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/ Preparation of Ta(a5-CjH~)2(CH2)(CH3)
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Multiple Metal-Carbon Bonds. 7 . Preparation and Characterization of Ta( r5-C5H5)2(CH2)( CH3), a Study of Its Decomposition, and Some Simple Reactions R. R. Schrock*2 and P. R. Sharp Contribution from the Department of Chemistry, Massachusetts Institute of Technology Cambridge, Massachusetts 021 39. Receired July 26, 1977
Abstract: Two moles of thallium cyclopentadienide react with MMe3C12 to give MCplMe3 ( M = N b or Ta). Trityl tetrafluoroborate attacks the central methyl group in TaCp2Me3 selectively to give Ph3CMe and [TaCp2Mel]+BF4-. Me3P=CH2 (and other bases) deprotonate [TaCpzMe2]+BF4- to give TaCpz(CH2)(CH3); k H / k o for this reaction is 3.4 f 0.3. The methylene ligand in pseudotetrahedral TaCp*(CH2)(CH3) is oriented perpendicular to the C-Ta-C plane and does not rotate readily on the ‘ H N M R time scale (IC*2 20 kcal mol-‘) for the same reason that ethylene in T ~ C P ~ ( C H ~ C H ~ ) does ( C Hnot ~ )rotate readily on the chemical time scale; there is no T orbital perpendicular to the one used to T bond to each which can assist this rotation. The methylene carbon atom is nucleophilic; TaCp2(CHz)(CH3) reacts with AIMe3, Me3SiBr, and CH31 to give TaCpz(CHzAIMe3)(CH,), [TaCp2(CH2SiMe3)(CH3)]+Br-, and TaCp2(CHrCHz)i, respectively. TaCp2(CH2AIMe3)(CH3) also forms in the reaction between TaCp2Me3 and AIMe3, and loses AIMe3 to bases such as NEt3. TaCpz(CH2)(CH3) I mol-] s-l). In the presence of PMe3 the decomposidecomposes at a rate which is second order in Ta (k3o.c = 3 f 1 X 1 mol-’ s - I ) and zero 1 mol-] s-l; k 6 p = ~ 5.4 f 0.4 X tion rate is again second order in T a ( k 3 p c = 3.1 f 0.3 X order in PMe3. The products of the decomposition in the absence of L (L = C2D4, CO, PMe3) are TaCp>(CH2CH2)(CH3) (0.5 per Ta) and a complex mixture of unidentified diamagnetic species; no methane evolves. I n the presence of L they are TaCp2(CH*CH2)(CH3) (0.5 per Ta) and TaCpz(L)(CH3) (0.5 per Ta). TaCpl(CH,)(CH3) reacts with neat Me3P=CH2 s-I) to give TaCp*(CH2CH2)(CHj) and PMe3. at a rate which is pseudo-first-order in Ta ( k 2 2 0 ~= 8.2 f 0.3 X
Introduction A major discovery in organo-transition metal chemistry in the past decade is the class of “carbene” complexes “stabilized” by at least one heteroatom (usually 0, N, or S) bound directly to the carbene’s a-carbon atom.3 “Unstabilized carbene complexes”, or what might better be called alkylidene c o m p l e x e ~ ,however, ~ were virtually unknown before 1973j when Casey6 prepared ( C O ) S W C ( C ~ Hand ~ ) ~Gie~-ing’~ isolated Fe(~5-C~H~)(CO)~(benzocyclobutenylidene).7b A few other examples of disubstituted methylene complexes have been reported since then.8 A monosubstituted methylene complex was discovered in 19749 by a reaction which might be viewed as deprotonation of a primary alkyl’s a-carbon atom.I0 This set the stage for preparation of an unsubstituted methylene complex, Ta($C5Hj)2(CH2)(CH3),’ I shortly thereafter. This is the first isolable transition metal methylene complex. In this paper we report the full details of its preparation, how it decomposes, and how it reacts with selected electrophiles, nucleophiles, and n-acid ligands like CO, PMe3, and ethylene. Results Preparation of Methyl Complexes. TaMe3Clz was first prepared in 1964 by reacting 1.5 mol of ZnMe2 with sublimed TaC15 in pentane.I2 A somewhat more convenient, high-yield method of preparing TaMe3Cl2 from ZnMe2 in ether (which is prepared as needed from ZnCl2 and LiMe) is reported here. This volatile, monomeric, pale yellow, pyrophoric compound is slightly unstable thermally but has been well characterized and used by several workers in the past few years to prepare Ta complexes such as TaMe5,I3 Ta(q8-C8H8)Me3,14 or Ta(acac)2Me3.I5It also reacts smoothly and rapidly with 1 mol of TICjH5 to give orange TaCpMe3C1.16TaCpMe3C1 is significantly more stable thermally than TaMe3Cl2 though not indefinitely at 25 “C under N2; it is best stored at -30 “C. Its ‘ H N M R spectrum in C6D6 shows only one peak for the three methyl groups. Therefore, if its structure is tetragonal pyramidal with an q5-CjH5 ligand at the apex, a common geometry for monocyclopenradienyl complexes,I7 then it must be fluxional in solution at 25 OC.I8 0002-7863/78/1500-2389$01 .OO/O
A second cyclopentadienyl group can be added to TaCpMe3Cl to give TaCp2Me3 using TIC5Hs in toluene or lithium or sodium cyclopentadienide in T H F at -78 “ C . TaCp2Me3 and Ta(v5-C5H4Me)2Me3 can also be prepared directly from TaMe3Cl2 (though considerably less cleanly) using lithium or sodium reagents. TaCpzMe3 is also not indefinitely stable a t 25 “ C under Nz. On heating in vacuo it begins to sublime slowly, then turns pale purple and suddenly decomposes, giving only methane ( I S 2 . 0 mol) and a paramagnetic red oil. On heating a 250-mg sample of TaCp2(CD3)3 in 5 mL of C6D6 at 125 “ C for 16 h 1.8 mol per Ta of methane evolved which was almost all CD3H (10% CD4, 87% CD3H, -0% CD2H2,2% CDH3, -0% CH4); clearly the Cp rings are the primary source of hydrogen atoms in this decomposition. TaCpzMe3 is slightly soluble in pentane and very soluble in aromatic hydrocarbons; the compounds containing one or two V5-CjH4Me rings are significantly more soluble but not noticeably more or less stable thermally. The ‘H N M R spectrum of TaCp2Me3 shows three singlets in the ratio 10:6:3. Almost certainly, therefore, and by analogy with compounds such as NbCp2(C2Hj)(C2H5),l9 whose structure is known,*O TaCplMe3 and related biscyclopentadienyl compounds are members of the family containing the “bent” biscyclopentadienyl unit. TaCp2Me3 is the only example of a MCp2L3 complex except for the well-known trihydrides of the type [ M C P ~ H ~ ] “ +The . ~ I structures of NbCp2H3 and TaCp2H3 are known;22the three hydrides (two “outside”, one “inside”) lie in a plane perpendicular to the (Cp centroid)-Nb-(Cp centroid) plane. The three methyl groups in TaCpzMe3 therefore most likelj lie in a similar plane. The two outside methyl groups can be distinguished from the inside methyl group; the outside methyl resonance (at 7 9.69) is found downfield (by -0.1 ppm) of the inside methyl resonance. TaCpzMe3 reacts readily with Brz in CH2C12. Slow addition of 1 mol of Br2 a t 0 “ C gives an ivory precipitate which analyzes as TaCpzMe2Br; it is nearly insoluble in common solvents and was not characterized. Part of the yellow product obtained on adding 2-4 mol of Br2 is not soluble in acetonitrile. It is a brilliant yellow powder which reacts with 3 equiv of methyllithium in ether to give TaCp2Me3 and is therefore postulated to be TaCp2Br3. Of greatest interest to us here are the aceto-
0 1978 American Chemical Society
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'Table 1 . O Reaction of "TaCp2(CH3)(CD3)(CD,)" Ph3C+BF4-
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mixed with ca. 20% [TaCpz(CDj)z]+BF4- as judged by the high Cp/CH3 proton ratio ( ' H N M R integration). This result is consistent with the finding above that ca. 80% (CH3)mh (CH3)i,b Ph3CCD3, Ph3CCH3, TaCp2(CH3)(CD3)(CD3) results from the reaction of Sample YO % 0x2 % [TaCp2(CH3)(Br)ItBr- with 2 mol of LiCD3. Loosely stated, A 85 15 84 (83'1 16 ( 1 7 ' ) the central methyl group appears to be more carbanionic; it B 77 23 89 11 enters the coordination sphere last and leaves it first. InterC 19 21 18C 22' estingly, Tebbe found that the unique hydride in complexes a All results w'ere obtained by ' H N M R integration at 60 (A), 90 of the type MCpzH, ( M = N b or Ta) is that to which Lewis (B),or 220 MHz (C) or by mass spectroscopy (as noted). Samples acids add, Le., the central hydride ligand is the most basic.21b A, 6. and C were prepared from different samples of [TaCp*(CH3)The results above now allow one to generalize, at least to the (Br)]+Br-. (CH3)o corresponds to the percentage TaCp2(CH3)analogous trialkyl complexes. (CD3)(CD3).23(CH3)i to the percentage T ~ C P ~ ( C D ~ ) ( C H ~ ) ( C D ~ ) * ~ So far the only successful analogous reactions where the in the mixture (see text and Experimental Section). L' Determined by metal is N b is the preparation of NbCpzMe3 from NbMe3Cl2 mass spectroscopy. and 2 mol of TICjH5 in toluene. NbCpzMe3 is nearly colorless, quite soluble in pentane, and rather unstable at 25 "C, as a solid or in solution. It has therefore been identified only by its ' H nitrile-soluble yellow and orange products obtained when 2-3 N M R spectrum, which is virtually identical with that of mol of Brz is added at 0 "C. TaCpzMe3. Since several T a complexes are themselves not The yellow and orange products are difficult to separate but especially stable thermally, one might predict that the correthe more soluble orange product sometimes can be obtained sponding N b complexes may be more difficult to isolate; they pure as plates; it analyzes as TaCpzMeBr4 and is postulated often decompose ca. 50 "C below the approximate decompoto be salt [TaCpz(Me)(Br)]+Br3-. Its IH N M R spectrum in sition point of the Ta compounds [compare the decomposition CD3CN ( T 3.25 ( l o ) , 9.05 (3)) is identical with that of the temperature of NbMes (ca. -30 "C) with that of TaMeS (ca. yellow product, and to [TaCpz(Me)(Br)]+BF4- prepared from 25 o C ) ] . 1 3 [TaCp2MeJ+BF4- (vide infra) and Br2. The yellow product Preparation of Methylene Complexes. One might postulate is therefore postulated to be [TaCpz(Me)(Br)]+Br-; it can be that TaCpzMe3, like some hypothetical benzyl and neopentyl converted to the BF4- salt using Ph3C+BF4- in dichlorocomplexes,l' could lose methane to give TaCpz(CH2j(CH3). methane or TI BF4 in acetonitrile. Under the conditions where methane evolves, however, the [TaCpz(CH,)(Br)]+Br- reacts smoothly with 2 mol of latter, if formed, must be unstable since more than I mol of LiCD3 in diethyl ether to give TaCp2(CH3)(CD3)2. Its ' H methane is formed (vide supra). But the cationic complexes, N M R spectrum clearly shows (by integration) that the major [TaCpzMez]+BF4-, which were formed instead of hoped-for component (ca. 80%) is TaCp2(CH,)(CD,)(CD,), that is, one [TaCp2Me2(CH2)lfBF4-, are analogous to phosphonium or in which CH3 is bound a t an outside position; ca. 20% is arsonium salts. They should be fairly acidic and deprotonate T ~ C P J ( C D ~ ) ( C H ~ ) ( C DIt ~would ) . * ~ seem likely, therefore, easily. that the first mole of LiCD3 gives largely "[TaCp2(CH3)[TaCpzMez]+BF4- is essentially insoluble in T H F but (CD,)]+Br-" which need not necessarily become neutral dissolves readily on addition of Me3P=CHz. Removing all TaCpz(CHl)(Br)(CDl) before the second mole of LiCD3 atsolvent and extracting the residue with toluene leaves an estacks almost exclusively a t the central position. sentially quantitative yield of white Me4P+BF4-. Pale crystals TaCpzMe3 reacts smoothly with Ph3CfBF4- in CH2C12 to form in the toluene filtrate after adding pentane and cooling. give a sparingly soluble yellow precipitate and triphenylAll data presented in the following sections suggest that this methylmethane in high yield. The yellow precipitate dissolves neutral complex is the methylene complex, TaCp2(CH2)in acetonitrile to give solutions whose equivalent conductance (CH3). Substituting [TaCpz(CD3)2]+BF4for is in the range expected for a monocationic salt. It crystallizes [TaCp2(CH3)2]+BF4- gives TaCp2(CD2)(CD3); no CH2 is on addition of ether as pale yellow needles. Its IH N M R present by ' H N M R . TaCp(q5-C~H4Me)(CH2)(CH3)and spectrum shows two sharp singlets in the ratio of 10 ( T 3.45) Ta(q5-CjH4Me)2(CHz)(CH3)can be prepared similarly. An to 6 ( T 9.45). I t is therefore formulated as [TaCpzMez]+BF4-. alternative base which can be used with some success is A similar reaction starting with TaCp(qS-CjH4Me)Me3 or LiN(SiMe3)2. Li alkyls, in general, give poor yields. Ta(qs-CcH4Me)zMe3 gives analogous, more soluble, pale TaCp2(CH2)(CH3) is a monomer in benzene. It can be reyellow, crystalline, cationic complexes. crystallized easily from toluene by adding pentane, in which The organic product of the reaction of TaCp2(CH3)it is also somewhat soluble. It decomposes slowly in the solid (CDjj(CD3) with Ph3C+BF4- is Ph3CCD3 (Table I). The state at 25 "C (more rapidly in solution in several days) and amount of Ph3CCH3 formed corresponds to the amount of reacts readily with oxygen or protonic solvents. T ~ C P ~ ( C D ~ ) ( C H ~ ) in ( Cthe D ~mixture. ) Therefore, Ph3C+ The kinetic deuterium isotope effect for the deprotonation attacks the central methyl group specifically (eq 1). At no reaction can be measured by starting with [TaCp2(CH3)/CH, (CD3)]+BF4- (containing ca. 20% [TaCp2(CD3)z]+BF4-, see Table I) and measuring (by 'H N M R integration) the ratio Cp,'Tta-CD, + PhrC+BF,Ph,CCD; of TaCp2(CHz)(CD3) to TaCpz(CD2)(CH3) formed. O n reaction with Me3P=CH2 the cation obtained from sample C gave a 33:lO mixture of TaCp2(CH2)(CD3) and /CH.t TaCp2(CD*)(CH3) (integration done a t 220 M H z in fre[Cp:Ta l+BF,- (11 quency sweep mode); therefore, kH/kD = 3.3. A similar ex'CD, periment with the cation from sample B gave kH/kD = 3.5 (integration done at 90 M H z in field sweep mode). Therefore, time is there any indication of H / D scrambling to give any the error in kH/kD so determined is estimated to be f0.3, i.e., significant amount of CHzD or CD2H ligands since the IH kH/kD = 3.4 f 0.3. This result may prove important in studies N MR resonances in labeled compounds are sharp singlets and of a-hydrogen atom abstraction reactions which are not strictly the mass spectrum of triphenylmethylmethane shows parent deprotonation reactions of the type described peaks due only to Ph3CCD3 and Ph3CCH3. The cationic product in each case is ca. 80% [ T ~ C P ~ ( C H ~ ) ( C D ~ ) ] + B F ~It- is important to note that the ratio of methylene protons
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/ Preparation of Tu(q j - C5H j ) 2/ CH2) (CH3)
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to methyl protons does not change (according to IH N M R ) in the above mixtures as the compound decomposes over several days. Therefore, hydrogen (or deuterium) does not transfer f r o m the methyl to the methylene ligand at a significant rate. One can estimate that the activation energy for this reaction, if it could be detected before the compound decomposes, must be on the order of or greater than about 20 kcal mol-'. Additional evidence that this conclusion is correct is the finding that H and D do not scramble in pure TaCp2(CH2)(CD3) (prepared from TaCp2(CDz)(CD3), vide infra) under conditions where it does not decompose. NMR Studies and Infrared Spectra. The gated decoupled 22.63-MHz I3C N M R spectrum of TaCp2(CH2)(CH3) is shown in Figure 1. The most pertinent feature is the triplet ( I J c H = 132 Hz) due to the methylene carbon atom 224 ppm downfield of Me&. This is the region in which one might expect to find it since the a-carbon atom resonance in stabilized carbene complexes is also normally found at low field.3 The C-H coupling constant is greater than the ca. 125 Hz expected for a tetrahedral carbon atom ( ' J c H for the methyl group in TaCp>(CH2)(CH3)is 122 f 1 Hz) though not as large as that found for olefinic carbon atoms (ca. 160 H z ) . ~ ~ The 'H N M R spectrum of TaCp2(CHl)(CH3) in C6D6 a t 60, 100, or 220 M H z consists of three singlets at r -0.1 1 (2) 4.88 (lo), and 10.0 (3) assigned to the CH2, Cp, and CH3 protons, respectively. The 'H N M R spectrum of TaCp($CjH4Me)(CH2)(CH3) shows the predicted cyclopentadienyl and methyl peaks but the methylene resonance, which is slightly broadened at 60 MHz, becomes an AB quartet at 220 (Figure 2a) or 100 M H z (Figure 2b) with 2 J ~ = A7.6 ~ fB0.1 H z . The ~ ~most reasonable explanation is that TaCp2(CH2)(CH3) is also a member of the "bent" biscyclopentadienyl family and that the CH2 ligand in this pseudotetrahedral molecule is oriented perpendicular to the C-Ta-C plane. The AB patterns at 220 or 100 M H z do not change on warming the sample to 95 'C (Figure 2b), a t which temperature decomposition is rapid. A lower limit to AG* for interconverting HA and HB can be conservatively estimated by assuming26 k , = 2-1/2n(Av2 6 J 2 ) 1 / 2a t a coalescence temperature which is 20'C above the highest attainable, Le., k , = 44 s-l at T , = 388 K. Therefore, ACT 1 ca. 20 kcal mol-'. The most believable manner in which HA and HB could exchange is by rotation of the methylene ligand 180' about the M=CH2 bond axis. We can postulate then that the methylene ligand does not rotate readily, a t least on the 'H N M R time scale. Note that another possible dynamic process, proton transfer from CH3 to CH2, has already been excluded (vide supra). The infrared spectra of TaCp2(CH2)(CH3) and TaCpzMe3 in Nujol are nearly identical. Only four additional sharp peaks [at 1350 (w), 1130 (w), 785 (m), and 670 cm-I (m)] are found between 2000 and 600 cm-I in the spectrum of the methylene complex; the latter two may be characteristic of methylene
+
C l O H z -4
Figure 2. The ' H NMR spectrum of the methylene ligand in TaCp(q5-
C5HdMe)(CH>)(CH3) at (a) 220 MHz, 25 "C.
OC,
and (b) 100 MHz, 95
bending and rocking modes (respectively) or possibly a Ta=C stretching mode (or a combination mode with the former), though this proposal remains uncertain at this time for want of additional examples. Three sharp bands at 3120 (w), 3 100 (w), and 3080 cm-' instead of the normally featureless absorption at ca. 3 100 cm-I due to $-CjHj could be ascribed to methylene C-H stretching modes (probably combined with cyclopentadienyl C - H stretching modes), though again any definitive statement must be postponed. Reactions of TaCpz(CHz)(CH3) with Electrophiles. TaCpz(CH2)(CH3) reacts immediately with 1 mol of AlMe3 to form a cream-colored adduct with similar solubility characteristics. Its IH and 13C N M R spectra show that (in comparison to TaCp2(CH>)(CHj)) (1) only the methylene IH N M R signal shifts (upfield from r -0.1 1 to 2.32) and (2) the methylene 13CN M R resonance shifts upfield from 224 to 177 ppm and IJCH decreases from 132 to 124 Hz. Though the range of ~ J Cfor Halkylidene ligands is not yet fully known, ~ J C for H tetrahedral carbon atoms in a methyl group bound to Ta or A1 in the compounds discussed here (and others in hand) does not deviate more than f 3 H z from 125 H z . A decrease in ' J C Hfrom 132 to 124 Hz, along with the upfield shift of the methylene carbon and proton resonances, therefore suggest that AlMe3 has added to the methylene group. Though conceivably one methyl group could bridge between A1 and Ta, it apparently does not, or at least that configuration is not static on the 'H N M R time scale. Adding Me3P=CH2 or Et3N to an 'H N M R sample of TaCp2(CHzAlMe3)(CH3) generates the spectrum of TaCp2(CH2)(CH3) and B.AlMe3 (B = Et3N or Me3P=CH2); TaCp2(CH2)(CH3) can be recovered pure by fractional crystallization from pentane in each case. Clearly, therefore, the methylene ligand is nucleophilic; it does not (in contrast to (CO)jW=CPh227) form an adduct with PMe3. The AlMe3 adduct is probably best described as having a formal positive charge on T a and a formal negative charge on A1 (cf. Me3PCH2AIMe328). TaCp2(CHzAlMe3)(CH3) may also be formed in good yield in toluene from TaCp2Me3 and AlMe3. An orange oil, believed to be [TaCpzMe2]+AlMe4- (see Experimental Section), separates rapidly but after several days redissolves as 1 mol of methane evolves. Though the mechanistic details of this reaction have not been explored, it is plausible and tempting to suggest that a methyl group in AlMe4- is the base which removes a proton from [TaCpzMez]+ to form TaCp2(CH2)(CH3), methane, and AlMe3 (eq 2). TaCp2(CH2)(CH3) reacts slowly with Me3SiBr in dichloromethane to give a pale yellow product which is moderately
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9.0 9.5 Figure 4. The IH NMR spectrum of the ethylene ligand i n (a) Ta(7‘C S H ~ ) ~ ( C ~ H ~ )at( C270 H ~MHz ) (chemical shifts i n hertz from MedSi, C & , solvent) and (b) a mixture of 75% Td(~5-C~H5)2(CH2CD2)(CD~) and 25% Ta(v5-C5H5)2(CH2CH2)(CD3) at 220 MHz (chemical shift in r , C.&, solvent)
postulated intermediate has not yet been observed by ‘H N M R . A neutral formulation may be sterically allowed but an ionic formulation (or ion pair) is also plausible; the precise and Ta(q5-C5H5)2(CDzCH2)I(chemical shifts in hertz from Me&, C& stereochemistry and exactly how D finds its way to CH3 are solvent). therefore uncertain a t this time. TaCp2(CH2CH2)1 reacts with K H in THF to give pale yellow TaCp2( C2H4) ( H ) (cf. NbCp2( CHzCH2)( H ) 9). Its TaCp,Me, + AIMe, -+ [TaCp,Me,]+[AIMe,j‘H N M R spectrum includes resonances due to outside CH2 ,CH,AlMe, a t T 9.2, inside CH2 a t T 9.7, and the hydride ligand a t T 13.4. --t CpLTa + CH, ( 2 ) The hydride resonance is a poor triplet ( J = 2 Hz) while the outside CH2 pattern is much more complex than the inside C ‘H CH2 pattern (which is of the normal A2B2 type). W e propose, soluble in dichloromethane and acetonitrile but insoluble in therefore, that the hydride is coupled to the outside CH2 of the nonpolar solvents. It can be recrystallized from acetonitrile bound ethylene. The isolation of TaCp2(CHzCH>)(H) at least in which its equivalent conductance is in the expected range illustrates that TaCp2(CHz)(CH3) is not the favored taufor a monocationic complex. Its ‘H N M R spectrum in CD3CN tomer. suggests that it is [ T ~ C ~ Z ( C H ~ S ~ M ~ ~ ) ( C ApparH~)]+B~ -. Decomposition of TaCpz(CH*)(CH3)and Reactions with ently Br- cannot coordinate to the metal for steric reasons. ?r-Bonding Ligands. A saturated C6D6 solution of Like [TaCp2Me2]+BF4-, [T~CP~(CH~S~M~~)(CH~)]+B~TaCpz(CH2)(CH3) begins to darken in 1 h and over several is insoluble in T H F , but dissolves smoothly on addition of days turns an opaque green-brown color. The strongest signals Me3P=CH2. The product is TaCpz(CHSiMe3)(CH3), the in the ‘ H N M R spectrum of this decomposed sample are those result of removing the more acidic trimethylsilymethyl a expected for T ~ C P ~ ( C H ~ C H ~ ) (Apparently C H ~ ) . no product proton; this complex will be described separately along with is paramagnetic since all signals are sharp. In a larger scale other members of this “substituted methylene” class. decomposition reaction only traces of methane evolve and TaCp2(CH2)(CH3) reacts more rapidly with CH31 in TaCp2(C2Hd)(CH3) can be isolated in 30-40% yield. Its benzene. The solution turns orange as methane (1 mol per T a ) 270-MHz ‘H N M R spectrum shows the expected A2B2 patevolves. TaCp2(CH2CH2)1 is obtained as dark red-orange tern due to bound ethylene (Figure 4a) and its I3C spectrum needles or plates which are moderately soluble in aromatic two triplets at 20.2 and 20.9 ppm downfield from Me4Si ( ~ J C H hydrocarbons, acetonitrile, and dichloromethane (with which = 149 H z for each carbon atom; cf. 27.6 and 29.4 ppm, ‘ J C H it slowly reacts). The ‘ H N M R spectrum in C& shows a = 155 and 153 Hz, respectively, for ethylene in singlet due to the cyclopentadienyl protons and an A2B2 patN ~ C P ~ ( C H ~ C H ~ ) ( C H ~inCaddition H ~ ) ~to~ the ) , appropriate tern near T 8 characteristic of q2-bonded ethylene in the ratio resonances for q5-C5H5 and CH3 in each case. We can prob10:4 (Figure 3a). We assume that its structure is analogous to ably safely assume that the N M R signal for the outside eththat of N ~ C P ~ ( C ~ H ~ ) ( CSubstituting ~ H ~ ) . ~ OCD31 for CH31 ylene protons in T ~ C P ~ ( C H ~ C H ~ ) occurs ( C H ~downfield ) of gives CH3D and a product whose ’H N M R spectrum shows that for the inside protons by analogy with the IH N M R the cyclopentadienyl singlet, but only two broad singlets with spectrum of TaCpzMe3. total area 2 in place of the A2B2 pattern, consistent with the When one allows an equimolar mixture of TaCp2(CH2)product being a 1:l mixture of TaCp2(CH2CDz)I and (CH3) and TaCp2(CDz)(CD3) to thermally decompose in TaCp2(CD2CH2)I (eq 3 and Figure 3b). A small isotope effect benzene the isolated ethylene complex is a mixture of TaCp2(CH2CH2)(R), T ~ C P ~ ( C H ~ C D ~ ) ( R TaCp2), (CD2CH2)(R), and TaCp2(CD2CD2)(R) ( R = CH3 or CD3), TaCpdCH,)(CH,) + CD:,I -+ “Cp,Ta-CH&DJ” according to its 270-MHz ‘ H N M R spectrum, which is anal\ CH, ogous to that obtained by combining the spectrum in Figure 3a (1/2the intensity) with that in 3b [see also Figure 4b (disCH, I - W D CD, ( 3 ) cussed in the next section)]. / \ /\ Decomposing TaCp2(CHz)(CH3) under ethylene gives 0.5 Cp,Ta-CD, 0 . 5 Cp,Ta-CHL essentially a quantitative yield of T ~ C P ~ ( C ~ H ~ ) (Under CH~). \I \I C2D4 (1 mol per Ta; total P = 0.2 atm) 0.5 mol of pure C2D4 remains after decomposition is complete. The 270-MHz I H accounts for the slight shift of each d2-ethylene CH2 resonance N M R spectrum of the product in the ethylene region is idenin these and other CHzCD2 complexes to higher field. The Figure 3. The 270-MHz IH N MR spectrum of the ethylene ligand in (a) Ta($-C5H5)z(C2H4)1 and (bj a 1 : I mixture of Ta(a5-CsHs)2rCH2CD2)1
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60
Figure 5. A plot of the disappearance of Ta(q5-CsH5)2(CHz)(CH3) in a 0.33 M sample at 30 f 2 OC in the presence of PMe3 ( X = 0.17 M, 0 = 1.7 M) in C6H6.
tical with that of TaCp2(C2H4)(CH?) (Figure 4a) except that the resonance due to the ethylene protons is only half as intense. The rest of the spectrum consists of two C p peaks and two methyl peaks, 1.5 Hz apart in each case, consistent with a 1: 1 mixture of TaCp2(CH2CH2)(CH3) and TaCp2(CD2CD2)(CH3). The inverse, decomposition of TaCp2(CD2)(CD3) under excess C2H4 (total P sz 3 atm), yields a product whose IH N M R spectrum shows an ethylene A2B2 pattern again essentially identical with that in T ~ C P ~ ( C ~ H ~ ) ( but C Hhalf ~), the intensity.29 [The peak due to CH,D3-x in the starting material (5-10% of one proton) is no larger in the product mixture.] We conclude, therefore, that little or no CH2CD2 complex is present in each case, only a 1:l mixture of TaCp2(CzH4)(R) and TaCp2(C2D4)(R)(R = CH3 or CD3). This result suggests that the CH2=CH2 ligand forms by combination of two methylene ligands in separate molecules and that L ( e g . , CzD4) coordinates to the fragment left after one of the methylene ligands has transferred (eq 4). CH, I
-
,c\H, Cp2Ta-CH2
+
“TaCp,(CH,)” ( 4 )
‘CHI
,L
/
L
In the presence of PMe3 TaCpl(CHl)(CH3) decomposes to give T ~ C P ~ ( C ~ H ~ ) (and C HTaCpz(PMe3)(CH3). ~) The rate at which TaCp2(CHz)(CH3) disappears can be monitored easily and accurately by ‘ H N M R . This rate is second order in T a for a sample 0.33 M in T a and 0.17 M in PMe3 in C6H6 (Figure 5) at 30 f 2 “ C (tl/2 = 26 h, k3o.c = 3.2 f 0.3 X L mol-’ s-l). Furthermore, a second sample, identical except 1.7 M in PMe3, decomposed a t an identical rate (Figure 5 ) . Therefore, the reaction is zero order in PMe3. Figure 6 shows two similar plots of 1 / C vs. T for a sample 0.37 M in Ta (0.50 M in PMe3) and one 0.18 M in T a (0.50 M in PMe3) in C6H6 a t 60 “C; t l p = 1.4 and 2.9 h, respectively, and k600C = 5.4 f 0.4 X L mol-’ s-I, again consistent with bimolecular
’ Ih,!
_c
Figure 6 . A plot of the disappearance of Ta(qS-CsH~)2(CHz)(CH3)in a 0.37 V sample ( X ) and a 0.18 M sample (O), each 0.50 M In PMe3, in C6H6 at 60 “c
decomposition of TaCp2(CH2)(CH3) to give TaCpz(C2Hd(CH3) and a fragment, “TaCp2(CH3)”, which is captured by PMe3 to give TaCpz(PMe3)(CH3) (eq 4, L = PMe3). The decomposition of TaCpz(CH2)(CH3) in the absence of PMe3 cannot be followed as accurately by integration (owing to interference by products resulting from “TaCp2(CH3)”, vide infra) but a 0.33 M sample in C6H6 decomposed a t 30 f 2 “C a t a rate not significantly different (k30oC = 3 f 1 X L mol-’ s-l) from that in the presence of PMe3. The decomposition in the presence of PMe2Ph proceeds similarly to give an equimolar mixture of TaCp*(C2H4)(CH3) and TaCp*(PMe2Ph)(CH3) and under 2 atm of C O an equimolar mixture of TaCp2(C2H4)(CH3) and TaCp2(CO)(CH3) (eq 4; L = PMe2Ph and CO, respectively). Both red TaCp*(L)(CHl) (L = PMe3 or PMelPh) and olive-green TaCp2(CO)(CH3) can be separated in good yield from the more soluble TaCpz(C2H4)(CH3). The ’H N M R and infrared spectra of all are entirely consistent with their formulation (details can be found in the Experimental Section). The fate of the “TaCpZ(CH3)” fragment in the absence of a-bonding ligands has still not been determined. In a typical decomposition reaction the T ~ C P ~ ( C ~ H ~ ) (isCremoved H~) from the crude solid product mixture by extraction into pentane or hexane. Some of the remaining dark solid (ca. 50% of the starting TaCp2(CHl)(CH3) by weight) is soluble in toluene and some of that which is not is soluble in tetrahydrofuran. The remainder (ca. 25% of the starting TaCp2(CHz)(CH3) by weight) is essentially insoluble in T H F . The 270-MHz ‘ H N M R spectrum of each soluble fraction contains many peaks. Each is apparently a mixture from which no one crystalline product has yet been obtained. It seems plausible that the q5-C5Hs rings do not remain intact, e.g., the end products may be related to the titanocenes30 or n i ~ b o c e n e Since . ~ ~ only traces of methane evolve (GLC), “[Ta(175-C5Hs)(~-)7’,174-CsH4)]2” must not be a major product (cf. formation of [Th($CsH5)2(lr-171,174-CgH4)]2 on decomposition of T ~ C P ~ R ~ ~ ) . Reaction of TaCpt(CH2)(CH3)with Me3P=CH2. An ‘ H N M R spectrum of TaCp2(CH2)(CH3) in neat Me3P=CH2 is a composite of the two individual spectra. However, over several days a t 25 OC the starting material disappears and a composite spectrum due to T ~ C P ~ ( C H ~ C H ~ ) ( C PMe3, H~), and Me3P=CH2 appears; the spectrum of an appropriate mixture of these compounds was identical.
Journal of the American Chemical Society
2394
1 100.3
April 12, I978 PMe,
/
3-
CH,
,’I
,‘
HCD,
+ CH2=PMe3
-+
‘
c~~T$---~D,
- PMe
/ \ Cp,Ta-CD, \
(5)
‘CD,
t ( h r ) -*
100
Figure 7. A plot of the disappearance of Ta(VS-CjHj)2(CH2)(CH3)(0.33 M) in neat Me3P=CH2 at 22 O C .
TaCp2(CHz)(CD3) come from “TaCp2(CD3)” and MeAP=CH2 since if TaCp2(CD*)(CD3) decomposes bimolecularly (to give “TaCp2(CD3)” and T ~ C P ~ ( C D ~ C D ~ ) ( C D ~ ) ) then some TaCpl(CD2CH2)(CD3) should form by reaction of TaCpz(CD2)(CD3) with TaCp2(CHz)(CD3) (vide supra). Therefore, TaCp2(CHz)(CD3) must form by exchange of CD2 (on Ta) with CH2 (on P). [IH N M R integration of the C p vs. the ethylene protons in the product mixture suggests that the appropriate amount of CH2 has been incorporated (relative areas 10.0 (defined) to 2.4 f 0.1) but confirmation that Me3P=CD2 is formed is virtually impossible owing to intraand intermolecular H / D scrambling.] Exchange cannot strictly occur from the transition state shown in eq 5 since loss of Me3P=CD2 is not microscopically the reverse reaction. Therefore, one must postulate that a second reaction pathway of slightly higher energy leads exclusively to CD2/CH2 exchange. It is possible that this second pathway consists of the sterically less likely “inside” attack on Ta followed by the energetically favored loss of Me3P=CD2 from the “outside” (eq 6), if, of course, “outside” attack is a readily reversible equi-
TaCpl(CH2CH2)(CH3) can be isolated quantitatively by removing PMe3, Me3P=CH2, and solvent in vacuo and is identical with an authentic sample. Formally Me3P==CH2 has donated its methylene group to Ta=CH2 where it combines to form an ethylene ligand. This reaction is pseudo-first-order in T a with k 2 2 0 ~= 8.2 f 0.3 X s-’ (Figure 7 ) . If only 1 mol of Me3P=CH2 per T a (0.33 M) is used in toluene-dg as solvent, TaCpz(PMej)(CH3) forms in addition to T ~ C P ~ ( C H ~ C H ~ ) ( Their C H ~ ratio ) . is approximately 1:3 (by ‘H N M R ) after the reaction is approximately 90% complete (7 days at 22 “C). Note that the reaction is considerably slower than in neat Me3P=CH2 (50% complete in 1 day, 95% complete in 4 days), more on the order of the rate a t which ,CD2PMe, p 2 TaCp2(CHz)(CH3) decomposes (vide supra). Most likely, / therefore, TaCp2(PMe3)(CH3) forms as a sufficient concenCpJa CH,=PMes -+ Cp,Ta-CH, tration of PMe3 builds up and captures the ‘‘TaCp2(CH3)” ‘CD, \ fragment resulting from reaction of TaCpz(CH2)(CH3) with CD, itself. Of course, it is also possible that “TaCp2(CH3)” or TaCp*(PMe3)(CH3) reacts with Me3P=CH2 to form Me,P=CD, + Cp2TaHCH2 6) TaCp*(CH2)(CH3). ( T ~ C P ~ ( C ~ H ~ ) is ( Cessentially H~) inert toward Me3P=CH2, even neat at 60 “C.) These complications ‘CD3 prevent a more accurate determination of the dependence of the rate of the reaction of TaCp2(CH2)(CH3) with Me3librium which lies toward TaCp*(CH2)(CD3) and M.3P=CH2 on Me3P=CH* concentration. However, it is reaP=CD2 (as the relatively slow rate of the reaction of sonable to assume that this dependence is also first order. In TaCp2(CH2)(CH3) with Me3P=CHz might suggest). Such that case (assuming that the density of the Me3P=CH2 = 0.8 a postulate does not seem unreasonable since the reaction of g mL-’ and V = 1 mL) [Me3P=CH2] = 10 M and k ‘ 2 2 0 ~= [TaCp2(CH,)(Br)]+Br- with 2 mol of LiCD3 did not give L mol-’ s-l where k220c = k1220c[Me3P=CH2]. T ~ C P ~ ( C H ~ ) ( C D ~ ) (exclusively. CD~) Both results may be Therefor6 Me3P=CH2 actually reacts a good deal more slowly taken as evidence that reactions of these biscyclopentadienyl with TaCp2(CH2)(CH3) (equal concentrations) than complexes are not completely specific. TaCp2(CH2) (CH3) reacts with itself (calculated k 2 2 0 ~= 1.4 It is interesting to note here that T ~ C P ~ ( C H ~ C D ~ ) ( C D ~ ) X L mol-’ s - ’ ) , ~as~the initial observation suggested. is configurationally stable, that is, ethylene does not “rotate” rapidly on the chemical time scale to give TaCp2(CD2CH2)The reaction of TaCp2(CD2)(CD3) with neat Me3P=CH2 provides some details concerning how methylene transfers from (CD3 ). Presumably there is no orbital of n-type symmetry and P to T a . After 5 days a t 22 OC the reaction was ca. 95% comappropriate energy perpendicular to the one used to n bond to plete. The product is largely (75%) T ~ C P ~ ( C H ~ C D ~ ) ( C Dethylene ~), in the ethylene-methyl plane which can assist this but little or no TaCp*(CD2CH2)(CD3) is present, according rotation (see Discussion). Interestingly, this same “missing” to the 220-MHz ‘ H N M R spectrum (Figure 4b), if we assume orbital is the one needed to P bond to the methylene ligand that the chemical shift of the outside ethylene protons in should it too rotate 90’ about its metal bond axis. As argued coordinated ethylene is greater than that of the inside ethylene in a previous section, this rotation is slow, at least on the ’ H protons (cf. TaCpzMe3). Therefore, when Me3P=CH2 N M R time scale (AG* 1 20 kcal mol-’, conservatively estitransfers its methylene it does so selectively from the “outside”, mated). possibly via a transition state as shown in eq 5 . But ca. 25% of The main point to be stressed in this section, however, is that the product mixture is T ~ C P ~ ( C H ~ C H ~ ) (and C Dthe ~ ) reMe3P=CH2 reacts with TaCp2(CH2)(CH3) in a manner maining 5% of starting material is almost exclusively (90%) similar to that in which TaCp2(CHl)(CH3) reacts with itself. This finding further strengthens the argument that TaCpz(CH*)(CD3) (by ’ H N M R ) . Presumably TaCp2(CH2CHz)(CD3) arises by reaction of TaCpz(CH2)TaCp2(CH2)(CH3) is “ylidelike”, Le., the methylene ligand (CD3) with Me3P=CH2. But TaCp2(ethylene)(Me) does not is a good nucleophile and presumably, therefore, negatively react with Me3P=CH2 to give TaCp2(CHz)(Me) nor can polarized relative to T a .
+
-
Schrock, S h a r p
/ Preparation of Ta(qS-C5H~)2(CH2)(CH3)
2395
CH3 interacts in any way with the methylene ligand. One possible interaction, H transfer from CH3 to CH2, is nondestructive, of course, and has been observed in other systems,46 Terminal methylene complexes have been postulated in the but apparently has a higher activation energy than the deCu-catalyzed decompositions of d i a ~ o m e t h a n ein , ~decom~ composition reaction in this case. One might expect typical positions of methyl c ~ m p l e x e s ,in ’ ~olefin ~ ~ ~ metathesis reacligands which are not ancillary in other hypothetical cases to t i o n ~in, ~reactions ~ of a-halo- or a-alkoxymethyl complexes,37 be subject to nucleophilic attack by -CH2 (e.g., CO, to give and in reactions of cyclopropanes with a W-based olefin meketene complexes4*)or electrophilic attack by +CH2 (e.g., PR3, tathesis catalyst.38 I n most cases, however, “carbenoid” into give “ylide” c ~ m p l e x e s ~An ~ ) .apparent complication of this termediates cannot be excluded as the reactive intermediate. type is the “insertion” of methylene into an Ir-CI bond to give Diazomethane has been the most popular methylene source an Ir-CH2Cl complex.39 in attempts to prepare isolable methylene complexes.39 Only The second reason why TaCp2(CH2)(CH3) is stable is that recently, however, has this method been successful to the extent readily dimerize by a dipolar [2 21 addition of the that bridging methylene complexes have been i ~ o l a t e d . ~ ~ , it~ cannot ~ Ta=CH2 bond to itself. Such a dimerization should be indeThe reaction of TaCp2Me3 with Ph3C+BF4- might be expendent of the polarization of the metal-carbon bond. Indeed, pected to give [ T ~ C P ~ M ~ ~ ( C H ~ )and ]+B Ph3CH F ~ - (cf. the ( C O ) S C ~ C O C H ~ C H ~does C H decompose ~ bim~lecularly,~~ preparation of [ FeCp(CO)~(benzocyclobutenylidene)]+,ref the olefin favored by combination of two electrophillic carbene 7 ) . The fact that [TaCpzMez]+BFq- is formed instead was fragments is, in fact, always a major decomposition p r o d ~ c t . ~ surprising a t the time since there are few examples of elecTherefore, we might postulate that a likely decomposition trophilic attack on an alkyl ligand at the a-carbon atom by pathway for any complex containing a carbenelike ligand, Ph3C+ to give Ph3CR. This may be largely because most alkyl however polarized, will be bimolecular, should alternative ligands contain more readily removed 0-hydrogen atoms (see, reactions of the carbenelike ligand with other ligands or other however, ref 7 ) . It seems less surprising now that decomposition pathways be unfavorable. Of course, the fact [TaCp2Mez(CH2)+] does not form since it is difficult to see that Me3P=CH2 transfers methylene to TaCp2(CHz)(CH3) how CH2 could be a bonded to Ta(V) (vide infra); the positive to give PMe3 and T ~ C P ~ ( C ~ H ~ ) ( respectively, CH~), is yet charge would have to be localized on the methylene carbon further evidence that a bimolecular reaction resulting in alkatom. ylidene transfer is reasonable. How this reaction can occur in such a crowded environment It would be premature to attempt to rationalize why the is still unclear. It does not seem too unreasonable to postulate Ta=CH2 bond is polarized +/-. We might point out that that Ph3C+ attacks the central Me group on the face opposite other members of the MCp2(alkylidene)(R) family50 as well Ta; how the methyl-CPh3 bond could form under these ciras M(CH2CMe3)3(CHCMe3)5’ (M = N b or T a ) and cumstances, however, is not obvious. More complex schemes TaCpCl2(CHCMe3) I also contain a nucleophilic alkylidene are possible, for example, one involving electron transfer to give carbon atom. Therefore at present we can only postulate that “[TaCp2Mej]+” followed by loss of the central M e group as this polarization is characteristic of any N b or Ta alkylidene a radical and capture by Ph3C. to give Ph3CMe.42 If this recomplex in which the metal is in a relatively high formal oxiaction is attempted with less crowded Ta(V) alkyl complexes, dation state (+3 or + 5 depending on one’s point of view). e.g., Ta(CH>CMe3)3Me2, Ph3CMe is formed but only neutral One acceptable description of how methylene bonds to Ta complexes containing fluoride bound to the metal could be in TaCp2(CH2)(CH3) consists of treating CH2 as an sp2found.43 [TaCpzMez]+ does not abstract fluoride from BF4-, hybridized 2e donor with an empty 2pz orbital. The filled sp2 most likely because BF4- cannot contact the metal easily in orbital donates electron density into an empty a-type orbital this crowded environment. on T a while a filled a-type orbital on Ta donates electron Steric crowding in [TaCpzMez]+BF4- almost certainly also density back into the empty 2p, orbital on the methylene liis one reason why Me3P=CH2 does not attack the metal but gand. This bonding picture is of course analogous to that which removes what must be a relatively accessible and fairly acidic describes how a simple olefin such as ethylene binds to a metal. proton instead. (A quantitative measure of the acidity of this Therefore, in any given circumstance where both the methproton is not yet available.) Of course, the overall result would ylene and the ethylene complexes are known, the M=CH2 be identical if Me3P=CH2 did attack the metal, methylene plane in one complex must be perpendicular to the MC2 plane were transferred, and Me4P+BF4- were lost. However, the in the other (compare TaCp2(CH2)(CH3) with TaCp2preparation of TaCp>(CD*)(CDj) from [TaCp*(CD3)2]+ (CH2=CH2)(CH3)). However, the opposite donor/acceptor and Me3P=CH2 and the successful preparation of TaCp2picture is equally appropriate. In fact, we propose that neither (CH2)(CH3) using LiN(SiMe3)2 clearly rule out this possidonor/acceptor bonding scheme alone is generally valid since bility. we believe that it would then be difficult to rationalize different The fact that TaCpz(CH2AIMe3)(CH3) forms from bond polarities. The postulate that an alkylidene will bond TaCp2Me3 and AlMe3 seems important for several reasons. orthogonal to an olefin should not be influenced by what deFirst, it demonstrates that an alkylidene complex can form scription is ultimately chosen. from an aluminum alkyl (aluminum alkyls a r e common “coSome controversy has arisen in the past few years concerning catalysts” in olefin metathesis systems36).Secondly, this alkthe number and spatial distribution of bonding and nonbonding ylidene is nucleophilic, now believed to be a likely type in a t orbitals in “bent” biscyclopentadienyl c o m p l e x e ~ . A~ ~ ~ ~ ~ , ~ ~ least some olefin metathesis systems.44Thirdly, this alkylidene molecular orbital approach seems to explain most of the is “protected” against bimolecular decomposition (for steric findings. Briefly, two orbitals lying in the plane passing beas well as electronic reasons; vide infra) by coordination of a tween the two Cp ligands and ca. 90’ to one another are used fairly labile Lewis acid, AlMe3. In general, however, reactions to u bond to CH2 (or CH2=CH2) and CH3; these bonds of such “carbenoid” species may not be significantly different complete the pseudotetrahedral MCp2L2 structure. A afrom those of the “unprotected”, or true, alkylidene ligand bonding orbital also lies in this plane. It is this orbital which where relatively nonbulky substrates, e.g., linear olefins, are can overlap with the 2p, orbital on CH2 or the T * orbital on concerned. Therefore, such adducts could be the most imporCH2=CH2. Neither CH2 nor CH2=CH2 rotates readily tant component of a metathesis system.45 about the metal-ligand bond axis since no a orbital orthogonal There appear to be two main reasons why TaCp*(CH*)to this “in-plane” a orbital exists to assist such a rotation. (CH3) is a stable, isolable species. The first is that other ligands Lauher and Hoffmand3 have discussed these ideas thoroughly are innocuous, Le., there is no evidence that either q5-C5H5 or
Discussion
+
2396
Journal of the American Chemical Society / 100.8 / April 12, 1978
stirred for 1-2 h and 52.5 mmol(4.62 g) of dry dioxane was then added and have used the hypothetical model, [TiCp2(CH2)(CH3)]-, dropwise. ZnClZdioxane was filtered off and the solvent removed from which is isoelectronic with TaCp2(CH2)(CH3) except for filled the filtrate in vacuo leaving a yellow residue which was extracted with shells, to confirm them through calculations; they predict AG* 200 mL of pentane. The mixture was filtered and the pentane removed for methylene rotation in [TiCp2(CH2)(CH3)]- to be ca. 27 in vacuo leaving 7.67 g of pale yellow TaMe3Clz (80% yield based on kcal mol-'. All of the postulates concerning the structure and TaC15). bonding in TaCp2(CH2)(CH3) have been confirmed by an 2. Preparation of TaCpMe3CI. Solid TIC5H5 (4.5 g) was slowly x-ray structure in which the hydrogen atoms on both CH2 and added to a vigorously stirred solution of 5.0 g of TaMe3Clz in 25 mL CH3 were located." of toluene. After 1 h the TIC1 was filtered off and the solvent removed The I3C spectrum of TaCp2(CH2)(CH3) illustrates that, in vacuo leaving an orange residue (5.0 g) of essentially pure TaCpMe3CI. Orange needles can be obtained easily by adding pentane contrary to the earliest t h e ~ r i e sthe , ~ formal charge on an alto a saturated toluene solution followed by standing the partially kylidene a-carbon atom is probably not the major factor which crystallized product in the mother liquor at -40 "C overnight. causes its resonance to occur a t low fields. Though CH2 is TaCpMe3C1 slowly decomposes in the solid state at 25 OC under ninegatively charged in TaCpz(CH2)(CH3) its resonance occurs trogen (weeks or months). in the same region (at 228 ppm) as that for PhQ (at 21 1 .4nal. Calcd for TaCsH14CI: C, 29.42; H , 4.32: CI, 10.85. Found: ppmS4).Phenomenologicallq it now seems that some multiple C , 29.19; H , 4.1 I ; CI, 10.69. bonding between carbon and a transition metal is probably the ' H N M R ( T ,C6D6) 4.45 ( s , 5), 8.88 (s, 9). single most important factor which causes the carbon reso3. Preparation of TaCprMe3 and TaCp2(CD3)3. TaMe3Cl2 (20.0 nance to occur in the 200-400-ppm range. However, for a seg) and 36.2 g of TIC5H5 were stirred in 200 m L of toluene for 16 h. ries of similar Fischer-type carbene complexes the chemical TIC1 was filtered off and the solution volume reduced in vacuo until a small crop of crystals formed. Three volumes of pentane were added shift of the carbene carbon atom does appear to depend directly and the solution was chilled a t -40 OC for 6 h to give 18.0 g of silin the expected manner on the electron-donating ability of very -white crystals. A second crop of 2.5 g was obtained similarly after substituents attached to it.3,5STherefore, it is at least not reducing the volume of toluene still further; total yield 20.5 g (85%). surprising to find that the nucleophilic methylene resonance The solid turns a pale purple color under Nz at 25 OC in 24 h, but not is found a t the high end of this region while the electrophilic at -30 "C. alkylidene a-carbon resonance in (C0)5W=CPh2 is found at Anal. Calcd for TaC13H)y: C , 43.83: H , 5.38. Found: C , 43.78; H, the low end (at 358 ppm). It is not inconsistent, therefore, to 5.37. find the methylene resonance in Me3P=CH2 near MedSi (2.3 ' H K M R ( T ,C6D6) 5.15 (s, 10, Cp), 9.69 (s, 6, outside Me). 9.79 ppm upfield with 'Jc- = 149 Hz);j6s5' it is nucleophilic and (s, 3, inside Me). A 1.30-mmol sample was pyrolyzed by gently heating in an evacnot attached to a transition metal. Clearly, however, more uated 100-mL flask. A small amount of white solid sublimed, then it detailed simplistic interpretations of 13Cchemical shifts should (and that which had not sublimed) turned a pale purple and suddenly receive more scrutiny than they have i n the past.j* decomposed very rapidly to give 1.59 mmol of gas and a benzene~ J C in H CH2 bound to Ta ( 1 32 Hz) is essentially the same soluble red solid whose ' H N M R spectrum showed only two very as in that bound to As in Me3As=CH2 ( 1 31 Hz)j6 but sigbroad peaks, one in the C p region, one in the Me region. A 1S2-mmol nificantly smaller than in that bound to P in Me3P==CH2 (149 sample gave 2.82 mmol of gas which was shown to be 96% CH4 conHz).j6 Since we know that the CH2 ligand in TaCp2(CH2)taining traces (ca. 1% each) of Hz. C2H4, and C2H6. (CH3) is planarllb we must conclude that the magnitude of TaCpz(CD3)3 was prepared similarly. A 250-mg sample in 5 mL ~ J C in H a unique situation will probably vary ~ o n s i d e r a b l y . ~ ~ of C6D6 at 125 "C gave off 1.8 mol of methane which was shown by mass spectroscopy to be 10% CD4, 87% CD3H, -0% CD>H2?2% This is clearly the case for neopentylidene complexes where ~ J C varies H from 84-90 Hz in some Ta c o m p l e x e ~ ~to, ~131 ~ I ~ CDH3, and -0% CH4. 4. Preparation of TaCp($-CsH4Me)Me3. A solution of 2.0 g of Hz in NbCp2(CHCMe3)C1.j0
Experimental Section All operations were done under N2, either in a Vacuum Atmospheres HE43 glovebox or by Schlenk techniques. All solvents were dried by passing through Linde 4A molecular sieves and were degassed thoroughly with nitrogen. Tetrahydrofuran was distilled from sodium benzophenone kctyl under nitrogen. TaCI5, NbC15, and TlCp were sublimed before use. Me3P=CHz was prepared from Me4P+Br- and NaNHz in THFsy and isolated by vacuum distillation (bp 60 "C, 100 mm). ' H N M R spectra were done on Varian, Perkin-Elmer, or Brucker 60-, 90-, 100-, 220-, or 270-MHz spectrometers and I3C spectra on Bruckcr 22.63- or 67.89-MHz spectrometers. Analyses were done by Alfred P. Bernhardt Mikroanalytisches Laboratorium. 1. Preparation of TaMe3Clz. TaMe3Clz was prepared by stirring 50 g of sublimed TaCl5 with 15.5 mL of ZnMe2 in 900 mL of pentane at 25 "C for 6 h. The ZnClz was filtered off, a small sample of filtrate was stripped, and the residue was analyzed by IH N M R in order to determine how much additional ZnMez is needed to convert any TaMezCI3 to TaMe3Clz. After more ZnMez was added (here 1.15 mL) the mixture was again filtered and the solvent removed in vacuo leaving 34 g of pale yellow TaMe3Cl2. ' H N M R ( T , C6D6) 8.47 (s) [ ' H N M R of TaMezCI3 ( T ,C6D6) 8.32 (s).] Mol W t (cryoscopic in benzene): 307 (calcd 297). The following preparation was developed in order to avoid using isolated ZnMe2. ZnClz (8.57 g, 63 mmol, I .2 X theory, dried with SOC12) in 50 mL of ether at -78 OC was treated slowly with 113 m L of 0.90 M LiMe (IO5 mmol) and the mixture was warmed to 0 "C. After stirring for 0.5 h the ZnMe2 in ether was removed in vacuo and trapped in a flask containing 33 mmol (0.95 of theory) of sublimed TaCls ( 1 1.88 g). This mixture was warmed to room temperature and
TaCpMejCI in 25 mL of T H F at -78 OC was treated with 0.55 g of LiC5H4Me in 10 mL of T H F . The mixture was warmed to room temperature with stirring and all T H F removed in vacuo. The residue was extracted with pentane (25 mL) and the LiCl removed by filtration. Pentane was removed in vacuo until crystals appeared and the solution was then allowed to stand at -30 "C for 6 h to give 1.40 g (62%) of white. platelike crystals of the product. It was identified by comparison of its ' H N M R spectrum to that of TaCpzMe, and Ta(q5-C5H4Me)>Me3(see 5). ' H N M R ( T ,C6D6) 5.15 (s, 5, c p ) , 5.26 (t, 2,J"rm 3Hz,C~H~ = 3 Hz, CsHz'set), 8.30 (s, 3, C5Me), 9.75 (s, set), 5.47 (t, 2, JHH, 6, outside Me), 9.87 (s, 3, inside Me). 5. Preparation of Ta(q5-CsH4Me)zMe3.A solution of 3.44 g of LiC5H4Me in 25 mL of T H F was added slowly to 5.95 g of TaMe3Cl2 in T H F at -78 OC with stirring. The mixture was warmed to room temperature and all solvent removed in vacuo. The residue was extracted with 500 mL of warm hexane and the mixture was filtered. Crops of silvery-white crystals were filtered off as the solvent was removed in vacuo; total yield 5.9 g (76%). Anal. Calcd for TaClsH23: C, 46.88: H, 6.03. Found: C , 46.88: H, 5.91. ' H N M R (T,C6D6. 220 MHz) 5.23 (t, 4, JHH, = 2.6 Hz, C5Hz set), 5.48 (t. 4, J H H ' = 2.6 Hz, CsH2' set), 8.26 (s, 6, C5Me), 9.79 (s, 6, outside Me), 9.92 (s, 3, inside Me). 6 . Preparation of [TaCpzMez]+BF4-. A solution of 14.24 g of TaCpzMe3 in 100 mL of CHzC12 was treated dropwise with 13.20 g of Ph3C+BF4- in 100 mL of CH2C12 to give a pale yellow precipitate of [TaCpzMez]+BF4- (16.5 g, 97%). The product was filtered off and the solvent removed from the filtrate in vacuo. The residue was extracted with pentane. The mixture was filtered and the filtrate was reduced to dryness to give 8.0 g (67%) of Ph3CMe which was identified by ' H N M R [ T 3.00 (br, 15, Ph), 7.98 (s, 3, Me), in C6D6] and mass
Schrock, Sharp
/
Preparation of Ta(qs-CsH5)z(CH2)(CH3)
spectroscopy. The pale yellow precipitate from above was recrystallized from acetonitrile with ether to give yellow needles from which the last traces of acetonitrile and ether were removed in vacuo. Anal. Calcd for TaC12H16BF4: C, 33.68; H , 3.76. Found: C, 33.66; H , 3.82. ' H N M R ( 7 , CD3CN) 3.45 (s, 10, Cp), 9.45 (s, 6, CH3). The resistance of a solution of 160 mg of the product in 50 m L of acetonitrile was 1000 'L ( A = 133). 7. Preparation of [TaCp(q5-C~&le)Me2]+BF4-.A solution of 1.32 g of Ph,C+BF4- in 30 m L of CHzCl2 was added to 1.48 g of TaCp(v5-C5H4Me)Me3 in 20 mL of CHzC12 with stirring. The solvent was removed in vacuo until the volume was about 10 m L and 30 mL of ether was added to complete crystallization, yield 1.57 g. Unlike [TaCp2Mez]+BF4-, this material is soluble enough in dichloromethane to obtain an N M R spectrum, which by comparison to that of [TaCp*Me2]+BF4- in CD3CN serves to identify it. ' H N M R ( 7 , CD2C12) 3.56 (s, 10, Cp), 3.83 (m, 4,C5H4), 7.56 (s, 3, CsMe), 9.48 (s, 6, TaMe). 8. Preparation of [Ta(q5-C$I.&ie)2Me2]+BF4-.The procedure was identical with that in 7 using 3.86 g of Ta(a5-C5H4Me)2Me3 and 3.30 g of Ph3C+BF4-, yield 4.3 g (93%). ' H N M R ( 7 , CD2C12, 220 M H z ) 3.61 (t, 4, J" = 2.6 Hz), 3.77 (t, 4, J" = 2.6 Hz), 7.52 (s, 6, CsMe), 9.54 (s, 6, TaMe). 9. Preparation of TaCpzMetBr. Br2 (0.45 g) in 10 mL of dichloromethane was added slowly at 0 "C to a solution of 1 g of TaCpzMe3 in 25 mL of dichloromethane. The ivory precipitate was filtered, washed with 2 X 10 mL of acetonitrile and 10 mL of ether, and dried in vacuo, yield 0.98 g (83%). Anal. Calcd for TaCl2Hl6Br: C, 34.21; H , 3.82. Found: C, 33.49; H, 3.69. 10. Preparation of [TaCpz(Me)(Br)]+X- (X- = Br-, Br3-). Neat Br2 (0.63 mL) was rapidly added to a solution of 1.89 g of TaCp2Me3 in 25 mL of dichloromethane. The dichloromethane was removed in vacuo and 15 mL of acetonitrile added to the residue. Filtration gave 0.91 g of canary yellow TaCpzBr3. Addition of one volume of ether to the filtrate gave 0.3 g of microcrystalline, yellow [TaCpz(Me)(Br)]+Br-. Further addition of ether followed by cooling at -30 OC gave 0.55 g of orange, crystalline [TaCpz(Me)(Br)]+Br3-. Anal. Calcd for TaCl1H13Br4:C, 20.45; H , 2.03; Br, 49.52. Found: C, 20.66; H, 2.00; Br, 49.78. IH N M R ( 7 , CD3CN) 3.20 (s, 10, Cp), 9.00 (s, 3, Me). 11. Preparation of [TaCpz(Me)(Br)]+BF4-.A solution of 0.12 mL of Br2 in 10 mL of dichloromethane was added dropwise with stirring to 1 .0 g of [TaCp>Mez]+BF4- in 20 mL of CH2C12 at 0 "C. The suspension was warmed to room temperature and stirred for 2 h. The CH2Cl2 was removed in vacuo to yield 0.92 g of yellow [TaCpz(Me)(Br)]+BF4- (80%). The yellow product may be recrystallized from acetonitrile with ether to give yellow plates or needles. Its IH N M R spectrum is identical with that of the Br- and Br3- salts (see 10) and its infrared spectrum shows a characteristic strong, broad absorption a t u = 1070 cm-l due to BFd-. It may also be prepared from [TaCp*(Me)(Br)]+Br- and TIBF4 in acetonitrile. 12. Preparation of NbCptMe3 and Identification by IH NMR. Orange NbMezCI3 was prepared by a procedure analogous to that used to prepare TaMe3Clz (stirred for 16 h) and converted to yellow NbMe3C1212 with an additional 0.5 mL of ZnMez in pentane. Solid TlCp was added to a solution of 0.42 g of NbMe3Cl2 in 25 mL of toluene. The white TIC1 was filtered off after 1 h (0.95 g, quantitative) and the solvent almost completely removed from the filtrate in vacuo to give an oil. Addition of a few milliliters of pentane caused pale shimmering crystals to form (0.28 8). An IH N M R spectrum in C6D6 (T 5.27 ( I O ) , 9.70 (6), 9.85 (3)) was essentially identical with that of TaCp2Me3. NbCp2Me3 readily decomposes near room temperature, as a solid or in solution. 13. Preparation of TaCp2(CH2)(CH3)and TaCp2(CD2)(CD3). (a) Using Me3P=CH2. To a suspension of 4.28 g of [TaCpzMe2]+BF4in 25 mL of T H F was added slowly 0.95 g of Me3P=CH2 in 10 mL of T H F and the mixture was stirred for 15 min. The solvent was removed in vacuo and the residue extracted with toluene leaving an 88% yield (1.75 g) of Me4P+BF4- which was identified by comparison of its infrared spectrum with that of an authentic sample. Toluene was removed in vacuo until crystals appeared, then about three volumes of pentane was added and the mixture stood a t -30 "C for 1 h. Filtration gave 2.55 g of shimmering greenish-white needles (second crop 0.22 g), total yield 2.77 g (82%). This procedure has been successfully scaled up by a factor of 5.
2391 (b) Using LiN(SiMe3)z. A suspension of 10.58 g of [TaCp*Mez]+BF4- in 200 mL of T H F was cooled to -78 " C and a solution of 4.15 g of LiN(SiMe3)z in 50 mL of T H F added slowly. The mixture was warmed to room temperature and all the T H F was removed in vacuo. The tan solid must be extracted immediately with toluene. The LiBF4 was filtered off and the filtrate's volume reduced in vacuo until crystals appeared. The product was isolated as in (a), total yield 6.35 g (78%). (c) From TaCp2(CHzAIMe3)(CH3) and Lewis Bases. (i) Et3N. TaCpz(CH2AIMe3)(CH3) (0.41 g) and 0.1 g of Et3N were mixed in 5 m L of ether. Addition of 5 m L of pentane and standing at -30 "C for 1 h gave 0.10 g of TaCpz(CH2)(CH3). (ii) Me3P=CH2. TaCpz(CH2AIMe3)(CH3) (0.41 g) and 90 mg of Me3P=CH were stirred in 5 m L of toluene. The solution was stripped to a thick liquid and 10 m L of pentane was added. The 0.41 g of pale crystals, which were filtered off, are a 1.2 mixture of TaCp2(CHz)(CH3) and Me3PCH2AIMe3. [ ' H N M R of the latter ( ~ , C 6 D 6 ) 9 , 2 7 ( d , 9 , J ~ p1 =3 H z . P M e 3 ) , 1 0 . 0 ( d , 2 , J ~ p =1 7 H z , CH2), 10.43 (s, 9, AIMej).] The filtratecontains pureTaCp2(CH2)(CH3) which may be recovered by removing the pentane in vacuo, yield 80 mg. Anal. Calcd for TaC12Hl5: C, 42.37; H , 4.44. Found: C , 42.10; H, 4.44. ' H N M R (7, C6D6) -0.11 (s, 2,=CH2), 4.88 (S, I O , c p ) , 10.0 (s, 3, CH3). I3C N M R (ppm from MedSi, gated decoupled, CDzC12) 224 (t, ' J C H = 132 Hz, CH2), 100 (d, 'JCH= 177 Hz, Cp), - 5 (9. ' J C H = 122 Hz, CH3). TaCpz(CD2)(CD3) was prepared as in (a). Its ' H N M R spectrum showed a C p resonance at r 4.88 but only barely detectable resonances a t T -0.1 1 or 10.0 at 1OX the amplitude. 14. Preparation of TaCp(q5-CsH4MeXCH2XCH3).A suspension of 0.60 g of [TaCp(a5-C5H4Me)Me2]+BF4- in 4 mL of T H F was treated with 0.12 g of Me3P=CH2 in 4 mL of T H F with stirring as in 13a. The residue was extracted with 25 mL of pentane leaving 0.18 g (75%) of MedP+BFd-. The pentane was removed in vacuo leaving 0.35 g (73%) of fluffy, pale yellow crystals which were identified by comparison of the 220-MHz 'H N M R with that of TaCpZ(CH2)(CH3). ' H N M R (T, toluene-dg, 220 MHz) 0.02 and 0.10 (AB quartet, JHH = 7.6 Hz, CH2), 4.92 (s, 5, Cp), 4.96 (m, 2, C5H2set), 5.16 (m, 2, CsH2 set), 8.01 (s, 3, CSMe), 10.06 (s, 3, TaMe). [The 220-MHz spectrum of TaCpz(CH*)(CH3) in toluene-dg shows the CH2 group as a singlet at T 0.0, C p at T 4.96, and Me at T 10.04.1 (See Figure 2.) 15. Preparation of T ~ ( T ~ - C ~ H ~ M ~ ) ~ ( C The H ~ procedure X C H ~ ) .is identical with that for TaCp(qS-CsH4Me)(CHz)(CH3) using 0.36 g of Me3P=CH2 and 1.83 g of [Ta(q5-CsH4Me)2Me2]+BF4-, yield 0.95 g (64%) of white crystals. IH N M R (7, C6D6, 220 MHz) 0.03 ( S , 2, CH2), 4.19 (m, 2, CSH), 5.14 (m,6, C5H3), 7.99 (s, 6, CsMe), 9.99 (s, 3,TaMe). 16. Preparation of TaCp2(CH2AIMe3)(CH3).(a) From TaCpzMe3 and AIMe3. AIMe3 (0.44 g) in 10 mL of toluene was added to a stirred solution of 2.14 g of TaCpzMe3 in 30 mL of toluene. An oily orange layer formed rapidly but after 10 days stirring the solution was again homogeneous. Nearly all the solvent was removed in vacuo and 25 mL of pentane was slowly added to give 2.15 g (87%) of cream-colored TaCp2(CHzAIMe3)(CH3). If the oily orange layer from above is washed three times with toluene and pentane is then added, 2.05 g of a yellow solid is obtained whose ' H N M R spectrum in CD2C12 a t -80 OC (I00 MHz) shows three broad singlets at T 3.4, 9.3, and 10.9 in the ratio of 10:6:12. At room temperature all are quite broad. The yellow solid is believed to be [TaCp2Mez]+[AlMe4]-. In CHzClz or acetonitrile it is only -'/IO as good a conductor (A = 10 for a 110-mg sample in 50 mL of CH2C12; h = 9 for a 120-mg sample in CH3CN) as [TaCpzMe*]+BF4- in acetonitrile ( A = 133 for a 160-mg sample in 50 mL). A sample of 1.07 g of TaCpzMe3 (3.0 mmol) and 0.22 g of AIMe3 (3.0 mmol) in toluene were sealed in vacuo in a flask equipped with a break-seal and the mixture was stirred for 4 days at room temperature. The evolved gas was then measured with a Toepler pump (2.1 mmol) and identified by mass spectroscopy; it was essentially pure CH4 containing only traces of ethylene and ethane. (b) From TaCp2(CH2)(CH3) and AIMe3. AIMe3 (0.080 g) and TaCp2(CHz)(CH3) (0.34 g) were mixed in 5 mL of toluene at 25 "C. Nearly all the toluene was removed and 10 mL of pentane was added. Standing at -40 " C for 3 h gave 0.280 g of product as fluffy, pale
2398
Journal of the American Chemical Society
yellow crystals. Anal. Calcd for TaC15H24AI: C, 43.70; H, 5.86. Found: C, 43.40; H, 5.73. ' H N M R ( T , C6D6) 2.32 ( s , 2, CH2), 4.88 (s, IO, Cp), 10.0 (s, 3, TaMe), 10.32 (s, 9, AIMe3). I3C N M R (ppm from Me4Si, gated decoupled, C6D6) 177 (t, ' J C H = 124 Hz, methylene C), 105 (d, ~ J C H = 178 Hz, Cp), 16.5 (q, ' J C H = 123 Hz, TaMe), -2.6 (broadened q, ~ J C = H 109 Hz, AIMe3). The last two peaks were assigned assuming that the broadening is due to the onset of coupling to 27AI. 17. Preparation of [TaCpz(CHzSiMe3)(CH$+Br-. Me3SiBr (3.06 g) in I O mL of dichloromethane was added to a solution of 6.80 g of TaCpz(CH2)(CH3) in 35 mL of dichloromethane. Pale yellow crystals (3.75 g) were filtered off after 12 h a n d 3.65 g of additional product on addition of 100 mL of diethyl ether to the filtrate, total yield 7.40 g (75%). The product recrystallizes slowly from dichloromethane on addition of diethyl ether to give ivory microcrystals. Anal. Calcd for TaCl~H24SiBr:C, 36.52; H, 4.90. Found: C, 36.75; H, 4.84. ' H N M R ( T , CD2C12) 3.25 ( s , lO,Cp), 8.61 (q, 2 , J = 1 Hz,CH2), 9.43 (t, 3, J =Z 1 Hz, TaMe), 9.87 (s, 9, SiMe3). A 100-mg sample in 50 m L of CH3CN gave A = 102. 18. Preparation of TaCp2(C2H4)(I).Methyl iodide (0.19 mL) was added to a solution of I .02 g of TaCp2(CH2)(CH3) in 5 mL of benzene. After 12 h all solvent was removed in vacuo leaving an orange powder (1. 13 g) which was recrystallized from a saturated toluene solution as metallic orange needles by cooling to -30 OC. Anal. Calcd for TaC12H14I: C, 30.92; H, 3.03; I, 27.22. Found: C, 31.11;H,3.00;1,27.16. ' H N M R ( T , C6D6.270 MHz) 5.20 (s, I O , Cp), 8.02 (t, 2, outside C H l ) , 8.74 (t, 2, inside CH?;);see Figure 3a. 19. Preparation of TaCp2(CH2CD2)I/TaCp2(CD2CH2)1 Mixture. The reaction between 0.68 g of TaCp2(CH2)(CH3) (2.0 mmol) and CD31 (2.0 mmol) in 5 mL of benzene in an evacuated sealed flask equipped with a break-seal at 25 OC for 16 h gave 2.0 mmol of methane which was shown to consist of 93% CH3D, 5% CHI, and 2% all others by mass spectroscopy. The ' H N M R spectrum of the orange product obtained by removing all volatiles showed a Cp singlet at T 5.20 and two broad singlets at T 8.05 and 8.76 in the ratio of 10.0 (defined):l .O: 1 .O (see Figure 3b). 20. Preparation of T ~ C P ~ ( C ~ H ~ XAC 100-mL H ~ ) . pressure bottle containing a solution of 1.7 g of TaCp2(CH2)(CH3) in I O mL of benzene was pressurized to 40 psi with ethylene and stirred and heated to 80 "C for 8 h. The solvent was then removed in vacuo and the residue dissolved in 200 mL of hexane. The solution was treated with decolorizing charcoal and filtered. The volume was decreased to 25 mL and this solution stood at -30 OC for 3 h. Filtration gave 1.2 g (68%) of gold crystals. Anal. Calcd for TaC13H17: C, 44.08; H , 4.83. Found: C, 43.78; H , 4.8 I . ' H N M R ( T , C6D6.220 MHz) 5.55 (s, IO, Cp), 9.02 (2nd order t, 2, outside CH2). 9.22 (2nd order t, 2, inside CH2), 9.50 (s, 3, CH3). I3C N M R (ppm from Me&, gated decoupled, C6D6) 97.6 (d, IJCH = 177 Hz, Cp), 20.9 (t, ' J C H = 148 Hz, CH2), 20.2 (t, ' J C H = 149 Hz, CH2), -5.4 (q, ' J C H= 122 Hz, CH3). 21. Reaction of TaCp2(CH2)(CH3)with C2D4. TaCp2(CH2)(CH3) (0.68 g, 2.0 mmol) and I O mL of benzene were placed in a 250-mL flask equipped with a break-seal. C2D4 (45 mL at 760 mm, 2.0 mmol) was condensed in and the flask was sealed and heated with stirring to 80 "C for 16 h. The flask was opened and all gas noncondensable at -78' measured; noncondensables 1.2 mmol; 92% ClD4, 4% C2D3H, 4% C2H4 by mass spectroscopy. Workup as in 20 gave 0.50 g of gold crystals whose ' H N M R spectrum was identical with that of TaCp2(C2Hd)(CH3) at 100 M H z except that the relative areas were 10.0 (defined):2.1:2.9. The ethylene pattern at 270 MHz was identical with that in Figure 4a. The Cp singlet and the methyl singlet in T ~ C P ~ ( C D ~ C D ~ ) are (CH located ~ ) I .5 Hz upfield (we propose) of the Cp and methyl singlets in T ~ C ~ Z ( C H ~ C H ~ ) ( C H ~ ) . 22. Preparation of TaCpl(PMe3)(Me)from TaCp2(CH2)(CH3).A mixture of 2.04 g of TaCpl(CH2)(CH3) and 0.50 g of PMe3 in 20 mL of toluene was heated to 40 OC for 5 days. The solution was then filtered and an equal volume of hexane added. Cooling to -30 OC yielded a red mixture of TaCpz(PMe3)(Me) and TaCp2(CaHd)(CH,) which was similarly recrystallized to give pure TaCp2(PMe3)(Me) (31%). Anal. Calcd for TaC14H22P: C, 41.80; H , 5.52; P, 7.70. Found: C, 39.92; H, 5.51; P, 8.13.
100.8
1 April 12, 1978
' H N M R ( T , C6D6) 5.78 (d, 10, J =Z 2 Hz, Cp), 9.02 (d, 9, J = 7 Hz, PMe3), 10.50 (d, 3, J = 8 Hz, Me). 23. Preparation of TaCpz(PMezPh)(Me)from TaCp2(CH2)(CH3). The procedure is identical with that in 22, yield 0.70 g (51%) of metallic red needles or plates. ' H N M R ( T , C6D6) 2.90 (br m, 5, Ph), 5.90 (d, 10, J = 2 Hz, Cp), 8.80 (d, 6, J = 7 Hz, PMez), 10.70 (d, 3, J = 7 Hz, Me). 24. Preparation of TaCpz(CO)(CH3)from TaCp2(CH2)(CH3).A pressure bottle containing a solution of TaCpz(CH2)(CH3) ( 1 .O g) in 5 mL of benzene was flushed with CO, then pressurized to 55 psi. The vessel was heated to 80 OC and the solution stirred vigorously for ca. 8 h. All benzene was removed in vacuo leaving a green residue whose IH N M R spectrum showed it to be a 1 : l mixture of TaCp2(ClH4)(CH3) and TaCp>(CO)(CH3). The latter is slightly less soluble in hexane than the former. If the reaction is repeated in 25 mL of hexane, 0.35 g of pure TaCp2(CO)(CH3) crystallizes out during the reaction. It can be recrystallized from minimal benzene by adding pentane and cooling. I n the solid state it is bluish-green; its solutions are green. Anal. Calcd for TaC12H130:C, 40.70; H, 3.70. Found: C, 40.40; H, 3.90. ' H N M R ( T , C6D6) 5.55 (s, 10, Cp). 10.40 (s. 3, CH3). IR (Nujol, cm-I) 1850 s (VC=O. 25. Preparation of TaCp2(C2H4)(H).TaCpz(C2H4)I (OS g) and KH (0.050 g) were stirred in T H F for 4 days. All solvent was removed and the residue was extracted with 5 mL of benzene. Pentane (20 mL) was added along with decolorizing charcoal and the solution was filtered. All solvent was once again removed in vacuo and the residue taken up in 25 mL of pentane. Pale yellow, fluffy needles formed after removing much of the solvent in vacuo and standing the remaining solution at -40 OC for 2 h, yield 0.130 g (36%). TaCpz(C2Hd)(H) was identified by ' H N M R (cf. N ~ C P ~ ( C ~ H ~ ) (IH H )N~M~R) (. T , C6D6) 5.50 (s, 10, Cp), 9.2 (m, 2, outside CH2), 9.7 (2nd order t, 2, inside C H l ) , 13.4 (poor t. I , J 4 2 Hz, hydride).
Acknowledgments. We wish to thank the National Science Foundation ( C H E 7 6 - 0 7 4 1 0 ) and the Research Corporation for support of this work a t M.I.T. and the Francis N . Bitter National Magnet Laboratory for use of their high-field N M R facilities. R.R.S. also wishes to acknowledge the support of E. I. du Pont de Nemours and Co. during the initial stages of part of this research a t the Central Research and Development Department, References and Notes Part 6:S. J. McLain, C. D. Wood, and R. R. Schrock, J. Am. Chem. SOC.,
99,3519 (1977). Alfred P. Sloan Fellow, 1976-1978. For reviews see D. J. Cardin, B. Cetinkaya, and M. F. Lappert, Chem, Rev., 72,545 (1972);F. A. Cotton and C. M. Lukehart, Prog. Inorg. Chem., 16,
487 (1972). Alkylidene is preferred since these "carbene" ligands contain only carbon and hydrogen, Le., they are derived from alkyl ligands. It is sometimes more convenient to name them as methylenederivatives, e.g., diphenyimethylene in (C0)5W=CPh2.6 Ofele prepared the only other example, (C0)5Cr(2,3-diphenylcyclopropenylidene), several years earlier: K. Ofele, Angew. Chem., h t . Ed. Engl.,
7,950 (1968). (a) C. P. Casey and T. J. Burkhardt, J. Am. Chem. Soc., 95,5833 (1973); (b) C.P. Casey, T. J. Burkhardt, C. A. Bunnell, and J. C. Caiabrese, ibid.,
99,2127 (1977). (a) A . Sanders, L. Cohen, W. P. Giering, D. Kenedy, and C. V. Magatti, J. Am. Chem. SOC.,95,5430 (1973). (b) It could be argued that in these two cases too the phenyl ring stabilizes the system by donating electron density. It is simpler, however, to place these complexes in the unstabilized or alkylidene class. (a) W. A. Herrmann, Chem. Ber., 108,486 (1975);(b) E. 0.Fischer. R. L. Ciough, G. Besi, and F. R. Kreissl, Angew. Chem., Int. Ed. Engl., 15,543 (1976):(c) E. 0.Fischer, R. L. Clough, and P. Stuckler, J. Organomet. Chem., 120,C6 (1976). R. R. Schrock, J. Am. Chem. SOC.,96,6796(1974). The full details of the deceptively simple formation of M(CH2CMe&(CHCMe3) (M = Nb or Ta) will be reported shortly: R. R. Schrock and J. Fellmann, part 8,J. Am. Chem. SOC.,in press. (a) R. R. Schrock, J. Am. Chem. SOC.,97,6577 (1975);(b) R. R. Schrock and L. J. Guggenberger. ibid., 97,6578 (1975). G. L. Juvinail, J. Am. Chem. SOC.,86,4202 (1964). R. R. Schrock, J. Organornet. Chem., 122,209 (1976). R. R. Schrock, L. J. Guaaenberaer, and A. D. English, J. Am. Chem. SOC.,
98,903 (1976).
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D. A. Williamson, C. Santini-Scampucci, and G. Wilkinson, J. Organornet. Chem., 77,C25 (1974).
Schrock, Sharp
/
Preparation of Ta(t75-C5H5J2(CH2)(CH3)
(16) Throughout this paper the usual abbreviations (Cp = q5-C5H5,Me = CH3, etc.) will be used for brevity. (17) J. W. Faller and A. S. Anderson, J. Am. Chem. Soc., 92, 5852 (1970), and references cited therein. (18) Complete details of the rearrangement of pseudo-five-coordinate complexes will appear in a future publication. (19) F. N. Tebbe and G. W. Parshall, J. Am. Chem. Soc., 93, 3793 (1971). (20) C.J. Guggenberger, P. Meakin, and f . N. Tebbe, J. Am. Chem. SOC.,96, 5420 (1974). (21) (a) M. L. H. Green, J. A. McCleverty, L. Pratt. and G. Wilkinson, J. Chem. Soc., 4854 (1961); (b) F. N. Tebbe, J. Am. Chem. Soc., 95, 5412 (1973). (22) R. D. Wilson, T. F. Koetzle, D. W. Hart, A. Kvick, D. L. Tipton, and R. Bau, J. Am. Chem. SOC.,99, 1775 (1977). (23) We will use this means of distinguishing between various labeled isomers in this compound (a member of the TaCp2X3 family) and in compounds from the TaCp2X2Y family (e.g., TaCp2(CH2CD2)1,see later) throughout this paper. (24) V. M. S. Gil and C. F. G. C . Geraldes in "Nuclear Magnetic Resonance Spectroscopy of Nuclei Other Than Protons", T. Axenrod and G. A. Webb, Ed., Wiley, New York, N.Y., 1974, Chapter 14. (25) J. W. Emsley, J. Feeney, and L. H. Sutcliffe, "High Resolution Nuclear Magnetic Resonance Spectroscopy", Vol. 1, Pergamon Press, Oxford, 1965, p 319. (26) D. Kost, E. H. Carlson, and M. Raban, Chem. Commun., 656 (1971). This formula fails as Au approaches J, but when Au =Z J, kc is only 20% too high compared with kc from a complete line shape analysis. Au = [(UT Y4)(U2 ~ 3 ) ] "= ~ 14.3 Hz at 220 MHz or 6.5 Hz at 100 J = 7.6 0.1 Hz. (27) F. R. Kreissl and W. Held, J. Organomet. Chem., 86, C10 (1975). (26) H. Schmidbaur and W. Tronich, Chem. Ber., 101, 595 (1968). (29) Small amounts of TaCp2(CHZCD2)(R)and TaCp2(CD2CH2)(R) in a mixture of TaCp2(CH2CH2)(R)and TaCp2(CD2CD2)(R)are difficult to measure since the signals due to CH2CD2 complexes are fairly broad, though the are shifted upfield slightly. In this case [TaCp2(CD2)(CD3)plus C2H4r the spectrum is consistent with -10% TaCp2(CH2CD2)(CD3) and 10% TaCp2(CD2CH2XCD3)being present in the mixture. A decomposition under higher ethylene pressures should produce more definitive results. These experiments (and other olefin reactions) are in progress. (30) (a) G. P. Pez, J. Am. Chem. Soc., 98, 8072 (1976); (b) A. Davison and S. S.Wreford, ibid., 96, 3017 (1974); (c) L. J. Guggenberger and F. N. Tebbe, ibid., 98, 4137 (1976). (31) L. J. Guggenberger, Inorg. Chem., 12, 294 (1973). (32) E. C. Baker, K. N. Raymond, T. J. Marks, and W. A. Wachter, J. Am. Chem. SOC.,96, 7586 (1974). (33) Calculated using k3pc and k60.c and the Arrhenius expression. (34) W. Kirmse, "Carbene Chemistry", 2nd ed, Academic Press, New York, N.Y.. 1971, Chapter 3. (35) (a) F. S. D'yachkovsky and N. E. Krusch, Zh. Obshch, Khim., 41, 1779 (1971); J. Gen. Chem. USSR(EngI. Trans/.), 41, 1787 (1971); (b)L. Farady and L. Marko, J. Organomet. Chem., 43, 5 1 (1972); (c) M. Michman and H. H. Zeiss, ibid., 13, P23 (1968); (d) J. R. C. Light and H. H. Zeiss, ibid., 21, 391 (1970);(e) M. Michman and H. H. Zeiss, ibid., 15, 139 (1968); (f)
-
*-
2399 T. lkariya and A. Yamamoto, J. Chem. SOC., Chem. Commun., 720 (1974); (9) N. J. Cooper and M. L. H. Green, ibid., 208 (1974); (h) ibid., 761 (1974); (i) T. lkariya and A. Yamamoto, J. Organomet. Chem., 118, 65 (1976); (j) E. L. Muetterties and P. L. Watson, J. Am. Chem. Soc., 98, 4665 (1976). (36) N. Calderon, E.A. Ofstead, and W. A. Judy, Angew. Chem., Int. Ed. Engl., 15, 401 (1976). (37) (a) P. W. Jolly and R. Pettit, J. Am. Chem. Soc., 88, 5044 (1966); (b) M. L. H. Green, M. ishaq, and R. N. Whiteley, J. Chem. SOC.A, 1508 (1967); (c) A. Davison, W. C. Krusell, and R. C. Michaelson, J. Organomet. Chem., 72, C7 (1974). (d) Note that M. Brookhart (private communication) has shown that addition of FeCp(CO)2CH2OMe in CD2C12 at -100 OC to HSO3F/SO2CIF at -100 OC gave a red solution containing only [F~CP(CO)~(CZH~)] and [FeCp(COh]+". (38) P. G. Gassman and T. H. Johnson, J. Am. Chem. Soc., 98,6057 (1976). (39) F. D. Mango and I. Dvoretsky, J. Am. Chem. Soc., 88, 1654 (1966). (40) W. A. Herrmann, B. Reiter, and H. Biersack, J. Organomet. Chem., 97,245 (1975). (41) R B. Caivert and J. R. Shapiey, J. Am. Chem. SOC.,99, 5225 (1977). (42) P. Krusic of Du Pont Central Research and Development Department detected Ph3C- by ESR on reaction of TaCp2Mea with PhsC'BF4in CH2C12. (43) R. R. Schrock, unpublished results. (44) P. G. Gassman and T. H. Johnson, J. Am. Chem. SOC.,99,622 (1977). (45) A version of this concept has been advanced by E. L. Muetterties (horg. Chem., 14, 951 (1975)). (46) Deuterium in (Me3CCH2)3Ta=CDCMe347 scrambles among the a-carbon decomDosition atoms with A& S= 28 kcal mol-' without any. significant of the complex.lD (47) L. J. Guggenberger and R. R. Schrock, J. Am. Chem. Soc., 97, 2935 (19751. - -, (48) TaCp2(0=C=CH2)(CH3) has been prepared.43it has not yet been found in the reaction of TaCp2(CH2)(CH3)with CO. (49) C . P. Casey and R. L. Anderson, J. Chem. Soc., Chem. Cornmun., 895 (1975). (50) Part 9: R. R. Schrock, L.W. Messerie, C. D. Wood, and L. J. Guggenberger, J. Am. Chem. SOC., in press. (51) R. R. Schrock, J. Am. Chem. Soc., 98, 5399 (1976). (52) J. L. Petersen and L. F. Dahl, J. Am. Chem. Sac., 97, 6418 (1975), and references cited therein. (53) J. W. Lauher and R. Hoffmann, J. Am. Chem. SOC.,98, 1729 (1976), and references cited therein. (54) G. A. Olah and A. M. White, J. Am. Chem. SOC.,91, 5801 (1969). (55) C. G. Kreiter and V. Formacek, Angew. Chem., Int. Ed. Engl., 11, 141 (1972). (56) H. Schmidbaur, W. Richter, W. Wolf, and F. H. Kohler, Chem. Ber., 108, 2649 (1975). (57) (a) K. A. 0. Starzewski and M. Fiegel, J. Organomet. Chem., 93, C20 (1975); (b) T. A. Albright, W. J. Freeman, and E. E. Sweizer, J. Am. Chem. Soc., 97, 940 (1975). (58) J. Evans and J. R. Norton, Inorg. Chem., 13, 3042 (1974). (59) R. Koster, D. Simic, and M. A. Grassberger, Justus Liebigs Ann. Chem., 739, 211 (1970). "
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