Lanthanides and actinides: Annual survey of their organometallic chemistry covering the years 2001 and 2002

Transition‐Metal‐Catalyzed Hydroamination Reactions

“…Benchmark reactivity for new catalyst systems is often established using diphenylacetylene, where regioselectivity is not a challenge (Table 15.2). Doye has carried out extensive investigations with a variety of amines and a range of catalysts (3a-c, 4a-c, 6a-c), including various preprepared imido complexes, 15 in the work completed in collaboration with Gade [31,32]. Notably, arylamines are the most reactive substrates, while less sterically demanding alkylamines, such as benzylamine and linear alkylamines, are some of the most challenging substrates (Table 15.2, entries [9][10][11][12][17][18][19].…”

“…These observations are consistent with the aforementioned [2+2] mechanism where the intermediate imido species that is formed in situ can undergo deleterious dimerization [33] thereby reducing catalytic reactivity. Indeed, the bulkier substrates that are less prone to such dimerization, such as tert-butylamine or cyclohexylamine (Table 15.2, entries 5-8, [13][14][15][16], show much improved yields using standardized reaction times. Interestingly, the Schafer group [34] has established that group 4 complexes can indeed be used for the intermolecular hydroamination of alkynes with secondary amines consistent with a shift in mechanism from the established [2+2] cycloaddition pathway.…”

“…While this alternative ligand system results in the preparation of discrete complexes that have been rigorously characterized, no significant advances in substrate scope or reactivity have been disclosed for these systems. 15 from Odom (13) takes advantage of the known fluxional binding modes (η 5 and η 1 ) of the pyrrolyl moiety ( Figure 15.4). Notably, the reported Ti version of this precatalyst is known to be a highly effective catalyst for intermolecular alkyne hydroamination [56], although for intramolecular alkene hydroamination, the Zr version shows much improved reactivity [45].…”

“…Notably, following these initial investigations on Zr, Ti complexes have been found to have particularly promising reactivity for both inter-and intramolecular reactions. 15 …”

“…Rare earth catalysts (including Sc, Y, and La) have been reviewed elsewhere and are not extensively discussed here [10,[12][13][14][15][16][17][18][19]. All recent results will be presented in the context of historical contributions, and primary references for selected contributions to the field previous to 2008 will be provided.…”