31 P M 1 H N NMR (162 MHz) spectrum of RuHCl[C(Me)(OCH CHOCH )](PPr i ) , showing the inequivalence of the phosphorus nuclei 2 caused 2 by the 3 2 epoxide carbon asymmetry. Starred peaks are impurities and the arrows indicate the outer lines of the AB pattern. 

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... this is the ground state structure of this molecule, reaction of RuHClL with excess C D in C H for 1 h at 20 ¡C shows ( 2 H NMR) 2 deuteration of 2 the 4 H on 6 6 Ru and also the methyl groups of coordinated PPr i . This is indicative of 3 reversible insertion of C D into the Ru È H bond and it also 2 4 indicates that the 16-electron oleÐn hydride form ( B ) is more stable than Ru(C H )ClL . Deuteration of the Pr i methyls is 2 5 2 accounted for by reversion to RuDCl[P(CH(CH ) ) ] and 3 2 3 2 then CH /RuD scrambling, as was independently established 3 for this species deuterated by two independent methods. Inser- tion of ethylene into Ru È H is also evidenced by the formation of ethane, detected by 1 H NMR. Its formation most likely occurs by alkane elimination from unstable Ru(C H )ClL , which has oxidatively added an Pr i methyl group (C 2 È H). 5 This 2 C È H activation also o†ers an additional explanation for deuteration of the Pr i methyl with C D . The metal-containing 2 4 products after CH CH elimination could not be identiÐed. 3 3 There is no isomerization of ethylene into the carbene ligand CH(CH ). 3 RuHClL also reacts within 30 min with the oleÐns 1- 2 hexene and styrene, but only 10% adduct is formed, with unreacted RuHClL comprising the bulk of the resulting 2 mixture at 25 ¡C. Both these adducts are identiÐed by a new hydride signal in 1 H NMR ( [ 23.7 ppm, m, for 1-hexene and [ 22.1 ppm, apparent triplet, for styrene) and corresponding 31 P M 1 H N NMR AB patterns centered at 37.2 ppm ( 2 J \ 287 Hz) for 1-hexene and at 85.9 ppm ( 2 J \ 34 Hz) for P v styrene. P P v P The spectroscopic similarity of the ethylene, 1-hexene, and ethyl vinyl ether adducts and large di†erence of the styrene adduct suggests that styrene may coordinate di†erently (perhaps as g 2 : g 1 h 2 -vinyl : arene or g 2 h 4 -arene). Longer reaction times yield no carbenes, but only complex mixtures of products. RuHClL rapidly e†ects a formal 1,2-hydrogen migration 2 [eqn. (7)] of vinyl ethers into the coordinated carbene. The reaction occurs for a variety of groups R, including those with SiMe , ether, alcohol, tertiary amino, Ñuoro, and epoxide functionality. 3 All products show diastereotopic Pr i methyl groups, consistent with the presence of three di†erent substituents, H, Cl and carbene, on Ru. While this reveals nothing about the square pyramidal vs . trigonal bipyramidal geometry around Ru, the hydride chemical shifts (Table 3), rather far upÐeld ( [ 21 ppm), could be interpreted in terms of the hydride being approximately trans to an empty site ( i . e ., square pyramidal). The hydride chemical shift is thus also perhaps the most generally sensitive indicator of whether there is a ligand (from functionality in the substituent R) coordinated trans to hydride. The similarity of the hydride chemi- cal shift for R Et (Table 3) to those for all components with functionalized alkyl groups in eqn. (7) suggests that none of the latter O, N or F donors coordinates to Ru. 4 Perhaps this is caused by the difficulty of forming six-membered rings. For the case of F, this conclusion is reinforced by a 19 F chemical shift that lies within 1 ppm of that of the free oleÐn, and by the absence of coupling to F in the 31 P NMR spectrum. Even at [ 80 ¡C, 19 F NMR spectra reveal that F remains uncoordi- nated. When O is from an epoxide ring, the presence of a chiral carbon b to the vinyloxy oxygen necessitates phosphine inequivalence. From the magnitude of their 31 P M 1 H N NMR (Fig. 2) chemical shift di†erence [ * d \ only 0.09 ppm (15 Hz), 2 J \ 220 Hz], it is safe to assume that the chiral center is P v P far from the phosphorus atoms, indicating no epoxide binding to ruthenium. The case of dihydrofuran [eqn. (8)] is interesting as it shows that a cyclic internal vinyl ether is also easily isomerized. 5 The hydride chemical shift is consistent with no donation to Ru ...