Synthesis and Reactivity of Aryl- and Alkyl-Rhenium(V) Imido−Triflate Compounds: An Unusual Mechanism for Triflate Substitution

Abstract

Treatment of the d2 rhenium tolylimido complex TpRe(NTol)X2 with RMgX, RLi, or organozinc reagents yields TpRe(NTol)(R)X [R = Ph, Me, Et, i-Pr, n-Bu; X = Cl or I; Tol = p-tolyl; Tp = hydrotris(1-pyrazolyl)borate] or TpRe(NTol)R2 (R = Ph, Me). Iodide for triflate metathesis with AgOTf yields TpRe(NTol)(X)OTf [X = Ph, Et, Cl, OTf (=OSO2CF3)]. Reaction of TpRe(NTol)(Et)I with excess rather than stoichiometric AgOTf generates the ethylene hydride cation [TpRe(NTol)(η2-C2H4)(H)][OTf], which slowly rearranges by ethylene insertion to form TpRe(NTol)(Et)OTf. Treatment of TpRe(NTol)(Ph)I with AgPF6 gives not iodide abstraction but rather [{TpRe(NTol)(Ph)I}2Ag][PF6], with two Re−I−Ag linkages. Excess pyridine (py) slowly displaces triflate in TpRe(NTol)Ph(OTf) (11) to give [TpRe(NTol)Ph(py)][OTf]. The reaction is first-order in 11 and first-order in py. Triflate substitution is similarly slow in the oxo-Tp* derivative, Tp*Re(O)Ph(OTf) [Tp* = HB(3,5-Me2pz)3]. These reactions are many orders of magnitude slower than...