Synthesis of the cobalt–alkyne complex (η5-C5H5)(PPh3)Co{η2-(Me3Si)CC(CO2Et)} and structural characterization of trimethylsilyl substituted cobaltacyclopentadiene complexes derived therefrom

Abstract

The reaction of (h 5-C 5 H 5)Co(PPh 3) 2 with TMSC^C(CO 2 Et) leads to the formation of the cobaltealkyne complex (h 5-C 5 H 5)(PPh 3)Co{h 2-(Me 3 Si)C^C(CO 2 Et)} (6). In benzene-d 6 solution containing PPh 3 , 6 undergoes slow conversion to the cobaltacyclopentadiene complex (h 5-C 5 H 5)(PPh 3)Co{k 2-(TMS)C] C(CO 2 Et)C(TMS)]C(CO 2 Et)} (7, TMS ¼ SiMe 3). Alternatively, reaction of 6 and PhC^CPh forms the metallacyclopentadiene regioisomers (h 5-C 5 H 5)(PPh 3)Co{k 2-(R 1)C]C(R 2)C(Ph) ¼ C(Ph)} [9-major, R 1 ¼ SiMe 3 , R 2 ¼ CO 2 Et; 9-minor, R 1 ¼ CO 2 Et, R 2 ¼ SiMe 3). The metallacycle substitution pattern in 9major and 9-minor is readily deduced from the 1 H NMR spectral resonances of the diastereotopic ethoxycarbonyl hydrogens. When the diastereotopic hydrogens of the ethoxycarbonyl have similar chemical shifts the ester is situated on the b-carbon of the metallacycle. When the methylene hydrogens give rise to well-separated resonances the ethoxycarbonyl is situated on the a-carbon of the metallacycle. The solid state structures of 7 and 9-major were determined by X-ray crystallography.

Metal-Alkyne and Metallacyclobutene Reactivity toward a Diazoacetamide: Conversion to Highly Functionalized 1,3-Diene Complexes and Oxametallacyclopentadienes

“…The 27% yield of 12 makes it unlikely that the CO oxygen originated from adventitious oxygen or water in the reaction mixture. Furthermore, in solution, the alkyne complexes 1-TMS and 1-TIPS decomposed upon exposure to air, and the reaction of 1-TMS with 7 in 18 OH 2 -saturated C 6 D 6 resulted in decomposition of 1-TMS, with no formation of 8-TMS or 12. 13 An alternative source for the oxygen in byproduct 12 is the sulfone group of an organometallic complex (e.g., 1-TMS), or an organic compound such as TMSCCSO 2 Ph.…”