Linear Tetramer Research Articles

ChemInform Abstract: THE MAGNETIC SUSCEPTIBILITY OF TWO COUPLED DIMERS CONSISTING OF S=1/2 SPINS

Tetramers consisting of two coupled dimers were classified as (a) linear, (b) cyclic, (c) rhombic, or (d) tetrahedral. The magnetic susceptibility for each tetramer model consisting of S=1/2 spins was obtained as an analytical equation. For the linear tetramer, the susceptibility equation was calculated numerically and compared with the observed values.

The Magnetic Susceptibility of Two Coupled Dimers Consisting of S=1/2 Spins

Abstract Tetramers consisting of two coupled dimers were classified as (a) linear, (b) cyclic, (c) rhombic, or (d) tetrahedral. The magnetic susceptibility for each tetramer model consisting of S=1/2 spins was obtained as an analytical equation. For the linear tetramer, the susceptibility equation was calculated numerically and compared with the observed values.

ChemInform Abstract: REACTION PATHS AND MECHANISMS IN THE CATALYTIC CYCLOADDITION OF ALLENE OVER NICKEL(0) TEMPLATE SYSTEMS

AbstractAllen (I) cyclooligomerisiert bei leichtem Erwärmen in Benzol in Gegenwart von Dicyclooctadien‐(1,5)‐Nickel(0) [Ni(cod)2] und eines Austauschliganden (Triphenylphosphin, Tri‐n‐butylphosphin, Tri‐o‐tolyl‐phosphit, bei ‐78°C zugesetzt) zu den Ver‐ ′ bindungen (II)‐(IV) (Gesamtausbeute 93‐100%), in Abwesenheit eines zusätzlichen Liganden aber zu dem Pentameren (IV) als einzigem Produkt (52%).

Reaction paths and mechanisms in the catalytic cycloaddition of allene over nickel(0) template systems

Catalytic cycloadditions of allene, CH2CCH2, have been effected with a variety of nickel(0)–phosphorus ligand systems. The selective catalytic reaction path leading to the cyclotetramer, cyclotetramer, or cyclopentamer depends primarily on the nature of the ligands. Intermediate nickel(0) complexes containing the linear trimer (C9H12) or tetramer (C12H16) have been detected spectroscopically or isolated by stabilisation with phosphorus ligands. On the basis of the structures of the isolated complexes and kinetics, multistep reaction paths are described and the roles of the phosphorous ligands in these catalysts discussed.

The synthesis and some reactions of a series of “skipped” polyacetylenes containing terminal acetylene groups

The synthesis and some reactions of a series of linear 1,4-polyynes containing terminal acetylene groups (Ia–e) are described. Reaction of propargyl bromide (II) with ethynylmagnesium bromide (III) in the presence of CuCl gave 1,4-pentadiyne (Ia). Rearrangement of Ia with KOBu t led to 1,3-pentadiyne (IV), while treatment with Br 2 furnished 1,2,4,5-tetrabromo-1,4-pentadiene (V). Oxidation of Ia with O 2, CuCl and NH 4Cl yielded the linear dimer (VIa) [rearranged to 2,4,6,8-decatetrayne (VIII) with KOH] and linear trimer (VIb). Hydrogenation of the crude oxidation product gave saturated hydrocarbons derived from VIa, VIb, the linear tetramer (VIc) and the cyclic tetramer (VII), but none derived from the cyclic dimer or cyclic trimer of Ia. Similarly, oxidation of Ia with Cu(OAc) 2 in pyridine and subsequent hydrogenation led to saturated hydrocarbons derived from VIa and VIb, but none derived from the cyclic dimer or cyclic trimer. In order to prepare cyclodecane as a comparison compound, the cycloethylenedithioketal (X) derived from cyclodecanone was treated with Raney Ni in boiling EtOH, but the reaction led mainly to cis-cyclodecene. Treatment of 1,4-dibromo-2-butyne (XIII) with an excess of III in the presence of CuCl yielded 1,4,7-octatriyne (Ib), 1,4,7,10,13-tetradecapentayne (Id) and 1,4,7,10,13,16,19-eicosaheptayne (Ie). Rearrangement of Ib with alkaline Al 2O 3, or KOBu t at room temp gave 2,4,6-octatriyne (XVII), while treatment with boiling ethanolic KOH or KOBu t in hot Bu tOH led to 2-ethoxy-2-octene-4,6-diyne (XVIIIa) or 2- t-butoxy-2-octene-4,6-diyne (XVIIIc), respectively. 1,4,7,10-Undecatetrayne (Ic) was prepared from crude Ia by conversion to the bis-Grignard derivative, followed by reaction with propargyl bromide (II) in the presence of CuCl.