2Pb:
In this pathway, (C5Me5)2Sm(OEt2) is used since it is more readily available than (C5Me5)3Sm and does not react THF.
(iii) additionally, (C5Me5)3Sm can also be prepared from trivalent precursors, without ring opening THF.
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F-block metallocene
In organometallic chemistry, f-block metallocenes are a class of sandwich compounds consisting of an f-block metal and a set of electron-rich ligands such as the cyclopentadienyl anion.
The first prepared and well-characterized f-block metallocenes were the tris(cyclopentadienyl) lanthanide complexes, (C5H5)3Ln (Ln = La, Ce, Pr, Nd, Sm and Gd). However, their significance is limited more to their existences and structures than to their reactivity. The cyclopentadienyl ligands of f-block metallocenes were considered as inert ancillary ligands, only capable of enhancing their stability and solubility, but not their reactivity. In addition, only late and small metals in the lanthanide series, i.e., elements from Sm to Lu, are trivalent metallocene complexes, [(C5H5)2LnZ]n In 1980, the pentamethylcyclopentadienyl ligand, C5Me−
5, was introduced to prepare the lanthanide complexes with all metals in the series. Apart from improving the stability and solubility of the complexes, it was demonstrated to participate in organometallic reactions. Subsequently, William J. Evans and his coworkers successfully isolated (C5Me5)2Sm(THF)2 and (C5Me5)2Sm, making a breakthrough in f-block metallocenes, since both of these two organosamarium(II) complexes were unexpectedly found to participate in the coordination, activation and transformation of a variety of unsaturated compounds, including olefins, dinitrogen, internal alkynens, phosphaalkynes, carbon monoxide, carbon dioxide, isonitriles, diazine derivatives, imines and polycyclic aromatic hydrocarbons (PAHs). Moreover, due to its strong reducing potential, it was used to synthesize [(C5Me5)2Sm(μ-H)]2 and other trivalent f-block element complexes. Subsequently, tris(pentamethylcyclopentadienyl) lanthanide complexes, (C5Me5)3Ln, and their relevant complexes were synthesized from Sm2+ complexes. These metallocenes included (C5Me5)3Sm, [(C5H3(SiMe3)2]3Sm, (C5Me5)2Sm(C5H5), [(C5Me5)2Sm]2(μ-C5H5). Later, one tris(pentamethylcyclopentadienyl) f-element halide complex, (C5Me5)3UCl, was successfully isolated as the intermediate of the formation of (C5Me5)2UCl2. It is worthy mentioning that (C5Me5)3UCl has a very similar structure as (C5Me5)3U and its uranium-chloride bond (2.90 Å) is relatively longer than the uranium-chloride bonds of other analogues. Its existence also indicates that the larger f-block elements are capable of accommodating additional ligands in addition to the three cyclopentadienyl ligands resulting in the isolation of the following complexes: (C5Me5)3UF, (C5H3(TMS)2)3Th and (C5Me5)3ThH.
I. the synthesis of the first f-block metallocenes is described by following equation:
II. Preparation of (C5Me5)3Sm:
(i) the first (C5Me5)3Sm was prepared via exploratory Sm2+ chemistry with cyclooctatetraene:
(ii) Similar to method (i), (C5Me5)3Sm can be efficiently synthesized from a Sm2+ precursor and (C5Me5)2Pb:
In this pathway, (C5Me5)2Sm(OEt2) is used since it is more readily available than (C5Me5)3Sm and does not react THF.
(iii) additionally, (C5Me5)3Sm can also be prepared from trivalent precursors, without ring opening THF.