Metal-catalyzed [2 + 2] cycloaddition reactions. Metallocyclic intermediate

2,5‐Norbornadiene C–C Coupling Reactions Mediated by Iridium Complexes

“…For this purpose we first studied the reaction of the chloro‐bridged complex [{Ir(µ‐Cl)(cod)} 2 ] with nbd in the absence of phosphane and ammonia. At this point we would like to recall that this reaction has already been reported to afford an insoluble yellow solid of uncertain nuclearity of composition [Ir(C 7 H 8 ) 3 Cl] x , based on analytical data and further reactivity studies . Following this synthetic approach, the treatment of a solution of the complex [{Ir(µ‐Cl)(cod)} 2 ] in toluene with an excess of nbd produced a bright‐yellow solid in excellent yield; however, the marked insolubility of this material precluded its full characterization in solution.…”

“…On the whole, the iridacycle entity of complex 2 is similar to that reported for the complex [Ir(acac)(κ C ,κ C ‐C 14 H 16 )(η 4 ‐C 7 H 8 )] (acac = acetylacetonate) in which two of the nbd molecules are coupled and the third one is coordinated in its original bidentate mode. [16a]…”

“…and the Supporting Information) readily comparable to that reported for a complex of stoichiometry [Ir(C 7 H 8 ) 3 Cl(PMe 3 )], which was suggested to contain a five‐membered iridacycle and an additional nbd molecule. [16b] However, species 3 has only a short existence, because it evolves in solution to eventually form an insoluble red microcrystalline solid characterized as the chloro‐bridged diiridium complex [{Ir(κ C ,κ C ‐C 21 H 24 )(µ‐Cl)(PEt 3 )} 2 ] ( 4 , see below). Complex 4 is insoluble in the usual organic solvents, a situation that precluded its characterization in solution.…”

Structure and conformations of 2‐substituted and 3‐substituted alumolanes in polar solvents: a direct NMR observation

“…Five‐membered saturated metallacarbocycles represent a large family of organometallic compounds, which are frequently postulated as reactive intermediates in catalysis, mainly in alkene oligomerization, polymerization, cycloadditions of olefins and diynes . Rather well‐known and spectroscopically characterized are cyclic compounds of some transition metals, e.g.…”

Darstellung und Eigenschaften von und Reaktionen mit metallhaltigen Heterocyclen, VII [1]. Heterolytische Spaltung der Re-Re-Bindung in den Zweikern-Anionen [(OC)4ReP(R2 )O]2 2- mit Elektrophilen - ein Weg zu Heterocyclen mit Re-σ-Bindung / Preparation and Properties of, and Reactions with, Metal-Containing Heterocycles, VII [1]. Heterolytic Cleavage of the Re-Re Bond in the Binuclear Anions [(OC)4ReP(R2)O]2

“…Sie spielen insbesondere bei übergangsmetallkatalysierten Reaktionen [2][3][4][5] und bei organischen Synthesen [6], z.B. der Olefin-Metathese [7], [2+2]-Cycloaddition [8] und Valenzisomerisierung [9] eine wichtige Rolle. Bekanntlich weisen offenkettige <7-AlkylVerbindungen wegen möglicher Eliminierungsreaktionen [10,11], welche vom M-C-C-H-Winkel abhängig sind [12], nur geringe Stabilität auf [13].…”