Jens Langer

A key step in the formation of acrylic acid from CO2 and ethylene: the transformation of a nickelalactone into a nickel-acrylate complex

The reaction of a nickelalactone with dppm, resulting in the formation of a stable binuclear Ni(I) complex with an acrylate, a Ph2P- and a dppm bridge, models a key step in the formation of acrylic acid from CO2 and ethylene.

An Efficient General Synthesis of Halide‐Free Diarylcalcium

Contradictory reports on the synthesis and stability of arylcalcium compounds can be found in the literature, which reflects the difficulties that has hampered the broad acceptance of these heavy Grignard reagents. First reports date back to 1905, when Beckmann first published the synthesis of phenylcalcium halides. Doubts concerning these results were raised by Gilman and Schulze, who also noticed that the obtained yields were usually far from satisfactory. Whereas some research groups heat the reaction solutions to complete the turnover, other groups recommend performing the direct synthesis at low temperatures and using the formed reagents immediately. The main reasons for contradictory reports on the preparative procedures and on the stability of arylcalcium derivatives in ether solutions are rooted in the large discrepancy between the rather unreactive metal itself and the high reactivity of the organocalcium derivative, the necessity to activate the metal prior to use, and, last but not least, the tendency for the ether solvent to be cleaved during the direct synthesis of arylcalcium halides. Re-investigation of the synthesis of arylcalcium compounds led to the isolation of oxygen-centered arylcalcium cages, calcium vinylate derivatives, and after prolonged heating of phenylcalcium iodide in THF even to aryl-free [(CaO)4{(thf)3Ca(m-I)2}4]. [8] For these reasons, the direct synthesis of arylcalcium iodides from activated calcium and aryliodides has to be performed at low temperatures. A solvent-dependent equilibrium leads to the formation of calcium diiodide and diarylcalcium. A separation was, however, only successful (in a rather low yield) for [(thf)3CaMes2] (Mes = 2,4,6-trimethylphenyl), but this derivative is extremely reactive because of the rather low coordination number of the calcium and its tendency to form more stable benzyl compounds. Metathesis reactions of [(thf)4Ca(aryl)I] with potassium compounds allow exchange of the halide by phosphanides and amides. An efficient high-yielding synthesis of halide-free diarylcalcium is necessary to expedite the development of organocalcium chemistry. In principle, two routes seem to be appropriate. Transmetalation of readily accessible diarylmercury allows the preparation of diarylcalcium. However, the reactions of calcium with other arylmetal compounds often yield metalates such as [(thf)3Ca(m-Ph)3Ca(thf)3] + [Ph-CuPh] . A quantitative shift of the Schlenk equilibrium toward diarylcalcium and calcium diiodide offers another preparative method. However, the 1,4-dioxane precipitation method, which was applied successfully in organomagnesium reactions, failed for the heavier congeners. Halide-free diphenylmanganese reacts readily with activated calcium powder to give an aryl-rich heterobimetallic ion pair [(thf)3Ca(m-Ph)3Ca(thf)3] + [(thf)2PhCa(m-Ph)3MnPh] (1) according to Equation (1). A complete substitution of manganese by calcium was impossible by this procedure. The complex cation of 1 is isostructural to the cation of the aforementioned cuprate. The anion has a remarkable structure since it contains a calcium as well as a manganese atom, which are bridged by three phenyl groups. Both metal atoms also bind to another terminal phenyl substituent. The coordination spheres of the calcium atoms are saturated by THF molecules. In heterobimetallic compounds, the cation contains the more electropositive metal whereas the anion contains the less electropositive ones. Here we report one of the very rare examples of a heterodimetallic manganate anion that contains the transition metal as well as the electropositive calcium.

Organic heterobimetallic complexes of the alkaline earth metals (Ae = Ca, Sr, Ba) with tetrahedral metallate anions of three-valent metals (M = B, Al, Ga, and V)

Heterobimetallic compounds with complex cations of the very electropositive alkaline earth metals (Ae) and organic tetrahedral anions of trivalent elements (M) form solvent-separated ions. Depending on the metals, they can be prepared by addition of carbanions or amides to MR3, via reduction of VMes4 with the alkaline earth metals and by transmetallation of VMes3. For comparison reasons selected alkali metal derivatives are also included in this study. Average structural parameters of the boranates [Ca(thf)6][BPh4]2 (1) and [CaI(thf)5][BPh4] (2), the alanates [Li(thf)2(tmeda)][AlPh3(tmp)] (3), [(thf)2K(N-carbazolyl)2AlMes2] (4), and [Sr(thf)7][AlPh4]2 (5), of the gallate [Ca(dme)4][GaEt3(N-carbazolyl)]2 (6), and of the vanadates [Li(thf)4][VMes4] (7), [CaI(thf)5][VMes4] (8), [Ca(thf)6][VMes4]2 (9), and [Sr(thf)6][VMes4]2 (10), are discussed. All these complexes contain complex cations of the type [(L)nM]+, and tetrahedral anions of the type [ER4]−. Only 4 crystallizes as a contact ion pair because the soft K+ cation shows no preference for hard bases such as ethers or for soft arene π-systems.

1‐Alkenylcalcium Iodide: Synthesis and Stability

To enhance the scope of heavy calcium-based Grignard reagents, 1,2-dihydro-4-iodonaphthalene (1) was reduced with calcium in THF giving tetrakis(thf) (1,2-dihydronaphth-4-yl)calcium iodide (2). This derivative represents a 1-alkenylcalcium complex based on X-ray structure determination and NMR data. The stability of this compound is significantly reduced compared with the aromatic naphthylcalcium iodide.

Formation of a Ph2PCH(BH3)P(BH3)Ph2 ligand via formal 1,2-borane migration

The transfer of the anionic Ph(2)P(BH(3))-CH-P(BH(3))Ph(2) ligand from potassium to barium results in the subsequent formation of a tetranuclear barium cluster which contains the hitherto unknown isomeric form Ph(2)P-CH(BH(3))-P(BH(3))Ph(2) of the ligand.

An unsymmetrical phosphonium diylide with a fluorenylidene subunit and its lithium complexes

The phosphonium ylide MePh2P(flu) (3) (flu = C13H8, fluorenylidene) was conveniently prepared by reaction of Ph2P(fluH) (1) (fluH = C13H9, fluorenyl) with iodomethane, followed by subsequent dehydrohalogenation of the resulting phosphonium salt [MePh2P(fluH)]I (2) by potassium tert-butoxide. Compound 3 was further deprotonated by n-butyllithium, yielding the corresponding lithium complex [Li{CH2PPh2(flu)}(tmeda)] (4) in presence of N,N,N′,N′-tetramethylethylenediamine (tmeda). This mononuclear lithium compound contains the monoanionic chelating diylidic ligand. An exchange of the neutral bidentate tmeda by tridentate N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (pmdta) enforces a change in coordination mode. Consequently, the diylide is monodentate in [Li{CH2PPh2(flu)}(pmdta)] (5). Compounds 1–5 were characterized by NMR spectroscopy and single-crystal X-ray diffraction experiments. Graphical abstract

Bis[μ-1,2-bis-(diphenyl-phosphino)methane-κP:P']bis-[(η-ethene)nickel(0)] toluene disolvate.

In the title compound, [Ni2(C2H4)2(C25H22P2)2]·2C7H8, each Ni atom is coordinated in a trigonal-planar geometry by two P atoms of the bridging 1,2-bis(diphenylphosphino)methane (dppm) ligands and by the centroid of the double bond of an ethene ligand. An eight-membered ring comprising the two Ni atoms, four P atoms and the CH2 groups of the two dppm ligands is thus formed. The methyl group in one of the solvent toluene molecules is disordered over two positions with equal occupancies.