Solid‐State NMR and DFT Studies on the Formation of Well‐Defined Silica‐Supported Tantallaaziridines: From Synthesis to Catalytic Application

Abstract

Single-site, well-defined, silica-supported tantallaaziridine intermediates [≡Si-O-Ta(η(2) -NRCH2 )(NMe2 )2 ] [R=Me (2), Ph (3)] were prepared from silica-supported tetrakis(dimethylamido)tantalum [≡Si-O-Ta(NMe2 )4 ] (1) and fully characterized by FTIR spectroscopy, elemental analysis, and (1) H,(13) C HETCOR and DQ TQ solid-state (SS) NMR spectroscopy. The formation mechanism, by β-H abstraction, was investigated by SS NMR spectroscopy and supported by DFT calculations. The C-H activation of the dimethylamide ligand is favored for R=Ph. The results from catalytic testing in the hydroaminoalkylation of alkenes were consistent with the N-alkyl aryl amine substrates being more efficient than N-dialkyl amines.

Evidence for Silica Surface Three- and Five-Membered Metallacycle Intermediates in the Catalytic Cycle of Hydroaminoalkylation of Olefins Using Single-Ti-Metal Catalysts

“…Interestingly, the isolated species was a three-membered cycle (called a metallaziridine 39−47 ) obtained at room temperature under vacuum (dynamic vacuum, 10 −5 mbar for 3 h) (Figure 5) and this three-membered metallacycle was very well characterized by FTIR, elemental analysis, SS NMR, and DNP SENS. 45,48 ■ THREE-MEMBERED-RING FRAGMENT: PREPARATION AND CHARACTERIZATION FTIR and elemental analysis have been carried out for the titanium tris(amido) complex. The obtained results were consistent with the proposed structure of the surface complex [(Si−O−)Ti(NMe 2 ) 3 ].…”

“…Interestingly, the isolated species was a three-membered cycle (called a metallaziridine − ) obtained at room temperature under vacuum (dynamic vacuum, 10 –5 mbar for 3 h) (Figure ) and this three-membered metallacycle was very well characterized by FTIR, elemental analysis, SS NMR, and DNP SENS. , …”

Supported Metal Pair-Site Catalysts

“… infrared (IR) spectroscopy for characterizing ligands on the metals; and  density functional theory (DFT) for understanding the structures and predicting reactivities. 13 C and 1 H NMR spectroscopies are also powerful for characterizing the organic ligands in metal complexes on supports, 35 but there are barely any examples of dinuclear species characterized by these methods, and we therefore provide no details here-but expect that the methods will become essential as the field emerges. We provide below brief summaries of characterization methods in addition to those in the list above.…”

Hydroamination and Hydroaminoalkylation of Alkenes by Group 3–5 Elements: Recent Developments and Comparison with Late Transition Metals

“…Hydroaminoalkylation of N -benzylmethylamine was also successful with these catalysts, but insertion occurred, in contrast to what was observed with tantalum amidate complexes, after activation of the methyl and not the benzylic group of the nitrogen atom. The general mechanism for the hydroaminoalkylation catalyzed by group 5 elements is represented in Scheme , with the reversible formation of the metallaziridine by C–H activation of the bisamide as a key step. This proposition has been supported thanks to labeling studies indicating important deuterium scrambling from the N -methyl- d 3 group of the labeled amine. ,, Olefin insertion, followed by protonolysis of the C–M bond and amido exchange, delivers the branched alkylated amine.…”