Kinetic Control and Multiple Mechanisms for CH Bond Activation by a ZrN Complex

Abstract

The [Cp*CpZrNCMe3(thf)] system provides the first direct measurement of kinetic selectivity in sp, sp2, and sp3 CH bond activation with Group 4 imido complexes. This feature allows the design of selectivity and mechanistic experiments to probe the 1,2‐RH‐addition event. Substrates reacting with the highest relative rates generally form the most thermodynamically stable products. Cp*=η5‐C5Me5, Cp=η5‐C5H5.

Mechanistic Studies and Expansion of the Substrate Scope of Direct Enantioselective Alkynylation of α-Ketiminoesters Catalyzed by Adaptable (Phebox)Rhodium(III) Complexes

“…The result suggests that C–H bond cleavage is not involved in the turnover-limiting step because normal kinetic isotope effects ( k H / k D > 1) are expected under such conditions. The observed inverse kinetic isotope effects could be due to hybridization-induced changes of the terminal carbon of the alkyne 3 from sp to sp 2 in the transition state . On the basis of the fact that hybridization of the carbon on alkynes changes from sp to sp 2 upon coordination to transition metal complexes, coordination of alkyne 3 to (amido)­rhodium­(III) complex 6 , rather than deprotonation of the terminal alkyne 3 , would be the turnover-limiting step in the overall catalytic cycle …”

Catalytic nitrene transfer by a zirconium(iv) redox-active ligand complex

“…1,2 Imido complexes of electrophilic early transition metals have highly polarized metal-nitrogen multiple bonds that enable non-redox reactivity such as catalytic hydroamination [3][4][5][6] and C-H bond activation. [7][8][9][10] In contrast, imido complexes of late transition metals are less polarized, but can effect olefin aziridination [11][12][13] and C-H bond amination. [14][15][16][17][18][19] It would be attractive to combine the features of early-and late-metal imido complexes such that species both with highly polarized metal-imido bonds and capable of two-electron reactivity could be studied.…”

Synthesis of Titanium Borylimido Compounds Supported by Diamide-Amine Ligands and Their Reactions with Alkynes

“…16a Finally, Bergman has proposed (on the basis of kinetic isotope data) that the reaction of Cp*CpZr(N t Bu)(THF) with t BuCCH to form the amide-acetylide Cp*CpZr{N(H) t Bu}(CC t Bu) proceeds via a (nonobserved) metallacycle intermediate. 30 We were interested to gain further insight into the mechanistic and energetic aspects of these alkyne C−H addition/ elimination reactions of borylimido complexes and to search for further examples of this type of kinetic versus thermodynamic control. Furthermore, the C−H activation reaction of 11 with Ar F CCH was too fast for convenient kinetic NMR analysis.…”

“…1.8 × 10 −3 mol dm −3 s −1 for the rate 1) is consistent with values reported for a number of other C−H bond activation and formation processes at group 4 metal centers. 4b, 28,30,32 The magnitudes of such isotope effects and their origins have been discussed in these previous papers and reviews. 1l, 33 The KIE for the reaction of 21 is indicative of a process having a transition state in which the transfer of H is relatively linear.…”