Synthesis, structures, isomerism, and dynamic behavior of metalated derivatives of methyl-substituted pyrroles in triruthenium clusters

Direct thermal reaction of [Ru-3(CO)(12)] with 1-methylpyrrole leads to the cluster [Ru-3(mu-H)(mu(3),eta(3)-C4H3NMe)(CO)(9)] (1), in which metalation has occurred at the 3-position of the ring. In solution, two isomers, la,b, detected by H-1 NMR at low temperature, are in dynamic equilibrium ([1a]/[1b] = 1.8 at 260 K in CDCl3), and coalesced signals are observed above room temperature. Crystals of 1 deposited from the mixed isomer solution were shown by single-crystal X-ray structure determination to be those of isomer la. The ligand mu(3),eta(3)-C4H3NMe in cluster la is coordinated in a previously uniidentified way to the Ru-3 triangle through sigma-Ru-C bonds to two metal atoms and through an eta(2)-interaction to the third. A zwitterionic description with positive charge largely located at the NMe group and a negative charge delocalized on the metal atoms is presented. The dynamic equilibrium between la and Ib involves a hydride shift between Ru-Ru edges and a 1,2-double bond shift within the mu(3)-ligand. Clusters [Ru-3(mu-H){mu(3),eta(3)-C4H(Me)(2)NMe}(CO)(9)] (2) and [Ru-3(mu-H){mu(3),eta(3)-C4H(Me)(2)NH}(CO)(9)] (3) obtained from 1,2,5-trimethylpyrrole and 2,5-dimethylpyrrole in refluxing THF adopt crystal structures corresponding to that of la but, unlike 1, exist in only one isomeric form in solution at low temperatures. However, different products are obtained from [Ru-3(CO)(12)] and 2,5-dimethylpyrrole in refluxing toluene: [Ru-3(mu-H){mu(3),eta(3)-CH=C4H2(Me)N}(CO)(9)] (4, X-ray structure reported) and [Ru-3(mu-H){mu(3),eta(2)-CHC4H2(Me)N}-(mu-CO)(CO)(9)] (5), our proposed structure of which is based on spectroscopic evidence. Changing the solvent for the reaction has resulted in cleavage on the N-H bond to give N-bonded ligands, in activation of a methyl group, and in loss of H-2. Thermal treatment of la,b in refluxing cyclohexane leads to a third isomer, [Ru-3(mu-H)(2)(mu(3),eta(2)-C4H2NMe)(CO)(9)] (6), completely analogous to a known, structurally characterized Os complex. In more polar solvents, 6 reverts to a mixture of la and Ib.