Pyridine, isocyanide, carbodiimide and allene adducts of hexakis (trifluoromethyl t-botoxy) ditungsten. A comparison of ligand binding to W2(OtBu)6 and W2(OCMe2CF3)6

Abstract W 2 (OR) 6 compounds where R t Bu and CMe 2 CF 3 , both reversibly bind pyridine in hydrocarbon solvents to form adducts W 2 (OR) 6 L 2 . Pyridine binds more strongly to the fluoroalkoxide but the structural parameters of the compounds W 2 (OCMe 2 CF 3 ) 6 (C 6 H 5 N) 2 and W 2 (O t Bu) 6 (4-CH 3 C 6 H 4 N) 2 reveal an essentially identical W 2 O 6 N 2 core with W  W = 2.39(1) A ,, W  O = 1.92–1.95 A and W  N = 2.26(1) A . Both compounds were crystallographically characterized in the space group C 2/ c and each molecule has rigorous C 2 symmetry. Allene and 1,3-di- p -tolycarbodiimide form 1:1 adducts with W 2 (OCMe 2 CF 3 ) 6 in which the substrate is bound parallel to the M-M axis, i.e. μ - η 2 , η 2 -C 3 H 4 and μ - η 2 , η 2 -ArNCNAr-W 2 (OCMe 2 CF 3 ) 6 . Also W 2 (OCMe 2 CF 3 ) 6 and W 2 (OSi t BuMe 2 ) 6 bind two equivalents of xylylisocyanide to afford W 2 (OR) 6 ( η 1 -CNAr) 2 . For W 2 (OCMe 2 CF 3 ) 6 ( η 1 -CNAr) 2 , the molecular structure has been determined by X-ray crystallography and shows a nearly eclipsed central W 2 O 6 C 2 skeleton with W  W = 2.44(1) A , W  O = 1.94(1) A (av.) and W  C = 2.14(1) A , whereas the WWO angles span the range of 105–114°, the WWC angles are 83(1)°. Similarly, W 2 (OCMe(CF 3 ) 2 ) 4 (NMe 2 ) 2 forms a bis adduct upon reaction with the isocyanide. However, the molecular structure of W 2 (OCMe(CF 3 ) 2 ) 4 (NMe 2 ) 2 ( η 1 -CNAr) 2 shows a staggered arrangement of the two ligands about the ditungsten center where W  W = 2.382(1) A , W  O = 2.00(1) A (av.), W  N = 1.93(1) A (av.) and W  C = 2.14(1) A (av.) with a CWWC dihedral angle of 41.9°. These reactions and their products are compared for W 2 (OR) 6 compounds where R  t Bu , t BuMe 2 Si and Cme 2 CF 3 .