Pyrazolyl complexes

The general problem of M—H-C interactions was brought into spotlight and analyzed in depth in a series of papers by Cotton and co-workers123 130 131). The molecules they studied were several interesting pyrazolyl complexes first synthesized by Trofimenko132). In an earlier section of this article, we drew attention to two... 

Other divalent germanium compounds include salts of GeClj, such as the substituted pyrazolyl complexes [Ge2(pz )3][GeCl3] (8-XXII) which is obtained in the reaction of Ba(pz )2 with GeCl2-dioxane.148 There are also a sulfide, GeS, several thiolato complexes,149 and a white to yellow hydroxide of no definite stoichiometry that is converted by NaOH to a brown material that has Ge—H bonds. 

Jesson 369, 370) has made a thorough study at 4.2°K of a series of pyrazolyl complexes of the type... 

In reactions with secondary amines containing a second nitrogen atom, the diphenylallenylidene ligand of 43 is active not only at the C -Cp double bond but also at the atom. Thus, the addition of pyrazoles to solutions of 43 leads to the pyrazolo[l,2-a]pyrazolyl complexes 85-87 (Scheme 25). Complexes 85 and 87 yield the functionalized alkynyl derivatives 88 and 89 by treatment with sodium methoxide. The formation of 85-87 involves novel 1,2,3-diheterocyclization reactions, where an organometallic complex is used for the first time [34]. 

The pyrazolyl complexes in most cases are colourless solids, soluble in THF and aromatic hydrocarbons. The solids can be handled during a short time on air, but they partially decompose during a few months in an inert-atmosphere box [46]. 

Scheme 8 Amido-b (pyrazolyl) complexes (69-70) by Carpentier and coworkers [83]...

The complexes (6) result from the irradiation of the platinum(ii) pyrazolyl complexes in the presence of [M(CO)e]. ... 

Classic A/-heterocychc ligands, eg, bipyridyl (bipy), terpyridyl, imidazole, pyrazine, phenanthroline, piperazine (including alkyl- and aryl-substituted derivatives), and polypyrazol-l-yl-borates (bis, tris, and tetra), have all been found to coordinate Th(IV) chlorides, perchlorates, and nitrates. The tripodal hydrotris(pyrazolyl)borates, HBPz, have been used to stabilize organometaHic complexes (31). Bis-porphyrin Th(IV) "sandwich" complexes have been... 

Cationic rings are readily reduced by complex hydrides under relatively mild conditions. Thus isoxazolium salts with sodium borohydride give the 2,5-dihydro derivatives (217) in ethanol, but yield the 2,3-dihydro compound (218) in MeCN/H20 (74CPB70). Pyrazolyl anions are reduced by borohydride to pyrazolines and pyrazolidines. Thiazolyl ions are reduced to 1,2-dihydrothiazoles by lithium aluminum hydride and to tetrahydrothiazoles by sodium borohydride. The tetrahydro compound is probably formed via (219), which results from proton addition to the dihydro derivative (220) containing an enamine function. 1,3-Dithiolylium salts easily add hydride ion from sodium borohydride (Scheme 20) (80AHC(27)151). 

S4N4 as a source thionitxosyl-metal complexes is limited to a single example. The first selenonitrosyl-metal complex TpOs(NSe)Cl2 (Tp = hydrotris(l-pyrazolyl)borate) was prepared recently by method (a). ... 

Chemistry of transition metal complexes supported by hydrotris(pyrazolyl) borates and chemistry of dioxygen complexes based on these ligands 99YGK619. 

Recent advances in complexes of group VIB metals (Mo, W) with poly-(pyrazolyl)borate ligands 98MI2. 

CHROMIUM ALKYLS WITH NITROGEN- AND OXYGEN-LIGANDS 3.1. Tris(pyrazolyl)borate complexes... 

In an attempt to change the electronics of the chromium atom, we are replacing the carbon based cyclopentadienyl ring with ligands containing harder donor atoms. For example, we have employed the tris(pyrazolyl)borate moiety, an isoclectronic replacement for Cp featuring tridentate N-coordination.[9] Figure 2 shows the molecular structure of Tp SU Cr-Ph, a representative Cr° alkyl. It will be noted, that this complex is mononuclear, due to the steric protection of the extremely bulky tris(pyrazolyl)borate. 

The obvious next step was oxidation of the tris(pyrazolyl)borate chromium alkyls to the catalytically active -t-III oxidation state. However, cyclic voltammetry experiments did not show a reversible oxidation in any case, and all attempts to prepare complexes of the type [Tp Bu,Meci-R]+X by chemical oxidation failed, yielding [Tp Cr(THF)n] X instekl. TTie reasons for the apparent instability of TpCr alkyls are not clear, and we arc continuing our efforts to isolate related compounds,... 

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