Construction of frustrated Lewis pair from nitride and phosphine for the activation and cleavage of molecular hydrogen

Activation and cleavage of molecular hydrogen (H₂) to proton and hydride is an important task for several reasons, especially as a reagent in hydrogenation. In this scenario, with the support of density-functional theory methods, a novel strategy has been devised for the conversion of coordinated nitride into ammonia using molecular hydrogen in the presence of tri-tert-butylphosphine (P^tBu₃). The proposed methodology is based on the formation of frustrated Lewis pair (FLP) from [Os^VI(tpy)(Cl)₂(N)]⁺ (tpy = 2,2′:6′,2′′-terpyridine ) and P^tBu₃ followed by reaction with molecular hydrogen to form an FLP–H₂ adduct. The FLP–H₂ adduct can further undergo H–H bond cleavage heterolytically to produce proton and hydride which can be eventually used for the functionalization of coordinated nitride to ammonia. The calculated energy profile comprising all possible intermediates and transition-state molecules suggests that the proposed reaction pathway is energetically viable at elevated temperatures.     

Carbocyclization of aromatic iodides, bicyclic alkenes, and benzynes involving a palladium-catalyzed C-H bond activation as a key step

A facile palladium-catalyzed carbocyclization reaction of aromatic iodides, bicyclic alkenes (norbornadiene, norbornene and oxabenzonorbornadiene), and benzynes to furnish various annulated 9,10-dihydrophenanthrene derivatives is described. The carbocyclization products from oxabenzonorbornadiene were further converted to polyaromatic hydrocarbons via a Lewis acid mediated deoxyaromatization reaction. [reaction: see text].     

Highly regio- and chemoselective palladium-catalyzed propargylallylation of activated olefins: a novel route to 1,7-enyne derivatives

An efficient method for the synthesis of 1,7-enyne derivatives via phosphine-palladium-catalyzed three-component assembling of activated olefins, allylic chlorides, and allenylstannanes is described. Substituted arylethylidene malononitriles 1a-g (RCH=C(CN)(2): R = C(6)H(5) (1a), p-ClC(6)H(4) (1b), p-OMeC(6)H(4) (1c), p-NO(2)C(6)H(4) (1d), 1-naphthyl (1e), 2-furyl (1f), and 2-thienyl (1g)) undergo propargylallylation with allylic chlorides 2a-e (allyl chloride (2a), methallyl chloride (2b), 4-chloropent-2-ene (2c), cinnamyl chloride (2d), and 3-chlorocyclohexene (2e)) and n-tributylallenylstannane (n-Bu(3)SnCH=C=CH(2), 3a) in the presence of Pd(PPh(3))(4) in toluene to afford the corresponding 1,7-enyne derivatives 4a-m in good to excellent yields. The catalytic reaction is highly regioselective, with the propargyl group adding to the carbon where the R group is attached and the allyl group adding to the carbon connected to the CN groups of activated olefins 1a-g. The present catalytic reaction is successfully extended to substituted arylethylidene-1,3-indanediones 5a-j (RCH = (1,3-indanedione): R = C(6)H(5) (5a), p-ClC(6)H(4) (5b), p-BrC(6)H(4) (5c), p-OMeC(6)H(4) (5d), p-NO(2)C(6)H(4) (5e), p-CNC(6)H(4) (5f), p-biphenyl (5g), 1-naphthyl (5h), 2-thienyl (5i), and 2-benzo[b]furane-2-yl (5j)) and substituted 2,2-dimethyl-5-(arylethylidene)-1,3-dioxane-4,6-diones 7a,b (RCH = (1,3-dioxane-4,6-dione): R = p-NO(2)C(6)H(4) (7a), p-OMeC(6)H(4) (7b)). The three-component assembling of these substrates with allylic chlorides (2a,b,d,e) and n-tributylallenylstannane (n-Bu(3)SnCH=C=CH(2), 3a) proceeds smoothly to afford the corresponding 1,7-enyne derivatives 6a-m and 8a-d in good to excellent yields. The catalytic propargylallylation can be further applied to the activated dienes, C(6)H(5)CH=CH=CR(2) (R(2) = (CN)(2) (9a), 1,3-indanedione (9b), 2,2-dimethyl-1,3-dioxane-4,6-dione (9c)), with allylic chlorides (2a,b,d) and allenylstannane 3a to give regio- and chemoselective 1,2-addition products 10a-h in good to excellent yields. A plausible mechanism based on an eta(1)-allenyl eta(3)-allyl palladium intermediate is proposed to account for the catalytic three-component reaction.     

One-pot synthesis of benzolactones and lactams via a cobalt-catalyzed regioselective [2 + 2 + 2] cocyclotrimerization of alkynyl alcohols and amines with propiolates

An efficient method for the synthesis of benzolactones and benzolactams via a cobalt-catalyzed [2 + 2 + 2] cocyclotrimerization of alkynyl alcohols and alkynyl amines with propiolates is described.     

Cobalt‐Catalyzed Cyclization of N‐Methoxy Benzamides with Alkynes using an Internal Oxidant through C−H/N−O Bond Activation

The cyclization of substituted N‐methoxy benzamides with alkynes in the presence of an easily affordable cobalt complex and NaOAc provides isoquinolone derivatives in good to excellent yields. The cyclization reaction is compatible with a range of functional group‐substituted benzamides, as well as ester‐ and alcohol‐substituted alkynes. The cobalt complex [Co^IIICp*(OR)₂] (R=Me or Ac) serves as an efficient catalyst for the cyclization reaction. Later, isoquinolone derivatives were converted into 1‐chloro and 1‐bromo substituted isoquinoline derivatives in excellent yields in the presence of POCl₃ or PBr₃.     

External energy transfer in amplified spontaneous emissions from MEH-PPV conjugated polymer

We observed amplified spontaneous emissions (ASEs) in solutions of conjugated polymer under high power neodymium-doped yttrium aluminum garnet (Nd:YAG) laser excitation. A solution of coumarin-485 dye (C₄₈₅) and conjugated polymer (MEH-PPV) was prepared in tetrahydrofuran (THF). Here, C₄₈₅ acted as a donor (with different ratios) while MEH-PPV served as an acceptor (with a constant ratio). Without the donor, MEH-PPV exhibited ASE only in the excimeric state; with the donor, however, it produced ASE in both the monomeric and excimeric states simultaneously. These results clearly show that it is possible to monitor and manipulate the excited state behavior of molecules by using an energy transfer process using laser-excited conjugated polymer.     

ortho‐Benzoxylation of N‐Alkyl Benzamides with Aromatic Acids Catalyzed by Ruthenium(II) Complex

A highly regioselective ortho‐benzoxylation of N‐alkyl benzamides with aromatic acids in the presence of [{RuCl₂(p‐cymene)}₂], AgSbF₆, and (NH₄)₂S₂O₈ in 1,2‐dichloroethane at 100 °C for 24 h affording ortho‐benzoxylated N‐alkyl benzamides by C?H bond activation is described. Further, Ru‐catalyzed alkenylation is done at the ortho C?H bond of benzoxylated N‐alkyl benzamides with alkenes in water solvent. Subsequently, the benzoxyl moiety of N‐alkyl benzamides was converted into a hydroxyl group in the presence of base or acid. A possible reaction mechanism was proposed to account for the present coupling reaction.