anti-Markovnikov Products Research Articles

Hydromethylthiolation of alkynes via nucleophilic addition of dimethyl disulfide in DMSO

A hydromethylthiolation method for various alkynes has been developed using dimethyl disulfide as a source of the nucleophilic methylthiolate anion in a DMSO/EtOH or DMSO/H2O solvent system, with KOH as the base. For terminal aromatic alkynes, the reactions predominantly yield (Z)-anti-Markovnikov hydromethylthiolation products. The ratio of anti-Markovnikov to Markovnikov products typically exceeds 10:1, while the ratio of (Z)- to (E)-anti-Markovnikov products usually surpasses 7:1. In contrast, terminal aliphatic alkynes primarily produce Markovnikov hydromethylthiolation products. Reactions of internal aromatic alkynes also successfully produce the corresponding hydromethylthiolation products, whereas internal aliphatic alkynes do not exhibit reactivity in this system. The proposed mechanism suggests that in a basic DMSO solvent system, each equivalent of dimethyl disulfide is converted into two equivalents of methylthiolate anion. This anion then undergoes nucleophilic addition to the alkyne substrates, yielding hydromethylthiolation products. The regioselectivity and stereoselectivity of the hydromethylthiolation are influenced by the stability of the vinyl carbanion intermediate. Additionally, this method is also applicable to the hydrothiolation of alkynes using other disulfides.

Review of recent development in Anti-Markovnikov addition reaction of olefins

The regioselective functionalization of terminal olefins is of significant importance in organic synthesis. Based on the critical observations of Markovnikov, the types of addition products can be identified as Markovnikov or anti-Markovnikov products. In recent years, the anti-Markovnikov addition reaction of olefins has caught many scientists’ eyes because of its broad application prospects in chemical and pharmaceutical industries and its perfectly compliant with green chemistry. Herein, we summarized the main methodologies developed for the functionalization of olefins and compared their advantages and disadvantages, hoping that this minireview can provide some inspiration for researchers to develop more effective pathways of functional group production based on olefins.

Ni–H-Catalyzed Chemo- and Regioselective Hydroarylation of Vinylsilanes

AbstractA chemo- and regioselective hydroarylation of vinylsilanes with (hetero)aryl iodides under Ni–H catalysis is reported. This mild and straightforward protocol furnishes the anti-Markovnikov products in good yields as single regioisomers. This study demonstrates excellent control over the chemoselectivity and complements existing methods for the construction of homobenzylic silanes.

Nickel-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination

The fluoroalkyl-containing organic molecules are widely used in drug discovery and material science. Herein, we report ligand regulated nickel(0)-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination, providing an atom- and step-economical synthesis route of two types of fluoroalkyl substituted silanes with exclusive regioselectivity. The anti-Markovnikov addition products (β-fluoroalkyl substituted silanes) are formed with monodentate phosphine ligand. Noteworthy, the bidentate phosphine ligand promote the generation of the more challenging Markovnikov products (α-fluoroalkyl substituted silanes) with tetrasubstituted saturated carbon centers. This protocol features with easy available starting materials and commercially available nickel catalysis, a wide range of substrates and excellent regioselectivity. The structure divergent products undergo a variety of transformations. Comprehensive mechanistic studies including the inverse kinetic isotope effects demonstrate the regioselectivity controlled by ligand structure through α-CF3 nickel intermediate. DFT calculations reveal a distinctive mechanism involving an open-shell singlet state, which is crucial for generating intricate tetra-substituted Markovnikov products.

Organo-Photocatalytic Anti-Markovnikov Hydroamidation of Alkenes with Sulfonyl Azides: A Combined Experimental and Computational Study.

The construction of C(sp3)-N bonds via direct N-centered radical addition with olefins under benign conditions is a desirable but challenging strategy. Herein, we describe an organo-photocatalytic approach to achieve anti-Markovnikov alkene hydroamidation with sulfonyl azides in a highly efficient manner under transition-metal-free and mild conditions. A broad range of substrates, including both activated and unactivated alkenes, are suitable for this protocol, providing a convenient and practical method to construct sulfonylamide derivatives. A synergistic experimental and computational mechanistic study suggests that the additive, Hantzsch ester (HE), might undergo a triplet-triplet energy transfer manner to achieve photosensitization by the organo-photocatalyst under visible light irradiation. Next, the resulted triplet excited state 3HE* could lead to a homolytic cleavage of C4-H bond, which triggers a straightforward H-atom transfer (HAT) style in converting sulfonyl azide to the corresponding key amidyl radical. Subsequently, the addition of the amidyl radical to alkene followed by HAT from p-toluenethiol could proceed to afford the desired anti-Markovnikov hydroamidation product. It is worth noting that mechanistic pathway bifurcation could be possible for this reaction. A feasible radical chain propagation mechanistic pathway is also proposed to rationalize the high efficiency of this reaction.

Catalytic Properties of [PSiP] Pincer Cobalt(II) Chlorides Supported by Trimethylphosphine for Alkene Hydrosilylation Reactions.

In this paper, six silyl [PSiP] pincer cobalt(II) chlorides 1-6 [(2-Ph2PC6H4)2MeSiCo(Cl)(PMe3)] (1), [(2-Ph2PC6H4)2HSiCo(Cl)(PMe3)] (2), [(2-Ph2PC6H4)2PhSiCo(Cl)(PMe3)] (3), [(2-iPr2PC6H4)2HSiCo(Cl)(PMe3)] (4), [(2-iPr2PC6H4)2MeSiCo(Cl)(PMe3)] (5), and [(2-iPr2PC6H4)2PhSiCo(Cl)(PMe3)] (6)) were prepared from the corresponding [PSiP] pincer preligands (L1-L6), CoCl2 and PMe3 by Si-H bond activation. The catalytic activity of complexes 1-6 for alkene hyrdosilylation was studied. It was confirmed that complex 1 is the best catalyst with excellent regioselectivity among the six complexes. Using 1 as the catalyst, the catalytic reaction was completed within 1 h at 50 °C, predominantly affording Markovnikov products for aryl alkenes and anti-Markovnikov products for aliphatic alkene substrates. During the investigation of the catalytic mechanism, the Co(II) hydrides [(2-Ph2PC6H4)2MeSiCo(H)(PMe3)] (8) and [(2-iPr2PC6H4)2MeSiCo(H)(PMe3)] (9) were obtained from the stoichiometric reactions of complex 1 and 5 with NaBHEt3, respectively. Complexes 8 and 9 could also be obtained by the reactions of preligands L1 and L5 with Co(PMe3)4 via Si-H bond cleavage. More experiments corroborated that complex 8 is the real catalyst for this catalytic system. Under the same catalytic conditions as complex 1, using complex 8 as a catalyst, complete conversion of styrene was also achieved in 1 h, and the selectivity remained unchanged. Based on the experimental results, we propose a plausible mechanism for this catalytic reaction. The addition of B(C6F5)3 to catalyst 1 can reverse the selectivity of styrene hydrosilylation from the Markovnikov product as the main product (b/l = 99:1) to the anti-Markovnikov product as the main product (b/l = 40:60). Further study indicated that using the (CoCl2 + L1) system instead of complex 1, the selectivity was changed from Markovnikov to anti-Markovnikov product (b/l = 1:99.7). Therefore, the selectivity for the substrate styrene is influenced by the presence of a PMe3 ligand. The different selectivities may be caused by different active species. For the system of complex 1, a cobalt(II) hydride is the real catalyst, but for the (CoCl2 + L1) system, a cobalt(I) complex is proposed as active species. The molecular structures of Co(II) compounds 5 and 9 were resolved by single-crystal X-ray diffraction.

Highly Anti-Markovnikov Selective Oxidative Arene Alkenylation Using Ir(I) Catalyst Precursors and Cu(II) Carboxylates.

The Ir(I) complex [Ir(μ-Cl)(coe)2]2 (coe = cis-cyclooctene) is a catalyst precursor for benzene alkenylation using Cu(II) carboxylate salts. Using [Ir(μ-Cl)(coe)2]2, propenylbenzenes are formed from the reaction of benzene, propylene, and CuX2 (X = acetate, pivalate, or 2-ethylhexanoate). The Ir-catalyzed reactions selectively produce anti-Markovnikov products, trans-β-methylstyrene, cis-β-methylstyrene, and allylbenzene, along with minor amounts of the Markovnikov product, α-methylstyrene. The selectivity for the anti-Markovnikov products changed as the reaction progressed. For example, in a reaction that uses 240 equiv of Cu(OHex)2 (related to Ir), the selectivity for the anti-Markovnikov products increases from 18:1 at 3 h to 42:1 at 42 h with 30 psig of propylene at 150 °C. Studies of product stability have revealed that the increase in the selectivity for anti-Markovnikov products is not the result of an isomerization process or the selective decomposition of specific products. Rather, the change in selectivity correlates with the ratio of Cu(II) to Cu(I) in the solution, which decreases as the reaction progresses. We propose that the identity of the active catalyst changes as Cu(I) is accumulated, resulting in the formation of an active catalyst that is more selective for anti-Markovnikov products. Using a 4:1 Cu(I)/Cu(II) ratio at the start of the reaction, a 65(3):1 anti-Markovnikov/Markovnikov ratio is observed.

Tuning light-driven oxidation of styrene inside water-soluble nanocages

Selective functionalization of innate sp2 C-H bonds under ambient conditions is a grand synthetic challenge in organic chemistry. Here we combine host-guest charge transfer-based photoredox chemistry with supramolecular nano-confinement to achieve selective carbonylation of styrene by tuning the dioxygen concentration. We observe exclusive photocatalytic formation of benzaldehyde under excess O2 (>1 atm) while Markovnikov addition of water produced acetophenone in deoxygenated condition upon photoexcitation of confined styrene molecules inside a water-soluble cationic nanocage. Further by careful tuning of the nanocage size, electronics, and guest preorganization, we demonstrate rate enhancement of benzaldehyde formation and a complete switchover to the anti-Markovnikov product, 2-phenylethan-1-ol, in the absence of O2. Raman spectroscopy, 2D 1H-1H NMR correlation experiments, and transient absorption spectroscopy establish that the site-selective control on the confined photoredox chemistry originates from an optimal preorganization of styrene molecules inside the cavity. We envision that the demonstrated host-guest charge transfer photoredox paradigm in combination with green atom-transfer reagents will enable a broad range of sp2 carbon-site functionalization.

Hydroboration and hydrosilylation of alkenes catalyzed by an unsymmetrical magnesium methyl complex.

The hydroboration and hydrosilylation of alkenes catalyzed by the unsymmetrical β-diketiminate magnesium methyl complex [(DippXylNacnac)MgMe (THF)] (1) have been reported. When complex 1 was employed as a highly efficient catalyst in the hydroboration of various alkenes with HBpin, only the anti-Markovnikov hydroboration products were obtained in high yields and with high regioselectivities under mild reaction conditions (60 °C). To our surprise, it showed different regioselectivities in the hydrosilylation of a range of alkenes with PhSiH3. Aromatic alkene substrates afforded the corresponding branched Markovnikov hydrosilylation products in high yields and with high regioselectivities; conversely, aliphatic alkenes produced the linear anti-Markovnikov products in moderate yields. This is completely consistent with the corresponding density functional theory (DFT) calculations. In addition, the practical utility was demonstrated via scale-up reactions of boronate esters and a preliminary plausible mechanism of hydroboration and hydrosilylation have been investigated as well.

The structures and reactivity of NHC-supported copper(i) triphenylgermyls.

Deprotonation of triphenyl germane with NHC-supported copper alkoxides afforded four novel (NHC)CuGePh3 complexes. Of these, (IPr)CuGePh3 (IPr = :C{N(2,6-iPr2C6H3)CH}2) was selected for further investigation. Analysis by EDA-NOCV indicates it to be a germyl nucleophile and its σ-bond metathesis reaction with a range of p-block halides confirmed it to be a convenient source of [Ph3Ge]-. The Cu-Ge bond of (IPr)CuGePh3 underwent π-bond insertions with tBuNCS, CS2, and PhNCO to furnish a series of germyl substituted carboxylate derivatives, (IPr)CuXC(Y)GePh3 (X = S, NPh; Y = S, NtBu, O), which were structurally characterised. (IPr)CuGePh3 inserted phenyl acetylene, providing both the Markovnikov and anti-Markovnikov products. The (NHC)CuGePh3 compounds were validated as catalytic intermediates; addition of 10 mol% of NHC-copper(i) alkoxide to a mixture of triphenyl germane and a tin(iv) alkoxide resulted in a tin/germanium cross coupling with concomitant formation of alcohol. Moreover, a catalytic hydrogermylation of Michael acceptors was developed with Ph3GeH adding to 7 activated alkenes in good conversions and yields in the presence of 10 mol% of NHC-copper(i) alkoxide. In all cases, this reaction provided the β-germylated substrate implicating nucleophilicity at germanium.

Nickel(II)/Lewis acid catalysed olefin hydroamination and hydroarylation under mild conditions.

Aniline derivatives are important nitrogen-containing compounds with wide applications in chemicals, pharmaceuticals and agrochemicals. In the work described herein, nickel(II)/Lewis acid (LA) catalysed olefin hydroamination with anilines was explored for use in aniline derivative syntheses. The Ni(II)/LA catalysis proceeded smoothly under mild conditions, whereas using Ni(OAc)2 alone, the catalyst was inactive. Remarkably, the Markovnikov addition type products were obtained when substituted styrenes were used as the olefin source, while the anti-Markovnikov addition type products were obtained when the electron-deficient olefins such as acrylonitrile and acrylates were used. The mechanistic studies revealed that hydroamination of the styrene derivates proceeded via the amino-Ni(II)/LA attacking the carbocation intermediate which was generated by the protonation of the olefin, whereas for acrylonitrile and acrylates, it proceeded by a direct amino-Ni(II)/LA attack on the olefin by nucleophilic addition. In addition, the hydroarylation product was generated by the Hofmann-Martius rearrangement of the hydroamination product.

Reaction of aromatic carboxylic acids with phenylacetylene with the participation of a zinc catalyst

The reaction of benzoic, 4-methylbenzoic, 2-bromobenzoic and 4-bromobenzoic acids with phenylacetylene was carried out in a toluene solution at a temperature of 110 0C in the presence of a catalyst - 1 mol % [Zn(C4H7S2)4](NO3)2. In the coupling reaction of carboxylic acids with phenylacetylene a mixture of coupling products is formed according to the Markovnikov and anti-Markovnikov rules. A reaction mechanism was proposed and it was found that the yield of vinyl esters increased in the serie 4-CH3-C6H4COOH< C6H5COOH< 4-Br-C6H4COOH< 2-Br-C6H4COOH. It was found that with an increasing acidity of the carboxylic acids, the product formed by Markovnikov rule has been formed in a larger amount. On the contrary, as the acidity of the starting compounds decreased, the amount of the anti-Markovnikov coupling product has increased. The total yield of reaction products of phenylacetylene with carboxylic acid is 44% (65/35) in 4-methylbenzoic acid, 67% (80/20) in benzoic acid, 78% (82/18) in 4-bromobenzoic acid, 82% (85 /15) in 2-bromobenzoic acid. The structure of the synthesized vinyl esters was proved on the base of the analysis of IR, 1H, 13C NMR and Mass spectrums.

Anti-Markovnikov Intermolecular Hydroamination of Alkenes and Alkynes: A Mechanistic View.

Hydroamination, the addition of an N-H bond across a C-C multiple bond, is a reaction with a great synthetic potential. Important advances have been made in the last decades concerning catalysis of these reactions. However, controlling the regioselectivity in the amine addition toward the formation of anti-Markovnikov products (addition to the less substituted carbon) still remains a challenge, particularly in intermolecular hydroaminations of alkenes and alkynes. The goal of this review is to collect the systems in which intermolecular hydroamination of terminal alkynes and alkenes with anti-Markovnikov regioselectivity has been achieved. The focus will be placed on the mechanistic aspects of such reactions, to discern the step at which regioselectivity is decided and to unravel the factors that favor the anti-Markovnikov regioselectivity. In addition to the processes entailing direct addition of the amine to the C-C multiple bond, alternative pathways, involving several reactions to accomplish anti-Markovnikov regioselectivity (formal hydroamination processes), will also be discussed in this review. The catalysts gathered embrace most of the metal groups of the Periodic Table. Finally, a section discussing radical-mediated and metal-free approaches, as well as heterogeneous catalyzed processes, is also included.

Catalytic Reaction with Benzoic Acid Phenylacetylene in the Presence of Complex Catalysts

In this work, we studied the processes of vinyl ester formation by the addition of benzoic acid to phenylacetylene in the presence of complex catalysts of diacetate-di (2-amino-5-methylthio-1,3,4-thiadiazolo) cobalt(II) ([Co(C3H5N3S2)2(CH3COO)2] and tetrakis(2-amino-5-ethylthio-1,3,4-thiadiazole)-zinc(II) dinitrate ([Zn(C4H7S2)4](NO3)2): 1-phenylvinyl benzoate and anti-Markovnikov coupling product - styryl benzoate were obtained. The effect of the nature of solvents on the yields of products in the presence of the [Zn(C4H7S2)4](NO3)2 complex catalyst was studied. The structure of the synthesized vinyl esters was proved by IR, 1H NMR, 13C NMR spectroscopies.

Thermally Robust and Highly Active PCP Cobalt(II) Catalyst for Linear-Selective Hydroboration of Terminal and Internal Olefins

We report the design and synthesis of cobalt complexes of L2X-type ligands for olefin hydroboration guided by the consideration of catalyst stability. Among the series of PCP-ligated Co(II) and Co(III) pincer complexes, the complex with iPr phosphino substituents exhibits broad scope, high functional group tolerance, and high catalytic activity at ppm catalyst loadings (17 ppm, 0.001 mol %) in the hydroboration of terminal olefins with pinacolborane (HBpin), furnishing anti-Markovnikov addition products. We also show that linear-selective hydroboration occurs with internal acyclic olefins at elevated temperatures, including those conjugated with the arene or carbonyl groups that are difficult to be achieved by previous catalysts. Such a catalytic property makes this cobalt catalyst suitable for terminally selective formal borylation of arylalkane through the dehydrogenation–hydroboration sequence. Experimental mechanistic data provide evidence for the involvement of a Co(II) hydride intermediate. Deuterium-labeling experiments show that the formation of terminal alkylboronate ester from internal olefins likely proceeds via the initial generation of secondary alkyl species, followed by chain-walking to form primary alkyl species, which then reacts with HBpin to produce the linear product and regenerate the hydride species.

Rhodium-Catalyzed Alkenylation of Arenes with Multi-Substituted Olefins: Comparison of Selectivity and Reaction Rate as a Function of Olefin Identity

Rhodium-catalyzed arene alkenylation using Cu(II) carboxylates as the in situ oxidant and mono-substituted olefins has been previously reported (e.g., J. Am. Chem. Soc. 2019, 139, 5474; J. Am. Chem. Soc. 2018, 140, 17007; Organometallics 2019, 38, 3860; J. Am. Chem. Soc. 2020, 142, 10534). Herein, studies are extended to multi-substituted olefins with the goal of evaluating the effect of olefin substitution pattern and substituent identity on selectivity and turnover frequency. The influence of olefin substitution is probed by comparing the conversion of benzene to alkenyl arenes with ethylene, propylene, 1-butene, cis-2-butene, trans-2-butene, isobutene, 2-methyl-2-butene, and tetramethylethylene as well as the phenyl-substituted olefins and isomers of propenylbenzene. The rate of oxidative hydrophenylation for multi-substituted olefins follows the trend monosubstituted > disubstituted > trisubstituted, and tetrasubstituted olefins are unreactive. To probe the effect of substituent size on Markovnikov/anti-Markovnikov regioselectivity, cyclohexyl, tert-butyl, isopropyl, ethyl, and methyl substituted α-olefins are compared. Selectivity for anti-Markovnikov products generally increases as substituent steric bulk is increased. Tolerance for some functionalized olefins is demonstrated. The ortho/meta/para regioselectivity with mono-substituted arenes reveals that arene and olefin identity influences selectivity. Further mechanistic studies provide evidence for Curtin–Hammet control of ortho/meta/para regioselectivity with monosubstituted arenes.

The Mechanism of Markovnikov-Selective Epoxide Hydrogenolysis Catalyzed by Ruthenium PNN and PNP Pincer Complexes.

The homogeneous catalysis of epoxide hydrogenolysis to give alcohols has recently received significant attention. Catalyst systems have been developed for the selective formation of either the Markovnikov (branched) or anti-Markovnikov (linear) alcohol product. Thus far, the reported catalysts exhibiting Markovnikov selectivity all feature the potential for Noyori/Shvo-type bifunctional catalysis, with either a RuH/NH or FeH/OH core structure. The proposed mechanisms of epoxide ring-opening have involved cooperative C-O bond hydrogenolysis involving the metal hydride and the acidic pendant group on the ligand, in analogy to the well-documented mechanism of polar double-bond hydrogenation exhibited by catalysts of this type. In this work, we present a combined computational/experimental study of the mechanism of epoxide hydrogenolysis catalyzed by Noyori-type PNP and PNN complexes of ruthenium. We find that, at least for these ruthenium systems, the previously proposed bifunctional pathway for epoxide ring-opening is energetically inaccessible; instead, the ring-opening proceeds through opposite-side nucleophilic attack of the ruthenium hydride on the epoxide carbon, without the involvement of the ligand N-H group. For both catalyst systems, the rate law and overall barrier predicted by density functional theory (DFT) are consistent with the results from kinetic studies.

A Terminal Hydride of Hafnium Supported by a Triamidoamine Ligand

A mononuclear hafnium hydride supported by an aryl-substituted triamidoamine ligand [HfH(thf)(Xy-N3N)] (Xy-N3N = {(3,5-Me2C6H3)NCH2CH2}3N3–) was synthesized by either hydrogenolysis of the hydrocarbyl complex [Hf(R)(thf)(Xy-N3N)] (R = Me, CH2SiMe3, η3-C3H5, CH2Ph) in tetrahydrofuran (THF) or, more conveniently, by salt metathesis of the chloro precursor [HfCl(thf)(Xy-N3N)] with NaBEt3H in methylcyclohexane. The structure of a terminal hydride with a distorted capped trigonal bipyramidal geometry was characterized by single crystal X-ray diffraction (d(Hf–H): 1.83(3) Å) and by 1H NMR spectroscopy. The unusually low field shifted 1H chemical shift for the hydride ligand was detected at δ 18.28 ppm. Dehydrogenative thermolysis of the hydride complex at 25 °C in benzene or toluene resulted in deprotonation of the α-hydrogen of one of the three XyNCH2CH2 groups in the ligand by the hydride, followed by the combination of this deprotonated anionic complex with cationic complex [Hf(Xy-N3N)]+ to give an unsymmetric dinuclear complex bridged by μ-H, μ-NXy, and μ,κN,κC-XyNCHCH2 groups. This decomposition product was characterized by single crystal X-ray diffraction and by 1H and 13C NMR spectroscopy and analyzed by density functional theory (DFT) calculations. Hydrogenation in THF at 25 °C reformed the hydride complex over a period of 48 h. The hydride complex reacted with olefins RHC═CH2 (R = H, Et, nHex, cHex, Ph) to give the corresponding anti-Markovnikov insertion products [Hf(CH2CH2R)(thf)n(Xy-N3N)]. Catalytic hydrogenation of olefins was achieved with 5 mol % of the hydride complex at 70 °C in THF or benzene.

Recyclable and convenient-to-handle Pt/ethylene glycol catalytic system – an approach to sustainable hydrosilylation

This study presents a highly efficient and simple recyclable catalytic system for heterophase hydrosilylation. This catalytic system consisting of a commercially available platinum precatalyst, namely K2PtCl4, and a cheap green solvent, namely ethylene glycol (EG), is easily prepared by dissolving K2PtCl4 in EG without employing ligands, additives, or inert atmosphere, at r.t. It was found that mononuclear Pt0-complex generated in the catalytic system is a single-atom catalyst. The method enables 36 recycles with quantitative yield in air at r.t. The reaction proceeds at a high rate even with small catalyst loadings. High values of TON (up to 105) and TOF (up to 106) were achieved. This approach is applicable to a wide range of unsaturated compounds, such as terminal or internal alkenes, alkynes, and alkyl-, phenyl-, and siloxy-containing hydrosilanes. Moreover, the heterophase catalytic system is suitable for synthesis of linear and cross-linked polyorganosiloxanes. In most cases, the reaction provides high yields (up to 95–99%) and selectivity. It gives mostly anti-Markovnikov products, which can be isolated from the catalytic system by simple decantation. The process is scalable to gram quantities.

Ether/Thioether-Functionalized Dianionic α-Iminopyridine Rare-Earth Metal Amido Complexes and Their Catalytic Activity toward Hydrophosphination of Alkenes

The double deprotonation of 2-aminomethyl pyridine by rare-earth metal triamido complexes was found to be an alternative strategy to anchor dianionic iminopyridine on rare-earth metal centers with the morpholinyl group previously. To verify the generality of the protocol with different appendant donor groups, reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with ether/thiotether-substituted 2-aminomethyl pyridine 2-(CH3DCH2CH2NHCH2)-6-R-C5H3N (D = O, R = H (1), Ph (2); D = S, R = H (3)) were performed, leading to the formation of ether/thioether-functionalized dianionic α-iminopyridine rare-earth metal amido complexes {μ-η2:σ1:κ1:κ1-2-[CH3ECH2CH2NCH]-6-R-C5H3N}2RE2[N(SiMe3)2]2 (D = O, R = H, RE = Dy (4a), Y (4b), Er (4c), Yb (4d), Lu (4e), R = Ph, RE = Dy (5a), Y (5b), Er (5c), Lu (5d); D = S, R = H, RE = Y (6a), Er (6b), Lu (6c)). These results supported the ability of oxygen or sulfur coordination in promoting the double deprotonation of 2-aminomethyl pyridine to construct new iminopyridine rare-earth metal complexes in the dianionic form. Further examination of these rare-earth metal amido complexes displayed good catalytic activity for hydrophosphination of alkenes, affording anti-Markovnikov addition products under solvent-free conditions.