The selective trimerisation of isoprene with chromium N,N-bis(diarylphosphino)amine catalysts

Bowen, Lucy E.; Charernsuk, Manutsavin; Wass, Duncan F.

doi:10.1039/b702331f

Cited by 23 publications

(15 citation statements)

References 14 publications

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“…13 C NMR (CDCl 3 ): d = 15.2 (d, 3 J CP = 20.7 Hz, CH 3 ), 27.3 (d, 3 J CP = 20.7 Hz, CH 2 ), 33.0 (s, NCH 3 ), 125.4 (s, CH), 127.9-129.9 (m, CH), 132.1-132.9 (m, CH), 136.5-136.9 (m, CH), 138. 4 (6). N,N¢-bis(dichlorophosphino)dimethylhydrazine (0.68 mL, 3.8 mmol) was dissolved in ether (25 mL) and added dropwise to ortho-tolyl magnesium bromide (60 mL in ether, 0.159 mol, prepared as before).…”

Section: Synthesis Of {2-c 6 H 4 (Ome)} 2 Pn(me)p(c 6 H 5 ) 2 (1)mentioning

confidence: 99%

“…Our previously reported method was followed. 4 The ligand (20 mmol) and chromium(III) chloride tetrahydrofuran complex, [CrCl 3 (THF) 3 ], (8 mg, 20 mmol) were dissolved in tetrahydrofuran (3 mL) and stirred at room temperature in a round bottomed Schlenk fitted with a condenser under nitrogen for 10 minutes. The solvent was removed and toluene (10 mL) was added to give a pink mixture.…”

Section: Chromium Carbonyl Complexationmentioning

confidence: 99%

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Ligand effects in chromium diphosphine catalysed olefin co-trimerisation and diene trimerisation

et al. 2010

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A series of symmetric and unsymmetric N,N-bis(diarylphosphino)amine ('PNP') ligands (Ar2PN(R)PNAr'2: R = Me, Ar2 = o-anisyl, Ar'2 = Ph, 1, R = Me, Ar2 = o-tolyl, Ar'2 = Ph, 2, R = Me, Ar2 = Ph(o-ethyl), Ar'2 = Ph, 3, R = Me, Ar2 = Ar'2 = o-anisyl, 4, R = iPr, Ar2 = Ar'2 = Ph, 5) and symmetric N,N'-bis(diarylphosphino)dimethylhydrazine ('PNNP') ligands (Ar2PN(Me)N(Me)PAr2: Ar2 = o-tolyl, 6, Ar2 = o-anisyl, 7) have been synthesised. Catalytic screening for ethene/styrene co-trimerisation and isoprene trimerisation was performed via the in situ complexation to [CrCl3(THF)3] followed by activation with methylaluminoxane (MAO). PNNP catalytic systems showed a significant increase in activity and selectivity over previously reported PNP systems in isoprene trimerisation. Comparing the symmetric and unsymmetric variants in ethene and styrene co-trimerisation resulted in a switch in selectivity, an unsymmetric catalytic (o-anisyl)2PN(Me)PPh2 (1) ligand system affording unique incorporation of two styrenic monomers into the co-trimer product distribution differing from the familiar two ethene and one styrene -substituted alkenes. Complexes of the type [(diphosphine)Cr(CO)4] 8-11 were also synthesised, the single-crystal X-ray diffraction of which are reported. We propose the mechanisms of these catalytic transformations and an insight into the effect of the ligand series on the chromacyclic catalytic intermediates.

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Section: Synthesis Of {2-c 6 H 4 (Ome)} 2 Pn(me)p(c 6 H 5 ) 2 (1)mentioning

confidence: 99%

Section: Chromium Carbonyl Complexationmentioning

confidence: 99%

Ligand effects in chromium diphosphine catalysed olefin co-trimerisation and diene trimerisation

et al. 2010

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“…4,5 In notable recent studies, Wass and coworkers have furthermore demonstrated the trimerization and co-trimerization of substrates other than ethylene. 6, 7 For example, ethylene/styrene cotrimerization and isoprene trimerization have been reported. 6,7 It is clear that an entirely different mechanism, to the traditional Cossee-Arlman mechanism, must be operating and a mechanism involving Cr-metallocycles is favoured.…”

Section: Introductionmentioning

confidence: 99%

A cw EPR and ENDOR investigation on a series of Cr(i) carbonyl complexes with relevance to alkene oligomerization catalysis: [Cr(CO)4L]+ (L = Ph2PN(R)PPh2, Ph2P(R)PPh2)

et al. 2010

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The preparation and characterisation of the Cr(I) complexes [Cr(CO)(4)L](+) (L = Ph(2)PN(R)PPh(2), Ph(2)P(R)PPh(2)), which are used as pre-catalysts for the selective oligomerization of ethylene, are reported. The electronic properties and structural features of these complexes in frozen solution have been established via continuous wave X-band Electron Paramagnetic Resonance (cw-EPR) and continuous wave (1)H, (14)N and (31)P Electron Nuclear Double Resonance (cw-ENDOR) spectroscopy. The EPR spectra are dominated by the g anisotropy, with notably large (P)A couplings from the two equivalent (31)P nuclei. The spin Hamiltonian parameters (g(perpendicular) (g(xx) = g(yy)) > g(e) > g(parallel) (g(zz))) are consistent with a low-spin d(5) system possessing C(2v) symmetry, with a SOMO where the metal contribution is primarily d(xy) for all complexes. The isotropic Fermi contact term ((P)a(iso), determined by EPR and ENDOR) was found to be largest for complexes containing ligands e, d, f and g, indicating that the (31)P 3 s character in the SOMO is higher for the PNP type ligands than the PCP type. Subtle structural differences in the complexes were also identified through variations in the Deltag shifts (identified by EPR), and through differences in the phenyl ring conformations (identified by (1)H ENDOR). Attempts to correlate trends in EPR-derived parameters with data measured for catalysis using these pre-catalysts are also made, but no clear connections were found.

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“…[13] New studies on these complexes with nitrogen-bridged diphosphine ligands (PNP donor ligands) have extended the range of substrates to dienes which allow a C-C reductive elimination to cyclic products as well. [14] Density-functional calculations with the assumption of no change in spin state give viable routes for both the Cr II/IV (S = 1) and Cr I/III (S = 3 = 2 ) catalytic cycles. [15] However, a change in spin state between the Scheme 1.…”

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confidence: 99%

Reactivity of Chromium Complexes under Spin Control

Köhn

2007

Angew Chem Int Ed

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The selective trimerisation of isoprene with chromium N,N-bis(diarylphosphino)amine catalysts

Abstract: Chromium catalysts supported by N,N-bis(diarylphosphino)amine ligands, on activation with methyl aluminoxane (MAO), selectively trimerise isoprene with unprecedented activity to predominantly linear materials.

Cited by 23 publications

References 14 publications

Ligand effects in chromium diphosphine catalysed olefin co-trimerisation and diene trimerisation

Ligand effects in chromium diphosphine catalysed olefin co-trimerisation and diene trimerisation

A cw EPR and ENDOR investigation on a series of Cr(i) carbonyl complexes with relevance to alkene oligomerization catalysis: [Cr(CO)4L]+ (L = Ph2PN(R)PPh2, Ph2P(R)PPh2)

Reactivity of Chromium Complexes under Spin Control

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