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An increasing number of biological roles are ascribed to S-nitrosothiol compounds. Their inherent instability in multicomponent solutions is recognized as forming the basis for their physiological effects, such as the release of nitric oxide or the posttranslational modification of protein cysteine residues. This reactivity also contributes to the lack of fundamental physical and spectroscopic data that have been reported. We have addressed this issue through characterization of the physical and spectroscopic properties of a group of commonly used S-nitrosothiols. The S-nitrosothiol Ph3CSNO, which is readily prepared by the biphasic nitrosation of Ph3CSH, is characterized by X-ray diffraction, vibrational spectroscopy, electrochemistry, and spectroelectrochemistry. Its behavior is contrasted with that of known S-nitrosothiols derived from glutathione and N-acetyl-d,l-penicillamine, which also are demonstrated to undergo facile electrochemical and chemical denitrosylation. The structure and vibrational data are contrasted with ab initio results calculated with density functional theory, B3LYP/6-311+G*, which indicates that electron transfer populates an orbital that is strongly ON−SR antibonding in character. The bond lengths observed for Ph3CSNO (N−O 1.18 Å, S−N 1.79 Å) indicate a formal nitrogen-to-oxygen double bond and sulfur−oxygen single bond. However, theoretical calculations show a measure of delocalization over the −CSNO framework. This is supported by experimental results that show low ν(NO) vibrational frequencies (1470−1515 cm-1) and a large ΔG ⧧ (10.7 kcal/mol) for syn−anti interconversion determined by variable-temperature 15N NMR. Together these results demonstrate an important new reactivity pattern for this biologically critical class of compounds.

Chelating Lewis acids have not been developed to the same degree as multidentate Lewis bases. Nonetheless, such compounds have attracted interest due to their potential for the enhanced activation of basic substrates and the selective binding of anions. Organodiboryl compounds form a class of bidentate Lewis acids which have a long, but relatively underdeveloped history. Many examples exist where donor groups on boron serve to stabilize the Lewis acid centers. More recently, advances in the chemistry of diboryls with highly Lewis acidic boron centers substituted with perfluoroaryl groups have been made. In particular, compounds of general formula (F5C6)2B−linker−B(C6F5)2 have been prepared and their chemistry examined. In this Microreview, we survey the classes of bifunctional boron Lewis acids known, including their synthesis, properties and anion binding chemistry. Particular emphasis is placed on the role these Lewis acids play in olefin polymerization catalyst generation from simple metallocene precursors.

The five-coordinate ruthenium boryl complexes, Ru(BR2)Cl(CE)(PPh3)2 (E = O, BR2 = BO2C6H4 (1a); E = O, BR2 = BO2C10H6 (1b); E = O, BR2= B(NH)2C6H4 (1d); E = O, BR2 = B(NH)SC6H4 (1e); E = S, BR2 = BO2C6H4 (2a); E = S, BR2 = B(NH)SC6H4 (2e); E = N-p-tolyl, BR2 = BO2C6H4 (3a)), result from the reactions of RuHCl(CE)(PPh3)3 with the appropriate borane. Related osmium compounds, Os(BR2)Cl(CE)(PPh3)2 (E = O, BR2 = BO2C6H4 (4a); E = O, BR2 = BO2C6H3CH3 (4c); E = O, BR2 = B(NH)2C6H4 (4d); E = O, BR2 = B(NH)SC6H4 (4e); E = S, BR2 = BO2C6H4 (5a)), cannot be prepared from the hydrides but are formed from reactions between Os(Ph)Cl(CE)(PPh3)2 and the appropriate borane. A boryl complex of ruthenium of formula Ru(BO2C6H4)Cl(PPh3)2·H2O (6) results from reaction of RuHCl(PPh3)3 with HBO2C6H4 (catecholborane). IR, 1H NMR, and 13C NMR data for the new boryl complexes are reported.

The reactions of chelating diboranes with PhCMe2Cl and related initiators were studied by variable-temperature NMR spectroscopy. Although thermally stable ion-pairs featuring weakly coodinating anions (WCA) are formed, isobutene polymerization is complicated by the tendency of these WCA to act as hindered bases toward Brønsted acidic chain ends.

Ethyne inserts readily into the Ru−B bond of the five-coordinate boryl complex Ru(BO2C6H4)Cl(CO)(PPh3)2 (1) to form the borylalkenyl (2). Complex 2 has been characterized by IR and multinuclear NMR spectroscopy and by an X-ray crystal structure determination. In the solid state, the Ru atom in 2 is six coordinate through weak attachment of a catechol oxygen to ruthenium. Two further (4), which result from transesterification of 2 with HOCH2CH2OH and 3 with CH3CH2OH, respectively, are also described. The relevance of the observed ethyne insertion for metal-catalyzed hydroboration is discussed.

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Die Verdrängung beider Chlorsubstituenten des Dichlorborylliganden von 1 durch Umsetzung mit 8‐Aminochinolin liefert den intern basenstabilisierten terminalen Borylenkomplex 2. Durch den Angriff von Ethanol am elektrophilen Borzentrum in diesem Komplex entsteht der Ethoxyborylkomplex [█Os{B(OEt)NHC9H6█N}Cl(CO)(PPh3)2] mit vom Chinolin‐N‐Atom koordiniertem Os‐Zentrum.