Synthese und Koordinationsverhalten von Selenoalkinylen R‐Se‐C≡C‐R′

Abstract

Synthesis and Coordination Ability of Selenoalkynes R ‐ Se ‐ C ≡ C ‐ R′ Several synthetic methods for the preparation of selenoalkynes R–Se–C≡C–R′ (1) are discussed. 1 reacts with octacarbonyl dicobalt to yield the η2‐π‐side‐on coordinated alkyne complexes R‐Se[(η2‐C≡C–R′)Co2(CO)6 (8) which contain a sterically hindered carbon–cobalt tetrahedrane cluster unit. The identity of compounds 1 and 8 is documented by analytical and spectroscopic [IR, MS, 1H‐, 77Se‐, and 13C‐NMR) data as well as by X‐ray analysis of C6H5)Co2‐(CO)6] (8a).

Strong distortions in hexacarbonyldicobalt complexes by push–pull effects

“…Our knowledge on the geometry of tetrahedral complexes between a CC triple bond and a [Co 2 (CO) 6 ] unit is important for understanding the mechanism of the Pauson-Khand reaction [1,2]. Especially in view of recent discussions concerning electronic effects [3][4][5] such a detailed knowledge is required.…”

“…Especially in view of recent discussions concerning electronic effects [3][4][5] such a detailed knowledge is required. Therefore, we searched for structural informations on possibly electronically perturbed alkyne-Co 2 (CO) 6 complexes. Among the 331 species listed in the Cambridge Crystallographic Data Base, 186 were not generated from symmetrically substituted alkynes.…”

“…Among the 331 species listed in the Cambridge Crystallographic Data Base, 186 were not generated from symmetrically substituted alkynes. Among those latter structures, the most prominent were the complexes of 1-6 depicted in Chart 1 [5][6][7]. In 1-5 the alkyne unit contains a chalcogen substituent on one side of the triple bond and an alkyl, aryl or ester group on the other.…”

“…In 6 two highly electronegative substituents are attached to the triple bond. Despite strong donor groups in the case of 1-3 and 5, donor and acceptor groups in 4, and strong acceptors in 6, the geometrical changes of the corresponding [Co 2 (CO) 6 ] complexes remain small. In continuation of our efforts to investigate electronically distorted alkynes, we designed a dicobaltatetrahedrane core consisting of an electron-donating group on one side and a very electron-withdrawing group on the other side of the former alkyne unit.…”

“…Co 2 (CO) 6 Co 2 (CO) 6 Scheme 1. Another parameter of interest are the torsion angles / of the pseudoaxial CO ligands; they attain values of 13-21°i n contrast to symmetrical complexes where this value is equal to 0°.…”