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Issue 39, 2007
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Mono- and dinuclear cobalt complexes with chelating or bridging bidentate P,N phosphino- and phosphinito-oxazoline ligands: synthesis, structures and catalytic ethylene oligomerisation

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Abstract

Cobalt(II) complexes of the type [CoCl2(P,N)], where P,N represents a heterobidentate phosphino- or phosphinito-oxazoline-type ligand, have been synthesised and characterised by infrared spectroscopy and elemental analysis. Their molecular structures were established by single-crystal X-ray diffraction in the solid state. Whereas the phosphino-oxazoline complex [CoCl2{Ph2PCH2oxMe2}] (Ph2PCH2oxMe2 = 2-[(diphenylphosphanyl)-methyl]-4,4-dimethyl-4,5-dihydro-oxazole) (8) and the phosphinito-oxazoline complexes [CoCl2{Ph2POCH2oxMe2}] (Ph2POCH2oxMe2 = 1-[4,4-dimethyl-2{1-oxy(diphenylphosphino)-1-methyl}]-4,5-dihydro-oxazole) (9) and [CoCl2{Ph2POCMe2oxMe2}] (Ph2POCMe2oxMe2 = 1-[4,4-dimethyl-2- [1-oxy(diphenylphosphino)-1-methylethyl]]-4,5-dihydrooxazole) (10) are mononuclear, the phosphino-oxazoline complexes [CoCl2{μ-i-Pr2PCH2ox}]2 (i-Pr2PCH2ox = 2-[(diisopropyl-phosphanyl)-methyl]-4,5-dihydro-oxazole) (6) and [CoCl2{µ-Ph2PCH2ox}]2 (Ph2PCH2ox = 2-[(diphenyl-phosphanyl)-methyl]-4,5-dihydro-oxazole) (7) are dinuclear compounds and contain two bridging phosphino-oxazoline ligands which form a 10-membered ring. In the course of this work, the zwitterionic complex [CoCl3{Ph2PCH2C(O)OCH2CMe2NH3] (11) was obtained and characterised by X-ray diffraction in which the oxazoline ring has been opened. Air-oxidation of the phosphine function of the mononuclear P,N chelate complex 8 yielded the blue N,O-bridged, centrosymmetric dinuclear complex [[upper bond 1 start]CoCl2{μ-OPPh2CH2[lower bond 1 start]C[double bond, length as m-dash]N[upper bond 1 end]CMe2CH2O[lower bond 1 end]}]2 (12) which contains a 12-membered ring. All these complexes are paramagnetic and their magnetic moments in solution were measured by the Evans method. Complexes 6–10 were evaluated in the catalytic oligomerisation of ethylene with AlEtCl2 or methylaluminoxane (MAO) as cocatalysts and provided moderate activities. In the presence of AlEtCl2 (6–14 equiv.), the selectivities for ethylene dimers were higher than 92% and complex 8 showed the highest turnover frequency with 14 equiv. of AlEtCl2. When MAO was used as cocatalyst, the catalytic activities were similar to those with AlEtCl2 but significant amounts of C6–C12 oligomers were produced.

Graphical abstract: Mono- and dinuclear cobalt complexes with chelating or bridging bidentate P,N phosphino- and phosphinito-oxazoline ligands: synthesis, structures and catalytic ethylene oligomerisation

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Publication details

The article was received on 08 May 2007, accepted on 29 Jun 2007 and first published on 13 Aug 2007


Article type: Paper
DOI: 10.1039/B706818B
Citation: Dalton Trans., 2007,0, 4472-4482
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    Mono- and dinuclear cobalt complexes with chelating or bridging bidentate P,N phosphino- and phosphinito-oxazoline ligands: synthesis, structures and catalytic ethylene oligomerisation

    S. Jie, M. Agostinho, A. Kermagoret, C. S. J. Cazin and P. Braunstein, Dalton Trans., 2007, 0, 4472
    DOI: 10.1039/B706818B

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