The α-diimine ligand ArNC(Me)C(Me)NAr (Ar = 2,6-C6H3-iPr2) reacts with Pd(OAc)2 in the presence of HBF4·Et2O, or [Pd(MeCN)4](BF4)2 in the absence of acid, to give ethylene polymerization catalysts. The reactions of a related β-diimine ligand with [Pd(MeCN)4](BF4)2 and (1,2-dimethoxyethane)NiBr2, and the polymerization activity of catalysts derived from it, are discussed.

1423actual dissociation (AD2 -AD + D) in which the leaving molecule carries away the excess energy. SummaryThe emission properties of jet-cooled adducts between ethers and some aromatic hydrocarbons may be accounted for by assuming an excited state that is a superposition of a van der Waals locally excited (LE) state and a charge-transfer (CT) state. The direct optical transition from the ground state to the C T state is forbidden by either symmetry or Franck-Condon considerations. Thus, the excitation spectrum is dominated by the LE state, and emission from the CT state has a longer decay time. The C T character of the excited state is more prominent in anthracene and its derivatives than in perylene. This is particularly so when a hydrogen atom is bound to a C-9 or C-IO carbon. It is therefore proposed that this atom may serve as a bridge in transmitting the charge from the oxygen lone pair orbital of the ether. Geometric factors appear to be decisive in determining the interaction as shown by the fact that tetrahydrofuran, in which the oxygen atom is constrained to be away from the 9-or 10-position, does not show exciplex-type emission with anthracene. Abstract:The reaction between W(C-t-Bu)(dme)CI, and ArNH(TMS) (Ar = 2,6-C,H3-i-Pr2) yields W(C-t-Bu)(NHAr)(dme)CI,.

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Neopentylidene complexes of the type W(CH-t-Bu)(NAr)(OR), (Ar = 2,6-C6H3-i-Pr2; OR = 0-t-Bu, OCMe2(CF3), OAr) react with ethylene to give trigonal-bipyramidal or square-pyramidal tungstacyclobutane complexes. A square-pyramidal form is observed when OR = 0-t-Bu. Both forms are present when OR = OCMe2(CFJ or OAr, and they interconvert at a rate that is on the order of the NMR time scale. A complex of the type W[CH,CH(R)CH,](NAr)(OAr), is a square pyramid when R = t-Bu but a trigonal bipyramid when R = SiMe3. Square-pyramidal tungstacycles are characterized by comparable chemical shifts for a-and @-protons, chemical shifts for a-and @-carbon atoms that differ by only -25 ppm, and aliphatic JcH values, as opposed to large differences in chemical shifts between a-and @-carbons and a-and @-hydrogens and olefinic JCH values in TBP tungstacycles. Unsubstituted metallacycles react with excesshas been characterized crystallographical 2 = 8, p = 40.05 cm-', R = 0.056, R, = 0.082). The most characteristic feature of the WC, ring in the SP complex is the relatively normal W---C, distance of -2.8 A and W-C, bond lengths of 2.15-2.20 A, as opposed to a short W---C, distance of -2.4 8, and W-C, bond lengths of 2.05-2.10 A in TBP complexes. It is proposed that square-pyramidal complexes form in order to avoid competition between a relatively basic axial alkoxide and an axial imido ligand in a trigonal bipyramid. The reaction between W[CH,CH(t-Bu)CH,](NAr)(OAr), and ethylene to give W[CH2CH2CH2] (NAr)(OAr), and tert-butylethylene is zero order in ethylene and first order in tungsten between 9 and 34 "C with AH* = 19.7 kcal mol-' and AS* = -6 eu. Reactions between ethylene and trigonal-bipyramidal W[CH,CH(Me,Si)CH,](NAr)(OAr),, W[CH2CH(Me3Si)CH2](NAr)-[OCMe(CF3),I2, and W[CH2CH(Me3Si)CH2] (NAr) [OC(CF3)2(CF2CF2CF3)]2 are analogous but have positive values for AS' (11-23 eu). It is proposed that square-pyramidal tert-butoxide complexes are relatively stable toward loss of an olefin because the WC3 ring is further from an "olefin/alkylidene" transition state than is the WC3 ring in a trigonal bipyramid and in general for that reason complexes that contain relatively electron-withdrawing alkoxides will lose an olefin more readily than those that contain relatively electron-donating alkoxides.(space group P4,/n, a = 25.26 (2) A, c = 9.720 (5) A, V = 6202 A3, M, = 711.48, p(ca1cd) = 1.524 g cm-P ,

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