H/D exchange via reversible pyridine ortho-metallation, and competition between CH oxidative addition and CO coordination in hydrido-carboxyl triangular rhenium clusters: a 1H-NMR investigation. X-ray crystal structure of the anion [Re3( μ-H)2(CO)11(Py)]−

摘要: The triangular cluster anion [Re3(μ-H)3(μ-NC5H4)(CO)10]− (2), containing an ortho-metallated pyridine bridging a edge, undergoes in acetone solution selective H/D exchange between the basal hydridic site and α-position of pyridine, with k = 1.9(1) × 10−6 s−1, at room temperature. process was studied by NMR on partially deuterated derivative [Re3(μ-H)2(μ-D)(μ-NC5D4)(CO)10]− equilibrium isotope effect observed, concentration isotopomer C-bound deuterium being about double that Re-bound deuterium. In pyridine-d5 solutions, contrast, preferential deuteration hydrides lateral edges rate half (k 2.9(1) 10−5 s−1 302 K for latter process). processes both solvents have been rationalized as arising from reversible reductive elimination pyridine. different behavior two is discussed. presence CO, 2 gave [Re3(μ-H)2(CO)12]− (4, t12 ≈ 48 h) solution, while it novel [Re3(μ-H)2(CO)11(Py)]− (3). py-d5, under resonances decreased same absence CO. competition ratio r CO coordination ortho-metallation intermediate generated CH has estimated 0.45(15). reaction [Re3(μ-H)4(CO)10]− (1) follows parallel paths, affording compounds 3 2, latter, turn, converting into slower rate. disappearance 1 measured 2.1(2) 10−4 K) value pathways leading to respectively, found be 0.5(1). Under high H2 pressure, slowly transforms back unsaturated parent 1, showing complete reversibility reaction. structure (3), [NEt4]+ salt, investigated X-ray analysis. crystals are monoclinic, space group P21/c, 14.327(3), b 12.310(2), c 17.437(3) A, β 91.67(2)° Z 4. refinements, performed full-matrix least-squares basis 2064 significant [I > 2σ(I)] reflections, final agreement indices R wR2 0.0397 0.0835, respectively. contains isosceles triangle rhenium atoms, one shorter edge [3.025(1) A], longer hydrogen-bridged [3.202(1) 3.209(1) A]; bears eleven terminal groups N-bonded molecule [ReN 2.21(2) A].