Tris hydroborato derivatives

VI. Anion Coordination by Protonated Tris(pyrazolyl)hydroborato Derivatives... 

The complexes [Tp ]MgR may be considered to be modifications of Grignard reagents. As such, these complexes may be expected to be subject to the facile ligand redistribution reactions of the Schlenk equilibrium. Indeed, although solutions of the tris(3,5-dimethylpyrazolyl)hydroborato derivatives [Tp ]MgR are stable at room temperature, heating to 80-120°C does result in ligand redistribution and the formation of the six-coordinate sandwich complex [Tp ]2Mg [Eq. (4), 21,22]... 

Bis and tris(pyrazolyl)hydroborato ligands are generally prepared as the potassium derivatives by the direct reaction of KBH4 with the appropriate pyrazole (RR pzH), as illustrated in Scheme 1 for the parent system (13). The reaction is extremely general and has been applied to a number of different derivatives, which have included the incorporation of chiral (14, 15) and tethered (16) substituents. However, if the alkyl substituents of the pyrazole are inequivalent (i.e., R + R ), a potential problem may be encountered with the formation of isomeric products, in which either of the R and R substituents may occupy the 3-position of the poly(pyrazolyl)borato ligand. Nevertheless, if the difference in steric demands of R and R is large, there is a strong... 

In contrast to the chemistry of the zinc complexes [TpRR]ZnR, the cadmium alkyl derivatives have not been used to prepare an extensive series of half-sandwich [TpRR]CdX complexes. However, several [Tp JCdX complexes supported by sterically demanding tris(pyrazolyl)hydroborato ligands, e.g., [TpBut]CdCl (98), [TpBut]CdI (91), [Tp lCdl (91), and [TpBut,Me]Cd(Tj2-02N0) (91), have been synthesized by metathesis between CdX2 and either K[TpRR ] or Tl[TpRR ] [Eq. (15)]. 

Finally, the tris(pyrazolyl)hydroborato ligand system has also provided an interesting example in which a crystallographic site is disordered between a vacancy and a chain of three atoms. Thus, the x-ray structure of the cobalt complex [TpAnt]CoNCS (Ant = 9-anthryl) revealed the presence of the cocrystallized thallium derivative... 

An S4 coordination sphere of the type seen in the Ada protein, where four cysteines coordinate, was achieved with the tridentate tris(2-mercapto-l-phenylimidazolyl)hydroborato ligand. The zinc thiophenolate derivative showed reactivity of the thiolate linkage (Figure 8).506... 

Recently, a series of bis- and tris(mercaptoimidazolyl)borate ligands [Bm and ffm ] , as well as tris(mercaptothiazolyl)borate [Tz], tris(mercaptobenzothiazolyl)borate [Tbz], and bis(mer-captoimidazolyl)(pyrazolyl)hydroborato [PzBm ], ligands and their thallium(I) derivatives have been synthesized and characterized. " The bis(mercaptoimidazolyl)(pyrazolyl)hydroborato represents a hybrid [S2N] system. 

II. SYNTHESES AND STRUCTURES OF MONOMERIC FOUR-COORDINATE TRIS(PYRAZOLYL)HYDROBORATO MAGNESIUM ALKYL DERIVATIVES... 

Tris(pyrazolyl)hydroborato ligands [HB(3,5-RR pz)3] (RR pz = C3N2RR H), which were introduced by Trofimenko in 1966 [10], are readily obtained as the potassium derivatives by the direct reaction of KBH4 with the appropriate pyrazole RR pzH [Eq. (2) 9],... 

Tris(pyrazolyl)hydroborato magnesium alkyl derivatives [Tp ]MgR are readily prepared by the reactions of [M][Tp ] (M = K, Tl) with solutions of the appropriate dialkyl-magnesium [Eq. (3) 14-17]. The reaction is very general and a series of primary, secondary tertiary, vinyl, and phenyl derivatives have been obtained, as illustrated in Table 1. The magnesium alkyl complexes [Tp ]MgR are all white crystalline solids that are soluble... 

The molecular structures of several [Tp ]MgR derivatives have been determined by single-crystal X-ray diffraction, which confirms that in each case the molecules are solvent-free monomers, and that the tris(pyrazolyl)hydroborato ligand is -coordinated to magnesium. The coordination environment about the magnesium may be described as... 

II. SyiithcjkO and Structures of Monomeric Four-Coordinate Tris(pyrazolyl)hydroborato Magnesium Alkyl Derivatives... 

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