Trispyrazolylborate ligands

Former studies of Moro-oka et al. with model complexes of the trispyrazolylborate ligands and have already shown,... 

Complexes of molybdenum form the largest set of any of the transition metals. Many of these compounds display spectroscopic properties, isomerism and structural features that illustrate the coordination chemistry of polypyrazolylborate complexes. In addition, this system illustrates that trispyrazolylborate ligands are more bulky than their formal analogue C5H5. 

OAT reactions interconvert dioxo-Mo(VI) and oxo-Mo(IV) complexes of tridentate trispyrazolylborate ligands such as L-Ng. Depending upon the co-ligands and reaction conditions, particularly solvent, a number of events follow OAT from (L-N3)Mo02X (X = Cl, Br, NCS, OPh, SPh) to PPhg (Scheme 4) these events dictate the final product of the reaction (127,128). In dry noncoordinating solvents such as toluene, the initially... 

Studies of the electron transfer reactions of oxomolybdenum complexes of trispyrazolylborate ligands with Fe(III) porphyrins show that the reduction of (TPP)Fe Cl by (L-NglMo OCUdmf) (Eq. (26)) proceeds cleanly and quantitatively in dmf and is first order in Mo and zero order in Fe (261). 

A trispyrazolylborate ligand ([HB(C3N2H3)3], hydridotris (pyrazoyl)borate) a highly sterically bulky ligand used to protect metals from attack by other ligands... 

Modern Applications of Trispyrazolylborate Ligands in Coinage Metal Catalysis... 

Copper and silver complexes bearing trispyrazolylborate ligands have shown catalytic activity towards several organic transformations involving the functionalization of unsaturated carbon-carbon bonds or several saturated E—H bonds, particularly of carbon-hydrogen bonds. The tunability of this class of ligands from both steric and electronic perspectives allows the control of those catalytic capabilities. On the basis of the work already described, the potential for their use on other, yet unreported transformations seems feasible. 

Dirhodium tetracetate or copper complexed by trispyrazolylborate ligands bring about the carbenoid addition of iCHCOaEt from ethyl diazoacetate to furans. Generally, mixtures of cyclopropane and ring opened dienones/als are produced. 

Many model studies have focused on methaemerythrin, i.e. the oxidized Fe(III)-Fe(III) form of haemerythrin which contains an 0x0 (rather than hydroxy) bridge. Methaemerythrin does not bind O2, but does interact with ligands such as [N3] and [SCN]. Reaction 28.8 makes use of the trispyrazolylborate ligand, [HBpz3] , to model three His residues the product (28.14) contains antiferro-magnetically coupled Fe(III) centres. 

There is just one example of a nonsubstituted pyridyHdene complex obtained as a 1 1 mixture together with the N-adduct (Scheme 27). This outstanding transformation was mediated by an iridium complex featuring two Ir-CH2 bonds that resulted from the metaUation of two methyl groups of mesityl substituents of the trispyrazolylborate ligand (Tp = hydrotris(5-mesitylpyrazolyl)borate). The presence of an Ir-CH2 bond within a chelate is essential for the tautomerization process. 

After the initial writing of this chapter, some results were published. Ethene and carbon monoxide adducts of copper(I) with novel trispyrazolylborate Hgands ([HB(3-CF3-5- 4-RPh pz)3] R = N02, CF3, Cl, F, H, OMe, NMc2) in a pseudotetrahedral coordination environment consisting of three N atoms of the trispyrazolylborate ligand and the carbonyl or r -coordinated ethene ligands were found. The first scorpionate ligand... 

The celebration of the Golden Jubilee of trispyrazolylborate ligands, first reported by Jerry Trofimenko in 1966, has reached our Serial thanks to Pettinari, which has taken over Trofimenko s task to disseminate the importance of these ligands in organometallic chemistry. A review of their role in organometallic and homogeneous catalysis in the last few years is presented in Chapter 4. 

The coordination of tris(pyrazolyl)amine and bis(pyrazolyl)amine ligands toward [Rh(/r-Cl)(cod)]2 was studied and the crystal structure of the trimetallic compound Rh3Cl3(cod)3(tdma) was reported. Trispyrazolylborate ligands also provided a series of complexes of the type TpRh(LL) (LL = nbd or cod), whose NMR spectroscopic properties and structural features were studied. The fluxional behavior of complexes of formula Tp Rh(LL) (LL = nbd, 2CO, cod R = H, Me, Ph, Br) was studied by means of NMR spectroscopy. Two K -square-planar isomers and one re -pentacoordinated complex were observed. The structure of the complex K -Tp Rh(nbd) was confirmed by X-ray diffraction. The hapticity of the Tp ligand was also studied on the basis of the i B-H) obtained by IR spectroscopy. Reactions of [Rh(/r-Cl)(nbd)]2 with a series of bis- and tris(azolyl) methanes 388, 389, 390, 391, and 392 were also reported. ... 

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