Relevance of the Electronegativity of Boron in η⁵‐Coordinating Ligands: Regioselective Monoalkylation and Monoarylation in Cobaltabisdicarbollide [3,3′‐Co(1,2‐C₂B₉H₁₁)₂]⁻ Clusters

Abstract

Regioselective monoalkylation and monoarylation in cobaltabisdicarbollide clusters has been achieved starting from Cs[8-I-3,3'-Co(1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))] by cross-coupling reactions between a B-I fragment and an appropriate Grignard reagent in the presence of a Pd catalyst and CuI. A considerable number of monoalkylated and monoarylated derivatives have been synthesized, which allowed study of the influence of boron in metallocene-type ligands and the effect of alkyl and aryl substituents on boron in boron anionic clusters. Experimental data from UV/Vis spectroscopy, E(1/2) measurements, and X-ray diffraction analysis, and supported by EHMO and ab initio analyses, indicate that the participation of metal d orbitals in the HOMO is less than that in typical metallocene complexes. This can be explained in terms of the lower electronegativity of boron compared to carbon. Related to this is the -I character of alkyl groups when bonded to boron in boron anionic clusters, contrary to the common belief that alkyl groups are generally electron-releasing moieties.

Relaxed but Highly Compact Diansa Metallacyclophanes

“…No P contribution to the HOMO occurs in [8] -. Of notice is the difference in E LUMO -E HOMO ) for monoansa [3] -and [4] -that is 0.19 eV and the diansa [7] -and [8] that is 0.03 eV as can be deduced in Table 10. The smaller E LUMO -E HOMO ) for [7] and [8] -has to be related to the synergistic effect of both ansa fragments discussed throughout the paper.…”

“…As expected for the oxidized phosphine, in [4] -the phosphorus does not contribute to the HOMO orbital, mostly constituted by a d orbital on cobalt. For diansa metallacyclophanes [7] -and [8] -, the largest fragment contribution to the HOMO is due to the benzene bridging moiety; the lone pair in [7] -also contributes to the HOMO but its participation is much less than in [3] -. No P contribution to the HOMO occurs in [8] -.…”

“…For diansa metallacyclophanes [7] -and [8] -, the largest fragment contribution to the HOMO is due to the benzene bridging moiety; the lone pair in [7] -also contributes to the HOMO but its participation is much less than in [3] -. No P contribution to the HOMO occurs in [8] -. Of notice is the difference in E LUMO -E HOMO ) for monoansa [3] -and [4] -that is 0.19 eV and the diansa [7] -and [8] that is 0.03 eV as can be deduced in Table 10.…”

Studies of Multicenter and Intermolecular Dihydrogen B–H···H–C Bonding in [4,8,8′‐exo‐{PPh3Cu}‐4,8,8′‐(μ‐H)3‐commo‐3,3′‐Co(1,2‐C2B9H9)(1′,2′‐C2B9H10)]

“…[21][22][23][24][25] Experimental data relating to electron density (ED) distribution are limited, to the best of our knowledge, to a metallacarborane of nontransition metals: {Na(thf) 2 [9-SMe 2 -7,8-C 2 B 9 H 10 ]} 2 . [26] QTAIM [27] is a powerful method with which to study various types of chemical bonding.…”

Chiral separability of hydrophobic boron cluster anions with native cyclodextrins in water–methanol background electrolytes

“…This review summarises the pieces of knowledge from eight original papers [16][17][18][19][20][21][22][23] devoted to chiral LC separations of zwitterionic boron cluster compounds with chemically bonded CDs. Three articles are focused on the isotachophoretic separations of several boron cluster anions [24][25][26] and four articles [27][28][29][30] briefly discuss the UV-Vis spectra of a few boron cluster compounds.…”