Ytterbium(II) Complex-Catalyzed Selective Single and Double Hydrophosphination of 1,3-Enynes

1,3-Enynes with conjugated alkene and alkyne moieties are attractive building blocks in synthetic chemistry. However, neither 4,1-hydrophosphination nor dihydrophosphination of 1,3-enynes has been reported. In this paper, the divalent ytterbium and calcium amide complexes supported by silaimine-functionalized cyclopentadienyl ligands (C5Me4-Si(L)=NR) were developed, which successfully catalyzed the efficient single and double hydrophosphination of 1,3-enynes with diarylphosphines. The hydrophosphination reactions selectively produced homoallenyl phosphines and (E)-propenylene diphosphines, respectively. This work demonstrated the potential of hemilabile silaimine-Cp ligands in the supporting the efficient and selective rare- and alkaline-earth catalysts.

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.

Barium phosphidoboranes and related calcium complexes

The attempted synthesis of [{Carb}BaPPh2] (1) showed this barium-phosphide and its thf adducts, 1·thf and 1·(thf)2, to be unstable in solution. Our strategy to circumvent the fragility of these compounds involved the use of phosphinoboranes HPPh2·BH3 and HPPh2·B(C6F5)3 instead of HPPh2. This allowed for the synthesis of [{Carb}Ae{PPh2·BH3}] (Ae = Ba, 2; Ca, 3), [{Carb}Ca{(H3B)2PPh2}·(thf)] (4), [{Carb}Ba{PPh2·B(C6F5)3}] (5), [{Carb}Ba{O(B(C6F5)3)CH2CH2CH2CH2PPh2}·thf] (6), [Ba{O(B(C6F5)3)CH2CH2CH2CH2PPh2}2·(thf)1.5] (7) and [Ba{PPh2·B(C6F5)3}2·(thp)2] (8) that were characterised by multinuclear NMR spectroscopy (thp = tetrahydropyran). The molecular structures of 4, 6 and 8 were validated by X-ray diffraction crystallography, which revealed the presence of Ba⋯F stabilizing interactions (ca. 9 kcal mol-1) in the fluorine-containing compounds. Compounds 6 and 7 were obtained upon ring-opening of thf by their respective precursors, 5 and the in situ prepared [Ba{PPh2·B(C6F5)3}2]n. By contrast, thp does not undergo ring-opening under the same conditions but affords clean formation of 8. DFT analysis did not highlight any specific weakness of the Ba-P bond in 1·(thf)2. The instability of this compound is instead thought to stem from the high energy of its HOMO, which contains the non-conjugated P lone pair and features significant nucleophilic reactivity.

N-Heterocyclic Carbene-Coordinated M(II) (M = Yb, Sm, Ca) Bisamides: Expanding the Limits of Intermolecular Alkene Hydrophosphination

A series of NHC-stabilized amido compounds (NHC)_nM[N(SiMe₃)₂]₂ (M = Yb(II), Sm(II), Ca(II); n = 1, 2) showed remarkable catalytic efficiency in addition of PhPH₂ and PH₃ to alkenes under mild conditions and low catalyst loading. The effect of σ-donor capacity of NHCs on catalytic activity in hydrophosphination of styrene with PhPH₂ and PH₃ was revealed. For the series of three-coordinate complexes 1-4M, a tendency to increase the catalytic activity with growth of σ-donating strength of the carbene ligand was clearly demonstrated. The complex (NHC)₂Sm[N(SiMe₃)₂]₂ (NHC = 1,3-diisopropyl-2H-imidazole-2-ylidene) (5Sm) proved to be the most efficient catalyst, which enabled hardly realizable transformations such as PhPH₂ addition across internal C═C bonds of norbornene and cis- and trans-stilbenes, providing the highest reaction rate for addition of PH₃ to styrene. Excellent regio- and chemoselectivities of alkylation of PH₃ with styrenes allow for a selective and good-yield synthesis of desired organophosphines─either primary, secondary, or tertiary. Stepwise alkylation of PH₃ with various substituted styrenes can be efficiently applied as an approach to nonsymmetric secondary phosphines. The rate equation of the addition of styrene to PH₃ promoted by 5Sm was found: rate = k[styrene]¹[5Sm]¹.

Synthesis of Secondary Amines with Long Chains Containing Ether Bonds

A novel class of secondary amines with long chains containing ether bonds were synthesized by a three-step protection–etherification–deprotection process from diethanolamine. The optimum reaction conditions were examined. This method has the advantages of simplicity, low cost, and high yield. Furthermore, some new downstream products (diglycolamides) were prepared from the ether-containing long-chain secondary amines as reactants, and their loading capacities in extractions of several metal ions were evaluated.

Synthesis, structure, and coordination chemistry of a neutral pyrrolyl-functionalized amidinate ligand

A new o-phenylene-bridged ligand incorporating neutral pyrrolyl and amidino moieties was designed and synthesized. The reactivity of the ligand was investigated and showed versatile coordination modes towards alkali- and rare-earth metals.

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.

Ln(II) amido complexes coordinated by ring-expanded N-heterocyclic carbenes - promising catalysts for olefin hydrophosphination

First Ln(ii) ring-expanded NHC complexes (er-NHC)Ln[N(SiMe3)2]2 (Ln = Sm, Yb) are synthesized and proved to be highly efficient pre-catalysts for the intermolecular hydrophosphination of such indolent substrates as 1-alkenes, cyclohexene and norbornene.

A versatile nitrogen ligand for alkaline-earth chemistry

A readily available and versatile bis(imino)carbazolate ligand is shown to allow for the synthesis of a broad range of solution stable heteroleptic complexes of the alkaline-earth metals Mg, Ca, Sr and Ba.