Transition metal complexes of substituted alkynes. IV. Some bridging alkynecobalt complexes

Abstract

Two new organocobalt complexes, Co2(CO)4(CF3C2CF3)3 and Co2(CO)4(CF3C3H)2- CF3C2CF3, have been isolated from the appropriate reactions of hexafluorobut-2-yne with octacarbonyldicobalt and of 3,3,3- trifluoropropyne with μ-hexafluorobut-2-yne-hexacarbonyldicobalt. The probable structures of these compounds are discussed in light of their infrared and nuclear magnetic resonance spectra. ��� The direct formation of complexes of the type Co3(CO)9CCH2R has been established in the reactions of several terminal alkynes, RC2H (R = H, CF3, C6H5), with octacarbonyldicobalt. The spectroscopic properties of the products so obtained are given.

Cyclic versus acyclic structures of six-carbon ligands in binuclear cobalt carbonyl derivatives: Some thermochemical observations

“…This is consistent with the synthesis of the lowest energy [C 6 (CF 3 ) 6 ]Co 2 (CO) 4 structure, namely the chain structure CF 3 -ch4-S (Fig. 6), as a stable molecule [9][10][11]. Table 2 reports the dissociation energies for loss of the C 6 R 6 benzene ring from the lowest-lying C 6 R 6 Co 2 (CO) n structures (n = 6, 5, 4, 3; R = H, F, CF 3 ) according to the following equation: C 6 R 6 Co 2 ðCOÞ n !…”

“…This may relate to difficulties in the cyclization of the C 6 chain with the more hindered F and CF 3 substituents relative to hydrogen on the end carbon atoms. These ''flyover'' tetracarbonyls appear to be thermodynamic ''sinks'' consistent with the experimental isolation of [C 6 (CF 3 ) 6 ]Co 2 (CO) 4 as a stable product from reactions of Co 2 (CO) 8 with CF 3 C"CCF 3 reactions [9][10][11].…”

“…So-called ''flyover'' (C 6 R 6 )Co 2 (CO) 4 complexes with an acyclic C 6 R 6 ligand connecting the two cobalt atoms as well as a Co-Co bond ( Fig. 1) have been recognized as intermediates in such cobalt carbonyl catalyzed reactions [9]. Such complexes have been isolated and characterized structurally in systems with large R substituents, e.g.…”

“…Cobalt carbonyls such as Co 2 (CO) 8 have been among the most frequently used catalyst precursors for such reactions [9][10][11]. So-called ''flyover'' (C 6 R 6 )Co 2 (CO) 4 complexes with an acyclic C 6 R 6 ligand connecting the two cobalt atoms as well as a Co-Co bond ( Fig.…”

“…The H and F substituents were chosen to provide examples of simple monoatomic substituents of rather different electronegativities. The CF 3 substituent provides an example of a bulkier substituent known to form the stable flyover [C 6 (CF 3 ) 6 ]Co 2 (CO) 4 complex [9][10][11]13] …”