Neue Calix[4]aren-Komplexe des vierwertigen Molybdäns

Abstract

Die Umsetzung von p‐tert.‐Butylcalix[4]aren Cax(OH)4 mit [Mo(NMe2)4] im äquimolaren Verhältnis in Toluol führt nach Extraktion mit Acetonitril zu Produktgemischen der Verbindungen [CaxO4Mo(NHMe2)(NCMe)] (1(NCMe)) und [(CaxO4Mo)2(NCMe)2] (2(NCMe)2). Wird diese Reaktion jedoch nicht in Toluol sondern in Acetonitril oder in Lösungsmittel‐Gemischen von Toluol und Acetonitril durchgeführt, so wird die Bildung von 2(NCMe)2 unterdrückt und ausschließlich 1(NCMe) isoliert. Von beiden Verbindungen wurden Kristallstrukturanalysen angefertigt. 1(NCMe): Raumgruppe: C2/c, Gitterkonstanten: a = 37, 987(8)Å, b = 13, 012(3)Å, c = 20, 271(4)Å, β = 103, 39°; 2(NCMe)2: Raumgruppe: P21/n, Gitterkonstanten: a = 11, 937(2)Å, b = 21, 078(4)Å, c = 19, 620(4)Å, β = 107, 31(3)°. Das Molybdänatom in 1(NCMe) weist eine verzerrt oktaedrische Koordinationssphäre auf, die von den vier Sauerstoffatomen des Calix[4]arenliganden, dem Stickstoffatom des Aminliganden und dem Stickstoffatom des innerhalb des Calix[4]aren‐Kohlenstoffgerüstes koordinierenden Acetonitrilmoleküls gebildet wird. Jeweils zwei dieser monomeren Komplexeinheiten sind über Wasserstoff‐Brückenbindungen miteinander verknüpft. Im Komplex 2(NCMe)2 sind zwei Komplexfragmente [CaxO4Mo(NCMe)] miteinander über Phenolateinheiten der Calix[4]arenliganden miteinander verknüpft. Der Mo‐Mo′‐Abstand von 261, 2(1)pm kann mit dem Vorliegen einer Mo‐Mo‐Doppelbindung in Einklang gebracht werden. Zur Untersuchung der Bindungsverhältnisse wurden an den Modellen [CaxO4Mo(NH3)(NCH)] (1′(NCH)) und [(p‐H‐CaxO4Mo)2 (NCH)2] (2′(NCH)2) dieser Verbindungen EH‐, DFT‐, und MP2‐Rechnungen durchgeführt. Die Ergebnisse der Berechnungen zeigen, dass das strukturbestimmende Merkmal in 2′(NCH2 nicht die Metall‐Metall‐Wechselwirkung zu sein scheint, sondern eher die Addition der elektronenreichen, basischen Sauerstoffatome der Calix[4]arenliganden an die Lewis‐aciden Metallatome.

The (Calix[4]arene)chloromolybdate(IV) Anion [MoCl(Calix)]-: A Convenient Entry into Molybdenum Calix[4]arene Chemistry

“…Recently, Floriani and co-workers reported the in situ generation of a reactive molybdenum calix[4]arene complex fragment, which presumably contains a d 2 -[Mo IV (Calix)] moiety, starting from the sodium or lithium salt of calixarene and [MoCl 4 (THF) 2 ], consistent with its reactivity toward alkynes and azobenzene 5j. In previous contributions we reported the stabilization and isolation of this fragment, which dimerizes without an additional ligands in the coordination sphere . The complex [Mo(NHMe 2 )(NCMe)(Calix)] was synthesized starting from [Mo(NMe 2 ) 4 ] and p - tert -butylcalix[4]arene and isolated in good to moderate yield 4e.…”

“…Experimental hints have been the only outcome of the reaction, i.e., the isolation of A and D and analogous tungsten compounds for the reaction using base-stabilized W(IV) chlorides. Additionally, the side product [{(Calix)W}{κ 2 ( O )-κ 1 ( O )-HCalix)}{WCl(Calix)}] was isolated and structurally characterized,4c a compound which seemed to be formed from a reaction of [WCl 2 (Calix)] and p - tert -butylcalix[4]arene. The dichlorides [MCl 2 (Calix)] themselves react cleanly with calix[4]arene under the reaction conditions employed in the disproportionation reaction, which supports the idea of the intermediacy of chloro-containing species.…”

“…These d 2 -[W IV (Calix)] and d 2 -[Nb III (Calix)] derivatives do not have a counterpart in molybdenum−calix[4]arene chemistry. Contrary to calix[4]arene tungsten complexes, the chemistry of calix[4]arene-supported complexes of its congener molybdenum is hampered by the unavailability of suitable starting material. , Calix[4]arene complexes of molybdenum are mainly restricted to nonreactive dimeric compounds such as [Mo 2 (Calix) 2 ] and [Mo 2 (Calix) 2 ] 2- or oxo, imido, and hydrazido complexes [Mo(E)(Calix)] (E = O, NR, NNR). None of these complexes can serve as a convenient and general starting material in molybdenum chemistry.…”

“…In previous contributions we reported the stabilization and isolation of this fragment, which dimerizes without an additional ligands in the coordination sphere . The complex [Mo(NHMe 2 )(NCMe)(Calix)] was synthesized starting from [Mo(NMe 2 ) 4 ] and p - tert -butylcalix[4]arene and isolated in good to moderate yield 4e. Furthermore, we reported the isolation of a molybdenum(VI) dichloro complex [MoCl 2 (Calix)] via disproportionation of molybdenum(IV) chlorides [MoCl 4 L 2 ] (L = Et 2 S, Et 2 O) in the presence of calix[4]arene and triethylamine (see Scheme ) and a subsequent reaction of product D with HCl 4c.…”

“…The complex [Mo(NHMe 2 )(NCMe)(Calix)] was synthesized starting from [Mo(NMe 2 ) 4 ] and p - tert -butylcalix[4]arene and isolated in good to moderate yield 4e. Furthermore, we reported the isolation of a molybdenum(VI) dichloro complex [MoCl 2 (Calix)] via disproportionation of molybdenum(IV) chlorides [MoCl 4 L 2 ] (L = Et 2 S, Et 2 O) in the presence of calix[4]arene and triethylamine (see Scheme ) and a subsequent reaction of product D with HCl 4c. This disproportionation reaction afforded the d 3 compound [(HNEt 3 ) 2 [M 2 (Calix) 2 ] ( A ) and the d 0 complex [Mo(H 2 Calix)(Calix)] ( D ).…”