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Dihydrogen activation by metallogermylenes was investigated experimentally and theoretically. A neutral NHC-coordinated chlorometallogermylene was synthesized and converted to a cationic base-free metallogermylene of molybdenum via chloride abstraction. The cationic molybdogermylene showed enhanced reactivity toward H2 compared to the tungsten analog. The reaction mechanism was investigated by theoretical calculations, which revealed a novel route that proceeds via a new type of metal–ligand cooperative activation between the metal and divalent germanium moiety. The activation energy of this route is much lower than that of the alternative route via an "oxidative addition" type of reaction on the single Ge(II) center, which is generally proposed for organotetrylenes. The features of the frontier orbitals and the origin of the metal effect on the H2 activation are also described. [ABSTRACT FROM AUTHOR]

Chemoselective hydrogenation of α,β‐epoxy ketones and α‐ketoamides is achieved at room temperature (25 °C) using 2.0 bar H2 and a pincer‐ligated Mn(I) catalyst that provides synthetically valuable α‐hydroxy epoxides and α‐hydroxy amides. This protocol applies to a wide range of alkyl‐ and aryl‐substituted α,β‐epoxy ketones, including terpenes (α‐ionone, nootkatone, and R‐carvone)‐ and steroids (testosterone and progesterone)‐derived epoxy ketones, and tolerates H2 sensitive functionalities, such as halides, acetyl, nitrile, nitro, epoxide, alkenyl and alkynyl groups. Additionally, α‐ketoamides bearing reducible functional groups, including acetyl and diazo benzene, were untouched under this protocol and selectively converted to α‐hydroxy amides. A preliminary mechanistic study highlighted the metal‐ligand cooperative H2 activation process. [ABSTRACT FROM AUTHOR]

By combining tandem asymmetric gold catalysis and subsequent stereoconvergent hydrolysis of enol ester in a one-pot process, hydroxylated propargylic esters are converted into chiral β-oxygenated ketones with mostly good enantiomeric ratios and in largely good to excellent yields. The product chiral center is formed via stereoselective cyclization of a hydroxylated allenyl ester intermediate, which is enabled by asymmetric gold-ligand cooperation.

By employing a chiral bifunctional phosphine ligand, a gold(I)-catalyzed efficient and highly enantioselective dearomatization of phenols is achieved via versatile metal-ligand cooperation. The reaction is proven to be remarkably general in scope, permitting substitutions at all four remaining benzene positions, accommodating electron-withdrawing groups including strongly deactivating nitro, and allowing carbon-based groups of varying steric bulk including tert-butyl at the alkyne terminus. Moreover, besides N-(o-hydroxyphenyl)alkynamides, the corresponding ynoates and ynones are all suitable substrates. Spirocyclohexadienone-pyrrol-2-ones, spirocyclohexadienone-butenolides, and spirocyclohexadenone-cyclopentenones are formed in yields up to 99 % and with ee up to 99 %.

Bond activation and catalysis using s‐block metals are of great significance. Herein, a series of calcium pincer complexes with deprotonated side arms have been prepared using pyridine‐based PNP and PNN ligands. The complexes were characterized by NMR and X‐ray crystal diffraction. Utilizing the obtained calcium complexes, unprecedented N2O activation by metal‐ligand cooperation (MLC) involving dearomatization‐aromatization of the pyridine ligand was achieved, generating aromatized calcium diazotate complexes as products. Additionally, the dearomatized calcium complexes were able to activate the N−H bond as well as reversibly activate H2, offering an opportunity for the catalytic hydrogenation of various unsaturated molecules. DFT calculations were applied to analyze the electronic structures of the synthesized complexes and explore possible reaction mechanisms. This study is an important complement to the area of MLC and main‐group metal chemistry. [ABSTRACT FROM AUTHOR]

Chemodivergent (de)hydrogenative coupling of primary and secondary alcohols is achieved utilizing an inexpensive nickel catalyst, (6‐OH‐bpy)NiCl2. This protocol demonstrates the synthesis of branched carbonyl compounds, α,α‐disubstituted ketones, and α‐substituted chalcones via borrowing hydrogen strategy and acceptorless dehydrogenative coupling, respectively. A wide range of aryl‐based secondary alcohols are coupled with various primary alcohols in this tandem dehydrogenation/hydrogenation reaction. The nickel catalyst, along with KOtBu or K2CO3, governed the selectivity for the formation of branched saturated ketones or chalcones. A preliminary mechanistic investigation confirms the reversible dehydrogenation of alcohols to carbonyls via metal‐ligand cooperation (MLC) and the involvement of radical intermediates during the reaction. [ABSTRACT FROM AUTHOR]

The utilization of formic acid as a liquid organic hydrogen carrier has taken a vast interest lately because of several desirable properties. The state-of-the-art homogenous catalysts known for formic acid dehydrogenation are mainly based on noble metals such as iridium or ruthenium. 3d metals are considered to be an attractive alternative due to their abundance and low toxicity. Exploration of 3d metals has achieved exciting results mainly with iron-based catalysts; however, manganese has not received much attention, and only a few examples are available. Here we report a manganese complex [Mn(PN3P)(CO) 2 ]Br containing a pincer backbone, as an efficient catalyst for formic acid dehydrogenation. Under the optimized condition, the complex afforded a TON of 15,200. To the best of our knowledge, this is considered one of the best TON achieved using a manganese-based complex with excellent selectivity. Mechanistic studies suggested that the imine arm participates in the formic acid activation/deprotonation step, emphasizing the importance of metal-ligand cooperativity during substrate activation to promote catalytic efficacy. • A phosphorus–nitrogen PN3P–Mn pincer complex catalyzes formic acid dehydrogenation. • Good reactivity (TOF), stability (TON), and selectivity were achieved. • The metal-ligand cooperation was involved during formic acid activation. • Mechanistic insights were supported by NMR and kinetic isotope effect. [ABSTRACT FROM AUTHOR]

Chemoselective transfer hydrogenation of C=C bond in α,β‐unsaturated ketones is demonstrated at room temperature employing a manganese(I) catalyst and half an equivalent of ammonia‐borane (H3N−BH3). A series of mixed‐donor pincer‐ligated Mn(II) complexes, (tBu2PN3NPyz)MnX2 [κP,κN,κN‐(N‐(di‐tert‐butylphosphaneyl)‐6‐(1H‐pyrazol‐1‐yl)pyridin‐2‐amine)MnX2] {X=Cl (Mn2), X=Br (Mn3), X=I (Mn4)} were synthesized and characterized. Amongst the Mn(II) complexes, (Mn2, Mn3, Mn4) and Mn(I) complex, (tBu2PN3NPyz)Mn(CO)2Br (Mn1) screened; the Mn1 acts as an efficient catalyst for the chemoselective C=C bond reduction in α,β‐unsaturated ketones. Various synthetically important functionalities like halides, methoxy, trifluoromethyl, benzyloxy, nitro, amine, and unconjugated alkene and alkyne groups, including heteroarenes, were compatible and provided saturated ketones in excellent yields (up to 97 %). A preliminary mechanistic study highlighted the crucial role of metal–ligand (M–L) cooperation through the dearomatization‐aromatization process in catalyst Mn1 for the chemoselective C=C bond transfer hydrogenation. [ABSTRACT FROM AUTHOR]

Protic pyrazoles (N-unsubstituted pyrazoles) have been versatile ligands in various fields, such as materials chemistry and homogeneous catalysis, owing to their proton-responsive nature. This review provides an overview of the reactivities of protic pyrazole complexes. The coordination chemistry of pincer-type 2,6-bis(1H-pyrazol-3-yl)pyridines is first surveyed as a class of compounds for which significant advances have made in the last decade. The stoichiometric reactivities of protic pyrazole complexes with inorganic nitrogenous compounds are then described, which possibly relates to the inorganic nitrogen cycle in nature. The last part of this article is devoted to outlining the catalytic application of protic pyrazole complexes, emphasizing the mechanistic aspect. The role of the NH group in the protic pyrazole ligand and resulting metal–ligand cooperation in these transformations are discussed. [ABSTRACT FROM AUTHOR]

Acceptorless alcohol dehydrogenation stands out as one of the most promising strategies in hydrogen storage technologies. Among various catalytic systems for this reaction, cost-effective molecular catalysts using phosphine-free ligands have gained considerable attention. However, the central challenge for using non-precious metals is to overcome the propensity of reacting by one-electron pathway. Herein, we synthesized a phosphine-free η5-C5Me5-Co complex by using the metal—ligand cooperative strategy and compared its activity with analogous catalysts toward acceptorless alcohol dehydrogenation. The catalyst showed excellent performance with a turnover number of 130.4 and a selectivity close to 100%. The improved performance among the class of η5-C5Me5-Co complexes could be attributed to the more accessible Co center and its cooperation with the redox-active ligand. To further study the systematic structure-activity relationship, we investigated the electronic structures of η5-C5Me5-Co complexes by a set of characterizations. The results showed that the redox-active ligand has a significant influence on the η5-C5Me5-Co moiety. In the meantime, the proximal O−/OH group is beneficial for shuttling protons. For the catalytic cycle, two dehydrogenation scenarios were interrogated through density functional theory, and the result suggested that the outer-sphere pathway was preferred. The formation of a dihydrogen complex was the rate-determining step with a ∆G value of 16.9 kcal·mol−1. The electron population demonstrated that the η5-C5Me5 ligand played a key role in stabilizing transition states during dehydrogenation steps. This work identified the roles of vital ligand components to boost catalytic performance and offered rationales for designing metal—ligand cooperative nonprecious metal complexes. [ABSTRACT FROM AUTHOR]

Transfer hydrogenation of azobenzene with ammonia borane mediated by pincer bismuth complex 1 was systematically investigated through density functional theory calculations. An unusual metal‐ligand cooperation mechanism was disclosed, in which the saturation/regeneration of the C=N functional group on the pincer ligand plays an essential role. The reaction is initiated by the hydrogenation of the C=N bond (saturation) with ammonia borane to afford 3CN, which is the rate‐determining step with Gibbs energy barrier (ΔG≠) and Gibbs reaction energy (ΔG) of 25.6 and −7.3 kcal/mol, respectively. 3CN is then converted to a Bi−H intermediate through a water‐bridged pathway, which is followed up with the transfer hydrogenation of azobenzene to produce the final product N,N′‐diphenylhydrazine and regenerate the catalyst. Finally, the catalyst could be improved by substituting the phenyl group for the tert‐butyl group on the pincer ligand, where the ΔG≠ value (rate‐determining step) decreases to 24.0 kcal/mol. [ABSTRACT FROM AUTHOR]

A series of hexamethylbenzene (HMB)–Ru complexes 2–5 bearing a 4,4'‐functionalized 2,2'‐bipyridine‐6,6'‐dionate (bpyO) ligand, which exhibits metal‐ligand cooperative catalysis, was prepared with the aim of developing excellent catalyst for dehydrogenative oxidation of alcohols. Interestingly, the catalytic activity increased in the order 3 (CF3) <4 (OMe)<2 (H) <5 (NMe2), where substituents at 4,4'‐positions of bpyO ligand are in parentheses. This is different from the order of simple electron‐donating ability. DFT calculations revealed that the rate‐limiting step is the concerted proton/hydride transfer from the alcohol to the complex. The activation energy decreases as the interaction between the alcoholic proton and the O atom of the bpyO ligand becomes stronger; hence, the introduction of the NMe2 group decreases the activation energy, whereas that of the CF3 group increases it. The unexpectedly lower catalytic ability of 4 than that of 2 results from the enthalpy–entropy compensation effect. [ABSTRACT FROM AUTHOR]

A gold(I)‐catalyzed enantioselective dearomatization is achieved via metal‐chiral ligand cooperation. A new and divergent synthesis of chiral bifunctional binaphthyl‐2‐ylphosphines is developed to allow rapid access to these ligands, which in turn facilitate the application of this chemistry to a broad substrate scope including 1‐naphthols, 2‐naphthols, and phenols. Enantiomeric excesses up to 98 % are achieved via selective acceleration of one enantiomer formation enabled by hydrogen bonding between substrate and ligand remote basic group. DFT calculations lend support to the cooperative catalysis and substantiate the reaction stereochemical outcomes. [ABSTRACT FROM AUTHOR]

A cobalt silylene (Co=Si) linkage enables a distinct metal/ligand cooperative activation of an organic azide, where nitrene transfer occurs to and from the Co⋅⋅⋅Si linkage without ligand dissociation from the 18‐electron cobalt center. This process utilizes the orthogonal binding affinities of the silicon and cobalt sites to avoid CO poisoning that would otherwise inhibit reactivity, leading to significantly improved catalytic isocyanate generation compared with related systems. The dual‐site approach demonstrates the potential of metal/main‐group bonds to access new and efficient catalytic pathways. [ABSTRACT FROM AUTHOR]

Protic pyrazoles (N-unsubstituted pyrazoles) have been versatile ligands in various fields, such as materials chemistry and homogeneous catalysis, owing to their proton-responsive nature. This review provides an overview of the reactivities of protic pyrazole complexes. The coordination chemistry of pincer-type 2,6-bis(1H-pyrazol-3-yl)pyridines is first surveyed as a class of compounds for which significant advances have made in the last decade. The stoichiometric reactivities of protic pyrazole complexes with inorganic nitrogenous compounds are then described, which possibly relates to the inorganic nitrogen cycle in nature. The last part of this article is devoted to outlining the catalytic application of protic pyrazole complexes, emphasizing the mechanistic aspect. The role of the NH group in the protic pyrazole ligand and resulting metal–ligand cooperation in these transformations are discussed.

We synthesized two 4Me−PNP ligands which block metal‐ligand cooperation (MLC) with the Ru center and compared their Ru complex chemistry to their two traditional analogues used in acceptorless alcohol dehydrogenation catalysis. The corresponding 4Me−PNP complexes, which do not undergo dearomatization upon addition of base, allowed us to obtain rare, albeit unstable, 16 electron mono‐CO Ru(0) complexes. Reactivity with CO and H2 allows for stabilization and extensive characterization of bis‐CO Ru(0) 18 electron and Ru(II) cis and trans dihydride species that were also shown to be capable of C(sp2) −H activation. Reactivity and catalysis are contrasted to non‐methylated Ru(II) species, showing that an MLC pathway is not necessary, with dramatic differences in outcomes during catalysis between iPr and tBu PNP complexes within each of the 4Me and non‐methylated backbone PNP series being observed. Unusual intermediates are characterized in one of the new and one of the traditional complexes, and a common catalysis deactivation pathway was identified. [ABSTRACT FROM AUTHOR]

The selective α‐deuteration of α,β‐unsaturated nitriles using the strong base tBuOK or a metal‐ligand cooperative Ru pincer catalyst is described. With D2O as deuterium source and glyme as solvent at 70 °C, tBuOK is an efficient catalyst for deuteration at the α‐C(sp2) position of cinnamonitriles, providing access to a broad range of deuterated derivatives in good to excellent yields and with very high levels of deuterium incorporation. While the tBuOK‐catalysed protocol does not tolerate base‐sensitive functional groups, cinnamonitrile derivatives containing a benzylic bromide or ester moiety were deuterated in excellent yields using Milstein's ruthenium PNN pincer catalyst. Moreover, the activity for H/D exchange of the metal‐ligand cooperative Ru catalyst is found to be significantly higher than that of tBuOK, allowing reactions to proceed well even at room temperature. A mechanistic proposal is put forward that involves deprotonation of the cinnamonitrile α‐CH position when using tBuOK as catalyst, whereas H/D exchange catalysis with the Ru PNN pincer likely proceeds via (reversible) oxa‐Michael addition of D2O. [ABSTRACT FROM AUTHOR]

This minireview discusses the accelerative role of alkali metal alkoxides in two important catalytic processes: hydrogenation of ketones and esters with Noyori‐type molecular catalysts. Here I offer my perspective on the unique mechanistic aspects of these reactions – a subject that remains controversial and often misunderstood. [ABSTRACT FROM AUTHOR]

• Two pincer-type Ru catalysts with proton-responsive group exhibited excellent performance for β-alkylation of alcohols. • The 2a catalyst exhibited excellent performance for β-alkylation of secondary alcohols with primary alcohols. • The role of protic NHC group on performance of β-alkylation have been investigated. This study investigated the catalytic activities of two pincer Ru complexes with bifunctional metal-ligand cooperativity, namely (HO-C 5 H 3 N-CH 2 -C 5 H 3 N-NHC)Ru(PPh 3) 2 Cl (1a) and (C 5 H 4 N-CH 2 -C 5 H 3 N-NHC)Ru(PPh 3) 2 Cl (2a), for C C bond formation through the borrowing hydrogen process. Surprisingly, complex 2a , which lacks the 2-hydroxypyridyl fragment, exhibited comparable activity to complex 1a with the same catalyst loading in the coupling of a broad range of primary and secondary alcohols. The efficiency of this straightforward system was further demonstrated in the challenging reaction of β-alkylation of 1-phenylethanol with benzyl alcohol, with a minimal catalyst loading of 0.0001 mol.%. The highest TOF observed for the cross-coupling of alcohols was 13,333 h−1. Additionally, complex 2a was found to be effective in catalysing β-alkylation of aliphatic secondary alcohols with primary alcohols and double C-alkylation of cyclopentanol. This finding holds promise for the development of more effective bifunctional catalysts for β-alkylation reactions of primary and secondary alcohols. [Display omitted] [ABSTRACT FROM AUTHOR]

A Cp*Ir(III) complex (1) of a newly designed ligand L1 featuring a proton‐responsive pyridyl(benzamide) appended on N‐heterocyclic carbene (NHC) has been synthesized. The molecular structure of 1 reveals a dearomatized form of the ligand. The protonation of 1 with HBF4 in tetrahydrofuran gives the corresponding aromatized complex [Cp*Ir(L1H)Cl]BF4 (2). Both compounds are characterized spectroscopically and by X‐ray crystallography. The protonation of 1 with acid is examined by 1H NMR and UV‐vis spectra. The proton‐responsive character of 1 is exploited for catalyzing α‐alkylation of ketones and β‐alkylation of secondary alcohols using primary alcohols as alkylating agents through hydrogen‐borrowing methodology. Compound 1 is an effective catalyst for these reactions and exhibits a superior activity in comparison to a structurally similar iridium complex [Cp*Ir(L2)Cl]PF6 (3) lacking a proton‐responsive pendant amide moiety. The catalytic alkylation is characterized by a wide substrate scope, low catalyst and base loadings, and a short reaction time. The catalytic efficacy of 1 is also demonstrated for the syntheses of quinoline and lactone derivatives via acceptorless dehydrogenation, and selective alkylation of two steroids, pregnenolone and testosterone. Detailed mechanistic investigations and DFT calculations substantiate the role of the proton‐responsive ligand in the hydrogen‐borrowing process. [ABSTRACT FROM AUTHOR]

The reconstitution of [Mn]‐hydrogenases using a series of MnI complexes is described. These complexes are designed to have an internal base or pro‐base that may participate in metal–ligand cooperative catalysis or have no internal base or pro‐base. Only MnI complexes with an internal base or pro‐base are active for H2 activation; only [Mn]‐hydrogenases incorporating such complexes are active for hydrogenase reactions. These results confirm the essential role of metal–ligand cooperation for H2 activation by the MnI complexes alone and by [Mn]‐hydrogenases. Owing to the nature and position of the internal base or pro‐base, the mode of metal–ligand cooperation in two active [Mn]‐hydrogenases is different from that of the native [Fe]‐hydrogenase. One [Mn]‐hydrogenase has the highest specific activity of semi‐synthetic [Mn]‐ and [Fe]‐hydrogenases. This work demonstrates reconstitution of active artificial hydrogenases using synthetic complexes differing greatly from the native active site. [ABSTRACT FROM AUTHOR]

In last two decades alcohol has drawn a special attention as a building blocks due to its abundance, low cost and less toxic nature which can be derived from various sustainable resources. By dehydrogenation of alcohol, aldehyde/ketone can be easily accessed which can be further coupled with several nucleophiles for the construction of complex molecules. Among the various strategies, metal‐ligand cooperation is a powerful and efficient tool for the utilization of alcohol to synthesize variety of value‐added products. Numerous alkyl phosphine based bifunctional complexes are well‐known in the literature for the alcohol dehydrogenative coupling reactions. However, the presence of alkyl phosphine moiety and air and moisture sensitive nature of the metal complexes hinder their broad application in catalysis. In this minireview, we highlighted air and moisture stable, metal‐ligand cooperative 5d, 4d and 3d metal‐based complexes which were effectively utilized to fabricate different value‐added compounds by alcohol dehydrogenative coupling reactions. [ABSTRACT FROM AUTHOR]

The non‐noble metal‐catalyzed asymmetric hydrogenation of N‐heteroaromatics, quinolines, is reported. A new chiral pincer manganese catalyst showed outstanding catalytic activity in the asymmetric hydrogenation of quinolines, affording high yields and enantioselectivities (up to 97 % ee). A turnover number of 3840 was reached at a low catalyst loading (S/C=4000), which is competitive with the activity of most effective noble metal catalysts for this reaction. The precise regulation of the enantioselectivity were ensured by a π–π interaction. [ABSTRACT FROM AUTHOR]

In contrast to conventional metal–ligand cooperative cleavage of a B−H bond, which provides a B cation on the ligand and an H anion on the metal, we report herein the umpolung of B−H bonds by novel cyclopentadienone iridium complexes. The B−H bonds of 4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane (HBpin) and 1,8‐naphthalenediaminatoborane (HBdan) were cleaved to give a B anion on the metal and an H cation on the phenolic oxygen atom of the ligand. Mechanistic investigation by DFT calculations revealed that the alkoxycarbonyl‐substituted cyclopentadienone ligand facilitated deprotonation from Ir−H after oxidative addition of the B−H bond to give the umpolung product. The generated boryliridium complex was found to undergo borylation of an allyl halide in the presence of base, thus showing the nucleophilic nature of the boron atom. [ABSTRACT FROM AUTHOR]

Bond activation and catalysis using s-block metals are of great significance. Herein, a series of calcium pincer complexes with deprotonated side arms have been prepared using pyridine-based PNP and PNN ligands. The complexes were characterized by NMR and X-ray crystal diffraction. Utilizing the obtained calcium complexes, unprecedented N 2 O activation by metal-ligand cooperation (MLC) involving dearomatization-aromatization of the pyridine ligand was achieved, generating aromatized calcium diazotate complexes as products. Additionally, the dearomatized calcium complexes were able to activate the N-H bond as well as reversibly activate H 2 , offering an opportunity for the catalytic hydrogenation of various unsaturated molecules. DFT calculations were applied to analyze the electronic structures of the synthesized complexes and explore possible reaction mechanisms. This study is an important complement to the area of MLC and main-group metal chemistry., (© 2024 Wiley-VCH GmbH.)

Hydrogenation of substituted styrenes and unactivated aliphatic alkenes by molecular hydrogen has been achieved using a Mn catalyst with a non‐pincer, picolylphosphine ligand. This is the second reported example of alkene hydrogenation catalyzed by a Mn complex. Mechanistic studies showed that a Mn hydride formed by H2 activation in the presence of a base is the catalytically active species. Based on experimental and DFT studies, H2 splitting is proposed to occur via a metal‐ligand cooperative pathway involving deprotonation of the CH2 arm of the ligand, leading to pyridine dearomatization. [ABSTRACT FROM AUTHOR]

The use of cyclopentadienyl ligands in organometallic chemistry and catalysis is ubiquitous, mostly due to their robust spectator role. Nonetheless, increasing examples of non‐innocent behaviour are being documented. Here, we provide evidence for reversible intramolecular C−H activation at one methyl terminus of C5Me5 in [(η‐C5Me5)Rh(PMe3)2] to form a new Rh−H bond, a process so far restricted to early transition metals. Experimental evidence was acquired from bimetallic rhodium/gold structures in which the gold center binds either to the rhodium atom or to the activated Cp* ring. Reversibility of the C−H activation event regenerates the RhI and AuI monometallic precursors, whose cooperative reactivity towards polar E−H bonds (E=O, N), including the N−H bonds in ammonia, can be understood in terms of bimetallic frustration. [ABSTRACT FROM AUTHOR]

Degradation of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy) propane-1,3-diol (1), a model compound for lignin β-O-4 linkage was examined with iron, ruthenium, rhodium and iridium complexes bearing cyclopentadienone ligand. Cyclopentadienone iron complex gave only a small amount of degraded product with reduced molecular weight. Cyclopentadienone ruthenium complex, so called Shvo's catalyst, afforded 3,4-dimethoxybenzaldehyde (a3) in 14.3% yield after CαCβ bond cleavage. On the other hand, cyclopentadienone group-9 metal complexes catalyzed CβO bond cleavage to afford guaiacol (b1) as a main product in up to 74.9% yield. [ABSTRACT FROM AUTHOR]

[Display omitted] • Distinct difference between the lone-pair-driven MLC and the tautomerism-driven MLC for catalytic hydrogenation. • The driving force of the tautomerism-driven MLC is of key importance for selectivity. • Theoretical guidelines for the design of lone-pair-driven MLC and the tautomerism-driven MLC catalysts for selective hydrogenation. Metal-ligand cooperation (MLC) is an important strategy in transition-metal (TM) catalysis. Tautomerism-driven MLC has recently been emerging as a novel type of catalyst design strategy. However, the difference between the conventional lone-pair-driven MLC and tautomerism-driven MLC in mechanism and selectivity remains unclear. Herein, a DFT study was performed to unveil the difference between them in the (iPrPHNN)Mn catalyzed selective hydrogenation of amide. The double deprotonated (iPrPHNN)Mn could lead to an active species with two functional sites, i.e., the N site and the C site, which would promote the lone-pair-driven MLC and the tautomerism-driven MLC for the catalytic hydrogenation, respectively. Systematic investigation of the full catalytic cycles, including hemiaminal formation, hydrogenation of amide, and the generation of alcohol and amine, reveals that the addition of H 2 onto amide prefers the lone-pair-driven MLC mechanism assisted by a proton shuttle. Then, the formed hemiaminal intermediate would competitively undergo the C-O bond cleavage to the secondary amine product or the C-N bond cleavage to the primary amine and alcohol products. Both the C-N bond cleavage and the C-O bond cleavage prefer the tautomerism-driven MLC, with the free energy barrier of the former being lower than that of the latter by around 12 kcal/mol. In the tautomerism-driven MLC mechanism, the lone-pair electrons on the innocent amido would increase the electron density of the metal center, which would lead to an easier electron transfer from the Mn center to the substrate, causing the favorable cleavage of the C-N bond. In the following hydrogenation step, the generation of aldehyde to alcohol or the hydrogenation of imine to amine can occur via either the lone-pair-driven MLC or the tautomerism-driven MLC. The driving force of the tautomerism-driven MLC is of key importance for selectivity. The results of the lone-pair-driven MLC and the tautomerism-driven MLC mechanisms in selectivity would be helpful for the design of MLC catalysis. [ABSTRACT FROM AUTHOR]

Deprotonation of the MnI NHC‐phosphine complex fac‐[MnBr(CO)3(κ2P,C‐Ph2PCH2NHC)] (2) under a H2 atmosphere readily gives the hydride fac‐[MnH(CO)3(κ2P,C‐Ph2PCH2NHC)] (3) via the intermediacy of the highly reactive 18‐e NHC‐phosphinomethanide complex fac‐[Mn(CO)3(κ3P,C,C‐Ph2PCHNHC)] (6 a). DFT calculations revealed that the preferred reaction mechanism involves the unsaturated 16‐e mangana‐substituted phosphonium ylide complex fac‐[Mn(CO)3(κ2P,C‐Ph2P=CHNHC)] (6 b) as key intermediate able to activate H2 via a non‐classical mode of metal‐ligand cooperation implying a formal λ5‐P–λ3‐P phosphorus valence change. Complex 2 is shown to be one of the most efficient pre‐catalysts for ketone hydrogenation in the MnI series reported to date (TON up to 6200). [ABSTRACT FROM AUTHOR]

As a candidate for bifunctional asymmetric catalysts containing a half-sandwich C–N chelating Ir(III) framework (azairidacycle), a dinuclear Ir complex with an axially chiral linkage is newly designed. An expedient synthesis of chiral 2,2′-bis(aminomethyl)-1,1′-binaphthyl (1) from 1,1-bi-2-naphthol (BINOL) was accomplished by a three-step process involving nickel-catalyzed cyanation and subsequent reduction with Raney-Ni and KBH4. The reaction of (S)-1 with an equimolar amount of [IrCl2Cp*]2 (Cp* = η5–C5(CH3)5) in the presence of sodium acetate in acetonitrile at 80 °C gave a diastereomeric mixture of new dinuclear dichloridodiiridium complexes (5) through the double C–H bond cleavage, as confirmed by 1H NMR spectroscopy. A loss of the central chirality on the Ir centers of 5 was demonstrated by treatment with KOC(CH3)3 to generate the corresponding 16e amidoiridium complex 6. The following hydrogen transfer from 2-propanol to 6 provided diastereomers of hydrido(amine)iridium retaining the bis(azairidacycle) architecture. The dinuclear chlorido(amine)iridium 5 can serve as a catalyst precursor for the asymmetric transfer hydrogenation of acetophenone with a substrate to a catalyst ratio of 200 in the presence of KOC(CH3)3 in 2-propanol, leading to (S)-1-phenylethanol with up to an enantiomeric excess (ee) of 67%.

The carbonylation of a nickel(II) anilido species 2 led to the formation of a dinickel(0)–CO complex (P2P‐PP2){Ni(CO)}23 with a P−P bond along with isocyanate generation. In this reaction, the central phosphide moiety of an anionic PPP ligand (PPP−=−P[2‐PiPr2C6H4]2) acts as a single‐electron donor to form a P radical. Alternatively, 3 can be synthesized from the reduction of (PPP)NiCl (1) in the presence of CO; thus, the reaction proceeds by radical coupling of a.P−Ni0−CO species. The reverse reaction occurred to generate 1 when 3 was treated with AgCl. Since the P−P bond is light‐sensitive, its homolysis is possible and was explored by EPR spectroscopy and DFT analysis. Finally, various bond‐activation reactions of 3 occurred under visible‐light conditions, thus indicating that a P−P bond can act as an active reaction site. Weigh up the options: A P−P moiety within a dinickel complex showed dual functionality as a redox center and a reaction site. Reversible electron exchange between Ni and P produced a P−P single bond, and its homolysis led to unique open‐shell reactivity (see picture). [ABSTRACT FROM AUTHOR]

Pincer complexes attract considerable attention both as interesting objects for fundamental studies and efficient catalysts. This review describes a relatively new offshoot of the field – namely, the chemistry of iridium complexes with aliphatic PC sp3 P non-innocent pincer ligands. High flexibility, often combined with possibility to activate internal C–H bonds, offers several new patterns of metal-ligand cooperation; some of them were successfully used in catalysis of acceptorless alcohol dehydrogenation, olefin hydroformylation and deuterium exchange, others opened up for remarkable stoichiometric reactions. [ABSTRACT FROM AUTHOR]

Herein we report the reversible activation of CO2 by the dearomatized complex [(tBuPNP*)Ir(COE)] (1) and by the aromatized complex [(tBuPNP)Ir(C6H5)] (2) via metal-ligand cooperation (MLC) (tBuPN = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine; tBuPNP* = deprotonated PNP; COE = cyclooctadiene). The [1,3]-addition of CO2 to 1 and 2 is reversible at ambient temperature. While the dearomatized complex 1 reacts readily at ambient temperature with CO2 in THF or benzene, complex 2 reacts with CO2 upon heating in benzene at 80 °C or at ambient temperature in THF. The novel aromatized complex [(tBuPNP)IrCl] (10) does not react with CO2. Based on the reactivity patterns of 1, 2, and 10 with CO2, we suggest that CO2 activation via MLC takes place only via the dearomatized species, and that in the case of 2 THF plays a role as a polar solvent in facilitating formation of the dearomatized hydrido phenyl complex intermediate (complex II). [ABSTRACT FROM AUTHOR]

Four NNN tridentate ligands L1–L4 containing 2‐methoxypyridylmethene or 2‐hydroxypyridylmethene fragment were synthesized and introduced to ruthenium centers. When (HOC5H3NCH2C5H3NC5H7N2) (L2) and (HOC5H3NCH2C5H3NC6H6N3) (L4) reacted with RuCl2(PPh3)3, two ruthenium chloride products Ru(L2)(PPh3)Cl2 (1) and Ru(L4)(PPh3)Cl2 (2) were isolated, respectively. Reactions of (MeOC5H3NCH2C5H3NC5H7N2) (L1) and (MeOC5H3NCH2C5H3NC6H6N3) (L3) with RuCl2(PPh3)3 in the presence of NH4PF6 generated two dicationic complexes [Ru(L1)2][PF6]2 (3) and [Ru(L3)2][PF6]2 (4), respectively. Complex 1 reacted with CO to afford product [Ru(L2)(PPh3)(CO)Cl][Cl]. The catalytic activity for transfer hydrogenation of ketones was investigated. Complex 1 showed the highest activity, with a turnover frequency value of 1.44 × 103 h−1 for acetophenone, while complexes 3 and 4 were not active. [ABSTRACT FROM AUTHOR]

The principle of frustrated Lewis acid/base pairs has reached gold chemistry. Based on sterical repulsion at the gold center, an otherwise typical coordination can be prevented, which induces new reactivity patterns. This review explains the basic principles and the development of this type of chemistry, and then summarizes the latest developments in this quickly-moving field. In addition, the future perspectives for combining stoichiometric gold chemistry and gold catalysis with FLP chemistry are discussed. [ABSTRACT FROM AUTHOR]

Iridium(III)-pyridone complexes are commonly found to react in a cooperative and redox-neutral manner with dihydrogen and alcohols. In this work, the reactivity preferences of IrI-pyridone complexes were investigated under a variety of conditions. We have found that, in contrast to IrIII-pyridones, IrI-pyridone complexes display a strong preference to react non-cooperatively. With a new chelating 2-hydroxy-8-diphenylphosphinoquinoline ligand that does not dissociate after hydrogen addition, oxidative addition is still preferred. In the preparation of mono- and bidentate neutral and anionic pyridone ligands, Vaska's complex was used as a point of reference. We expect these findings to have implications for catalyst development in the field of metal-ligand cooperation. [ABSTRACT FROM AUTHOR]

Pincer-type complexes [OsH2(CO){PyCH2NHCH2CH2NHP tBu2}] and [OsH2(CO){HN(CH2CH2P iPr2)2}] catalyze the disproportionation reaction of aldehydes via an outer-sphere bifunctional mechanism achieving turnover frequencies up to 14 000 h−1. The N−H group of the catalysts is a key player in this process, elucidated with the help of DFT calculations. [ABSTRACT FROM AUTHOR]

By employing a chiral bifunctional phosphine ligand, a gold(I)-catalyzed efficient and highly enantioselective dearomatization of phenols is achieved via versatile metal-ligand cooperation. The reaction is proven to be remarkably general in scope, permitting substitutions at all four remaining benzene positions, accommodating electron-withdrawing groups including strongly deactivating nitro, and allowing carbon-based groups of varying steric bulk including tert-butyl at the alkyne terminus. Moreover, besides N-(o-hydroxyphenyl)alkynamides, the corresponding ynoates and ynones are all suitable substrates. Spirocyclohexadienone-pyrrol-2-ones, spirocyclohexadienone-butenolides, and spirocyclohexadenone-cyclopentenones are formed in yields up to 99 % and with ee up to 99 %., (© 2023 Wiley-VCH GmbH.)

Iron(0) complex bearing a phenanthroline‐based meridional PNNP ligand [{Fe(PNNP)}2(μ‐N2)] (1) (PNNP=2,9‐bis((diphenylphosphino)methyl)‐1,10‐phenanthroline) smoothly reacted with CH3I at ambient temperature to cleave C–I bond, resulting in the formation of the corresponding oxidative addition product, [Fe(CH3)(I)(PNNP)] (2). Complex 2 was fully identified by NMR and its structure was determined by a single crystal X‐ray diffraction study. Mechanistic study using cyclopropylmethyl bromide as a radical clock supported a radical pathway for the C–I bond cleavage of CH3I. Complex 2 underwent deprotonation on treatment with NaOtBu to form 4, which possessed a dearomatized phenanthroline backbone. Complex 4 further reacted with H2 to cleave H–H bond. The reaction was mediated by metal‐ligand cooperation process that involves re‐aromatization of the phenanthroline backbone of the PNNP ligand. [ABSTRACT FROM AUTHOR]