Polyhedron p. 2993 - 3004 (1998)
Update date:2022-08-05
Topics:
Conole, Grainne
Kessler, Maggie
Mays, Martin J.
Pateman, Giles E.
Solan, Gregory A.
Three alkyne-bridged dicobalt carbonyl complexes, [Co2(μ-RCCH)(CO)6] (R=H 1a, Me 1b, CH2OH 1c) have been reacted with Ph2P(SPh) and with the new thiophosphine ligands, Ph2P(SR′) (R′ = Bun, But), to give, initially, both mono-substituted [Co2(μ-RCCH)(CO)5{PPh2(SR′)}] [(R′ = Ph; R = H 2a, Me 2b, CH2OH 2c), (R′ = Bun; R = H 3a, Me 3b, CH2OH 3c), (R′ = But; R = H 4a, Me 4b)] and bis-substituted [Co2(μ-RCCH)(CO)4{PPh2(SPh)}2] [(R′ = Ph; R = H 5a, Me 5b, CH2OH 5c), (R′ = Bun; R = H 6a, Me 6b, CH2OH 6c), (R′ = But; R = H 7a, Me 7b)] products. Thermolysis of complexes 2-4 gives [Co2(μ-PPh2){μ-SR′C(O) CRCH}(CO)4] [(R′ = Ph; R = H 8a, Me 8b, CH2OH 8c), (R′ = Bun; R = H 9a, Me 9b), (R′ = But; R = H 10a, R = Me 10b)] in which sulphur-phosphorus bond cleavage and sulphur-carbon bond formation at the dicobalt centre have occurred to generate SR′C(O)CRCH ligands incorporated into 5-membered ring metallacycles. The transformations are regiospecific with the bulky substituents (R = H) in all cases being located adjacent to the CO moiety of the metallacycle. Treatment of the complex [Co2(μ-PPh2){μ-SPhC(O)CHCH}(CO)4] 8a with 13CO and monitoring of the reaction via 13C-{1H}-NMR spectroscopy reveals the formation of a selectively labelled species, [Co2(μ-PPh2){μ-SPh13C(O)CHCH}( 13CO)2(CO)2], in which the ketonic bridging carbonyl signal has been enhanced, while only two of the four signals due to the terminal carbonyl groups have been similarly enhanced. The mechanistic implications of this labelling study are discussed and pathways postulated for the reversible fragmentation of the SR′C(O)CRCH-bridged dicobalt systems. Single crystal X-ray diffraction studies have been performed on [Co2(μ-HCCH)(CO)4{PPh2(SBu n)}2] 6a, revealing axially substituted thiophosphine groups and on [Co2(μ-PPh2){μ-SBunC(O)CHCH} (CO)4] 9a, in which an almost planar Co-S-C-C=C metallacycle-coordinated to the other cobalt is observed.
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