The racemic isomers of C 2 H 4 (1-Ind) 2 TiCl 2 and Me 2 Si(2-Me-Benzind) 2 TiMe 2 were synthesized and structurally characterized. Reactions of these and related ansa-titanocene complexes with methylaluminoxane or with the cationizing reagent [CPh 3 ] + [B(C 6 F 5 ) 4 ] -/Al 2 -Me 6 were monitored by UV/vis, 1 H NMR, and EPR methods. Under conditions approaching those typically used in olefin polymerizations, heterobinuclear cations of the type [DianTi IV (µ-Me) 2 AlMe 2 ] + (with Dian ) bridged ligand dianion) dominate in each of these reaction systems, which catalyze the polymerization of propene at temperatures below ambient. Above 0 °C, these cations are reduced, mainly to neutral heterobinuclear species DianTi III (µ-Me) 2 AlMe 2 , which appear to be inactive with regard to polymerization catalysis. In the absence of monomer, the main reducing agent appears to be ethyl aluminum admixtures in Al 2 Me 6 . Addition of monomer increases the rate of reduction rather drastically, probably via formation of titanium hydrides. spectrometer. EPR signals were quantified by double integration using copper chloride as standard.Crystal Structures. X-ray diffraction analyses were carried out on a Siemens P4 or an Enraf-Nonius CAD 4 diffractometer using Mo KR radiation (71.073 pm) and a graphite monochromator. Crystal decay was monitored by measuring three standard reflections every 100 reflections. Details of the X-ray diffraction analysis are given in Table 6. Crystallographic data for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications CCDC 230670, 230738, 230750, and 230753.
Reaction of Me,Si(lnd),ZrCI, with excess methylalumoxane (MAO) gives rise to ion pairs containing zirconocenium cations of the type [Me2Si(lnd)2ZrMe]+ in contact with two types of anions, MeMAO A-and MeMAO B-, which differ in their coordinative strengths: More strongly coherent contact-ion pairs [Me 2 Si(lnd)2 ZrMe+'>MeMAO B-] are converted by a sufficiently high excess of MAO to more easily separable contact-ion pairs [Me,Si(lnd),ZrMe+"MeMAO A-J, which react with AIMe, to form the outer-sphere ion pairs [Me,Si(lnd),Zr(fL-Me),AIMe,j+ MeMAO A-, and are likely to be required also for the formation of the olefin-containing reaction complexes responsible for catalytic activity.
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