Olefin Polymerization Catalyzed by Titanium−Tungsten Heterobimetallic Dinitrogen Complexes¹

Abstract

Et, Ph), has been developed, in which the tungsten dinitrogen fragment acts as a novel metallonitrogen ligand to the catalytically active titanium center. Alkylation of 1d (Cp′ ) C 5 Me 5 , L ) 1/2 Et 2 PCH 2 CH 2 PEt 2 ) with MeLi gave di-and trimethyl derivatives 2d and 3d, which were structurally characterized.Polymerization of olefins catalyzed by soluble, welldefined transition metal complexes has been one of the most attractive subjects in organometallic chemistry. 2 In particular, monocyclopentadienyl titanium catalysts containing amide, phosphinimide, and aryloxy ligands have extensively been studied, and some of them are now employed commercially. 3,4 On the other hand, some examples of olefin polymerization by using heterobimetallic complexes have been reported where bis(cyclopentadienyl)M (M ) Zr, Hf) moieties are connected to other transition metals such as Mo, 5a,b Fe, 5c,d,f Co, 5f Rh, 5e-h and Ni 5a via cyclopentadienyl or phosphido ligands. However, significant enhancement in catalytic activity has rarely been observed. 5c,d,g During our long-standing study on chemical nitrogen fixation by transition metal complexes, 6 we have recently synthesized the titanium-tungsten heterobimetallic bridging dinitrogen complexes 1a and 1b ( Figure 1) having a half-sandwich titanium fragment from the reaction of tungsten dinitrogen complexes [W(N 2 ) 2 (L) 4 ] (L ) PMe 2 Ph, 1/2 dppe; dppe ) Ph 2 PCH 2 CH 2 PPh 2 ) with CpTiCl 3 . 7 We have now found that the heterobimetallic complexes of this class are excellent catalyst precursors for copolymerization of ethylene and 1-hexene. Preliminary results are described here.Copolymerization of ethylene and 1-hexene was studied using the titanium-tungsten heterobimetallic dinitrogen complexes 1a-1g as catalyst precursors, in which several new complexes, 1c-1g, were synthesized from similar reactions. The constrained geometry catalyst [(t-BuNSiMe 2 C 5 Me 4 )TiCl 2 ] (CGC) 2 was chosen as a reference in the copolymerization because it also contains both cyclopentadienyl and nitrogen-based ligands on titanium. Table 1 summarizes the polymerization results in which Al(i-Bu) 3 and [Ph 3 C][B(C 6 F 5 ) 4 ] were used as cocatalysts. The heterobimetallic dinitrogen complex 1a showed a very high catalytic activity of 376 kg mmol (cat) -1 h -1 . The copolymers produced have relatively high molecular weights (M w ) 77 × 10 4 ) and unimodal molecular weight distribution (M w /M n ) 2.2), indicating that the copolymers were produced by a single active species. It should be noted that the catalytic activity of 1a was more than 3 times as high as that of CGC under the same conditions, although the 1-hexene content was one-third of that observed in CGC.Complexes 1c-1e with depe (Et 2 PCH 2 CH 2 PEt 2 ) ligands also exhibited high catalytic activity. Complex (1) Preparation and Properties of Molybdenum and Tungsten Dinitrogen Complexes. Part 72. Part 71: Arita, C.; Seino, H.; Mizobe, Y.; Hidai, M. Nabika, M.; Imai, A.; Miyashita, A.; Watanabe, T.; Johohji, H.; Oda, Y.; Hanaoka, H. ...

Synthesis and structural analysis of phenoxy-substituted half-titanocenes with different anionic ligands, Cp*TiX(Y)(O-2,6-iPr2C6H3): Effect of anionic ligands (X,Y) in ethylene/styrene copolymerization

“…Modified half-titanocenes containing anionic donor ligands of the type, Cp TiX 2 (L) (Cp = cyclopentadienyl group, X = halogen, alkyl, L = aryloxo, ketimide, phosphinimide etc. ), are promising candidates [5,[7][8][9][10][11][12][13][14][15][16][17][18][19][20], especially in terms of syntheses of new polymers by ethylene copolymerizations [9,14,17c].…”

Reaction of Methyllithium with Group 6 Phosphine Dinitrogen Complexes

“…Under thermal (Mo) or photochemical (W) activation, MeLi was found to attack at the metal by dissociative displacement of one of the N2 ligands, a behavior that can be paralleled to the one of W(0)-nitrosyl-carbonyl complexes. [26] Rare, low valent and very labile methyl-dinitrogen complexes [27][28][29][30] are thus obtained.…”

Olefin Polymerization with Half-Metallocene Catalysts

“…Ethylene polymerization and copolymerization of ethylene with 1-hexene catalyzed by heterobimetallic dinitrogen complex (7, Scheme 2.5) were reported [106]. The complex exhibited high activities, but the 1-hexene incorporation was not sufficient probably due to bulky substituent in the anionic donor ligand.…”