Comparison of Decamethyldizincocene [(η⁵-Cp*)₂Zn₂] versus Decamethylzincocene [Cp*₂Zn] and Diethylzinc Et₂Zn As Precatalysts for the Intermolecular Hydroamination Reaction

Abstract

A comparison of the Zn−Zn bonded species [(η 5 -Cp*) 2 Zn 2 ] versus the related organometallic zinc compound [Cp* 2 Zn] and ZnEt 2 for the intermolecular hydroamination reaction in the presence of equimolar amounts of [PhNMe 2 H][B(C 6 F 5 ) 4 ] is reported. All compounds show high reaction rates under mild conditions and a good functional group tolerance for the addition of aniline derivatives to primary alkynes. Within this series the metallocene [Cp* 2 Zn] is the most active one, whereas the zinc−zinc bonded species [(η 5 -Cp*) 2 Zn 2 ] shows the best selectivity. Most remarkable is the unexpected excellent catalytic performance of the zinc−zinc bonded species [(η 5 -Cp*) 2 Zn 2 ].

Ethyl‐Zinc(II)‐Cation Equivalents: Synthesis and Hydroamination Catalysis

“…In our earlier studies we observed, in some hydroamination reactions of arylacetylene with substituted anilines, the formation of side products in small quantities that were not identified. [29] By using the very activec atalyst 4,w ecan now show that an intermolecular double-hydroamination of arylacetylene with differently substituted anilinest oab is-enamine takes place ( Table 3). Some of us published zinc-catalyzed domino hydroamination/alkyne addition reactions of secondary amines with terminal alkynes to give quaternary propargylamines.…”

“…Recently,s omeo fu sr eported an intermolecularh ydroamination reactionc atalyzed by [(h 5 -Cp*) 2 Zn 2 ], [Cp* 2 Zn],a nd ZnEt 2 , 1.943(6)114.6(6) Et-Zn-Et [25] (exp./calc. MP2/def2-QZVPP)1 .948 (5) 11 Cl 11 ] À ·(C 6 H 6 ) [3] 1.964 (6) [29,30] All compounds showed high reactionr ates under mild conditions and ag ood functional group tolerance for the addition of aniline derivatives to primary alkynes. As catalytic species for these and othera lkyl zinc catalyzed reactions, ac ationic species [RZn] + is anticipated.…”

“…For the latter reaction, in af ew cases we observed, besides the hydroamination product,s ome byproduct that we have not so far identified. [29] For theser eactions, we applieda na mine to alkyne ratio of 1:1.5, which turned out to be beneficial for the reactionr ate. Usually al arger excesso fa lkyne does not significantly influence the rate.…”

“…For comparison, the recentlyr eported results of our screening with the ZnEt 2 /[PhNMe 2 H][B(C 6 F 5 ) 4 ]s ystem as catalyst are given (italice ntries in Ta ble 2) althoughs lightly different conditions were used in the earlier studies (amine to alkyner atio of 1:1.5). [29] We chose the 1:2r atio for ab etter comparison with the results of the doubleh ydroamination (see below). Althought he conditions are different in some cases, compound 4 is, in general,m ore active than the ZnEt 2 /[PhNMe 2 H][B(C 6 F 5 ) 4 ] catalystsystem.…”

H2‐Aktivierung, Hydridbildung und katalytische Hydrierung von Iminen mit Zinkkomplexen von C5Me5 und N‐heterocyclischen Carbenen

“…Die Organozinkverbindungen [ZnCp* 2 ] und [Zn 2 Cp* 2 ] wurden von Blechert und Roesky et al. erfolgreich in katalytischen Hydroaminierungen getestet 11. Beller et al.…”