Tetra­aceto­nitrile­lithium tetra­iso­thio­cyanato­borate

The crystal structure of the title salt, [Li(CH3CN)4][B(NCS)4], is composed of discrete cations and anions. Both the Li and B atoms show a tetra­hedral coordination by four equal ligands. The aceto­nitrile and iso­thio­cyanate ligands are linear. The bond angles at the B atom are close to the ideal tetra­hedral value [108.92 (18)–109.94 (16)°], but the bond angles at the Li atom show larger deviations [106.15 (17)–113.70 (17)°]

A triclinic polymorph of bis­(μ-di-tert-butyl­phosphanido)bis­[(di-tert-butyl­phosphane)palladium(I)]

A new polymorph of the title compound, [Pd2(C8H18P)2(C8H19P)2], has been found. It belongs to the triclinic P-1 space group, whereas the known form [Leoni, Sommovigo, Pasquali, Sabatino & Braga (1992 ▶), J. Organo­met. Chem. 423, 263–270] crystallizes in the monoclinic C2/c space group. The title compound features a dinuclear palladium complex with a planar central Pd2(μ-P)2 core (r.m.s. deviation = 0.003 Å). The Pd—Pd distance of 2.5988 (5) Å is within the range of a PdI—PdI bond. The mol­ecules of both polymorphs are located on a crystallographic centre of inversion. The mol­ecular conformations of the two polymorphs are essentially identical. The crystal packing patterns, on the other hand, are slightly different

Reactivity of Phosphaboradibenzofulvene toward Hydrogen, Acetonitrile, Benzophenone, and 2,3-Dimethylbutadiene

The reaction of 9-bromo-9-borafluorene (<b>1</b>) with Li­[P<i>t</i>Bu₂] in toluene gave quantitatively the corresponding di-<i>tert</i>-butyl-phosphaboradibenzofulvene (9-di-<i>tert</i>-butylphosphanyl-9-borafluorene, <b>2</b>). Degradation of thf occurred by treatment of <b>2</b> with thf in toluene at room temperature. In this paper the reaction of <b>2</b> with gaseous H₂ in toluene solution at room temperature is described, by which the corresponding H₂ addition product <b>4</b> was formed. The hydrogen addition product <b>4</b> crystallizes from benzene in the monoclinic space group <i>P</i>2₁/<i>n</i>. Addition reactions of <b>2</b> with acetonitrile, benzophenone, and 2,3-dimethylbutadiene were also investigated. Treatment of <b>2</b> with a 20-fold excess of acetonitrile afforded the corresponding adduct, which itself dimerized to a mixture of <i>cis</i> and <i>trans</i> isomers of the corresponding cycloiminoborane <b>6</b>. Cocrystals of <i>cis</i>-<b>6</b> and <i>trans</i>-<b>6</b> (ratio 2:1) were obtained from toluene in the presence of 20 equiv of acetonitrile at 6 °C (monoclinic space group <i>P</i>2₁/<i>c</i>). The isolation of the pure <i>trans</i>-<b>6</b> was achieved from toluene in the presence of 2 equiv of acetonitrile at −30 °C (triclinic space group <i>P</i>1̅). Benzophenone reacted with the phosphaboradibenzofulvene <b>2</b>, forming the corresponding addition product <b>7</b> (orthorhombic space group <i>Pbca</i>). The reaction of <b>2</b> with a 6-fold excess of 2,3-dimethylbutadiene gave the related Diels–Alder adduct <b>8</b> (monoclinic space group <i>P</i>2₁/<i>c</i>)

Synthesis and Reactivity of <i>o</i>‑Phosphane Oxide Substituted Aryl(hydro)borates and Aryl(hydro)boranes

The reaction of 1,2-C₆H₄(P­(O)-<i>t</i>-Bu₂)­(Li) (Ph*Li) with B­(OMe)₃ furnishes a mixture of Li­[Ph*B­(OMe)₃] (Li­[<b>2a</b>]) and Ph*B­(OMe)₂ (<b>2b</b>). Further treatment with Li­[AlH₄] provides the trihydroborate Li­[Ph*BH₃] (Li­[<b>3</b>]), which can subsequently be converted into the intramolecular PO–B adduct Ph*BH₂ (<b>4</b>) through hydride abstraction with Me₃SiCl. Addition of C₆F₅MgBr yields Mg­[Ph*BH₂(C₆F₅)]₂ (Mg­[<b>5</b>]₂), which is inert toward Me₃SiCl but reacts with water to give Ph*B­(H)­C₆F₅ (<b>6</b>). Upon addition of further C₆F₅MgBr, a mixture is formed, from which crystals of Mg­[Ph*BH­(C₆F₅)₂]₂ (Mg­[<b>7</b>]₂) were obtained. The reaction of Ph*Li with (C₆F₅)₂BH·SMe₂ provides access to Li­[<b>7</b>], but again with limited product selectivity. The targeted acidic hydrolysis of Li­[<b>7</b>] furnishes Ph*B­(C₆F₅)₂ (<b>8</b>), while Mg­[<b>7</b>]₂ reacts back to <b>6</b>. The anions of the hydroborates Li­[<b>3</b>] and Mg­[<b>5</b>]₂ act as BH₂,O-chelating ligands toward their metal ions. Therefore, Li­[Ph*₂BH₂] (Li­[<b>13</b>]) was also synthesized to obtain the corresponding pincer-type species. <b>4</b>, <b>6</b>, and <b>8</b> exist as water-stable intramolecular PO–B adducts both in solution and in the solid state. X-ray crystallography and ³¹P NMR spectroscopy indicate an increase in the Lewis acidity of the boryl groups in the order <b>4</b> < <b>6</b> < <b>8</b>

Reactivity of Phosphaboradibenzofulvene toward Hydrogen, Acetonitrile, Benzophenone, and 2,3-Dimethylbutadiene

The reaction of 9-bromo-9-borafluorene (<b>1</b>) with Li­[P<i>t</i>Bu₂] in toluene gave quantitatively the corresponding di-<i>tert</i>-butyl-phosphaboradibenzofulvene (9-di-<i>tert</i>-butylphosphanyl-9-borafluorene, <b>2</b>). Degradation of thf occurred by treatment of <b>2</b> with thf in toluene at room temperature. In this paper the reaction of <b>2</b> with gaseous H₂ in toluene solution at room temperature is described, by which the corresponding H₂ addition product <b>4</b> was formed. The hydrogen addition product <b>4</b> crystallizes from benzene in the monoclinic space group <i>P</i>2₁/<i>n</i>. Addition reactions of <b>2</b> with acetonitrile, benzophenone, and 2,3-dimethylbutadiene were also investigated. Treatment of <b>2</b> with a 20-fold excess of acetonitrile afforded the corresponding adduct, which itself dimerized to a mixture of <i>cis</i> and <i>trans</i> isomers of the corresponding cycloiminoborane <b>6</b>. Cocrystals of <i>cis</i>-<b>6</b> and <i>trans</i>-<b>6</b> (ratio 2:1) were obtained from toluene in the presence of 20 equiv of acetonitrile at 6 °C (monoclinic space group <i>P</i>2₁/<i>c</i>). The isolation of the pure <i>trans</i>-<b>6</b> was achieved from toluene in the presence of 2 equiv of acetonitrile at −30 °C (triclinic space group <i>P</i>1̅). Benzophenone reacted with the phosphaboradibenzofulvene <b>2</b>, forming the corresponding addition product <b>7</b> (orthorhombic space group <i>Pbca</i>). The reaction of <b>2</b> with a 6-fold excess of 2,3-dimethylbutadiene gave the related Diels–Alder adduct <b>8</b> (monoclinic space group <i>P</i>2₁/<i>c</i>)

Electronic communication in oligonuclear ferrocene complexes with anionic four-coordinate boron bridges

The di- and trinuclear ferrocene species Li[Fc-BPh2-Fc] (Li[9]) and Li2[Fc-BPh2-fc-BPh2-Fc] (Li2[10]) have been investigated with regard to their electrochemical properties and the degree of intervalence charge-transfer after partial oxidation. Li[9] shows two distinct one-electron redox waves for its chemically equivalent ferrocenyl substituents in the cyclic voltammogram (E1/2 = −0.38 V, −0.64 V; vs. FcH/FcH+). The corresponding values of Li2[10] are E1/2 = −0.45 V (two-electron process) and −1.18 V. All these redox events are reversible at r. t. on the time scale of cyclic voltammetry. X-ray crystallography on the mixed-valent FeII2FeIII complex Li(12-c-4)2[10] reveals the centroid–centroid distance between the cyclopentadienyl rings of each of the terminal ferrocenyl substituents (3.329 Å) to be significantly smaller than in the central 1,1′-ferrocenediyl fragment (3.420 Å). This points towards a charge-localized structure (on the time scale of X-ray crystallography) with the central iron atom being in the FeIII state. Mößbauer spectroscopic measurements on Li(12-c-4)2[10] lend further support to this interpretation. Spectroelectrochemical measurements on Li[9] and Li2[10] in the wavelength range between 300–2800 nm do not show bands interpretable as intervalence charge-transfer absorptions for the mixed-valent states. All data accumulated so far lead to the conclusion that electronic interaction between the individual Fe atoms in Li[9] and Li2[10] occurs via a through-space pathway and/or is electrostatic in nature