A new class of coordinatively unsaturated, monomeric organoscandium compounds, Cp*2Sc-R (Cp* = (rj5-C5Me5); R = halide, hydride, alkyl, alkenyl, alkynyl, aryl), has been prepared. Cp*2Sc-Cl is obtained from reaction of ScCl3(THF)3 (THF = tetrahydrofuran) with LiCp*, and Cp*2Sc-R (R = CH3, C6H5, C6H4CH3, CH2C6H5) from treatment of Cp*2Sc-Cl with the appropriate organoalkali reagent. These organoscandium compounds react with dihydrogen rapidly to yield R-H and Cp*2Sc-H. The tetrahydrofuran adducts Cp*2ScX(THF) (X = Cl, H, CH3) are obtained upon treatment of Cp*2Sc-X with tetrahydrofuran. Rapid exchange of dihydrogen with the hydride ligands of Cp*2Sc-H and Cp*2ScH(THF) occurs even at low temperatures. Other alkyl derivatives may be conveniently prepared by treatment of Cp*2Sc-H (or Cp*2ScH(THF)) with -olefins, e.g., Cp*2ScCH2CH3 from Cp*2Sc-H and ethylene. Aliene and Cp*2Sc-H afford Cp*2Sc(7j3-C3H5). Cp*2Sc-R (R = H, CH3, aryl) reacts with pyridine to yield Cp*2Sc(C, N-j;2-C5H4N), which crystallizes in the orthorhombic space group

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The mechanism of insertion of olefins into transition metal-hydride bonds has been examined for a series of olefin hydride complexes of niobocene, permethylniobocene, tantalocene, and permethyltantalocene. The insertion rates were measured for several meta-substituted styrene complexes of permethylniobocene and found to be comparable to those found for the para-substituted analogues, indicating that the electronic effects are largely inductive in origin. An X-ray crystal structure determination for the parent styrene complex (Pka; a = 14.626 (3) A, b = 18.134 (4) A, c = 18.147 (4) A; a, @, y = 90°) offers an explanation for this observation: the phenyl ring is bent out of resonance with the olefin ?r system by 32'. A comparison of the rates for the entire series of ethylene compounds (where steric effects are minimal) indicates that there are significant electronic effects acting within this family (kNb > k,, and kcp, > kCp*; Cp = (q5:C5H5), Cp* = ($-C5Me5)). In contrast to endo exo Insertion of olefin into the Nb-H bond ( k , ) is reversible, and a lower limit for kl (>lookl) can be estimated (eq 1) from the undetectably small concentrations ('H N M R ) of the alkyl tau-(1) (a) Halpcrn, J.; Okamoto, T.; Zakchariev, A. J. Mol. Catal. 1976, 2, 65-68. (b) Byme, J. W.; Blaser, H. U.; Osborn, J. A. J. Am. Chem. SOC. 1975. 97, 3871-3873. (c) Chaudret, B. N.; Cole-Hamilton, D. J.; Wilkinson, G.