Abstract

The H-H distance of the dihydrogen ligand in [Ru(H....H)(C{sub 5}Me{sub 5})(dppm)]BF{sub 4} is 1.08(3) A as determined by neutron diffraction on a crystal of volume 3.2 mm{sup 3} at 15 K: monoclinic, space group P2{sub 1}, a = 10.833(3), b = 15.045(4), c = 10.781(2) A, {beta} = 114.47(2){degree}, V = 1599.3(7) A{sup 3}, and D{sub c} = 1.473 g cm{sup -3} for Z = 2; R(F) = 0.071, R(F{sup 2}) = 0.151, R{sub w}(F{sup 2}) = 0.099 for 4198 reflections. The H-H distance, when corrected for the effects of thermal motion, lengthens slightly from 1.08(3) to 1.10(3) A. The complex contains an elongated dihydrogen ligand which is symmetrically, side-on bonded to the ruthenium as one leg of a three-legged piano stool structure. The H{sub 2} ligand lies parallel to the C{sub 5}Me{sub 5} ligand plane, an orientation where {pi}-overlap with an orbital on the metal is optimum. The T{sub 1} NMR method gives an H H distance of 1.10(1) A for the case of restricted rotation. The present structure provides a model for coordinated H{sub 2} at an intermediate stage of oxidative addition. The {sup 1}J(H, D) coupling in the Ru(H-D) isotopomer increases with decreasing temperature: this is interpretedmore » as a slight shortening of the H-D distance. The structural and {sup 1}H NMR data are compared for dihydrogen complexes which have been studied by single crystal neutron diffraction. 34 refs., 3 figs., 4 tabs.« less

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