Organometallics 1995, 14, 3423-3434
3423
Synthesis and Theoretical Analysis of Palladium(11) Complexes Containing a q1 Metallacarbyne Ligand Philippus F. Engel and Michel Pfeffer* Laboratoire de Synthtses Mktallo-induites (URA41 6 du CNRS), Universitk Louis Pasteur, 4, rue Blaise Pascal, F-67070 Strasbourg Cedex, France
Alain Dedieu” Laboratorie de Chimie Quantique (UPR 139 du CNRS),Universitk Louis Pasteur, 4, rue Blaise Pascal, F-67070 Strasbourg Cedex, France
Received March 8, 1995@ Metallacarbyne complexes such as ($-CsHs)M(CO)z=CR (M = Mo, W; R = p-Tol) afford simple adduct complexes when reacted with cyclopalladated compounds derived from benzo(h)quinoline, 8-alkylquinoline, or N,N-dimethylnaphthylamine.The interaction between the metallacarbyne and the palladium atom occurs primarily via the carbyne carbon atom, suggesting a qJ interaction between the M z C unit and Pd(I1). The bound metallacarbyne is easily displaced by two-electron donor ligands such as pyridine or trialkylphosphines. Comparison of the results of SCF calculations carried out on the [Cp(CO)zMoCHI[PdClz(NH3)], [Cp(CO)~MoCHI[AlH3)1,and [Cp(CO)zMoCHCH31f model systems indicates that the bonding between the metallacarbyne and the palladium complex is best described as involving a Lewis acid-Lewis base interaction together with a strong electrostatic component. It is suggested that these adducts are intermediates in the coupling reaction that occurs between the carbyne atom and the palladated carbon atom of the cyclopalladated complexes.
Introduction It is generally accepted1 that the first step in the insertion of an alkyne into a Pd-C bond is the formation of a complex in which the alkyne is r$coordinated to the metal center. In this step, the alkyne simply substitutes a labile halogen substituent X on palladium (see Scheme 1; for example, the C-Y represents a cyclopalladated ligand, X = C1, I).2 Recently, kinetic data have been obtained for these reaction^,^ and the results support the formation of a halide-bridged bimetallic coordination complex (Scheme 1). None of these proposed alkyne coordination complexes has been well-characterized. Only one complex, [PdzC14(tBuCeCtBu)2], has been isolated, but no X-ray structure is a ~ a i l a b l e .In ~ contrast, a number of planar M”L3 (olefin) complexes have been characterized, and their structures show that the olefin is coordinated perpendicularly t o the metal plane.5 Since olefins and alkynes both possess ?c and 3t* orbitals, it can be expected that alkynes are able to adopt similar coordination modes. The intermediate q2 complexes such as those depicted in Scheme 1can also be advanced on the basis of known To whom correspondence should be addressed. Abstract published in Advance ACS Abstracts, May 15, 1995. (1)Maitlis, P. M. Acc. Chem. Res. 1976, 9, 93. Maitlis, P. M. J . Organomet. Chem. 1980,200,161. Huggins, J. M.; Bergman, R. G. J . Amer. Chem. SOC.1981, 103, 3002. Samsel, E. G.; Norton, J. R. J. A m . Chem. SOC.1984, 106, 5505. ( 2 ) Pfeffer, M. Recl. Trau. Chim. Pays-Bas 1990, 109, 567. (3)Ryabov, A. D.; Van Eldik, R.; Le Borgne, G.; F’feffer, M. Organometallics 1993, 12, 1686. ( 4 )Hosokawa, T.; Moritani, I.; Nishioka, S. Tetrahedron Lett. 1969, 3833. (5)Allbright, T. A,; Hoffmann, R.; Thibeault, J. C.; Thorn, D. L. J . A m . Chem. SOC.1979, 101, 3801. ‘p
Chart 1 Tnl
alkyne complexes of Pt(I1). For instance, in the complex [ ( ~ - T O ~ ) N H ~ ) C ~ Z P ~ ( ~ ~ - ~ B the U Ccarbon-carbon IC~BU)], triple bond is coordinated symmetrically to the platinum center, the triple bond being perpendicular to the plane of the “PtL3”fragment (Chart 1L6 Another interesting model system is found in the coordination chemistry of certain metallacarbynes, L,M=CR. It is well-known that alkynes and metallacarbynes display analogous ligand properties toward zero-valent metal centers.7a These properties can therefore be expected to apply to higher valent metals like Pd(I1) as well. Unfortunately, complexes with a metallacarbyne coordinated to a Pd(I1) center have never been reported. p-Alkylidyne complexes of Pd(0) are also very rare: only the labile complex [PdWz@-C(4-T01))2(CO)4(Cp)21has been isolated, but no X-ray structure could be obtained.7b We have shown recent19 that some so-called “Fischer metallacarbynes” formally insert into the metal-carbon bond of cyclopalladated complexes. For example, the 16) Davies, G. R.; Hewertson, W.; Mais, R. H. B.; Owston, P. G.; Patel, C. G. J . Chem. Soc. A. 1970, 1873. t 7 ) i a )Stone, F. G. A. Angew. Chem., Int. Ed. Engl. 1984, 23, 89. t b Ashworth, ~ T. V.; Chetcuti, M. J.; Howard, J. A. IC;Wisbey, S. J.; Stone, F. G. A. J . Chem. Soc.. Dalton Trans. 1981, 763. (8) Engel, P. F.; Pfeffer, M.; Fischer, J. Organometallics 1994, 13, 4751.
0276-733319512314-3423$09.00/00 1995 American Chemical Society
3424 Organometallics, Vol. 14, No. 7, 1995
Engel et al.
x = CI, I chloride-bridged complex of NJV-dimethylbenzylamine (dmba) reacts smoothly with Cp(CO)zMorC-4-Tol to give a p-alkylidene complex (eq 1). It corresponds to the
Chart 2
0
H
2
H
3 Me
H
4
formal insertion of the metal-carbon triple bond into the palladium-carbon bond. The overall analogy between the insertions of alkynes and metallacarbynes is evidenced by a number of similar reactions. This puts the study of the insertion reaction of metallacarbynes in an interesting perspective, since it may shed some light upon the insertion reaction of alkynes as well. In the reactions between these metallacarbynes and some cyclopalladated ligands, transient, deeply colored complexes were observed prior to the actual C-C coupling between the carbyne carbon and the ligand.8 In this paper, we present the synthesis and characterization of some of these species, and their importance to the understanding of the mechanism of the insertion reaction will be discussed. Ab initio calculations have been carried out on a model of one of these complexes in order t o obtain a detailed bonding description. Part of this study has been published in a preliminary
Results and Discussion Reactions of CyclopalladateaQuinoline Ligands. While the cyclopalladated complexes undergo an insertion reaction with the metallacarbynes Cp(C0h(9)Engel, P. F.; Pfeffer, M.; Fischer, J.; Dedieu, A. J. Chem. Soc., Chem. Commun. 1991, 1274.
M=C-4-Tol (la, M = Mo; lb, M = W) a rapid color change from orange to deep red brown is observed;8 a t the same time, the insoluble dimeric palladium complex dissolves. This color then disappears during the formation of the final product, a p-alkylidene compound similar to the dmba complex shown in eq 1.8As a rule, these transient red brown complexes are difficult to characterize fully, due to this irreversible transformation. However, it turns out that chloride-bridged complexes of benzo(h)quinoline(bhq, 2),8-methylquinoline(8mquin, 31, and 8-ethylquinoline (8equin, 4) (Chart 2) are generally less reactive in the C-C coupling reaction than the other cyclopalladated complexes. It is also apparent that the tungsten metallacarbyne, lb, reacts more slowly with cyclopalladated ligands than its molybdenum analogue, la. Therefore, the right combination of a metallacarbyne and a cyclopalladated ligand may result in slowing down the reaction, which allows for the isolation and full characterization of the transient complexes. Benzo(h)quinolineComplexes. Adding 2 equiv of the metallacarbynes la or lb to a suspension of the bhq complex 2 in dichloromethane results in a rapid dissolution of the poorly soluble palladium complex. Deep
Synthesis and Analysis of PdW) Complexes
Organometallics, Vol. 14, No. 7, 1995 3425
red brown species are formed, which are stable enough t o be isolated in about 77% yield. They have been characterized as the first Pd(I1)p-akylidyne complexes [Cp(C0)2Ml~-C(4-Tol)][Pd(bhq)C1)1(5a, M = Mo; 5b, M = W, eq 2). Complex 5b has been characterized by an
(z CI
Chart 3 Me
U
Cp(C0)2M&-R
l a M = Mo, R = 4-c l b M=W,R=4-Tol I C M = W, R = 4-C,jH4BUt
6
(2)
7
Chart 4
2
8
9
coordination complex similar to 5 is to be formed, it has a lifetime too short to allow observation by proton NMR. It seems that the formation of coordination complexes like 5 is seriously hindered by the presence of bulky groups close to the carbyne carbon. This remarkable X-ray diffraction study, which has been discussed behavior of the metallacarbyne Id has been noted b e f ~ r e .Clearly, ~ the labile chloride bridge trans to the already in the C-C-coupling reaction between Id and nitrogen donor atom in 2 has been substituted by the a cyclopalladated complex of the ligand benzylmethylmetal-carbon triple bond of the metallacarbyne. Comsulfide.8 plexes 5a,b are therefore directly related to the proposed Methyl- and Ethylquinoline Complexes. The coordination complexes shown in Scheme 1. Complexes 8-methylquinoline complex 3 is significantly more reac5a,b are stable for a few days in the solid state when tive toward the metallacarbynes 1 than is the bhq kept at -20 “C, but they decompose in solution within complex 2, and only in the reaction between 3 and the 2 days at this latter temperature. When 2 equiv of l a less reactive tungsten metallacarbyne l b can a coordiare reacted with the iodide-bridged analogue of 2 in nation complex be isolated. Complex 3 reacts instandichloromethane, a coordination complex similar t o 5a taneously with 2 equiv of l b in dichloromethane to give can be observed by infrared and proton NMR spectrosthe deep red brown p-alkylidyne complex [Cp(CO)2Wlcopy. It cannot be characterized further at room tem~-C(4-Tol)l[Pd(8mquin)Cl)l, 6 (Chart 3). Complex 3 is perature, since the reaction proceeds rapidly to the p-alkylidene complex [Cp(CO)(pu-CO)Mo1~-C(4-Tol)- so reactive that during the isolation of 6 the p-alkylidene complex is formed. Attempts to purify 6 via crystal(bhq)lPd(I)1.8 lization at -20 “C also afford some of the p-alkylidene To investigate the influence of the nature of the complex [Cp~CO)(p-CO)Wl[CL-C(4-Tol)(8mquin)l[PdCl~l. carbyne carbon in this coordination reaction, the metComplexes containing the 8-ethylquinoline ligand 4 allacarbyne C ~ ( C O ) Z W ~ C - ~ - C ~IC, H~ ~ Bbeen U , prehas are the least reactive of the cyclopalladated complexes pared. The carbyne carbon in IC should be somehow that undergo an insertion reaction with the metallamore electron rich than in lb. As for lb, 2 equiv of IC carbynes 1.8 A 2 equiv amount of l b reacts instantareacts with the bhq complex 2 and rapidly forms a deep neously with 4 in dichloromethane to form a deep red red brown complex, which can be isolated and characbrown solution. In the isolated solid, a p-alkylidyne terized. Its spectral data suggest it to be the impure complex can be recognized as the major product, which p-alkylidyne complex [Cp(CO)2WI[CL-C(4-CgH4tB~)1[Pd7. is probably [Cp(CO)2WI[CL-C(4-Tol)l[Pd(8equin~Cl~l, (bhq)Cl)], 5c (eq 2). Clearly, the electronic differences Molecular models suggest that the bulky Cp(CO)2W between the para methyl group in l b and the para tertfragment will be in an anti position relative to the butyl group in ICare not important in the formation of methyl group on the palladated carbon. Three minor complexes 5. products are also present, but the attempts to purify 7 From the X-ray structure of 5b it can be expected that via repeated precipitation from a dichloromethanebulky substituents on the ortho position of the carbyne hexane mixture have only led to the formation of other phenyl ring will hinder the formation of the coordination undefined products. complex. To verify this, the metallacarbyne Cp(CO)2Reactions of Other Cyclopalladated Ligands. W=C-2,6-CsH3Mez, Id, has been prepared, which posBenzylmethylsulfide Complexes. The cyclopallasesses two methyl groups in the ortho position relative dated complex with a benzylmethylsulfide ligand (bms, t o the carbyne carbon. Addition of Id to a solution of 8 , Chart 4) reacts almost instantaneously with the the bhq complex 2 in dichloromethane does not result metallacarbynes l 4 b to give the p-alkylidene complexes in a color change, the orange color of the metallacarbyne [Cp(CO)~-CO)MI~-C(4-Tol)(bms)l[Pd(Cl~l (M = Mo, W). being maintained. The proton NMR spectrum of the During this reaction, two rapid color changes from reaction mixture in d-chloroform confirms that only the orange to deep red brown and back again to red orange reactants Id and 2 are present in solution. If a
3426 Organometallics, Vol. 14,No. 7, 1995
Engel et al.
Chart 5
Cp(CO)2MFragment. In the infrared spectra, two stretching frequencies are found close to the values of the free metallacarbynes (la, 1993,1917 cm-'; lb, 1984, 1906 cm-l; IC,1984,1907 cm-'), and they indicate the presence of two terminal carbonyl ligands. For compounds 5a-c and 11 they are found at somehow higher frequencies which indicate some electron release from the metallacarbyne unit when coordinated to Pd (see below, theoretical calculations). The YCO values of complexes 6 and 7 are rather lower L J in energy, this being due to the least electron withdrawloa M = M o 11 ing groups, 8-alkylquinoline us benzo(h)quinoline or 10b M = W naphthylamine. In the carbon NMR spectra, the carTable 1. Selected Spectral Data for Complexes bonyl carbons are found as two signals around 220 ppm. 5-7 and 11 The cyclopentadienyl protons appear as a singlet 'H NMR (ppm)b between 5.91 and 5.76 ppm in the proton NMR spectra, slightly downfield of the values encountered for the free compd no. IR vco (cm-lP Cp (SI 4-Me (s) CsHJ (la, 5.62 ppm; lb, 5.67 ppm; IC,5.67 metallacarbynes 5a 1998, 1932 5.76 2.33 8.06 ppm). This small downfield shift of 0.14-0.24 ppm is 5b 1984,1913 5.91 2.29 8.03, 7.10 5c 1984,1910 5.90 8.05 typical for this coordination of the metallacarbyne to Sd 1966,1896 5.85 2.29 7.94-7.13 Pd(II), and it is a sign of the increased electron donation 7 1961, 1891 5.78 2.29 8.06, 7.15 from the Cp ligand to its metal center. The chemical 11 1982, 1913 5.85 2.31 7.99, 7.13 shift of the Cp ligand in the carbon NMR spectra, I3C NMR ( p p m p however, is not much affected, and it is found around compd no. co ,u-c Cp 4-Me 95 ppm. 5a 229.5, 227.7 312.8 95.9 22.0 The chirality of the p-alkylidyne complexes is reflected 5b 221.1, 219.1 303.3 95.1 22.3 in compounds 6 and 11 by the diastereotopicity of the 5c 220.6,218.3 302.9 94.5 NMe2 and CH2 fragments of the cyclopalladated ligands. 6 222.1, 221.4 302.1 94.0 21.9 When a solution of 6 in &-benzene is quickly heated to 7e 75 "C, the CH2 protons of the metallated carbon remain 11 220.8, 218.6 306.5 94.3 22.0 diastereotopic, which confirms that the metallacarbyne In CHZC12. In CDC13. Doublets with 3&H = 8-9 Hz, not is still coordinated to the palladium center. always visible. In CDZClz. e Not available. The carbon bridging the two metals is found in the carbon NMR spectra around 300 ppm, which is a normal are observed. We assume that in this reaction the coordination complexes [ C ~ ( C O ) ~ M I ~ - C ( ~ - T O ~ ) Ivalue [ P ~ -for a free metallacarbyne (285-330 ppm).1° It indicates that the sp character of the carbyne carbon (bmdC11(loa, M = Mo; lob, M = W) are formed (Chart has been preserved and that the Cp(C0)2MC-4-Tol 5) although these complexes could obviously not be fragment can still be considered as a metallacarbyne. isolated because of the rapid insertion reaction that It must be noted, however, that the sp2 carbons of takes place with the cyclopalladated ligand. terminal metallacarbenes can also resonate above 300 NJV-DimethylnaphthylamineComplexes. The ppm (240-370 ppm),'l and that this chemical shift must ligand Nfl-dimethylnaphthylamine (dmna) forms cythus be interpreted with care. clopalladated complexes in which a rigid five-membered Solid State Structure of [Cp(C0)2WI[CI-C(4-Tol)lmetallacycle is present, as in the quinoline complexes [Pd(bhq)Cl],5b. Complex 5b has been fully charac2-4. Neither the chloride complex 9 nor its iodideterized by an X-ray diffraction study. Details of the bridged analogue reacts cleanly with the metallacarcrystal structure determination have been p ~ b l i s h e d . ~ bynes 1 t o give p-alkylidene complexes. However, in Some important features of the structure will be dethese reactions, the formation of deeply colored species scribed here, however (see Table 2 and Figure l). was also observed upon mixing the palladium complex It is at first sight apparent that 5b is built up from with 1, accompanied by the dissolution of the Pd dimer. two fragments that are connected via a short contact For example, the reaction between 2 equiv of lb and 9 between palladium and the carbyne carbon c14. Neither in dichloromethane is instantaneous, and the deep red the metallacarbyne nor the palladium fragment has brown p-alkylidene complex [Cp(C0)2WIb-C(4-Tol)l[Pdundergone any major changes with respect to the (dmna)Cll, 11, can be isolated in about 60% yield (Chart starting complexes lb and 2. 5). As usual, the complex decomposes in solution at room temperature within a few hours, but it may be The geometry around the palladium atom is that of a kept at -20 "C in the solid state for several weeks. square plane, the tungstacarbyne unit occupying the fourth coordination site. The w-c14 bond is coordiCharacterization of the Complexes. Spectral nated almost perpendicularly to the coordination plane Data. The metallacarbyne fragment in the complexes of Pd(W-Cl4-Pd = 89.27(2)")as would be expected from 5-7 and 11 displays very characteristic signals in the the geometry of Pd(I1) (alkyne) complexes. However, infrared and NMR spectra, which indicates that all since the carbon C14 is almost exactly in the fourth these complexes belong to the same class of p-alkylidyne compounds. Table 1lists selected spectral data of these (10)Fischer, E. 0.;Schubert, U. J . Organomet. Chem. 1975,100, complexes which concern the metallacarbyne fragment. 59. Heesook, P. K.; Angelici, R. J. Adu. Organomet. Chem. 1987,27, The 13C NMR spectrum for 7 is not available because 51. (11)Herrmann, W. A. Pure Appl. Chem. 1982,I , 65 the complex could not be obtained sufficiently pure. ~~
Organometallics, Vol. 14, No. 7, 1995 3427
Synthesis and Analysis of Pd(II) Complexes
8$"'
c2
C25
C6
Figure 1. ORTEP diagram of [Cp(CO)~WI[CI-C(4-Tol)][Pd(bhq)Cl], fib, with the corresponding atom-labeling scheme. Table 2. Selected Bond Distances (A),Angles (deg) and Dihedral Angles (deg) of 5ba Bond Distances 2.084(7) W-cl4 2.107(6) W-.*Pd 2.400(2) w-c27 1.998(7) w-c28 3.839(7) W-Cp" 2.666( 7 1 C14-cl5 2.773(7) c27-01
C 11-Pd-Cl C14-Pd-N C11-Pd-Ci4 C 11-Pd-N N-Pd-C1 C14-Pd-Cl c2l-w-c28
Cp'-W-C14C
Angles 169.8(2) c27-w-c14 172.7(2) c28-W-cl4 92.4(3) w-c14-c15 81.7(2) W-Ci4-Pd 92.4(2) Pd-C14-C15 92.8(2) W-c27-01 91.0(4) w-c2!3-02 122.45(4)
1.897(7) 2.8001(6) 1.95(1) 1.995(9) 2.024( 1) 1.438(9) 1.15(1) 87.8(3) 109.1(3) 151.9(4) 89.27(2) 117.91(3) 176.84(5) 173.53(5)
Dihedral Angles plane 1 Cp'-W-C14C W-Ci4-Pd W-Ci4-Pd
plane 2 W-Ci4-Pd ~15-~16-~17-~18-~19
CM-P~(C~)(CII)-N
122.9(3) 7.3(1.5) 83.9(2)
From ref 9. H(C16) is the hydrogen substituent of the tolyl carbon c16. Cp' is the centroid of the v5-C5H5 ligand.
coordination position of Pd trans to the nitrogen atom ((314-Pd-N = 172.7(2)"),the interaction of the W=C unit to the palladium atom may be considered as nonsymmetrical; a more symmetrical tungstacarbyne to Pd interaction would correspond to a situation whereby W and C are roughly equidistant from the coordination plane of Pd. The W-Pd distance (2.8001(6)A) is significantly smaller than the sum of the covalent radii of these atoms (2.986A),13thus suggesting that there is some interaction between the two metals. The W-cl4
Chart 6 To1
12
distance (1.897(7)A) is intermediate between the W-C distances in the free metallacarbyne Cp(CO)2WW-4To1 (1.82(2)All4 and in the related dimetallacyclopro12 pene complex [C~(CO)~WI~-C(~-TO~)I[P~(PM~~P~) (1.97A) (Chart 6).15a3b The fragment Cp(CO)2WW-4To1 in Sb seems thus to have preserved its metallacarbyne character. The Pd-Cl4 separation (2.084(7)A) is within the range generally observed for Pd-C u bonds (1.99-2.15A); however, it is somewhat longer than that normally found for such a bond trans to a pyridine nitrogen atom, i.e., an atom that is known to have a rather small trans influence.12 The plane bisecting the Cp and both carbonyl ligands makes an unusual dihedral angle of 122.9(3)' with the (12) For a selection of relevant references, see: Bruce, M. I. In Comprehensive Organometallic Chemistry; Pergamon Press: Oxford, U.K., 1982; Vol. 9, pp 1399-1405. (13)Bender, R.; Braunstein, P.; Jud, J . M.; Dusausoy, Y. Inorg. Chem. 1963,22, 3394. (14) Huttner, G.; Frank, A.; Fischer, E. 0. Isr. J . Chem. 1976, 15, 133. (15)(a)Ashworth, T. V.; Howard, J. A. K.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1980,1609. (b)We are not aware of any report of the molecular structure determination of a dimetallacyclopropene compound built up by the reaction of a metallacarbyne compound with a palladium(0) complex. However, we have recently succeeded in obtaining the crystal structure of Pd{W(~-CCeH3Mez-2,6)(CO)z(rlC&)}2, which contains two such units and which is isostructural to the closely related compounds of E% and NFb (Engel, P. F.; Pfeffer, M.; Fischer, J. Unpublished results, 1993).
Engel et al.
3428 Organometallics, Vol. 14, No. 7,1995 Chart 7
-r
a
b
C
of Sb in d-chloroform results in a mixture of la,b and Sa,b, as is clear from the proton NMR spectrum. This confirms that l a can partially displace l b when the latter is coordinated to the palladium center. The fact that both Sa and 5b are present in solution indicates that the metallacarbynes la and lb have the same ligating properties toward a Pd(I1) center. Another typical reaction of the p-alkylidyne complexes is the displacement of the metallacarbyne by a twoelectron donor ligand. Upon adding pyridine or triphenylphosphine to a solution of a p-alkylidyne complex in dichloromethane, a rapid color change from deep red brown to orange is observed. This reaction can be easily monitored by proton MMR spectroscopy. d s - w d i n e reacts instantaneously with a solution of 5b in CDC13, and the spectrum of the mixture obtained confirms that &-pyridine has displaced the metallacarbyne ligand entirely (eq 3). The
Figure 2. ORTEP diagram of Sb, viewed along the C14Pd axis, from c14 to Pd (Pd is hidden behind C d . plane of the tolyl group, whereas this angle is 90" in the structure of the free metallacarbyne lb14 (Figure 2). It is not clear if this torsion around the W-C14 axis is due to steric interactions between the protons of the Cp ligand and other substituents in its vicinity. It is most likely, though, that an interaction between Cp and the chloride group forces the Cp(C0)zMfragment in his position. It is clear from Figure 2 that the plane of the tolyl ligand is almost parallel to the plane W-Cl4-Pd (7.31(1.48)"between the planes), which is expected from the orbital interaction between the p orbitals on CU and the d orbitals on Pd. The p orbital lying in the tolyl plane is not delocalized onto the aromatic ring, and it is therefore more available for the interaction with Pd than the p orbital perpendicular to the plane. To maximize the overlap between the p and d orbitals, the tolyl plane has to be oriented parallel to the C14-Pd bond. In this orientation of the tolyl plane, the hydrogen substituent of the carbon CISis positioned above the palladium plane (Pd-H(Cl6) = (2.773(7)A). This Pd-H distance compares well with those found in several other Pd complexes having an agostic interaction between the C-H bond and the Pd atom.16 Lability of the Metallacarbyne Ligand, The complexes 5-7 and 11 have in common a weakly coordinated metallacarbyne ligand, which may be exchanged in solution for other donor ligands. The addition of the molybdenum metallacarbyne l a to a solution (16)(a) Dehand, J.; Fischer, J.; Pfeffer, M.; Mitschler, A,; Zinsius, M. Inorg. Chem. 1976,15, 2675. (b) Brammer, L.; Chamoch, J. M.; Goggin, P. L.; Goodfellow, R. J.; Orpen, A. G.; Koetzle, T. F. J.Chem. Soc., Dalton Trans. 1991, 1789 and references cited therein.
a
N Y d 5
+
monomeric pyridine complex formed in this reaction is a well-known compound, which is easily obtained by reacting the dimeric complex 2 directly with pyridine. A similar monomeric complex has been obtained from the reaction between 2 and triethylphosphine. This pyridine complex does not react further with the metallacarbyne lb to form Sb, which confirms that the substitution of the metallacarbyne by pyridine in Sb is irreversible. It seems that the metallacarbynes 1 behave toward a Pd(I1) center as simple, but unusual, two-electron donor ligands.
Discussion The Nature of the Bonding: Structural and Theoretical Considerations. Three different limiting forms can be used to describe the structure of the coordination complex Sb: a zwitterionic metallacarbene (a),a dimetallacyclopropene(b),and a complex in which the metallacarbyne binds mostly to the metal center via the carbyne carbon ( c ) (Chart 7, R = 4-Toll.
Synthesis and Analysis
of
Organometallics, Vol. 14,No. 7,1995 3429
PdUI) Complexes Chart 8
The W-C14 distance in 5b is significantly shorter than the W-C bond in a normal metallacarbene such as (CO)SW=C(OMe)Ph (2.04 A).17 Together with the fact that the Pd-C14-W angle is 89.27(2)" this seems to exclude the metallacarbene structure a as an adequate description of 5b. The nonsymmetric bonding mode of the W X ! unit with respect to the Pd coordination plane (vide supra) associated with the rather short W-C14 distance and a relatively long Pd-C14 interaction led us also to conclude that the dimetallacyclopropane limiting form is an inadequate structure for 5b. Related examples of bimetallic compounds in which carborane tungstacarbyne derivatives are coordinated to Au(I),18"Pt(II)lsband R u ( I I P complexes and which display short W-C distances and long C-M interactions have been described earlier. These compounds were analyzed as containing a semibridging carbyne carbon atom supporting a strong metal-metal interaction. But they all exhibit a disposition of the WGC unit that is more symmetrical than the one found in 5b. For instance, the P- Au-C angle in [AuW(p-CCsH4Me-4)(C0)2(PPh3)(q5-C2B9HgMe2)] amounts to 163"18"whereas the corresponding N-Pd-C angle in 5b amounts to 173". It is in fact the whole palladium-metallacarbyne unit which is rotated by about 10" in 5b,thus leading to the observed asymmetry. The third limiting form is c for 5b,Le., a metallacarbyne +coordinated to a metal center via its carbyne carbon. In this description,the metal-metal interaction would be the weakest, and the Pd-C bond would be the result of an electron transfer from the triple bond to palladium via the carbon C14. Preliminary EHT calculations carried out on the [Cp(C0)2WCCH3][PdCl(NH& (CH3)] system, 13,9 indeed indicated that a major component of the binding is a two-electron stabilizing interaction between the doubly occupied n type orbital of the metallacarbyne and the empty dx2-y2orbital of the T-shaped palladium fragment, see Chart 8. Compound 5b can thus be considered as a Lewis acid (the palladium fragment) coordinating a Lewis base (the metallacarbyne). A second interaction, although less important, was also found to be operative. This interaction is of CJ back-donation type, between the dz2 orbital of palladium (doubly occupied) and the empty n* orbital of the metallacarbyne, see Chart 8. Note at this stage (17)Mills, 0. S.; Redhouse, A. D. J . Chem. SOC.A 1968, 642. ( 18)( a )Green, M.; Howard, A. P. J.; Nunn, C. M.; Stone, F: G. A. J . Chem. SOC.,Dalton Trans. 1987, 61. Goldberg, J. E.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A. J . Chem. SOC.,Dalton Trans. 1992, 2495. (b)Devore, D. D.; Howard, J. A. K.; Jeffrey, J. C.; Pilotti, M. V.; Stone, F. G. A. J . Chem. SOC.,Dalton Trans. 1989, 303. Carr, N.; Gimeno, C.; Stone, F. G. A.; J . Chem. SOC.,Dalton Trans. 1990, 2617. ( c )Green, M.; Howard, J. A. K.; Jelfs, A. N. de M.; Johnson, 0.;Stone, F. G. A. J . Chem. SOC.,Dalton Trans. 1987, 73.
Chart 9 H
15
14
l+ \ 2.04
16
of the discussion that, given the geometry of the system and in particular because of the N-Pd-C linear arrangement, the positive overlap between the lower lobe of the Pd dz2 orbital and one upper lobe of the Mo dyz orbital might give rise to some metal-metal bonding. In order to put these preliminary findings on more firm grounds, the geometry and the electronic structure of three related systems, uiz. [Cp(C0)2MoCHI[PdCl~(NH3)1, 1-4, [Cp(CO)2MoCH][AlH3)], 15, and [Cp(C0)2MoCHCH#, 16,see Chart 9, were determined through SCF ab initio calculations. These three systems were chosen to scan various types of bonding. Compound 14 was taken as a model of the metallacarbyne palladium complex 5b. The substitution of the PdC12(NH3) palladium fragment by the prototypical Lewis acid AlH3 was aimed at assessing, through the comparison between 15 and 14,the extent of Lewis acidLewis base type of binding. The substitution by CH3+ to yield 16 should provide instead a reference for a true metallacarbene. The nature of the bonding in 14 was further investigated by analyzing the distribution of the fragment electron deformation density obtained by subtracting the electron density of the two fragments, PdCldNH3) and Cp(C0)2MoCH, from the total electron density of the composite system, [Cp(C0)2MoCH][PdC12(NH3)].A similar analysis was also performed for 15. Chart 9 displays the three computed geometries as obtained from the geometry optimization procedure (with the most important bond distances and bond angles). We first note the good agreement between the optimized structure of 14 and the related structure of 5b. But the most salient feature of the chart is the strong similarity between 14 and 15. In both structures the Mo-C bond is short, 1.81A, consistent with a triplebond character. l9 The angular disposition around the carbyne atom is also similar in 14 and 15 with a Mo-
3430 Organometallics, Vol. 14, No. 7, 1995
W-
HjN-
a/
c
*d,MO-O ' "\
Engel et al.
--LZLl
co Figure 3. Map of the fragment electron deformation density of the [Cp(C0)2MoCHI[PdC12(NH3)1system in the Mo-C-H-Pd plane. The fragments are [Cp(C0)2MoCHl and [PdCMNhdI. Solid lines for zero- and positive-density contours, dashed lines for negative-density contours; contour interval, 0.050 e
a-3.
C-H angle of about 160" and a Mo-C-Pd or Mo-CAl angle of about 100". We note, however, that the Pd-C bond in 14 is comparatively much shorter than the Al-C bond in 16 (2.17us 2.33 A). This points to a stronger interaction in the palladium case: the SCF heterolytic bond dissociation energies are 30.9 and 17.2 kcdmol, respectively.20 But the aforementioned geometrical features are clearly indicative of the retention of the sp character of the carbyne atom. This is in agreement with the chemical shift observed in the experimental system (vide supra). In contrast, the carbon atom in 16 is clearly of sp2 character with the Mo-C-C and Mo-C-H angles amounting to 125.6" and 123.6",respectively. The Mo-C bond length is also much greater, 2.04 A, i.e., typical of a Mo-C double bond. The two maps of the fragment deformation density are shown in the Figures 3 and 4 for 14 and 15, respectively. They both display a buildup of electron density on the carbyne atom and between this carbyne atom and either Pd or Al. The buildup of electron density on the carbyne atom might seem contradictory with the Lewis base character of the metallacarbyne. But a closer look at the maps (and also at the population analysis) shows that, upon metallacarbyne coordination, a complete reorganization of the electron density takes place. This reorganization is shown schematically in Chart 10. It involves an electron flow from the Mo atom (and from the ligands attached to it>toward the palladium and its ligands (see, for instance, the increase of electron density on NH3) via the carbyne atom. This accounts for the shifts observed experimentally in the carbonyl IR frequencies and the " M R signal of the Cp protons (vide supra). For 14 electron depletion is also found in the immediate vicinity of Pd. This is traced t o the D back-donation (d,z JC*)sketched in Chart 8. In 15 no such back-
-
(19)The MoBCo bond length was optimized to 1.80 A in the free Cp(CO)zMo=CH metallacarbyne system. (20)These values computed with the full split valence basis set refer to unrelaxed fragments. The basis set superpositionerror is not taken into account.
Figure 4. Map of the fragment electron deformation density of the [Cp(C0)2MoCHl[AlH31system in the MoC-H-AI plane. The fragments are [Cp(C0)2MoCHland [AlHs]. Solid lines for zero- and positive-density contours, dashed lines for negative-density contours; contour interval, 0.050 e
a-3.
Chart 10
f!P
H
/
donation interaction can occur due to the lack of occupied do orbitals in the AlH3 fragment. The consequence is a smaller electron buildup between Mo and Al and the weaker Mo-Al bond. That the flow of electron density originating from the metallacarbyne will spread on the whole palladium Sragment is a feature of interest. It explains in particular that the quinoline ligand with its framework of It* accepting orbitals is well suited to stabilize the +coordination mode of the metallacarbyne ligand. Similarly the greater electronegativity of chlorine compared to iodine accounts for the greater stability of chlorine derivatives which is found experimentally bide supra). The differential density map of the [Cp(C0)2MoCHl[PdCldNH3)1system is also indicative of a slight electron buildup between the Mo and the Pd atom, see Figure 3. This buildup is traced, as mentioned above, to the positive overlap between the lower lobe of the Pd dz2 orbital and one upper lobe of the Mo dYzorbital in the dz2 a* combination, Chart 8. The palladium metallacarbyne complex may therefore be seen as having a weak P d * - * M ointeraction. The optimized Pd-C-Mo angle is indeed somewhat smaller than the Al-C-Mo angle, see Chart 9. But this component of the bonding remains weak, and it cannot account for the overall stability of the system. Finally, one should not overlook some additional contribution of the electrostatic interactions to the bonding. The metallacarbyne system is polarized, see Chart 11, the carbon atom being highly negative and
+
Organometallics, Vol. 14, No. 7, 1995 3431
Synthesis and Analysis of PdUI) Complexes
Chart 11
I"
c
-0.39
the molybdenum atom being positively charged. We have seen that the +binding of the metallacarbyne will reinforce this polarization. Since the palladium atom is positively charged, the electrostatics favor the q1 rather than the r2 mode of binding. The above overall picture of the bonding for this class of systems is consistent with previous theoretical and experimental findings on other metallacarbyne or alkyne complexes. Iron metallacarbyne complex [Cp(C0)2M(C=R)][Fe(C0)31and [Cp(C0)2M(C=R)I[Fe(C0)41 (M = Mo, W) have been structurally characterized and theoretically analyzed by Stone and co-workers.21 They show a v2 mode of binding, accounted for by the two stabilizing interactions sketched in Chart 12. The main difference with our systems lies in the d, + n* back-donative interaction of Chart 12. In the iron complexes the n* metallacarbyne orbital will interact preferentially with the d,, orbital: this orbital is the HOMO of the Fe(C0)3 or Fe(C0)4 fragment, thus quite high in energy. It is also polarized toward the metallacarbyne. In 13 and 14 the HOMO of the palladium fragment is not the dYzbut the dz2orbital (Chart 8). The dvz orbital is not hybridized and lies at much lower energy, therefore precluding any strong interaction with the JC*metallacarbyne orbital. Moreover, since the iron atom is in the 0 oxidation state, it is probably less positively charged (despite the back-donation to the carbonyls)than the palladium atom in the +2 oxidation state. It will therefore exert a much weaker electrostatic attraction on the carbon atom of the metallacarbyne. The electrostatic contribution to the bonding is also best exemplified by our recent study of the PdC1(CH3)(NH3)(C2H2)system:22 In C2H2 the two carbon atoms are equivalent and bear the same charge. A SCF geometry optimization starting from a geometry did not ended with an intermediate having this coordination mode but led directly to the r2 geometry. The electronic structure of the [Cp(C0)2WCHl[Au(PH3)]+system taken as a model of various [Cp(CO)2W(C=R)][Au(PPh3)]+ and related complexes has been recently investigated through extended Huckel calculasignificant orbital interactions between the t i o n ~ No .~~ [Cp(C0)2WCHland the [Au(PH3)1+fragment were found (due to the large energy gap between the d orbitals of
Au and the valence orbital of the metallacarbyne), with the exception of a weak interaction between the empty sp hybrid of [Au(PH3)]+ and the doubly occupied n orbital of the metallacarbyne. PdC12(NH3) is isolobal to [Au(PH3)1+and the n + d,Z-,:! interaction (Chart 8) is the analog of the n + sp interaction in the gold system. There is one difference,however: the dz2orbital is much higher in energy in [PdC12(NH3)]than in [Au(PH3)]+and it can therefore interact with the n* orbital of the metallacarbyne, provided that a good overlap exists between the two orbitals. We have seen that this requirement is fulfilled if the carbon atom lies in the palladium coordination plane. Stability of the p-Alkylidyne Complexes. The metallacarbyne ligand in the p-alkylidyne complexes can be easily displaced by other donor ligands like pyridine. This seems to indicate that the Pd-p-C bond is relatively fragile. However, when the 8mquin complex 6 is heated in &-benzene to 75 "C, the chirality of the molecule is maintained, as is clear from the diastereotopic CH:! protons in the proton NMR spectrum. This can mean either that the rotation of the metallacarbyne ligand along the Pd-C bond is slow on the NMR time scale or that the decoordinatiodrecoordination of the metallacarbyne to Pd is too slow a process to be observed. Geometry of the p-AIkylidyne Complexes. In the structure of 5b, the plane of the tolyl ring is virtually coplanar with the plane W-Cl4-Pd. Orbital considerations show that this orientation of the tolyl ring is the most favorable for the overlap between the p orbitals on C14 and the d orbitals on palladium. An additional reason for the orientation may be the interaction between palladium and one of the ortho protons of the tolyl ring. This can be possibly described as a threecenter four-electron interaction. The position of the Cp(COhW unit must be influenced by the steric repulsions between the cyclopentadienyl ring on the one hand and the chloride and tolyl substituents on the other hand. Implications for the C-C-Coupling Reaction between Metallacarbynes and Cyclopalladated Complexes. A number of cyclopalladated complexes react with the metallacarbynes l a or l b to give p-alkylidene complexes, resulting from a carbon-carboncoupling reaction between the carbyne carbon and the cyclopalladated ligand.8 In the reactions of the quinoline complexes [Pd(bhq)I], and [Pd(8mquin)Xl2(X = C1, I) transient species are formed, which are the analogues of the characterized coordination complexes 5 and 6. In the coupling reaction between the bms complex 8 and the metallacarbynes 1, similar coordination complexes may be formed. It is therefore tempting to assume that p-alkylidyne
Chart 12
/
A
x + sp
dx
+
x*
z4
Engel et al.
3432 Organometallics, Vol. 14,No. 7, 1995
least in the C2Hz case the q1 geometry corresponds to the transition state.22
Chart 13 R
Conclusions
5:
R'
d
e
complexes like 5 are actual intermediates in these insertion reactions, and that the formation of these complexes is a necessary step in all coupling reactions of cyclopalladated ligands with the metallacarbyne 1. However, no coordination complexes seem to be formed during the reaction of the cyclopalladated complexes of NJV-dimethylbenzylamine (dmba) or 2-benzylpyridine (bzpy) and l a or lb. When these reactions are monitored by proton NMR spectroscopy in CDC13, only the starting materials and the final p-alkylidene products are observed. Attempts to follow the reaction between [Pd(bhq)Ihand l a by UV/vis spectroscopyhave so far failed to prove whether a coordination complex can be transformed into a y-alkylidene or not. Still, the best working hypothesis remains that complexes like 5 are real intermediates, which undergo subsequent rotation around the Pd-p-C bond, and then an insertion to form the p-alkylidene products. It may be that the coordination complexes are formed in all of the coupling reactions but that their lifetimes are often too short to observe them by proton NMR spectroscopy. The fact that coordination complexes are formed with quinoline ligands and dmna may indicate that a rigid five-membered metallacycle stabilizes these structures. Other cyclopalladated ligands may not be able to stabilize the complexes sufficiently to be observed. Another reason could be that the formation of the coordination complex is slow compared to the formation of the carbon-carbon bond. The proposed intermediate would then be consumed too rapidly to be observed. On the basis of the available data it is not possible to make a clear choice. Kinetic experiments will be required to gain further insight into the mechanism of these reactions. Implications for Alkyne Complexes. As noted in the introduction, no alkyne complexes of Pd(I1) have been structurally characterized. The metallacarbynes Cp(C0)2M=C-R (M = Mo, W) are isolobal with alkynes, and they can be considered as models for highly asymmetrical alkynes. The structure of complex 5b thus provides a strong indication that alkyne complexes like d or e may actually exist, although they would be too labile to be isolated (Chart 13). When the alkyne is symmetrical, the v2 geometry d will probably be adopted, but the greater the difference between the alkyne substituents R and R , the more geometry e will be favored. As Silvestre and Hoffmann suggested,24the q1 geometry e may also play a role in the course of the insertion reaction, even when it is less stable than the q2 geometry d. Our recent theoretical study of the acetylene insertion into the palladium methyl bond of P ~ C ~ ( C H ~ ) ( N H ~ ) indicated ( C ~ H Z )that at 121) Dossett, S. J.; Hill, A. F.; Jeffrey, J. C . ; Marken, F.; Shenvood, P.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1988, 2453. (22)De Vaal, P.; Dedieu, A. J . Organomet. Chem. 1994, 478, 121. (23)Jemmis, E. D.; Prasad, B. V. Organometallics 1992, 11, 2528. (24)Silvestre, J.; Hoffmann, R. Helu. Chim. Acta 1986, 68, 1461.
In the reactions between the metallacarbynes Cp(C0)2M=C-4-Tol (M = Mo, W) and the cyclopalladated ligands benzo(h)quinoline, 8-methylquinoline, 8-ethylquinoline, and Nfl-dimethylnaphtylamine, coordination complexes are formed, which are characterized as p-alkylidyne complexes with a higher valent group 10 metal. The X-ray data show that the metallacarbyne is bound to Pd essentially through the carbon atom. A theoretical analysis based on ab initio SCF calculations reveals that this 41 coordination mode results from the maximization of two bonding interactions: the first is due to the strong Lewis acid character of the Pd(IUL3 fragment, and the second is a weaker interaction involving donation from the Pd dZ2orbital into the x* orbital of the metallacarbyne. This last interaction is peculiar t o T-shaped d8 ML3 fragments. In addition to these orbital interactions, an electrostatic interaction between the positively charged palladium atom and the negatively charged carbyne atom should also favor the q1 coordination mode. It can be advanced that these simple coordination complexes are actually intermediates in the C-C coupling reactions between metallacarbynes and cyclopalladated complexes. However, additional studies have to be carried out to test the validity of this hypothesis. The structural features of the coordination complex 5b imply that alkynes may also be able t o form complexes in which the C-C triple bond is coordination perpendicularly to the palladium plane. This provides a support for the proposed intermediates in the reaction between alkynes and metal-carbon bonds.
Experimental Section General Considerations. All reactions were performed in a nitrogen atmosphere, using standard Schlenck techniques. Solvents were dried on sodium (ether, hexane) or calcium dihydride (dichloromethane) prior to use. The NMR spectra were recorded on a Bruker WP 200 SY spectrometer or a Bruker AC 300 spectrometer. Infrared spectra were recorded on a Bruker IFS 66 spectrometer (in CH2C12, v in cm-9. Microanalyses were carried out by the Service de Microanalyse du CNRS in Strasbourg. FAB ( + I mass spectra were provided by the Service de spectrometrie de mass (URA 31 du CNRS) in Strasbourg (in 3-nitrobenzyl alcohol). The coordination complexes were often too labile to be characterized by elemental analysis. FAB mass spectrometry was preferable, and the complexes are prepared and characterized in situ. The metallacarbynes Cp(C0)2M=C-R (1, M = Mo, W; R = 4-To1, 4-CeH4tBu)were prepared via a general method reported by Stone et al.I9 The cyclopalladated complexes were prepared according to literature procedures: [Pd(bhq)Cl]n, Z,25 IPd(8mquin)Cll2,3,26[Pd(8equin)Cl]z,4," [Pd(bms)Cl]n,8,rsand [Pd(dmna)Cllp,9.2g (25)Hartwell, G. E.; Laurence, R. V.: Smas, M. J. Chem. Commun. 1970, 912.
126)Pfeffer, M. Inorganic Synthesis; Kaesz, H. D., Ed.; Wiley-Interscience: New York, 1989; Vol. 26, pp 213. 127) Sokolov. V. I.; Sorokina, T. A.; Troitskaya, L. L.; Solovieva, L. I.; Reutov, 0. A. J . Organornet. Chem. 1972, 36, 389. l28)Dupont, J.: Beydoun, N.; Pfeffer, M. J . Chem. Soc., Dalton Trans. 1989. 1715.
Synthesis a n d Analysis of Pd(II) Complexes
Organometallics,
Vol. 14,No. 7, 1995 3433
Syntheses. [Cp(CO)&Iol[Ir-C(4-Tol)l[Pd(bhq)C11, 5a. [Cp(CO~WI[Ir-C(4-Tol)l[Pd(bequin)C11,7. To a suspenTo a solution of Cp(CO)zMorC-4-Tol (102 mg 0.32 mmol) in sion of [Pd(8equin)ClI~ (88mg, 0.15 mmol) in dichloromethane dichloromethane (10 mL) was added [Pd(bhq)Cl]z(121 mg, 0.19 (10 mL) was added Cp(CO)~W=C-4-To1(126 mg, 0.31 mmol), mmol), whereupon most of the dimer dissolved over 1 min, whereupon the dimer dissolved instantaneously, and a deep and a deep red brown color was formed. After being stirred red brown color was formed. After being stirred 5 min, the mixture was filtered over a Celite pad and the solvent was 10 min, the mixture was filtered over a Celite pad, and the concentrated near dryness. Addition of hexane (15 mL) gave solvent was removed from the filtrate in vacuo. The oily residue was washed with diethyl ether (2 x 10 mL) and hexane a suspension, from which the supernatant was decanted. (2 x 10 mL). The solid was filtered off, and drying in vacuo Washing the residue with hexane (4 x 15 mL) and drying in gave 5a (156 mg, 77%) as a black powder. Anal. Calcd for vacuo gave impure 7 as a light brown powder. The proton CzsHzoClMoNOzPd (MW 640.29): C, 52.52; H, 3.15; N, 2.19. NMR spectrum showed that the solid was a mixture of 7 with Found: C, 51.8; H, 2.95; N, 2.3. FAB m l z : M' invisible, 1245 probably three other minor products. Attempts t o purify 7 (5, recombination), 656 (61, 606 (28, M-Cl), 585 (261, 548 (42), further via repeated precipitation from dichloromethane with 440 (14), 322 ([Pd(bhq)Cl HI+, 161, 281 (37), 180 (100). 'H hexane or via crystallization from dichloromethane-hexane NMR (CDC13) d 9.72 (d, 1 H arom, 3 J =~5.1), only resulted in the decomposition of 7. Complex 7 is therefore ~ 8.39 (d, 1 H arom, 3 J =~8.21, ~ 8.06 (d, 2 H, 4-T01, 3 J =~8.11, ~ 7.79-7.65 only partially characterized, by analogy with the spectral data (m, 3 H arom), 7.55 (d, 1 H arom, 3 5 H H = 7.7), 7.30-7.07 (m, of the bhq and 8mquin complexes. 'H NMR (CDC13) d 9.72 4 H arom), 5.76 (s, 5 H, Cp), 2.33 (s, 3 H, 4-Me); 13C NMR = 4.0), 8.36 (d, H arom, JHH = 8.2), 8.06,7.15 (d, H arom, JHH (CD2Clz) d 312.8 (pu-c),229.5, 227.7 (CO), 154.1, 152.5, 148.6, (AB pattern, H arom, 3 J =~7.9), ~ 7.8-7.3 (m, H arom), 5.77 142.4, 138.4, 136.7, 135.0 ,132.2, 129.2, 128.7, 127.2, 124.1, (S, 5 H, c p ) , 3.71 (q, 1 H, MeCH, 3 J =~7.21, ~ 2.29 (5, 3 H, 122.6 (C arom), 95.9 (Cp), 22.0 (4-Me); IR vco 1998, 1932. 4-Me), 0.75 (d, 3 H, HCMe, 3 J =~7.3); ~ IR vco 1961, 1891. The 13C NMR spectrum is difficult to interpret, due to the [Cp(CO)2Wl~-C(4-T01)1[Pd(bhq)Cl], 5b. Following the presence of several minor compounds. same procedure as for 5a,a black powder (77%) was obtained. [Cp(C0)2~[Ir-C(4-Tol)l[Pd(dmna)Cl], 11. To a solution Anal. Calcd for CzsHzoClNOzPdW (MW 728.20) (+0.5CHzof Cp(CO)zW/'C-4-T01(126mg, 0.31 mmol) in dichloromethane Clz): C, 44.41; H, 2.75; N, 1.82. Found: C, 44.05; H, 2.71; N, (10 mL) was added [Pd(dmna)Cl]z (118 mg, 0.19 mmol), 1.91. FAB m l z : M+ not visible, 1421 (4, recombination), 1013 whereupon the dimer dissolved instantaneously, and a deep (5, recombination), 692 (40, [M-Cl]+j, 673 (211, 636 (46), 528 red brown color was formed. After being stirred 5 min, the ( l o ) , 408 (100, [CP(CO)ZWC-~-TO~]+), 380 (341, 351 (561, 284 mixture was filtered over a Celite pad and the solvent was (26, [Pd(bhq)]+),180 (51). 'H NMR (CDC13) d 9.72 (d, 1 H removed from the filtrate in vacuo. After drying the residue ~ (d, 1 H arom, 3 J = ~7.9), ~ 8.03 (d, 2 H, arom, 3 J =~4.8),8.39 in uacuo, it was washed with hexane (2 x 15 mL). Drying in 4-To1, 3 J =~8.0), ~ 7.78-7.65 (m, 3 H arom), 7.55 (d, 1H arom, 3 J =~6.8), ~ 7.27-7.23 (m, 2 H arom), 7.10 (d, 2 H, 4-T01, 3 J ~ ~uucuo gave 11 (128 mg, 58%) as a brown powder. Anal. Calcd for CZ,HZ&lNOzPdW (MW 720.22): C, 45.03; H, 3.36; N, 1.95. = 8.01,5.91 (s, 5 H, Cp), 2.29 (s, 3 H, 4-Me); 13CNMR (CDC13) Found: C, 44.6; H, 3.1; N, 2.15. 'H NMR (CDCl3)B 7.99 (d, 2 d 303.3 (,u-C),221.1, 219.1 (CO), 153.4, 152.6, 149.1, 142.9, H arom, 3 J =~8.0 ~1,7.67 (d, 1 H arom, 3 J =~7.4), ~ 7.54142.1, 139.1, 137.0, 135.5, 132.2, 129.9, 129.6, 128.0, 124.8, 7.42 (m, 3 H arom), 7.13 (d, 2 H arom, 3 5 H H = 8.0),7.09-7.01 123.2 (C arom), 95.2 (Cpj, 22.3 (4-Me); IR vco 1984, 1913. ~ 6.89 (d, 1H arom, 3 J =~7.3), ~ 5.85 (d, 1H arom, 3 J = ~8.0), [Cp(CO)2WI[Cr-C(4-CsH4tBu)l[Pd(bhq)C11, 512. Following (s, 5 H, Cp), 3.62, 3.42 (s, 6 H, NMeZ), 2.31 (s, 3 H, 4-Me); I3C the same procedure as for 5a,a brown powder was obtained. NMR (CDzClz)d 306.5 (,u-C),220.8, 218.5 (CO), 155.9, 151.8, Complex 5c is contaminated with some free metallacarbyne. 148.0, 141.7, 135.7, 135.5, 132.0, 129.0, 127.9, 126.4, 126.1, Attempts t o remove the latter with hexane remained unsuc124.1, 123.6, 117.2, 116.2 (C arom), 94.2 (Cp), 53.0, 51.7 cessful, so the yield could not be determined. However, the (NMeZ),22.0 (4-Me);IR vco 1982, 1913. product is pure enough to attribute the spectral data. 'H NMR (CDC13) d 9.71 (d, 1 H arom, 3 J =~5.1), ~ 8.38 (d, 1 H arom, Computational Details 3 J =~8.01, ~ 8.05 (d, 2 H arom, 3 J =~8.3,~ 7.75 (d, 1 H arom, 3 J =~8.71, ~ 7.70-7.64 (m, 2 H mom), 7.55 (d, 1H arom, 3 J ~ ~ The SCF calculations were carried out with the ASTERM = 6.4), 7.36-7.24 (m, 4 H atom), 5.90 (s, 5 H, Cp), 1.26 (s, 9 system of programs.30 For the geometry optimization we used H, tBuj; I3C NMR (CDZClz) d 302.9 (pU-C),220.6, 218.3 (CO), a split valence type basis set for the Mo=C(H)Pd bonding unit 154.3, 151.7, 148.5, 138.4, 136.2, 134.9, 131.5, 129.3, 128.9, and a minimal basis set for the ligands, Le., (15,10,8) con127.2, 125.4, 124.1, 122.5 (C arom), 94.5 (Cp), 35.4 (CMe3), tracted to (6,4,4) for the molybdenum and palladium atoms;31 31.1 (CMe3); IR vco 1984, 1910. (9,5)contracted to (3,2) for the carbyne atom;33(4)contracted to (2) for the hydrogen atom of the carbyne atom,34and STO[Cp(COzWlb-C(4-Tol)][Pd(Bmquin)Cl], 6. To a suspen3G35for the cyclopentadienyl, the carbonyl, the amine, and sion of [Pd(8mquin)C112 (119 mg, 0.21 mmol) in dichlorothe chlorine ligands. Single-point calculations were then methane (15 mL) was added Cp(CO)zW=C-4-T01(154mg, 0.38 carried out on these optimized geometries with the split mmol), whereupon most of the dimer dissolved instantaneously valence basis set on all atoms (this corresponds to a (11,7) and a deep red brown color was formed. After being stirred 5 contracted to (4,3) basis set for the chlorine atom3% We min, the mixture was filtered over a Celite pad and the solvent checked by a geometry optimization carried out on [Cp(CO)zwas concentrated to 3 mL. Addition of hexane (30 mL) gave MoCHl with both basis set sets that the smallest basis set gave a suspension, from which the supernatant was decanted. reliable results for the geometry optimization. The electron Washing the residue hexane (2 x 15 mL) and drying in vacuo density deformation maps were obtained with the split valence gave impure 6 as a light brown powder. The 'H NMR basis set. spectrum confirmed that the solid was a mixture of 6 with about 6% of a p-alkylidene complex, formed via the C-C(30)(ai Emenwein, R.; Rohmer, M.-M.; Benard, M. Comp. Phys. coupling reaction. It was thus deemed useless to try to purify Commun. 1990.58, 305. [b)Rohmer, M.-M.; Demuynck, J.; Benard, 6 any further. 'H NMR (CDC13)d 9.72 (d, 1 H arom, 3 J =~ ~ M.; Wiest, R.Ibid. 1990,60, 127. (c)Wiest, R.; Demuynck, J.; Benard, M.; Rohmer, M.-M.; Ernenwein, R. Ibid. 1991, 62, 107. 4.9),8.36(d,lHarom,35~~=8.3),7.98(d,2H,4-Tol,35~~= (31)The original (15,9,8) basis set32 was modified by adding p 8.0),7.70-7.46(m,4Harom),7.11(d,2H,4-T0l,~J~~=8.0), function of exponent 0.15 and 0.08386 to describe the 5p shell of the 5.86 (s, 5 H, Cpj, 3.15 (m, 2 H, CHz), 2.28 (s, 3 H, 4-Me); I3C molybdenum and palladium atoms, respectively. NMR (CDZClz) d 303.4 (p-C),222.1, 220.6 (CO), 150.2, 147.2, 132)Veillard, A,; Dedieu, A. Theoret. Chim. Acta 1984, 65, 215. 133) Huzinaga, S. Technical Report. University of Alberta: Ed141.0, 139.0, 130.2, 129.8, 129.1, 128.3, 124.8, 122.2 (C arom), monton, Canada, 1971. 94.0 (Cp), 36.2 (CHz), 22.0 (4-Me);IR vco 1966, 1896.
+
(29)Cope, A. C.; Friedrich, E. C. J . Am. Chem. SOC.1968,90,909.
(34)Huzinaga, S. J. Chem. Phys. 1965, 42, 1293. (35)Hehre, W. J.; Stewart, R. F.; Pople, J. A. J. Chem. Phys. 1969, 51, 2657.
3434 Organometallics, Vol. 14, No. 7, 1995 The geometry optimization was carried out from analytical energy first derivatives by using a n implemented BFGS a l g ~ r i t h m .The ~ ~ convergence thresholds for the geometry optimization were set to 0.002 for the gradient norm and for each individual component of the energy gradient. This led in every optimized geometry t o a value equal t o or less than 0.001 for the gradient norm. Some internal coordinates were kept constant to insure a n overall C,9symmetry and local C31. symmetry for the NH3, CH3, and AlH3 groups. (36)de Vaal, P.;Benard, M.; Pouchan, C. Unpublishedresults, 1992.
Engel et al.
Acknowledgment. The calculations were carried out on the IBM 3090 computer of the Centre de Calcul de Strasbourg Cronenbourg and on the c u y 2 computer of the ccvRinPdaiseau. The cdculations and the stay of P.E. in both laboratories were made possible (Science through a pant of the European Co"unitJ' Program, Contract NO. SC1-0319-C(GDF)). OM9501825
