289 Journal of Organometallic Chemistry, 424 (1992) 289-300 Elsevier Sequoia S.A., Lausanne JOM 22118 Unsolvated lanthanidocene hydrides and borohydrides. X-Ray crystal structure of [( q5-C5HBtBu2),Ln(p-H)], (Ln = Ce, Sm) and [(r5-C,H,‘Bu,),Sm(~-BH,)], Yurii K. Gun’ko, Boris M. Bulychev l Department of Chemistry, M. K Lomonosoc Moscow State lJnicersi&, Moscow B-234, 119899 (USSR) Grigorii L. Soloveichik l Institute qf Chemical Physics, USSR Academy of Sciences, Chernogolocka 142432 (USSR) and Vitalii K. Belsky L.Ya. Karpov Physico-Chemical Institute, Moscow 103064 (USSR) (Received June 18, 1991) Abstract The treatment of lanthanidocene alumohydrides (Cp;LnAIH,.LJ2 having bulky cyclopentadienyl ligands C,H,‘Bu, with an excess of triethylaminalane yields related unsolvated hydrides [(C,H,‘Bu,),Ln(~-H)]~ (Ln = Ce (I), Sm (II)). Complex II was also obtained by the redox reaction vf Cp;Sm.THFOwith AIH,.NEt,. Crystals of I are triclinic, Pi, a=10.741(2) A, b= 11.302(2) A, c = 12.425(2) A, a = 6520(l)“, p =73.93(l)“, y =89.69(l)“, Z = 2, R = 0.031, R, = 0.034. Crystals of II are triclinic, Pi, a = 10.723(2) A, b = 11.305(3) A, c = 12.289(3) A, a = 115.73(2)“, /3= 105.15(2) O, y = 90.43(2) O, Z = 2, R = 0.054, R, = 0.057. Unlike the lanthanidocene alumohydrides the related borohydrides are resistant to Lewis bases and crystallize from donor solvents as unsolvated dimers (CpGLnBH,),. For complex ((C,H,‘BU,),S~(CL-BH,)~, WI) X-ray structural information is conve- nient with the presence of bridge [(~3-H)2B(~2-H)Zl groups. Crystals of VI are rhombic, Pnaa, a = 24.448(4) A, b = 13.023(2) A, c = 17.218(3) A, Z = 8, R = 0.088, R, = 0.084. Introduction Unsolvated hydrides of lanthanidocenes attract the attention of researchers owing to their intriguing catalytic properties in some processes, e.g. C-H bond activation in alkanes [1,2] and hydrogenation of alkynes [31. The structure and degree of association of these compounds depend very much on the nature of the ligand and on metal atom size and may vary from polymers of compounds with an ordinary C,H, ligand [4] to trimers of [(775-C,H,Me,),Y(CL-H)]~ [51 and dimers of [(775-C,Me,),Lu(~-H)]* [ll and [(175-C,H:Bu,),Lu(~-H)1, [61. Methods of prepa- ration of homonuclear metallocene hydrides are based on hydrogenolysis [2-41 and