Synthesis of Methyl Metallocenecarboxylates [{η⁴‐Ph_4–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

The 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)

Synthesis, reactivity and structural studies of (η5-methylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt and its derivatives

“…2) the cobalt atom makes a distance of 1.680(1) Å with the centroid of the Cp ring and is at a distance of 1.700(1) Å from the centroid of cyclobutadiene ring which is similar to the distances for the carbomethoxy derivative of (g 5 -Cp)Co(g 4 -C 4 Ph 4 ) of 1.679(1) Å A 0 and 1.689(1) Å A 0 , respectively [20]. The four phenyl rings of compound 4 make angles of 25.29°, 32.23°, 38.84°and 44.84°with the cyclobutadiene ring.…”

Chemistry of the highly stable hindered cobalt sandwich compound (η5-Cp)Co(η4-C4Ph4) and its derivatives

“…79 desilylated using NMe 4 F.3H 2 O in DMSO to give compound 342 in 89% yield [130]. Similarly, compound 343 prepared using (2-phenylethynyl)trimethylsilane can be easily desilylated to give compound 344 [131]. Compound 345 has been synthesized using the appropriate cyclic diyne with CpCo(COD) in 46% yield [132].…”