New highly active heteroscorpionate-containing lutetium catalysts for the hydroamination of aminoalkenes: Isolation and structural characterization of a dipyrrolidinide-lutetium complex

Antonio Otero*, Agustín Lara-Sánchez, Carmen Nájera, Juan Fernández-Baeza, Isabel Márquez-Segovia, José Antonio Castro-Osma, Javier Martínez, Luis F. Sánchez-Barba, Ana M. Rodríguez

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The reactions of the hybrid scorpionate/cyclopentadiene compounds, as a mixture of regioisomers-1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]- 1,3-cyclopentadiene and 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]- 1,3-cyclopentadiene (bpzcpH) and 1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert- butylethyl]-1,3-cyclopentadiene and 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert- butylethyl]-1,3-cyclopentadiene (bpztcpH)-with [Lu(CH 2SiMe 3) 3(thf) 2] proceed in very high yields to give the free solvent neutral heteroscorpionate dialkyl lutetium complexes [Lu(CH 2SiMe 3) 2(bpzcp)] (1) and chiral [Lu(CH 2SiMe 3) 2(bpztcp)] (2). The structures in solution of 1 and 2 were investigated by VT NMR spectroscopy, and a fluxional behavior corresponding to an exchange between the alkyl groups was observed. The lutetium complex [Lu(CH 2SiMe 3) 2(bpztcp)(thf)] (3) was isolated as an enantiomerically enriched complex. Supramolecular CH-π interactions between molecules in crystals of 3 have been identified in its X-ray molecular analysis, and they explain the formation of a conglomerate among molecules of 3. Complexes 1-3 are efficient catalysts for the intramolecular hydroamination of aminoalkenes, giving TOF values of up to 475 h -1 at 90 °C for 2,2-diphenyl-pent-4-enylamine (4) by using complex 3 as catalyst. Enantioselectivities up tp 70% ee were achieved in the cyclization of the 1,2-disubstituted olefin 6 with the high enantiopurity complex 3. The hydroamination reactions show apparently zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration. Additionally, bicyclization of 2-allyl-2-methylpent-4-enylamine (10) was achieved at 60 and 100 °C, giving exo,exo-2,4,6-trimethyl-1-azabicyclo[2.2. 1]heptane (12). The protonolysis reaction of complex [Lu(CH 2SiMe 3) 2(bpztcp)] (2) with 2 equiv of 2,2-diphenyl-pent-4- enylamine (4) yielded a dipyrrolidinide lutetium complex [Lu(NC 4H 5-2-Me-4,4-Ph 2) 2(bpztcp)] (13) as a mixture of two diastereoisomers. The structures of the complexes were determined by spectroscopic methods, and the X-ray crystal structures of 3 and 13 were also established.

Original languageEnglish
Pages (from-to)2244-2255
Number of pages12
JournalOrganometallics
Volume31
Issue number6
Early online date6 Mar 2012
DOIs
Publication statusPublished - 26 Mar 2012

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