Hydrogenative Catalysis with Three‐Coordinate Zinc Complexes Supported with PN Ligands is Enhanced Compared to PNP Analogs

Abstract

This work details the synthesis, characterization, and catalytic activity of reactive low-coordinate organozinc complexes. The complexes activate hydrogen and they appear to be more active in hydrogenation of ketones and imines than their tridentate pincer analogs. This is thought, in part, to be due to the lack of trailing third phosphorus arm present in previous work. DFT computations reveal a sigmabond metathesis mechanism is comparable to an alternative aromatization/dearomatization metal-ligand cooperative mechanism.

Synthesis and Characterization of Dearomatized Pyridine‐Derived Alkyl‐Amido‐tert‐Butylphosphine Iron(II) Complexes

“…The [PN'À FeÀ CH 2 R] complexes are closely analogous to the known [PN'À ZnÀ X] complexes that we prepared earlier (Scheme 1, middle left). [12] In addition, we recognized that three-coordinate [PN'À FeÀ CH 2 R] complexes approach satisfying the criteria and sought to synthesize iron alkyls as part of our coordination chemistry project with the pyridine derived PN ligands. [12][13][14] The iron targets included well-defined [PN'À Fe II À (CH 2 R) n ] 1À n (n = 1 or 2) complexes with dearomatized backbones, such as the ones shown above formed using the PNÀ FeCl 2 starting materials (i. e., 1 R , R=H, Me) (Scheme 1, bottom).…”

“…[12] In addition, we recognized that three-coordinate [PN'À FeÀ CH 2 R] complexes approach satisfying the criteria and sought to synthesize iron alkyls as part of our coordination chemistry project with the pyridine derived PN ligands. [12][13][14] The iron targets included well-defined [PN'À Fe II À (CH 2 R) n ] 1À n (n = 1 or 2) complexes with dearomatized backbones, such as the ones shown above formed using the PNÀ FeCl 2 starting materials (i. e., 1 R , R=H, Me) (Scheme 1, bottom). Despite some success (topic of this report), we initially abandoned the chemistry because of the exceptional reactivity of the complexes leading to "decomposed" ill-defined black solutions, precipitates, or paramagnetic oils that defied our attempts at purification and crystallography.…”

Catalytic, Z-Selective, Semi-Hydrogenation of Alkynes with a Zinc–Anilide Complex

“…14 Very recently, Lacy and co-workers have reported a well-defined Zn catalyst for the hydrogenation of benzophenone and N-benzyl-1-phenylmethanimine. 15 Despite these reports, the application of zinc to hydrogenation catalysis remains understudied, with substrates limited to highly polarized species. Furthermore, the issue of selective hydrogenation with these types of catalysts is yet to be addressed.…”

“…Stephan and co-workers also used a zinc-based catalyst for the hydrogenation of imines and ketones. , Milstein and co-workers provided an example of zinc-catalyzed hydrogenation of imines and ketones, using a PNP pincer ligand to facilitate dihydrogen activation through metal-ligand cooperation . Very recently, Lacy and co-workers have reported a well-defined Zn catalyst for the hydrogenation of benzophenone and N-benzyl-1-phenylmethanimine . Despite these reports, the application of zinc to hydrogenation catalysis remains understudied, with substrates limited to highly polarized species.…”

Aminophthalimide as a mimetic of purines and a fluorescent RNA base surrogate for RNA imaging

“…14 Tor et al established a whole set of fluorescent and isomorphic thienonucleoside surrogates, for instance the G analog th G, as an emissive “RNA alphabet”. 15,16 They all, in common, bind specifically to one of the natural RNA components as complementary counterbases. This restricts their usage to specific sites given by the sequence of the RNA probe.…”