INSERTION CHEMISTRY OF CP-ASTERISK(2)Y(2-PYRIDYL) AND MOLECULAR-STRUCTURE OF THE UNEXPECTED CO INSERTION PRODUCT (CP-ASTERISK(2)Y)2(MU-ETA-2-ETA-2-OC(NC5H4)2)

Pyridine is metalated selectively at the 2-position by (Cp2YH)2 to yi eld Cp2Y(2-pyridyl) (1). Compound 1 reacts with H2 to give the hydrid e addition product Cp2Y(NC5H6) (2). With THF and pyridine the adducts Cp2Y(eta2-2-pyridyl)(THF) (3) and Cp*2Y(eta1-2-pyridyl)-(py) (4) are formed. The pyridine complex 4 is not stable at higher temperatures, and after organic work up a stoichiometric amount of the C-C coupling product 2,2'-bipyridine is obtained. Ethylene and propylene react with 1 to give the monoinsertion products Cp2-YCH2CH2(2-NC5H4) (5) and Cp 2YCH2CHMe(2-NC5H4) (6). With alkynes HCCR, C-H activation to form the acetylides Cp2Y(CCR)(py) (7, R = H; 8, R = Me) is the dominant react ion. Also with 2-butyne C-H activation is observed yielding the propar gylic metalation product Cp2YCH2CCMe (9). 2-Pentyne gives a mixture o f insertion products Cp2Y(CEtCMe(2-NC5H4)) (10) and Cp*2Y(CMeCEt(2-NC 5H4)) (11). A surprising reaction with CO to form (Cp2Y)2(mu-eta2:eta 2-OC(2-NC5H4)2) (12) was observed. The molecular structure of 12 was d etermined by X-ray diffraction: Space group P2(1)/c with unit cell par ameters a = 14.194(4) angstrom, b = 17.559(4) angstrom, c = 18.717(5) angstrom, beta = 109.61(2)degrees, and Z = 4. Least-squares refinement based on 6867 reflections converged to R1 = 0.09. Compound 5 gives si gma-bond metathesis with pyridine to form 1 and 2-ethylpyridine. By us ing 1 as a catalyst, alkylation of pyridine to 2-ethylpyridine is poss ible. Also minor amounts of 2-n-butylpyridine, 2-n-hexylpyridine, and polyethylene were formed in this catalytic process. Compound 5 is not thermally stable and decomposes to the isomers Cp2Y(2-NC5H3(6-Et)) (1 3) and Cp2YCHMe(2-NC5H4) (14) at 80-degrees-C (60:40). Attempts to co nvert 5 to 1 and 2-ethylpyridine by hydrogenolysis of the Y-C bond als o resulted in the formation of a mixture of 13 and 14 (55:45). In this reaction the formation of an intermediate hydride complex seems likel y because (Cp2YH)2 and 2-ethylpyridine also give products 13 and 14.