Tungsten alkylidene complexes that contain the 2,6-dichlorophenylimido ligand (NArCl), W(NArCl)(CHCMe3)(ORF6)2 and W(NArCl)(CHCMe3)(Biphen)(THP) (ORF6 = OCMe(CF3)2; Biphen2- = 3,3‘-di-t-Bu-5,5‘,6,6‘-tetramethyl-1,1‘-biphenyl-2,2‘-diolate; THP = tetrahydropyran), have been prepared from W(NArCl)(CHCMe3)(OSO2CF3)2(dme). Reaction of W(NArCl)(CHCMe3)(ORF6)2 with excess ethylene gave the tungstacyclobutane complex W(NArCl)(ORF6)2(C3H6), while reaction of W(NArCl)(CHCMe3)(ORF6)2 with internal olefins gave the dimer, [W(μ-NArCl)(ORF6)2]2. W(NArCl)(CHCMe3)(Biphen)(THP) reacted with excess ethylene to give W(NArCl)(Biphen)(C3H6), which yielded W(NArCl)(Biphen)(C2H4)(THF) upon addition of THF. The tungstacyclopentane complex, W(NArCl)(Biphen)(C4H8), was formed upon treatment of W(NArCl)(Biphen)(C2H4)(THF) with ethylene. W(NArCl)(Biphen)(C3H6) decomposed to yield (inter alia) the dimeric, heterochiral methylidene complex, [W(NArCl)(Biphen)(μ-CH2)]2, which decomposed further to yield homochiral [W(NArCl)(Biphen)]2(μ-CH2CH2). Finally, [W(NArCl)(Biphen)]2(μ-CH2CH2) loses ethylene reversibly to yield [W(NArCl)(Biphen)]2, which could not be isolated in pure form. {W(μ-NArCl)[OC(CF3)2Me]2}2, W(NArCl)(Biphen)(C3H6), W(NArCl)(Biphen)(C2H4)(THF), W(NArCl)(Biphen)(C4H6), [W(NArCl)(Biphen)(μ-CH2)]2, and [W(NArCl)(Biphen)]2(μ-CH2CH2) were characterized through X-ray studies.

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.

Metal-catalyzed metathesis is a powerful method in chemical synthesis. 1 Different versions of this important transformation include catalytic ring-closing, ring-opening, 2 and cross metathesis; 3 several approaches have been devised that employ these processes in combination. 4 With the availability of chiral complexes 1a, 1b, 5 and 2, 6 which promote efficient asymmetric ring-closing

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