Platinum-Catalyzed Intramolecular Hydrohydrazination: Evidence for Alkene Insertion into a Pt−N Bond

N-Amino-1,8-Naphthalimide is a Regenerated Protecting Group for Selective Synthesis of Mono-N-Substituted Hydrazines and Hydrazides

A new route to synthesis of various mono-N-substituted hydrazines and hydrazides by involving in a new C-N bond formation by using N-amino-1,8-naphthalimide as a regenerated precursor was invented. Aniline and phenylhydrazines are reproduced upon reacting these individually with 1,8-naphthalic anhydride followed by hydrazinolysis. The practicality and simplicity of this C-N dihalo alkanes; developed a synthon for bond formation protocol was exemplified to various hydrazines and hydrazides. N-amino-1,8-naphthalimide is suitable synthon for transformation for selective formation of mono-substituted hydrazine and hydrazide derivatives. Those are selective mono-amidation of hydrazine with acid halides; mono-N-substituted hydrazones from aldehydes; synthesis of N-aminoazacycloalkanes from acetohydrazide scaffold and inserted to hydroxy derivatives; distinct synthesis of N,N-dibenzylhydrazines and N-benzylhydrazines from benzyl halides; synthesis of N-amino-amino acids from α-halo esters. Ecofriendly reagent N-amino-1,8-naphthalimide was regenerated with good yields by the hydrazinolysis in all procedures.

Synthesis of N,O-Chelating Hydrazidopalladium Complexes from 1,2-Bis(trifluoroacetyl)hydrazine

N,O-chelating dicarbonylhydrazido-palladium complexes were synthesized by treatment of 1,2-bis(trifluoroacetyl)hydrazine with a mixture of a Pd(0) source, [Pd(dba)2] (DBA = dibenzylideneacetone), and four-electron donors including 1,3-bis(diphenylphosphino)propane (DPPP), N,N,N’,N’-tetramethylethylenediamine (TMEDA), and two equivalents of triphenylphosphine. The same products from DPPP and TMEDA could be obtained alternatively by using Pd(OAc)2 through deprotonation of the diacylhydrazine. The five-membered chelate structure was confirmed by NMR spectra and X-ray crystal structure determination. The X-ray structures indicate that the products are formally considered as Pd(II) complexes with a hydrazido(2–) ligand. In the case of the triphenylphosphine-coordinated complex, a fluxional behavior in dichloromethane-d2 was observed by variable temperature NMR experiments, possibly due to structural changes between the square planar and pseudo-tetrahedral geometries.

Development of highly efficient platinum catalysts for hydroalkoxylation and hydroamination of unactivated alkenes

Hydrofunctionalization, the direct addition of an X-H (e.g., X=O, N) bond across an alkene, is a desirable strategy to make heterocycles that are important structural components of naturally occurring molecules. Described here is the design and discovery of "donor-acceptor"-type platinum catalysts that are highly effective in both hydroalkoxylation and hydroamination of unactivated alkenes over a broad range of substrates under mild conditions. A number of alkene substitution patterns are accommodated, including tri-substituted, 1,1-disubstituted, (E)-disubstituted, (Z)-disubstituted and even mono-substituted double bonds. Detailed mechanistic investigations suggest a plausible pathway that includes an unexpected dissociation/re-association of the electron-deficient ligand to form an alkene-bound "donor-acceptor"-type intermediate. These mechanistic studies help understand the origins of the high reactivity exhibited by the catalytic system, and provide a foundation for the rational design of chiral catalysts towards asymmetric hydrofunctionalization reactions.

External electric field: a new catalytic strategy for the anti-Markovnikov hydrohydrazination of parent hydrazine

The anti-Markovnikov hydroamination reaction is considered to be a particular challenge, and one of the reactants, parent hydrazine, is also regarded as a troubling reagent. In this study, we first studied the hydrohydrazination of parent hydrazine via an effective and green catalyst—external electric field (EEF). The calculation results demonstrated that the anti-Markovnikov and Markovnikov pathways are competitive when there was no catalyst. EEF oriented along the negative direction of the X axis (F_x) accelerated the anti-Markovnikov addition reaction. Moreover, it lowered the barrier height of the first step by 16.0 kcal mol⁻¹ (from 27.8 to 11.8 kcal mol⁻¹) when the field strength was 180 (×10⁻⁴) au. Under the same conditions, the Markovnikov reaction pathway was inhibited, which means that EEF achieved the specificity of hydrohydrazination. The solvents are favorable for the first step addition reaction, particularly the synergy between solvents and F_x lowered the barrier heights by 8.3 (C₆H₆) and 10.7 (DMSO) kcal mol⁻¹ for an F_x = −60 (×10⁻⁴) au. Besides, the introduction of the electron-withdrawing substituent (trifluoromethyl) is also a good strategy to catalyze hydrohydrazination, while the electron-donating group (methoxy) is unfavorable.

The anti-Markovnikov hydrohydrazination of parent hydrazine were catalyzed by external electric field (EEF) to a large extent. Furthermore, the solvent effects and the substituent effects of the hydrohydrazination were enhanced in the presence of EEF.

Brønsted acid-promoted hydroamination of unsaturated hydrazones: access to biologically important 5-arylpyrazolines

A novel and efficient Brønsted acid-promoted hydroamination of hydrazone-tethered olefins has been developed. A variety of pyrazolines have been easily obtained in good to excellent yields with high chemo- and regioselectivity under simple and mild conditions. This method represents a straightforward, facile, and practical approach toward biologically important 5-arylpyrazolines, which are difficult to access by previously reported radical hydroamination of β,γ-unsaturated hydrazones.

An efficient, chemo- and regioselective Brønsted acid-promoted hydroamination reaction of hydrazone-tethered olefins towards 5-arylpyrazolines was developed.

Atomic Pt-Catalyzed Heterogeneous Anti-Markovnikov C-N Formation: Pt10 Activating N-H for Pt1δ+-Activated C═C Attack

C-N formation is of great significance to synthetic chemistry, as N-containing products are widely used in chemistry, medicine, and biology. Addition of an amine to an unsaturated carbon-carbon bond is a simple yet effective route to produce new C-N bonds. But how to effectively conduct an anti-Markovnikov addition with high selectivity has been a great challenge. Here, we proposed a strategy for highly regioselective C-N addition via hydroamination by using supported Pt. It has been identified that atomic-scale Pt is the active site for C-N addition with Pt₁²⁺ for Markovnikov C-N formation and atomic Pt (Pt₁^δ+ and Pt₁⁰) contributing to anti-Markovnikov C-N formation. A selectivity of up to 92% to the anti-Markovnikov product has been achieved with atomic Pt in the addition of styrene and pyrrolidine. A cooperating catalysis for the anti-Markovnikov C-N formation between Pt₁^δ+ and Pt₁⁰ has been revealed. The reaction mechanism has been studied by EPR spectra and in situ FT-IR spectra of adsorption/desorption of styrene and/or pyrrolidine. It has been demonstrated that Pt₁⁰ activates amine to be electrophilic, while Pt₁^δ+ activates C═C by π-bonding to make β-C nucleophilic. The attack of nucleophilic β-C to electrophilic amine affords the anti-Markovnikov addition. This strategy proves highly effective to a variety of substrates in anti-Markovnikov C-N formation, including aromatic/aliphatic amines reacting with aromatic olefins, aromatic/aliphatic olefins with aromatic amines, and linear aliphatic olefins with secondary aliphatic amines. It is believed that the results provide evidence for the function of varied chemical states in monatomic catalysis.

Enhancing the catalytic properties of well-defined electrophilic platinum complexes

Platinum complexes have been often considered as the least reactive of the group 10 triad metals. Slow kinetics are behind this lack of reactivity but, still, some industrially relevant catalytic process are dominated by platinum compounds and sometimes different selectivities can be found in comparison to Ni or Pd. Nevertheless, during the last years, it has been reported that the catalytic behaviour of well-defined platinum derivatives can be improved through a judicious choice of their electronic and steric properties, leading to highly electrophilic or low-electron count platinum systems. In this feature article, we highlight some catalytic processes in which well-defined electrophilic platinum complexes or coordinatively unsaturated systems play an important role in their catalytic activity.

Aminimide Synthesis Using Concerted Amination Reactions of Alkenes: Scope and Mechanistic Information

Aminimides are key intermediates in the thermal cycloadditions of suitable alkenyl-hydrazine derivatives. Substrate modifications (β-N,N-dialkyl) allowed the isolation of these reactive intermediates, and the analysis of their stereochemistry provided support for concerted (Cope-type) hydroamination and concerted [3 + 2] aminocarbonylation reaction pathways. This work also establishes the applicability of these approaches to form complex aminimides in moderate to excellent yields.

Heterobimetallic Catalysis: Platinum-Gold-Catalyzed Tandem Cyclization/C-X Coupling Reaction of (Hetero)Arylallenes with Nucleophiles

Heterobimetallic catalysis offers new opportunities for reactivity and selectivity but still presents challenges, and only a few metal combinations have been explored so far. Reported here is a Pt-Au heterobimetallic catalyst system for the synthesis of a family of multi-heteroaromatic structures through tandem cyclization/C-X coupling reaction. Au-catalyzed 6-endo-cyclization takes place as the first fast step. Pt-Au clusters are proposed to be responsible for the increased reactivity in the second step, that is, the intermolecular nucleophilic addition which occurs through an outer-sphere mechanism by hybrid homogeneous-heterogeneous catalysis.

Diethylzinc-Mediated Metalloamination-Alkylation of N, N-Dimethylhydrazinoalkenes. Catalysis of C-Zn Alkylation Using Simple Cu(I) Salts

Metalloamination-alkylation of representative N,N-dimethyl-hydrazinoalkenes has been shown to be effectively catalyzed by CuBr-SMe₂, CuCN, and Cul. The current method obviates the use of stoichiometric CuCN(LiCl)₂ as a promoter for the electrophilic functionalization event.

1,2-Disubstituted Alkenes as Migratory Insertion Participants in Zn(II)-Promoted Metalloamination/Cyclization of N,N-Dimethylhydrazinoalkenes

Diethylzinc-mediated metalloamination/cyclization of unsaturated N,N-dimethylhydrazines has been extended to the use of 1,2-disubstituted alkenes as N-Zn migratory insertion acceptors. Representative 2-arylethenes and vinylcyclopropanes readily serve as reaction participants in metalloamination/cyclization-allylation cascades.

Metal-free synthesis of 3,5-disubstituted 1H- and 1-aryl-1H-pyrazoles from 1,3-diyne-indole derivatives employing two successive hydroaminations

The uncatalyzed synthesis of 3,5-disubstituted 1H- and 1-aryl-1H-pyrazoles derived from 1,3-diyne indoles was successfully carried out in PEG 400. The scope and limitations of the reaction were studied.

Room-temperature hydrohydrazination of terminal alkynes catalyzed by saturated abnormal N-heterocyclic carbene-gold(I) complexes

A number of saturated abnormal N-heterocyclic carbene (NHC) complexes of gold, in combination with KBAr(F) 4 as activator, were successfully applied in the chemoselective addition of hydrazine to alkynes. The reaction proceeds even at room temperature, which was not possible to date with gold catalysts. The reaction can be applied to a number of substituted arylalkynes. With alkylalkynes the yields are low. The saturated abnormal NHC ligands are resistant to isomerization to the saturated normal NHC coordination mode under basic reaction conditions. Under acidic conditions, a simple protonation at the nitrogen atom not neighboring the carbene center was observed and unambiguously characterized by an X-ray crystal-structure analysis. Computational studies confirm that such an isomerization would be highly exothermic, the observed kinetic stability probably results from the need to shift two protons in such a process.

Diastereoselective Pt catalyzed cycloisomerization of polyenes to polycycles

Application of a tridentate NHC containing pincer ligand to Pt catalyzed cascade cyclization reactions has allowed for the catalytic, diastereoselective cycloisomerization of biogenic alkene terminated substrates to the their polycyclic counterparts.

Enantioselective synthesis of 2-substituted and 3-substituted piperidines through a bromoaminocyclization process

A catalytic enantioselective bromocyclization of olefinic amides using amino-thiocarbamates as the catalysts has been developed. The resulting enantioenriched 2-substituted 3-bromopiperidines can readily be transformed to 3-substituted piperidines through a silver salt-mediated rearrangement. This process has been applied to the synthesis of a dopaminergic drug, Preclamol.

Mononuclear five- and six-coordinate iron hydrazido and hydrazine species

This article describes the synthesis and characterization of several low-spin iron(II) complexes that coordinate hydrazine (N(2)H(4)), hydrazido (N(2)H(3)(-)), and ammonia. The sterically encumbered tris(di-meta-terphenylphosphino)borate ligand, [PhBP(mter)(3)](-), is introduced to provide access to species that cannot be stabilized with the [PhBP(Ph)(3)](-) ligand ([PhBP(R)(3)](-) = PhB(CH(2)PR(2))(3)(-)). Treatment of [PhBP(mter)(3)]FeMe with hydrazine generates the unusual 5-coordinate hydrazido complex [PhBP(mter)(3)]Fe(η(2)-N(2)H(3)) (1), in which the hydrazido serves as an L(2)X-type ligand. Upon coordination of an L-type ligand, the hydrazido shifts to an LX-type ligand, generating [PhBP(mter)(3)]Fe(L)(η(2)-N(2)H(3)) (L = N(2)H(4) (2) or NH(3) (3)). In contrast, treatment of [PhBP(Ph)(3)]FeMe with hydrazine forms the adduct [PhBP(Ph)(3)]Fe(Me)(η(2)-N(2)H(4)) (5). Complex 5 is thermally unstable to methane loss, generating intermediate [PhBP(Ph)(3)]Fe(η(2)-N(2)H(3)), which undergoes bimolecular coupling to produce {[PhBP(Ph)(3)]Fe}(2)(μ-η(1):η(1)-N(2)H(4))(μ-η(2):η(2)-N(2)H(2)). The oxidation of these and related hydrazine and hydrazido species is also presented. For example, oxidation of 1 or 5 with Pb(OAc)(4) results in disproportionation of the N(2)H(x) ligand (x = 3, 4), and formation of [PhBP(R)(3)]Fe(NH(3))(OAc) (R = Ph (9) and mter (11)).

Intramolecular Pd(II)-catalyzed aerobic oxidative amination of alkenes: synthesis of six-membered N-heterocycles

Use of a base-free Pd(DMSO)(2)(TFA)(2) catalyst system enables the synthesis of six-membered nitrogen heterocycles via a Wacker-type aerobic oxidative cyclization of alkenes bearing tethered sulfonamides. Various heterocycles, including morpholines, piperidines, piperazines, and piperazinones, are accessible by this method.

Reversible alkene insertion into the Pd-N bond of Pd(II)-sulfonamidates and implications for catalytic amidation reactions

Alkene insertion into Pd-N bonds is a key step in Pd-catalyzed oxidative amidation of alkenes. A series of well-defined Pd(II)-sulfonamidate complexes have been prepared and shown to react via insertion of a tethered alkene. The Pd-amidate and resulting Pd-alkyl species have been crystallographically characterized. The alkene insertion reaction is found to be reversible, but complete conversion to oxidative amination products is observed in the presence of O(2). Electronic-effect studies reveal that alkene insertion into the Pd-N bond is favored kinetically and thermodynamically with electron-rich amidates.

Rhodium phosphine-π-arene intermediates in the hydroamination of alkenes

A detailed mechanistic study of the intramolecular hydroamination of alkenes with amines catalyzed by rhodium complexes of a biaryldialkylphosphine is reported. The active catalyst is shown to contain the phosphine ligand bound in a κ(1), η(6) form in which the arene is π-bound to rhodium. Addition of deuterated amine to an internal olefin showed that the reaction occurs by trans addition of the N-H bond across the C═C bond, and this stereochemistry implies that the reaction occurs by nucleophilic attack of the amine on a coordinated alkene. Indeed, the cationic rhodium fragment binds the alkene over the secondary amine, and the olefin complex was shown to be the catalyst resting state. The reaction was zero-order in substrate, when the concentration of olefin was high, and a primary isotope effect was observed. The primary isotope effect, in combination with the observation of the alkene complex as the resting state, implies that nucleophilic attack of the amine on the alkene is reversible and is followed by turnover-limiting protonation. This mechanism constitutes an unusual pathway for rhodium-catalyzed additions to alkenes and is more closely related to the mechanism for palladium-catalyzed addition of amide N-H bonds to alkenes.

Intramolecular alkene aminopalladation reactions of (dppf)Pd(Ar)[N(Ar(1))(CH(2))(3)CH=CH(2)] complexes. insertion of unactivated alkenes into Pd-N bonds

The synthesis of (dppf)Pd(C(6)H(4)-p-F)[N(Ar(1))(CH(2))(3)CH horizontal lineCH(2)] complexes (3), which are thought to be intermediates in Pd-catalyzed alkene carboamination reactions, is described. These complexes undergo syn-migratory insertion of the alkene into the Pd-N bond to yield observable (dppf)palladium(aryl)(pyrrolidin-2-yl-methyl) complexes 6. Reductive elimination from 6 provides 2-benzylpyrrolidine derivatives 4. The rates of conversion of 3 to 6 (k(1)) and 6 to 4 (k(2)) were measured and are within 1 order of magnitude of each other. The syn-migratory insertion stereochemistry was confirmed through a deuterium labeling experiment. These are the first examples of syn-migratory insertions of unactivated alkenes into Pd-N bonds of well-defined complexes.