Imido Alkylidene Bispyrrolyl Complexes of Tungsten Thorsten Kreickmann, Stefan Arndt, Richard R. Schrock,* and Peter Mu ¨ller Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 ReceiVed July 16, 2007 We have prepared tungsten bispyrrolyl (Pyr) or bis-2,5-dimethylpyrrolyl (Me 2 Pyr) complexes W(NAr)- (CHCMe 2 Ph)(η 1 -Pyr) 2 (DME) (1), W(NAr)(CHCMe 2 Ph)(η 1 -Me 2 Pyr)(η 5 -Me 2 Pyr) (2), W(NAr Cl )(CHCMe 3 )- (η 1 -Pyr) 2 (DME) (3b), and W(NAr Cl )(CHCMe 3 )(η 1 -Me 2 Pyr)(η 5 -Me 2 Pyr) (4) (Ar ) 2,6-diisopropylphenyl, Ar Cl ) 2,6-dichlorophenyl) in excellent yields by treating the appropriate W(NR)(CHCMe 2 R′)(OTf) 2 - (DME) species with LiPyr or LiMe 2 Pyr. Compounds 2 and 4 react with ethylene slowly to yield stable methylene complexes, W(NAr)(CH 2 )(η 1 -Me 2 Pyr)(η 5 -Me 2 Pyr) (5) and W(NAr Cl )(CH 2 )(η 1 -Me 2 Pyr)(η 5 - Me 2 Pyr) (6). In contrast, treatment of what is believed to be a fortuitous 1:1 mixture of 3b and [W(NAr Cl )(CHCMe 3 )(η 1 -Pyr) 2 ][W(NAr Cl )(CHCMe 3 )(η 1 -Pyr)(η 5 -Pyr)] with ethylene leads to formation of [W(µ-NAr Cl )(η 1 -Pyr) 2 ] 2 (7) in moderate (54%) yield. Compounds 2 and 4 react with [HNMe 2 Ph]- [B(Ar F ) 4 ] (Ar F ) 3,5-(CF 3 ) 2 C 6 H 3 ) in dichloromethane to yield cationic species that contain one η 5 -Me 2 - Pyr ligand and one 2,5-dimethylpyrrolenine ligand formed through addition of a proton to C(2) of a dimethylpyrrolyl ligand, e.g., [W(NAr Cl )(CHCMe 3 )(Me 2 Pyr){NC 4 (H 3 -2,3,4)(Me 2 -2,5)}] + [B(Ar F ) 4 ] - (9). X-ray studies were carried out on 1, 2, 6, 7, and 9. Introduction We reported recently that bispyrrolyl (or bispyrrolide) 1 molybdenum complexes can be prepared that have the empirical formula Mo(NR)(CHCMe 2 R′)(pyrrolyl) 2 (where pyrrolyl ) NC 4 H 4 (Pyr) 2 or 2,5-NC 4 H 2 Me 2 (Me 2 Pyr), 3 R′ ) Ph or Me, and R ) 2,6-diisopropylphenyl, 1-adamantyl, or 2-CF 3 C 6 H 4 ). An X-ray study of Mo(N-2,6-i-Pr 2 C 6 H 3 )(CHCMe 2 Ph)(Pyr) 2 showed it to be a dimer in which the coordination at one end is of the type Mo(NAr)(CHCMe 2 Ph)(η 1 -Pyr)(η 5 -Pyr), where Mo has an 18-electron count, and that at the other end is of the type Mo(NAr)(CHCMe 2 Ph)(η 1 -Pyr) 2 (donor), where the lone pair on the nitrogen atom in the η 5 -Pyr ligand is bound to the second Mo. Low-temperature NMR spectra are consistent with the dimer being the lowest energy species in solution. In contrast, low-temperature NMR studies of Mo(NR)(CHCMe 2 R′)(Me 2 - Pyr) 2 species suggested that they are 18e monomers of the type Mo(NR)(CHCMe 2 R′)(η 1 -Me 2 Pyr)(η 5 -Me 2 Pyr). 3 Both Pyr and Me 2 Pyr complexes are highly fluxional on the NMR time scale in solution at room temperature as a consequence of intercon- version of η 1 -pyrrolyl and η 5 -pyrrolyl ligands. The Pyr and Me 2 - Pyr complexes are of interest in their own right in view of the paucity of pyrrolyl complexes in general, and especially those of Mo and W. However, we are interested in pyrrolyl complexes primarily as precursors to monoalkoxide or bisalkoxide com- plexes that are formed upon addition of alcohols to bispyrrolyl complexes in solution 2,3 or upon addition of bispyrrolyl complexes to SiOH on a silica surface. 4 We became interested in extending this type of chemistry to tungsten. In this paper we report W(NR)(CHCMe 2 R′)(pyrrolyl) 2 complexes where R is 2,6-diisopropylphenyl or 2,6-dichlorophenyl and the pyrrolyl is Pyr or Me 2 Pyr, along with some reactions involving them. Results Synthesis of Pyrrolyl Complexes That Contain the NAr Ligand. The reaction between W(NAr)(CHCMe 2 Ph)(OTf) 2 - (DME) (Ar ) 2,6-i-Pr 2 C 6 H 3 , OTf ) OSO 2 CF 3 ) 5 and 2 equiv of LiNC 4 H 4 in toluene at 20 °C produces yellow W(NAr)- (CHCMe 2 Ph)(Pyr) 2 (DME) (1) in 80% yield (eq 1). Compound 1 can be recrystallized from pentane. An X-ray study showed 1 to have a structure analogous to that of Mo(NAr)(CHCMe 3 )- (OTf) 2 (DME), 6 i.e., a distorted octahedron containing a syn alkylidene ligand, trans η 1 -pyrrolyl ligands, and dimethoxy- ethane bound trans to the imido and alkylidene ligands (Table 1 and Figure 1). Bond distances and angles are unexceptional. 7 (See figure caption for selected values.) Compound 1 has an 18-electron count at the metal if the lone pair on the imido nitrogen is included. The proton NMR spectrum of 1 at 20 °C in C 6 D 6 shows sharp resonances for two types of pyrrolyl protons at 6.77 and 6.44 * Corresponding author. E-mail: rrs@mit.edu. (1) In analogy with cyclopentadienide, “pyrrolide” describes an often main group salt containing the anion of pyrrole, e.g., lithium pyrrolide. “Pyrrolide” has also been employed to describe transition metal species, sometimes regardless of the hapticity and mode of coordination of the pyrrolide. However, in analogy with cyclopentadienyl, “pyrrolyl” appears to be the preferred term for transition metals. Therefore “pyrrolyl” is the descriptor employed in this paper. (2) Hock, A.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2006, 128, 16373. (3) Singh, R.; Czekelius, C.; Schrock, R. R.; Mu ¨ ller, P. Organometallics 2007, 26, 2528. (4) Blanc, R.; Berthoud, R.; Salameh, A.; Basset, J.-M.; Cope ´ret, C.; Singh, R.; Schrock, R. R. J. Am. Chem. Soc. 2007, 128, 8434. (5) Schrock, R. R.; DePue, R. T.; Feldman, J.; Yap, K. B.; Yang, D. C.; Davis, W. M.; Park, L.; DiMare, M.; Schofield, M.; Anhaus, J.; Walborsky, E.; Evitt, E.; Kru ¨ger, C.; Betz, P. Organometallics 1990, 9, 2262. (6) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare, M.; O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875. (7) Schrock, R. R. Chem. ReV. 2002, 102, 145, and references therein. 5702 Organometallics 2007, 26, 5702-5711 10.1021/om7006985 CCC: $37.00 © 2007 American Chemical Society Publication on Web 10/11/2007