Synthesis of Methyl Metallocenecarboxylates [{η4‐Ph4–n(SiMe3)nC4}Co{η5‐MeOC(O)C5H4}] (n = 1, 2) and Their Desilylation Reactions: Structural Studies and Conversion to Metallocenecarboxylic Acids and Their Alcohol Derivatives

Abstract

AbstractThe reaction of (2‐phenylethynyl)trimethylsilane (Me3SiC≡CPh) with [{η5‐MeOC(O)C5H4}Co(PPh3)2] generated in situ results in the exclusive formation of two isomers of methyl metallocenecarboxylates, namely [{trans‐η4‐Ph2(Me3Si)2C4}Co{η5‐MeOC(O)C5H4}] (1) and [{cis‐η4‐Ph2(Me3Si)2C4}Co{η5‐MeOC(O)C5H4}] (2). The reaction of [{η5‐MeOC(O)C5H4}Co(PPh3)(Me3SiC≡CPh)] with PhC≡CPh yields the methyl metallocenecarboxylate [{η4‐Ph3(Me3Si)C4}Co{η5‐MeOC(O)C5H4}] (3) along with [{η4‐Ph4C4}Co{η5‐MeOC(O)C5H4}] (4). The reactions of 1, 2 and 3 with Bu4NF in dmso results in the desilylated complexes [(trans‐η4‐Ph2H2C4)Co{η5‐MeOC(O)C5H4}] (5), [(cis‐η4‐Ph2H2C4)Co{η5‐MeOC(O)C5H4}] (6) and [(η4‐Ph3HC4)Co{η5‐MeOC(O)C5H4}] (7), respectively. Compounds 5, 6 and 7 yield the carboxylic acids [(trans‐η4‐Ph2H2C4)Co{η5‐HOC(O)C5H4}] (8), [(cis‐η4‐Ph2H2C4)Co{η5‐HOC(O)C5H4}] (9) and [(η4‐Ph3HC4)Co{η5‐HOC(O)C5H4}] (10) upon treatment with KOtBu in dmso. Reduction of 5 and 7 with LiAlH4 in thf gives the alcohol complexes [(trans‐η4‐Ph2H2C4)Co(η5‐HOCH2C5H4)] (11) and [(η4‐Ph3HC4)Co(η5‐HOCH2C5H4)] (12) in good yields. Compounds 1–7 and 11 were characterized structurally. These structural studies show interesting variations in the orientations of the cyclobutadiene‐bound phenyl groups when the silyl groups are systematically removed from the cyclobutadiene moiety. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)