Fung-E Hong

Density Functional Studies on Palladium‐Catalyzed Suzuki–Miyaura Cross‐Coupling Reactions Assisted by N‐ or P‐Chelating Ligands

DFT studies with the B3LYP functional have been carried out on the Suzuki-Miyaura cross-coupling reactions of phenyl chloride and phenylboronic acid catalyzed by palladium complexes with N- or P-chelating ligands. The full catalytic cycle, from the addition of reactants to the catalyst to the release of the cross-coupled product from the complexed intermediate, has been examined. The stages within the cycle, such as oxidative addition, transmetalation, and reductive elimination, were validated by linking the mechanistically relevant intermediates and transition states. Various derivatives of diimine, diphosphine, and diamine were considered as potential model ligands. The catalytic reaction employing diimine as the chelating ligand has been verified as the one with the most energetically feasible route.

Density functional studies on diimine chelated palladium complex catalyzed Suzuki–Miyaura cross-coupling reaction: the impact of Lewis base employed in transmetallation process

The transmetallation processes of disubstituted diimine (RN=CH-CH=NR) chelated palladium complexes catalyzed Suzuki-Miyaura cross-coupling reactions of phenyl chloride (PhCl) and phenylboronic acid [B(OH)(2)Ph] in the presence of diverse Lewis bases (OH(-), F(-), O(t)Bu(-), CO(3)(2-) and PO(4)(3-)) were studied by DFT methods with the B3LYP functional. Activation strain model has also been employed to investigate the extent of deformation of the reactants including the catalyst in the transition state. The transmetallation processes for all the cases are exothermic. The energy barriers for the process with multivalent bases are smaller than that of univalent cases, while, the amounts of the released energies are on the opposite course. The high valent oxoanions such as CO(3)(2-) and PO(4)(3-) provide more versatile bonding modes in the processes. The flexibility of diimine either as mono- or bi-dentate ligand in the mechanism provides a valuable channel for lowering the energy barriers of this process. The simplicity and efficiency of this type of ligand make it a potential alternation to the most commonly used phosphine.

Diphenyl-2-pyridylphosphine as a bidentate ligand in the coordination of dicobalt octacarbonyl; X-ray crystal structures of Co2(CO)4(μ-P,N-PPh2py){μ-HCCSiMe3}, and Co4(CO)10(μ-P,N-PPh2py)

Abstract Under mild conditions, the reaction of Co 2 (CO) 8 with HCCSiMe 3 in the presence of PPh 2 py gave a binuclear cobalt carbonyl complex, Co 2 (CO) 4 (η 2 -μ 2 -HCCSiMe 3 )(μ-PPh 2 py) ( 1a ), which has both zero-valent cobalt centers coordinated by a bidentate ligand, PPh 2 py. PPh 2 py is also an effective ligand in promoting the yield of 2,5-bis(trimethylsilanyl)cyclopenta-2,4-dien-1-one. A cobalt cluster complex, Co 4 (CO) 10 (μ- P , N -PPh 2 py) ( 9 ) was obtained when two equivalents of Co 2 (CO) 8 were reacted with PPh 2 py at a higher temperature. The phosphorus and nitrogen atoms of the ligand coordinate to cobalt in the basal and apical positions, respectively. These two compounds, 1a and 9 were characterized by spectroscopic means as well as X-ray crystal structure determination.

Synthesis and structural characterization of novel palladium complexes chelated by bulky cobalt-containing phosphine ligands: unusual palladium–cobalt bond formation

The reaction of a bulky phosphine, [Co2(CO)5{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}] 1 with P(OMe)3 gave a phosphite substituted tetracobalt-complex, [Co2(CO)4{P(OMe)3}{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}] 5. Further reaction of 5 with (COD)PdCl2 yielded a 5 -coordinated palladium complex, [Co2(CO)4{P(OMe)3}}{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)3(μ-CO){μ-P-(μ-PPh2CCPPh2)}]PdCl27. Similar results were obtained for the reaction of 1 with (COD)PdCl2, which yielded [Co2(CO)5{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)3(μ-CO){μ-P-(μ-PPh2CCPPh2)}]PdCl26. Likewise, reaction of another bulky phosphine [(μ-Ph2PCH2PPh2)Co2(CO)4(μ-PPh2CCP(O)Ph2)] 3 with (COD)PdCl2 yielded [{μ-P,P-PPh2CH2PPh2}Co2(CO)3(μ-CO){μ-PPh2CCP(O)Ph2}]PdCl28. The X-ray structural studies of 6, 7 and 8 reveal that unusual palladium–cobalt bonds were formed. A Suzuki type reaction employing complexes 6, 7 and 8, as catalysts in the reaction of 2-bromothiophene with boronic acid did not show encouraging signs.

Reactions of molybdenum-cobalt complex with phenylacetylene: X-ray crystal structure of [MoCo(CO)4{CPhCHCHCPh}(η5-C5H5)]

Reaction of [MoCo(CO)(5)(PPh(3))(2)(eta(5)-C5K5)] (1) with phenylacetylene in tetrahydrofuran at 60 degrees C produced a heterobimetallic compound, [MoCo(CO)(4)(CPhCHCHCPh)(eta(5)-C5H5)] (2), in high yield. Compound 2 was characterized by mass, infrared and H-1, C-13 and P-31 NMR spectra. The X-ray crystal structure of 2 was determined: orthorhombic, P-bca, a = 12.479(3), b = 15.975(3), c = 21.570(3) Angstrom, V = 4299.8(15) Angstrom(3) and Z = 8, R(W)(F) = 4.00% for 2143 (F > 4 sigma(F)) observed reflections. In 2, the cobalt fragment is at apical and the molybdenum fragment is at basal position of the pseudo-pentagonal pyramidal structure. [MoCo(CO)(4){mu-PhC(2)H}(PPh(3))(eta(5)-C5H5)] (3) was obtained in excellent yield from the reaction of 1 with phenylacetylene at lower temperature. Compound 3 can be quantitatively converted into 2 by reaction with excess phenylacetylene at 60 degrees C.

Molecular structure of thallium(III) meso-tetraphenylporphyrin acetate: Tl(tpp)(OAc)

Abstract X-ray diffraction data and solid-state 13C CP/MAS spectra of thallium(III) mesotetraphenylporphyrin acetate, Tl(tpp)(OAc), provide evidence for a chelating-bidentate acetato group coordinated to the thallium(III) atom. The displacement of the thallium atom from the porphyrin mean plane was 0.842 A. The geometry around the thallium centre of the Tl(tpp)(OAc) molecule has TlO(1) = 2.361(9), TlO(2) = 2.229(10) and TlN = 2.219(7) A. Fourier-transform IR spectra (400–4000 cm−1) of Tl(tpp)(OAc) in KBr discs and in CH2Cl2 solvent are reported and assigned by comparison with the spectra of Tl(tpp)(CN). It is concluded that the intramolecular exchange of the acetato group between asymmetric pseudo-chelating c and d result in the adaptation of the chelating bidentate, a for the carboxylate at low temperature and that of the symmetric pseudochelating b at high temperature for Tl(tpp)(OAc) in CH2Cl2 solvent. This explains the resonances of 13C and 1H of the axial acetato group in low- and high-temperature solution NMR measurements.

Nucleophilic substitution reactions of (η6-fluorotoluene)Cr(CO)3 and (η6-fluoroanisole)Cr(CO)3 toward phenylacetylide, fluorenyl, indolinyl and carbazolinyl lithium: crystal structures of tricarbonyl[η6-(1,2-diphenylethynyl)benzene]chromium and tricarbonyl[η6-(1,4-fluorenyl)toluene]chromium

Abstract Tricarbonyl[η6-(1,2-diphenylethynyl)benzene]chromium (8a) was obtained along with tricarbonyl[η6-(2-phenylethynyl)anisole]chromium (7b) and tricarbonyl[η6-(3-phenylethynyl)anisole]chromium (7a) from the reaction of tricarbonyl(η6-fluoroanisol)chromium (4c) with lithium phenylacetylide (3). The formation of ortho- and meta-products, 7b, 8a and 7a, produced in the above reaction demonstrates that the reaction was by no means through a straightforward nucleophilic substitution mechanism. These results provided support for the mechanism proposed by Pauson and Brookhart, in which the nucleophile attacked the carbon atom of the phenyl ring not bearing the leaving group, followed by hydrogen migration and finally elimination of the leaving group to achieve aromaticity. 8a was obtained presumably from the reaction of 7b with excess 3. Compounds were characterized by mass, infrared, 1H, 13C NMR spectra. The molecular structure of 8a has been determined by X-ray diffraction studies. Crystal data are as follows: orthorhombic, PBCA, a = 18.690(2) A , b = 10.666(2) A , c = 20.463(2) A , V = 4079.3(8) A 3 , Z = 8, R =4.41%, R w = 5.56% . Tricarbonyl(η6-4-fluorenyltoluene)chromium (10) was obtained as the only separated product from the reaction of tricarbonyl[η6-4-flurotoluene)chromium (5) with fluorenyl lithium. The X-ray crystal structure of 10 was determined: monoclinic, P2 1 /c, a = 12.318(1) A , b = 11.498(1) A , c = 13.585(2) A , β = 100.35(1)°, V = 1892.8(5) A 3 , Z = 4, R = 3.63%, R w = 5.65% . Tricarbonyl[η6-4-fluorenylanisole)chromium (11a), tricarbonyl[η6-3-fluorenylanisole)chromium (11b) and tricarbonyl[η6-2-fluorenylanisole)chromium (11c) were also produced in moderate to good yields. Moreover, tricarbonyl[η6-4-indolinyltoluene)chromium (12) and tricarbonyl[η6-4-carbazolinyltoluene)chromium (14) were synthesized from the reaction of 5 with indolinyl and carbazolinyl lithium, respectively. Tricarbonyl[η6-4-indolinylanisole)chromium (13a), tricarbonyl[η6-3-indolinylanisole)chromium (13b) and tricarbonyl[η6-2-indolinylanisole)chromium (13c) were obtained in high yields from the direct nucleophilic substitution reactions of related compounds.

Preparation of a new cobalt-containing diphosphine ligand and its reaction towards dicobalt octacarbonyl; X-ray crystal structure of [Co2(CO)4(μ-CO)2{μ-P,P-(μ-PPh2CCPPh2)Co2(CO)6}]

Abstract Consecutive reactions of bis(diphenylphosphino)acetylene with Co2(CO)8 resulted in an alkyne-bridged, diphosphine-chelated tetracobalt complex, [Co2(CO)4(μ-CO)2{μ-P,P-(μ-PPh2CCPPh2)Co2(CO)6}] (2), which has been characterized by spectroscopic means as well as X-ray studies.

Palladium(II)-catalyzed Heck reaction of aryl halides and arylboronic acids with olefins under mild conditions.

Summary A series of general and selective Pd(II)-catalyzed Heck reactions were investigated under mild reaction conditions. The first protocol has been developed employing an imidazole-based secondary phosphine oxide (SPO) ligated palladium complex (6) as a precatalyst. The catalytic coupling of aryl halides and olefins led to the formation of the corresponding coupled products in excellent yields. A variety of substrates, both electron-rich and electron-poor olefins, were converted smoothly to the targeted products in high yields. Compared with the existing approaches employing SPO–Pd complexes in a Heck reaction, the current strategy features mild reaction conditions and broad substrate scope. Furthermore, we described the coupling of arylboronic acids with olefins, which were catalyzed by Pd(OAc)2 and employed N-bromosuccinimide as an additive under ambient conditions. The resulted biaryls have been obtained in moderate to good yields.

Synthesis and characterization of tricarbonyl[η6-(phenylethynyl)arene]chromium complexes: crystal structure of tricarbonyl[η6-(3-phenylethynyl)anisole]chromium

Abstract Tricarbonyl(η6-diphenylacetylene)chromium (4) was prepared from the reaction of tricarbonyl(η6-fluorobenzene)chromium (3) with lithium phenylacetylide (2) at a low temperature using hexamethylphosphoric triamide as cosolvent. A concomitant tricarbonyl(η6-butoxylbenzene)chromium (6) was also obtained in this reaction probably owing to both the air oxidation of n-BuLi and the ring opening of tetrahydrofuran by n-BuLi. The overwhelming abundance of meta and ortho products 9b and 10b produced in the substitution reaction of tricarbonyl(η6-fluoroanisole)chromium (8a) by lithium phenylacetylide demonstrates that the reaction was by no means through the straightforward SNAr mechanism. The results provide support for the mechanism proposed by Pauson and Brookhart, in which the nucleophile attacked a carbon of the phenyl ring not bearing the leaving group, followed by hydrogen migration and finally elimination of the leaving group to achieve aromaticity. In addition, compounds were characterized by mass, IR, 1H and 13C NMR spectra, and elemental analysis. The molecular structure of tricarbonyl[η6-(3-phenylethynyl)anisole]chromium (9b) has been determined by X-ray diffraction studies. Crystal data are as follows: P 1 ; a = 7.782(2) A and c = 12.688(3) A ; α = 108.46(3)°, β = 96.05(3)° and γ = 103.19(3)°; V = 797.3(4) A 3 ; Z = 2; R = 3.23%; R w = 4.37% .