Chemistry at the alkyne-carbene intersection: a metallacyclobutene-η3-vinylcarbene equilibration.

Synthesis of a sterically congested metallacyclobutene complex has led to the first observation of metallacyclobutene-η(3)-vinylcarbene equilibration. The structure of the η(3)-vinylcarbene complex was elucidated by spectroscopy, HRMS, and ab initio computations. The vinylcarbene complex was trapped by reactions with ethyl diazoacetate and (C5H5)Co(PPh3)2 to give cobalt-diene and dicobalt complexes, respectively.

Cobalt 1,3-Diisopropyl-1H-imidazol-2-ylidene Complexes: Synthesis, Solid-State Structures, and Quantum Chemistry Calculations.

The reaction of (η(5)-C(5)H(5))Co(PPh(3))(2) with 1,3-bis(isopropyl)imidazol-2-ylidene (Im(i)Pr(2)) leads to the formation of (η(5)-C(5)H(5))Co(PPh(3))(Im(i)Pr(2)). In a similar fashion (η(5)-C(5)H(5))Co(Im(i)Pr(2))(CO) is formed from (η(5)-C(5)H(5))Co(CO)(2). The barrier to rotation about the Co-C(carbene) bond in the latter complex has been determined by variable-temperature (1)H NMR spectroscopy (13.6 kcal/mol) and by computation (13.3 kcal/mol). The structural and dynamic properties of (η(5)-C(5)H(5))Co(ImMe(2))(CO) (ImMe(2) = 1,3-dimethylimidazol-2-ylidene) and (η(5)-C(5)H(5))Co(ImAr(2))(CO) (ImAr(2) = 1,3-dimesityl-2-ylidene) were examined by quantum chemistry calculations.