Alpha-metalated N,N-dimethylbenzylamine rare-earth metal complexes and their catalytic applications

This perspective summarizes our group's extensive research in the realm of organometallic lanthanide complexes, while also placing the catalytic reactions supported by these species within the context of known lanthanide catalysis worldwide, with a specific focus on phosphorus-based catalytic reactions such as intermolecular hydrophosphination and hydrophosphinylation. α-Metalated N,N-dimethylbenzylamine ligands have been utilized to generate homoleptic lanthanide complexes, which have subsequently proven to be highly active lanthanum-based catalysts. The main goal of our research program has been to enhance the catalytic efficiency of lanthanum-based complexes, which began with initial successes in the stoichiometric synthesis of organometallic lanthanide complexes and utilization of these species in catalytic hydrophosphination reactions. Not only have these species supported traditional lanthanide catalysis, such as the hydrophosphination of heterocumulenes like carbodiimides, isocyanates, and isothiocyanates, but they have also been effective for a plethora of catalytic reactions tested thus far, including the hydrophosphinylation and hydrophosphorylation of nitriles, hydrophosphination and hydrophosphinylation of alkynes and alkenes, and the heterodehydrocoupling of silanes and amines. Each of these catalytic transformations is meritorious in its own right, offering new synthetic routes to generate organic scaffolds with enhanced functionality while concurrently minimizing both waste generation and energy consumption. Objectives: We aim for the research summary presented herein to inspire and encourage other researchers to investigate f-element based stoichiometric and catalytic reactions. Our efforts in this field began with the recognition that potassium salts of benzyldimethylamine preferred deprotonation at the α-position, rather than the ortho-position, and we wondered if this regiochemistry would be retained in the formation of lanthanide complexes. The pursuit of this simple idea led first to a series of structurally fascinating homoleptic organometallic lanthanide complexes with surprisingly good stability. Fundamental studies of the protonolysis chemistry of these complexes ultimately revealed highly versatile lanthanide-based precatalysts that have propelled a catalytic investigation spanning more than a decade. We anticipate that this summative perspective will animate the synthetic as well as biological communities to consider La(DMBA)3-based catalytic methods in the synthesis of functionalized organic scaffolds as an atom-economic, convenient, and efficient methodology. Ultimately, we envision our work making a positive impact on the advancement of novel chemical transformations and contributing to progress in various fields of science and technology.

Regioselective One-Pot Synthesis of Vicinal Bisphosphine Derivatives from Nitroalkenes by Hydrophosphinylation/Elimination/Hydrophosphinylation

Herein, a facile method is developed for the synthesis of vicinal bisphosphine derivatives based on a cascade of hydrophosphinylation, elimination, and hydrophosphinylation of secondary phosphine oxides with nitroalkenes. This cascade reaction provides step-economy access to a series of vicinal bisphosphine derivatives with high to excellent yields (up to 99%). This method was further extended to prepare, in one-pot, regioselective vicinal bisphosphine derivatives that incorporated two different phosphorus functional groups.

Superfast Formation of C(sp2 )-N, C(sp2 )-P, and C(sp2 )-S Vinylic Bonds in Water Microdroplets

We report examples of C(sp2 )-N, C(sp2 )-S, and C(sp2 )-P bond-forming transformations in water microdroplets at room temperature and atmospheric pressure using N2 as a nebulizing gas. When an aqueous solution of vinylic acid and amine is electrosprayed (+3 kV), the corresponding C(sp2 )-N product is formed in a single step, which was characterized using mass spectrometry (MS) and tandem mass spectrometry (MS2 ). The scope of this reaction was extended to other amines and other unsaturated acids, including acrylic (CH2 =CHCOOH) and crotonic (CH3 CH=CHCOOH) acids. We also found that thiols and phosphines are viable nucleophiles, and the corresponding C(sp2 )-S and C(sp2 )-P products are observed in positive ion mode using MS and MS2 .

Blue-Light Driven Iron-Catalyzed Oxy-phosphinylation of Activated Alkenes for β-Ketophosphine Oxide Synthesis

We have developed an original blue-light mediated iron-catalyzed oxy-phosphinylation of activated alkenes by secondary phosphine oxides under air at room temperature. Various β-ketophosphine oxides were then obtained in 43-97 % isolated yields. Control experiments revealed that radical process is involved in the mechanism.

Manganese(I)-Catalyzed Asymmetric Hydrophosphination of α,β-Unsaturated Carbonyl Derivatives

Here we report catalytic asymmetric hydrophosphination of α,β-unsaturated carbonyl derivatives using a chiral Mn(I) complex as a catalyst. Through H-P bond activation, various phosphine-containing chiral products can be accessed via hydrophosphination of various ketone-, ester-, and carboxamide-based Michael acceptors.

Recent advances in catalytic pnictogen bond forming reactions via dehydrocoupling and hydrofunctionalization

An examination of several catalytic reactions among the group 15 elements is presented. The connections between the chemistry of the pnictogens can sometimes be challenging, but aspects of metal-pnictogen reactivity are the key. The connecting reactivity comes from metal-catalyzed transformations such as dehydrocoupling and hydrofunctionalization. Pivotal mechanistic insights from E-N heterodehydrocoupling have informed the development of highly active catalysts for these reactions. Metal-amido nucleophilicity is often at the core of this reactivity, which diverges from phosphine and arsine dehydrocoupling. Nucleophilicity connects to the earliest understanding of hydrophosphination catalysis, but more recent catalysts are leveraging enhanced insertion activity through photolysis. This photocatalysis extends to hydroarsination, which may also have more metal-arsenido nucleophilicity than anticipated. However, metal-catalyzed arsinidene chemistry foreshadowed related phosphinidene chemistry by years. This examination shows the potential for greater influence of individual discoveries and understanding to leverage new advances between these elements, and it also suggests that the chemistry of heavier elements may have more influence on what is possible with lighter elements.

Synthesis and Characterization of Phosphinecarboxamide and Phosphinecarbothioamide, and Their Complexation with Palladium(II) Complex

Reactions of isocyanates/isothiocyanates with primary and secondary phosphines without solvent at room temperature afforded phosphinecarboxamide/phosphinecarbothioamide, respectively, in excellent yields. Furthermore, palladium complex Pd(COD)Cl₂ was allowed to react with Ph₂PC(O)NHPh (1a) to afford [Pd{Ph₂PC(O)NHPh-κP}₂Cl₂] (3). On the other hand, the reaction of Pd(COD)Cl₂ with 1 eq. of Ph₂PC(S)NHPh (2a) afforded [PdCl₂{Ph₂PC(S)NHPh-κP,S}] (4). In the case of a 1:2 molar ratio, [PdCl{Ph₂PC(S)NHPh-κP,S}{Ph₂PC(S)NHPh-κP}]Cl (5) was formed. The newly obtained compounds were fully characterized using multielement NMR measurements and elemental analyses. In addition, the molecular structures of Ph₂PC(O)NH(CH₂)₂Cl (1j), Ph₂PC(S)NHPh(4-Cl) (2c), and 3–5 were determined using single-crystal X-ray diffraction.

Broken Promises? On the Continued Challenges Faced in Catalytic Hydrophosphination

In this Perspective, we discuss what we perceive to be the continued challenges faced in catalytic hydrophosphination chemistry. Currently the literature is dominated by catalysts, many of which are highly effective, that generate the same phosphorus architectures, e.g., anti-Markovnikov products from the reaction of activated alkenes and alkynes with diarylphosphines. We highlight the state of the art in stereoselective hydrophosphination and the scope and limitations of chemoselective hydrophosphination with primary phosphines and PH₃. We also highlight the progress in the chemistry of the heavier homologues. In general, we have tried to emphasize what is missing from our hydrophosphination armament, with the aim of guiding future research targets.

Reported Catalytic Hydrofunctionalizations that Proceed in the Absence of Catalysts: The Importance of Control Experiments

The enlarged landscape of catalysis lies in the heart of chemistry. As the journey has set a milestone in organic synthesis, its darker side has not entered into the limelight. Studies disclose that the reported reactions by using catalysts were also attainable in the absence of catalysts in many cases. This article presents a literature collection that includes the significance of control experiments in hydrofunctionalization reactions. Systematic analysis reveals that the catalysts are ambiguous and might be unessential in chemical reactions enlisted here.

Catalysis and regioselectivity in hydrofunctionalization reactions of unsaturated carbon bonds. Part III

The review addresses the possibility of obtaining Markovnikov and anti-Markovnikov isomers in the reactions of unsaturated hydrocarbons with organophosphorus and organosulfur compounds having P–H and S–H bonds using metal salts or complexes as catalysts.

The bibliography includes 247 references.

Organophosphorus and Iron Catalysis: Good Partners for Hydrometalation of Olefins and Alkynes

The last decades have seen an impressive development of iron complexes involving organophosphorus ligands applied in homogeneous catalyzed hydrometalation of olefins and alkynes. Two main topics will be covered in this JOCSynopsis: (i) an overview of the achievements in the area of iron-catalyzed hydrophosphination and then (ii) hydrosilylation, hydroborylation, and hydromagnesiation reactions promoted by catalysts based on organophosphorus ligands and iron.

Homoleptic mono-, di-, and tetra-iron complexes featuring phosphido ligands: a synthetic, structural, and spectroscopic study

We report the first series of homoleptic phosphido iron complexes synthesized by treating either the β-diketiminato complex [(Dippnacnac)FeCl₂Li(dme)₂] (Dippnacnac = HC[(CMe)N(C₆H₃-2,6-iPr₂)]₂) or [FeBr₂(thf)₂] with an excess of phosphides R₂PLi (R = tBu, tBuPh, Cy, iPr). Reaction outcomes depend strongly on the bulkiness of the phosphido ligands. The use of tBu₂PLi precursor led to an anionic diiron complex 1 encompassing a planar Fe₂P₂ core with two bridging and two terminal phosphido ligands. An analogous reaction employing less sterically demanding phosphides, tBuPhPLi and Cy₂PLi yielded diiron anionic complexes 2 and 3, respectively, featuring a short Fe-Fe interaction supported by three bridging phosphido groups and one additional terminal R₂P^- ligand at each iron center. Further tuning of the P-substrates bulkiness gave a neutral phosphido complex 4 possessing a tetrahedral Fe₄ cluster core held together by six bridging iPr₂P moieties. Moreover, we also describe the first homoleptic phosphanylphosphido iron complex 5, which features an iron center with low coordination provided by three tBu₂P-P(SiMe₃)^- ligands. The structures of compounds 1-5 were determined by single-crystal X-ray diffraction and 1-3 by ¹H NMR spectroscopy. Moreover, the electronic structures of 1-3 were interrogated using zero-field Mössbauer spectroscopy and DFT methods.

Convenient synthesis of phosphinecarboxamide and phosphinecarbothioamide by hydrophosphination of isocyanates and isothiocyanates

Convenient synthesis of phosphinecarboxamidein by hydrophosphination of isocyanates (and isothiocyanates) was achieved without catalyst and solvent. This system shows shorter reaction time, high yield, and good functional group tolerance.

Thermally Stable Ln(II) and Ca(II) Bis(benzhydryl) Complexes: Excellent Precatalysts for Intermolecular Hydrophosphination of C-C Multiple Bonds

A series of Ln(II) and Ca(II) bis(alkyl) complexes with bulky benzhydryl ligands, [( p- tBu-C₆H₄)₂CH]₂M(L _n) (M = Sm, L = DME, n = 2 (1); M = Sm, Yb, Ca, L = TMEDA, n = 1 (2, 3, 4), were synthesized by the salt-metathesis reaction of MI₂(THF) _n ( n = 0-2) and [( p- tBu-C₆H₄)₂CH]^-Na⁺. In complex 1, the benzhydryl ligands are bound to the metal center in η²-coordination mode. Unlike complex 1, in isomorphous complexes 3 and 4, due to the coordination unsaturation of the metal center, the both benzhydryl ligands coordinate to the metal in η³-fashion. In complex 2, one ligand is η³-coordinated while the second one is η⁴-coordinated to the Sm(II) ion. Complexes 2-4 demonstrated unprecedented thermal stability: no evidence of decomposition was observed after heating their solutions in C₆D₆ at 100 °C during 72 h. Complex 1 behaves differently: thermolysis in C₆D₆ solution at 75 °C results in total decomposition in 8 h. Addition of DME promotes decomposition of 2-4 and makes it feasible at 40 °C. Complexes 1-4 demonstrated high catalytic activity and excellent regio- and chemoselectivities in intermolecular hydrophosphination of double and triple C-C bonds with both primary and secondary phosphines. Complexes 2 and 3 enable addition of PhPH₂ toward the internal C═C bond of Z- and E-stilbenes with 100% conversion under mild conditions. Double sequential hydrophosphination of phenylacetylene with Ph₂PH and PhPH₂ was realized due to the application of Yb(II) complex as a catalyst.

Hydrophosphination of alkenes and alkynes with primary phosphines catalyzed by zirconium complexes bearing aminophenolato ligands

Zirconium complexes stabilized by amine-bridged bis(phenolato) ligands showed good activity and chemo-selectivity in catalyzing intermolecular hydrophosphination of C-C multiple bonds with primary phosphines under mild conditions. A broad range of alkenes and alkynes underwent a mono-addition reaction with phenylphosphine, which generated secondary phosphines in 39-99% yields and >7 : 1 selectivity (over double hydrophosphination).

Evidence for Iron-Catalyzed α-Phosphinidene Elimination with Phenylphosphine

The ubiquitous half-sandwich iron complex [CpFe(CO)₂ Me] (Cp=η⁵ -C₅ H₅ ) appears to be a catalyst for α-phosphinidene elimination from primary phosphines. Dehydrocoupling reactions provided initial insight into this unusual reaction mechanism, and trapping reactions with organic substrates gave products consistent with an α elimination mechanism, including a rare example of a three-component reaction. The substrate scope of this reaction is consistent with generation of a triplet phosphinidene. In all, this study presents catalytic phosphinidene transfer to unsaturated organic substrates.

Visible-light and thermal driven double hydrophosphination of terminal alkynes using a commercially available iron compound

An air-stable, commercially available iron catalyst provides fast efficient double hydrophosphination of alkynes under thermal or photochemical conditions.

Synthesis and molecular structures of divalent bridged bis(guanidinate) europium complexes and their application in intermolecular hydrophosphination of alkenes and alkynes

Bimetallic Eu^IIcomplexes supported by bridged bis(guanidinate) ligands are efficient precatalysts for the intermolecular hydrophosphination of alkenes and alkynes.