Reactivity of rhenium(V) oxo Schiff base complexes with phosphine ligands: Rearrangement and reduction reactions

The symmetric rhenium(V) oxo Schiff base complexestrans-[ReO(OH2)(acac(2)en)]Cl and trans-[ReOCl(acac(2)pn)], where acac(2)en and acac(2)pn are the tetradentate Schiff base ligands N,N'-ethylenebis(acetylacetone) dimine and N,N'-propylenebis(acetylacetone) diimine, respectively, were reacted with monodentate phosphine ligands to yield one of two unique cationic phosphine complexes depending on the ligand backbone length (en vs pn) and the identity of the phosphine ligand. Reduction of the Re(V) oxo core to Re(Ill) resulted on reaction of trans-[ReO-(OH2)(acac(2)en)]Cl with triphenylphosphine or diethylphenylphosphine to yield a single reduced, disubstituted product of the general type trans-[Re-III(PR3)(2)(acac(2)en)](+). Rather unexpectedly, a similar reaction with the stronger reducing agent triethylphosphine yielded the intramolecularly rearranged, asymmetric cis-[(ReO)-O-V(PEt3)(acac(2)en)](+) complex. Reactions of trans-[(ReO)-O-V(acac(2)pn)Cl] with the same phosphine ligands yielded only the rearranged asymmetric cis-[(ReO)-O-V(PR3)(acac(2)pn)](+) complexes in quantitative yield. The compounds were characterized using standard spectroscopic methods, elemental analyses, cyclic voltammetry, and single-crystal X-ray diffraction. The crystallographic data for the structures reported are as follows: trans-[Re-III(PPh3)(2)(acac(2)en)]PF6 (H48C48N2O2P2-Re-PF6), 1, triclinic (P1), a = 18.8261(12) angstrom, b = 16.2517(10) angstrom, c = 15.4556(10) angstrom, a = 95.522(1), beta = 97.130(1)degrees, gamma = 91.350(1)degrees, V = 4667.4(5) angstrom(3), Z = 4; trans-[Re-III(PEt2Ph)(2)(acac(2)en)]PF6 (H48C32N2O2P2Re-PF6), 2, orthorhombic (Pccn), a = 10.4753(6) angstrom, b = 1 8.4315(10) angstrom, c = 18.9245(11) angstrom, V = 3653.9(4) angstrom(3), Z = 4; cis-[(ReO)-O-V(PEt3)(acac(2)en)]PF6 (H33C18N2O3PRe center dot 1.25PF(6)), 3, monoclinic (C2/c), a = 39.8194(15) angstrom, b = 13.6187(5) angstrom, c = 20.1777(8) angstrom, beta = 107.7730(10)degrees, V = 10419.9(7) angstrom(3), Z = 16; cis-[(ReO)-O-V(PPh3)(acac(2)pn)]PF6(H35C31N2O3-PRe center dot PF6), 4, triclinic (P1), a = 10.3094(10) angstrom, b =12.1196(12) angstrom, c = 14.8146(15) angstrom, alpha = 105.939(2)degrees, beta = 105.383(2)degrees, gamma = 93.525(2)degrees, V = 1698.0(3) angstrom(3), Z = 2; cis-[(ReO)-O-V(PEt2Ph)(acac(2)pn)]PF6 (H35C23N2O3PRe center dot PF6), 5, monoclinic (P2(1)/n), a = 18.1183(18) angstrom, b = 11.580(1) angstrom, c = 28.519(3) angstrom, beta = 101.861(2)degrees, V = 5855.9(10) angstrom(3), Z = 4.