Ligand Bite Angle Effects in Metal-catalyzed C-C Bond Formation

A Pd-H/Isothiourea Cooperative Catalysis Approach to anti-Aldol Motifs: Enantioselective α-Alkylation of Esters with Oxyallenes

The biological and therapeutic significance of natural products is a powerful impetus for the development of efficient methods to facilitate their construction. Accordingly, and reflecting the prevalence of β-oxy-carbonyl motifs, a sophisticated arsenal of aldol-based strategies has evolved that is contingent on the generation of single enolate isomers. Since this has the potential to compromise efficiency in reagent-based paradigms, direct catalysis-based solutions would be enabling. To complement the array of substrate-based strategies, and regulate enolate geometry at the catalyst level, a direct catalytic alkylation of esters with oxyallenes has been developed. Synergizing metal hydride reactivity with Lewis base catalysis has resulted in a broad reaction scope with useful levels of stereocontrol (up to >99 % ee). Facile derivatization of these ambiphilic linchpins is demonstrated, providing access to high-value vicinal stereocenter-containing motifs, including 1,2-amino alcohols.

Copper-Catalyzed Markovnikov Selective 3,4-Hydrosilylation of 2-Substituted 1,3-Dienes

A copper-catalyzed regioselective Markovnikov 3,4-hydrosilylation of 2-substituted 1,3-dienes has been accomplished. A wide range of 2-substituted 1,3-dienes and trihydrosilanes are compatible under the optimal conditions. The bisphosphine ligand with a rigid backbone provides the Markovnikov 3,4-hydrosilylation product in better yield and selectivity. Besides, the synthetic utilities of the allylsilanes also were demonstrated by their flexible derivatizations.

One-pot synthesis of phosphorylnaphth[2,1-d]oxazoles and products as P,N-ligands in C-N and C-C formation

Phosphanylnaphtho[2,1-d]oxazoles were synthesized successfully through one-pot phosphonation of naphthoquinone with diaryl(alkyl)phosphine oxides and Cu-catalyzed oxidative condensation with imines, followed by methylation and reduction. Upon applying 4-phosphanylnaphtho[2,1-d]oxazole as a P,N-chelating ligand, Pd-catalyzed C-N formation of amines or nitrobenzene as well as Ni-catalyzed C-C formation and the synthesis of quinoline proceeded successfully. The reaction was facilely scaled up to give N-benzylaniline 15a in a gram scale synthesis. This research provided a facile and convenient protocol to synthesize phosphanylnaphtho[2,1-d]oxazoles, which could be applied as an efficient P,N-ligand in transition-metal-catalyzed C-N and C-C formation to produce the desired products in high yields with wide functional group tolerance under small catalyst loading, solvent-free conditions in many reactions.

Transition Metal Catalysis Controlled by Hydrogen Bonding in the Second Coordination Sphere

Transition metal catalysis is of utmost importance for the development of sustainable processes in academia and industry. The activity and selectivity of metal complexes are typically the result of the interplay between ligand and metal properties. As the ligand can be chemically altered, a large research focus has been on ligand development. More recently, it has been recognized that further control over activity and selectivity can be achieved by using the "second coordination sphere", which can be seen as the region beyond the direct coordination sphere of the metal center. Hydrogen bonds appear to be very useful interactions in this context as they typically have sufficient strength and directionality to exert control of the second coordination sphere, yet hydrogen bonds are typically very dynamic, allowing fast turnover. In this review we have highlighted several key features of hydrogen bonding interactions and have summarized the use of hydrogen bonding to program the second coordination sphere. Such control can be achieved by bridging two ligands that are coordinated to a metal center to effectively lead to supramolecular bidentate ligands. In addition, hydrogen bonding can be used to preorganize a substrate that is coordinated to the metal center. Both strategies lead to catalysts with superior properties in a variety of metal catalyzed transformations, including (asymmetric) hydrogenation, hydroformylation, C-H activation, oxidation, radical-type transformations, and photochemical reactions.

Deconstructive Cycloaromatization Strategy toward N,O-Bidentate Ligands from Indolizines and Cyclopropenones

The innovative construction of novel N,O-bidentate ligands represents a long-standing challenge for chemists. Here, we report an unprecedented approach for the construction of N,O-bidentate derivatives via the merging of ring deconstruction with cycloaromatization of indolizines and cyclopropenones. Without any catalysts, our method can deliver a series of polyaryl 2-(pyridin-2-yl)phenols in excellent yields. In addition, N,O-bidentate organic BF₂ complexes can also be constructed via this one-pot protocol.

Advances on the Merger of Electrochemistry and Transition Metal Catalysis for Organic Synthesis

Synthetic organic electrosynthesis has grown in the past few decades by achieving many valuable transformations for synthetic chemists. Although electrocatalysis has been popular for improving selectivity and efficiency in a wide variety of energy-related applications, in the last two decades, there has been much interest in electrocatalysis to develop conceptually novel transformations, selective functionalization, and sustainable reactions. This review discusses recent advances in the combination of electrochemistry and homogeneous transition-metal catalysis for organic synthesis. The enabling transformations, synthetic applications, and mechanistic studies are presented alongside advantages as well as future directions to address the challenges of metal-catalyzed electrosynthesis.

Nickel/Brønsted acid dual-catalyzed regio- and enantioselective hydrophosphinylation of 1,3-dienes: access to chiral allylic phosphine oxides

While chiral allylic organophosphorus compounds are widely utilized in asymmetric catalysis and for accessing bioactive molecules, their synthetic methods are still very limited. We report the development of asymmetric nickel/Brønsted acid dual-catalyzed hydrophosphinylation of 1,3-dienes with phosphine oxides. This reaction is characterized by an inexpensive chiral catalyst, broad substrate scope, and high regio- and enantioselectivity. This study allows the construction of chiral allylic phosphine oxides in a highly economic and efficient manner. Preliminary mechanistic investigations suggest that the 1,3-diene insertion into the chiral Ni-H species is a highly regioselective process and the formation of the chiral C-P bond is an irreversible step.

Forever young: the first seventy years of ferrocene

The discovery of ferrocene, [Fe(η5-C5H5)2], seventy years ago has significantly influenced chemical research and provided a key impetus for establishing and rapidly expanding organometallic chemistry, which has continued at a...

Betti base derived P-stereogenic phosphine-diamidophosphite ligands with a single atom spacer and their application in asymmetric catalysis

Small bite-angle P-chirogenic PNP ligands have been synthesized stereo-selectively and employed in Rh-catalyzed asymmetric hydrogenation and Pd-catalyzed asymmetric allylic substitution resulting in moderate to excellent enantioselectivities.

Origin of Ligand Effects on Stereoinversion in Pd-Catalyzed Synthesis of Tetrasubstituted Olefins

The mechanism and origin of ligand effects on stereoinversion of Pd-catalyzed synthesis of tetrasubstituted olefins were investigated using DFT calculations and the approach of energy decomposition analysis (EDA). The results reveal that the stereoselectivity-determining steps are different when employing different phosphine ligands. This is mainly due to the steric properties of ligands. With the bulkier Xantphos ligand, the syn/anti-to-Pd 1,2-migrations determine the stereoselectivity. While using the less hindered P(o-tol)₃ ligand, the 1,3-migration is the stereoselectivity-determining step. The EDA results demonstrate that Pauli repulsion and polarization are the dominant factors for controlling the stereochemistry in 1,2- and 1,3-migrations, respectively. The origins of differences of Pauli repulsion and polarization between the two stereoselective transition states are further identified.

Group 11 metal complexes of the dinucleating triazole appended bisphosphine 1,4-bis(5-(diisopropylphosphaneyl)-1-phenyl-1H-1,2,3-triazol-4-yl)benzene

The synthesis of a triazole appended dinucleating bisphosphine 1,4-bis(5-(diisopropylphosphaneyl)-1-phenyl-1H-1,2,3-triazol-4-yl)benzene (2) and its coinage metal complexes are described. The dinucleating bisphosphine 2 was obtained by the temperature-controlled lithiation of 1,4-bis(1-phenyl-1H-1,2,3-triazol-4-yl)benzene (1a) and 1,4-bis(1-(2-bromophenyl)-1H-1,2,3-triazol-4-yl)benzene (1b) followed by the reaction with ⁱPr₂PCl. The reactions of 2 with copper(I) halides in 1 : 2 molar ratios yielded the [Cu(μ₂-X)]₂ dimeric complexes [{Cu(μ₂-X)}₂(PⁱPr₂N₃PhC₂)₂C₆H₄] (3, X = Cl; 4, X = Br; and 5, X = I), whereas the reaction of 2 with AgBr resulted in the formation of hetero-cubane complex [{Ag₄(μ₃-Br)₄}{(PⁱPr₂N₃PhC₂)₂C₆H₄}₂] (7). Similar reactions of 2 with AgX in 1 : 2 molar ratios yielded disilver complexes [{Ag(μ₂-X)}₂{(PⁱPr₂N₃PhC₂)₂C₆H₄}] (6, X = Cl and 8, X = I). Treatment of 2 with AgOAc in a 1 : 2 molar ratio afforded a dinuclear complex [Ag₂(μ₂-OAc)₂{(PⁱPr₂N₃PhC₂)₂(C₆H₄)}] (9) with one of the acetate ligands bridging the two metal centres in the side-on mode, whereas the other one adopting the end-on mode keeping the >CO group uncoordinated. The reaction of 2 with two equivalents of [AuCl(SMe₂)] afforded the digold complex [(AuClPⁱPr₂N₃PhC₂)₂C₆H₄] (10). The molecular structures of 2-5 and 7-10 were confirmed by single crystal X-ray analysis. Non-covalent interactions between Cu and C_arene were observed in the molecular structures of 3, 4 and 5. These weak interactions were also assessed by DFT calculations in terms of their non-covalent interaction plots (NCI) and QTAIM analyses.

Inhibition of (dppf)nickel-catalysed Suzuki-Miyaura cross-coupling reactions by α-halo-N-heterocycles

A nickel/dppf catalyst system was found to successfully achieve the Suzuki-Miyaura cross-coupling reactions of 3- and 4-chloropyridine and of 6-chloroquinoline but not of 2-chloropyridine or of other α-halo-N-heterocycles. Further investigations revealed that chloropyridines undergo rapid oxidative addition to [Ni(COD)(dppf)] but that α-halo-N-heterocycles lead to the formation of stable dimeric nickel species that are catalytically inactive in Suzuki-Miyaura cross-coupling reactions. However, the corresponding Kumada-Tamao-Corriu reactions all proceed readily, which is attributed to more rapid transmetalation of Grignard reagents.

Rhodium-Catalyzed Asymmetric Hydrogenation of 3-Benzoylaminocoumarins for the Synthesis of Chiral 3-Amino Dihydrocoumarins

An asymmetric hydrogenation of 3-benzoylaminocoumarins was achieved for the first time using our BridgePhos-Rh catalytic system, providing chiral 3-amino dihydrocoumarins in high yields (up to 98 %) and with excellent enantioselectivities (up to 99.7 % ee). The relationship between the enantioselectivities of the hydrogenations and the dihedral angles and the resulting π-π stacking effects of the BridgePhos-Rh complexes, which were determined by X-ray diffraction analysis, are discussed. The corresponding hydrogenated products allow for many transformations, providing several chiral skeletons with important physiological and pharmacological activities.

Pd-Catalyzed Oxidative Aminocarbonylation of Arylboronic Acids with Unreactive Tertiary Amines via C-N Bond Activation

An efficient synthesis of tertiary amides from aryl boronic acids and inert tertiary amines through the oxidative carbonylation via C(sp³)-N bond activation is presented. This protocol significantly restricts the homocoupling biarylketone product. It involves the use of a homogeneous PdCl₂/CuI catalyst and a heterogeneous Pd/C based catalyst, which promotes C(sp³)-N bond activation of tertiary amines with aryl boronic acids. This process represents a ligand-free, base-free, and recyclable catalyst along with an ideal oxidant like molecular oxygen.

Nickel-Catalyzed Intramolecular Hydroalkenylation of Imines

A ligand-enabled nickel-catalyzed intramolecular hydroalkenylation of imines with unactivated alkenes has been developed. A variety of five- and six-membered cyclic allylic amines were synthesized in high yields. The use of both wide-bite-angle diphosphine ligand and Brønsted acid is crucial for realizing the reaction. Preliminary investigation of the asymmetric intramolecular hydroalkenylation of imines shows promising potential for the application of the method in the synthesis of enantio-enriched cyclic allylic amines.

Carbene-Catalyzed Enantioselective Hydrophosphination of α-Bromoenals to Prepare Phosphine-Containing Chiral Molecules

Disclosed herein is the first carbene-organocatalyzed asymmetric addition of phosphine nucleophiles to the in situ generated α,β-unsaturated acyl azolium intermediates. Our reaction enantioselectively constructs carbon-phosphine bonds and prepares chiral phosphines with high optical purities. The phosphine products are suitable for transforming to chiral ligands or catalysts with applications in asymmetric catalysis. The diarylalkyl or trialkyl phosphine products from our catalytic reactions, air-sensitive and reactive in nature, can be trapped (and stored) in their sulfur-oxidized form for operational simplicities.

Ir-Catalyzed Cycloaddition of Tribenzocyclyne with Biphenylenes

We demonstrate that Ir-catalyzed C-C bond activation in biphenylenes followed by a reaction with tribenzocyclyne is a suitable method for synthesizing strained and unknown monoadducts with the tetradehydrotetrabenzo[a,c,e,i]cyclododecene scaffold ([12]annulenes). Modification of reaction conditions also furnished [12]annulene products with cis and/or trans double bonds formed by hydrogen transfer. The [9]annulene side product was formed upon the reaction of the benzyl radical with tribenzocyclyne during the Bergman cyclization. All isolated compounds were fully characterized by HRMS, NMR, and X-ray diffraction analysis.

Force-modulated reductive elimination from platinum(ii) diaryl complexes

Coupled mechanical forces are known to drive a range of covalent chemical reactions, but the effect of mechanical force applied to a spectator ligand on transition metal reactivity is relatively unexplored. Here we quantify the rate of C(sp2)-C(sp2) reductive elimination from platinum(ii) diaryl complexes containing macrocyclic bis(phosphine) ligands as a function of mechanical force applied to these ligands. DFT computations reveal complex dependence of mechanochemical kinetics on the structure of the force-transducing ligand. We validated experimentally the computational finding for the most sensitive of the ligand designs, based on MeOBiphep, by coupling it to a macrocyclic force probe ligand. Consistent with the computations, compressive forces decreased the rate of reductive elimination whereas extension forces increased the rate relative to the strain-free MeOBiphep complex with a 3.4-fold change in rate over a ∼290 pN range of restoring forces. The calculated natural bite angle of the free macrocyclic ligand changes with force, but 31P NMR analysis and calculations strongly suggest no significant force-induced perturbation of ground state geometry within the first coordination sphere of the (P-P)PtAr2 complexes. Rather, the force/rate behavior observed across this range of forces is attributed to the coupling of force to the elongation of the O⋯O distance in the transition state for reductive elimination. The results suggest opportunities to experimentally map geometry changes associated with reactions in transition metal complexes and potential strategies for force-modulated catalysis.

Mixed-diphosphine-protected chiral undecagold clusters Au11(S,S-DIOP)4(rac-/R-/S-BINAP): effect of the handedness of BINAP on their chiroptical responses

In this article, we report a preference of homochiral-type ligation of BINAP that produces SS-type ligand assembly onto the Au11 clusters protected by diphosphine S,S-DIOP. The Au11 clusters synthesized and isolated are Au11(S,S-DIOP)4(rac-/R-/S-BINAP), and their optical/chiroptical responses are characterized. Absorption spectra of these Au11 clusters are almost identical to each other, but their CD profiles are dependent on the handedness of BINAP. In Au11(S,S-DIOP)4(rac-BINAP), the yield of S-BINAP or R-BINAP coordination is roughly comparable, but we found a small but distinctive preference in the S-BINAP ligation; that is, homochiral-type (SS-type) ligand assembly formation. Quantum chemical calculations for simplified model clusters suggest equal contributions of S- and R-form BINAP coordination. The experimentally-observed preference of homochiral-type ligation can then be due to that of the whole ligand structures and assemblies involving interligand interactions. Chiral sorting and amplification processes through the assembly control of homochirality or heterochirality are of primary importance for the development of enantioselective reactions, so we anticipate this finding will contribute to further understanding of such processes based on various metal clusters with chiral ligands.

Trends in computational molecular catalyst design

Computational methods have emerged as a powerful tool to augment traditional experimental molecular catalyst design by providing useful predictions of catalyst performance and decreasing the time needed for catalyst screening. In this perspective, we discuss three approaches for computational molecular catalyst design: (i) the reaction mechanism-based approach that calculates all relevant elementary steps, finds the rate and selectivity determining steps, and ultimately makes predictions on catalyst performance based on kinetic analysis, (ii) the descriptor-based approach where physical/chemical considerations are used to find molecular properties as predictors of catalyst performance, and (iii) the data-driven approach where statistical analysis as well as machine learning (ML) methods are used to obtain relationships between available data/features and catalyst performance. Following an introduction to these approaches, we cover their strengths and weaknesses and highlight some recent key applications. Furthermore, we present an outlook on how the currently applied approaches may evolve in the near future by addressing how recent developments in building automated computational workflows and implementing advanced ML models hold promise for reducing human workload, eliminating human bias, and speeding up computational catalyst design at the same time. Finally, we provide our viewpoint on how some of the challenges associated with the up-and-coming approaches driven by automation and ML may be resolved.

Ligand-Controlled Regiodivergent Thiocarbonylation of Alkynes toward Linear and Branched α,β-Unsaturated Thioesters

Thiocarbonylation of alkynes offers an ideal procedure for the synthesis of unsaturated thioesters. A robust ligand-controlled regioselective thiocarbonylation of alkynes is developed. Utilizing boronic acid and 5-chlorosalicylic acid as the acid additive to in situ form 5-chloroborosalicylic acid (5-Cl-BSA), and bis(2-diphenylphosphinophenyl)ether (DPEphos) as the ligand, linear α,β-unsaturated thioesters were produced in a straightforward manner. Switching the ligand to tri(2-furyl)phosphine can turn the reaction selectivity to give branched products. Remarkably, this approach also represents the first example on thiocarbonylation of internal alkynes.

Catalytic Cyclotrimerization Pathway for Synthesis of Selaginpulvilins C and D: Scope and Limitations

A facile and unified approach to the main selaginpulvilin's framework was achieved by catalytic [2 + 2 + 2]-cyclotrimerization of a triyne with monosubtituted alkynes. The reaction proceeded with high "ortho" selectivity by using Wilkinson's catalyst (RhCl(PPh₃)₃) under ambient conditions with reasonable yields. The scope of the reaction with respect to the alkyne as well as the catalytic system was evaluated. The formal total modular syntheses of selaginpulvilin C and D were accomplished by transformation of the cyclotrimerization's products.

Dibismuthanes in catalysis: from synthesis and characterization to redox behavior towards oxidative cleavage of 1,2-diols

A family of aryl dinuclear bismuthane complexes has been successfully synthesized and characterized. The two bismuth centers are bonded to various xanthene-type backbones, which differ in ring-size and flexibility, resulting in complexes with different intramolecular BiBi distances. Moreover, their pentavalent Bi(v) analogues have also been prepared and structurally characterized. Finally, the synergy between bismuth centers in catalysis has been studied by applying dinuclear bismuthanes 5-8 to the catalytic oxidative cleavage of 1,2-diols. Unfortunately, no synergistic effects were observed and the catalytic activities of dinuclear bismuthanes and triphenylbismuth are comparable.

Backbone-Modified C2-Symmetrical Chiral Bisphosphine TMS-QuinoxP*: Asymmetric Borylation of Racemic Allyl Electrophiles

A new C₂-symmetrical P-chirogenic bisphosphine ligand with silyl substituents on the ligand backbone, (R,R)-5,8-TMS-QuinoxP*, has been developed. This ligand showed higher reactivity and enantioselectivity for the direct enantioconvergent borylation of cyclic allyl electrophiles than its parent ligand, (R,R)-QuinoxP* (e.g., for a piperidine-type substrate: 95% ee vs 76% ee). The borylative kinetic resolution of linear allyl electrophiles was also achieved using (R,R)-5,8-TMS-QuinoxP* (up to 90% ee, s = 46.4). An investigation into the role of the silyl groups on the ligand backbone using X-ray crystallography and computational studies displayed interlocking structures between the phosphine and silyl moieties of (R,R)-5,8-TMS-QuinoxP*. The results of DFT calculations revealed that the entropy effect thermodynamically destabilizes the dormant dimer species in the catalytic cycle to improve the reactivity. Furthermore, in the direct enantioconvergent case, detailed calculations indicated a pronounced enantioselective recognition of carbon-carbon double bonds, which is virtually unaffected by the chirality at the allylic position, as a key for the borylation from both enantiomers of racemic allyl electrophiles.

Palladium(0) complexes of diferrocenylmercury diphosphines: synthesis, X-ray structure analyses, catalytic isomerization, and C-Cl bond activation

Palladium(0) phosphine complexes are of great importance as catalysts in numerous bond formation reactions that involve oxidative addition of substrates. Highly active catalysts with labile ligands are of particular interest but can be challenging to isolate and structurally characterize. We investigate here the synthesis and chemical reactivity of Pd⁰ complexes that contain geometrically adaptable diferrocenylmercury-bridged diphosphine chelate ligands (L) in combination with a labile dibenzylideneacetone (dba) ligand. The diastereomeric diphosphines 1a (pSpR, meso-isomer) and 1b (pSpS-isomer) differ in the orientation of the ferrocene moieties relative to the central Ph₂PC₅H₃-Hg-C₅H₃PPh₂ bridging entity. The structurally distinct trigonal LPd⁰(dba) complexes 2a (meso) and 2b (pSpS) are obtained upon treatment with Pd(dba)₂. A competition reaction reveals that 1b reacts faster than 1a with Pd(dba)₂. Unexpectedly, catalytic interconversion of 1a (meso) into 1b (rac) is observed at room temperature in the presence of only catalytic amounts of Pd(dba)₂. Both Pd⁰ complexes, 2a and 2b, readily undergo oxidative addition into the C-Cl bond of CH₂Cl₂ at moderate temperatures with formation of the square-planar trans-chelate complexes LPd^IICl(CH₂Cl) (3a, 3b). Kinetic studies reveal a significantly higher reaction rate for the meso-isomer 2a in comparison to (pSpS)-2b.

Coordination Behavior of a P4 -Butterfly Complex towards Transition Metal Lewis Acids: Preservation versus Rearrangement

The reactivity of the P4 butterfly complex [{Cp'''Fe(CO)2 }2 (μ,η1:1 -P4 )] (1, Cp'''=η5 -C5 H2 tBu3 ) towards divalent Co, Ni and Zn salts is investigated. The reaction with the bromide salts leads to [{Cp'''Fe(CO)2 }2 (μ3 ,η2:1:1 -P4 ){MBr2 }] (M=Co (2Co), Ni (2Ni), Zn (2Zn)) in which the P4 butterfly scaffold is preserved. The use of the weakly ligated Co complex [Co(NCCH3 )6 ][SbF6 ]2 , results in the formation of [{(Cp'''Fe(CO)2 )2 (μ3 ,η4:1:1 -P4 )}2 Co][SbF6 ]3 (3), which represents the second example of a homoleptic-like octaphospha-metalla-sandwich complex. The formation of the threefold positively charged complex 3 occurs via redox processes, which among others also enables the formation of [{Cp'''Fe(CO)2 }4 (μ5 ,η4:1:1:1:1 -P8 ){Co(CO)2 }][SbF6 ] (4), bearing a rare octaphosphabicyclo[3.3.0]octane unit as a ligand. On the other hand, the reaction with [Zn(NCCH3 )4 ][PF6 ]2 yields the spiro complex [{(Cp'''Fe(CO)2 )2 (μ3 ,η2:1:1 -P4 )}2 Zn][PF6 ]2 (5) under preservation of the initial structural motif.

Building a Toolbox for the Analysis and Prediction of Ligand and Catalyst Effects in Organometallic Catalysis

Computers have become closely involved with most aspects of modern life, and these developments are tracked in the chemical sciences. Recent years have seen the integration of computing across chemical research, made possible by investment in equipment, software development, improved networking between researchers, and rapid growth in the application of predictive approaches to chemistry, but also a change of attitude rooted in the successes of computational chemistry-it is now entirely possible to complete research projects where computation and synthesis are cooperative and integrated, and work in synergy to achieve better insights and improved results. It remains our ambition to put computational prediction before experiment, and we have been working toward developing the key ingredients and workflows to achieve this.The ability to precisely tune selectivity along with high catalyst activity make organometallic catalysts using transition metal (TM) centers ideal for high-value-added transformations, and this can make them appealing for industrial applications. However, mechanistic variations of TM-catalyzed reactions across the vast chemical space of different catalysts and substrates are not fully explored, and such an exploration is not feasible with current resources. This can lead to complete synthetic failures when new substrates are used, but more commonly we see outcomes that require further optimization, such as incomplete conversion, insufficient selectivity, or the appearance of unwanted side products. These processes consume time and resources, but the insights and data generated are usually not tied to a broader predictive workflow where experiments test hypotheses quantitatively, reducing their impact.These failures suggest at least a partial deviation of the reaction pathway from that hypothesized, hinting at quite complex mechanistic manifolds for organometallic catalysts that are affected by the combination of input variables. Mechanistic deviation is most likely when challenging multifunctional substrates are being used, and the quest for so-called privileged catalysts is quickly replaced by a need to screen catalyst libraries until a new "best" match between the catalyst and substrate can be identified and the reaction conditions can be optimized. As a community we remain confined to broad interpretations of the substrate scope of new catalysts and focus on small changes based on idealized catalytic cycles rather than working toward a "big data" view of organometallic homogeneous catalysis with routine use of predictive models and transparent data sharing.Databases of DFT-calculated steric and electronic descriptors can be built for such catalysts, and we summarize here how these can be used in the mapping, interpretation, and prediction of catalyst properties and reactivities. Our motivation is to make these databases useful as tools for synthetic chemists so that they challenge and validate quantitative computational approaches. In this Account, we demonstrate their application to different aspects of catalyst design and discovery and their integration with computational mechanistic studies and thus describe the progress of our journey toward truly predictive models in homogeneous organometallic catalysis.

Redox activity of a dissymmetric ligand bridging divalent ytter-bium and reactive nickel fragments

The reaction of a reactive nickel dimethyl 1 bearing a redox-active, dissymmetric ligand, which is obtained by deprotonation of 2-pyrimidin-2-yl-1H-benzimidazole (Hbimpm) with a divalent lanthanide complex, Cp*₂Yb(OEt₂), affords an unprecedented, trimeric 2 with C(sp³)-C(sp³) bond formation between two ligands in an exo position. Meanwhile, the transient, dimeric species 3 can be isolated with the same ligand coupling fashion, however, with a drastic distorsion angle of the bimpm ligand and reactive NiMe₂ fragment, revealing the possible mechanism of this rearrangement. A much more stable dimeric congener, 5, with an exo ligand coupling, is synthesized in the presence of 18-crown-6, which captures the potassium counter ion. The C-C coupling formation between two bimpm ligands results from the effective electron transfer from divalent lanthanide fragments. Without the divalent lanthanide, the reductive coupling occurs on a different carbon of the ligand, nicely showing the modulation of the spin density induced by the presence of the lanthanide ion. The electronic structures of these complexes are investigated by magnetic study (SQUID), indicating a ²F_7/2 ground state for each ytterbium in all the heterometallics. This work firstly reports ligand coupling reactivity in a redox-active, yet dissymmetric system with divalent organolanthanides, and the reactive nickel moiety can impact the intriguing transition towards a stable homoleptic, trinulear lanthanide species.

Z-Selective Dienylation Enables Stereodivergent Construction of Dienes and Unravels a Ligand-Driven Mechanistic Dichotomy

Development of stereoselective and efficient reactions for construction of conjugated dienes and polyenes has remained at the forefront of organic chemistry, due to their key roles in medicinal chemistry, organic synthesis, and materials science. The synthesis of conjugated dienes and polyenes is typically accomplished in a multistep manner by sequential installation of individual C=C bonds because it allows for control of stereoselectivity and efficiency of formation of each double bond. A conceptually distinct dienylation approach entails a stereoselective appendage of a four-carbon unit, shortcutting diene synthesis. Dienylation with sulfolene provided a direct route to E-dienes, but the synthesis of substantially more challenging Z-dienes remained elusive. Here, we report that a highly Z-selective dienylation can be now achieved by a simple adjustment of a ligand, enabling stereodivergent synthesis of E- and Z-dienes from one reagent and in one step. A detailed mechanistic investigation of the E- and Z-selective dienylation provided insight into the divergent behavior of the two catalytic systems and revealed that differences in relative stabilities of catalytically active palladium phosphine complexes have a major impact on the stereochemical outcomes of the dienylation.

Aggregation and Solvation of Sodium Hexamethyldisilazide: Across the Solvent Spectrum

We report solution structures of sodium hexamethyldisilazide (NaHMDS) solvated by >30 standard solvents (ligands). These include: toluene, benzene, and styrene; triethylamine and related trialkylamines; pyrrolidine as a representative dialkylamine; dialkylethers including THF, tert-butylmethyl ether, and diethyl ether; dipolar ligands such as DMF, HMPA, DMSO, and DMPU; a bifunctional dipolar ligand nonamethylimidodiphosphoramide (NIPA); polyamines N,N,N',N'-tetramethylenediamine (TMEDA), N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDTA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), and 2,2'-bipyridine; polyethers 12-crown-4, 15-crown-5, 18-crown-6, and diglyme; 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane ([2.2.2] cryptand); and tris[2-(2-methoxyethoxy)ethyl]amine (TDA-1). Combinations of 1H, 13C, 15N, and 29Si NMR spectroscopies, the method of continuous variations, X-ray crystallography, and density functional theory (DFT) computations reveal ligand-modulated aggregation to give mixtures of dimers, monomers, triple ions, and ion pairs. 15N-29Si coupling constants distinguish dimers and monomers. Solvation numbers are determined by a combination of solvent titrations, observed free and bound solvent in the slow exchange limit, and DFT computations. The relative abilities of solvents to compete in binary mixtures often match that predicted by conventional wisdom but with some exceptions and evidence of both competitive and cooperative (mixed) solvation. Crystal structures of a NaHMDS cryptate ion pair and a 15-crown-5-solvated monomer are included. Results are compared with those for lithium hexamethyldisilazide, lithium diisopropylamide, and sodium diisopropylamide.

A Type of Structurally Adaptable Aromatic Spiroketal Based Chiral Diphosphine Ligands in Asymmetric Catalysis

ConspectusWhile spectacular successes have been achieved in homogeneous catalysis with the use of achiral diphosphine ligands featuring a wide natural bite angle, such as XantPhos, chiral diphosphines that can induce a large P-M-P bite angle in their transition metal complexes are conspicuously less explored in asymmetric catalysis, probably due to the challenges in the identification and efficient construction of a suitable chiral backbone. In the past decade, a highly efficient synthesis of chiral aromatic spiroketals and the corresponding diphosphine ligands (SKPs) has been developed in this group.Based on a one-pot catalytic tandem double asymmetric hydrogenation-spiroketalization ring-closure reaction sequence, these SKP ligands featuring an extraordinarily long P···P distance and a flexible backbone have been readily prepared in large scale. Remarkably versatile coordination modes have been found in the complexes of SKP with some catalysis-relevant transition metals, for example, Pd, Cu, Au, and Rh. Whereas SKP enforces an unusually large bite angle in [Pd(SKP)Cl₂] and [Cu(SKP)Cl] complexes (160.1° and 132.8°, respectively), it also allows for a bimetallic Au-Au interaction (3.254 Å) in the complex of [Au₂(SKP)Cl₂] or a square-planar coordination geometry for the [Rh(SKP)(cod)]SbF₆ complex. Such an adaptable nature of SKP ligands for transition metal coordination has profound consequences in homogeneous asymmetric catalysis, as demonstrated by their unique performance in several types of catalytic asymmetric reactions. One of the most exciting examples is SKP/Pd-catalyzed asymmetric allylic amination of Morita-Baylis-Hillman (MBH) adducts, in which SKP/Pd complexes demonstrated excellent control of regio- and enantioselectivities and exhibited exceptionally high efficiency (with a TON up to 4750) in the catalysis. SKP ligands have also found a diversity of successful applications in Cu-, Au-, or Rh-catalyzed asymmetric reactions, further attesting their wide utilities in asymmetric catalysis. Overall, this class of readily accessible SKP ligands featuring a chiral aromatic spiroketal skeleton have demonstrated unique adaptable structures in a variety of transition metal complexes and provided outstanding performance in some difficult asymmetric transformations. The works delineated herein would be expected to stimulate further research efforts on the application of this type of chiral ligand and to provide useful clues in the design of new chiral diphosphine ligands with adaptable bite angles for transition metal catalyzed asymmetric reactions.