Ligand effects in chromium diphosphine catalysed olefin co-trimerisation and diene trimerisation
作者:Lucy E. Bowen、Manutsavin Charernsuk、Thomas W. Hey、Claire L. McMullin、A. Guy Orpen、Duncan F. Wass
DOI:10.1039/b913302j
日期:——
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 ω-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.
一系列对称和不对称的N,N-bis(diarylphosphino)胺(‘PNP’)配体(Ar2PN(R)PNAr′2: R = Me, Ar2 = o-甲氧基苯基, Ar′2 = 苯, 1; R = Me, Ar2 = o-甲苯基, Ar′2 = 苯, 2; R = Me, Ar2 = 苯(o-乙基), Ar′2 = 苯, 3; R = Me, Ar2 = Ar′2 = o-甲氧基苯基, 4; R = iPr, Ar2 = Ar′2 = 苯, 5)和对称的N,N′-bis(diarylphosphino)二甲基肼(‘PNNP’)配体(Ar2PN(Me)N(Me)PAr2: Ar2 = o-甲苯基, 6; Ar2 = o-甲氧基苯基, 7)已被合成。通过原位与[CrCl3(THF)3]复合后激活的甲基铝氧烷(MAO)进行乙烯/苯乙烯共三聚化和异戊二烯三聚化的催化筛选。PNNP催化体系在异戊二烯三聚化中表现出了显著的活性和选择性的提高,相较于之前报道的PNP体系。在乙烯和苯乙烯共三聚化中,对称和不对称变体的比较导致选择性的转换,不对称催化(o-甲氧基苯基)2PN(Me)PPh2(1)配体体系在共三聚产物分布中独特地引入了两个苯乙烯单体,与熟悉的两个乙烯和一个苯乙烯的ω-取代烯烃有所不同。类型为[(双膦)Cr(CO)4]的配合物8-11也已合成,并报告了其单晶X射线衍射结果。我们提出了这些催化转化的机制,并深入探讨了配体系列对铬环催化中间体的影响。