Organometallics 1983,2,457-459
long-term pseudoestrogenic effects even a t low levels resulting in testicular atrophy.14 The acute oral toxicity (LD50) of dimethylsila-14-crow-5 for rats is 9900 mg/kg, compared to 1020 mg/kg for 15-crown-5.16 During the course of the studies histologic examination indicated no significant changes in testicular function.ls Registry No. I, 838W22-6;II, 84332-76-3;III, 84332-77-4; LiC1, 7447-41-8; NaBr, 7647-15-6; KBr, 7758-02-3; KN3, 20762-60-1; KCN, 151-50-8;KOA^, 127-082;m,7789-23-3;moz,775809-0; dimethylsila-14-crown-5,70851-49-9;dimethylsila-20-crown-7, 83890-23-7;ethylmethylsila-14-crown-5, 84332-75-2;vinylmethylsila-14-crown-5,83890-248; phenylmethylsila-14-crown-5, 83890-27-1;vinylmethylsila-17-crown-6,83890-25-9;methoxymethylsila-17-crown-6, 83890-26-0;vinylmethyldiethoxysilane, 5507-44-8;tetraethylene glycol, 112-60-7;benzyl chloride, 100-4-4-7; benzyl bromide, 100-39-0;allyl bromide, 106-95-6; hexyl bromide, 111-25-1; octyl bromide, 111-83-1; octyl chloride, 111-85-3; [(p(m)-(chloromethyl)phenyl)ethyl]trimethoxysilane,68128-25-6; trimethylsilyl chloride, 75-77-4; benzyl cyanide, 140-29-4; allyl cyanide, 109-75-1; crotononitrile, 4786-20-3; hexyl cyanide, 62908-3;octyl cyanide, 2243-27-8;[((cyanomethyl)phenyl)ethyl]trimethoxysilane, 84332-74-1; cyanotrimethylsilane,7677-24-9;benzyl acetate, 140-11-4; benzyl fluoride, 350-50-5; benzyl azide, 622-79-7; benzyl nitrite, 935-05-7. ~
457
H'
2.236
\
9~~
/7
.H
100.0 1.930
r
Figure 1. STO-3G optimized structure for HzTiCHz/CIAIHz (bond lengths in angstroms and angles in degrees).
tathesis of terminal olefinss and an excellent methylenation agent.' Hence 1 is often represented as a "protected" akylidene complex, Le., a weak complex between ClAlMe2 and Cp2Ti=CH2. ,Me $1I
+I\\' #'Me
~~~
(13) Leong, B. K J. Cheh. Eng:%ews 1976,53 (4), 5. (14) Leong, B. K. J.; Ts'o, T. 0. T.; Chenoweth, M. B. Toxicol. Appl. Pharmacol. 1974,27, 342. (15) Hendrixaon, R. R.; Mack, M. P.; Palmer, R. A.; Ottolenghi, A.; Ghirardelli, R. G.; Toxicol. Appl. Pharmacol. 1978,44 (2), 263. (16) Toxicology performed by Springbom Institute for Bioresearch at
Spencerville,OH, under direction of Richard Hila. Two survivorsof the highest dose level (12300 mg/kg) showed lowest teste weight, although at lower levels no correlationwas observed. The significance of this result is uncertain, but testicular function was normal in the animals. The lowest lethal dose observed (LDLO) was 4300 mg/kg.
Cp = 9 5-C,H,
Support for such a structure derives primarily from the parallels in observed chemistry. lH NMR results: however, are more suggestive of a cyclic structure, i.e.
CP II l l i l -cqH
4 CP Structure of the Tebbe Reagent. An Intramolecular Complex? Michelle M. Francl' and Warren J. Hehre' Department of Chemistty, University of California Irvine, California 927 17 Received August 24, 1982
Summary: The geometry of the Tebbe reagent, Cp,TiCH,/CIAIMe,, is explored theoretically via ab initio (STO-3G) calculations on a model complex, H,TiCH,/ CIAIH,. The calculated structure of the model shows the Lewis acid CIAIH, to be strongly bound to the titanium alkyliiene, rather than, as often represented, only weakly associated.
Transition-metal carbene complexes are ubiquitous species in organometallic chemistry, exhibiting behavior ranging from methylene transfer2 to catalysis of olefin metathesis3 and oligomeri~ation.~ The Tebbe reagent,5 Cp2TiCH2/CMlMe2(l),displays a strikingly similar pattern of reactivity; it is a highly selective catalyst for me(1) Chevron Fellow. (2) R. R. Schrock, J. Am. Chem. Soc., 98, 5399 (1976). (3) For a review see: T. J. Katz, Adu. Organomet. Chem. 16, 283 (1978). (4) (a) R. R. Schrock, S. McLain, and J. Sancho, Pure Appl. Chem., 62,729 (1980); (b) J. D. Fellman, R. R. Schrock, and G. A. Rupprecht, J.Am. Chem. Soc., 103,5753 (1981). (5) F. N. Tebbe, G. W. Parshall, and G. S. Reddy, J. Am. Chem. Soc., 100, 3611 (1978).
H
Unfortunately, a lack of structural and thermochemical information about 1 makes it difficult to experimentally distinguish between these two limiting representations. We report here the preliminary results of our theoretical investigations into the complexation of titanium alkylidenes with aluminum alkyl halides. Using the STO-3G8v9 basis set, we have obtained a structure for a model of the Tebbe reagent, H2TiCH2/C1A1H2. This somewhat simplified model, in which hydrogen has been substituted for cyclopentadienyl ligands on titanium and for methyl groups on aluminum, was chosen to make the ab initio calculations more tractable. The titanium center on the model is extremely electron deficient, much more so than (6) F. N. Tebbe, G. W. Parshall, and D. W. Ovenall, J. Am. Chem. Soc., 101, 5074 (1979). (7) S. H. Pine, R. Zahler, D. A. Evans, and R. H. Grubbs, J. Am. Chem. SOC.,102, 3270 (1980). (8) Although minimal basis sets have traditionally been thought to be
inappropriate for use in ab initio calculations on transition metals, we have not found this to be so for all applications. While basis sets such as STO-3G do indeed perform poorly in some capacities, e.g., calculation of orbital energies, other tasks yield reasonable results. A brief comparison of available experimental and higher level theoretical data for group 4 metals with data from STO-3G calculations is presented in an earlier paper.'* The results indicate a reasonable performance for STO3G in the task of structure determinations, although it is clear that improved theoretical methods are necessary to accurately determine relative energetics. First row: (a) W. J. Hehre, R. F. Stewart, and J. A. Pople, J . Chem. Phys., 61, 2657 (1969). Second row: W. J. Hehre, R. Ditchfield, R. F. Stewart, and J. A. Pople, ibid., 62, 2769 (1970). Firstand second-row transition metals: (c) W. J. Pietro and W. J. Hehre, J. Comput. Chem., in press. (9) All calculations have been performed by using the GAUSSIAN 83 programlo on Harris Corp. Slash 6, H100, and HSOO digital computers. (IO) R. F. Hout, Jr., M. M. Francl, E. S. Blurock, W. J. Pietro, D. J. DeFrees, S. K. Pollack, B. A. Levi, R. Steckler,and W. J. Hehre, Quantum Chemistry Program Exchange, Indiana University, to be submitted for publication.
0276-733318312302-0457$01.50/00 1983 American Chemical Society
458 Organometallics, Vol. 2, No. 3, 1983
Figure 2. Left:
?r
bond in H2Ti=CH2. Center:
Communications
?r
bond in weak complex H2Ti=CH2/ClAlH2. Right:
in the actual Tebbe reagent. Previous work has established that while geometrical changes accompanying saturation of the metal center are significant, they are uniform and easily anticipated. The T i c linkage in Cp2Ti(CH3)H,for example, is 2.14 A at STO-3G, 0.05 A longer than that in H3TiCH3;the multiple bond in Cp2Ti=CH2 is 1.876 A compared to 1.833 A in the 10-electron complex H2Ti= CHpl1 Bond distances and angles calculated at STO-3G f for Cp2TiCH2CHRCH212 are in reasonable agreement with those determined experimentally for Cp2TiCH2CHRCH2.13Thus, the model structure, while not the Tebbe reagent, would be expected to mimic the resultant changes in the alkylidene fragment upon complexation. The calculated geometry of 2, shown in Figure 1,differs greatly from those of separated metal carbene and Lewis acid fragments, which are also depicted. It does not support the notion that the two form a weakly bound complex. The T i c bond is nearly 0.2 A longer than that in H2Ti= CH2 and approaches one appropriate for a normal single 2.053 in linkage, e.g., 2.096 A in tetramethyltitani~m,'~ titanacy~lobutane'~ at the STO-3G level. Both the titanium-chloride and carbon-aluminum lengths, 2.236 A and 1.930 A,respectively, are only slightly longer than normal single bonds,16 e.g., 2.167 A in TiC1417and 1.899 A in at the STO-3G level. On the other hand, the AlCl linkage in 2 is much longer than that in free Lewis acids, e.g., 2.050 A in AlC13 at STO-3G.20 All of these features, as well as the predicted orientation of the plane of the AH2 i
(11)M. M. Francl, W. J. Pietro, R. F. Hout, Jr., and W. J. Hehrs, Organometallics, 2, 281-286 (1983). (12)M. M. Francl and W. J. Hehre, unpublished results. (13)J. B. Lee, G. J. Gajda, W. P. Schaefer, T. R. Howard, T. Ikariya, D. A. Straws, and R. H. Grubbs, J. Am. Chem. SOC.,103,7358 (1981). (14)Tic bond lengths in low-temperature crystal structure for Ti(CH2Ph), range from 2.04 to 2.21 A. G. R. Davies, J. A. Jarvis, and B. T. Kilbourn, J . Chem. SOC.,Chem. Commun. 1511 (1971). (15)2.127 and 2.113 A in crystalstructure for Cp2TiCH2CHPhCHp13 (16)In electron-deficient metal complexes, typical M-Cl bonds are much shorter than those in similar saturated systems, indicating significant donation by chlorine lone pairs to the metal. For example, the TiCl linkage in TiCl, is 2.170A:' almost 0.2 A shorter than in Cp2TiC12.18We have observed this facility of donation by C1 theoretically as well. (17)2.170 A from gas-phase electron diffraction. Y. Morino and U. Uehara, J. Chem. Phys., 45,4543 (1966). (18)A. Clearfield, D. Warner, A. Saldarriaga-Molena,R. Ropal, and I. Bernal, Can. J. Chem., 53, 1622 (1975). (19)1.957 A from gas-phase electron diffraction. A. Almenningen, S. Halvorsen, and A. Haaland, Acta Chem. Scand., 25,1937 (1971). (20)2.06 A from gas-phase electron diffraction. I. Hargittai and M. Hargittai, J. Chem. Phys., 60,2563 (1974). d
?r
bond in H2TiCH2/ClAlH2.
group (perpendicularrather than parallel to the Tic bond) suggest that the most appropriate representation of the model Tebbe reagent is in terms of a intramolecular complex, chlorine acting as the electron donor, aluminum as the acceptor, i.e.
\ITi -CP The lengthening of T i c linkage in 2 strongly implies the destruction of the reactive T bond upon addition of the Lewis acid. Compare the highest occupied ( T ) molecular orbital of the uncomplexed alkylidene (Figure 2(left))with that of a hypothetical weakly bound aluminum-alkylidene complex (Figure 2(center)).21 (We have simulated the weak complex by fixing the geometries of the alkylidene and Lewis acid at their respective STO-3G optimum values and optimizing only the intermolecular parameters.) The latter easily reveals its origin as the T bond of the uncomplexed structure and would be expected to react similarly. In contrast, the corresponding molecular orbital in the fully optimized complex 2, also the highest occupied (Figure 2(right)), bears little resemblance to its antecedents. However, its reactivity should not be entirely different from that of the T bond in the weak complex. The symmetry of this orbital is the same, and it remains bonding between carbon and titanium (aswell as between carbon and aluminum). As in the free carbene and in the weak complex, most of the density is localized on carbon, suggesting this as the likely site for electrophilic attack. We do not expect these results to alter significantly on increased saturation of the titanium center. The principal structural changes expected, i.e., lengthening of the T i c and TiCl bonds, would, however, contribute to changes in the bonding of the complex. Reducing the Ti-CH2 interaction should strengthen the A1-C bond, forcing the chlorine to continue in its role as donor to aluminum. On the other hand, the lessening of electron donation by chlorine to the transition-metal center will encourage donation to aluminum instead, probably at the expense of the Al-C bonding. The resultant effect of these opposing ~
~~
(21)(a) R. F. Hout, Jr., W. J. Pietro, and W. J. Hehre, J. Comput. Chem., in press; (b) R. F. Hout, Jr., W. J. Pietro, and W. J. Hehre, 'Orbital Photography. A Pictorial Approach to Molecular Structure and Reactivity", Wiley, New York, in press. (c) R. F. Hout, Jr., W. J. Pietro, and W. J. Hehre, Quantum Chemistry Program Exchange, Indiana University, to be submitted for publication.
Organometallics 1983,2, 459-460
forces on the overall electronic structure of the complex should be minimal. Despite the apparent dissimilarity between the free carbene and the protected system studied here, the Tebbe reagent effectively mimics the known chemistry of alkylidene complexes. Since the theoretical structure of 2 suggests that it is very strongly bound, it seems unlikely that the similarity arises from formation of a highly reactive free alkylidene complex via unaided equilibration with the Lewis acid. More likely, an incoming substrate or solvent molecule (or both) displaces the Lewis acid in a concerted fashion. G r u b b P has noted that extremely bulky Lewis bases facilitate the formation of titanacyclobutanes from 1 and olefins, implying that the Lewis acid fragment is removed by the base. Exploration of these possibilities via further theoretical work is in progress. Registry No. 1, 67719-69-1.
Reactlon of HCi with Photoproduced Base-Substituted Manganese Carbonyl Radlcals Blaine H. Byers," Timothy P. Curran, Michael J. Thompson, and Linda J. Sauer Department of Chemistry, College of the How Cross Worcester, Massachusetts 0 16 10 Received August 16, 1982
Summary: Near-UV irradiation of Mn,(CO),L, (L = PBu,, P(OEt),) in the presence of HCI and a variety of solvents yields both HMn(CO),L and Mn(CO),(L)CI. Evidence suggests the mechanism involves oxidative addition of HCI to 15- and 17-electron metal carbonyl radicals.
Evidence for the presence of metal carbonyl radicals (both neutral and ionic) in a variety of chemical reactions is growing rapidly.' By studying the chemistry of these radicals, a better understanding of probable chemical mechanisms is achieved. In addition to numerous CO substitution reactions,2 neutral manganese carbonyl radicals have been observed to react, by a variety of proposed mechanisms, with small molecules, including cc14,302,4 12,4Br2,5H2,6and HBrS7 In these reactions only single mononuclear produds were detected. In comparison, while looking at the reaction of Mn2(CO)A2(L = PBu,, P(OEt)3, and CO) with H20under acidic conditions,we observe that the reaction of HCl with photochemically generated Mn(CO)4Lradicals is unique in that it produces two carbon(1) (a) Nalesnik, T. E.; Orchin, M. Organometallics 1982,1,222-223. (b) Hershberger, J. W.; Klingler, R. J.; Kochi, J. K. J. Am. Chem. SOC. 1982, 104, 3034-3043. (c) Bruce, M. I.; Kehoe, D. C.; Matisons, J. G.; Nicholson, B. K.; Rieger, P. H.; Williams, M. L. J. Chem. SOC.,Chem. Commun. 1982,442-444. (d) Krusic, P. J.; San Filippo, J., Jr.; Hutch1981, 103, inson, B.; Hance, R. L.; Daniels, L. M. J. Am. Chem. SOC. 2129-2131. (2) McCullen, S. B.; Brown, T. L. Znorg. Chem. 1981,20, 3528-3533 and references therein. (3) Wrighton, M. S.; Ginley, D. S. J. Am. Chem. SOC. 1975, 97, 2065-2072. (4) (a) Haines, L. I. B.; Hopgood, D.; P&, A. J. J. Chem. SOC. A 1968, 421-428. (b) Jackson, R. A.; P d , A. Inorg. Chem. 1978,17,997-1003. (c) Kramer, G.; Patterson, J.; Po& A.; Ng, I,. Ibid. 1980, 19, 1161-1169. (5) (a) Hopgood, D. J. Ph.D. Thesis, London University, 1966. (b) Kramer, G.;Patterson, J. R.; Poi$ A. J. J. Chem. SOC.,Dalton Trans. 1979, 1165. (6) Byers, B. H.; Brown, T. L. J.Am. Chem. SOC. 1977,99,2527-2532. (7) Bamford, C. H.; Burley, J. W.; Coldbeck, M. J.Chem. SOC.,Dalton Trans. 1972, 1846-1852.
0276-7333f 83 f 23Q2-Q459$Q1.5Q fQ
459
yl-containing products, ~ i s - H M n ( c 0 ) ~and L cis-Mn(CO),(L)Cl. This report describes these HCl reactions under a variety of conditions and utilizes the appearance of two products for partial mechanism elucidation. Most of the solvent combinations employedsareflect the attempt to study the reaction of these water-insoluble compounds with water. The substituted carbonyls show only small solvent effects. When Mn2(C0)8L2(L = PBu, and P(OEt),) is dissolved in any of the solvent systems used" and irradiated,sb complete conversion of cis-HMn(CO)4Land cis-Mn(CO),(L)Cl is observed within about 30 min.g The rate of conversion shows some dependence on the HC1 concentraction. A small amount of hydrogen gas is also detected'O when the HC1 concentration is high. In contrast, Mn2(CO)loexhibits very marked solvent effects. Irradiation of Mn2(CO)loin the heterogeneous system (aqueous HCl/hexane) slowly produces HMn(CO&, Mn(CO),Cl, and some [Mn(CO),Cl],. After 24 h small amounts of hydrogen are also detected. However, irradiation of Mn2(CO)loin the homogeneous system (aqueous HCl/ethanol/isopropyl ether) causes only slow decomposition. When Mn2(CO)lois irradiated in the anhydrous HCl/hexane system, Mn(C0)&1 begins forming after 5 min. The concentration of Mn(CO)6C1increases for about 1h and then gradually converts to [Mn(CO),Cl],. There is no IR spectroscopic evidence for HMII(CO)~under these conditions even when high concentrations of Mn2(CO)lo are employed.'l This is consistent with the reported reaction between HBr and Mn2(CO)loin cyclohexane where only Mn(C0)6Br was d e t e ~ t e d . ~ When H2S04or HC2H302are employed in these photochemical reactions at concentrations comparable to those of HC1, HMII(CO)~L(L = PBu3, P(OEt),) forms but much more slowly than when HC1 is used. HN03causes almost complete decomposition within 1 h. Photochemically generated radicals have been shown to be substitutionally labile: and there is significant evidence suggesting that facile dissociation of CO from these 17electron radicals is involved in substitution reactions.12 It follows that 15-electron radicals Mn(CO),L are also involved in these presently reported reactions with HC1. If so, running reactions under an atmosphere of CO should significantly decrease the concentrationof these 15-electron radicals and, thereby, alter the reaction. Indeed, when these HC1 reactions are conducted under an atmosphere of CO, no hydride is formed and the rate of formation of chloride is reduced.', In light of these findings we propose (8) (a) Two sources of HC1 were examined. Homogeneous conditions were obtained in the following manner: gaseous hydrogen chloride was bubbled through hexane, isopropyl ether, or a 4% (by volume) ethanol/isopropyl ether mixture; aqueous hydrochloric acid was mixed with a 4% (by volume) ethanol/isopropyl ether mixture. Heterogeneous conditions (two phases) resulted when aqueous hydrochloric acid was stirred with hexane. (b) Typically, reaction solutions are prepared under a nitrogen atmosphere by using pure solvents stored over molecular sieves or alumina. The solutions are then purged for 15 min by using oxygenfree nitrogen (Linde) and kept under a positive pressure of nitrogen during irradiation. A 250-W mercury high intensity discharge lamp (GE H250A37-5) is used in conjunction with Pyrex filtering (A >300 nm). When a band-pass fiiter (Coming CS7-60 A- 352 nm with a band width at half-height of 60 nm) is employed, the reaction is slower (presumably due to the decrease in intensity), but the same products are formed. Samples for IR and GC analysis are taken via a serum cap and syringe. (9) Products are characterized by IR spectra: HMn(CO)4PBu3,YCO (cm-', isopropyl ether) 2057 (m), 1976 (m), 1960 (s), 1949 ( 8 ) ; Mn(CO),(PBu3)Cl,YCO (cm-', isopropyl ether) 2087 (m), 2018 (m), 2006 (a), 1948 (S).
(10)Hydrogen is detected by GC using Porapak Q packing. (11) Due to overlapping peaks, it is difficult to identify HMn(CO), spectroscopicallyuntil it is in high enough concentration so that the weak vibration at 2116 cm-l appears. (12) Wegman, R. W.; Olsen, R. J.; Gard, D. R.; Faulkner, L. R.; Brown, T. L. J. Am. Chem. SOC. 1981, 103, 6089-6092 and references therein.
0 1983 American Chemical Society
