Synthesis and Solution Behavior of (Tetraisopropylcyclopentadienyl)calcium Acetylide Complexes. Molecular Structure of {[(C3H7)4C5H]Ca(μ-C⋮CPh)(thf)}2

• Published in: Organometallics Vol. 15; no. 23; pp. 4971 - 4976
• Main Authors: Burkey, David J, Hanusa, Timothy P
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12.11.1996
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om960126y

The reaction of (Cp4i)Ca[N(SiMe3)2](thf) (Cp4i = (i-Pr)4C5H) (1) with several terminal alkynes HC⋮CR in either toluene or hexanes produces the corresponding calcium acetylide complexes (Cp4i)Ca[C⋮CR](thf) (2) (R = Ph (2a), Fc (2b), SiMe3 (2c), Si(i-Pr)3 (2d), SiPh3 (2e)) in good yield. The (Cp4i)Ca[C⋮CR](thf) complexes do not react with excess alkyne. (Cp4i)Ca[C⋮CPh](thf) crystallizes from toluene as an acetylide-bridged dimer, [(Cp4i)Ca[μ-C⋮CPh)(thf)]2·C7H8, with a pentahapto [Cp4i]- ligand and a terminal THF ligand on each calcium. The calcium−carbon bond distances for the bridging [C⋮CPh]- ligands are 2.551(8) and 2.521(7) Å; the average Ca−C(ring) bond distance is 2.713(15) Å. As with other (Cp4i)CaX(thf) n complexes, the (Cp4i)Ca[C⋮CR](thf) compounds are kinetically stabilized against disproportionation in the solid state and in THF solution; (Cp4i)Ca[C⋮CSi(i-Pr)3](thf) is also indefinitely stable in aromatic solutions. Slow but substantial dissociation of the THF ligand in (Cp4i)Ca[C⋮CR](thf) (R = Ph, Fc, SiMe3) occurs over several days in aromatic solution, leading to partial disproportionation of the complexes into (Cp4i)2Ca and {Ca[C⋮CR]} n . THF dissociation is even more pronounced in aromatic solutions of (Cp4i)Ca[C⋮CSiPh3](thf), leading to rapid disproportionation in minutes. Attempts to isolate the unsolvated complex {(Cp4i)Ca[C⋮CPh]} n (3a) are frustrated by its facile disproportionation at elevated temperatures.