Cationic Bis- and Tris(η 2 -(pyrazol-1-yl)methane) Acetyl Complexes of Iron(II) and Ruthenium(II): Synthesis, Characterization, Reactivity, and Interionic Solution Structure by NOESY NMR Spectroscopy Alceo Macchioni,* ,² Gianfranco Bellachioma, ² Giuseppe Cardaci, ² Volker Gramlich, ‡ Heinz Ru¨ egger, § Silvia Terenzi, ² and Luigi M. Venanzi § Dipartimento di Chimica, Universita` di Perugia, Via Elce di Sotto 8, 06100 Perugia, Italy, Laboratorium fu¨ r Anorg. Chemie, ETH-Zentrum, Universita¨ tstrasse 6, CH-8092 Zu¨ rich, Switzerland, and Institut fu¨ r Kristallographie und Petrographie, ETH-Zentrum, Sonneggstrasse 5, CH-8092 Zu¨ rich, Switzerland Received November 6, 1996 X The complexes trans,cis-M(PMe 3 ) 2 (CO) 2 (Me)I (M ) Fe and Ru, 1a,b) react with bis- and tris(pyrazol-1-yl)methane, in the presence of NaBPh 4 , affording trans-[M(PMe 3 ) 2 (CO)(COMe)- (pz 2 -CH 2 )]BPh 4 (2a,b) and trans-[M(PMe 3 ) 2 (CO)(COMe)(η 2 -pz 3 -CH)]BPh 4 (3a,b), respectively (pz ) pyrazolyl ring). The reactions of 1b with 5,5′-Me 2 -pz 2 -CH 2 and 3,5′-Me 2 -pz 2 -CH 2 produce trans-[Ru(PMe 3 ) 2 (CO)(COMe)(5,5′-Me 2 -pz 2 -CH 2 )]BPh 4 (4) and trans-[Ru(PMe 3 ) 2 (CO)- (COMe)(3,5′-Me 2 -pz 2 -CH 2 )]BPh 4 (5), respectively. A mixture of trans,cis-[Ru(PMe 3 ) 2 (CO) 2 - (η 1 -3,3′-Me 2 -pz 2 -CH 2 )(Me)]BPh 4 (6) and trans-[Ru(PMe 3 ) 2 (CO)(COMe)(3,3′-Me 2 -pz 2 -CH 2 )]BPh 4 (7) is obtained from reaction of 1b and 3,3′-Me 2 -pz 2 -CH 2 . The reactions of 2-7 with nucleophiles either give back the starting complex (Nu ) I - ) or analogous complexes (Nu ) Br - and Cl - ) or produce decomposition products of the complexes (Nu ) I 2 , Br 2 , Cl 2 , and OMe - ). The solid state structures of 2b and 3b were obtained using single-crystal X-ray diffraction. For all complexes, 2-7 as well as complex 8 (analogue to 2a, having a BF 4 - counterion instead of BPh 4 - ), the ion-pair structures and the localization of the counterion in solution with respect to the organometallic moiety were investigated by the detection of interionic contacts in the 1 H-NOESY and 19 F{ 1 H}-HOESY NMR spectra. Introduction The previously described methyl complexes trans,cis- M(PMe 3 ) 2 (CO) 2 (Me)I (M ) Fe 1 and Ru, 2 1a,b, respec- tively), prepared by oxidatively adding MeI to M(PMe 3 ) 2 - (CO) 3 , are a useful class of compounds for the investi- gation of the stereochemistry and energetics of the insertion reaction. It has been shown that the ionic dissociation of the M-I bond, which occurs very readily, plays an important role in the mechanism of this reaction. 3,4 From the synthetic point of view, as an ionic dissocia- tion of iodide and migration of the methyl group, with formation of the M-COMe fragment, generate two vacant sites, in principle, it should be possible to coordinate any bidentate ligand (or two monodentate ligands). However, in practice, only ligands exerting a moderate steric hindrance promote the insertion pro- cess. In the last few years, complexes containing nitrogen- coordinating ligands have become more and more important in homogeneous catalysis. 5 An increasing number of transition metal complexes containing poly- (pyrazol-1-yl)borato ligands have been synthesized. 6,7 Instead, the isosteric poly(pyrazol-1-yl)methane ligands have been studied relatively little. 8 Here, we report the results of our studies on the reactivity of complexes 1a,b with several bis- and tris- (pyrazol-1-yl)methane ligands, which has allowed us to synthesize complexes 1-8, shown in Chart 1, and to develop a methodology, based on the nuclear Over- hauser effect (NOE), for investigating the ion-pair solution structures of organometallic complexes. 9 This last point may be relevant in connection with the well- documented importance of charged organometallic com- plexes in homogeneous catalysis, 10 in particular, of the role of the counterion in activating or preventing these catalytic processes, and the lack of techniques for “directly” investigating the relative position of the counterion with respect to the organometallic fragment in solution. Results and Discussion Synthesis and Reactivity. (a) Bis(pyrazol-1-yl) Complexes. The reaction of 1a,b with pz 2 -CH 2 (pz ) ² Dipartimento di Chimica. ‡ Institut fu¨ r Kristallographie und Petrographie. § Laboratorium fu¨ r Anorganische Chemie. X Abstract published in Advance ACS Abstracts, March 15, 1997. (1) Reichenbach, G.; Cardaci, G.; Bellachioma, G. J. Chem. Soc., Dalton Trans. 1982, 847. (2) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Madami, A. Inorg. Chem. 1993, 32, 554. (3) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Reichenbach, G. Inorg. Chem. 1992, 31, 3018. (4) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Reichenbach, G. J. Organomet. Chem. 1992, 427, C37. (5) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1994, 33, 497. (6) Trofimenko, S. Chem. Rev. 1993, 93, 943. (7) Trofimenko, S. Prog. Inorg. Chem. 1986, 34, 115. (8) (a) Byers, P. K.; Canty, A. J.; Honeyman, R. T. Adv. Organomet. Chem. 1992, 34,1-65 and references therein. (b) Fajardo, M.; de la Hoz, A.; Diez-Bara, E.; Jalon, F. A.; Otero, A.; Rodriguez, A.; Tejeda, J.; Belletti, D.; Lanfranchi, M.; Pellinghelli, M. A. J. Chem. Soc., Dalton Trans. 1993, 1935. (c) Pettinari, C.; Lorenzotti, A.; Sclavi, G.; Cingolani, A.; Rivarola, E.; Colapietro, M.; Cassetta, A. J. Organomet. Chem. 1996, 496, 69. 2139 Organometallics 1997, 16, 2139-2145 S0276-7333(96)00944-2 CCC: $14.00 © 1997 American Chemical Society