ARTICLE IN PRESS UNCORRECTED PROOF S0021-9517(03)00441-X/FLA AID:8118 Vol.•••(•••) ELSGMLTM(YJCAT):m5 2003/11/25 Prn:3/12/2003; 11:16 yjcat8118 P.1(1-8) by:ML p. 1 Journal of Catalysis ••• (••••) •••–••• www.elsevier.com/locate/jcat 1 57 2 58 3 59 4 60 5 61 6 62 7 63 8 64 9 65 10 66 11 67 12 68 13 69 14 70 15 71 16 72 17 73 18 74 19 75 20 76 21 77 22 78 23 79 24 80 25 81 26 82 27 83 28 84 29 85 30 86 31 87 32 88 33 89 34 90 35 91 36 92 37 93 38 94 39 95 40 96 41 97 42 98 43 99 44 100 45 101 46 102 47 103 48 104 49 105 50 106 51 107 52 108 53 109 54 110 55 111 56 112 Homo- and heterometallic carboxylate cage complexes as precatalysts for olefin polymerization—Activity enhancement through “inert metals” Paul-Gerhard Lassahn, a Vasile Lozan, a Grigore A. Timco, b Paul Christian, b Christoph Janiak, a,∗ and Richard E.P. Winpenny b a Institut für Anorganische und Analytische Chemie, Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany b Department of Chemistry, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK Received 29 July 2003; revised 31 October 2003; accepted 31 October 2003 Abstract The polymerization behavior of novel polynuclear cage complexes as precatalysts in the vinyl or addition polymerization of norbornene has been investigated and correlated with the results of the known mononuclear precatalyst M(acac) x (M = Ni II , Co III , Cr III , and Fe III , acac = acetylacetonate, x = 2 or 3) and mixtures thereof. The cage complexes can be activated with the Lewis acids methylalumoxane (MAO) as well as with tris(pentafluorophenyl)borane, B(C 6 F 5 ) 3 , in combination with or without triethylaluminum (AlEt 3 ). It is shown that nickel is the most active metal in the polymerization of norbornene with heterometallic precatalysts. The homo- and heterometallic nickel cage compounds reveal a maximum activity per nickel in the presence of “inert metal” atoms—an effect which is not seen when Ni(acac) 2 is only physically mixed with other metal-acac salts. The inert metal effect may be advantageously applicable to other valuable catalysts when used as heterometallic polynuclear compounds.  2003 Elsevier Inc. All rights reserved. Keywords: Polymerization; Norbornene; Nickel; Tris(pentafluorophenyl)borane; Methylalumoxane; Cluster 1. Introduction Heterometallic compounds may offer significant advan- tages as catalysts. The presence of one metal may influence the reactivity of another, or cooperative binding of different components of a catalyzed reaction may bring the substrates into close proximity. Most previous work on heterometal- lic homogeneous catalysts has concentrated on low-valent metal clusters [1]. We have begun an investigation into the use of small heterometallic carboxylate cages in catalysis. Metal carboxylate cages are already known to act as cat- alysts for the oxidation of alkenes [2,3]. Initial results re- ported here show that some simple cages also show promis- ing reactivity for olefin polymerization, e.g., for the ho- mopolymerization of norbornene. The homopolymerization of norbornene can be accomplished by three different routes with each route leading to its own polymer type with differ- ent structure and properties (Scheme 1). * Corresponding author. E-mail addresses: janiak@uni-freiburg.de (C. Janiak), richard.winpenny@man.ac.uk (R.E.P. Winpenny). Scheme 1. Polymers produced via ring-opening metathesis polymer- ization (ROMP) still contain double bonds in the polymer backbone and can be obtained by a number of transition met- als in high oxidation state [4–6]. Only few reports describe the formation of low-molar-mass oligomeric materials with 2,7-connectivity of the monomer from the cationic or radi- cal homopolymerization of norbornene [7]. Finally, the vinyl or addition polymerization of norbornene yields saturated 2,3-inserted rotationally constrained polymers in which the bicyclic structural unit remains intact and only the double 0021-9517/$ – see front matter  2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2003.10.028