H₂ Activation across Manganese(I)–C Bonds: Atypical Metal–Ligand Cooperativity in the Aromatization/Dearomatization Paradigm

Abstract

Dehydrohalogenation of fac-Mn­(κ2-N,P-PicP)­(CO)3Br (1 H ) and fac-Mn­(κ2-N,P-LutP)­(CO)3Br (1 Me ) with equimolar K­[N­(SiMe3)]2 afforded the reactive, aromatized 18-electron complexes fac-Mn­(κ3-N,C,P-PicP)­(CO)3 (2 H ) and fac-Mn­(κ3-N,C,P-LutP)­(CO)3 (2 Me ), respectively, with atypical binding modes. 2 H and 2 Me activate H2 across the Mn­(I)–C bond to furnish hydride complexes fac-Mn­(κ2-N,P-PicP)­(CO)3H (4 H ) and fac-Mn­(κ2-N,P-LutP)­(CO)3H (4 Me ), respectively. Both 2 H and 2 Me were observed to produce dearomatized 18-electron complexes Mn­(κ2-N,P-PicP*)­(CO)4 (3 H ) and Mn­(κ2-N,P-LutP*)­(CO)4 (3 Me ), respectively, when reacted with CO. The reactive Mn­(I)–C moiety of 2 H and 2 Me reacts with a variety of electrophiles: benzyl cyanide to form fac-Mn­(κ3-N,N′,P-(LutP-BnCN))­(CO)3 (6), E-chalcone to form fac-Mn­(κ3-N,C,P-LutP-chalcone)­(CO)3 (7), and AlCl3 to form fac-Mn­(κ3-N,Cl,P-PicP-AlCl3)­(CO)3 (8 H ) and fac-Mn­(κ3 -N,Cl,P-LutP-AlCl3)­(CO)3 (8 Me ) featuring a rare intramolecular Mn-(μ-Cl)-Al moiety. Mn­(I)-catalyzed Michael addition was explored. Dehydrohalogenation of 1 H with alkoxides afforded the substituted complex fac-Mn­(κ2-N,P-PicP)­(OR)­(CO)3 (10 H ) that was also reactive toward H2 forming 4 H . Under identical conditions with alkoxide bases, 1 Me affords 2 Me demonstrating dichotomous behavior. We also explored the iPr-substituted analogues of 1 H and 1 Me (11 H and 11 Me , respectively) and found them to be essentially identical in behavior. Complexes 1 R and 11 R were found to be excellent catalysts for styrene hydrogenation. The relevance of the κ3-N,C,P binding mode discovered herein to catalysis is briefly discussed.

Impact of the Methylene Bridge Substitution in Chelating NHC‐Phosphine Mn(I) Catalyst for Ketone Hydrogenation

“…31 P NMR spectrum of 3 e exhibited a sole resonance at δ P 60.9 ppm indicating the transformation of both isomers of 2 e into a single compound. The 13 C resonance of the coordinated bridging carbon atom in 3 e was observed as a doublet at δ C 40.7 ppm ( 1 J PC =19.5 Hz) deshielded compared to those in 3 a (δ C 22.7 ppm) [19] or related κ 3 ‐PCN (δ C 9.6–10.1 ppm) and κ 3 ‐PCP (δ C −10.1–−12.8 ppm) cyclometallated Mn(I) species derived from phosphine‐pyridine [29] and dppm‐type [20] scaffolds, respectively. Finally, the signals of coordinated NHC and carbonyl ligands in 3 e were observed as a doublet at δ C 180.0 ppm ( 2 J PC =16.8 Hz) and two broad resonances at δ C 227.5 and 223.6 ppm, similar to those of compound 3 a [19] …”

Hydrogenation of Carboxylic Esters Catalyzed by Phosphine-Free Bis-N-heterocyclic Carbene Manganese Complexes

“…64%) and three broad minor signals (ν 1/2 = 35 Hz) at −9.60, −9.87, and −14.14 ppm (ca. 12%, 4%, and 20%, respectively) . At 60 °C, the same signals were observed after only 1 h, along with a complete conversion (Figure S7).…”

“…12%, 4%, and 20%, respectively). 28 At 60 °C, the same signals were observed after only 1 h, along with a complete conversion (Figure S7). The signal at −6.91 ppm is very similar to that reported by Royo in 2018 for the [Mn(BisNHC Me )(CO) 3 H] complex (δ = −6.82 ppm in CD 3 CN).…”

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

“…The [PN‘−Fe−CH 2 R] complexes are closely analogous to the known [PN‘−Zn−X] complexes that we prepared earlier (Scheme 1, middle left) [12] . In addition, we recognized that three‐coordinate [PN‘−Fe−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 [12–14] . The iron targets included well‐defined [PN‘−Fe II −(CH 2 R) n ] 1−n (n=1 or 2) complexes with dearomatized backbones, such as the ones shown above formed using the PN−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.…”