Organometallics 1992,11, 3517-3525 by the different behavior of complexes 2 and 3 with respect to their isomers 2‘ and 3’ when they react with AgC104in the presence of acetonitrile. The former give [PdR(bpy)(MeCN)]C104(6) and [PdR(phen)(MeCN)]C104(7), respectively, while the latter gives the cyclometalated [Pd(a2-R’)(bpy)]C104(8) [ G O ) , 1510 cm-’1 and [Pd(T2R’)(phen)]ClO, (9) [v(CO), 1505 cm-’I, respectively, although, in the last case, a mixture of 9 and some species containing MeCN (by IR), presumably [PdR’(phen)(MeCN)]C104,was initially obtained, however, stirring this mixture in acetone removes MeCN, yielding pure 9. The low solubilities of 6-9, as well as 1, have prevented measurements of their NMR spectra. Crystal Structure of Complex 2. Figure 3 shows the expected tetracoordination of the metal center. The geometry at Pd is not exactly planar, because the atom N(2) lies 0.22 A out of the plane of Pd, C(ll), C1, and N(1). The dihedral angle between the rings of the bpy ligand is 12’. Its bite angle is 79.6’. The Pd-N bond distances (Table 111) show a clear difference in the trans influences of the aryl [Pd-N(1), 2.107 (3) A] and chloro ligands [Pd-N(2), 2.039 (3) A]; both are significantly shorter than those found6 in the cationic complexes 5 and 5’ [2.143 (4), 2.137 (3) A and 2.099 (4), 2.114 (3) A, respectively] which can be explained as a consequence of greater Pd to N A-
3517
back-bonding in neutral complex 2 than in cationic 5 and 5’. This difference is probably also responsible for the different orientation of the formyl group with respect to the palladium atom; in 5 and 5’ the formyl oxygen makes a short contact to Pd (2.921 (5) and 2.926 (3) A, respectively) whereas in 2 the hydrogen atom is involved (Pd-H, 2.70 A). All these formally nonbonded distances are appreciably longer than expected values for covalent bonds (Pd-O,2.2 A; Pd-H, 1.6 A).’2 The Pd-C bond distance (1.992 (4) A) is similar to those in 5 (2.010 (5) A) and 5’ (1.986 (3) A).
Acknowledgment. We thank the Fonds der Chemischen industrie and Direccidn General de Investigacidn Cientifica y Tgcnica (Grant PB89-0430) for financial support. Supplementary Material Available: Complete listings of bond lengths and angles, anisotropic displacement parameters, and H atom coordinates (4 pages). Ordering information is given on any current masthead page. OM9202128 (12) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, 0.; Watson,
D.G.;Taylor, R. J. Chem. SOC.,Dalton Trans. 1989, S1.
(Aryne)metallocene- and (A1kyne)metallocene-Derived Dimetallic Zirconium/Aluminum Complexes Containing Planar-Tetracoordinate Carbon Gerhard Erker’ and Markus Albrecht Organisch-Chemlsches Instnut der Unlverslt Munster, Correnssttasse 40, D-4400 Mcinster, Qermany
Carl Kruger, Stefan Werner, Paul Blnger, and Franz Langhauser Max-Plenck-Institut fiK Kohlenforschung, Kalser- WllhelmPletz 1, 04330 M i i W m a. d. Ruhr, Germany
Recelved Aprll2 7, 1992
Compounds X-[M2]of Lewis acidic main group metals can be added to very reactive alkyne-transition metal complexes (q2-RC=CR)[MI]to form dimetallabicyclic organometallic compounds [M’] (p-$:q2RCCR)(p-X)[M2]containing a planar-tetracoordinate carbon atom, which is stabilized by the combined u-donor/r-acceptor properties of the specific metal/ligand combination. This general synthetic scheme has been used to prepare such planar-tetracoordinate carbon complexes by reacting e.g. ($-aryne)(PMe3)ZrCp2(12) with 2 molar equiv of diisobutylaluminum hydride. Initial Me3P.HAl(iBu)zadduct formation generates the reactive (q2-aryne)ZrCp2intermediate, which is then tra ped by additional hydridoaluminum reagent to yield the thermodynamicallystable complex CpJr0l-qP:t12-C6H4)( -H)Al(iBu), (14s). Complex 14a crystallizes in space group ml/n with cell parameters a = 16.749 (3) b = 13.833 (1)A, c = 20.178 (2) A, B = 90.74 ( 1 ) O , R = 0.088, and R, = 0.093. It contains a planar-tetracoordinate carbon center [C(2)] at the bridgehead position of the dimetallabic clic framework which is bonded to two carbon atoms [d(C(2)4(1))= 1.37 (2) A, d(C(2)4(3!= 1.41 (1)i ] , the zirconium [d(C(2)-Zr) = 2.430 (8) A], and the aluminum.atom [d(C(2)-Al) = 2.09 (1) , all values averaged over the two independent molecules; the s u m of b o n k angles around C(2) is 360’1. The reaction between 12 and trimethylaluminum gave the analogously structured Cp2Zr(p-q1:q2-C6H4)(p-CH3)AlMe2 complex 14b; treatment of 12 with triethylaluminum furnished Cp2Zr(p-q’:.r12-C6H4) (p-CH2CH3)A1Eh(14c). Complex 14b was characterized by X-ray diffraction (space group ml/n, a = 9.151 (1)A, b = 14.022 (1)A, c = 14.415 (1)A, B = 104.56 (1)O, R = 0.042, R, = 0.057). Again, carbon atom C(2) is planar-tetracoordinate [d(C(B)-C(l)) = 1.383 (4), d(C(2)4(3))= 1.423 (5), d(C(2)-Zr) = 2.481 (31, d(C(2)-Al) = 2.082 (3) A; the s u m of bonding angles at C(2) is 360°]. The general synthetic scheme for the preparation of dimetdabicyclic“anti-van’tHoff/LeBel compounds” can also be applied to reaction sequences starting from stable (112-alkyne)metnecomplexes. Thus, the reaction of (q2-cyclohexyne)(PMe&rCp2 ( 1 1 4 or (q2-diphenylacetylene)(PMe3)ZrCp2(llb)with excess trimethylaluminum gave the respective Cp2Zr(p-$:~2-RCCR)(p-CH3)AlMe2 products (7d,e). The reaction between the (tolane)metaJlocenecomplex llb with a mixture of 9-BBN and triethylboron produced CpzZr(p-q1:T2-PhCCPh)(p-H)BEt, (15) in low yield.
1,
Since 1874, when van’t Hoff s and LeBel’s pioneering and imaginative thoughts and conclusions were inde0276-7333/92/2311-3517$03.00/0
pendently published, it is well-known that tetracoordinate carbon in organic compounds favors a tetrahedral coor0 1992 American Chemical Society
Erker et a1.
3518 Organometallics, Vol. 11, No. 11, 1992 Scheme I
Chart I
1
2
H2C-C-CH2
(t-Bu)o.,,
-
( f B u )0
I / \I
Aoy - \ l o
(t-Bu)
,~~,O(t-B'J)
-
( t B u) (1-Bu)
[ M e ~ ~ O M ~ ] 2
eo'^"?, v=v,
-Meo*,oM: 'li M e O $ O M e
-2
H,L--AIR~, 7c
Scheme I1
P 11
(Me,P)AIR.
7
often cited example is 1,l-dilithiocyclopropane(2), which should be a thermodynamically stable planar-tetracoordinate carbon compound. Here the combined a-donor/ *-acceptor properties of lithium serve to stabilize the "unnatural" planar coordination geometry of the tetravalent carbon center. Only very few examples of stable and isolable compounds containing planar-tetracoordinate carbon centers have been reported so far. The (p-allene)ditungstencomplex 3, prepared by Chisholm et al.,' represents a rare example where the electronic features of which come close to those of the calculated 1,l-dimetallamethane systems. The few reported additional examples (4-7) have in common that the occupied p-orbital at the planar-tetracoordinate carbon center is part of a *-system. This may be an aromatic system (4-6)8 or just a simple carbon-carbon double bond (7): The discovery that complex 7 contains a planar-tetracoordinate carbon center has opened simple new synthetic ways to novel thermodynamically stable "anti-van't (1)van't Hoff, J. H. Arch. Nederl. Sci. Eractes Nat. 1874,445. LeBel, J. A. Bull. SOC. Chim. Fr. 1874,22,337. (2)Olah, G. A.; Prakash, G. K. S.; Williams, R. E.; Field, L. D.; Wade, K. Hypercarbon Chemistry; Wiley: New York, 1987;and referenm cited therein. Chmi, P.; Longoni, G.; Albano, V. G. Adu. Organomet. Chem. 1976,14,285.Tachikawa, M.; Muetterties, E. L. hog. Inorg. Chem.1981, 28, 203. Schmidbaur, H.; BrachthHuser, B.; Steigelmann, 0. Angew. Chem. 1991, 103, 1552;Angew. Chem., Int. Ed. Engl. 1991,30, 1488. (3)Keeae, R;Pfenniger, k, Roesle, A. HeZu. Chim. Acta 1979,62,326. Keese, R. Nachr. Chem. Techn. Lab. 1982,30,844.Krohn, K. Nachr. Chem. Techn. Lab. 1987,35,264.See also: Wiberg, K. B.; Acc. Chem. Res. 1984,17,379. Greenberg, A.; Liebmann, J. F. Strained Organic Molecules, Academic Press: New York, 1978. Agosta, W. C.Chem. Rev. 1987,87,399. Hoeve, W. T.;Wynberg, H. J. Org. Chem. 1980,45,2925, 2930. Georgian, V.; Saltzman, M. Tetrahedron Lett. 1972,42, 4315. (4)Hoffmann, R.;Alder, R. W.; Wilcox, C. F., Jr.; J. Am. Chem. SOC. 1970,92,4992.See also: Hoffmann, R. Pure Appl. Chem. 1971,28,181. (5)Collins, J. B.; Dill, J. D.; Jemmis, E. D.; Apeloig, Y.; Schleyer, P. v. R.; Seeger, R.; Pople, A. J. Am. Chem. SOC.1976,98,5419and references cited therein. (6)Chandrasekhar, J.; Schleyer, P. v. R. J. Chem. Soc., Chem. Commun. 1981,lN,260. Bachrach, S.M.; Streitwieser, A., Jr.; J. Am. Chem. SOC.1984,5818. Chandraaekhar, J.; Wkthwein, E X . ; Schleyer, P. v. R. Tetrahedron 1981,37,921.Chandraaekhar,J.; Schleyer,P. v. R. J. Chem. Soc., Chem. Common. 1981,260. Glukhovtaev, M. N.; Simkin, B. Ya.; Minkin, V. I. J. Og. Chem. USSR 1990,26, 1933. Schleyer, P.v. R.; Boldyrev, A. I. Chem. SOC.,Chem. Commun.1991,1536. Reed, A. E.; Schleyer, P. v. R.; Janoschek, R. J . Am. Chem. SOC.1991,113, 1885.
(7)Cayton, R. H.; Chacon, S.T.; Chisholm, M. H.; Hempden-Smith, M. J.; Huffman, J. C.; Folting, K.; Ellis, P. D.; Huggins, B. A. Angew. Chem. 1989, 101, 1547;Angew. Chem., Int. Ed. Engl. 1989,28, 1523. Chacon, S.T.; Chisholm, M. H.; Folting, K.; Huffman, J. C.; HampdenSmith, M. J. Organometallics 1991,10,3722.Beringhelli, T.; Ciani, G.; D'Alfonso, G.; Freni, M. J. Chem. SOC.,Chem. Commun.1986,978. (8) (a) Cotton, F. A.; Miller, M. J. J. Am. Chem. SOC. 1977,99,7886. (b) Harder, S.;Boersma, J.; Brandsma, L.; van Heteren, A.; Kanters, J. A.; Bauer, W.; Schleyer, P. v. R. J. Am. Chem. SOC.1988,110,7802.(c) Harder, S.;Brandsma, L.; Kanters, J. A.; Duisenberg, A. J. M. Acta Crystallogr. 1987,C43, 1535. Harder, S.;Boersma, J.; Brandsma, L.; Kanters, J. A. J. Organomet. Chem. 1988,339,7. Harder, S.;Boersma, J.; Brandsma, L.; Kanters, J. A.; Bauer, W.; Pi, R.; Schleyer, P. v. R.; Schallborn, H.; Thewalt, U. Organometallics 1989,8,1688.Harder, S.; Boersma, J.; Brandsma, L.; Kanters, J. A.; Bauer, W.; Schleyer, P. v. R. Organometallics 1989,8,1696. Harder, S.;Boersma, J.; Brandsma, L.; van Mier, G. P. M.; Kanters, J. A. J. Organomet. Chem. 1989,364, 1. Stucky, G. D.; Eddy, M. M.; Harrison, W. H.; Lagow, R.; Kawa, H.; Cox, D. E. J . Am. Chem. SOC.1990,112,2425.Baran, J. R.,Jr.; Lagow, R. J. J. Am. Chem. SOC. 1990,112,9415.Harder, S.; Boersma, J.; Brandsma, L.; Kanters, J. A.; Duisenberg, A. J. M.; van Lenthe, J. H. Organometallics 1991,10,1623.Bosold, F.; Zulauf,P.; Marsch, M.; Harms, K.; Lohrenz, J.; Boche, G. Angew. Chem. 1991,103,1497;Angew. Chem., Int. Ed. Engl. 1991,103,1465.Uhl, W.; Layh, M.; Mama, W. Chem.Ber. 1991, 124,1511. Layh, M.; Uhl, W. Polyhedron 1990,9,277.(d) Buchwald, S.L.; Lucae, E. A.; Davies, W. M. J. Am. Chem. SOC.1989,111, 397. (9) Erker, G.; Zwettler, R.; Kriiger, C.; Noe, R.; Werner, S. J. Am. Chem. SOC.1990,112,9620.
Organometallics, Vol. 11, No. 11,1992 3619
Dimetallic ZrlAl Complexes
Hoff/LeBel compounds". Thus, treatment of dimethylzirconocene (8) or -hafnocene with alkynylaluminum compounds RC=CAW2 (9) led to the formation of novel very stable examples of these unusually structured dimetallabicyclic compounds.1o Depending on the reaction conditions, alkyl- or alkynyl-bridged complexes were isolated in high yield. All these reaction sequences probably have in common that a very reactive (q2-alkynelmetallocene intermediate (10) is formed along the way which is then trapped by either the alkynealuminum reagent or by an alkylaluminum scavenger formed in the initial stages of the reaction (see Scheme I). This general reaction scheme has allowed the development of an improved synthesis of stable dimetallic zirconium/aluminum complexes containing planar-tetracoordinate carbon. A variety of phosphane-stabilized (alkyne)zirconocene complexes of the general type ( R C s CR)(PMe3)zrCp2(11) are readily available." From these the stabilizing trimethylphoaphane ligand can be removed by treatment with a suitable Lewis-acid reagent (e.g. R',Al) to generate the reactive (q2-alkyne)zirconoceneintermediate (10). This can then be trapped e.g. by the added AW3 reagent to give the respective dimetallabicyclic planar-tetracoordinate carbon compound 7 directly. This general synthetic route to differently substituted complexes 7 is depicted in Scheme 11. We have used this general reaction sequence to prepare a variety of organometallic planar-tetracoordinate carbon compounds containing zirconium and aluminum. We here describe several examples of such syntheses where (q2aryne)metallocenes derived from readily available (q2-aryne)(PMe3)ZrCp2(12)12are trapped by added Lewis acidic organoaluminum reagents. The (q2-aryne)ZrCp2intermediate (13)13has bonding features that are very similar to those of the (q2-alkyne)metallocenemoiety used in Scheme I1 and can thus successfully be employed as an (alkyne)ZrCp2-equivalentsynthetic building block in this general synthetic scheme. The resulting dimetallabicyclic "anti-van't Hoff/LeBel compounds" obtained by the AIR3/(q2-aryne)zirconocene addition reaction exhibit properties similar to those of the planar-tetracoordinate carbon compounds (4-6) previously prepared and described by the groups of Schleyer and Brandsma, Cotton, and Buchwald, respectively? In addition, three examples are described where similarly composed stable planartetracoordinate compounds have been prepared by means of the analogous reaction sequence starting from (q2-alkyne) (trimethy1phosphane)zirconocenecomplexes (1 1).
Results and Discussion Synthesis and Spectroscopic Characterization of the Dimetallic Planar-Tetracoordinate Carbon Complexes. Dimetallic (p-C6H4)Zr,A1complexes containing a planar-tetracoordinate carbon center were prepared by starting from (q2-1,2-didehydrobenzene)(trimethylphosphane)zirconocene (12). This is a readily available (10) (a) Erker, G.; Albrecht, M.; Krtiger, C.; Werner, S. Organometallics 1991,10,3791. (b) Albrecht, M.; Erker, G.; Nolte, M.; Kriiger, C. J. Organomet. Chem. 1992,427, C21. (c) Erker, G.Comments Znorg. Chem. 1992,13,111. (d) Erker, G.; Albrecht, M.; Werner, S.;N o h , M.; K m e r , C. Chem. Ber. 1992,125,1953. (11) Buchwald, S. L.; Lum, R. T.; Dewan, J. C. J. Am. Chem. SOC. 1988,108,7441. Takehashi, T.; Swanson, D. R.; Negishi, E.-I. Chem.Lett. 1987, 623. Binger, P.; Miiller, P.; Benn, R.; Rufineka, A.; Gabor, B.; Kr@er, C.; Betz, P. Chem. Ber. 1989,122, 1035. (12) Buchwald, S. L.; Watson, B. T.;Huffman, J. C . J . Am. Chem. SOC. 1986,108, 7411. (13) Buchwald, S. L.; Nieleen, R. B. Chem. Rev. 1988,88,1047. Bennett, M. A.; Schwemlein, H. P. Angew. Chem. 1989,101, 1349; Angew. Chem., Int. Ed. Engl. 1989,28, 1296 and references cited therein.
starting material. For this study complex 12 was synthesized according to Buchwald's route by means of a thermally induced intramolecular benzene elimination from diphenylzirconocene in the presence of PMe8.12 Since (q2-aryne)zirconocenecannot be prepared as an isolable compound and employed as such,13we have tried to generate the reactive (q2-C6H4)ZrCp2 intermediate (13) in situ in the presence of a suitable aluminum reagent as a scavenger. Many aluminum hydride or aluminum alkyl reagents react as strong Lewis acids with the PMe3Lewis base. Therefore, it was tempting to use in a variety of casea the added HAlR2 or AlR3 reagent to carry out both functions consecutively in the anticipated t m ~ s t e preaction sequence and thus allow for a simple "one-pot" synthesis of the desired (p-q1:q2-C6H,)Zr,Alcomplexes (14). This worked out beautifully in a variety of cases. We have treated the aryne complex 12 with 2 molar equiv of diisobutylaluminumhydride in toluene solution at room temperature. A rapid reaction ensues which goes
12
14a
)- '
to completion within 2 h. Removal of the solvent and crystallization of the residue affords the dimetallic CP2zr(p-q1:q2-C6H4)GL-H)Al(iBU)2 complex 14a crystalline in ca 50% yield. Complex 14a is air and moisture sensitive but rather thermally stable. It can be heated to about 80 OC before it decomposes. Complex 14a was characterized spectroscopically and by X-ray diffraction (see below). It contains a planar-tetracoordinated carbon atom which is bridging between zirconium and aluminum and is part of the aromatic ring system. Both factors seem to be of importance for stabilizing this uncommon coordination geometry of carbon to make it thermodynamically favored. The reaction probably proceeds straightforwardly as anticipated. The HAl(iBuI2 reagent removes the trimethylphosphine ligand from the zirconium complex by means of Me,P[HAl(iBu),] adduct formation. The resulting very reactive (q2-benzyne)zirconoceneintermediate is then effectively trapped by free HAl(iBuI2present in the solution to give the stable dimetallic reaction product (14a). Trialkylaluminum reagents can be used analo-
H& --klEt2
14b
12
Hjd
14c
gously. The reaction between the (aryne)metallocene complex (12) and trimethylaluminum proceeds equally easily at room temperature. Here the formed Me&PMe3 adduct is removed from the reaction mixture together with the toluene solvent by vacuum distillation. Crystallization of the residue from pentane at low temperature gave the pure crystalline Zr,Al product 14b in close to 80% yield. The Cp2ZrG-q1:q2-aryne)(p-ethyl)A1Et2complex 14c was obtained analogously by reacting 12 with triethylaluminum (2 equiv). These examples showed that the simple synthetic concept as outlined above could successfully be realized for the preparation of stable and isolable "anti-van't Hoff/ LeBel compounds" by adding an organoaluminum reagent to in situ generated (q2-aryne)zirconocene.This apparently simple access to planar-tetracoordinatecarbon compounds
Erker et al.
3520 Organometallics, Vol. 11, No. 11,1992 prompted us to check for the potential use of similarly structured (q2-alkyne)(PMe3)ZrCp2complexes (11) as starting materials in analogous synthetic sequences. The formation of the (p-q':q2-alkyne)(p-X)Zr,Al complexes (7) (X = H, alkyl) turned out to be equally facile. (q2Cyclohexyne)(PMe,)ZrCp, (1la) (prepared as described
Table I. *F NMR Chemical Shifts of the p-r)':q2-C=C Moiety in the Dimetallabicyclic Complexes 7 and 14, Where C2 Is Planar-Tetracoordinatea Ph
\
u A
P CPlZr,
2 AIMe3
PMe3
lla
MesP.AIMe3
Q
- cpzzi H3C-AlMez
7d
qPh
n
I
\
X-AIR2
6(C1) 6(C1) 6(Cz) 6(C2)
206.1b 207.6 143~5~ 148.5
m
.
\
X-h,
207.6b 207.5 108.gb 110.3
,
\
X--AIR2
193.4 193.9 114.9 116.1
X-AIR2 H-Al(iBu), H3C-A1Mez H-Al(iBu), H&-AlMe2
Chemical shifts relative to tetramethylsilane, 6 scale, measured in
C6D6solution. bFrom ref 10c,d.
prochiral/tetracoordinate and thus exhibits an ABX type pattern of the AICHzCH moieties [6 0.52,0.45 (CH,), 2.26 (CHI]. The corresponding methyl groups of the Al(iBu), CPzZr, X p t , - Me3P.AIMe32 AIMe3 building block are pairwise diastereotopic (6 1.29; 1.26). The hydrogen atoms at the bridging C6H4ring give rise PMe3 H3 -AIMez to absorptions at 6 8.17 (1H), 7.78 (1H), and 7.18 (2 H). llb 70 There is a sharp singlet at 6 5.40 representing 10 cycloby Buchwald et al.") is a suitable starting material for our pentadienyl hydrogens. synthesis. It reacts with trimethylaluminum at room The 13CNMR spectrum of 14a exhibits signals at 6 28.9 temperature in toluene solution to give a high yield (and 27.1 (diastereotopic methyl groups), 28.5 (CH), and 70%) of the dimetallic Zr,Al complex 7d, which contains 26.4 (CH,) corresponding to the A ~ ( ~ B part U ) ~of the a planar-tetracoordinate carbon center, bonded to the d molecule. The Cp resonance is at 6 105.6, and the expected element and the main group metal. In 7d this carbon atom four aromatic CH signals are observed at 6 137.4, 135.0, is part of an olefinic C = C moiety. 134.7, and 134.3. Most interesting are the chemical shift Acyclic alkynes bonded to an early transition metal can values of the quaternary carbon centers (C1and C2)of the be used for the conversion into the (p-q1:q2-RCCR)Zr,Al p-q1:q2-C6H4 bridge. The C' resonance is at 6 193.4. The moiety as well. Thus, Cp2Zr(p-q':q2-PhCCPh)(p-CH,)characteristically high value of the C' resonance seems to AlMe2 (78)was formed when the (alkyne)zirconocene be very typical of such dimetallic %,AI complex. For most complex (PhC=CPh)(PMe,)ZrCp, (llb) was reacted with complexes of this type C' chemical shifts > 6 180 have been 2 molar equiv of trimethylaluminum at the usual reaction o b s e r ~ e d . ~Most ~ J ~ values were found in a rather narrow conditions. Complex 7e was not obtained analytically pure range between ca. 6 180 and 220 (see Table I), although but could be unambiguously identified by ita characteristic there are a few exceptions showing 13C chemical shift NMR spectra (see below). values of the C' carbon atom as high as 6 290. The This synthetic scheme not only can be used for making chemical shift of the planar-tetracoordinate carbon center Zr,Al compounds. In one case we used it successfully in C2is at markedly lower 6 values, although still within the the preparation of a dinuclear (pq1:q2-alkyne)Zr,Bcomrange of sp2-hybridizedolefinic carbon atoms. For complex pound. However, here the overall reaction sequence was 14a we have observed the 13C NMR resonance of the slightly more complicated. Triethylboron is known to Zr,Al-bridging C2 carbon atom at 6 114.9. effectively trap the phosphane from (L)(PR,)ZrCp, comA comparison of two series of dimetallic %,AI complexes plexes. When we added a mixture of triethylboron and each containing a planar-tetracoordinate carbon center (C2; 9-borabicyclo [ 3.3. llnonane (9-BBN) to (q2-tolane)see Table I) has revealed that the C2 I3C NMR chemical (PMe,)ZrCp, (llb), a reaction did occur and we could shift is not very dependent on the nature of the p-X bridge (here CH3or H) although it does characteristically depend on the nature of the p-q1:q2-alkynetype bridging system. Going from the aryne-to the cyclohexyne-bridgedsystems seems to result in a small reduction of the 6(C2)values whereas a marked increase is noticed when one compares the p-q1:q2-PhCCPh-bridged Zr,Al complexes. The Cp2Zr(p-q':q2-C6H4)(p-CH2CH3)ALEt, ( 1 4 4 and Cp2Zr(pisolate a dimetallic (p-alkyne)Zr,B complex, albeit in low q':q2-PhCCPh)G-H)BEt, (15) systems fit very well into this yield ( 10%). To our surprise, this did not contain the overall chemical shift pattern [6(C1) at 193.9 (14c), 211.4 9-borabicyclo[3.3.1]nonanemoiety as a building block but rather turned out to be Cp2ZrGL-q':q2-PhCCPh)(p-H)BEt, (15);6(C2)(planar-tetracoordinate)at 118.5 (144 and 146.8 (15), respectively]. We thus conclude that the planar(15). Thus, it is likely that the 9-BBN reagent had untetracoordinate carbon center of the complexes described dergone some &l vs hydride exchange reaction with BEh in this study seems to behave as expected for sp2-hybridwith concomitant formation of HBEt,, which in turn was ized carbon as judged from the 13CNMR spectra. This used to trap the in situ formed (tolane)ZrCp2intermediate appears also to hold for the IR spectra since complex 7d to give the observed final product 15. exhibita an IR (C=C) band at v = 1571 cm-'. The 'H NMR spectrum of the Zr,B containing complex X-ray Crystal Structure Analyses of 14a,b. In view 15 shows the signals of the ethyl groups at boron at 6 1.13 of the spectral data (see above), it was necessary to have (CH,) and 0.98 (CH,). There is a Cp singlet at 6 5.66 X-ray crystal structure analyses of representative examples representing 10 hydrogens and the p-H resonance at 6 -2.07 of this new class of compounds to reveal their extraordi(broad singlet). The hydride resonance of the (p-q1:q2-aryne)(p-H)Zr,Al complex 14a appears at 6 -0.74. The Al center in 14a is (14) Erker, G.;Schlund, R.;Kriiger, C.Organometallics 1989,8,2349. Ph
N
cp"zL
Organometallics, Vol. 11, No. 11, 1992 3521
Dimetallic ZrlAl Complexes Table 11. Selected Bond Lengths (A) and Angles (deg) for the Two Independent Molecules of 14a in the Crystal mol 1 mol 2 2.166 (9) 2.436 (9) 1.90 2.09 (1) 1.94 (2) 2.08 (2) 1.85 1.37 (1) 1.39 (1) 1.41 (1) 1.37 (2) 1.35 (2) 1.37 (2)
2.160 (9) 2.425 (9) 1.81 2.08 (1) 1.94 (1) 2.05 (1) 1.80 1.37 (2) 1.40 (1) 1.41 (1) 1.37 (2) 1.35 (2) 1.39 (2)
83.7 117.6 33.9 (4) 117.9 (7) 108.8 (5) 107.3 (5) 95.6 122.5 (9) 153.6 (8) 84.0 (6) 116.9 (8) 101.5 (7) 179.0 (7) 141.6 (7) 62.2 (5) 79.4 (3) 121 (1) 120 (1) 121 (1) 118 (1) 101.3
82.1 116.1 34.1 (4) 116.1 (5) 108.4 (4) 110.7 (5) 92.8 121.0 (9) 155.1 (8) 83.7 (6) 117.2 (9) 101.4 (7) 176.0 (7) 141.4 (7) 62.3 (5) 79.1 (3) 122 (1) 120 (1) 120 (1) 120 (1) 105.9
C30
'i
c15
Figure 1. View of the molecular geometry of complex 14a in the solid state. Only one of the chemically equivalent independent molecular entities observed is depicted.
nary structural feature, namely the presence of a central planar-tetracoordinate carbon atom. We have obtained crystals of the (aryne)metallocene-derivedZr,Al complexes 14a,b that were suitable for X-ray crystal structure determinations. Complex 14a crystallizes in space group ml/n,with 2 = 8. The only numerical values of bonding parameters
Table 111. Positional Parameters for 14a atom
X
0.4695 (1) 0.5968 (1) 0.4338 (2) 0.5849 (2) 0.4145 (5) 0.4079 (5) 0.3714 (6) 0.3462 (6) 0.3554 (6) 0.3889 (6) 0.3331 (9) 0.312 (1) 0.2293 (9) 0.330 (1) 0.518 (1) 0.558 (2) 0.616 (1) 0.559 (1) 0.6059 (7) 0.5842 (7) 0.5803 (7) 0.5987 (7) 0.6150 (6) 0.410 (1) 0.4321 (9) 0.376 (1) 0.3316 (7) 0.3490 (9) 0.4701 (6) 0.4886 (5) 0.4264 (7) 0.3501 (6) 0.3333 (6) 0.3923 (7) 0.6015 (8) 0.671 (1) 0.669 (1) 0.743 (1) 0.5690 (8) 0.642 (1) 0.611 (1) 0.712 (1) 0.6771 (7) 0.610 (1) 0.5452 (8) 0.571 (1) 0.652 (1) 0.634 (2) 0.6997 (9) 0.686 (2) 0.610 (2) 0.5791 (9) 0.4794 0.6542
Y
0.2190 (1) 0.6844 (1) 0.2084 (2) 0.6797 (2) 0.0777 (6) 0.0994 (6) 0.0296 (8) -0.0567 (8) -0.0764 (7) -0.0101 (8) 0.255 (1) 0.331 (1) 0.338 (1) 0.419 (1) 0.157 (1) 0.198 (3) 0.171 (1) 0.299 (2) 0.266 (1) 0.188 (1) 0.108 (1) 0.135 (1) 0.233 (1) 0.287 (1) 0.368 (1) 0.363 (1) 0.286 (1) 0.239 (1) 0.6624 (6) 0.6629 (6) 0.6434 (7) 0.6240 (8) 0.6229 (8) 0.6442 (7) 0.5636 (9) 0.551 (1) 0.467 (2) 0.548 (2) 0.8051 (8) 0.841 (1) 0.934 (1) 0.845 (2) 0.816 (1) 0.8093 (9) 0.8368 (9) 0.8626 (8) 0.8522 (9) 0.575 (1) 0.582 (1) 0.538 (2) 0.504 (1) 0.526 (2) 0.2918 0.6982
2
0.2164 (1) 0.2919 (1) 0.3565 (2) 0.1494 (2) 0.2223 (5) 0.2280 (5) 0.3285 (5) 0.3029 (7) 0.2378 (7) 0.1958 (5) 0.3904 (7) 0.4328 (9) 0.4609 (7) 0.4044 (9) 0.4246 (8) 0.462 (2) 0.5177 (9) 0.469 (1) 0.183 (1) 0.1418 (6) 0.181 (1) 0.2455 (9) 0.2464 (8) 0.1136 (7) 0.155 (1) 0.2074 (7) 0.1979 (9) 0.1441 (9) 0.2780 (5) 0.2123 (5) 0.1668 (5) 0.1869 (7) 0.2519 (8) 0.2987 (5) 0.0978 (6) 0.0538 (9) 0.014 (1) 0.098 (1) 0.0964 (6) 0.0556 (9) 0.0161 (9) 0.089 (1) 0.340 (1) 0.3798 (6) 0.3409 (9) 0.2801 (9) 0.2810 (8) 0.3836 (6) 0.348 (1) 0.291 (1) 0.289 (1) 0.344 (2) 0.2961 0.2173
presented and discussed are averaged over the two observed independent molecular entities of 14a in the solid state (Tables 11 and 111). The Zr,Al complex 14a contains a bent group 4 metallocene unit. The W ( C p ) bond distances are in the usual range (2.47-2.54A). The u-ligand angle [C(l)-Zr-H(0) = 116.9'; see Figure 11 is rather large. This indicates the presence of three coordinative interactions in the u-ligand plane of the bent metallocene c o m ~ l e x ? Indeed, ~ complex 14a exhibits an unusual dimetallabicyclic central framework oriented in the major plane of the bent metallocene moiety, i.e. the plane bisecting the Cp(centroid)-Zr-Cp(centroid) angle. This central dimetallabicyclo[2.1.0]pentane type framework consists of the metal atoms zir(15) Lauher, J. W.; Hoffmann, R. J. Am. Chem. SOC.1976, 98, 1729. Cardin, D. J.; Lappert, M. F.; Raaton, C. L. Chemistry of Organo-Zirconium and -Hafnium Compounds, Wiley: New York, 1986, and references cited therein.
Erker et al.
3522 Organometallics, Vol. 11, No. 11, 1992 Clla n
A
Table IV. Selected Bond Lengths (A) and Angles (deg) for 14b Zl-C(l) 2.165 (3) Zr-C(2) 2.481 (3)
ClOa
Zr-C(9) M-C(7) '4l-C(9) C(1)4(6) C(3)-C(4) C(5)-C(6)
C15a
c9
87.8 (1) 33.8 (1) 105.4 (2) 116.3 (2) 109.6 (2) 152.7 (3) 117.4 (3) 177.9 (2) 60.5 (2) 120.1 (4) 119.6 (4) 78.3 (1)
\
O C 7
Figure 2. Projection of the molecular structure of 14b. conium and aluminum and the phydride ligand bridging between them [d(Zr-H(O)) = 1.86, d(Al-H(O)) = 1.83 Alls and is completed by the C$I, ligand. The latter is oriented in the a-ligand plane and is bonded q1 to aluminum and T+ to zirconium. The aromatic ring annulated to the central dimetallabicyclic framework is only slightly distorted. Three bonds of the nearly hexagonal perimeter are close to the expected aromatic C(sp2)-C(sp2)bond lengths [C(l)-C(2), C(3)-C(4), C(5)-C(6) = 1.37 (2) A; C(4)-C(5) = 1.35 (2) A]. Only the C(1)-C(6) and C(2)-C(3) bond distances are marginally longer at 1.40 (1) and 1.41 (3) A, respectively. The C-C-C bonding angles within the sixmembered ring are close to 120O. The adjacent aluminum center is tetracoordinate. It is bonded to carbon atoms C(2), C(15), and C(19) and to the phydride ligand H(0) (see Table I). The extraordinary structural feature of 14a (Figure 2) is that it contains a planar-tetracoordinate carbon. The carbon atom C(2) is coordinated to four ad'acent atoms. The corresponding bond lengths are 1.37 (2) [C(2)4(1)], 1.41 (1) A [C(2)-C(3)], 2.09 (1)A [C(%)-Al],and 2.431 (9) A [C(2)-Zr]. All four bonds are coplanar. The sum of the bonding angles at C(2) is 360O. The corresponding bond angles are as follows: 117.1 (9)O [C(l)-C(2)-C(3)], 101.5 (7)' [C(3)
