Vanadium(IV) and -(V) Complexes with O,N-Chelating Aminophenolate and Pyridylalkoxide Ligands

Abstract

Two different monoanionic O,N-chelating ligand systems, i.e., [OC6H2(CH2NMe2)-2-Me2-4,6]- (1) and [OCMe2([2]-Py)]- (2), have been applied in the synthesis of vanadium(V) complexes. The tertiary amine functionality in 1 caused reduction of the vanadium nucleus to the 4+ oxidation state with either [VOCl3], [V(=NR)Cl3], or [V(=NR)(NEt2)3] (R = Ph, (3a, 5a), R = p-Tol (3b, 5b)), and applying 1 as a reducing agent resulted in the synthesis of the vanadium(IV) complexes [VO(OC6H2(CH2NMe2)-2-Me2-4,6)2] (4) and [V(=NPh)(OC6H2(CH2NMe2)-2-Me2-4,6)2] (6). In the case of [V(=N-p-Tol)(NEt2)(OC6H2(CH2NMe2)-2-Me2-4,6)2] (7b), the reduction was sufficiently slow to allow its characterization by 1H NMR and variable-temperature studies showed it to be a five-coordinate species in solution. Although the reaction of 1 with [V(=N-p-Tol)(O-i-Pr)3] (9b) did not result in reduction of the vanadium nucleus, vanadium(V) compounds could not be isolated. Mixtures of the vanadium(V) (mono)phenolate, [V(=N-p-Tol)(O-i-Pr)2(OC6H2(CH2NMe2)-2-Me2-4,6)] (10), and the vanadium(V) (bis)phenolate, [V(=N-p-Tol)(O-i-Pr)(OC6H2(CH2NMe2)-2-Me2-4,6)2] (11), were obtained. With the pyridylalkoxide 2, no reduction was observed and the vanadium(V) compounds [VOCl2(OCMe2([2]-Py))] (12) and [V(=N-p-Tol)Cl2(OCMe2([2]-Py)] (13) were obtained. 51V NMR showed 7b and 12 to be five-coordinate in solution, whereas for 10, 11, and 13 a coordination number of 6 was found. Compounds 12 and 13 showed decreased activity compared to their nonchelated vanadium(V) analogues when applied as catalysts in ethene polymerization. Two polymorphic forms with a difference in the V-N-C angle of 12.5 degrees have been found for 6. Crystal data: 6.Et2O, triclinic, P1, a = 11.1557(6) A, b = 12.5744(12) A, c = 13.1051(14) A, alpha = 64.244(8) degrees, beta = 70.472(7) degrees, gamma = 87.950(6) degrees, V = 1547(3) A3, Z = 2; 6.C6H6, triclinic, P1, a = 8.6034(3) A, b = 13.3614(4) A, c = 15.1044(5) A, alpha = 98.182(3) degrees, beta = 105.618(2) degrees, gamma = 107.130(2) degrees, V = 1551.00(10) A3, Z = 2; 12, orthorhombic, Pbca, a = 11.8576(12) A, b = 12.6710(13) A, c = 14.722(2) A, V = 2211.9(4) A3, Z = 8.

Vanadium(III) and -(IV) Complexes withO,N-Chelating Aminophenolate Ligands: Synthesis, Characterization and Activity in Ethene/Propene Copolymerization

“…Recently we reported that the use of ortho-aminophenolates in vanadium(V) chemistry gave rise to the formation of vanadium(IV) compounds. [5] Consequently, the formation of a vanadium(V) chloride in the reaction of 5 with SOCl 2 would immediately result in the reduction of the vanadium(V) nucleus to yield a vanadium(IV) vanadate species and a quaternary ammonium substituent (see Scheme 5). As two amine functionalities are present in the molecule, the reaction sequence can occur twice.…”

“…[4] It turns out that these ligands cannot be employed in vanadium(V) chemistry, since the ortho-amino function causes reduction of the vanadium(V) center to vanadium(IV). [5] Therefore, in our further studies we have focused on employing these ortho-aminophenolate ligands in systems with the vanadium center in the formal 3 ϩ or 4 ϩ oxidation state. …”

Transition Metal Imido Compounds as Ziegler–Natta Olefin Polymerisation Catalysts

“…[78] The imido compound {V(N-4-MeC 6 3 ] (note that ranges of activities are quoted here since many different conditions were used by these authors). In all cases very high molecular weight polymer was produced making GPC analysis difficult, and no information on the molecular weight distribution was reported.…”

Homogeneous Vanadium‐Based Catalysts for the Ziegler—Natta Polymerization of α‐Olefins

“…18). 36 Ligand a was used in vanadium (V) showed almost no activity under similar circumstances and for both complexes the activities were much lower than those of the non-chelated counterparts. We tentatively assign this decrease in activity to a smaller number of catalytically active species.…”