1,2-Addition of Formic or Oxalic Acid to ^–N{CH₂CH₂(PiPr₂)}₂-Supported Mn(I) Dicarbonyl Complexes and the Manganese-Mediated Decomposition of Formic Acid

Abstract

PN H P)Mn(CO) 2 (I) carboxylate complexes (PN H P = HN{CH 2 CH 2 (PiPr 2 )} 2 ) were prepared via 1,2-addition of either formic or oxalic acid to (PNP)Mn(CO) 2 (PNP = the deprotonated, amide form of the ligand − N{CH 2 CH 2 (PiPr 2 )} 2 ). The structural and spectral properties of these complexes were compared. The manganese formate complex was found to be dimeric in the solid state and monomeric in solution. Half an equivalent of oxalic acid was employed to form the bridging oxalate dimanganese complex. The catalytic competencies of the carboxylate complexes were assessed, and the formate complex was found to decompose formic acid catalytically. Both dehydrogenation and dehydration pathways were active as assessed by the presence of H 2 , CO 2 , and H 2 O. The addition of LiBF 4 exhibited a strong inhibitory effect on the catalysis. C atalytic storage and release of dihydrogen from small molecules has been explored as an alternative energy source. 1 Relevant to this work is the recent progress made in the dehydrogenation of formic acid (FA) to yield H 2 and CO 2 . The original exploration of FA decomposition focused on heavier metals such as ruthenium, 2 rhodium, 3 and iridium. 4 Beller was then able to extend FA decomposition to iron, 5 followed by other groups using pincer ligands. 6 Several studies by Beller and Laurenczy have explored the fundamental properties of this reaction with iron. 7 PN H P (PN H P = HN{CH 2 CH 2 (PiPr 2 )} 2 )-supported ruthenium was also shown to be particularly active as an alcohol dehydrogenation catalyst. 8 The analogous PN H P-supported iron complex (PN H P)Fe(H)-(CO)(CO 2 H) was shown to be effective in the decomposition of formic acid and methanol/water dehydrogenation. 9 Hazari and Bernskoetter also first reported the importance of Lewis acids in the catalysis of FA decomposition. 9b This is a pointed example of how iron compounds have the ability to achieve catalytic transformations that previously had been performed by noble metals.As iron compounds supported by PN H P have successfully mirrored the FA decomposition catalysis of PN H P-supported ruthenium compounds, we sought to extend similar reactivity to isoelectronic Mn(I) complexes supported in a similar fashion. An easy extension of the iron(II) hydride/PNP amide is to use the isoelectronic Mn(I) dicarbonyl complex ( Figure 1). We recently reported the synthesis of ( iPr PN H P)Mn-(CO) 2 Br. 10 The desired amide complex was formed in a simple dehydrohalogenation step, giving ( iPr PNP)Mn(CO) 2 .We are interested in FA decomposition as a source of gas pressure to perform pressure−volume work (PV-work), e.g., to move an actuator. Although our end-goal differs from fuel cell use, the formation of two moles of gas from one mole of liquid (FA) prompted this investigation. Our PV-work requires lower temperatures than most of the previously described reaction conditions (typically 90°C or higher). Attempting the catalysis with a PNP-supported Mn(I) complex has allowed us to investigate an alternative system under conditio...

Oxidative Transformations of Biosourced Alcohols Catalyzed by Earth‐Abundant Transition Metals

“…In addition, the N−H stretching band is observed at δ =3095 cm −1 . The solid‐state molecular structure features a distorted octahedral geometry similar to that of [Mn(OCOH)(CO) 2 {(Ph 2 PC 2 H 4 ) 2 NH}] reported by Tondreau and Boncella . The PNP tridentate ligand is coordinated in an meridional fashion.…”

Manganese Complexes for (De)Hydrogenation Catalysis: A Comparison to Cobalt and Iron Catalysts

“…[96] Formic acid is then dehydrogenated to CO 2 and H 2 [95] as demonstrated by Tondreau and Boncella. [97] Without the addition of water, the reaction would proceed as outlined in the next Section (Scheme 13) leading to methyl formate as the main product of areaction known as dehydrogenative coupling. [98] Scheme 9.…”

Homogeneous Catalysis by Manganese‐Based Pincer Complexes

“…Inspired by previously developed processes for formic acid dehydrogenation in the presence of iron‐based PNP pincer complexes, Boncella and co‐workers extended this kind of reaction to manganese‐based pincer complexes For their studies they chose ( i Pr PNP)Mn(CO) 2 Br complex 10a and evaluating the success of the reaction by focussing on the occurred pressure‐volume work by the decomposition of formic or oxalic acid.…”