“…[7,11,17] The MMA and MO ligands presented a supine coordination as expected for the disposition of the five-membered metallacycle folded through the O-C(1) vector, with a dihedral angle of about 103°, as in related oxametallacyclic tantalum compounds. A comparison of the O-C and C-C bond lengths of the coordinated MMA and MO ligands in complexes 1a, 2a, and 2c with the corresponding average bond lengths of vinyl ether and α,β-unsaturated carbonyl compounds (Table 1) [18] showed that the O-C and the internal C-C bond values are closer to a vinyl ether disposition (metallacycle), mainly for derivatives 1a and 2c, whereas the C(1)-C(2) bond lengths present values intermediate between these two situations.…”