Dianionic borates

Bochmann has also produced a novel class of large dianionic borates XV based on the non-labile fefra-cyano Ni and Pd(II) metallates [K12 M(CN) i 2. 215a The metals in these WCAs are strictly square planar and as such the anion assumes a flat rather than spherical shape, with a torus of fluorination on the periphery of the plane. The bis-trityl salts of these dianions afford catalysts that are not as productive as those formed from the XIV class (X = CN), although they are still much more active than borane activated catalysts. The lower activity was attributed to the inherently greater cation/anion attraction in a monocation/dianion pair. 

Cox et al. (1981) found, as expected, that the trianion of 2,3-dihydroxynaph-thalene-6-sulfonic acid has a higher reactivity than the dianion. They observed a specific catalytic effect of borate buffers, but unfortunately they did not investigate it further. 

Anions of weak acids can be problematic for detection in suppressed IEC because weak ionization results in low conductivity and poor sensitivity. Converting such acids back to the sodium salt form may overcome this limitation. Caliamanis et al. have described the use of a second micromembrane suppressor to do this, and have applied the approach to the boric acid/sodium borate system, using sodium salt solutions of EDTA.88 Varying the pH and EDTA concentration allowed optimal detection. Another approach for analysis of weak acids is indirect suppressed conductivity IEC, which chemically separates high- and low-conductance analytes. This technique has potential for detection of weak mono- and dianions as well as amino acids.89 As an alternative to conductivity detection, ultraviolet and fluorescence derivatization reagents have been explored 90 this approach offers a means of enhancing sensitivity (typically into the low femtomoles range) as well as selectivity. 

Figure 1. XANES spectra for crystallographically characterized Mn(II), Mn(III), and Mn(IV) model compounds. Long dashed lines indicate Mn(II) compounds solid lines indicate Mn(III) compounds short dashed lines indicate Mn(IV) complexes. The models chosen to illustrate this phenomenon are[Mn(ll)HB(3,5-iPr2pz) 3]2(OH) 2and(pyrazolyl) 2Mn(OCfi3) 3Mn(ll) (HB 3,5-iPr2pz)3 [where HB(3,5-iPr2pz)3 is hydrotris(3,5-diisopropyl-1-pyrazolyl borate) Mn(II)(hexakisimidazole)Cl2 Mn(III)(acac)3 Mn(III)2, [2-OH-(5-Cl-SAL)PN]2(CH3OH), [Mn(IV) (n2-0) (SALPN)]2, and [Mn(IV)-(SALPN)]2(h2-0)(h2-OH) [where SALPN is l,3-bis(salicylideneimanato) propane] [Mn(III) (SALAHP) (AcO)]2 [where SALAHP is 3-(salicylideneim-inato)-2-methyl- 1,3-dihydroxy propane] and Mn(IV) (SALADHP) 2 [where SALADHP is the dianion of 2-methy 1-2-(salicylideneamino)-1,3-dihydroxy-propane].

Chemoselective (V-ethylation of Boc-amino acids can be accomplished without racemization via the corresponding dianions. Thus, (V-t-butoxycarbonylamino acid (35) was converted into dianion (36) by treatment with 2 equiv. of Bu Li, followed by the reaction with 1 equiv. of triethyloxonium tetrafluoro-borate to give (V-ethyl derivative (37) along with a trace of ethyl ester (38). On treatment with 2.2 equiv. of the triethyloxonium salt (36 R = Ph) gave (38 R = Ph) in 95% yield (Scheme 17). ... 

W. Preetz and G. Peters (1999) European Journal of Inorganic Chemistry, p. 1831 - A review The hexahydro-c/oio-hexa-borate dianion [BgHg] and its derivatives . 

This study provides the first reasonably precise molecular dimensions of the rhodi-zonate dianion, which lends support to the aromaticity of this nonbenzenoid cyclic oxocarbon. Notably, the measured C-C bond lengths [1.421(5) — 1.458(5) A] of the rhodizonate in 21, which exhibits approximate D(,h molecular symmetry, are significantly shorter than the corresponding values (1.488 and 1.501 A) in Rb2C60e [46] and the calculated values (1.500 and 1.501 A) for the C2 structure of this dianion [47]. Compound 21 provides yet another example of the use of urea and its derivatives for stabilizing elusive molecular anions such as allophanate [5h] and dihydrogen borate [5c] in a hydrogen-bonded host lattice. 

Dianionic cyclopentadienylbis(oxazolinyl)borates 163 were prepared as diprotonated species in two steps from the appropriate oxazolines. The corresponding Ti, Zr, and FIf diamide complexes behaved as highly efficient, enantioselective catalysts for cyclization of aminoalkenes to afford five-, six-, and seven-membered AT-heterocyclic amines (13JA7235). 

The hydrolysis of both penicillins and cephalosporins are often catalysed by buffers. Catalysis by borate and phosphate buffers is usually found for the hydrolysis of some cephalosporins, but buffer catalytic effects are not always observed. Sometimes catalysis by phosphate monoanion is kinetically more important than that by the dianion (Lumbreras et al., 1982). 

The types of reactions that borane clusters undergo depend upon the class and size of the cage. The clusters [BgHg] and [Bi2Hi2l provide examples of closo-) yAro-borate dianions B5H9 and B4H10 are examples of small nido- and arac/zwo-boranes, respectively. 

In 2014, the first two examples of mono- and dianionic Janus-type dicarbenes were isolated and characterized. The group of Chiu proposed the spiroborate-linked di-benzimidazol-2-ylidene ligand 26 and its rhodium(I) complex. TEP measurements demonstrated that the electron-donating abihty of this anionic Hgand is intermediate between neutral and anionic NHC, probably because the negative charge of the borate bridge is redistributed over two carbene moieties. 

It was already pointed out in the introductory remarks that non-nucleophilic reaction conditions are one prerequisite for the synthesis of silylium ions in the condensed phase. The use of weakly coordinating anions is particularly decisive. Halogenated closo-carborate monoanions and - more recently - closo-borate dianions have found the most widespread use besides fluorinated tetraarylborates. While with bulky substituents these anions form silylium ions salts with well-separated cations and borate anions [10, 20, 22, 42], silylium ions with smaller alkyl substituents tend to coordinate directly to the anion forming zwitterionic compounds [7, 31, 32, 47]. For example, upon reaction of trimethylsUane with trityl-cZoso-carborate 86 in excess trimethylsUane the trimethylsUylium carborate 87 is formed (Scheme 27) [44]. 

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