Pyridylazole chelation of oxorhenium(V) and imidorhenium(V).: Rates and trends of oxygen atom transfer from ReVO to tertiary phosphines

The concerned azoles are 2-(2-pyridyl)benzoxazole (pbo) and 2-(2-pyridyl)benzthiazole (pbt). These react with ReOCl3(PPh3)(2) in benzene, affording (ReOCl3)-O-V(pbo) and (ReOCl3)-O-V(pbt), which undergo facile oxygen atom transfer to PPh2R (R = Ph, Me) in dichloromethane solution, furnishing Re-III(OPPh2R)Cl-3(pbo) and Re-III(OPPh2R)Cl-3(pbt). The oxo species react with aniline in toluene solution, yielding the imido complexes Re-V(NPh)Cl-3(pbo) and Re-V-(NPh)Cl-3(pbt). The X-ray structures of pbt, ReOCl3(pbt), Re(OPPh3)Cl-3(pbt), and Re(NPh)Cl-3(pbo) are reported. The lattice of plot consists of stacked dimers. In all the complexes the azole ligand is N,N-chelated and the ReCl3 moiety is meridionally disposed. In ReOCl3(pbt) the metal-oxo bond length is 1.607(9) Angstrom. The second-order rates and the associated activation parameters of the oxygen atom transfer reactions of the (ReO)-O-V chelates with PPh2R are reported. The large and negative entropy of activation (similar to -24 eu) is consistent with an associative pathway involving nucleophilic phosphine attack. The rate increases with phosphine basicity (PPh2Me > PPh3) and azole heteroatom electronegativity (O(pbo) > S(pbt)). Logarithmic rate constants for ReOCl3(pbo), ReOCl3(pbt), and ReOCl3-(pal) are found to correlate linearly with (ReO)-O-VI/(ReO)-O-V reduction potentials (pal is pyridine-2-(N-p-tolyl)aldimine). The relatively low rate constant of ReOCl3(pbt) compared to that of ReOCl3(pal) is consistent with the observed shortness of the metal-oxo bond in the former. Crystal data are as follows: (pbt) empirical formula C12H8N2S, crystal system orthorhombic, space group Pca2(1), a = 13.762(9) Angstrom, b = 12.952(8) Angstrom, c = 11.077(4) Angstrom, V = 1974(2) Angstrom(3), Z = 8; (ReOCl3(pbt)) empirical formula C12H8Cl3N2OSRe, crystal system monoclinic, space group P2(1)/c, a = 11.174(7) Angstrom, b = 16.403(10) Angstrom, c = 7.751(2) Angstrom, beta = 99.35(4)degrees, V = 1401.8(13) Angstrom(3), Z = 4; (Re(NPh)Cl-3(pbo)) empirical formula C18H13C13N3ORe, crystal system monoclinic, space group P2(1)/c, a = 9.566(6) Angstrom, b = 16.082(8) Angstrom, c 11.841(5) Angstrom, beta = 94.03(4)degrees, V = 1817(2) Angstrom(3), Z = 4.