J. Am. Chem. SOC.1994,116,7677-7681
7677
Single Crystal Neutron Diffraction Study of the Complex [Ru(H-H)( C5Me5)(dppm)] BF4 Which Contains an Elongated Dihydrogen Ligand Wim T. Klooster,S Thomas F. Koetzle,*l#Guochen Jia,o Tina P. Fong,? Robert H. Morris,**+and Albert0 Albinatil Contributionfrom the Chemistry Departments of Brookhaven National Laboratory, Upton, New York 11973-5000,Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, and the University of Toronto, St. George and Scarborough Campuses, Toronto, Ontario, M5S 1 AI, Canada; and Istituto di Chimica Farmaceutica, Universitb di Milano, I-20131 Milano, Italy Received February 16,1994'
Abstract: The H-H distance of the dihydrogen ligand in [Ru(H...H)(C5Me5)(dppm)]BF4 is 1.08(3) A as determined by neutron diffraction on a crystal of volume 3.2 mm3 at 15 K: monoclinic, space group P21, a = 10.833(3), b = 15.045(4), c = 10.781(2) A, /3 = 114.47(2)', V = 1599.3(7) A3, and D, = 1.473 g cm-3for Z = 2; R(F) = 0.071, R ( F ) = 0.151, R , ( F ) = 0.099 for 4198 reflections. The H-H distance, when corrected for the effects of thermal motion, lengthens slightly from 1.08(3) to l.lO(3) A. Thecomplexcontains an elongateddihydrogenligand which is symmetrically, side-on bonded to the ruthenium as one leg of a three-legged piano stool structure. The H2 ligand lies parallel to the CsMes ligand plane, an orientation where *-overlap with an a"d orbital on the metal is optimum. The T INMR 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 H2 at an intermediate stage of oxidative addition. The 'J(H,D) coupling in the Ru(H-.D) isotopomer increases with decreasing temperature; this is interpreted as a slight shortening of the H-D distance. The structural and 'H NMR data are compared for dihydrogen complexes which have been studied by single crystal neutron diffraction.
Introduction An X-ray diffraction study of the title compound failed to yield the locations of the hydrogen atoms.' However solution NMR data suggested that this complex contained an elongated dihydrogen ligand with an H-H distance of 1.1 We decided to carry out a neutron diffraction study because such a distance is intermediate to those observed so far by neutron diffraction studies of dihydrogen complexes. There is a group of complexes with short (
