(eta(3)-Allyl)palladium Complexes Bearing Diphosphinidenecyclobutene Ligands: Highly Active Catalysts for the Hydroamination of 1,3-Dienes This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture, Japan

Palladium-Catalyzed Regiodivergent Three-Component Alkenylamination of 1,3-Dienes with Alkyl and Aryl Amines

We report a palladium-catalyzed method for 4,3- or 4,1-selective alkenylamination of terminal dienes. Three-component couplings proceed with alkenyl triflates and several amines, giving vicinal carboamination with a Xantphos-supported catalyst and distal difunctionalization with a phosphoramidite ligand. A number of constitutionally different disubstituted dienes also participate in regiodivergent carboaminations. Experimental evidence indicates that selectivity in the Xantphos reactions is largely influenced by the substrate, whereas the phosphoramidite-promoted process is catalyst controlled, orchestrated by a key π-stacking interaction among the ligand, solvent, and substrate.

Progression of Hydroamination Catalyzed by Late Transition-Metal Complexes from Activated to Unactivated Alkenes

ConspectusCatalytic intermolecular hydroamination of alkenes is an atom- and step-economical method for the synthesis of amines, which have important applications as pharmaceuticals, agrochemicals, catalysts, and materials. However, hydroaminations of alkenes in high yield with high selectivity are challenging to achieve because these reactions often lack a thermodynamic driving force and often are accompanied by side reactions, such as alkene isomerization, telomerization, and oxidative amination. Consequently, early examples of hydroamination were generally limited to the additions of N-H bonds to conjugated alkenes or strained alkenes, and the catalytic hydroamination of unactivated alkenes with late transition metals has only been disclosed recently. Many classes of catalysts, including early transition metals, late transition metals, rare-earth metals, acids, and photocatalysts, have been reported for catalytic hydroamination. Among them, late transition-metal complexes possess several advantages, including their relative ease of handling and their high compatibility of substrates containing polar or sensitive functional groups.This Account describes the progression in our laboratory of hydroaminations catalyzed by late transition-metal complexes from the initial additions of N-H bonds to activated alkenes to the more recent additions to unactivated alkenes. Our developments include the Markovnikov and anti-Markovnikov hydroamination of vinylarenes with palladium, rhodium, and ruthenium, the hydroamination of dienes and trienes with nickel and palladium, the hydroanimation of bicyclic strained alkenes with neutral iridium, and the hydroamination of unactivated terminal and internal alkenes with cationic iridium and ruthenium. Enantioselective hydroaminations of these classes of alkenes to form enantioenriched, chiral amines also have been developed.Mechanistic studies have elucidated the elementary steps and the turnover-limiting steps of these catalytic reactions. The hydroamination of conjugated alkenes catalyzed by palladium, rhodium, nickel, and ruthenium occurs by turnover-limiting nucleophilic attack of the amine on a coordinated benzyl, allyl, alkene, or arene ligand. On the other hand, the hydroamination of unconjugated alkenes catalyzed by ruthenium and iridium occurs by turnover-limiting migratory insertion of the alkene into a metal-nitrogen bond. In addition, pathways for the formation of side products, including isomeric alkenes and enamines, have been identified during our studies. During studies on enantioselective hydroamination, the reversibility of the hydroamination has been shown to erode the enantiopurity of the products. Based on our mechanistic understandings, new generations of catalysts that promote catalytic hydroaminations with higher rates, chemoselectivity, and enantioselectivity have been developed. We hope that our discoveries and mechanistic insights will facilitate the further development of catalysts that promote selective, practical, and efficient hydroamination of alkenes.

P,N-type phosphaalkene-based Ir(i) complexes: synthesis, coordination chemistry, and catalytic applications

Iridium P,N phosphaalkene complexes show a rich coordination chemistry with unusual twofold C–H activation. The Ir(i) chloride complex can be applied for C–N coupling and alcohol upgrading reactions.

Activation of the C[double bond, length as m-dash]P bond in phosphanylphosphaalkenes (C[double bond, length as m-dash]P-P bond system) in the reaction with nucleophilic reagents: MeLi, nBuLi and tBuLi

Three reactions of phosphanylphosphaalkene (1) with nucleophiles were performed to activate the diphosphorus monomer. We observed similar results in the reactions with MeLi and nBuLi, in which the P-P bond is cleavaged and triphosphorus systems [P(Me)₂-CH(biph)-CH(biph)-P-(PtBu₂)]^- (1a'') and [P(nBu)₂-CH(biph)-CH(biph)-P-(PtBu₂)]^- (1b''), respectively, are formed depending on the nucleophilic reagent (biph = biphenyl). In the case of tBuLi, the P-P bond remains intact; on the phosphorus atom, only one -tBu group is substituted, and as a result, [(biph)(H)C-P(tBu)-PtBu₂]^- (1c) is generated as a stable carbanion. We additionally investigated the effect of substitution in the phenyl ring in the course of these reactions by involving two other phosphanylphosphaalkenes (3 and 4). All initial reactions were conducted in tetrahydrofuran (THF) solution at ambient temperature.

Chemistry of Several Sterically Bulky Molecules with P=P, P=C, and C≡P Bond

Several sterically protected, low-coordinate organophosphorus compounds with P=P, P=C, and C≡P bond are described in this study. Molecules such as diphosphenes, phosphaalkenes, 1-phosphaallenes, 1,3-diphosphaallenes, 3,4-diphosphinidenecyclobutenes, and phosphaalkynes are stabilized with an extremely bulky 2,4,6-tri-t-butylphenyl (Mes*) group. The synthesis, structures, physical, and chemical properties of these molecules are discussed, together with some successful applications in catalytic organic reactions.

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

This review continues consideration of the regioselectivity problem in the catalyzed hydrofunctionalization of unsaturated organic compounds and addresses hydroamination of unsaturated hydrocarbons. Particular parts of the review deal with reactions of alkenes, alkynes, allenes and dienes. It is shown that the selectivity of hydroamination depends on the natures of the reactants and the catalyst. Conditions of the reactions are described; in some cases, reaction mechanisms are discussed. Reactions for which divergent regioselectivity is possible are noted.

The bibliography includes 249 references.

Dedicated to the memory of V.V.Markovnikov.

Asymmetric synthesis of allylic compounds via hydrofunctionalisation and difunctionalisation of dienes, allenes, and alkynes

This review article provides an overview of progress in asymmetric synthesis of allylic compounds via hydrofunctionalisation and difunctionalisation of dienes, allenes, and alkynes.

Metal-catalyzed regiodivergent organic reactions

This review discusses metal-catalysed regiodivergent additions, allylic substitutions, CH-activation, cross-couplings and intra- or intermolecular cyclisations.

Low-coordinate organophosphorus compounds: some stereochemical considerations

Utilizing 2,4,6-tri-tert-butylphenyl as a sterically demanding group (abbreviated as Mes*), we have been successful in isolation, characterization, physical and chemical property investigation of low-coordinate organophosphorus compounds such as those carrying P=P and P=C bonds. Diphosphene, 1-phosphaethene, 1,3-diphosphaallene, 1-phosphaallene, and 3,4-diphosphinidenecyclobutenes are discussed in terms of stereochemistry including E/Z isomerization around P=P or P=C bond and R/S resolution of rotational isomers around crowded P–C bonds with chiral HPLC column. (π-Allyl)palladium complexes ligated with 3,4-diphosphinidenecyclobutene are useful in such catalytic organic reactions as the Tsuji-Trost reaction by which from a chiral s-alcohol, the corresponding chiral amine is obtained with retention of chirality suggesting double inversion process.

Selective Synthesis of (Z)-Diazadiphosphafulvalene from 2,2'-bis-Azaphosphindole

The unprecedented 2,2'-bis(azaphosphindole) has been synthesized via a new route. Reaction with NaH afforded a dianion derivative 5, which is easily transformed to alkylated bis(azaphosphindole) or (Z)-P,P,N,N-cisoid diazadiphosphafulvalene. The reaction features good regioselectivity and high steroselectivity. Relatively strong fluorescence is observed with diazadiphosphafulvalenes. The X-ray crystal structure analysis showed that dianion ligand 5 is bonded to two Na atoms in a bridging cis-fashion, which allows the synthesis of diazadiphosphafulvalene in a highly stereoselective approach.

Intermolecular Hydroamination of 1,3-Dienes To Generate Homoallylic Amines

We report a Rh-catalyzed hydroamination of 1,3-dienes to generate homoallylic amines. Our work showcases the first case of anti-Markovnikov selectivity in the intermolecular coupling of amines and 1,3-dienes. By tuning the ligand properties and Brønsted acid additive, we find that a combination of rac-BINAP and mandelic acid is critical for achieving anti-Markovnikov selectivity.

Enantioselective Intermolecular Addition of Aliphatic Amines to Acyclic Dienes with a Pd-PHOX Catalyst

We report a method for the catalytic, enantioselective intermolecular addition of aliphatic amines to acyclic 1,3-dienes. In most cases, reactions proceed efficiently at or below room temperature in the presence of 5 mol % of a Pd catalyst bearing a PHOX ligand, generating allylic amines in up to 97:3 er. The presence of an electron-deficient phosphine within the ligand not only leads to a more active catalyst but also is critical for achieving high site selectivity in the transformation.

Rhodium-Catalyzed Hydrofunctionalization: Enantioselective Coupling of Indolines and 1,3-Dienes

We communicate a strategy for the hydrofunctionalization of 1,3-dienes via Rh-hydride catalysis. Conjugated dienes are coupled to nucleophiles to demonstrate the feasibility of novel C-C, C-O, C-S, and C-N bond forming processes. In the presence of a chiral JoSPOphos ligand, hydroamination generates chiral allylic amines with high regio- and enantioselectivity. Tuning both the pKa and steric properties of an acid-additive is critical for enantiocontrol.

Generating Active "L-Pd(0)" via Neutral or Cationic π-Allylpalladium Complexes Featuring Biaryl/Bipyrazolylphosphines: Synthetic, Mechanistic, and Structure-Activity Studies in Challenging Cross-Coupling Reactions

Two new classes of highly active yet air- and moisture-stable π-R-allylpalladium complexes containing bulky biaryl- and bipyrazolylphosphines with extremely broad ligand scope have been developed. Neutral π-allylpalladium complexes incorporated a range of biaryl/bipyrazolylphosphine ligands, while extremely bulky ligands were accommodated by a cationic scaffold. These complexes are easily activated under mild conditions and are efficient for a wide array of challenging C-C and C-X (X = heteroatom) cross-coupling reactions. Their high activity is correlated to their facile activation to a 12-electron-based "L-Pd(0)" catalyst under commonly employed conditions for cross-coupling reactions, noninhibitory byproduct release upon activation, and suppression of the off-cycle pathway to form dinuclear (μ-allyl)(μ-Cl)Pd2(L)2 species, supported by structural (single crystal X-ray) and kinetic studies. A broad scope of C-C and C-X coupling reactions with low catalyst loadings and short reaction times highlight the versatility and practicality of these catalysts in organic synthesis.

P-stereogenic PNP pincer-Pd catalyzed intramolecular hydroamination of amino-1,3-dienes

A new P-stereogenic PNP pincer-Pd complex was readily prepared and was used in the asymmetric intramolecular hydroamination of amino-1,3-dienes, with the desired products being obtained in good yields and with excellent regioselectivities and up to moderate enantioselectivities.

Intermolecular hydroamination of 1,3-dienes catalyzed by bis(phosphine)carbodicarbene-rhodium complexes

A carbodicarbene (CDC)-based pincer ligand scaffold is reported, along with its application to site-selective Rh(I)-catalyzed intermolecular hydroamination of 1,3-dienes with aryl and alkyl amines. To the best of our knowledge, this is the first example of the use of a well-defined CDC complex as an efficient catalyst. Transformations proceed in the presence of 1.0-5.0 mol % Rh complex at 35-120 °C; allylic amines are obtained in up to 97% yield and with >98:2 site selectivity.

Unusual thiolate-bridged diiron clusters bearing the cis-HN═NH ligand and their reactivities with terminal alkynes

A series of well-defined thiolate-bridged diiron clusters bearing the cis-HN═NH ligand, [Cp(†)Fe(μ-SEt)(2)(μ-η(1):η(1)-HN═NH)FeCp(†)][PF(6)] (Cp(†) = η(5)-C(5)Me(4)H or η(5)-C(5)Me(5)), are successfully prepared in high yields and fully characterized by spectroscopy and X-ray crystallography. Under moderate conditions, these new Fe/S clusters exhibit high activity, not only for the catalytic cleavage of the N-N bond of hydrazines but also for the activation and coupling of terminal alkynes.

Palladium-catalyzed hydroarylation of 1,3-dienes with boronic esters via reductive formation of pi-allyl palladium intermediates under oxidative conditions

A palladium-catalyzed reductive cross-coupling of 1,3-dienes with boronic esters in which a pi-allyl Pd species is generated directly from a 1,3-diene via a Pd-catalyzed aerobic alcohol oxidation is reported. Both the scope of the process and the origin of a highly selective 1,2-addition are discussed.

Theoretical study of the tautomerism, structures, and vibrational frequencies of the phosphaalkenes XP=C(CH3)2 (X = H, F, Cl, Br, OH, Ar(F) (Ar(F) = 2,6-(CF3)2C6H3))

Ab initio theoretical calculations have been used to study the influence of phosphorus substituents, Y, on the tautomerism between the vinylphosphine XP(H)C(CH(3))=CH(2) and the phosphaalkene XP=C(CH(3))(2) (X = H, F, Cl, Br, OH, and Ar(F); Ar(F) = 2,6-(CF(3))(2)C(6)H(3)) and on the acidity of the aforementioned vinylphosphine. The stabilization of the phosphaalkene and the increased acidity of the vinylphosphine by Ar(F) are possible factors in the successful synthesis of certain isolable phosphaalkenes. In this work, the properties of Ar(F) are assessed theoretically. Density functional theory using the B3LYP functional has been used for all substituents. In addition, coupled-cluster singles and doubles with noniterative triples (CCSD(T)) has been used for X = H, F, Cl, Br, and OH. The phosphaalkene is favored over the vinylphosphine for all substituents, with F having the strongest stabilizing effect. Cl, Br, and OH have stronger stabilizing effects than Ar(F). In contrast, the most acidic vinylphosphine is that with Ar(F). To aid in the interpretation and analysis of future experimental work, CCSD(T) calculations were used to provide structures and vibrational frequencies for the series XP=C(CH(3))(2) (X = H, F, Cl, Br). The influence of the substituent on geometries and C=P and X-P stretching frequencies was examined, and comparisons were made with the CH(2)=PX series.

Imino-bridged bisphosphaalkenes (2,4-diphospha-3-azapentadienes)

Deprotonation of aminophosphaalkenes (RMe(2)Si)(2)C=PN(H)(R') (R=Me, iPr; R'=tBu, 1-adamantyl (1-Ada), 2,4,6-tBu(3)C(6)H(2) (Mes*)) followed by reactions of the corresponding Li salts Li[(RMe(2)Si)(2)C=P(M)(R')] with one equivalent of the corresponding P-chlorophosphaalkenes (RMe(2)Si)(2)C=PCl provides bisphosphaalkenes (2,4-diphospha-3-azapentadienes) [(RMe(2)Si)(2)C=P](2)NR'. The thermally unstable tert-butyliminobisphosphaalkene [(Me(3)Si)(2)C=P](2)NtBu (4 a) undergoes isomerisation reactions by Me(3)Si-group migration that lead to mixtures of four-membered heterocyles, but in the presence of an excess amount of (Me(3)Si)(2)C=PCl, 4 a furnishes an azatriphosphabicyclohexene C(3)(SiMe(3))(5)P(3)NtBu (5) that gave red single crystals. Compound 5 contains a diphosphirane ring condensed with an azatriphospholene system that exhibits an endocylic P=C double bond and an exocyclic ylidic P((+))-C((-))(SiMe(3))(2) unit. Using the bulkier iPrMe(2)Si substituents at three-coordinated carbon leads to slightly enhanced thermal stability of 2,4-diphospha-3-azapentadienes [(iPrMe(2)Si)(2)C=P](2)NR' (R'=tBu: 4 b; R'=1-Ada: 8). According to a low-temperature crystal-structure determination, 8 adopts a non-planar structure with two distinctly differently oriented P=C sites, but (31)P NMR spectra in solution exhibit singlet signals. (31)P NMR spectra also reveal that bulky Mes* groups (Mes*=2,4,6-tBu(3)C(6)H(2)) at the central imino function lead to mixtures of symmetric and unsymmetric rotamers, thus implying hindered rotation around the P-N bonds in persistent compounds [(RMe(2)Si)(2)C=P](2)NMes* (11 a, 11 b). DFT calculations for the parent molecule [(H(3)Si)(2)C=P](2)NCH(3) suggest that the non-planar distortion of compound 8 will have steric grounds.