Reactivity of Rhenium(V) Oxo Schiff Base Complexes with Phosphine Ligands: Rearrangement and Reduction Reactions

The symmetric rhenium(V) oxo Schiff base complexes trans-[ReO(OH2)(acac2en)]Cl and trans-[ReOCl(acac2pn)],
where acac2en and acac2pn are the tetradentate Schiff base ligands N,N‘-ethylenebis(acetylacetone) diimine 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(III) resulted on reaction of trans-[ReO(OH2)(acac2en)]Cl with triphenylphosphine or diethylphenylphosphine to yield a single reduced, disubstituted product
of the general type trans-[ReIII(PR3)2(acac2en)]+. Rather unexpectedly, a similar reaction with the stronger reducing
agent triethylphosphine yielded the intramolecularly rearranged, asymmetric cis-[ReVO(PEt3)(acac2en)]+ complex.
Reactions of trans-[ReVO(acac2pn)Cl] with the same phosphine ligands yielded only the rearranged asymmetric
cis-[ReVO(PR3)(acac2pn)]+ 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-[ReIII(PPh3)2(acac2en)]PF6 (H48C48N2O2P2Re·PF6), 1, triclinic (P1̄), a = 18.8261(12) Å, b = 16.2517(10) Å, c = 15.4556(10) Å, α = 95.522(1)°, β =
97.130(1)°, γ = 91.350(1)°, V = 4667.4(5) Å3, Z = 4; trans-[ReIII(PEt2Ph)2(acac2en)]PF6 (H48C32N2O2P2Re·PF6),
2, orthorhombic (Pccn), a = 10.4753(6) Å, b =18.4315(10) Å, c = 18.9245(11) Å, V = 3653.9(4) Å3, Z = 4;
cis-[ReVO(PEt3)(acac2en)]PF6 (H33C18N2O3PRe·1.25PF6), 3, monoclinic (C2/c), a = 39.8194(15) Å, b = 13.6187(5)
Å, c = 20.1777(8) Å, β = 107.7730(10)°, V = 10419.9(7) Å3, Z = 16; cis-[ReVO(PPh3)(acac2pn)]PF6 (H35C31N2O3PRe·PF6), 4, triclinic (P1̄), a = 10.3094(10) Å, b =12.1196(12) Å, c = 14.8146(15) Å, α = 105.939(2)°, β =
105.383(2)°, γ = 93.525(2)°, V = 1698.0(3) Å3, Z = 2; cis-[ReVO(PEt2Ph)(acac2pn)]PF6 (H35C23N2O3PRe·PF6), 5,
monoclinic (P21/n), a = 18.1183(18) Å, b = 11.580(1) Å, c = 28.519(3) Å, β = 101.861(2)°, V = 5855.9(10) Å3,
Z = 4.