Scope and Limitations of the s-Block Metal-Mediated Pudovik Reaction

Hydrophosphanylation of Alkynes via Magnesium Complexes: Evidence for Ligand Dependency in Structure-Activity Relationships

Pursuing practical, straightforward, and sustainable methods for forming carbon-phosphorus bonds is crucial in academia and industry. In this study, we showed that bis(diiminate)-based magnesium complexes [L(Mg-nBu)2] (nBu = n-butyl) could effectively catalyze the hydrophosphanylation of alkynes, resulting in monophosphanylated vinyledene- and 1,2-diphosphanylated alkanes in a stepwise manner. This transformation showcases an excellent atom economy, broad functional group tolerance, and gram-scale synthesis for organophosphorus compounds. Through controlled experiments and with the support of DFT calculations, we elucidated the reaction mechanism, identifying the active catalytic species and revealing a stepwise hydrophosphanylation process of alkynes. Although complex Mg-1 showed its potential in this transformation, complexes Mg-2 and Mg-3, having ethyl and phenyl spacers, produced a lower yield of hydrophosphanylated products, indicating the role of ligand (spacer) in this catalytic reaction. Further, the activity of Mg-1 was compared with a monomeric magnesium complex, Mg-4, and it was found that the performance of the Mg-4 in alkyne hydrophosphanylation is quite lower than the results obtained by using Mg-1. This work demonstrated that a dimeric magnesium complex with a suitable spacer can enhance the catalytic activity manyfolds in the hydrophosphanylation of alkynes.

Syntheses and structures of dimesitylphosphinite complexes of alkali metals and their catalytic activity in hydrophosphorylation reactions

Metalation of dimesitylphosphane oxide, Mes2P(O)H (1), with alkali metal reagents (nBuLi, NaH, and A(hmds); A = K, Rb, and Cs) in THF yields the corresponding dimesitylphosphinites of lithium (2-thf), sodium (3-thf), potassium (4-thf), rubidium (5-thf), and caesium (6). Their molecular structures exhibit a broad and fascinating variety. Dinuclear compounds 2-thf, 3-thf, and 5-thf have central four-membered A2O2 rings, whereas the potassium congener crystallises as a tetranuclear complex with an inner A4O4 heterocubane cage. The tetranuclear caesium congener precipitates without thf coligands and exhibits a quite unique structure in its crystalline state. Due to their catalytic activity in hydrophosphorylation reactions, we focus on the solvent-structure relationship of the potassium derivatives. In hydrocarbons, [K4(O-PMes2)4]2 (4) is formed, and bidentate Lewis bases like dme and tmeda are unable to deaggregate this tetranuclear cage compound, but bases with a higher denticity (diglyme, triglyme, and pmdeta) split this cage compound into dinuclear complexes with central K2O2 rings. In addition, very bulky P-bound aryl groups like 2,4,6-triisopropylphenyl in dinuclear 8-thf hinder the formation of tetranuclear cage compounds, whereas 2-methylnaphthyl substituents are not bulky enough and the tetranuclear cage compound 7-thf is stabilised. For the 2,4,6-triisopropylphenyl substituent, the rubidium and caesium congeners 11 and 12 crystallise with two central A2O2 rings interconnected by π-interactions. A heteroleptic potassium complex 9-hmds, containing hmds as well as phosphinite anions, represents a snapshot on the way from the starting K(hmds) to the phosphinite-based heterocubane congener. Finally, heterobimetallic [{(thf)K}2Mg(O-PMes2)4] (10-thf) with tetrahedrally coordinated Mg centres has been isolated.

Coordination chemistry of alkali metal dimesityl-thio- and dimesityl-selenophosphinites [(L)2A-EPMes2]2 (A = Li, Na, K; E = S, Se; L = THF, THP) and [(18C6)K-SPMes2]

The reactions of dimesitylphosphane oxide Mes2P(O)H with Lawessons reagent and dimesitylphoshane with selenium yield Mes2P(E)H with E = S (1a) and E = Se (1b), respectively, with moderate yields. Metalation of dimesitylphosphane sulfide 1a with n-butyllithium, sodium hydride or potassium hydride in THF allows the isolation of dinuclear dimesityl-thiophosphinites of the type [(thf)2A-S-PMes2]2 [A = Li (4), Na (5), K (2a)] with central four-membered A2S2 rings. The weaker base THP leads to the very similar aggregate [(thp)2K-S-PMes2]2 (3a) as has also been observed for the homologous potassium dimesityl-selenophosphinites of the type [(L)2K-Se-PMes2]2 [L = thf (2b), thp (3b)]. Addition of 18-crown-6 ether leads to deaggregation and expectedly to formation of mononuclear [(18C6)K-S-PMes2] (6). Moderate yields have been obtained due to dismutation reactions that yield the corresponding phosphinates AE2PMes2 and phosphanides APMes2, a degradation process which has been observed earlier also for Li-O-PMes2. This side reaction hampers the application of these thio- and selenophosphinites as catalysts in the addition of phosphane sulfides and selenides across alkynes.

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.

Recent advances in the carbon-phosphorus (C-P) bond formation from unsaturated compounds by s- and p-block metals

Researchers around the globe have witnessed several breakthroughs in s- and p-block metal chemistry. Over the past few years, several applications in catalysis associated with these main group metals have been established, and owing to their abundance and low cost and they have proved to be essential alternatives to transition metal catalysts. In this review, we present a detailed discussion on the catalytic addition of P-H bonds from various phosphine reagents to multiple bonds of unsaturated substrates for the synthesis of organophosphorus compounds with C-P bonds promoted by various s- and p-block metal catalysts, as published in the last decade.

Lanthanide Silylamide-Catalyzed Synthesis of Pyrano[2,3-b]indol-2-ones

A lanthanide silylamide-catalyzed tandem reaction of isatins, diethyl phosphite, and 2,3-diarylcyclopropenones has been developed. A series of pyrano[2,3-b]indol-2-ones were synthesized in high yields. The cooperation of the Lewis acidity of the lanthanide center and the Bronsted basicity of the N(SiMe₃)₂ anion may be the key factor affecting the catalytic activity of lanthanide amides.

Alkali-Metal Mediation: Diversity of Applications in Main-Group Organometallic Chemistry

Organolithium compounds have been at the forefront of synthetic chemistry for over a century, as they mediate the synthesis of myriads of compounds that are utilised worldwide in academic and industrial settings. For that reason, lithium has always been the most important alkali metal in organometallic chemistry. Today, that importance is being seriously challenged by sodium and potassium, as the alkali-metal mediation of organic reactions in general has started branching off in several new directions. Recent examples covering main-group homogeneous catalysis, stoichiometric organic synthesis, low-valent main-group metal chemistry, polymerization, and green chemistry are showcased in this Review. Since alkali-metal compounds are often not the end products of these applications, their roles are rarely given top billing. Thus, this Review has been written to alert the community to this rising unifying phenomenon of "alkali-metal mediation".

Scope and Limitations of the s-Block Metal-Mediated Pudovik Reaction

The hydrophosphorylation of phenylacetylene with di(aryl)phosphane oxides Ar2 P(O)H (Pudovik reaction) yields E/Z-isomer mixtures of phenylethenyl-di(aryl)phosphane oxides (1). Alkali and alkaline-earth metal di(aryl)phosphinites have been studied as catalysts for this reaction with increasing activity for the heavier s-block metals. The Pudovik reaction can only be mediated for di(aryl)phosphane oxides whereas P-bound alkyl and alcoholate substituents impede the P-H addition across alkynes. The demanding mesityl group favors the single-hydrophosphorylated products 1-Ar whereas smaller aryl substituents lead to the double-hydrophosphorylated products 2-Ar. Polar solvents are beneficial for an effective addition. Increasing concentration of the reactants and the catalyst accelerates the Pudovik reaction. Whereas Mes2 P(O)H does not form the bis-phosphorylated product 2-Mes, activation of an ortho-methyl group and cyclization occurs yielding 2-benzyl-1-mesityl-5,7-dimethyl-2,3-dihydrophosphindole 1-oxide (3).