Synthesis, structure, and butadiene polymerization behavior of alkylphosphine cobalt(II) complexes

Synthesis, Structure and 1,3-Butadiene Polymerization Behavior of Vanadium(III) Phosphine Complexes

“…As a general observation, the V-P bond lengths, ranging on average from 2.520(1) to 2.570(1) Å (2.537 to 2.587 Å from UM06 calculations) in the compounds here investigated, appear to be much longer than the Mt-P (Mt = metal) ones as found in tetrahedral MtCl 2 (PR n Ph 3-n ) 2 complexes, suggesting weaker bonds with scarce or null π-character for the vanadium complexes. For example, in the extended series of CoCl 2 (PR n Ph 3-n ) 2 complexes previously reported by some of us [18][19][20]39], the longest Co-P bond distance was found to be 2.437(6) Å for the more sterically hindered CoCl 2 (PCy 3 ) 2 complex [19], well below the V-P shortest distance here reported. Along the series of 1b, 1c, 1g and 2a complexes, the trend in the V-P and, in a lesser extent, the V-Cl average bond lengths generally follows the combined effect of the bulkiness of the phosphine ligand and its π-character.…”

“…The molecular weight distributions (M w /M n ) were fairly narrows, although tending to a certain broadening in some cases. Finally, by comparing the results obtained with the vanadium systems described in the present paper with those obtained with catalysts based on other transition metals phosphine complexes (e.g., Cr, Co, Fe and Ti), we can draw the following conclusions: (i) as far as catalytic activity is concerned, at the same polymerization conditions (i.e., monomer and catalyst concentration, solvent and temperature polymerization), vanadium systems are considerably less active than chromium (e.g., CrCl 2 (dmpe) 2 /MAO) [15] and cobalt (e.g., CoCl 2 (P i PrPh 2 ) 2 /MAO) [18] ones, while they are comparable to those titanium-based (e.g., TiCl 2 (dmpe) 2 /MAO) [39] and clearly more active than the iron-based ones [39] just because the latter are practically inactive; (ii) concerning instead the catalytic selectivity, vanadium systems are characterized by the lowest stereospecificity since they essentially provide poly(1,3-butadiene)s with mixed 1,4/1,2 structure, while titanium based systems allow to obtain predominantly cis-1,4 poly(1,3-butadiene)s (≥80%) [39] and cobalt based systems can give highly cis-1,4 or highly 1,2 syndiotactic poly(1,3-butadiene)s, depending on the type of phosphine ligand on the cobalt atom [18][19][20]39]. …”

Novel Allyl Cobalt Phosphine Complexes: Synthesis, Characterization and Behavior in the Polymerization of Allene and 1,3-Dienes

“…The different behavior, regarding activity and stereospecificity, exhibited by the various cobalt complexes in the polymerization of the different diene monomers is even more difficult to interpret, but it is, in some way, in agreement with that observed in the polymerization of 1,3-dienes with the catalytic systems CoCl2(PRPh2)2/MAO (R = methyl, ethyl n-propyl, i-propyl, cyclohexyl) [20,21]. We reported in previous papers that, in general, the stereoselectivity in the polymerization of 1,3-dienes with transition metal complex-based catalysts [e.g., CrCl2(L)/MAO (L = bidentate phosphine); FeCl2(L)2-MAO (L = phenanthroline); CoCl2(L)2/MAO (L = monodentate phosphine)] was strongly affected by the catalyst structure (i.e., type of ligand bonded to the metal atom) and by the monomer structure [22][23][24][25][26][27][28][29][30]. The obtained results clearly indicated that (i) the exo-exo orientation of the allyl group of the growing chain and of the coordinated monomer was strongly favored in case of 1,3-butadiene and terminally substituted monomers, and of hindered ligands on the cobalt atom; (ii) the exo-endo orientation was instead favored in case of internally substituted 1,3-butadienes (e.g., isoprene and 3-methyl-1,3-pentadiene) and low hindered ligands on the metal atom [18].…”

Butadiene Polymerization Catalyzed by Tri(aryloxo)aluminum Adduct of Cobalt Acetate

“…6 Recent academic activities have focused on the construction of metal dichloride complexes coordinated by elaborate ligands, which can be activated with methylaluminoxane (MAO) or [Ph 3 C] + B(C 6 F 5 ) 4 − , to elucidate the effect of ligand structure on the polymerization reactivity. [7][8][9][10][11][12][13][14][15][16][17][18][19] However, considering the high price of MAO or [Ph 3 C] + B(C 6 F 5 ) 4 − and the cost of constructing the elaborate complexes, these catalytic systems are seldom relevant for commercial use. A simple Ziegler-Natta system composed of an off-the-shelf metal complex and an inexpensive, simple alkylaluminum, such as triethylaluminum (AlEt 3 ), is more attractive from the perspective of commercial use.…”