Die Umsetzung von p-tert.-Butylcalix[4]aren Cax(OH)4 mit [Mo(NMe2)4] im aquimolaren Verhaltnis in Toluol fuhrt 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 Losungsmittel-Gemischen von Toluol und Acetonitril durchgefuhrt, so wird die Bildung von 2(NCMe)2 unterdruckt und ausschlieslich 1(NCMe) isoliert. Von beiden Verbindungen wurden Kristallstrukturanalysen angefertigt. 1(NCMe): Raumgruppe: C2/c, Gitterkonstanten: a = 37, 987(8)A, b = 13, 012(3)A, c = 20, 271(4)A, β = 103, 39°; 2(NCMe)2: Raumgruppe: P21/n, Gitterkonstanten: a = 11, 937(2)A, b = 21, 078(4)A, c = 19, 620(4)A, β = 107, 31(3)°. Das Molybdanatom in 1(NCMe) weist eine verzerrt oktaedrische Koordinationssphare auf, die von den vier Sauerstoffatomen des Calix[4]arenliganden, dem Stickstoffatom des Aminliganden und dem Stickstoffatom des innerhalb des Calix[4]aren-Kohlenstoffgerustes koordinierenden Acetonitrilmolekuls gebildet wird. Jeweils zwei dieser monomeren Komplexeinheiten sind uber Wasserstoff-Bruckenbindungen miteinander verknupft. Im Komplex 2(NCMe)2 sind zwei Komplexfragmente [CaxO4Mo(NCMe)] miteinander uber Phenolateinheiten der Calix[4]arenliganden miteinander verknupft. Der Mo-Mo′-Abstand von 261, 2(1)pm kann mit dem Vorliegen einer Mo-Mo-Doppelbindung in Einklang gebracht werden. Zur Untersuchung der Bindungsverhaltnisse 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 durchgefuhrt. 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.
Novel Calix[4]arene Complexes of Tetravalent Molybdenum
The reaction of p-tert.-Butylcalix[4]aren Cax(OH)4 with [Mo(NMe2)4] in equimolar amounts at 80°C in toluene affords after extraction into acetonitrile a mixture of [CaxO4Mo(NHMe2)(NCMe)] (1(NCMe)) and [(CaxO4Mo)2(NCMe)2] (2(NCMe)2). If the same reaction is carried out in acetonitrile or in mixtures of toluene and acetonitrile instead of toluene, the formation of 2(NCMe)2 is suppressed and only 1(NCMe) has been isolated. Both compounds have been characterized by X ray crystal structure determinations. 1(NCMe): space group: C2/c, lattice constants: a = 37, 987(8)A, b = 13, 012(3)A, c = 20, 271(4)A, β = 103, 39°; 2(NCMe)2: space group: P21/n, lattice constants: a = 11, 937(2)A, b = 21, 078(4)A, c = 19, 620(4)A, β = 107, 31(3)°. The molybdenum atom in 1(NCMe) is coordinated with four oxygen atoms of the calix[4]arene ligand, a nitrogen atom of the amine ligand, and the nitrogen atom of the endohedrally coordinated acetonitrile molecule in a slightly distorted octahedron. Two of these monomer units are linked via hydrogen bridges. In 2(NCMe)2 two complex fragments [CaxO4Mo(NCMe)] are linked via phenolate units of the calix[4]arene. The Mo-Mo′ distance of 261.2(1)pm is in accordance with a Mo-Mo double bond. EH-, DFT-, und MP2- calculations have been performed on model complexes [CaxO4Mo(NH3)(NCH)] (1′(NCH)) and [(p-H-CaxO4Mo)2(NCH)2] (2′(NCH)2) for a closer inspection of the binding in these compounds. The results of the calculations suggest that addition of the electron rich, basic oxygen atom is the structure determining feature of 2′(NCH)2 and not a metal metal bond.
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