Cobalt-catalyzed chemoselective insertion of alkene into the ortho C-H bond of benzamide

Insertion of 1-alkene, 2-alkene, and styrene into the ortho C-H bond of benzamide in the presence of an inexpensive cobalt catalyst, DMPU as a crucial ligand, and cyclohexylmagnesium chloride proceeds smoothly at 25 °C to selectively give the ortho-alkylated product. Notable features of this reaction include the structural variety of the alkene and the amide substrate and the tolerance of functional groups such as halide, olefin, ester, and amide groups.     

Reversible double insertion of aryl isocyanates into the Ti-O bond of titanium(IV) isopropoxide

The insertion of phenyl isocyanate into titanium isopropoxide leads to the formation of a dimeric complex [Ti(OⁱPr)₂(μ-OⁱPr){C₆H₅N(OⁱPr)CO}]₂ (1) which has been structurally characterized. Reaction of titanium isopropoxide with two and more than 2 equiv. of phenyl isocyanate is complicated by competitive, reversible insertion between the titanium carbamate and titanium isopropoxide. The ligand formed by insertion of phenyl isocyanate into the titanium carbamate has been structurally characterized in its protonated form C₆H₅N{C(OⁱPr)O}C(O)N(H)C₆H₅ (3aH). Insertion into the carbamate is kinetically favored whereas insertion into isopropoxide gives the thermodynamically favored product.     

Pd(II)- and Pd(0)-cocatalyzed reactions of sulfonamides with MCPs

[reaction: see text] MCPs can efficiently react with sulfonamides in the presence of Pd(0) and Pd(II) catalysts to give the corresponding ring-opened products in high yields.     

Structurally characterized intermediates in the stepwise insertion of CO-ethylene or CO-methyl acrylate into the metal-carbon bond of Pd(II) complexes stabilized by (phosphinomethyl)oxazoline ligands

The initial CO-ethylene or CO-methyl acrylate insertion steps into the Pd-Me bond of methylpalladium(II) complexes with (phosphinomethyl)oxazoline ligands, leading to metallacycles, have been fully characterized, including by X-ray diffraction.     

Reversible formal insertion of CO2 into a remote C-H bond of a ligand in a Ru(II) complex at room temperature

Here we report a reversible formal insertion of CO(2) into a remote C-H bond of the diazafluorenide ligand (L(-)) in a Ru(II) complex which occurs at ambient temperature.     

Enantioselective Pd(II)-catalyzed aerobic oxidative amidation of alkenes and insights into the role of electronic asymmetry in pyridine-oxazoline ligands

Enantioselective intramolecular oxidative amidation of alkenes has been achieved using a (pyrox)Pd(II)(TFA)(2) catalyst (pyrox = pyridine-oxazoline, TFA = trifluoroacetate) and O(2) as the sole stoichiometric oxidant. The reactions proceed at room temperature in good-to-excellent yields (58-98%) and with high enantioselectivity (ee = 92-98%). Catalyst-controlled stereoselective cyclization reactions are demonstrated for a number of chiral substrates. DFT calculations suggest that the electronic asymmetry of the pyrox ligand synergizes with steric asymmetry to control the stereochemical outcome of the key amidopalladation step.     

Yttrium (amidate) complexes for catalytic C-N bond formation. Rapid, room temperature amidation of aldehydes

Yttrium (amidate) precatalysts are highly active for the mild amidation of aldehydes with amines. Reactions occur at room temperature within 5 min in up to 98% isolated yield. These rare-earth systems are effective for this transformation in the absence of supplementary heat, light, base, or oxidants. The reaction proceeds with functionalized amines and/or aldehydes. A comparison of various amidate precatalysts in combination with reaction monitoring suggests that the targeted amide products formed during the reaction promote the formation of alternative catalytically active amidate species in situ.     

Insertion reactions into Pd[bond]O and Pd[bond]N bonds: preparation of alkoxycarbonyl,carbonato, carbamato,thiocarbamate, and thioureide complexes of palladium(II)

Mononuclear palladium hydroxo complexes of the type [Pd(N[bond]N)(C(6)F(5))(OH)] [(N[bond]N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me(2)bipy), 1,10-phenanthroline (phen), or N,N,N',N'-tetramethylethylenediamine (tmeda)] have been prepared by reaction of [Pd(N[bond]N)(C(6)F(5))(acetone)]ClO(4) with KOH in methanol. These hydroxo complexes react, in methanol, with CO (1 atm, room temperature) to yield the corresponding methoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)Me)]. Similar alkoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)R)] (N[bond]N = bis(3,5-dimethylpyrazol-1-yl)methane); R = Me, Et, or (i)Pr) are obtained when [Pd(N[bond]N)(C(6)F(5))Cl] is treated with KOH in the corresponding alcohol ROH and CO is bubbled through the solution. The reactions of [Pd(N[bond]N)(C(6)F(5))(OH)] (N[bond]N = bipy or Me(2)bipy) with CO(2), in tetrahydrofuran, lead to the formation of the binuclear carbonate complexes [(N[bond]N)(C(6)F(5))Pd(mu-eta(2)-CO(3))Pd(C(6)F(5))(N[bond]N)]. Complexes [Pd(N[bond]N)(C(6)F(5))(OH)] react in alcohol with PhNCS to yield the corresponding N-phenyl-O-alkylthiocarbamate complexes [Pd(N[bond]N)(C(6)F(5))[SC(OR)NPh]]. Similarly, the reaction of [Pd(bipy)(C(6)F(5))(OH)] with PhNCO in methanol gives the N-phenyl-O-methylcarbamate complex [Pd(bipy)(C(6)F(5))[NPhC(O)OR]]. The reactions of [(N[bond]N)Pd(C(6)F(5))(OH)] with PhNCS in the presence of Et(2)NH yield the corresponding thioureidometal complexes [Pd(N[bond]N)(C(6)F(5))[NPhCSNR(2)]]. The crystal structures of [Pd(tmeda)(C(6)F(5))(CO(2)Me)], [Pd(2)(Me(2)bipy)(2)(C(6)F(5))(2)(mu-eta(2)-CO(3))].2CH(2)Cl(2), and [Pd(tmeda)(C(6)F(5))[SC(OMe)NPh]] have been determined.     

Preparation of Pd(II) enolate complexes and their reactions

Palladium(II) enolate complexes have been prepared by the reaction of Pd(II)Cl₂-(PhCN)₂ with trimethylsilyl enol ethers and reacted with CO and ethylene.     

Effective binuclear Pd(II) complexes for Suzuki reactions in water

A series of new ionic binuclear Pd(II) complexes supported by water‐soluble bis(α‐diimine) ligands were prepared and employed as catalysts for the palladium‐catalyzed Suzuki reaction in aqueous media. The binuclear nature of the complexes increased the reaction rate, while electronic and steric modification of the ligand frameworks had a remarkable influence upon the catalytic activity of the palladium complexes. The catalysts were shown to be homogeneous through mercury poisoning experiments and complexes could be recycled more than 10 times without loss of catalytic activity. Copyright © 2013 John Wiley & Sons, Ltd.     

Palladacyclic imidazoline-naphthalene complexes: synthesis and catalytic performance in Pd(II)-catalyzed enantioselective reactions of allylic trichloroacetimidates

A new family of air- and moisture-stable enantiopure C,N-palladacycles (PIN-acac complexes) were prepared in good overall yield in three steps from 2-iodo-1-naphthoic acid and enantiopure β-amino alcohols. Three of these PIN complexes were characterized by single-crystal X-ray analysis. As anticipated, the naphthalene and imidazoline rings of PIN-acac complexes 18a and 18b were canted significantly from planarity and projected the imidazoline substituents R(1) and R(2) on opposite faces of the palladium square plane. Fifteen PIN complexes were evaluated as catalysts for the rearrangement of prochiral (E)-allylic trichloroacetimidate 19 (eq 2) and the S(N)2' allylic substitution of acetic acid with prochiral (Z)-allylic trichloroacetimidate 23. Although these complexes were kinetically poor catalysts for the Overman rearrangement, they were good catalysts for the allylic substitution reaction, providing branched allylic esters in high yield. However, enantioselectivities were low to moderate and significantly less than that realized with palladacyclic complexes of the COP family. Computational studies support an anti-acetoxypalladation/syn-deoxypalladation mechanism analogous to that observed with COP catalysts. The computational study further suggests that optimizing steric influence in the vicinity of the carbon ligand of a chiral C,N-palladacycle, rather than near the nitrogen heterocycle, is the direction to pursue in future development of improved enantioselective catalysts of this motif.     

Pd(0) or Pd(II)-catalyzed ring-opening reactions of benzylidene- and alkylidenecyclopropyl ketones and aldehydes

Pd(0) catalyzed reactions of methylenecyclopropyl carbonyl compounds afforded a convenient method for the synthesis of conjugate (E,E)-1,3-diene derivatives 2 in good to excellent yields. Moreover, we also found that Pd(II)-catalyzed reactions of methylenecyclopropyl carbonyl compounds with water gave 1,5-diketones in good to high yields via a carbene-palladium intermediate. The plausible reaction mechanisms have also been provided on the basis of control and ¹⁸O-labeling experiments.     

Coordination insertion reactions of acrylonitrile into Pd-H and Pd-methyl bonds in a diimine-palladium(II) system

Acrylonitrile (AN) displaces the ethyl ether ligand of the cationic complex [Pd(N-N)Me(Et₂O)]⁺ (N-N = (2,6-(i-Pr)₂C₆H₃)-NCMeCMeN-(2,6-(i-Pr)₂C₆H₃)) to form the N-bonded AN complex [Pd(N-N)Me(AN)]⁺, which exists as two interconverting rotamers. On standing or heating, [Pd(N-N)Me(AN)]⁺ undergoes 2,1-insertion to give [Pd(N-N)(CH(CN)CH₂Me)(AN)]⁺, which undergoes β-hydrogen elimination to give the intermediate hydride, [Pd(N-N)H(AN)]⁺, which in turn inserts AN to give the cyanoethyl complex [Pd(N-N)(CH(CN)Me)]⁺. Dimerization of the [Pd(N-N)(CH(CN)CH₂CH₃)]⁺ moiety via bridging nitrile groups also occurs, giving the dicationic species . Although [Pd(N-N)Me(AN)]⁺ does behave as a typical Brookhart ethylene polymerization catalyst, it does not catalyze AN polymerization and in fact added AN suppresses ethylene polymerization.     

Shape-dependent catalytic activity of copper oxide-supported Pd(0) nanoparticles for Suzuki and cyanation reactions

Palladium nanoparticles supported on different shapes of nanocrystalline CuO are prepared by the treatment of Cu(NO₃)₂ and Pd(OAc)₂ in polyethylene glycol (PEG-6000). The shapes of the CuO/Pd composite are dependent on the amount of PEG used. Suzuki coupling was catalyzed efficiently by the oval-shaped material, whereas the rod shape facilitates the cyanation reaction. The CuO/Pd catalyst is recovered and reused for subsequent Suzuki reactions; however, cyanation poisons the catalyst for further use. Both these reactions are very clean and high yielding.     

Pd(II)-catalyzed enantioselective oxidative tandem cyclization reactions. Synthesis of indolines through C-N and C-C bond formation

We have developed an efficient Pd(II)-catalyzed enantioselective oxidative tandem cyclization strategy using molecular oxygen as a green oxidant for the double 5-exo-trig cyclizations of N-(2-allylaryl) amides to afford a variety of indolines in good yields without the formation of undesired monocyclization products. By employing Pd(TFA)2/(-)-sparteine as the chiral catalyst, we obtained tandem cyclization products with high enantioselectivity (up to 91% ee).     

Syntheses and catalytic activities of Pd(II) dicarbene and hetero-dicarbene complexes

A series of palladium(II) complexes (1-6) bearing cis-chelating homo-dicarbene ligands with varying alkyl bridges (C1-C3) and N-heterocyclic backbones (imidazole and benzimidazole) have been synthesized by reaction of Pd(OAc)₂ with the respective diazolium bromides (A·2HBr - F·2HBr) in DMSO. A comparative catalytic study employing aryl chlorides in the Mizoroki-Heck reaction revealed the superiority of methylene- and propylene-bridged dibenzimidazolin-2-ylidenes over their imidazole-derived analogues. Based on these results, two new propylene-bridged hetero-dicarbene complexes (7 and 8) were designed containing a mixed benzimidazole/imidazole-derived NHC-donor set. Notably, both complexes outperformed their homo-dicarbene analogues, which may be due to the electronic asymmetry induced by hetero-dicarbene ligands. The molecular structures of complex 6 and 8 are also presented.     

Co-ligand effects in the catalytic activity of Pd(II)-NHC complexes

Three cis-chelating di-N-heterocyclic carbene palladium(II) complexes [PdX₂(diNHC)] (X = I, 1; X = SCN, 2; X = CF₃CO₂, 3) bearing different anionic co-ligands were synthesized and fully characterized. A comparison of their catalytic activities in the Mizoroki-Heck reaction and conjugate addition of arylboronic acids to cyclic enones revealed increasing efficiency in the order SCN⁻ < I⁻ < CF₃CO₂⁻. The di(trifluoroacetato) complex 3 showed the best activity in both transformations highlighting the importance of co-ligands effects in catalysis. In addition, the molecular structure of an unusual poly-heteronuclear complex salt 4 is reported, which has been isolated as a byproduct in the synthesis of complex 3.     

Co-complexes derived from alkene insertion to alkyne-dicobaltpentacarbonyl complexes: insight into the regioselectivity of pauson-khand reactions of cyclopropenes

Described are the X-ray crystallographic and spectral properties of Co-complexes that were isolated from two Pauson-Khand reactions of chiral cyclopropenes. These are the first examples of isolated Co-complexes derived from the putative alkene-insertion intermediates of Pauson-Khand reactions. The binuclear Co-complexes are coordinated to mu-bonded, five-carbon "flyover" carbene ligands. It is proposed that the complexes result from cyclopropane fragmentation subsequent to alkene insertion. The observation of these metal complexes provides a rationale for the origin of regioselectivity in Pauson-Khand reactions of cyclopropenes.