Azolyl Bonding

CHAPTER 4 COVALENT (x-TVPE) LIGANDS BOUND THROUGH METAL-HETEROATOM BONDS 

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Cp deriva ti ves.163 In the sold state, the two Tp ligands of 510 bind in an asymmetric k3 fashion, such that two pyrazolyl donors are strongly bound (d(Pd—N) 2.16 A), while the third interacts weakly (d(Pd—N) 2.64 A). This was interpreted as a formal 5-coordinate geometry correlating with the presumed intermediate responsible for equilibration of all pyr-azolyl groups in the solution phase. The metal metal bond of 510 was considered to be weak, on the basis of full occupancy of the a and n orbitals of the Pd2(CNXyl)2 core. 

In their initial attempts to prepare classical chelate complexes containing TmMe, Hill and co-workers155 have encountered an unprecedented class of reaction for tris(azolyl)borate, namely the intramolecular activation of the bridgehead B—H bond which provides the first example of a metallaboratrane. The reaction of TmMe with [Ru(R)ClCOPPh3] (CH=CHCPh2OH) likely yield... 

Homolytic cleavage of the /V-halogen bond to form the azolyl and the halogen radicals. This pathway may take place in radical halogenation and the addition to a multiple bond, initiated by UV irradiation, or by means of radical initiators.This route may be found in some oxidative reactions (Scheme 24). 

Heterocyclic Bond Distances (A), Angles (°), and Secondary Contacts (A) for Multi- 1,2,3, 5-dithi adi azolyls... 

Claramunt et al. dedicated several publications to the study of the structure of polyazolyl-benzenes (propellenes) (97M12). These compounds present several N-C bonds between five (azoles) and six-membered rings (benzenes). Besides the dihedral angles the position (up or down) of the azolyl residues are characteristic of these compounds hexa(3,5-dimethyl-pyrazol-l-yl)benzene (16, R = 3,5-dimethyl) (95JCS(P2)1359), hexakis(pyr-azol-l-yl)benzene (16, R = H) (96JPOC137, 02EJ1C3178), 1,2,4,5-tetrakis (pyrazol-l -yl)-3,6-bis(3",5"-dimethylpyrazol-l -yl)benzene (16, R = H... 

Atropisomerism was demonstrated in 379. It arose from aryl-C=0 and amide rotations. The rotation about the N-p5u-azolyl-aryl bond was not blocked (09BMCL1767). 

Anion displacement of halides with azolyl anions is one common route to azolyl complexes. One example of such a synthesis is shown in Equation 4.21. In other cases, azolyl complexes have been prepared by proton transfer between the free azole and a metal alkox-ide or hydroxide. An example involving the synthesis of palladium-azolyl complexes is shown in Equation 4.22. In some rare cases, reactions of pyrrole and d early metal alkyls also lead to the formation of a metal-nitrogen bond via o-bond metathesis, as shown in Equation 4.23. Finally, several late-transition-metal-azolyl complexes possessing accompanying hydride Hgands have been prepared by N-H activation of pyrrole and other azoles. 

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