Yttrium and Aluminum Alkyl Complexes of a Rigid Bis-Anilido NON-Donor Ligand: Synthesis and Hydroamination Catalysis

Abstract

The palladium-catalyzed coupling of 4,5dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene (XBr 2 ) with 2 equiv of 2,4,6-triisopropylaniline afforded the proligand 4,5bis(2,4,6-triisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H 2 XN 2 ), and reaction of H 2 XN 2 with [Y-(CH 2 SiMe 2 R) 3 (THF) 2 ] (R = Me, Ph) produced the monoalkyl yttrium complexes [(XN 2 )Y(CH 2 SiMe 2 R)(THF)] (R = Me (1a), Ph (1b)). Neutral 1a showed near-zero ethylene polymerization activity (1 atm, 20 and 80 °C), and in the presence of AlMe 3 , 1a converted to [(XN 2 )Y{(μ-Me) 2 AlMe 2 }(THF)] (2). Compound 2 is thermally robust, and transfer of the XN 2 ligand from yttrium to aluminum was not observed even at elevated temperatures. However, [(XN 2 )AlMe] (3) was accessible via the reaction of H 2 XN 2 with AlMe 3 , demonstrating the ability of the wide-bite-angle XN 2 ligand to coordinate to much smaller aluminum(III). Neutral 1a proved to be highly active for both intra-and intermolecular hydroamination with various substrates, yielding Markovnikov products in the intermolecular hydroamination reactions with 1-octene. Article pubs.acs.org/Organometallics

Rigid NON-donor pincer ligand complexes of lutetium and lanthanum: synthesis and hydroamination catalysis

“…These complexes were targeted in order to probe the effectiveness of the rigid XN 2 pincer ligand to support robust alkyl derivatives of smaller and larger rare earth elements, and to assess the activity of the complexes for alkene and alkyne hydroamination. , which we previously reported, 10 and is indicative of C s symmetry in solution, with two Ar-H, ortho-CHMe 2 and CMe 2 peaks. Compound 1 was found to be fairly thermally stable, being only 25% decomposed aer 24 h at 90 C.…”

“…Nevertheless, the ability of 1 and the yttrium analogue to catalyze these more challenging intramolecular hydroamination reactions at room temperature stands these catalysts apart from most others. 10 Compound 1 also catalyzed intermolecular hydroamination with 4-tert-butylaniline, 4-tert-butylbenzylamine and octylamine in combination with 1-octene and diphenylacetylene, and in all reactions with 1-octene, the Markovnikov product was formed selectively. These reactions were performed in toluene at 110 C and the degree of conversion was determined by GC-MS (Table 2).…”

“…This orientation is mirrored in [(XN 2 )Y(CH 2 SiMe 3 )(THF)], which displayed a backbone angle of 25 and a very similar geometry at the rare earth metal. 10 Lutetium is 5-coordinate with the three anionic donors and coordinated THF arranged in an approximate tetrahedron around the metal center. The largest angle in this approximate tetrahedron is the N(1)-Lu-N(2) angle of 130 , and the smallest is the O(2)-Lu-C(54) angle of 97 , while the other angles are between 102 and 110 .…”

“…1) reported recently by the Emslie group. 10 For trivalent rare earth catalyzed alkene hydroamination, catalytic activity typically increases in parallel with metal ionic radius. For example, in cyclization reactions with H 2 C] CHCH 2 CMe 2 CH 2 NH 2 , the activity of [Cp {C 6 H 4 (CH 2 NMe 2 )-o}] (c in Fig.…”

“…[19][20][21][22][23][24][25][26][27][28][29] As noted above, we previously described the synthesis and hydroamination activity of [(XN 2 )Y(CH 2 SiMe 3 )(THF)] (XN 2 ¼ 4,5-bis(2,4,6-triisopropylanilido)-2,7-di-tert-butyl-9,9dimethylxanthene; d in Fig. 1), 10 and in this work we report the synthesis of lutetium and lanthanum XN 2 complexes. These complexes were targeted in order to probe the effectiveness of the rigid XN 2 pincer ligand to support robust alkyl derivatives of smaller and larger rare earth elements, and to assess the activity of the complexes for alkene and alkyne hydroamination.…”