Methane, tris 3- pyrazolyl

The pyrazolylalkane ligands, HC(pz)3, MeC(pz)3 and H2C(pz)2 (tris(pyrazolyl)-methane, tris(pyrazolyl)ethane and bis(pyrazolyl)methane, respectively), shown in Chart 3 are neutral analogues of the corresponding pyrazolylborate versions and display remarkably similar ligand properties. 

The tris(pyrazolyl)borate and tris(pyrazolyl)methane systems represent an important class of tridentates which lead to spin crossover behaviour in iron(II) but they belong to a totally different structural category and are... 

Solution Studies of Tris(pyrazolyl)methane Complexes. 118... 

Compounds of structure 5 have yet to be realized but terminal tridentates of the tris(pyrazolyl)hydridoborate [49], tris(pyrazolyl)methane [50] or tri-azacyclononane [5] types could be contemplated. 

Thus, upon treatment with NaTp or HCpz3/NH4PF6, the complexes TpM (ri1 ri2-C8H120Me) (M = Pd 184, Pt 185) and their anionic tris(pyrazolyl) methane counterparts [(HCpz3)M(ri1 ri2-C8Hi20Me)]PF6 (M = Pd 187. PF6, Pt 188.PF6) were obtained in high yield as moderately moisture-sensitive materials (Scheme 15, Section III.B.l). These compounds were confirmed to be 5-coordinate in the solid state (by X-ray) and fluxional in solution, resulting in equilibration of all three pyrazole donors. 

Some of the first catalytic model systems for the simulation of the function of methane monooxygenase comprise monomeric as well as dimeric iron-containing model complexes bearing hydro-tris(pyrazolyl)borate ligands [6]. These complexes, e.g. 3, catalyze the oxidation of aromatic and aliphatic carbon-hydrogen bonds in the presence of oxygen (1 atm), acetic acid and zinc powder at room temperature (Scheme 2). 

Catalytic transformations involving the C-H bonds of thiophene are rare, but recently there has been a report on the catalytic addition of the C(2)-H bond of thiophene across ethylene to form 2-ethylthiophene <20040M5514>. Reaction of the ruthenium complex TpRu(CO)(NCMe)(Me) (where Tp = hydrido tris(pyrazolyl)borate) with thiophene produces the 2-thienyl complex 249 and methane. This complex catalyzes the formation of 2-ethylthiophene from a solution of thiophene and ethylene (Equation 121). The mechanism of this reaction has been explored. 

Four- and five-coordinated precious metal complexes with tris(pyrazolyl)methane have been described, many of which are stereochemically non-rigid.225 In particular, the X-ray structure of [Au(Me2)(HC(pz)3)]N03 shows a cis-planar coordination, with one pyrazolyl group involved in a weak axial Au- N interaction.242... 

The applications of these ligands have been limited to the work by Nakazawa et al.244 who found tris(pyrazolyl)methane titanium complexes to be high-activity catalysts for the polymerization of olefins, and the use of tris(pyrazolyl)methane zinc complexes to model zinc-containing enzymes, such as dihydrorootase and carbonic anhydrase.245 The structure of the free ligand HC(Me2pz)3 has also been reported.246... 

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