Verbindungen mit planar‐tetrakoordinierten Boratomen: Anti‐van't‐Hoff/Le‐Bel‐Geometrie ohne Metallzentren

Abstract

7] a) Programm DMol V2.3 der Biosym Technologies Inc. Es wurden doppelte numerische Basissdtze rnit Pobarisationsfunktionen verwendet ; die inneren Orbitale wurden nicht explizit berucksichtigt (frozen core). Die Vosko-Wilk-Nusdir-Korrelationsfunktion [7 b] und die Becke-Austauschfunktion [7c] rnit nichtlokalen Korrekturen wurden eingesetzt. Rechnungen fur die Anionen mit einer gerdden Zahl von negativen Ladungen wurden ,,spin restricted", d. h. rnit gleichen Orbitalen fur Elektronen rnit a-und [&Spin, durchgefuhrt; die Struktur wurde ohne Geometriebeschrankung optimiert. Die elektronischen Strukturen und Details zu den Geometrien werden in einer ausfuhrlichen Originalmitteilung veroffentlicht werden. b) S. [9] Partialladungen der Atome fur [M,,(CN),J: Zn + 0.59. Cd + 0.69; C,,,, -0.21 (Zn), -0.24 (Cd); N,.,, -0.14 (Zn), -0.15 (Cd); CB,, -0.18 (Zn), -0.21 (Cd); N,, -0.10 (Zn), -0.11 (Cd); Dielektrizitatskonstante = r ; quadratische Winkelkonstanten (kJ rad-* mol-') C-M-C 125, C-M-N 125, M-C-N 209, M-N-C 209; Parameter der Potentialmulde fur nichtbindende Wechselwirkungen r* [A]. E* [kJmol-'] 2.03,0.63 (C); 1.96,0.71 (N); 1.90.0.62 (Zn); 2.30, 0.96 (Cd); Berechnungen rnit Discover V2.9

1,2‐Diboracyclopentanes without Strong Donor Substituents: Synthesis, Reactions, and Computational Analysis

“…[12] The 11 B NMR chemical shift of 7a (δ = 23 ppm) corresponds to δ = 21.8 ppm described for closely related 1,2-trimethylenediborane (6). [13] Only one 11 B NMR signal at δ = 21 ppm is observed for both boron centers of 8b·Li(Et 2 O) in n-pentane or [D 6 ]benzene. This indicates a fast exchange of the hydride between the tricoordinate and tetracoordinate sites in solution [8a·Li(Et 2 O) n in diethyl ether: 3 ppm, both boron centers tetracoordinate].…”

“…Thus, the signal at δ( 11 B) = 29 ppm for 5a is identical to that of a known nonclassical diborirane derivative containing a dimethylphenylsilyl and a bis(trimethylsilyl)methyl substituent instead of the trimethylsilyl and one duryl substituent, respectively, in 5a. [11] Notably, the proton of the BHB bridge of aromatic diborirane 5a . The NMR spectra of borylmethyleneborane 6a are strongly dependent on temperature.…”

A Diboracyclopropane with a Planar‐Tetracoordinate Carbon Atom and a Triborabicyclobutane

“…However, the correlation between metal configurations and the bridge type also requires consideration, especially when using alternatives to the often studied d 5 /d 6 combination, [1,3] familiar from prototypes, such as the Creutz±Taube ion [3a] [(H 3 N) 5 Ru-(m-pz)Ru(NH 3 ) 5 ] 5+ (pz = pyrazine) or partially oxidized biferrocenyl species. [4] Herein we describe the extraordinarily varied results for two different mixed-valent configurations that are accessible by single-electron transfer from the structurally characterized diruthenium(iii) complex 1. [5] The distinguishing feature of the ligand bridge is an unsaturated, cumulene-like, C 4 spacer which, in contrast to other C 4 -bridged dinuclear systems, [6] interacts with the metals through conventional Werner-type coordination, namely through b-diketonato chelate ligation.…”

“…[9] Tetrahedra of CB 3 anions are, like those of the isoelectronic B 4 dianions, distorted. [10] There are three forms for distorted tetrahedra of the type 6 a: two enantiomers with short CÀBDur edges (the transition state between 3 b and 3 a), and one with a short CÀBCH 2 R edge (the transition state of the degenerate rearrangement of 3 a).…”

“…Derivatives of the lower energy isomer 2 u with planar-tetracoordinate boron atoms [4] 16.9 kcal mol À1 . [4] For the dianion of B 4 Me 4 [10] the distorted tetrahedral form according to our computations lies only 4.9 kcal mol À1 above the folded two-electron aromtic compound; its planarization requires 7.3 kcal mol À1 . Thus, an increasing number of boron atoms in four-membered twoelectron aromatic compounds facilitates the planarization as well as the fluctuation of the skeletal bonds.…”