Oxo Ligand Reactivity in the [ReO(2)L(4)](+) Complex of 1-Methylimidazole. Preparation and Crystal Structures of Salts Containing the ReOL(4)(3+) Core and Apical CH(3)O(-), BF(3)O(2)(-), and (CH(3)O)(2)PO(2)(-) Groups.

Abstract

The oxo group of [ReO(2)(1-MeIm)(4)](+) can be methylated with excess methyl trifluoromethanesulfonate in CH(2)Cl(2) under mild conditions, leading to [ReO(OCH(3))(1-MeIm)(4)](CF(3)SO(3))(2), which is converted to the B(C(6)H(5))(4)(-) and PF(6)(-) salts. When the reaction is carried out in methanol in the presence of excess PF(6)(-), the phosphate ester complex [ReO{OP(O)(OCH(3))(2)}(1-MeIm)(4)](PF(6))(2) is isolated. [ReO(2)(1-MeIm)(4)](+) in the presence of acid, 2,2-dimethoxypropane, and excess BF(4)(-) transforms to the oxo-boron adduct [ReO(OBF(3))(1-MeIm)(4)](+). The presence of the trans-O=Re-OR core was demonstrated by crystallographic studies on one compound of each type: [ReO(OCH(3))(1-MeIm)(4)](PF(6))(2), tetragonal, P4/ncc, Z = 4, a = 13.022(3) Å, c = 17.218(5) Å, R = 0.0271; [ReO{OP(O)(OCH(3))(2)}(1-MeIm)(4)](PF(6))(2).toluene, monoclinic, P2(1)/c, Z = 4, a = 14.165(4) Å, b = 13.052(6) Å, c = 20.931(6) Å, beta = 95.83(2) degrees, R = 0.0373; [ReO(OBF(3))(1-MeIm)(4)](I(3)), monoclinic, P2(1)/c, Z = 4, a = 13.373(4) Å, b = 13.237(3) Å, c = 16.689(6) Å, beta = 103.67(3) degrees, R = 0.0445. The IR spectra show nu(Re=O) vibrations near 960 cm(-)(1) in all cases. The solution UV-vis spectra of the CH(3)O(-) and BF(3)O(2)(-) compounds are similar to that of the parent oxo-hydroxo [ReO(OH)(1-MeIm)(4)](2+) species, whereas the visible spectrum of the blue phosphate ester compound resembles that of the oxo-aquo [ReO(OH(2))(1-MeIm)(4)](3+) ion. The compounds were also characterized by solution (1)H, (13)C, and (31)P NMR spectroscopy. This work confirms earlier conclusions that ReO(2)L(4)(+) units with good sigma-donor imidazole ligands are more resistant to ligand loss than the pyridine analogues.