Carbon monoxide (CO) is increasingly recognized as a cell-signalling molecule akin to nitric oxide (NO). CO has attracted particular attention as a potential therapeutic agent because of its reported anti-hypertensive, anti-inflammatory and cell-protective effects. We discuss recent progress in identifying new effector systems and elucidating the mechanisms of action of CO on, e.g., ion channels, as well as the design of novel methods to monitor CO in cellular environments. We also report on recent developments in the area of CO-releasing molecules (CORMs) and materials for controlled CO application. Novel triggers for CO release, metal carbonyls and degradation mechanisms of CORMs, are highlighted. In addition, potential formulations of CORMs for targeted CO release are discussed.

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Das aus Lithium‐dihydrogenphosphid. DME(1) und Ethylformiat im Molverhältnis 2 : 1 mit 87 proz. Ausbeute isolierte, flüssige Lithium‐formylphosphid. DME liegt als Lithoxy‐methylidenphosphan. DME (1) mit einem an den Sauerstoff der Carbonylgruppe gebundenen, DME‐komplexierten Lithium vor. Nach Röntgenstrukturanalysen an kristallinen Derivaten [5, 6] dimerisieren Verbindungen dieses Typs unter Ausbildung eines viergliedrigen LiOLiO‐Ringes; die Auswertung der NMR‐Spektren ergibt für die an der PC‐Gruppe E‐ und Z‐konfigurierten Isomeren (δ1H P: 3,87 u. 4,49; 1JHP: 150,8 u. 136,5; δ1H C: 11,4 u. 10,05; 2JHP: 6,1 u. 81,2; 3JHH: 6,6 u. 13,9; δ31P: 38,6 u. 8,8; δ13C = P: 225,0 u. 215,4 ppm; 1JCP: 41,2 u. 65,0 Hz) des in 1,2‐Dimethoxyethan gelösten Acylphosphids 1 ein Molverhältnis von 1,86 : 1. Lithium‐bis(trimethylsilyl)phosphid. 1,6 THF(1) setzt sich in 1,2‐Dimethoxyethan mit Dimethylcarbonat im Überschuß nach einem bisher nicht völlig geklärten Mechanismus zu Lithoxy‐methylidinphosphan. 2DME (2) um. Die auch aus Lithium‐dihydrogenphosphid. DME zugängliche Verbindung 2 kristallisiert monoklin in der Raumgruppe P21/n {a = 880,6(2); b = 1296,6(2); c = 1267,4(2)pm; β = 96,07(2)° bei ‐ 100 ± 3°C; Z = 4}. Nach der Röntgenstrukturanalyse (Rw = 0,052) weist der zu 155,5 pm bestimmte PC‐Abstand einen für die Dreifachbindung typischen Wert auf, während der CO‐Abstand mit 119,8 pm gegenüber dem für eine Einfachbindung gültigen Standard von 139 pm stark verkürzt ist. Mit Winkeln von 178,5° und 170,7° am Kohlenstoff‐und Sauerstoffatom ist das P COLi‐Fragment erwartungsgemäß linear. Charakteristische NMR‐Daten sind: δ31P −384,2; δ13C 166,6 ppm; 1JCP 41,5 Hz.

The reaction of bromo-2,4,6-triphenylbenzene with activated magnesium in THF yielded the Grignard reagent [(thf)(2)Mg(Br)-C(6)H(2)-2,4,6-Ph(3)] (1) with a Mg-C bond length of 214.8(3) pm. A similar reaction of bromo-2,4,6-triphenylbenzene with activated calcium led to an "inverse" sandwich complex [(thf)(3)Ca{mu-C(6)H(3)-1,3,5-Ph(3)}Ca(thf)(3)] (2) with the calcium atoms on opposite sides of the central arene ring showing small Ca-Ca' and Ca-C distances of 427.9(3) and 259.2(3) pm. This extremely air- and moisture-sensitive complex exhibits thermochomic and solvatochromic behavior. It is paramagnetic with spin of S = 1 (triplet) with an ESR resonance at g = 2.0023. Quantum chemical calculations shed light on the bonding situation in this very unusual dinuclear Ca(I) compound.

A novel and efficient calcium alkoxide initiating system, generated in situ from bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide] and an alcohol, for the ring-opening polymerization of cyclic esters has been developed. The solution polymerization in THF using mild conditions is living, yielding polyesters of controlled molecular weight and tailored macromolecular architecture. The polymerizations initiated with the 2-propanol-Ca[N(SiMe 3)2]2(THF)2 system are first-order in monomer with no induction period. At high 2-propanol/Ca[N(SiMe3)2]2(THF)2 ratios, complete conversion of 2-propanol occurs due to fast and reversible transfer between dormant and active species.

The direct synthesis of activated calcium with aryl halides in tetrahydrofuran (THF) gave the following compounds of the type RCaX in fair to good yields: [MesCaI(THF) 4 ] (1), [(p-tolyl)CaI(THF) 4 ] (2), [PhCaI(THF) 4 ] (3), and [PhCaBr(THF) 4 ] (5). All of these "heavy Grignard reagents" contain a calcium atom in a slightly distorted octahedral environment. They must be handled at low temperatures in order to avoid ether cleavage reactions. The Ca-C bond lengths vary between 2.556(5) Å (3) and 2.583(3) Å ( 5). The thermal stability is enhanced when the coordination number of calcium is increased. The calcium in the seven-coordinate complex [PhCaI(THF)(DME) 2 ] (4) has a distorted-pentagonal-bipyramidical configuration. This complex is thermally more stable and can be handled at 0 °C. The larger coordination number results in a longer Ca-C bond of 2.621(5) Å.

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Compounds of the type aryl--M--X, with M=Ca, Sr, Ba and X as any kind of ligand (such as halide, phosphanide, amide, aryl), are presented. The low reactivity of the heavy alkaline earth metals calcium, strontium, and barium enforces an activation prior to use for the direct synthesis. The insertion of these metals into C--I bonds of aryl iodides (direct synthesis) yields aryl metal iodides and has to be performed at low temperatures and in THF. Aryl alkaline-earth-metal compounds show some characteristics: 1) the ease of ether cleavage enforces low reaction temperatures, 2) for Sr and Ba the Schlenk equilibrium is shifted towards homoleptic MI2 and MPh2, 3) high solubility of diaryl alkaline-earth-metal derivatives in THF even at low temperatures initiated quantum chemical investigations on the aggregation behavior, and 4) a strong low field shift of the 13C resonances of the ipso carbon atoms in NMR spectra was observed. First results from quantum chemical calculations on diaryl dicalcium(I) suggest a long Ca--Ca bond with a considerable Ca--Ca bond dissociation energy. Initial results on a selection of applications such as metallation, metathesis, and addition reactions of aryl calcium compounds are presented as well.