Computational Studies Explain the Importance of Two Different Substituents on the Chelating Bis(amido) Ligand for Transfer Hydrogenation by Bifunctional Cp*Rh(III) Catalysts

Abstract

ABSTRACT:A computational approach (DFT-B3PW91) is used to address previous experimental studies (Chem Commun. 2009, 6801) that showed that transfer hydrogenation of a cyclic imine by Et 3 N·HCO 2 H catalyzed by 16-electron bifunctional Cp*Rh III (XNC 6 H 4 NX ), is faster when XNC 6 H 4 NX = TsNC 6 H 4 NH than when XNC 6 H 4 NX = HNC 6 H 4 NH or TsNC 6 H 4 NTs (Cp* =  5 -C 5 Me 5 , Ts = toluenesulfonyl). The computational study also considers the role of the formate 2 complex observed experimentally at low temperature. Using a model of the experimental complex in which Cp* is replaced by Cp and Ts by benzenesulfonyl (Bs), the calculations reveal that dehydrogenation of formic acid generates CpRh III H(XNC 6 H 4 NX H) via an outer-sphere mechanism. The 16-electron Rh complex + formic acid are shown to be at equilibrium with the formate complex, but the latter lies outside the pathway for dehydrogenation. The calculations reproduce the experimental observation that the transfer hydrogenation reaction is fastest for the non-symmetrically substituted complex CpRh III (XNC 6 H 4 NX ) (X = Bs and X = H).The effect of the linker between the two N atoms on the pathway is also considered. The Gibbs energy barrier for dehydrogenation of formic acid is calculated to be much

Dehydrogenation, disproportionation and transfer hydrogenation reactions of formic acid catalyzed by molybdenum hydride compounds

“… 56 In contrast, formic acid is available from renewable sources, and the release of CO 2 as a byproduct renders the reaction effectively irreversible. 56 However, catalysts that are commonly used to effect transfer hydrogenation using formic acid are largely restricted to the platinum group metals, namely Ru, Rh, Pd and Ir, 59 – 61 with few reports employing other metals, 62 and none employing Mo. It is, therefore, noteworthy that CpMo(CO) 3 H is also capable of effecting transfer hydrogenation of a variety of carbonyl compounds, namely RCHO (R = Me, Pr i ), RC(O)Me (R = Me, Pr i , Bu t , Ph) and Ph 2 CO, using formic acid as the reductant, 63 as illustrated in Scheme 6 .…”

Computational Studies of Synthetically Relevant Homogeneous Organometallic Catalysis Involving Ni, Pd, Ir, and Rh: An Overview of Commonly Employed DFT Methods and Mechanistic Insights

“…In a recent study, Perutz and Eisenstein confirmed and explained previous experimental findings at the importance of two different substituents on the bis(amido) ligand of the CpRh(III) catalyst during transfer hydrogenation. 380 B3PW91 calculations showed that the presence of two different amide substituents creates a good bifunctional catalyst as it is bearing both an electrophilic Rh center for accepting H − and a nucleophilic NH group for coordinating H + during the dehydrogenation of formic acid (Scheme 30).…”

Tuning PtII‐Based Donor–Acceptor Systems through Ligand Design: Effects on Frontier Orbitals, Redox Potentials, UV/Vis/NIR Absorptions, Electrochromism, and Photocatalysis

“…[19] Perutz and co-workers studied rhodium(III)c omplexes with symmetrically and asymmetrically sulfonylated bis(amido)benzenes for transfer hydrogenation,s howingt he catalytic applications of these ligands. [20][21][22] Interestingly,t hey also observed the dimerization of the aforementioned rhodium compounds, in which the oxygen atoms of the sulfonyl group bridge two rhodiumc enters. [20] Kavallieratosa nd co-workerso bserved the formation of coordination polymers using lead(II)s alts, emphasizing the versatile and dynamic coordinationc hemistry these ligandsmay engage in.…”