Note Unusual Bis(imido)metalloporphyrins. The synthesis of M(4-R- TPP)(NC 6 H 4 NO 2 ) 2 (M /Ru, R /H; M /Os, R /Cl) and structural study of the osmium derivative Joanne A. Smieja a, *, Khalid Shirzad a , Michelle Roy a , Kevin Kittilstved a , Brendan Twamley b a Department of Chemistry, Gonzaga University, E. 502 Boone Avenue, Spokane, WA 99258, USA b University Research Office, University of Idaho, P.O. Box 443010, Moscow, ID 83844-3010, USA Received 25 October 2001; accepted 7 February 2002 Abstract Reaction of [Ru(TPP)] 2 with p -nitrophenylazide yields Ru(TPP)(NC 6 H 4 NO 2 ) 2 in high yield as indicated by 1 H NMR spectroscopy. All attempts to isolate a pure crystalline sample of this new bis (arylimido)ruthenium porphyrin were unsuccessful due to its high reactivity. Os(4-Cl-TPP)(NC 6 H 4 NO 2 ) 2 was synthesized and structurally characterized. The structure of Os(4-Cl- TPP)(NC 6 H 4 NO 2 ) 2 is similar to the previously characterized Os(TTP)(NC 6 H 4 NO 2 ) 2 but quite different from other bis (imido)os- mium complexes. The imido bonds in the new bis (arylimido)osmium porphyrin are bent with average Os Ã/N Ã /C bond angles of 142.58 suggesting the imido ligands act as four-electron donors. The eclipsed orientation of the imido ligands indicates the presence of one p bonding and one non-bonding molecular orbital. In solution, 1 H NMR spectroscopy indicates the structure of Os(4-Cl- TPP)(NC 6 H 4 NO 2 ) 2 is dynamic with free rotation around the imido N Ã /C and N Ã /Os bonds. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Imido; Osmium porphyrin; Ruthenium porphyrin; X-ray diffraction 1. Introduction Transition metal porphyrin complexes possessing oxo ( Ä/O), imido ( Ä/NR), and carbene ( Ä/CR 2 ) ligands are of interest as potential models for biological processes and as possible reagents for organic synthesis. Of special interest is the use of these complexes as reagents to affect alkene epoxidation, aziridination, and cyclopropanation reactions, respectively. The reactivity of these isoelec- tronic ligands when coordinated in the axial positions of a transition metal porphyrin complex depends on the identity of the metal and whether one or two ligands are present. Although many metals have been studied, the Group 8 metals have been studied the most extensively due to the biological significance of iron. In general, the reactivity of the Group 8 complexes follows the expected periodic trend with the iron analogs being the most reactive and the osmium analogs being the least reactive. In the presence of (N -(p -tolylsulfonyl)imino)phenylio- dinane, PhI /NTs, iron porphyrins catalyze the N - tosylaziridination of alkenes via an intractable (tosyli- mido)iron porphyrin intermediate [1]. On the other hand, bis (tosylimido)ruthenium [2] and bis (tosylimi- do)osmium porphyrins [3] have been isolated. The ruthenium compound is an effective stoichiometric aziridination reagent but the osmium analog is not. Further, the di-substituted Group 8 complexes are typically more reactive toward ligand transfer reactions than the mono-substituted analogs. The di-oxo ruthe- nium porphyrins epoxidize [4], the bis (tosylimido)ruthe- nium porphyrins aziridinate [2], and the bis (carbene)osmium porphyrins cylopropanate alkenes [5]. In each case, the corresponding mono-substituted porphyrins do not undergo ligand transfer reactions to alkenes [5,6] or do so less efficiently than the di- substituted analogs [7]. * Corresponding author. Tel.:  /1-509-323 6630; fax:  /1-509-323 5804. E-mail address: smieja@gonzaga.edu (J.A. Smieja). Inorganica Chimica Acta 335 (2002) 141  /146 www.elsevier.com/locate/ica 0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0020-1693(02)00839-3