from first principles PP-I-1

PP-II-15NMR Spectroscopic Trapping of Nickel(II)-Alkyl Species in the Course ofPolymerization of Ethylene with Neutral Ni(II) ComplexesSoshnikov I.E. 1 , Semikolenova N.V. 1 , Osichow A. 2 , Bryliakov K.P. 1 , Zakharov V.A. 1 ,Mecking S. 2 , Talsi E.P. 11 Boreskov Institute of Catalysis, Lavrentieva 5, 630090 Novosibirsk, Russia2 University of Konstanz, Chair of Chemical Material Science, Department of Chemistry,Universitätstrasse 10, D-78457 Konstanz, Germanytalsi@catalysis.ruCF 3The salicylaldiminato complex [1] of Ni(II) [(N,O)Ni(CH 3 )(Py)] {1 Me ;[(N,O) = 2 -N,O-(2,6-(3,5-(F 3 C) 2 C 6 H 3 ) 2 C 6 H 3 -N=CH-(3,5-I 2 -2-OC 6 H 2 )}was used as well defined precursor that enables directH 3 C Py observation of various Ni-alkyl species formed in the course ofNiN Oethylene polymerization (Figure 1). Nickel(II)-alkyl complexesHCI[(N,O)Ni(alkyl)(Py)], where alkyl = ethyl, n-propyl, n-butyl and,probably, n-hexyl were found in the catalyst system 1 Me /C 2 H 4 (50 C,Itoluene−d 8 , n(C 2 H 4 )/n(1 Me ) = 30/1) at the initial stage ofFigure 1. The structure ofthe complex 1 Mepolymerization. At the end of polymerization, these diamagneticcomplexes disappear, and two new paramagnetic complexes of nickel(II) (2 and 3, [3]:[2] < 1:3)arise. The quantitative measurements show, that in the course of polymerization, the major part of1 Me converts into 2. Complex 2 exhibits broad paramagnetically shifted resonances ofsalicylaldiminato ligand. The chemical shifts of the resonances of 2 substantially increase andtheir widths decrease with time. Apparently, 2 is a mixture of complexes [(N,O)Ni(R)(Py)], whereR is polymeryl ligand. At the beginning of polymerization, 2 contains a growing polymeryl ligandR, and is unobservable by NMR due to some dynamic processes broadening NMR signals. At theend of polymerization, these processes begin to decline, and [(N,O)Ni(R)(Py)] becomesobservable by NMR. As polymerization proceeds, more and more nickel atoms become bondedto sterically crowded tertiary carbon atoms of branched polymeryl ligand R. This bondingincreases paramagnetism of [(N,O)Ni(R)(Py)] and deactivates complex 2. Formation of inactiveparamagnetic complexes of Ni(II) is a still unexplored route of nickel polymerization catalystsdeactivation. The positions and widths of the resonances of 3 do not essentially change in thecourse of polymerization and with changing temperature. Low paramagnetism of 3 evidences infavor of its dinuclear structure. Tentatively, 3 can be assigned to hydride-bridged nickel(II)complex [(N,O)Ni(-H) 2 Ni(N,O)].F 3 C CF 3CF 3[1] Göttker-Schnetmann, I.; Wehrmann, P.; Röhr, C.; Mecking, S. Organometallics 2007, 26, 2348–2362.146