Synthesis, Coordination Behavior, and Reduction Chemistry of Cymantrenyl‐1,3‐bis(2,3,4,5‐tetraphenyl)borole

Abstract

We describe the synthesis of base-free bisborole [Cym(†)(BC(4)Ph(4))(2)]-Cym(†)=(OC)(3)Mn(η(5)-C(5)H(3))-and its transformation into two fully characterized Lewis acid-base adducts with pyridine bases of the type 4-R-NC(5)H(4) (R=tBu, NMe(2)). The results of electrochemical, as well as NMR and UV/Vis spectroscopic studies on [Cym(†)(BC(4 Ph(4))(2)] and the related monoborole derivative [Cym(BC(4)Ph(4))]-Cym=(OC)(3)Mn(η(5)-C(5) H(4))-provided conclusive evidence for 1) the enhanced Lewis acidity of the two boron centers that result from conjugation of two borole fragments, and 2) the fact that Mn-B bonding interactions between the Lewis acidic borole moieties and the Mn center are considerably less pronounced for bisborole [Cym(†)(BC(4)Ph(4))(2)]. In addition, the reduction chemistry of [Cym(†)(BC(4)Ph(4))(2)] has been studied in detail, both electrochemically and chemically. Accordingly, chemical reduction of [Cym(†)(BC(4)Ph(4))(2)] with magnesium anthracene afforded the corresponding tetraanion, which features a rare Mg-OC bonding mode in the solid state.

Tris(3,5‐dimethylpyrazolyl)methane‐Based Heterobimetallic Complexes that Contain Zn and CdTransition‐Metal Bonds: Synthesis, Structures, and Quantum Chemical Calculations

“…[24] In good agreement with the IR spectroscopic data, the atomic distances of the CÀ O bonds in the isocarbonyl bridges (average bond length = 120.8 (3 a) and 119.6 pm (3 b)) are approximately 3 pm longer than in the terminal CO ligands (average bond length 116.9 (3 a) and 117.1 pm (3 b)).…”

“…[10,22] [10] [MgBr(thf) 4 {6-[(Me 6 B 3 N 3 )Cr(CO) 3 }] (ñ = 1763, 1694 cm À1 ; KBr), [23] and [Mg(thf) 2 {m-Cym*(BC 4 Ph 4 ) 2 }Mg(thf) 3 ] (ñ = 1774 cm À1 ; ATR, Cym* = {(OC) 3 Mn(h 5 -C 5 H 3 )}). [24] To confirm these assignments, the structures of 3 a/b* were optimised and the corresponding IR vibrations calculated by using DFT methods (RI-DFT/BP86-D3/def2-TZVPP). In good agreement with the corresponding experimental values, the asymmetric stretching vibration of the isocarbonyl unit in 3 a/b* was calculated to be ñ asym (CO iso ) = 1676 and 1669 cm À1 for 3 a* and 3 b*, respectively, whereas the corresponding symmetric vibration was predicted to appear at ñ sym (CO iso ) = 1719 and 1715 cm À1 for 3 a* and 3 b*, respectively.…”

A theoretical study of the aromaticity in neutral and anionic borole compounds

“…In addition, we have investigated corresponding NICS values for the negatively charged derivatives. As previously reported by the groups of Herberich, [52] Yamaguchi [18] and Braunschweig, [15,17,[53][54][55] the synthesis and isolation of various dianionic and a monoanionic species has been successfully achieved ( Figure 4). The addition of one electron noticeably decreases the antiaromatic character of boroles, as judged by both the NICS and multicenter indices.…”

“…[51,55,[57][58][59] Figure 7 displays all derivatives used for this study. By comparing the 1,3-and 1,4-disubstituted bis(borolyl)benzenes 10 and 11, [57] respectively, compound 11 was found to be 4.3 kcal/mol more stable than 10.…”

“…Figure 11 shows the NICS profiles for the series of cymantrene-containing mono-and bis(borole) systems. [55] As the borole units in 1,3-bis(borolyl)cymantrene 17 are not equivalent in the geometry-optimized structure, each BC4Ph4 group was treated separately. As one might expect from their different arrangement with respect to the metal fragment, the two borolyl substituents in 17 exhibit a slightly different degree of antiaromaticity.…”