Ligand effects in chromium diphosphine catalysed olefin co-trimerisation and diene trimerisation.
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.
Bowen
Lucy E
LE
School of Chemistry, University of Bristol, Cantock's Close, Bristol, UK BS8 1TS.
Charernsuk
Manutsavin
M
Hey
Thomas W
TW
McMullin
Claire L
CL
Orpen
A Guy
AG
Wass
Duncan F
DF