Earth-abundant metal pincer complexes have played an important role in homogeneous catalysis during the last ten years. Yet, despite intense research efforts, the synthesis of iron PC carbene P pincer complexes has so far remained elusive. Here we report the synthesis of the first PC NHC P functionalized iron complex [(PC NHC P)FeCl 2 ] ( 1 ) and the reactivity of the corresponding trans -dihydride iron(II) dinitrogen complex [(PC NHC P)Fe(H) 2 N 2 )] ( 2 ). Complex 2 is stable under an atmosphere of N 2 and is highly active for hydrogen isotope exchange at (hetero)aromatic hydrocarbons under mild conditions (50 °C, N 2 ). With benzene- d 6 as the deuterium source, easily reducible functional groups such as esters and amides are well tolerated, contributing to the overall wide substrate scope (e.g., halides, ethers, and amines). DFT studies suggest a complex assisted σ-bond metathesis pathway for C(sp 2 )–H bond activation, which is further discussed in this study.

The Z-selective functionalization of terminal alkynes is a useful transformation in organic chemistry and mainly catalyzed by noble metals. Here, we present the Z-selective hydroboration of terminal alkynes catalyzed by a stable trans-dihydride iron complex [(PCNHCP)­Fe­(H)2N2)] (2). Overall, the reaction occurs at room temperature and provides near quantitative yields of the Z-vinylboronate ester. Interestingly, the same catalyst could also provide the E-vinylboronate by heating the reaction mixture at slightly elevated temperatures (50 °C). If, however, the reaction is performed in the absence of HBpin, rapid Z-selective alkyne dimerization is observed, which is further discussed in this report.

No abstract

Catalytic aldehyde hydrogenation is an essential and routinely used chemical synthesis process in both academia and industry. However, there is a serious scarcity of efficient homogeneous catalysts for this process to work under highly demanding atmospheric-pressure, base-free, and aqueous conditions. Addressing this problem, herein, we report an iridium-based catalyst for facile atmospheric-pressure and base-free hydrogenation of various aromatic, heteroaromatic, and aliphatic aldehydes. The catalyst also displays excellent chemoselectivity toward aldehyde over other carbonyl functionalities and unsaturated motifs. Moreover, the catalyst is found to work in H 2 O (and in H 2 O−ethanol) medium at ambient temperature. All of the above attributes have been possible to incorporate into this unique catalyst via employing a hybrid bifunctional ligand, which plays a crucial role in facilitating the cleavage of H 2 as well as effectively delivering hydride to the substrate without any help of base or pressure.

Acceptorless alcohol dehydrogenation is a powerful reaction in sustainable synthesis. When combined in a tandem reaction with dehydrogenative coupling or hydrogen borrowing, acceptorless dehydrogenation can be used for the environmentally benign construction of C−C, C−N, and C−O bonds. While many of these reactions rely on using precious metals, in the past decade the use of earth-abundant metals has become more prevalent. If a green and renewable feedstock could be introduced as well, the sustainability of the acceptorless dehydrogenation could further be increased. Methanol would be such a substrate and could serve as a renewable C1 source when used for the methylation of a wide variety of substrates. Herein, we report the efficient manganesecatalyzed α-methylation of ketones and indoles. The manganese catalyst is based on a PC NHC P pincer platform containing a rare central carbene donor. The reaction supports a diverse set of functional groups, occurs at moderate temperatures (110 °C), and provides the corresponding methylated ketones and indoles in excellent yields. In contrast to previously reported mechanisms, the herein reported mechanism does not depend on metal−ligand cooperativity but rather proceeds via (i) a metal-based mechanism featuring a manganese hydride or (ii) via a ligand-centered mechanism where a manganese-carbonyl acts as catalytic center, depending on the used additive.