Insertion Chemistry of Yttrium Complex Cp*2Y(2-pyridyl) and Molecular Structure of an Unexpected CO Insertion Product (Cp*2Y)2(.mu.-.eta.2:.eta.2-OC(NC5H4)2)

Abstract

Pyridine is metalated selectively at the 2-position by (Cp*2YH)2 to yield Cp*2Y(2-pyridyl) (1). Compound 1 reacts with H2 to give the hydride addition product Cp*2Y(NC5H6) (2). With THF and pyridine the adducts Cp*2Y(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 Cp*2-YCH2CH2(2-NC5H4) (5) and Cp*2YCH2CHMe(2-NC5H4) (6). With alkynes HCCR, C-H activation to form the acetylides Cp*2Y(CCR)(py) (7, R = H; 8, R = Me) is the dominant reaction. Also with 2-butyne C-H activation is observed yielding the propargylic metalation product Cp*2YCH2CCMe (9). 2-Pentyne gives a mixture of insertion products Cp*2Y(CEtCMe(2-NC5H4)) (10) and Cp*2Y(CMeCEt(2-NC5H4)) (11). A surprising reaction with CO to form (Cp*2Y)2(mu-eta2:eta2-OC(2-NC5H4)2) (12) was observed. The molecular structure of 12 was determined by X-ray diffraction: Space group P2(1)/c with unit cell parameters 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 sigma-bond metathesis with pyridine to form 1 and 2-ethylpyridine. By using 1 as a catalyst, alkylation of pyridine to 2-ethylpyridine is possible. 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 Cp*2Y(2-NC5H3(6-Et)) (13) and Cp*2YCHMe(2-NC5H4) (14) at 80-degrees-C (60:40). Attempts to convert 5 to 1 and 2-ethylpyridine by hydrogenolysis of the Y-C bond also resulted in the formation of a mixture of 13 and 14 (55:45). In this reaction the formation of an intermediate hydride complex seems likely because (Cp*2YH)2 and 2-ethylpyridine also give products 13 and 14.