Synthesis of Methyl Metallocenecarboxylates [{η 4 ‐Ph 4– n (SiMe 3 ) n C 4 }Co{η 5 ‐MeOC(O)C 5 H 4 }] ( n = 1, 2) and Their Desilylation Reactions: Structural Studies and Conversion to Metallocenecarboxylic Acids and Their Alcohol Derivatives

The reaction of (2‐phenylethynyl)trimethylsilane (Me 3 SiC≡CPh) with [{η 5 ‐MeOC(O)C 5 H 4 }Co(PPh 3 ) 2 ] generated in situ results in the exclusive formation of two isomers of methyl metallocenecarboxylates, namely [{ trans ‐η 4 ‐Ph 2 (Me 3 Si) 2 C 4 }Co{η 5 ‐MeOC(O)C 5 H 4 }] ( 1 ) and [{ cis ‐η 4 ‐Ph 2 (Me 3 Si) 2 C 4 }Co{η 5 ‐MeOC(O)C 5 H 4 }] ( 2 ). The reaction of [{η 5 ‐MeOC(O)C 5 H 4 }Co(PPh 3 )(Me 3 SiC≡CPh)] with PhC≡CPh yields the methyl metallocenecarboxylate [{η 4 ‐Ph 3 (Me 3 Si)C 4 }Co{η 5 ‐MeOC(O)C 5 H 4 }] ( 3 ) along with [{η 4 ‐Ph 4 C 4 }Co{η 5 ‐MeOC(O)C 5 H 4 }] ( 4 ). The reactions of 1 , 2 and 3 with Bu 4 NF in dmso results in the desilylated complexes [( trans ‐η 4 ‐Ph 2 H 2 C 4 )Co{η 5 ‐MeOC(O)C 5 H 4 }] ( 5 ), [( cis ‐η 4 ‐Ph 2 H 2 C 4 )Co{η 5 ‐MeOC(O)C 5 H 4 }] ( 6 ) and [(η 4 ‐Ph 3 HC 4 )Co{η 5 ‐MeOC(O)C 5 H 4 }] ( 7 ), respectively. Compounds 5 , 6 and 7 yield the carboxylic acids [( trans ‐η 4 ‐Ph 2 H 2 C 4 )Co{η 5 ‐HOC(O)C 5 H 4 }] ( 8 ), [( cis ‐η 4 ‐Ph 2 H 2 C 4 )Co{η 5 ‐HOC(O)C 5 H 4 }] ( 9 ) and [(η 4 ‐Ph 3 HC 4 )Co{η 5 ‐HOC(O)C 5 H 4 }] ( 10 ) upon treatment with KO t Bu in dmso. Reduction of 5 and 7 with LiAlH 4 in thf gives the alcohol complexes [( trans ‐η 4 ‐Ph 2 H 2 C 4 )Co(η 5 ‐HOCH 2 C 5 H 4 )] ( 11 ) and [(η 4 ‐Ph 3 HC 4 )Co(η 5 ‐HOCH 2 C 5 H 4 )] ( 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)