Trinuclear Cluster Complexes Containing the Furyne Ligand:  Synthesis, Structure, and Properties of the Cycloalkyne Complexes (CpCo)n(Cp*Co)3-n(CO)(μ3-η2-C4H4O) (n = 3, 2)

<p> Cyclopentadienyl-based tricobalt clusters containing the cyclic <em> furyne </em> ligand, CH2C&vellip;CCH2O, have been prepared by the pyrolysis of the butynediol complexes (CpCo)3(CO)(RCCR), 1, and (CpCo)2(Cp*Co)(CO)(RCCR), 2 (R = CH2OH). The solid state structures of the furyne complexes, (CpCo)3(CO)(&mu;3-&eta;2-CH2C&vellip;CCH2O), 3, and (CpCo)2(Cp*Co)(CO)(&mu;3-&eta;2-CH2C&vellip;CCH2O), 4, verify the presence of the five-membered heterocycle, which formally contains an alkyne group interacting with the tricobalt framework. Chemically and electrochemically reversible one-electron oxidative and reductive couples are observed for 3 at +0.235 and &minus;1.466 V (CH2Cl2 solution, Pt electrode, Fc0/+1 = +0.482 V), respectively, which are similar to redox features observed for noncyclic analogues. At 171 K, the methylene signals of the furyne ligand in 4 are observed as doublets, indicating that furyne rotation is slow at this temperature. Reversible coalescence of the methylene signals occurs at 195 K, and at room temperature, a single sharp methylene resonance is observed. Total line shape analysis of the coalescing spin system yields the activation parameters for the motion of the furyne ring:&thinsp; &Delta; <em> G </em> ⧧ (300 K) = 39.4(2) kJ/mol, &Delta; <em> S </em> ⧧ = &minus;18(2) J/mol, and &Delta; <em> H </em> ⧧ = 34.0(4) kJ/mol.</p>