Liang-Fu Tang

Synthesis and reactivity of Group 6 metal carbonyl complexes containing bis(triazol-1-yl)methane: linkage coordination polymers

Abstract The reaction of bis(3,5-dimethyl-1,2,4-triazol-1-yl)methane, CH2(3,5-Me2Tz)2, with M(CO)6 (M=Cr, Mo or W) in refluxing DME produces CH2(3,5-Me2Tz)2M(CO)4 in moderate yield. The crystal structures determined by X-ray analysis show that bis(3,5-dimethyl-1,2,4-triazol-1-yl)methane acts as a chelating bidentate ligand with two endodentate nitrogen atoms in these complexes. Reactions of complexes CH2(3,5-Me2Tz)2M(CO)4 (M=Mo or W) with R2SnX2 (R=Ph or Me; X=Cl or Br) in a 1:1 or 1:2 ratio, respectively, only yield 1:1 adducts. In these adducts, bis(3,5-dimethyl-1,2,4-triazol-1-yl)methane may coordinate to tin atom through exodentate nitrogen atoms on the 4-position of triazole rings to form linkage coordination polymers. Possibly owing to weak donors of 4-position exonitrogen atoms on triazole rings to organotin acceptors, the dissociation of these adducts in solution could exist. Adduct of CH2(3,5-Me2Tz)2W(CO)4·SnPh2Br2 absorbs one water molecule while crystals are growing and becomes the hydrolysis product [SnPh2Br2(H2O)]·(CH2(3,5-Me2Tz)2W(CO)4), which is characterized by X-ray crystallography, indicating that tin atom is five coordinate with a trigonal bipyramid geometry, the water molecule coordinates to the tin atom, and is simultaneously connected to the exonitrogen atoms on the 4-position of triazole rings of two adjacent CH2(3,5-Me2Tz)2W(CO)4 units through hydrogen bonds to form linkage coordination polymers, in which two coordination modes are observed.

Synthesis, structures and electrochemical properties of Group 6 metal carbonyl complexes containing ferrocenylpyrazole ligands

Abstract A series of carbonylchromium, molybdenum and tungsten complexes containing ferrocenylpyrazole ligands, (M(CO)5L) (M=Cr, Mo or W; L represents ferrocenyl pyrazole), have been prepared by the photochemical reactions of ferrocenylpyrazole ligands with M(CO)6. Their electrochemical behaviors have also been investigated by cyclic voltammetry, indicating that chromium complexes exhibit two one-electron reversible or quasi-reversible couples, while molybdenum and tungsten complexes have one reversible couple corresponding to the ferrocenyl group and one irreversible oxidation process for the molybdenum or tungsten center. The crystal structures of 3-ferrocenylpyrazole pentacarbonyltungsten (3) and 3-methyl-5-ferrocenylpyrazole pentacarbonyltungsten (6) are determined by X-ray diffraction method, indicating that both 3(5)-ferrocenylpyrazole and 3(5)-methyl-5(3)-ferrocenylpyrazole act as a monodentate ligand, and the central metal of W is six-coordinate with a quasi-octahedral coordination geometry in both complexes. Complex 3 is linked into a one-dimensional chain in solid through intermolecular hydrogen bonds formed by metal carbonyl as hydrogen bond acceptors, while complex 6 forms a dimer by similar intermolecular hydrogen bond interactions. The N–H⋯O distances in complexes 3 and 6 are 2.932(11) and 2.900 A, respectively. All new compounds have been characterized by elemental analyses, IR, 1H-NMR. 13C-NMR spectra of molybdenum and tungsten complexes have also been determined.

Synthesis and crystal structures of Group 6 metal carbonyl complexes containing S-rich bis(pyrazol-1-yl)methane ligands

Abstract The reaction of 3(5)-methylthio-5(3)-phenylpyrazole with dibromomethane under phase-transfer catalytic conditions only affords a new ligand, bis(3-phenyl-5-methylthiopyrazol-1-yl)methane. However, the reaction of 3(5)-methylthio-5(3)-p-methoxyphenylpyrazole or 3(5)-methylthio-5(3)-tert-butylpyrazole with dibromomethane under the same conditions yields three isomers, respectively, indicating that the substituents significantly affect the steric and electronic properties of pyrazole ring during the formation of ligands. Treatment of these potential polydentate ligands with M(CO)6 (M=Cr, Mo or W) under UV irradiation at room temperature affords (NN)M(CO)4 derivatives, in which some complexes contain asymmetric substituted bis(pyrazol-1-yl)methane ligands. The X-ray crystal structure analyses indicate that the sulfur atoms in these complexes do not take part in the coordination to the metal centers, and S-rich bis(pyrazol-1-yl)methanes actually act as bidentate chelating ligands by two nitrogen atoms. It is also interesting that in order to reduce the repulsion of methyl groups with carbonyls, the methyl groups in these complexes are oriented away from the metal centers.

Synthesis of bis(pyrazol-1-yl)methanes with organogermyl and organosilyl groups on the methine carbon and their reaction with W(CO)5(THF). X-ray crystal structures of Ph3GeCHPz2W(CO)4 and Me3SiCHPz2W(CO)4 (Pz=3,5-dimethylpyrazole)

Abstract A series of new bis(pyrazol-1-yl)methane ligands with organogermyl and organosilyl groups on the methine carbon, MCHPz 2 (M=Ph 3 Ge, PhMe 2 Si, i Pr 3 Si or Me 3 Si; Pz=3,5-dimethylpyrazole or 3,4,5-trimethylpyrazole), have been prepared by the reaction of bis(pyrazol-1-yl)methyllithium with triphenylgermanium bromide and organosilyl chloride. Treatment of these ligands with W(CO) 5 (THF) in refluxing THF resulted in new heterobimetallic complexes MCHPz 2 W(CO) 4 as major products, accompanied by partial decomposition of ligands to yield a certain amount of PzW(CO) 5 as by-products. These new ligands and complexes have been characterized by 1 H-NMR, IR and elemental analysis. The molecular structures of complexes Ph 3 GeCHPz 2 W(CO) 4 and Me 3 SiCHPz 2 W(CO) 4 (Pz=3,5-dimethylpyrazole) have been determined by X-ray structure analysis, indicating that bis(pyrazol-1-yl)methanes act as chelating bidentate ligands in these complexes, and organometallic groups lie in the axial position of the methine carbon.

Tetranuclear heterodimetallic metallamacrocyles with M-Sn(IV) (M = Mo or W) bonds. Crystal structures of {p-[(CO)3MoC5H4C(O)]2C6H4} {(Ph2Sn)2S} and {p-[(CO)3MoC5H4C(O)]2C6H4} {(Ph2Sn)2CH2}

Abstract The dianions {[ p -(CO) 3 MC 5 H 4 C(O)] 2 C 6 H 4 } 2− reacted with Ph 2 SnBr 2 in a 1:2 or 1:1 ratio to give tetranuclear heterodimetallic complexes p -[(Ph 2 BrSn)(CO) 3 MC 5 H 4 C(O)] 2 C 6 H 4 (M=Mo ( 1 ) or W ( 2 ), respectively), and with CH 2 (SnPhBr 2 ) 2 to yield tetranuclear heterodimetallic metallamacrocycles { p -[(CO) 3 MC 5 H 4 C(O)] 2 C 6 H 4 }{(Ph 2− n Br n Sn) 2 CH 2 } ( n =1, M=Mo ( 5 ) and W ( 6 ); n =0, M=Mo ( 7 ) and W ( 8 ), respectively). Only one bromide on the tin atom was replaced by the metallic anions owing to the electron-withdrawing groups on the cyclopentadienyl rings greatly decreasing the nucleophilicity of the metallic anions. Treatment of complexes 1 and 2 with Na 2 S·9H 2 O yielded the novel metallamacrocyclic complexes { p -[(CO) 3 MC 5 H 4 C(O)] 2 C 6 H 4 }{(Ph 2 Sn) 2 S} (M=Mo ( 3 ) and W ( 4 ), respectively). All compounds have been characterized by elemental analyses, IR and 1 H-NMR spectra. The crystal structures of complexes 3 and 7 determined by X-ray crystallography indicate a novel 14-membered organometallic metallamacrocyclic ring system in which two Mo–Sn units are linked by the bridging cyclopentadienyl ligand and the sulfur or carbon atom. In addition, the carbonyl group π-system is coplanar with the adjacent cyclopentadienyl ring system, but markedly deviates from the bridging phenyl plane.

Synthesis and catalytic activity of pyrazolyl-functionalized N -heterocyclic carbene palladium complexes

Three pyrazolyl-functionalized N-heterocyclic carbene (NHC) palladium complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole have been synthesized and characterized by physico-chemical and spectroscopic methods, and the structures of two of the complexes have been confirmed by single-crystal X-ray diffraction. The pyrazolyl-functionalized NHCs act as chelating N,C-bidentate ligands in these three complexes. Catalytic tests have proved that these complexes exhibit highly effective catalytic activity for the Suzuki–Miyaura and Mizoroki–Heck coupling reactions in water or aqueous/organic media under air. The substituents on the pyrazolyl ring exert different influences on the catalytic activity of the complexes in these coupling reactions.

Synthesis, structure and characterization of MSn (M=Mo, W) bonded heterobimetallic complexes containing bis(pyrazol-1-yl)methane ligands

Abstract The reaction of bis(pyrazol-1-yl)methane tetracarbonylmolybdenum(0) or tungsten(0) complexes with RSnCl3 (R=Ph, Cl) at room temperature yielded heterobimetallic complexes CH2(Pz)2M(CO)3(Cl)(SnCl2R) (Pz represents substituted pyrazole; M=Mo or W; R=Ph or Cl) in good yields, which have been characterized by elemental analysis, 1H NMR and IR spectroscopy. The reaction of bis(3,5-dimethyl-4-halopyrazol-1-yl)methane tetracarbonyl tungsten with PhSnCl3 did not take place even in refluxing CH2Cl2. The electronic and steric characteristics of substituents on the pyrazole ring remarkably influence the structures of the products. The structures of CH2(3,5-Me2-4-BrPz)2W(CO)3(Cl)(SnCl3) (8) and CH2(4-BrPz)2Mo(CO)3(μ-Cl)(SnCl2Ph) (17) (Pz: pyrazole) determined by X-ray crystallography show that no chlorine-bridged WSn bond is observed in complex 8, while one chlorine-bridged MoSn bond exists in complex 17. The SnM bond length is 2.7438(5) A in complex 8 (WSn) and 2.7559(4) A in complex 17 (MoSn).

Synthesis and characterization of bidentate organotin Lewis acid derivatives containing bis(pyrazol-1-yl)alkanes: X-ray crystal structure of PhBr2(L)SnCH2SnPhBr2 (L = bis(4-chloropyrazol-1-yl)methane)

Abstract The reaction between bis(dibromophenylstannyl)methane, [CH2(SnPhBr2)2], with bis(pyrazol-1-yl)alkanes, [(CH2)nPz2] (n=1 or 2; Pz=substituted pyrazole) in a 1:1 or 1:2 ratio yields only 1:1 adducts of PhBr2[(CH2)nPz2]SnCH2SnPhBr2, which have been confirmed by elemental analysis, 1H NMR and IR spectroscopy. The electronic and steric characteristics of substituents on the pyrazole rings markedly influence the donating ability of bis(pyrazol-1-yl)alkanes to the bidentate organotin Lewis acid acceptor. The investigations on the reaction of the adducts with DMSO and NMR spectra of the adducts show the weak interactions between ligands and the bidentate organotin Lewis acid acceptor. X-Ray analysis of PhBr2(CH2(4-ClPz)2)SnCH2SnPhBr2 showed that bis(4-chloropyrazol-1-yl)methane acts as a chelating bidentate ligand to only one tin atom.

Synthesis and characterization of polymeric triphenyltin and cyclotetrameric tricyclohexyltin 2-(1H-imidazol-1-yl)acetates

The reaction of 2-(1H-imidazol-1-yl)acetic acid with (Ph3Sn)2O or Cy3SnOH (Cy = cyclohexyl) yields triphenyltin 2-(1H-imidazol-1-yl)acetate (1) and tricyclohexyltin 2-(1H-imidazol-1-yl)acetate (2), respectively. 2-(1H-imidazol-1-yl)acetates in these two complexes show remarkably different coordination modes. Complex 1 forms a polymeric chain structure through intermolecular Sn–N interactions, while 2 displays a 28-membered macrocyclic tetranuclear structure by the assembly of Sn–N coordination bonds.

Synthesis and catalytic activity of N-heterocyclic carbene metal carbonyl complexes based on 1-[2-(pyrazol-1-yl)phenyl]imidazole

A series of N-heterocyclic carbene transition metal (molybdenum, tungsten and ruthenium) carbonyl complexes derived from 1-[2-(pyrazol-1-yl)phenyl]-imidazole have been synthesized and characterized by physico-chemical and spectroscopic methods, and the structures of five complexes have been confirmed by X-ray crystal structure analyses. The azaaryl-functionalized N-heterocyclic carbenes act as chelating N,C-bidentate ligands in these five complexes. Preliminary catalytic tests of these NHC-molybdenum (tungsten) carbonyl complexes in the oxidation of styrene have been carried out, showing that benzaldehyde was the main oxidation product when hydrogen peroxide was used as the oxidant, while 2,5-diphenyl-1,4-dioxane was obtained as the exclusive product in the oxidation by tert-butyl hydroperoxide.