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

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 have been found for 6. Crystal data: 6·Et2O, triclinic, P, a = 11.1557(6) Å, b = 12.5744(12) Å, c = 13.1051(14) Å, = 64.244(8), = 70.472(7), = 87.950(6), V = 1547(3) Å3, Z = 2; 6·C6H6, triclinic, P, a = 8.6034(3) Å, b = 13.3614(4) Å, c = 15.1044(5) Å, = 98.182(3), = 105.618(2), = 107.130(2), V = 1551.00(10) Å3, Z = 2; 12, orthorhombic, Pbca, a = 11.8576(12) Å, b = 12.6710(13) Å, c = 14.722(2) Å, V = 2211.9(4) Å3, Z = 8.