Synthesis, Structures, Isomerism, and Dynamic Behavior of Metalated Derivatives of Methyl-Substituted Pyrroles in Triruthenium Clusters Alejandro J. Arce,* Rube ´n Machado, Ysaura De Sanctis, Mario V. Capparelli, and Reinaldo Atencio Centro de Quı ´mica, Instituto Venezolano de Investigaciones Cientı ´ficas (IVIC), Apartado 21827, Caracas 1020-A, Venezuela Jorge Manzur Departamento de Quı ´mica, Universidad de Chile, Avenida Tupper 2069, Casilla 2777, Santiago, Chile Antony J. Deeming Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, Great Britain Received October 3, 1996 X Direct thermal reaction of [Ru 3 (CO) 12 ] with 1-methylpyrrole leads to the cluster [Ru 3 (µ- H)(µ 3 ,η 3 -C 4 H 3 NMe)(CO) 9 ](1), in which metalation has occurred at the 3-position of the ring. In solution, two isomers, 1a,b, detected by 1 H NMR at low temperature, are in dynamic equilibrium ([1a]/[1b] ) 1.8 at 260 K in CDCl 3 ), 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 1a. The ligand µ 3 ,η 3 - C 4 H 3 NMe in cluster 1a is coordinated in a previously unidentified way to the Ru 3 triangle through σ-Ru-C bonds to two metal atoms and through an η 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 1a and 1b involves a hydride shift between Ru-Ru edges and a 1,2-double bond shift within the µ 3 -ligand. Clusters [Ru 3 (µ-H){µ 3 ,η 3 -C 4 H(Me) 2 NMe}(CO) 9 ] (2) and [Ru 3 (µ-H){µ 3 ,η 3 - C 4 H(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 1a 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 (µ-H){µ 3 ,η 3 - CHdC 4 H 2 (Me)N}(CO) 9 ](4, X-ray structure reported) and [Ru 3 (µ-H){µ 3 ,η 2 -CHC 4 H 2 (Me)N}- (µ-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 1a,b in refluxing cyclohexane leads to a third isomer, [Ru 3 (µ-H) 2 (µ 3 ,η 2 -C 4 H 2 NMe)(CO) 9 ](6), completely analogous to a known, structurally characterized Os complex. In more polar solvents, 6 reverts to a mixture of 1a and 1b. Introduction The reaction of 1-methylpyrrole with [Os 3 (CO) 10 - (MeCN) 2 ] leads by metalation at the 2-position to the zwitterionic product [Os 3 (µ-H)(µ,η 1 -C 4 H 3 NMe)(CO) 10 ], in which the N-methylpyrrolyl ligand bridges through the 2-carbon as an alkylidene bridge (Scheme 1). 1a This compound contrasts with the stoichiometrically equiva- lent furyl and thienyl complexes, which have µ,η 1 ,η 2 - bridges of the vinyl type. We have shown that this 1-methylpyrrolyl isomer converts in solution very slowly at room temperature to an equilibrium mixture includ- ing isomers metalated at the 3-position. 1b Decarbony- lation of these 1-methylpyrrolyl complexes leads to the 1-methylpyrrol-2,3-yne complex [Os 3 (µ-H) 2 (µ 3 ,η 2 -C 4 H 2 - NMe)(CO) 9 ], the crystal structure of which shows that it contains a parallel pyrrolyne ligand. 2 Seeking to explore the chemistry of pyrroles with the iron triad, we have now examined the chemistry of [Ru 3 - (CO) 12 ] with 1-methylpyrrole and the related hetero- cycles 1,2,5-trimethylpyrrole and 2,5-dimethylpyrrole. It is known that the chemistry of thiophenes with triosmium clusters leads exclusively to C-H activation (no ring opening), 1,3 whereas with triruthenium clusters both C-H and C-S cleavages take place. 4 With iron carbonyls, C-S cleavage dominates their chemistry with thiophenes. 5 In the light of these changes of chemistry between iron, ruthenium, and osmium, we anticipated X Abstract published in Advance ACS Abstracts, March 15, 1997. (1) (a) Arce, A. J.; Manzur, J.; Ma ´ rquez, M.; De Sanctis, Y.; Deeming, A. J. J. Organomet. Chem. 1991, 412, 177. (b) Arce, A. J.; Manzur, J.; Ma ´ rquez, M.; De Sanctis, Y., unpublished results. (2) Deeming, A. J.; Arce, A. J.; De Sanctis, Y.; Day, M. W.; Hardcastle, K. I. Organometallics 1989, 8, 1408. (3) Arce, A. J.; Deeming, A. J.; De Sanctis, Y.; Machado, R.; Manzur, J.; Rivas, C. J. Chem. Soc., Chem. Commun. 1990, 1568. 1735 Organometallics 1997, 16, 1735-1742 S0276-7333(96)00847-3 CCC: $14.00 © 1997 American Chemical Society