Preparation of bis and tris(arylimido) complexes of rhenium(VII), including bis(arylimido) neopentylidene complexes, candidates as olefin metathesis catalysts

Polyhedron Vol. 7, No. 19/20, pp. 184-1853, Printed in Great Britain

0277~5387188 Q 1988 Pamon

1988

S3.00+.00 Press

plc

PREPARATION OF BIS AND TRIS(ARYLIMID0) COMPLEXES OF RHENIUM(VII), INCLUDING BIS(ARYLIMID0) NEOPENTYLIDENE COMPLEXES, CANDIDATES AS OLEFIN METATHESIS CATALYSTS ANDREW D. HORTON

and RICHARD

R. SCI-IROCK”

Department of Chemistry 6-331, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. Abstract-The reaction between ReO,(OSiMe,) and 3 equiv. of ArNCO (Ar = 2,6-C,H\Pr,) yields mixtures of (ArN)3Re-O-Re(0)(NAr)2 (l), Re(NAr),(OSiMe,) (2a), and what is proposed to be Re(0)(NAr)2(OSiMe3) (3). Conditions can be altered in order to yield 1 or 2a in satisfactory yield, but 3 has not been prepared in pure form. Analogous reactions between Re03(0SiMe3) and 3 equiv. of Ar’NCO (Ar’ = 2,6-C&I,MeJ yield (Ar’N),Rti -Re(NAr’), (4) and Re(NAr’)3(0SiMe3) (2b), while those between ReO,(OSiMe,) and 3 equiv. of Ar”NC0 (Ar” = 2,6-C,H3ClJ yield only Re(NAr”),(OSiMe,) (2c). Complexes of the type Re(NR)3(CH21Bu) (R = Ar, Ar’, Ar”) have been prepared straightforwardly. Complexes of the type Re(NR),Cl,(py) (6) can be prepared by treating tris(imido) complexes 2 with 3 equiv. of pyHC1. These can be alkylated to give mononeopentyl bis(imido) derivatives, Re(NR)2(CH2’Bu)C12 (8), in high yield. Dehydrohalogenation of Re(NAr), (CH;Bu)C12 yields Re(NAr)2(CH’Bu)Cl, from which several monoalkoxide derivatives have been prepared (OR = 0CH(CF3)2, 0CMe(CF3)2, or O-2,6-C,H,‘Pr,). Dehydrohalogenation of Re(NAr’),(CHiBu)Cl, or Re(NAr”),(CH2Bu)C12 did not yield neopentylidene complexes analogous to Re(NAr)2(CH’Bu)C12. None of the neopentylidene complexes showed any well-defined metathesis activity, even with norbornene.

We recently discovered that a bulky imido ligand will stabilize high oxidation state molybdenum and tungsten alkylidene complexes of the type M(CH’Bu)(NAr)(OR), (Ar = 2,6-CJ-13’Pr2; OR = 0CMe3, OCMe2(CF3), etc.).’ A dianionic ligand is required in order to form a four-coordinate complex in which the metal is in its highest possible oxidation state (“do”), a type of complex that we now feel is the most desirable for forming intermediate metallacyclobutane or metallacyclobutadiene complexes in Group 6 olefin’ or acetylene3 metathesis systems, respectively. Bulky imido ligands should continue to be successful relative to 0x0 ligands or unhindered imido ligands because if a metal centre of low coordination number is electrophilic enough to react with an olefin, then it should also strongly coordinate an 0x0 or a sterically accessible imido nitrogen atom (if no other good donors are present) to form complexes

*Author to whom correspondence should be addmssed.

that contain bridging 0x0 or imido4 ligands [eq.

(111. 2 M=X

-

MO’\M ‘X’ X = OarsmallNRligand

(1)

It is not surprising that the alkoxide ligands in M(CH’Bu)(NAr)(OR), complexes also must be bulky in order to avoid formation of dimers, for example, [V(N-p-C6H4Me)(O-2,6-CsH3Me2)2Cl]2.5 The tactic is to use ligands that arc large enough to prevent formation of complexes containing bridging ligands and slow down or prevent intermolecular decomposition reactions, but still not so large as to prevent access to the metal by relatively small molecules. We feel that the principles of olefin and acetylene metathesis by “do” metal complexes should extend to rhenium(VI1). Several years ago6 we developed an entry into Rev” t-butylimido chemistry based on Re(IVBu)3(OSiMe3)4b as a starting material. We

1841

A. D. HORTON

1842

and R. R. SCHROCK

found that we could prepare a large number and variety of new molecules, including relatively attractive target molecules such as Re(N’Bu), (CH’Bu)(CH,‘Bu). However, several features of the chemistry limited their usefulness, among them the high solubility and often thermal and hydrolytic instability of t-butylimido derivatives, and the fact that t-butylamine generated as a product of protonation reactions often remained firmly bound to the metal. The ultimate disappointment was that species such as Re(N’Bu),(CH’Bu)(CH,‘Bu) do not react readily with olefins.7 We sought an entry into rhenium(VI1) arylimido chemistry in the belief that arylimido ligands might significantly increase the electrophilicity of the metal to the point where it would react with olefins. Unfortunately, reactions designed to prepare Re(NAr),(OSiMe,) (where Ar = 2,6C,H,‘Pr& i.e. procedures involving ArNHSiMe, analogous to that used to prepare Re(N’Bu)3(0SiMe3),4b gave a mixture of products, none of which could be isolated or identified.’ Attempts to exchange t-butylimido by NAr in Re(N’Bu),(OSiMe,) and related derivatives looked promising,8 but the procedures were tedious and circuitous. In searching for a new, general entry into rhenium arylimido chemistry we settled on reactions between an isocyanate and a metal oxide [eq. (211, a type of reaction that is a known route to several imido complexes,4a although the generality of the reaction has not been fully explored. In this paper we report high yield routes to Rev” complexes containing two or three arylimido ligands of the type N-2,6_C,H,‘Pr,(NAr), N-2,6C6H3Me2 (NAr’), or N-2,6-C6H3C12 (NAr”). Some of these results were reported in the form of a preliminary communication.’

the two ends of the molecule can freely rotate on the NMR time scale. We have not been able to replace the last terminal 0x0 ligand in 1, presumably because of steric congestion about the metal (cf. 4 below). It should be noted that the electron count on each Re exceeds 18 if 7~electrons from the terminal 0x0 and all imido ligands are included. Therefore we cannot be certain that all Re-N-C,, angles are of the order of 170” or greater in the solid state, as would be the case if an imido ligand fully donates its rr electron pair to the metal. However, if both “bent” and “linear” imido ligands are present in 1, they must interconvert rapidly on the NMR time scale. NMR examination of the crude mixture obtained in the reaction shown in eq. (3) reveals that 1 comprises only N 60% of the diamagnetic product mixture. Approximately 30% of the crude mixture has been identified as Re(NAr),(OSiMe,) (2a), while - 10% of the mixture is what we speculate to be Re(O)(NAr),(OSiMe,) (3). The fraction of 2a in the crude mixture can be increased to 65% (20% 1, 15% 3) by employing Me$iOSiMe, as the reaction solvent, and red crystalline 2a can be isolated in 46% yield in this manner [eq. (4)]. For this reason we suspect that ReOSiMe3 species are in equilibrium with Re-CLRe species and Me$iOSiMe,, a type of reaction that has been observed when DMF is added to a solution of Re03(0SiMeJ in ether or MeSiOSiMe, [eq. (5)l.l’ ReO,(OSiMe,)+

3ArNC0

Me3::I:r3

bRe(NAr),(OSiMe,)

(4)

2a (46%) WCinetheror

M=O + ArNCO + M=NAr + CO,.

(2)

2ReOs(OSiMe,) + 2DMF w Rez07@MF)*+

RESULTS

AND DISCUSSION

Re20Z(NAr)S can be prepared in 27% isolated yield as shown in eq. (3). An ‘H NMR spectrum of 1 shows that methyl groups in the three imido ligands on one metal are equivalent while pairs of methyl groups in each of the two equivalent imido ligands on the second metal are diastereotopic. ReO,(OSiMe,) + 3ArNC0 z

1/2(ArN),Re--O-Re(O)(NAr),.

(3)

1(27%)

A Re=O stretch can be observed in the IR spectrum of 1 at 903 cm-‘. There is no reason to believe that 1 is not an oxo-bridged species as shown in which

Me$iOSiMe,.

(5)

Therefore running the reaction in Me$iOSiMe, maximizes the amount of 2a by minimizing the formation of Re-O-Re species. It is important to note that once 2a is formed it does not lose Me$iOSiMe, in refluxing toluene to give as yet unknown (ArN),Re--O-Re(NAr), (cf. 4 below). Therefore only ReO,(NAr),_,(OSiMeJ complexes where x = 1, 2 or 3 could be involved in equilibria analogous to that shown in eq. (5). If the reaction is carried out in toluene (70”, 20 h) or in Me,SiOSiMe, (with shorter reflux times), the crude reaction mixture contains only - 20% of 2a; -80% of the mixture consists of a complex that cannot be isolated, but which NMR and IR evidence suggests is Re(O)(NAr),(OSiMe,) (3). Therefore we propose that the reaction between

1843

Preparation of bis and tris(arylimido) complexes of rhenium(VI1) ReO,(OSiMe,) and ArNCO proceeds stepwise as shown in eq. (6), and that one or more of the intermediate complexes ReOflAr)3-X(OSiMe,) decomposes to Re-O-Re species, which can then react further with ArNCO to give 1. If less than 3 equiv. of ArNCO are used in reactions of this type, then relatively complicated mixtures result. It seems plausible that species such as ReO, (NAr)(OSiMeJ, Re,O,(NAr),, or RezO,(NAr), are formed under these conditions, in addition to varying amounts of 1,2a, or 3. Initial studies of reactions between ArNHSiMe, and ReO,(OSiMe,)* were discouraging perhaps because similar multiple equilibria and reaction stages gave rise to complex mixtures. Re03(0SiMe,)

B

Re(O),(NAr)(OSiMe,)

a

Re(O)(NAr),(OSiMe,) 3

s

Re(NAr),(OSiMe,). 2a

(6)

Reactions between Re03(0SiMe,) and Ar’NCO (Ar’ = N-2,6-C6H3Me,) or Ar”NC0 (Ar” = N-2,6C6H3C12) proceed more cleanly than those involving ArNCO. In refluxing toluene 4 [eq. (7)] is formed in high yield and can be isolated in 65% yield. ReOS(OSiMe,) + 3Ar’NC0 5

formation of any species analogous to 1 or 3. ReO,(OSiMe,) + 3Ar’NC0 Me,SiOSiMe,

r&lx

(7)

4 (65%) Evidently the NAr’ ligand is small enough so that bimolecular elimination of Me,SiOSiMe, in ReO, (NAr’),_,(OS’M1 e3) complexes to give Re-O-Re complexes is more facile than in the case of NAr complexes, and ultimately complete replacement of all terminal 0x0 ligands is now sterically possible. NMR examination of the crude reaction mixture shows that only one other diamagnetic product, Re(NAr’),(OSiMe,) (2b), is present in N 10% relative yield. It is virtually the only product of an analogous reaction that is carried out in Me3SiOSiMe3 [eq. (8) ; only traces of 4 are observed]. As with 2a, 2b does not decompose to 4 in refluxing toluene, nor does 4 yield 2b upon being refluxed in Me,SiOSiMe,. The reaction between Ar”NC0 and Re03(0SiMe3) in refluxing xylene yields only Re(NAr”),(OSiMe,) [2c; eq. (9)], isolated in 79% yield ; there is no evidence (by NMR examination of the crude mixture) for

Re(NAr’)3(0SiMe3)

(8)

2b (82%) ReO,(OSiMe,) + 3Ar”NC0 “lene bRe(NAr”),(OSiMe,). renux48h

(9)

242(79%)

Note that 2c shows no tendency to eliminate Me,SiOSiMe3 to form Rez(0)(NA&. It is not yet clear how electronic and steric differences determine the course of reactions of this general nature. What is clear is that the isocyanate route appears to have some general utility for forming Rev” complexes that contain bulky imido ligands. Neopentyl derivatives of the tris(imido) complexes can be prepared straightforwardly and isolated in high yield as red-purple crystals [eq. (lo)]. Note that preparation of 5a requires the lithium reagent ; presumably the trimethylsiloxide cannot be substituted by the less reactive Grignard reagent. Re(NR),(OSiMe,)

+ ‘BuCH2MgCl or

2a (R = Ar) 2b (R = Ar’) 2c (R = Ar”) LiCHiBu s

1/2(Ar’N),R&Re(NAr’)~.

)

Re(NR),(CH,‘Bu).

(10)

5a (R = Ar; 77%) 5b(R=Ar’;80%) 5c (R = Ar” ; 73%) In the case of the formation of 5h and 5c the Grignard is required ; use of the lithium reagent produces what are believed to be reduced rhenium complexes ; they will be reported elsewhere. An alternative preparation of the NAr’ derivative starts with Re(NAr’),Cl (see later). NMR spectra of these presumably pseudotetrahedral molecules are unexceptional. This series of complexes was prepared in order to examine how they react with HCl (see later) ; 5b and 5c are important precursors. The reaction between 1 and pyridinium chloride yields &I [eq. (1 l)] in N 80% isolated yield as green crystals. We propose that 6a is octahedral with imido ligands cis to one another in order to minimize competition between the ILbonds. However only at - 60” are the two arylimido ligands inequivalent (pairs of methyl groups in each are diastereotopic) as a result of the pyridine binding to the metal, most likely in a position tram to one of the imido ligands.

A. D. HORTON

1844

and R. R. SCHROCK

At normal temperatures the imido and pyridine resonances are broad, we presume as a result of reversible loss of pyridine to give Re(NA&Cl,. 6a is an 18 electron complex if one of the imido ligands (presumably a bent one4”) does not donate its electron pair to the metal. It seems more likely that pyridine would bind tram to the bent imido ligand, as the linear imido ligand should be more tram lab&zing. The feasibility of 6a as a starting material increases substantially as a result of its isolation in -75% yield #eral~ from ReO~(OSiMe~) upon addition of pyridinium chloride to the crude product (containing 2 and 3 and probably traces of related oxo/imido complexes) of the reaction between ReOJ(OSiMeJ and ArNCO in refluxing toluene [eq. (3)]. An analogous two-step reaction sequence leads to 6h [eq. (1211 while the reaction between Re(N~)~(OSiMe~) (available in high yield) and pyridinium chloride yields 6e [eq. (13)]. NMR spectra of 6h and 6e suggest that they are entirely analogous to 6a.

Key compounds in the quest for neopentyhdene complexes are of the type Re(NR) &!H 2’Bu)C12.The NAr’ and NAr” derivatives are readily available from the Re(NR),(CH,‘Bu) complexes as shown in eq. (15). The analogous reaction of Re(NAr), (CH,‘Bu) with gaseous HCI yielded several products in what is evidently a relatively non-specific reaction, at least in our hands so far. However, Re(NAr)z(CHz’Bu)Clz can be prepared in good yield by alkylating Re(NAr),Cl,(py) [eq. (1611.(Addition. of 1 equiv. of ‘BuCH2MgC1 to Re~~)~Cl~~y~ does not yield 8a cleanly or in high yield ; it is not a suitable preparative method.) Similar selective alkylation reactions involving Re(NAr’)&l,(py) or Re(NAr”),Cl,(py) have not yet been successful, but the routes shown in eq. (15) are satisfactory because of the ready availabi~ty of Re(NAr‘~~(CH~~Bu)and Re~Ar~)~(CH~Bu). Re(NR)3(CH2’Bu) “,gk-r~

3

Re(NR),(CH2’Bu)C12

(15)

8b (R = Ar’; 75%) & (R = Ar”; 78%) da

ReO~(OSiMe~}

1.3equiv. ~NCO/~olu~ 2.3 equiv. pyHCi/CH,Cl~

Sa (72%).

6h (62%) RemAr”) ,(OSiMesj

3 WV. ~~“‘~~2~~

,

Re@IAr”),CI,@y).

(13)

& (79%) If 3 equiv. of gaseous anhydrous HCl (in dichloromethane) are added to the crude product mixture (in dichloromethane) obtained in the reaction shown in eq. (7), than an insoluble material is obtained that reacts with 3 equiv. of pyridine to give 6h, and with 3 equiv. of triethylamine to give 7 [eq. (14)] in good overall yield from Re03 (OSiMe3). On the basis of these reactions we speculate that the insoluble green material is [Ar’NH,] [Re(NAr’),ClJ. We propose that 7 is a monomeric pseudo-tetrahedral complex on the basis of its high solubility in pentane.

Re(NAr’),Cl

Thus 8a-c are all available on a relatively large scale (10 g). Unlike Re(N’Bu),(CH2*Bu)C1,, which decomposes over a period of several hours in the solid state at 25”C,6 8a-c are all stable in the solid state in the absence of air and moisture for months. NMR data suggest that their structures are analogous ; for example, only one kind of imido ligand is present and the isopropyl methyl groups are diastereotopic. One possible structure that is consistent with these data is a trigonal bip~~d~ species in which the imido ligands are located in equatorial positions and the neopentyl ligand is located in an axial position. However a recent report of the unusual structure of Re(N’Bu),(O-C&14Me)CI,,” a tetragonal pyramid containing a bent axial imido ligand with the shortest Re=N bond length, suggests that predictions concerning the structure of 8a-c, and indeed other imido complexes we have prepared here, are dangerous, even though the

(14)

7 [67% vs ReO,(OSiMe&

8 (R=Ar,Ar’,Ar”)

Preparation imido

ligands

are

equivalent

1845

of bis and tris(aryIimido) complexes of rhenium(VI1) (as

they

are

in

Re(N’Bu)z(O-C,H.,Me)Cl~‘l) on the NMR time scale. The alkylation shown in eq. (16) is very sensitive to the amount of dineopentylzinc that is used. If N 1.7 equiv. of dineopentylzinc is used then the reaction proceeds in high yield to give 9a [eq. (17)]. The mechanism of the reaction may involve dehydrohalogenation of Re(NAr),(CH,‘Bu)&l by pyridine (see below). A similar reaction of the NAr’ derivative gives Re(NAr’),(CH’Bu)(CH,‘Bu) (9b). Preliminary experiments show that other alkylation reactions (e.g. with Me or CHzPh groups) lead to complexes of the type Re(NAr)2R3. Similar behaviour was observed for the analogous t-butylimido complexes6 So far, Re(NAr”)(CH’Bu)(CH,‘Bu) has not yet been prepared pure by an analogous route.

Re(NAr),(CH*Bu)(CHr’Bu).

(NAr)(C’Bu)Cl,], and an alkylidyne C, resonance has been observed in the 13C NMR spectrum of [DBUH][Re(NAr’)(C’Bu)Cl,] at 313.7 ppm (cf. 3 14.7 ppm in [DBUH] [Re(NAr)(C’Bu)Cl,]‘*). We could only speculate on the mechanism of this disproportionation reaction. The important point is that disproportionation does not take place with the sterically more bulky NAr analogues. Re(NR),(CH,‘Bu)Cl, +DBU C,D,at -5°C -0.5 [DBUHjCI

> 0.5

Re(NR),(CH,‘Bu)

+0.5 [DBUH][Re(NR)(C’Bu)C13].

(19)

10 sometimes is contaminated to a significant extent by pseudo-tetrahedral Re(O)(NAr),(CH,‘Bu) (11). 11 may be prepared in good yield and in multigram quantities as shown in eq. (20).

(17)

9a

Re(NAr)2(CHfBu)C1 MeTzfcou* 1

It is possible to cleanly dehydrohalogenate Re(NAr)JCHz’Bu)Clz to give red 10 [eq. (IS)] virtually quantitatively. Although 10 is very soluble in pentane, it cap be isolated from it in N 75% yield. We have tried a wide variety of other bases (among them pyridine, 2,4-lutidine, triethylamine or Ph$=CHMe), solvents and temperatures, but so far we have not been able to discover other conditions that give a good yield of 10. It would appear, therefore, that HCl must be removed effectively from the system, perhaps in order to prevent a destructive reprotonation reaction. Details of the NMR spectra of 10 are discussed later along with those of related neopentylidene complexes.

DBU in ether at - 20°C

b Re(NAr),(CH’Bu)Cl.

(18)

10 Unfortunately, analogous dehydrohalogenation reactions starting with Re(NAr’)z(CHz’Bu)C1l or Re(NAr”),(CH,‘Bu)Cl, so far have not been successful. Reactions carried out in C6D6and examined by ‘H NMR showed the only significant products to be those shown in eq. (19) in approximately a 1: 1 ratio. The [DBUHj[Re(NAr’)(C’Bu)Cl,] and [DBUH][Re(NAr”)(C’Bu)Cl,] complexes appear to be analogous to isolated [DBUHJ[Re(NAr) (C’Bu)Cl,] ;I* all resonances for [DBUH][Re(NAr’) (C’Bu)Cl,] and PBUH] [Re(NAr”)(C’Bu)Cl,] are analogous to those observed for [DBUH][Re

Re(O)(NAr),(CH,‘Bu).

(20)

11

We propose that the reaction proceeds via intermediate Re(NAr)2(CH’Bu)(OH) followed by a proton shift from oxygen to carbon. It is interesting to note that Re(NAr),(CH’Bu)Cl reacts only slowly with 1 equiv. of water in ether at 25°C (N 50% of 11 formed after 2 h). Re(NAr)2(CH,‘Bu)C12 also reacts with Me,NOH under similar conditions, but a mixture of products is formed that does not include a substantial amount of 11. Therefore we believe that DBU dehydrohalogenates Re(NAr)* (CHiBu)Cl* to give 10, and completely reacts with traces of water to give the hydroxide ion that then reacts with 10 to give 11. NMR spectra of 11 show that the imido ligands are equivalent on the NMR time scale, and two sets of diastereotopic methyl groups are present. At this stage we are assuming that 11 is a pseudo-tetrahedral monomer in which one of the imido ligands is bent, and the other is linear. So far attempts to form 11 by treating Re(NAr)3(CH2’Bu) with water have only produced it in low yield in an apparently complex messy reaction. Treating Re(NAr),(CH’Bu)Cl with alkoxides yields complexes 12a-c virtually quantitatively [eq. (2111.Complexes 12 are all red or orange and highly soluble in pentane, so soluble, in fact, that only 12a and 12~have been isolated as nicely crystalline samples suitable for elemental analysis. However, on the basis of NMR spectra there is no doubt that

A. D. HORTON and R. R. SCHROCK

1846 12b is correctly formulated. Re(NAr),(CH’Bu)Cl

+

Re(Ndu),(CH’Bu)(OR)

(21)

12a ; OR = OCH(CF& 12b ; OR = OCMe(CF,), 12c ; OR = O-2,6-C,H,Pr,. Selected NMR data for all neopentylidene complexes are collected in Table 1. The values for 6H,, 6C, and Jcn(Hz) are all similar to the respective values in Re(IVBu),(CH’Bu)(CH,‘Bu)6 (11.95 ppm in toluene ds, 262.2 ppm in CsDa, JCH= 134 Hz). Resonances for H, and C, were found to shift downfield in complexes of the type M(NAr) (CH’Bu)(OR), (M = MO or W) as OR became electron-withdrawing.’ Therefore we had expected SH, and SC, for the complexes containing the NAr ligand to reflect to a greater extent the greater electron-withdrawing ability of the phenyl substituent versus that for the t-butyl group in the analogous N’Bu complexes. The most important features of the NMR spectra for all neopentylidene complexes are the inequivalent imido ligands and diastereotopic pairs of methyl groups in each. Inequivalent imido ligands also were observed in Re(N’Bu), (CHCMe3)(CH2CMe3).6 The phenomenon in each case could be ascribed to orientation of the neopentylidene ligand so that the 6! proton lies in a N-Re-C plane and points towards or away from one of the imido ligands, see Fig. 1. Again an X-ray study is required. In these complexes if each imido ligand donates its n: electron pair the metal electron count is brought up to 18. Qualitative olefin metathesis experiments We summarize the results of several tests for metathesis activity in Table 2. In short there was no evidence for metathesis, even when norbornene was employed. The sporadic polymerization activity in the case of norbornene must be ascribed to impurit-

ies. These results prove incorrect our hypothesis that aryl imido complexes could be active even though t-butylimido analogues are not. We suspect that electronic saturation at the metal centre in these complexes is the primary obstacle to their reaction with olefins. So far attempts to synthesize potentially more reactive analogous alkylidene complexes with less bulky, poorer electron donating imido ligands has been hindered by decomposition reactions ; we presume at this stage that decomposition is the result of intermolecular reactions that are now more favourable because of the relatively unhindered nature of the coordination sphere. The complexes described here have proven to be useful as facile entries into monoarylimido rhenium chemistry, and a monoimido neopentylidyne complex now has been shown to be an active acetylene metathesis catalyst.13 Therefore we presume that our continued search for a well-characterized Rev” olefin metathesis catalyst ultimately will be successful, although what the nature of that species might be is still in doubt.

EXPERIMENTAL

General experimental procedures may be found elsewhere.14 NMR chemical shifts are reported relative to TMS. Expected intensities, multiplicities and coupling constants are usually omitted. The NMR solvent is C6D6 and the temperature -25°C unless otherwise specified. DBU (1,8-diazabicyclo [5.4.0]undec-7-ene) was purchased commercially and distilled before use. Re03(0SiMe3)i5 and OCN-2,6-CsHiPr2i6 were prepared by literature

Table 1. Selected NMR data for complexes of the type Re(NR),(CH’Bu)X NR 2,6-CsH,‘Prz 2,6-CsH,Pr, 2,6-CsHS’Pr, 2,6-C,H,‘Pr, 2,6-C,H,%‘r* 2,6-CJ-I,Me,

X CH,CMe, Cl OCH(CFA OCMe(CF& O-2,6-C,H,‘Pr, CH2CMe3

6 H, (Ppm)

6 C, @pm)

12.28 12.27 11.88 11.56 11.25 12.24

269.0 269.4 260.5 256.4 256.7 270.5

&W) 139 136 137 139 146 137

1847

Preparation of bis and tris(arylimido) complexes of rhenium(VI1) Table 2. Results of tests for olefIn metathesis activity” Compound 12a 10, lzc 9a, 10,12a, 12b, 12~

Olefin (equiv.)

Solvent

Time/temp

Method

20 cis-Zpentene 10 cis-2pentene 20 norbornene’

Toluene C,D, CsD,

3 days/25”C 1 day/25”C 18 h/25”C

GLC NMR NMR

a Sample size l&l 5 mg. *Some polymer (< 50%) was observed sporadically ; such experiments could not be repeated and starting material was not consumed.

Other arylisocyanates commercially.

methods.

Re?Or(N-2,6-C6HiPr&

were purchased

(1)

2,6-Diisopropylphenylisocyanate (1 .OO g, 4.93 mmol) was added to a toluene (30 cm3) solution of Re03(0SiMe3) (0.50 g, 1.55 mmol). The mixture rapidly turned orange and was refluxed for 5 h. An intermediate olive-brown colour was observed which turned to an intense red-orange colour after 30 min. The solvent was removed in uucuo and the residue extracted with pentane (200 cm3). The extract was filtered, concentrated and cooled to 0°C to give dark red crystals (0.27 g, 27%). The analytical sample was recrystallized from a.mixture of dichloromethane and pentane : ‘H NMR 6 7.05 (d, 10, H,), 6.90 (m, 5, H,), 3.83 (sept, 4, CHMe,), 3.71 (scpt, 6, CHMe2), 1.20, 1.19, 1.17 (d, 12, 12, 36, CHMe,); 13CNMR S 152.6 and 151.9 (C,,,), 144.3 and 142.4 (C,), 128.1 and 127.2 (C,), 122.6 and 122.4 (C,), 29.0 and 28.8 (CHMe2), 23.7 (CHMer); IR (Nujol) 903 cm-’ (Rc==O). Found : C, 56.6 ; H, 7.1; N, 5.8. Calc. for Re2CsoHssNzOz: C, 56.3 ; H, 6.7 ; N, 5.5%. Re(N-2,6-C,&,‘Pr,),(OSiMe3)

(2a)

ArNCO (7.88 g, 38.3 mmol) was added to a solution of Re03(0SiMe3) (4.0 g, 12.32 mmol) in (Me,Si),O (400 cm3). The initial olive-orange solution became intense orange after refhtxing the reaction mixture for 18 h. Removing the solvent invacua afforded an oily orange residue that upon extraction with pentane (200 cm3) left behind dark red crystals of Re202(NAr)5 (0.35 g). Concentrating and cooling the pentane extract gave 4.56 g (four crops, 46%) of Re(NAr),(OSiMe, ) as red crystals. Contamination of the product with RezOz(NAr), can be avoided by extracting the product into a minimal amount of pentane and slowly recrystallizing it at - 30°C : ‘H NMR 6 7.06 (d, 6, H,), 6.92 (t, 3, HP), 3.59 (sept, 6, CHMer), 1.13 (d, 36, CHMe2), 0.40 (s, 9, OSiMe,) ; r3C NMR 6 152.3 (C,,,), 141.2 (C,),

125.8 (C,), 122.0 (C,), 28.4 (CHMeJ, 23.9 (CHMe2), 1.9 (OSiMe3). Found : C, 58.2 ; H, 7.6 ; N, 5.1. Calc. for ReC39H6N30Si : C, 58.5 ; H, 7.5 ; N, 5.2%. Although the ‘H NMR spectrum of the crude product mixture showed it to contain Re(NAr),(OSiMe,), RezOz(NAr)S, and Re(0) (NAr),(OSiMe,) (see below) in the approximate ratio 65 : 20 : 15, the extremely high solubility of Re(NAr),(OSiMe3) prevented its recovery in higher yield. Re(N-2,6-C&13MeZ),(0SiMe3) (2b) Ar’NCO (7.05 g, 48.0 mmol) was added to a solution of ReO,(OSiMe), (5.0 g, 15.1 mmol) in (Me3Si)r0 (250 cm’) and the mixture was heated to reflux for 18 h. Dichloromethane (60 cm’) was added to the intense orange solution to dissolve some orange precipitate. Filtration of the solution through Celite and concentration of the filtrate in uacuogave orange microcrystals of the product (8.0 g, 82%). Traces of Re,(O)(NAr’), are removed when a sample is recrystallized slowly at -30°C from a mixture of dichloromethane and pcntane: ‘H NMR 6 6.89 (d, 6, H,), 6.70 (t, 3, HP), 2.31 (s, 18, Me), 0.30 (s, 9, OSiMe,) ; i3C NMR 6 155.4 (C,,,), 131.8 (C,), 127.7 (C,), 125.6 (C,>, 18.7 (Me), 1.7(0SiMe3). Found:C,51.2; H,5.8;N,6.1.Calc. for ReC27H36N30Si : C, 5 1.2 ; H, 5.7 ; N, 6.6%.

Re(N-2,6-C6H3ClZ),(OSiMe3) (2e) Ar”NC0 (9.45 g, 50.8 mmol) was added as a solid to a solution of Re03(0SiMe3) (5.46 g, 16.9 mmol) in xylene (300 cm3). Upon refluxing the reaction mixture for several hours the initial brown colour changed to an intense orange. After 48 h the reaction mixture was cooled and the solvent was removed in uucuo, leaving a red microcrystalline solid. The solid was redissolved in a mixture of dichloromethane (200 cm’) and pentane (150 cm3) and the solution filtered through Celite. Con-

1848

A. D. HORTON and R. R. SCHROCK

centrating and cooling the filtrate in uucuo gave 11.1 g (two crops, 79%) of red crystalline product that was essentially pure (by ‘H NMR) : ‘H NMR 6 6.83 (d, 6, H,), 6.08 (t, 3, H,,), 0.40 (s, 9, OSiMeJ ; 13C NMR 6 151.3 (C&o), 130.0 (Co), 127.7 (Cm), 125.9 (C,), 1.7 (OSiMq). Found: C, 33.6; H, 2.7; N, 5.4; Cl, 27.8. Calc. for ReC2,H&16N30Si: C, 33.4; H, 2.7; N, 5.6; Cl, 28.2%. Observation ofRe(O)(N-2,6-C,H,PrPr,),(OSiMeJ

(3)

Treatment of Re03(0SiMe3) with 2 equiv. of ArNCO either in toluene at 70°C (2-20 h) or in (Me$ihO over the temperature range 45-100°C (for various time periods) in closed systems gave, in each case, a mixture of the desired product and Re(NAr),(OSiMe,). The best reaction ReO, (OSiMe3) (0.10 g, 0.31 mmol) plus ArNCO (0.128 g, 0.62 mmol), ds-toluene (2 cm3), 7O”C, 20 h] gave an 85: 15% mixture of Re(O)(NAr), (OSiMe,) and Re(NAr),(OSiMq). The best ratio in (Me$i&O was 80: 20% [lOOC, 1 h or 85°C 2 h] ; lower temperatures gave more of the minor product as well as unreacted ArNCO. The very high solubility of the two products in pentane prevented their separation by fractional crystallization. ‘H NMR 6 7.01 (d, 4, H,), 6.89 (t, 2, HP), 3.66 (sept, 4, Chime,), 1.17 and 1.15 (each a d, 2, CHMe,), 0.20 (s, 9, OSiMe,). ReGWN-2,6-C6H3Me2)6 (4) Ar’NCO (1.46 g, 9.93 mmol) was added to a solution of Re03(0SiMe,) (1.0 g, 3.09 mmol) in xylene (50 cm3). An intense red-orange colour resulted upon heating the reaction mixture to reflux temperature for 48 h. The solvent was removed in vacua and the residue was extracted with pentane (300 cm3). The extract was filtered through Celite, cooled and concentrated in V~C~O to give a red microcrystalline solid (1.1 g, 64%). Large red crystals were obtained by recrystallization from pentane : ‘H NMR 6 6.85 (d, 12, H,), 6.66 (t, 6, H,), 2.34 (s, 36, Me); 13C NMR 6 155.6 (C,,), 131.9 (C,), 127.6 (C,,,), 125.9 (CJ, 18.6 (Me). Found: C, 52.3 ; H, 5.0. Calc. for Re&HYN60 : C, 52.2 ; H,

Re(N-2,6_C,H,‘P&(CH,‘Bu)

(5a)

LiCH,‘Bu (0.227 g, 2.92 mmol) was added to a solution of Re(NAr),(OSiMe,) (1.80 g, 2.25 mmol) in ether (20 cm3) at -40°C. The mixture was allowed to warm to 25°C over a period of 15 min. After stirring the reaction mixture for 2 h, the solvent was removed in vucuo. The oily residue was extracted with pentane (50 cm3) and the extract filtered through Celite. The filtrate was taken to dryness in wcuo and the residue was dissolved in pentane (2 cm’). Red crystals (three crops, 1.35 g, 77%) of product were obtained upon cooling the solution to - 30°C : ‘H NMR 6 7.06 (m, 9, Hary,), 3.89 (sept, 6, CHMe,), 3.85 (s, 2, CH,CMe,), 1.23 (s, 9, CH2CMe3), 1.20 (d, 36, CHMe2) ; 13C NMR 6 153.1 (Cipso),142.4 (Co), 126.5 CC,>,122.5 (Cm), 51.6 (CHiCMe3), 35.1 (CH,CMe,), 33.1 (CH2CMe3), 28.2 (CHMe,), 23.6 (CHMeJ. Found : C, 63.3; H, 8.1; N, 5.2. Calc. for ReC41H62N3: C, 62.9 ; H, 8.0 ; N, 5.4%. Re(N-2,6-C6H3Me2)3(CH,‘Bu) (Sb) ‘BuCH2MgC1(9.0 cm3 of 0.6 M solution in ether, 5.40 mmol) was added to a solution of Re(NAr’)3C1 (3.06 g, 5.29 mmol) in ether (150 cm3) at - 40°C. A precipitate of MgClz was formed after stirring for several hours at 25°C. After 48 h, the mixture was filtered through Celite to remove MgClz and the filtrate was reduced to dryness. The red oily residue was extracted with pentane (300 cm3) and the extract was filtered through Celite. Concentrating and cooling the extract gave red crystals of the product (three crops, 2.58 g, 80%). The analytical sample was prepared by recrystallization from pentane : ‘H NMR 6 6.91 (d, 6, H,), 6.81 (t, 3, H,), 3.87 (s, 2, CH,CMe,), 2.36 (s, 18, Me), 1.18 (s, 9, CH&Me3); 13C NMR 6 156.3 (Cipso), 132.0 (C,), 128.1 (C,), 125.7 (C,), 48.8 (C’H,CMe3), 34.6 (CH2CMe3), 33.4 (CH2CMe3), 19.3 (Me). Found: C, 56.9 ; H, 6.1. Calc. for ReCZ9H3sN3: C, 56.6 ; H, 6.2%. The product also may be obtained in virtually quantitative yield by treating Re(NAr’),(OSiMe,) with ‘BuCH2MgC1 in ether at 25°C.

4.9%.

The ‘H NMR spectrum of the crude reaction mixture (after the initial extraction with pentane) showed it to contain N 10% Re(NAr’),(OSiMe,) (see above) and several other minor products. The proportion of additional products increased slightly when toluene was used as the reaction medium. Using 2 equiv. of Ar’NCO in refluxing toluene gave a large number of complexes in low yield and virtually none of the above major product.

Re(N-2,6-C,H,Cl,),(CH,‘Bu)

(5~)

‘BuCH,MgCl (3.7 cm3 of 2.1 M solution in ether, 7.77 mmol) was added to a suspension of Re(NAr”),(OSiMe,) (5.0 g, 6.62 mmol) in ether (400 cm’) at -40°C. The solution turned a darker red colour on warming to 25°C over 30 mm. After stirring the solution for 2 h, the volume was reduced to 250 cm3 in zxxuo and pentane (100 cm3)

1850

A. D. HORTON and R. R. SCHROCK

and 133.6 (imido C&, 129.0 (imido C,,,), 124.9 (py C,,,). The imido C,,, resonance was not observed due to the low solubility of the complex in CD&&. Found: C, 29.0; H, 2.0; N, 5.5; Cl, 35.7. Calc. for ReCr7H1,C17N3: C, 29.5; H, 1.6; N, 6.1; Cl, 35.9%.

Re(N-2,6-CsH3Me&C1 (7) A solution of ReO,(OSiMe,) (3.0 g, 9.28 mmol) and Ar’NCO (4.09 g, 27.8 mmol) in toluene (100 cm3) was heated to reflux for 24 h. The solvent was removed in vacua and the residue was redissolved in dichloromethane (50 cm’). The solution was cooled to -78°C in a Schlenk flask and HCl gas (excess) added by syringe through a rubber septum. The initial red colour of the solution changed to green as the solution was warmed to 25°C over 30 min. After 2 h, 6.8 g of a dirty green precipitate was collected and washed with dichloromethane. The precipitate is believed to consist primarily of [Ar’NH,][Re(NAr’),Cl,] on the basis of its reactions, although the > 100% theoretical yield by weight indicates that other products are also present. “[Ar’NH,][Re(NAr’),CL,]” is virtually insoluble in all common solvents with which it does not react. IR (Nujol) cn- ’ 3120 (v br, N-H). “[ArNH,][Re(NAr’),ClJ (3.0 g) was suspended in dichloromethane (100 cm3) at - 20°C. NEt3 (2.0 cm3, 14.4 mmol) was added and the mixture was warmed to 25°C over 30 min to give an intense red solution as the dark solid dissolved. The solvent was removed in vacua and the residue extracted with pentane. The extract was filtered through Celite and the filtrate was reduced to dryness in vacua. Red crystals of the product [two crops, 1.60 g, 67% based on ReO,(OSiMe,)] were obtained from pentane : ‘H NMR 6 6.82 (d, 6, H,), 6.69 (t, 3, H,), 2.26 (s, 18, Me); 13C NMR 6 155.4 (C&J, 132.4 (C,), 127.8 (C,,,), 127.2 CC,>, 18.6 (Me). Found: C, 50.2; H, 4.8; Cl, 6.3. Calc. for ReC2.,H2C1N3: C, 49.8; H, 4.7; Cl, 6.1%.

Re(N-2,6-CgH3’Pr2)Z(CH2[Bu)Clz (8a) A solution of Zn(CH;Bu)z (1.15 g, 5.54 mmol) in pentane (30 cm3) at - 20°C was added to a stirred solution of Re(N-2,6-C,H3’PrJ&13(py) (6.15 g, 8.52 mmol) in dichloromethane (200 cm’) at -20°C. Upon warming the reaction mixture to 25°C over 15 min a red-orange solution was obtained, to which NEt,Cl (0.917 g, 5.54 mmol) was added. After 30 min, pentane (60 cm3) was added and the precipitate of [EtdlrJ1[ZnC13]and excess NEtJl was removed by filtration through Celite. The solvent was removed from the filtrate and the residue was

redissolved in dichloromethane (5 cm3). Pentane (100 cm3) was added and the solution was filtered through Celite. The solution was concentrated and cooled to give red crystals (two crops, 4.16 g, 72%) : ‘H NMR 6 6.87 (s, 6, phenyl), 4.00 (s, 2, (X&Me,), 3.61 (sept, 4, CHMeJ, 1.17 (s, 9, CH,CMe,), 1.14 and 0.99 (each a d, 12, CHMe*) ; r3C NMR 6 15 1.2 (C,,,), 147.8 (C,), 132.3 (C,), 123.7 (C,,,), 67.4 (CH,CMe,), 36.7 (CH,CMe3), 34.5 (CH2CMe3), 28.9 (CHMe& 25.5 and 23.1 (CHMeJ. Found : C, 51.2; H, 6.6; N, 4.1. Calc. for ReCr9H4&1~NZ: C, 51.3; H, 6.7; N, 4.1%.

Re(N-2,6-C6H3MeJ2(CHiBu)Clz

(Sb)

A solution of Re(NAr)3(CH:Bu) (1.15 g, 1.87 mmol) in a mixture of dichloromethane (10 cm3) and pentane (400 cm3) was cooled to -78°C in a Schlenk flask. HCl gas (148 cm3, 6.6 mmol) was added by syringe through a septum to give an immediate white precipitate of ArNH3Cl. The reaction was kept at -78°C for 20 ruin, then warmed to 25°C over 45 min. Dichloromethane (50 cm3) was added to dissolve some of the orange precipitate and the solution was filtered through Celite. Concentrating and cooling the solution gave orange crystals (two crops, 0.79 g, 75%) of product. The analytical sample was prepared by crystallization from a mixture of dichloromethane and pentane. ‘H NMR 6 6.59 (m, 6, H,,), 3.92 (s, 2, CH,CMe,), 2.31 (s, 12, Me), 1.10 (s, 9, CH,CMe,); 13CNMR 6 154.2 (C,,), 137.8 (C,), 132.0 CC,>,128.3 (C,,,), 69.5 (CHrCMe,), 37.0 (CH,CMe,), 34.3 (CH,CMe,), 18.7 (imido Me). Found: C, 44.7; H, 5.4; N, 5.5; Cl, 12.8. Calc. for ReC2,H2&12NZ : C, 44.5 ; H, 5.2 ; N, 4.9; Cl, 12.5%.

Re(N-2,6-C6H3Cl&(CHr’Bu)Clr

(8c)

A solution of Re(NAr”),(CH,‘Bu) (1.50 g, 2.04 mmol) in a mixture of dichloromethane (80 cm3) and ether (300 cm3) was cooled to -78°C in a Schlenk flask. HCl gas (137 cm3, 6.1 mmol) was added by syringe through a septum. The mixture was maintained at - 78°C for 20 min as the solution colour slowly changed from red to red-green. The solution was warmed to 25°C over a period of 45 min and filtered through Celite. The filtrate was concentrated and cooled to give a red microcrystalline solid. The solid was fIltered off and recrystallized from a mixture of ether and pentane to yield 1.04 g (two crops, 78%) : ‘H NMR 6 6.54 (d, 4, H,), 6.07 (t, 2, HP), 4.57 (s, 2, CH,CMe3), 1.12 13C NMR 6 150.4 (C,,), 134.1 (s, 9, CHD4e3); (C,), 133.2 (C,), 128.3 (C,), 77.3 (CHCMe,), 38.1

Preparation

of bis and tris(arylimido) complexes of rhenium(VI1)

(CH2CMe3), 33.9 (CH2CMe3). Found : C, 31.4 ; H, 2.8 ; N, 4.5 ; Cl, 32.5. Calc. for ReCi7H,&&NZ : C, 31.5; H, 2.6; N, 4.3; Cl, 32.8%.

Found : C, 55.3 ; H, 7.1. Calc. for ReCz6H3,N, : C, 55.2 ; H, 6.9%.

Re(N-2,6-CaHiPrJz(CHfBu)CI Re(N-2,6-C,H,‘PrJz(CHLBu)(CHiBu)

(9a)

A solution of Zn(CH,‘Bu), (0.99 g, 4.77 mmol) in pentane (20 cm3, - 20°C) was added to a solution of Re(NAr),Cl,(py) (2.0 g, 2.77 mmol) in dichloromethane (20 cm3, -20°C). The reaction was warmed to 25°C and stirred for 2 h. The red-green solution immediately changed to an intense yellow colour upon the addition of solid NEt,Cl (0.79 g, 4.77 mmol). After 30 min the mixture was filtered through Celite and the filtrate was taken to dryness in vacua. The residue was extracted with pentane (50 cm3), and the extract was f&red through Celite and again taken to dryness. The resulting yellow solid (1.70 g, 900/,) was pure according to its ‘H NMR spectrum ; it was too soluble in pentane to obtain an analytical sample on this scale : ‘H NMR 6 12.28 (s, 1, CHCMe3), 7.06-7.03 (m, 6, H,J, 3.84 and 3.62 (each a sept, 2, CHMe2), 3.20 (m, 2, CH2CMe3), 1.30 (s, 9, CHCi14e3), 1.30, 1.22, 1.21 and 1.11 (each a d, 6, CHMe&, 1.20 (CH2CMe3) ; r3C NMR 6 269.0 (d, JCH = 139, CHCMe,), 153.2 and 152.7 (C,,,), 142.7 and 141.6 (C,), 126.3 and 125.7 (C,), 122.9 and 122.8 (C,), 47.1 (CHCMe,), 44.8 (CH$Me,), 33.6 (CH,CMe3), 33.5 (CHCMe3), 32.2 (CH&Me,), 29.1 and 28.8 (CHMe2), 23.9, 23.3, 23.2 and 22.9 (CHMe,).

(9b)

A solution of Zn(CH,‘Bu)z (0.62 g, 2.99 mmol) in pentane (10 cm3, -40°C) was added to a solution of Re(NAr’)zC13(py) (1.0 g, 1.64 mmol) in dichloromethane (- 40°C). A dirty red-green solution was formed rapidly upon warming the mixture to 25°C over a period of 15 min. A bright red-yellow solution was formed instantly when NEtCl(O.50 g, 3.02 mmol) was added. The solution was filtered through Celite after 1 h, and the filtrate was taken to dryness in vmuo. Careful crystallization of the residue from pentane (2 cm3) gave large red crystals (0.60 g, 65%) : ‘H NMR 6 12.24 (s, 1, CHCMe3), 6.96-6.83 (m, 6, Hary& 3.23 (m, 2, CH2CMe3), 2.37 and 2.23 (each a s, 6, Me), 1.24 (s, 9, CHCA4e3), 1.13 (s, 9, CH$Xfe,) ; r3C NMR 6 270.5 (d, JCH = 137, CHCMe,), 156.1 and 155.9 (&o), 133.5 and 131.4 (C,,), 128.1 (C,,,), 125.7 and 124.8 CC,>, 46.1 (CHCMe,), 41.2 (CH&Me,), 33.6 (CHCMe3), 33.3 (CH&Me,), 32.1 (CH,CMe3), 19.6 (imido Me).

(10)

An ether (5 cm3) solution of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene, 0.70 g, 4.6 mmol) at -20°C was added to a solution of Re(N-2,6C6H~Pr&(CH~Bu)Clz (3.0 g, 4.42 mmol) in ether (50 cm’) at -20°C. The mixture was allowed to warm to 25°C over a period of 15 min to give a bright red solution and a white precipitate of DBU - HCl. After 2 h, the solution was filtered through Celite and all the solvent removed from the filtrate in vacua. The residue was extracted with pentane (50 cm’) and the extract was filtered through Celite. The solvent was removed from the filtrate in vacua to give a microcrystalline solid that was shown by ‘H NMR to be an essentially pure product. Recrystallization from minimal pentane gave red crystals (four crops, 2.09 g, 74%): ‘H NMR 6 12.27 (s, 1, CK!Me3), 7.04-6.98 (m, 6, phenyl), 3.70, 3.58 (each a sept, 2, Chime,), 1.25 (s, 9, CHCMe3), 1.25, 1.20, 1.04 (d, 6, 12, 6, CHMeJ ; r3C NMR 6 269.4 (d, JCH = 125, CHCMe3), 153.5 and 151.8 (Cilia), 142.9 and 142.3 (C,), 127.6 and 127.3 CC,>, 123.1 and 122.8 (C,), 47.2 (CHCMe3), 32.3 (CHCMe3), 29.4 and 28.6 (CHMe,), 23.9, 23.4, 23.0 and 22.7 (CHMeJ. Found: C, 54.1; H, 6.9; N, 4.3. Calc. for ReCz9H&1NZ : C, 54.2 ; H, 6.9 ; N, 4.4%.

Re(O)(N-2,6-C6H
1851

(11)

Me,NOH (0.264 cm3 of a 1.86 M solution in methanol, 0.491 mmol) was added to a solution of Re(N-2,6C,&,‘Pr&(CH’Bu)CI (0.30 g, 0.468 mmol) in THF (15 cm’) at 25°C. The solution changed immediately from red to bright orange and a white precipitate of Me,NCl formed. The solution was stirred for 15 min and filtered through Celite. The filtrate was reduced to dryness in vacua, the residue extracted with pentane (10 cm3) and the mixture filtered through Celite. Removal of the solvent in vacua gave an orange solid that was virtually pure by ‘H NMR. A sample was prepared for analysis by recrystallization from minimal pentane : ‘H NMR 6 7.10-6.88 (m, 6, phenyl), 3.77 (sept, 4, CNMe2), 3.58 (s, 2, C&CMe,), 1.19 and 1.17 (each a d, 12, CHMe2), 1.18 (s, 9, CH2CMe3) ; 13CNMR 6 152.7 (CM), 143.2 (C,), 128.2 (C,>, 122.9 (C,), 53.6 (CH,‘Bu), 33.9 (CH,CMe3), 32.8 (CH&iWe,), 28.7 (CHMe,), 23.8 and 23.1 (CHit4e2). IR (Nujol) cm-’ 907 (Re=O). Found: C, 55.8; H, 7.3. Calc. for ReGsH,SN20 : C, 55.8 ; H, 7.3%.

1852

A. D. HORTON

Re(N-2,6-C,H,‘Pr,),(CH’Bu)[OCH(CF&]

and R. R. SCHROCK

(12a)

A solution of LiOCH(CFJ2 (0.325 g, 1.87 mmol) in ether (3 cm3) that had been cooled to -40°C was added to a -40°C solution of Re,(N-2,6C&H~Pr&CH’Bu)Cl (1.O g, 1.56 mmol) in ether (3 cm3). Upon warming the solution to 25°C over a period of 15 min a cloudy precipitate formed and the colour changed from red to orange. After 3 h LiCl was removed by filtration through Celite, the solvent was removed in uacuo and the crude residue was extracted with pen&me (5 cn?). The ‘H NMR spectrum of the product after removal of pentane suggested that essentially only one compound was present in high yield. Crystallization of the oily residue from pentane (1 cm3) yielded highly pentane-soluble red crystals (0.55 g, 46%). The analytical sample was obtained as large red crystals by very slow recrystalization from pentane (0.5 cm3) at -40°C: ‘H NMR 6 11.88 (s, 1, CHCMe,), 7.126.99 (m, 6, phenyl), 4.73 (sept, 1, JHF = 6.0, OCH(CF,),), 3.57 and 3.49 (each a sept, 2, CHMe&, 1.26, 1.20, 1.15 and 1.02 (each a d, 6, CHMQ), 1.14 (s, 9, CHCMe,); i3C NMR 6 260.5 (d, JCH= 137, CHCMe3), 153.2 and 151.5 (C,,), 143.4 and 142.0 (C,), 127.8 and 127.0 (C,), 123.5 (q, JCF = 285,OCH(CF,)J, 123.1 and 122.6 (C,), 92.1 (d, sept, JCH = 147, JCF = 30, OCH(CF&), 47.3 (CHCMe3), 33.0 (CHCMe3), 29.4 and 28.5 (CHMe,), 23.7, 23.6, 22.7 and 22.6 (CHMQ. Found : C, 49.8 ; H, 6.1. Calc. for ReC32H4SF60N2: C, 49.7 ; H, 5.9%.

Re(N-2,6C,&PrJ,

(CH’Bu)[OCMe(CF,),]

(12b)

Re(NAr)*(CHCMe,)Cl (0.50 g, 0.78 mmol) was treated with LiOCMe(CF& (0.150 g, 0.80 mmol) in ether as in the preparation of 5a above. The ‘H NMR specm of the crude solid showed that the product was formed essentially quantitatively, although Re(0)(NAr)z(CHzCMe3) was present as a trace contaminant. The product was too soluble to obtain analytically pure material on this scale. In only one case very slow recrystallization of the crude product from pentane gave 0.10 g (16%) of red crystals whose ‘H NMR spectrum did not show the trace impurity: ‘H NMR 6 11.56 (s, 1, CHCMe3), 7.06 6.97 (m, 6, phenyl), 3.64 and 3.45 (each a sept, 2, CHMe& 1.38 (s, 3, 0CMe(CF3)2), 1.28, 1.21, 1.19 and 1.OO(each a d, 6, CHMe2), 1.22 (s, 9, CHCMe3) ; 13CNMR 6 256.4 (d, JCH = 139, CHCMe& 153.2 and 151.4 (CbsO), 143.3 and 142.5 (C,), 127.6 and 127.1 (C,), 124.5 (q, JCF = 289, OCMe(CF3)J, 123.2 and 122.6 (C,,,), 79.6 (sept, JCF = 28,OCMe(CF&), 47.1 (CHCMe3), 33.2 (CHCA4e3), 29.2 and 28.4

(CHMe,), 23.9, 23.5, 22.8 and 22.5 (CHMe& 19.9 (OCMe(CF&).

Re(N-2,6-C6H3Pr&CH’Bu)C1 (0.35 g, 0.55 mmol) was treated with Li(O-2,6-C,H,‘Pr,) (0.144 g, 0.56 mmol) in ether and the reaction mixture worked up as in the preparation of 5a above. The ‘H NMR spectrum of the crude solid showed the product yield to be essentially quantitative. Recrystallization from pentane (3 cm3) gave a 63% yield of orange crystals (0.27 g) : ‘H NMR 6 11.25 (s, 1, CHCMe3), 7.12-6.93 (m, 9, phenyl), 4.05 (sept, 2, phenoxide CHMe2), 3.79 (sept, 4, imido CHMeJ, 1.39 and 1.35 (each a d, 6, phenoxide CHMeJ, 1.27, 1.26,1.24 and 1.05 (each a d, 6, iniido CHMe*), 1.Ol (s, 9, CHCMe3) ; 13CNMR 6 256.7 (d, JCH= 146, CHCMeJ, 167.4 (phenoxide C,,), 153.4 and 152.4 (imido C,,), 143.0 and 142.4 (imido C,), 137.7 (phenoxide C,), 127.1 and 126.6 (imido C,), 123.2 (imido C,), 122.7 (phenoxide C,), 122.3 (phenoxide C,), 46.5 (CHCMe,), 32.5 (CHCA4e3), 29.1 and 28.3 (imido CHMeJ, 27.1 (phenoxide CHMe2), 24.1, 24.0,23.3 and 23.0 (imido CHMeJ, 23.6 (phenoxide CHMe2). Found : C, 63.3 ; H, 7.9; N, 3.6. Calc. for ReC4,H6,N20 : C, 62.8 ; H, 7.8 ; N, 3.6%.

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1853

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