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Treatment of 1-phenylthiomethyl-3,5-dimethylpyrazole with n-butyllithium, and subsequently with phenyl isothiocyanate yielded 2-(3,5-dimethylpyrazol-1-yl)-2-(phenylthio)thioacetanilide, 2-(3,5-dimethylpyrazol-1-yl)thioacetanilide, N,N′-diphenyl-2-(3,5-dimethylpyrazol-1-yl)propanedithioamide and 5-anilino-4-(3,5-dimethylpyrazol-1-yl)-3-phenylimino-1,2-dithia-4-cyclopentene, respectively. Reaction of the propanedithioamide derivative with W(CO)5THF has been investigated, which gave a bis(chelate) tungsten complex through two relatively soft sulfur atoms. All these newly synthesized compounds were characterized by NMR and HRMS spectroscopy (or elemental analysis), and their structures were unambiguously confirmed by X-ray crystallography. Two possible pathways, including a carbanion or a carbene intermediate formed via the C S bond cleavage, have been suggested to explain the formation of propanedithioamide and 1,2-dithiole derivatives.

A series of N-heterocyclic carbene (NHC) silver and palladium complexes derived from N-[bis(pyrazol-1-yl)methyl]phenyl-N′-benzylimidazolium and N-[bis(pyrazol-1-yl)methyl]phenoxy- methyl-N′-benzylimidazolium salts have been synthesized and characterized by elemental analysis, NMR spectroscopy and single-crystal X-ray diffraction. The NHCs functionalized by bis(pyrazol-1-yl)methyl groups show three different coordination modes in these complexes. N-[Bis(pyrazol-1-yl)methyl]phenyl-N′-benzylimidazol-2-ylidene (L) and N-[bis(3,5-dimethylpyrazol-1-yl)methyl]phenyl-N′-benzylimidazol-2-ylidene (L′) act as monodentate ligands through the carbene carbon in cationic complexes [L2Ag][AgCl2] and [L′4Ag3Br2][AgBr2]. A bridging [C,N] bidentate coordination mode, through one pyrazolyl nitrogen and the carbene carbon to two palladium centers, was observed in macrocyclic complex L′2Pd2Br2. While in the coordination polymer [L2Ag2]n[PF6]2n and macrocyclic complex [L′2Ag2][PF6]2, L and L′ act as bridging [C,N,N] tridentate ligands through two pyrazolyl nitrogens and the carbene carbon. Although N-[bis(pyrazol-1-yl)methyl]phenoxymethyl-N′-benzylimidazol-2-ylidene (L″) also acts as a bridging [C,N] bidentate ligand in L″2Ag2Cl2 and a bridging [C,N,N] tridentate ligand in L″2Ag2X2 (X = BF4 or PF6), like L′ and L in L′2Pd2Br2 as well as [L2Ag2]n[PF6]2n and [L′2Ag2][PF6]2, respectively, an obvious difference among them is present. L″ prefers to coordinate to two silver atoms in a head (carbene)–to tail (nitrogen) coordination mode, while L and L′ show head (carbene)–to head (carbene) and tail (nitrogen)–to tail (nitrogen) coordination modes to two silver atoms. Additionally, these silver complexes exhibit good catalytic activity in the three-component coupling reaction of alkyne, aldehyde and amine forming propargylamines.

Three new bis(3,5-dimethylpyrazol-1-yl)methanes [(2-XC 6 H 4 )CH(3,5-Me 2 Pz) 2 , X = F, Cl and Br] functionalized by 2-halophenyl groups on the methine carbon atom have been synthesized. Upon heating (2-XC 6 H 4 )CH(3,5-Me 2 Pz) 2 with Mo(CO) 6 or W(CO) 5 THF in THF at reflux, complexes (2-XC 6 H 4 )CH(3,5-Me 2 Pz) 2 M(CO) 4 ( X = F or Cl, M = Mo or W) were obtained. While the similar reaction of (2-BrC 6 H 4 )CH(3,5-Me 2 Pz) 2 led to the oxidative addition of the C–Br bond to the Mo or W center to give complexes (C 6 H 4 )CH(3,5-Me 2 Pz) 2 M(CO) 3 Br (M = Mo or W). In addition, 2-ImC 6 H 4 CH(3,5-Me 2 Pz) 2 (Im = imidazol-1-yl) has been obtained by the reaction of (2-BrC 6 H 4 )CH(3,5-Me 2 Pz) 2 with imidazole, which subsequently reacted with PhCH 2 Cl to form 1-{2-[bis(3,5-dimethylpyrazol-1-yl)methyl]phenyl}-3-benzylimidazium chloride. Treatment of this imidazole salt with Ag 2 O and succeedingly with W(CO) 5 THF or Ru 3 (CO) 12 yielded N -heterocylic carbene complexes LW(CO) 5 and LRu 3 (CO) 8 ( μ -H)( μ -Cl) ( L = 1-{2-[bis(3,5-dimethylpyrazol-1-yl)methyl]phenyl}-3-benzylimidazol-2-ylidene), respectively. In the former, L acts as a monodentate ligand by the carbene carbon to the tungsten atom, and two pyrazolyl nitrogen atoms do not take part in the coordination to the metal center. While in the latter, L serves as a bridging bidentate ligand by one pyrazolyl nitrogen and the carbene carbon atoms to a Ru–Ru bond, and a hydride along with a chloride ligand bridges this metal–metal bond.

Reaction of 1-arylthiomethyl-3,5-dimethylpyrazole [ArSCH2(3,5-Me2Pz), Ar = phenyl or 2-pyridyl, Pz = pyrazol-1-yl] with Mo(CO)6 produces complexes ArSCH2(3,5-Me2Pz)Mo(CO)4, while similar reaction with W(CO)6 yields analogous complexes ArSCH2(3,5-Me2Pz)W(CO)4 and concomitant desulfurized complex (3,5-Me2PzH)W(CO)5 in the reaction of PhSCH2(3,5-Me2Pz). Succedent treatment of complexes PhSCH2(3,5-Me2Pz)M(CO)4 with SnCl4 gives heterobimetallic complexes PhSCH2(3,5-Me2Pz)M(CO)3(Cl)(SnCl3) (M = Mo or W) in good yields. ArSCH2(3,5-Me2Pz) act as S,N chelating bidentate ligands through the sulfur and the pyrazolyl nitrogen atoms in the aforementioned complexes. The modification of ArSCH2(3,5-Me2Pz) by organotin group at the methylene group has been successfully carried out, which yields functionalized ligands Ph3SnCH(SAr)(3,5-Me2Pz). Markedly different reactions are observed, upon treatment of Ph3SnCH(SPh)(3,5-Me2Pz) and Ph3SnCH(SPy)(3,5-Me2Pz) (Py = 2-pyridyl) with W(CO)5THF. The former yields complex Ph3SnCH(SPh)(3,5-Me2Pz)W(CO)4, as well as PhSCH2(3,5-Me2Pz)W(CO)4 with a partial loss of the organotin moiety, while no reaction takes place in the latter. In addition, reaction of Ph3SnCH(SPy)(3,5-Me2Pz) with Mo(CO)6 results in the oxidative addition reaction of the Sn–Csp3 bond to the molybdenum(0) atom to yield novel heterometallacyclic complex CH(SPy)(3,5-Me2Pz)Mo(CO)3SnPh3, in which [(2-pyridyl)thiomethyl](3,5-dimethylpyrazol-1-yl)methide acts as a tridentate κ3-[N,C,N] chelating ligand through the carbon atom, the pyrazolyl and the pyridyl nitrogen atoms, as the sulfur atom does not coordinate to the molybdenum atom anymore. Interestingly, treatment of this heterometallacyclic complex with P(OR)3 (R = Ph or Et) gives rise to the isomerization of the C–S bond to the C–N bond, generating the thione–S coordinated complex CH(NC4H4C = S)(3,5-Me2Pz)Mo(CO)2(P(OR)3)SnPh3, in which the ligand binds in a novel tridentate, monoanionic κ3-[N,C,S] chelating mode to the molybdenum atom.

The modification of bis(pyrazol-1-yl)methanes by organotin halide on the methine carbon atom has been successfully carried out, and their related reactions have also been studied. Bis(3,5-dimethylpyrazol-1-yl)(iododiphenylstannyl)methane [Ph2ISnCH(3,5-Me2Pz)2] can be obtained by the selective cleavage of the Sn–Csp2Sn–Csp2 bond in bis(3,5-dimethylpyrazol-1-yl)triphenylstannylmethane with I2 in a 1:1 molar ratio, while {di(tert-butyl)chlorostannyl}bis(3,5-dimethylpyrazol-1-yl)methane [(t-Bu)2ClSnCH(3,5-Me2Pz)2] and {di(tert-butyl)chlorostannyl}bis(3,4,5-trimethylpyrazol-1-yl)methane [(t-Bu)2ClSnCH(3,4,5-Me3Pz)2] are easily prepared by the reaction of the bis(3,5-dimethylpyrazol-1-yl)methide or bis(3,4,5-trimethylpyrazol-1-yl)methide anion with di(tert-butyl)tin dichloride. The molecular structure of [(t-Bu)2ClSnCH(3,5-Me2Pz)2] determined by X-ray structure analysis indicates that bis(3,5-dimethylpyrazol-1-yl)methide acts as a bidentate monoanionic κ2-[C,N] chelating ligand. Reaction of these bis(pyrazol-1-yl)methanes functionalized by organotin halide with W(CO)5THF results in the oxidative addition of the relative electrophilic Sn–X (X = Cl or I) bond instead of the Sn–Csp3Sn–Csp3 bond to the tungsten(0) atom, yielding new metal–metal bonded complexes R2SnCHPz2W(CO)3X (R = Ph or t-Bu, Pz represents substituted pyrazol-1-yl). Furthermore, treatment of the oxidative addition product (t-Bu)2SnCH(3,5-Me2Pz)2W(CO)3Cl with n-BuLi results in known complex CH2(3,5-Me2Pz)2W(CO)4 with the loss of the organotin fragment. In addition, reaction of Ph2ISnCH(3,5-Me2Pz)2 with 2-PySNa (Py = pyridyl) leads to the replacement of iodide by 2-PyS− anion to give Ph2(2-PyS)SnCH(3,5-Me2Pz)2, which subsequently reacts with W(CO)5THF to result in the decomposition of this ligand, also yielding the known bis(3,5-dimethylpyrazol-1-yl)methane derivative of CH2(3,5-Me2Pz)2W(CO)4.