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Competing Pathways in the Reaction of Bis(pentafluorophenyl)borane with Bis(5-cyclopentadienyl)dimethylzirconium Methane Elimination versus MethylЦHydride Exchange and an Example of Pentacoordinate Carbon.

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[l] S. Omura, H. Tanaka in Mucrolide Antihiotics: Chemisrr?, Biology und Practice
(Ed.: S . Omura). Academic Press, New York. 1984. p. 351.
[2] Configurational assignment by X-ray analysis: a) amphotericin B: W. Mechlinski, C. P. Schaffner, P. Ganis, G. Avitable, Tetrahedron Lett. 1970, 3873;
b) roxaticin: H . Maehr, R. Yang. L:N. Hong. C.-M. Liu, M. H. Hatada. L. J.
Todaro. J. Org. Chem. 1989,54. 3816; configurational assignment by degradation. NMR analysis. and synthesis of partial units: mycoticin: c) S. L.
Schreiber. M. T. Goulet, Tetrahedron Lett. 1987. 28, 6001; d ) S . L. Schreiber,
M. T. Goulet, T. Sammakia, ibul. 1987. 28, 6005; e) J. Am. Chrm. Sor. 1987,
109, 8120; Nystatin: f ) J.-M. Lancelin, J.-M. Beau, Terruhedron Lett. 1989, 30,
4521; g) J. Prandi. .I-M. Beau, !hid. 1989. 30, 4517; h ) K . C. Nicolaou. K. H.
Ahn, rbid. 1989. 30, 1217; partial structure of lienomycin: i) J. Pawlak, K .
Nakanishi, T. Iwashita, E. Borowski. J. Org. Chem. 1987, S2, 2896; roflamycoin:]) S. D . Rychnovsky, G. Griesgraber, R. Schlege, J. Am. Chem. Sol. 1994,
116, 2623; pentamycin: k) T. Oishi. Pure AppL Chcm. 1989. 61, 427; I) T.
Nakata. N . Hata. T. Suenaga. T. Oishi, Tmnen-Yuki Kugobuton Toronkui Koen
YoshiJhu 30th 1988 (Chem. Nut. Prod. Synzp. Pap.). Fukuoka, 1988. 540; configurational assignment by N M R spectroscopy: pimaricin: m) J.-M. Lancelin,
I.-M. Beau. J. Am. Chem. Suc. 1990. 112, 4060: Candidin: n) J. Pawlak. P.
Sowinski. E. Borowski, P. Gariboldi, J. Antihior. 1993. 46. 1598.
a) J. Bolard, Biochin?. Biophp. Actu 1986, 865. 257; b) 0 . Behnke, J. TranumJensen. B. Van Deurs, Eur. J Ce// Em/. 1984, 35, 189.
R. A. Coxey, P. G. Pentchev, G. Campbell, E. J. Blanchette-Mackie, J. Lipid
Rm. 1993. 34, 1165.
a) J. Milhaud. J. Mazerski, E. J. Dufourc, Eur. Biophys. J. 1989, 17. 151; b)
M. A. R. 8 . Casranho, M. J. E. Prieto, Eur. J Biochem. 1992, 207, 125.
a) G. B. Whitefield, T. D. Brock, A. Ammann, D. Gottlieb, H . E. Carter, J
Am. Chem. So(. 1955, 77, 4799; b) A. Ammann, D . Gottlieb, H. E. Carter,
Plunt Dis. Rep. 1955. 39, 219.
M. E. Bergy, T. E. Eble, Biochemi.ylrj, 1968, 7. 653.
a) B. Berkoz, C. Djerassi, Proc. Chem. SOC.London 1959, 316; b) C. Djerassi,
M. Ishikawa, H . Budzikiewicz, J. N. Shoolery, L. F. Johnson, Tetrahedron Lett.
1961.383; c) B. T. Golding. R. W. Rickards, M . Barber, ibid. 1964,2615; d ) 0 .
Ceder. R. Ryhage. Arm Chem. Scund. 1964, 18. 558.
R. C. Pandey, K. L. Rinehart. J. Anrihiot. 1970. 23,414.
D . M. E Edwards, J. Antihior. 1989, 42, 322.
R. C. Pandey, N. Narasimhachari. K. L. Rinehart. D. S. Millington, J Am.
Chem. Soc. 1972, 94. 4306.
a) S . D. Rychnovsky. D. J. Skalitzky. Tetrahedron Lett. 1990,31, 945; b) D. A.
Evans. D . L. Rieger, J. R. Gage, ihid. 1990,31, 7099; c) S. D . Rychnovsky, B.
Rogers, G. Yang, J. Org. Chem. 1993, 58, 3511.
Filipin complex was obtained from Sigma (F-9765) as a crude mixture containing about 50% filipin 111 or from Upjohn (Lot 2923-DEV-39) containing
about about 8 % filipin 111. It can be purified by reversed-phase preparative
HPLC.
The location of the C1’ acetates in 3 and 4 were determined by their cross-peak
in the COSY spectra with the readily identifiable C2 proton. The C15 acetate
in 3 was identified by the simplicity of its coupling pattern. The location of the
C7 acetate in 4 is less secure, and was assigned from the COSY spectrum. The
second acetate in 4 must be at either at C7 or C11, and its location does not
affect the stereochemical analysis. The assignments for these protons are listed
in Fable 1.
K. Pihlaja, M . Kivimaki, A,-M. Myllyniemi, T. Nurmi, J. Org. Chem. 1982, 47,
4688.
S. D . Rychnovsky, G. Yang, J. P. Powers. J. Org. Chem. 1993, 58, 5251.
J. Mulzer, A. Angermann, W. Munch, G. Schlichthorl, A. Hentzschel, Liehigs
Ann. Chem. 1987, 7.
9: ‘ T N M R (125 MHz, C,D,), 1,2-diolacetonide mixture: 6 = 29.03. 27.76.
27.61, 26.10; 1,3-diolacetonide: 6 = 30.81, 30.69, 30.66, 30.22. 20.04, 19.92,
19.83. 19.00.
I. 0htani.T. Kusomi, Y. Kashman. H. Kakisawa. J. Am. Chem. So<. 1991,113,
4092
Competing Pathways in the Reaction
of Bis(pentafluoropheny1)borane with
Bis(q5-cyclopentadienyl)dimethylzirconium :
Methane Elimination versus Methyl -Hydride
Exchange and an Example of Pentacoordinate
Carbon**
Rupert E. von H. Spence, Daniel J. Parks,
Warren E. Piers,* Mary-Anne MacDonald,
Michael J. Zaworotko, and Steven J. Rettig
The combination of group 4 bent metallocene compounds
with group 13 Lewis acids often leads to catalysts capable of
polymerizing olefinic substrates by ring opening metathesis[’] or
Ziegler-Natta type mechanisms.[’] The activation in the latter
systems commonly involves treatment of dichloro metal complexes [Cp,MCI,] with an excess of methylaluminoxane (MAO)
which leads to [Cp,MCH,]+[MAO]-, the cation of which is
generally accepted to be the active species in these catalyst^.'^^
Alternatively, the reaction of [Cp,ZrR,] derivatives (R = H,
alkyl) with equimolar amounts of B(C6F5)3[3b,41
has proven to
be an effective means of producing active centers by alkyl abstraction, minimizing the need for excessive amounts of cocatalyst.
Spurred by these discoveries, we have developed synthetic
routes to the electrophilic borane HB(C,F,), (l)[’I as a reagent
for incorporating the B(C,F,), moiety into the structural framework of ancillary ligands which support soluble Ziegler-Natta
catalysts. During these studies, we found borane 1 to be reactive
towards simple alkylzirconium complexes as exemplified by its
reaction with [Cp,Zr(CH,),] (2). In addition to methyl-hydrogen exchange pathways,[611 was found to induce methane elimination from 2, ultimately leading to an intriguing compound
containing a rare example of pentacoordinate carbon. The
chemistry reported herein is summarized in Scheme 1.
The reaction of 1 with one equivalent of 2 in benzene, led to
an intractable mixture of several zirconium- and/or B(C,F,),containing products. Conversely, the same reaction in hexanes
resulted in the evolution of methane (confirmed by ‘HNMR
spectroscopy) and isolation of a single product, a brick red solid,
3, in 86% yield.
The product 3 decomposed at room temperature in benzene
over one to two hours to give several species but could be stabilized with PMe, with which it forms a 1 : 1 adduct 3.PMe3.
Spectroscopic data indicated that 3 contained a four-coordinate
boron”] (“B NMR, 6 = - l . l ) , a Zr-H-B arrangement
(‘HNMR, 6 = - 0.75, broad; IR, i = 1602 cm-’), and a
deshielded methylene group bonded to boron as evidenced by
quadrupolar broading of the ‘H NMR signal (‘H NMR,
6 = 5.30). These data are consistent with the structure shown
[*I Prof. W E. Piers, Dr. R. E. von H. Spence, D . J. Parks
Guelph-Waterloo Centre for Graduate Work in Chemistry
Guelph Campus, Department of Chemistry and Biochemistry
University of Guelph
Guelph, Ontario. N l G 2Wl (Canada)
Telefax: Int. code + (519) 766 1499
M.-A. MacDonald, Prof. M. J. Zaworotko
Department of Chemistry, Saint Mary’s University
Halifax, Nova Scotia (Canada)
Dr. S. J. Rettig
Department of Chemistry, University of British Columbia
Vancouver, British Columbia (Canada)
[**I Financial support for this work was provided by the Novacor Research and
Technology Corporation of Calgary. Alberta and by the Natural Sciences and
Engineering Council of Canada in the form of a Postgraduate Scholarship for
D. J. P.
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C
Scheme 1. Reactions of HB(C,F,), (1) with [CplZr(CH,),] ( 2 ) . a) 1. hexane;
e) 4 1, benzene: -CH,,
-CH,; b) PMe,; c) 1, d) 2 1, -CH,[B(C,F,),],;
-CH,B(C,,F,), and -CH,[B(C,F,),],;
4:5 =z 1 :2.
for 3 in Scheme 1, a species which may formally be described
as a zirconocene methylidene unit in a state of arrested hydroboration, stabilized by HB(C,F,), in a similar bonding arrangement to that found in [Cp,Ti(p-CH,)(p-CI)AIMe,], Tebbe's
reagent.[*]
This formulation was confirmed by an X-ray crystallographic
analysis of 3.PMe3 (Fig. I).", 'I The PMe, ligand occupies an
ex0 coordination site, quenching the electron deficiency of the
zirconium center in unligated 3. The methylene unit resides in
the central position and is shielded by the PMe, ligand as evidenced by the upfield shift of its signal in the 'H NMR spectrum
relative to the corresponding signal of 3 (6 = 0.93). The Zr-Cl
and C1 -B distances of 2.300(7) and 1.586(12) A, respectively,
are typical of single bonds for these bonding partners. While the
position of the p-H ligand had to be calculated, the spectroscopic and structural evidence is clearly indicative of a four-
membered Zr-C-B-H["] unit in 3.PMe3 and presumably also
in 3.
When [Cp,Zr(CH,),] was treated with an excess of borane
1 in benzene, two zirconium-containing products, 4 and 5,
were formed in a ratio of approximately 1.2. The minor
product was identified as the bis(dihydroborate) complex
[Cp,Zr{H,B(C,F,),],] (4) by NMR spectroscopy, characteristic IR absorptions for the Zr-(p-H),-B units",] at 2184, 2110,
and 2028 cm-' (Zr-(p-D),-B, C = 1597 cm-'), and its synthesis
by a separate route from [Cp,ZrH,]['31 and two equivalents
of 1.
The major product in the reaction, 5, apparently arises from
complexation of 3 with a further equivalent of borane. The
' H N M R spectrum of 5 consists of singlets at 6 = 5.23, 2.29
(broad), and -2.05 (very broad) in a 10:2:2 ratio, suggesting
retention of the methylene unit to form a complex of
stoichiometry [Cp,ZrH, CH,{B(C,F,),},]. Four-coordinate
boron was implied by the ''B chemical shift at about 6 = O.O.[']
The signal for the methylene carbon was not detected with standard pulse sequences, but by using the HMQC experiment['41a
= 120 Hz).
broad signal at d = 0.5 was identified
These spectral features of 5 were consistent with the general
formulation given above but an X-ray analysis['5, 'I of the
compound as a benzene solvate revealed a unique bonding arrangement in which the methylene carbon is five coordinate by
virtue of a bonding contact with the zirconium center (Fig. 2).
c2
-
C6
F15
C13
Fig. 2. Molecular structure of 5; noncyclopentadienyl hydrogens were located and
refined. The C,F, groups have been omitted for clarity. Selected bond lengths [A]
and angles [^I: Zrl-C11 2.419(4), Zrl-H22 1.9?(3), Zrl-H23 1.94(3), C11-B1
1.697(7). C l l - B 2 1.693(7), BILH22 1.13(3), B2-H23 1.2?(3). Zrl-Cpl.,,, 2.19.
Zrl-Cp2,,,, 2.19; H22-Zrl-H23 126(1), B1-C11-B2 149.3(4). BI-Cll-Zrl 76.6(2),
B2-Zrl-Cll 78.0(2), Zrl-H22-B1 112(2), Zrl-H23-B2 110(2), C12-Bl-CI8
108.4(4), C24-B2-C30 106.0(4); Cpl,..,-Zrl-Cp2,,,, 128.6.
F24
bw
Fig. 1 . Molecular structure of 3.PMe,. Selected bond lengths [A] and angles ['I:
Zr-P 2.726(3). Zr-C1 2.300(7), B-CI 1.586(12), B-H 1.51(5), Zr-H 1.99(5),
Zr-Cpl,,,, 2.232. Zr-CpZ,.., 2.225: P-Zr-C1 72.83(19), Zr-C1-B 85.0(4), C1-BC11 116.?(7). Cl-B-C21 116.4(7), Cll-B-C21 108.5(7), Zr-H-B 98(3); Cplcent-ZrCp2,,., 131.4.
A n g e w Chrm. In1 EN'. Engl. 1995, 34, N o . I 1
0 VCH
The Zrl -C11 distance is 2.419(4) A, only slightly longer than
the distances of about 2.27 8, for 2[16]and Zr-Cl in 3.PMe3.
Both the H22-Zrl-H23 (126(1)") and B1-C11-B2 (149.3(4)")
angles are significantly greater than expected values,l'" '*I allowing for interaction between Zrl and C11, which is approximately trigonal bipyramidal in geometry. The unusual coordination environment around C11 is reflected in its upfield
chemical shift in the 13C(1H}NMR spectrum, compared to
chemical shifts of 6 > 30 which we have observed for the B-C-B
carbons in "free" chelating boranes of general formula
[RCH,CH{B(C,Fd,},]
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The sum of the angles between C11 and the three atoms in the
equatorial plane is 358" but the atoms are not in an ideal trigonal arrangement, that is the Zrl-C1 I-HI 1 angle of 107(2)" is
decidely more acute than the Zrl-C1 I-HI2 angle of 149(2)".
No evidence, however, was found for an agostic interaction
i n the solution N M R data. Previous examples of five-coordinate carbon involved either the three-center, two-electron bonding type of an alkyl ligand bridging two transition metals,['g1
o r "ate" complexes with lithium counterions.I2'' If one views
5 formally as a complex of [Cp,Zr]'+ and the dianion
[CH,{HB(CbF,),),]2-, one might expect negative charge localization on the methylene carbon which is donated to the electrophilic zirconium center; computational studies are required
to define this interaction more precisely.
A plausible means of formation of 5 would involve complexation of 1 with the Tebbe-type complex 3 if the borane approaches from the pmethylene side of the metallocene wedge.
Interestingly, when 3 is treated with excess borane 1, bod?4 and
5 are formed, again in a ratio of approximately 1 :2, suggesting
that approach from the p-hydride side is also occuring. This
approach would produce the intermediate shown in square
brackets in Scheme 1. We have not isolated this species, but
signals in the 'H NMR spectrum of the reaction of 3 plus one
equivalent of 1 a t S = 4.95 (Cp) and 6 = 2.81 (CH,) are
assignable to this compound. Further reaction with 1 resulted in
the disappearance of these signals and growth of resonances for
4.[2'1Another pathway by which 4 may be formed from I and
2 involves methyl-hydride exchange''] and complexation of further equivalents of l to Zr-H units. The identification of the
compound CH,B(C,F,),'41 in the product mixture of reaction
(e) in Scheme 1 is consistent with this scenario.
Complex 5 is also significant because of its inactivity as an
ethylene polymerization catalyst under ambient conditions. On
the basis of recent disclosures by Marks et. al.[''l one might
expect an isomer, 5'. to be accessible and function as a highly
active catalyst [Eq. (f)]. The implications of structure 5 for the
5
5'
use of counterions of general formula [RCH,CH{B(C,F,),),(pH)]-' in homogenous Ziegler-Natta catalysts remain to be determined but if the isomers depicted in Equation f a r e interconvertible under realistic polymerization conditions, some
attenuation of catalyst activity may be expected. We are currently exploring these issues further as well as the mechanistic details
of the reactions of 1 with dialkylzirconium complexes.
Experimental Procedure
All N M R spectra were performed in C,D, on a Varian Unity 400 instrument.
3 : Hexane (15 mL) was condensed into a vessel containing 1 (115 mg, 0.33 mmol)
and 2 (84 mg, 0.33 mmol) at - 78 "C. The reaction was allowed to warm to room
temperature. After stirring and sonicating for 1 hour a red precipitate was isolated
byfiltration.Yield 164mg,0.28 mmol.86%. ' H N M R : 6 = 5.70(10H;C,H5), 5.30
(2H; CH,), -0.75 (IH, br; Zr-H-B): I9F NMR (referenced to CFCI, at d = 0.0):
6 = - 132.3, - 160.4, -165.2; "B NMR (referenced to BF,.Et,O at 0 = 0.0):
6 = -1.1. IR (KBr, Nujol. cm-I): i. =1640 m, 1602 w (B-H-Zr), 1509 m. 1305 w,
1282 w. 1374 w. 1094 s, 1017 s, 967 s. 830 s. 775 m.
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3.PMe,: To a frozen suspension of 3 (147 mg. 0.25 mmol) in benzene (3 mL) at
-78 C was condensed excess PMe, (1.5 equivalents). The reaction mixture was
warmed to room temperature and filtered: hexane ( 1 5 mL) was added to precipitate
the product as a lime green solid which was isolated by filtration. Yield, 113 mg,
0.17 mmol. 6X%. Crystals were obtained by recrystallization from benzene
' H N M R : 6 = 5.07 (d. 10H. J(P.H) = 2.4 Hz; C,H,), 0.93 (dd. 2H. 'J(P,H) =
12.7 Hz. 'J(H.H) = 3.9 Hz; CH2), 0.54 (d. 9H. 'J(P,H) = 6.4Hz; PCH,). -1.9
(br. 1H: Zr-H-B). 13C('HJ N M R (referenced to benzene at 0 =128.0, HMQC
[14]): S =105.1 (C,H,), 33.0 (CH,. 'J(C.H) = 128 Hz), 15.6 (d, 'J(P,C) = 24.4 Hz,
PCH,);"BNMR:S = - 30.3;"FNMR:ii = -131.8, -162.1, -165.9:31P{'HJ
NMR (referenced to 8 5 % H,PO, at 6 = 0.0): 6 -3.0.
4.C,Hb: Benzene (25 mL) was condensed into a vessel containing [Cp,ZrH,]
(44.5 mg. 0.2 mmol) and 11138 mg. 0.4 mmol) at -78 -C. The reaction mixture was
heated to reflux; on cooling. white crystalline needles o f 4 appeared. The crystals
were isolated by filtration and dried under vacuum. Yield: 122 mg. 0.13 mmol,
67%. Recrystallization from benzene gave clear cubes of the benzene solvate of 4.
' H N M R : 6 = 5.42 (s. C,H,); 0.38 (br. p H ) : "B N M R : 6 = -12.9 (t.
'J(H.B) = 64 Hz): I9F N M R : 6 = - 133.0, -156.8. - 163.4. Elemental analysis:
calcd. for C,,H,,F,,B,Zr~C,H,:
C 48.36, H 2.03; found (separate samples): C
47.61. 47.71; H 1.77. 1.81. IR (KBr, Nujol. cm-'):: = 2184 w (br). 2110 w (br),
2028 w (br). 1645 m, 1514 s. 1288 m. 1260 m, 1114 m, 1094 m, 957 s, 826 m.
5.C,Hb: Benzene (7 mL) was added lo a flask containing 2 (126 mg, 0.5 mmol) and
1 (346 mg. 1 mmol). Upon stirring, the reaction mixture became dark red and gas
evolution was observed. After 30 minutes, the reaction mixture was heated to reflux:
on cooling, colorless crystals formed which were isolated by filtration, washed with
benzene. and dried in vacuo. Yield 225 mg. 0.22 mmol, 45%. ' H N M R . S = 5.23 (s.
10H; C,H,). 2.29 (s. 2H; CH,), -2.05 (br, 2H; Zr-H-B); ',C{'H} (HMQC):
6 =111.1 (C,H,). 0.5(CH2, 'J(C.H) =120Hz); I 9 F N M R : d = -132.4, -157.2,
=1937w,1902w,
-163.4. "BNMR:O.O(fwhm. 135 Hz).IR(Nujolmull,KBr):i;
1857 m, 1822 w, 1779 w. 1644 m. 1516 s. 1284 m, 1128 w, 1098 s. 1025 rn. 1015 w,
978 s, 895 w, 883 w, 855 w. 838 w, 824 m, 818 m, 793 w. 766 w. 754 w. 744 w, 702
C 49.35, H 2.35; found: C
w, 647 m. Elemental analysis: calcd for C,,H,,B,F,,Zr:
49.49. H, 2.14.
Received: January 10, 1995 [Z7621 IE]
German version: AnRrw. Chrm. 1995, 107, 1337-1340
Keywords: bordnes . catalysis. five-coordinate carbon
wich complexes . zirconium compounds
sand-
[I] R . H. Grubbs, W. Tumas, Science 1989. 243. 907.
(21 H. Sinn, W. Kaminsky, Adv. Orgunoinrt Cliem. 1980, 18, 99.
[3] a) J. J. Eisch, A. M. Piortrowski, S. K . Brownstein, E. J. Gabe, F. L. Lee, J. Am.
Chrm. Suc. 1985. 107, 7219; b) X. Yang. C. L. Stern, T. J. Marks, ;hid. 1991.
113. 3623; c) T. J. Marks, Acc. Chem. Re.s. 1992, 2.5. 57; d) R. F. Jordan, Adv.
Orgunumct.Chem. 1991. 32, 325: e) P. G. Gassman. M. R. Callstrom. J. Am.
Cheni. Suc. 1987, 109. 7875.
[4] X. Yang, C. L. Stern, T. J. Marks, J. Am. Chein. Soc. 1994, 116. 10015.
[5] D. J. Parks. R. E. von H . Spence, W. E. Piers, Angew. Chem. 1995, /07, 895;
A i i g w . Chc,m. I n [ . Ed. Engl. 1995. 34. 809.
[6] J. A. Marsella. K. G . Caulton, J. Am. C'hem. Soc. 1982, 104, 2361.
[7] R. G . Kidd in N M R Uf Newly Accessible Nuclri, Vol. 2 (Ed.: P. Laszlo), Academic Press. New York. 1983.
[XI F. N. Tebbe, G . W. PdrhSdll. G . S. Reddy, J. Am. Chrm. Soc. 1978, 100, 3611.
[9] Crystal data for 3.PMe3: C,,H,,F,,BPZr,
0.40 x 0.60 x 0.70 mm, monoclinic. P2,/n. u =10.884(4). h =16.002(5), c =15.312(6).&, fl =103.71(3)'.
Z = 4,p,,,,, = 1.686 mgm-3, 20,,,, = 5 0 , Mo,,radiation,
V = 2590.8(16)
.; = 0.70930 A. w-scan. T = 298 K , 4731 measured reflections, 4552 independent. 3129 reflections with I , , > 3.0u(Ine,),p = 0.55 mm-', minimax transmission = 0.735 and 0 999, R ( F ) = 0.057, R, = 0.052. GOF = 4.31, no. of
parameters = 356. After anisotropic refinement of all non-hydrogen atoms.
planar and methylene hydrogen atoms were placed in calculated positions
(D, ,, = 1.00 A and 1.08 A) and methyl hydrogen atoms were located by inspection of a difference Fourier map. All hydrogens were given temperature
Factors based upon the atom to which they are bonded and fixed during least
squares refinement. All crystallographic calculations were conducted with the
PC version of the NRCVAX program package locally implemented on an IBM
compatible 80486 computer: E. J. Gabe. Y. Le Page. J.-P. Charland. F. L.Lee,
P. S. White J. Appl. CrwuNugr.. 1989. 22. 384.
[lo] Further details of the crystal structure investigations are available on request
from the Director of the Cambridge Crystal!ographic Data Centre, 12 Union
Road, GB-Cambridge CB2 1 EZ (UK) on quoting the full journal citation.
[ l l ] R. T. Baker. D. W. Ovenall. J. C. Calabrese. S. A. Westcott. N. J. Taylor. I. D.
Williams. T. B. Marder, J. Am. Ckem. Soc. 1990, 112, 9399.
[12] W. K. Kot, N . M. Edelstein, A. Zdlkin. Inorg. Chein. 1987. 26. 1339.
[13] P. C. Wailes, H. Weigold, J. Orgunutnt.t. Chrw. 1970, 24, 405.
[I41 a) V. J. Robinson. A. D. Bain. Mugn. Reson. Chem. 1993. 31, 865; b) A. Bax,
S. Subramanian. J. Mugn, Rrsun. 1986, 67. 565.
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Angrn.. Cheni. Int. Ed. Engl. 1995, 34. No. I 1
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[IS] Cysral data foi- 5.1.SC,H6: C,,H,,F,,,B,Zr, 0.15 ~ 0 . 3 0.50
0 ~ nim, triclinic,
P1 (no. 2 ) . ( I =14.8025(8), h =14.9622(7), L' = 9.8708(7) 8, 5 = 93.972(8),
[i= 108.340(7). 7 = 94.416(8)". V = 2058.8(3) A3. Z = 2. pcxlcd=1.685 m g m - 3 .
20,,, = 55 . Mo, radiation, L = 0.71069 A. lo-scan, T = 294 K, 9839 measured reflections, 9467 independent. 3885 reflections with I,,, > 3.0u(InJ.
11 = 3.91 c m - ' , minimax transmission = 0.9023 and 1.0000, R(F) = 0.039.
K, = 0.032, GOF = 1.60. no. of parameters = 620. The structure was solved
by the Patterson method and was refined by full-matrix least-squares procedures. All non-hydrogen atoms were refined with anisotropic thermal parameters and the B-H and methylene C-H hydrogen atoms were refined with
imtropic thermal parameters. The remaining hydrogen atoms were fixed In
calculated positions with C-H = 0.98 A and B(H) =1.2 B(honded atom). All
calculations were performed on a Silicon Graphics Indigo Workstation using
the WX.WJ C'ry.;tal Structure Analysis Package: Molecular Structure Corporalion. Thc Wuodlanda. TX, USA 1992.
[I61 a ) W E . Hunter. D. C. Hrncir. R. Vann Bynum, R. A. Penttila. J. L. Atwood.
~ ) ~ , ~ ~ i n r ~ n1983.2,
~ r / a / 750.
/ r ~ h)
\ R. F. Jordan. C. S. Bajgur. R. Willett. B. Scott,
J. An?. Chenr. SOC. 1986. f(J8. 7410.
[I71 MMZ minimization of CH,[B(C,F,),], lead to a B-C-B angle of about 122..
[IS] Typical L-Zr-1. values for Zr'" metallocenes are about 95- : D. J. Cardin. M. F.
Lapperr. C'. L. Raston, P. I . Riley, in Comprehensive Orgunonir/al/ic C'hiJmi . \ / i y . Lo/. 3 (Ed.: G. Wilkinson. F. G. A. Stone, E. W. Abel). Pergamon, New
York. 1982, p. 551
[I91 J. Holton, M . F. Lappert, R . Pearce, P. I. W. Yarrow, C/iem. Ruv. 1983.83.135.
[20] n) D. L. C'lark. J. C Gordon, J. C. Huffman. J. G . Watkin. B. D. Zwick,
O~~fia~~"nie/u//i[,.\
1994. 13. 4267; b) R. J. Morris, G. S. Girolami. ibirl. 1989. 8,
1478: c.) U:J. Evans. T. A. Uliharri, 1 W. Ziller, ;hi/. 1991, 10. 134.
[Zl] A broad nirthylene i-esonance at about 6 z 3.1 IS consistent with the presence
of free CH2[B(ChFJ2I2.which must he produced in these reactions.
[22] L. Jia. X. Yang, C. Stern. T. J. Marks. Organonietallrcs 1994, 13. 3755.
Crystal Structure of Dilithioacetylacetone:
A Twenty-Four Vertex Li-0 Cage Molecule
with Limited Li - C(termina1) Bonding
and Selective THF Solvation""
William Clegg, Lynne Horsburgh, Robert E. Mulvey,*
and Michael J. Ross
Dienolate anions generated by double metallation of a pdiketone with alkali metals are important building blocks in
organic
In reality these are dimetallo intermediates. whose precise identities are normally concealed by the in
situ manner of their utilization. Here we report the isolation and
crystallographic characterization of the representative dilithium
dienolate 1 . Though derived from the simplest 1,3-diketone,
acetylacetone (acac), 2, its structure is surprisingly complicated,
containing twelve Li+ ions in an odd cage architecture. which is
totally out of line with the regular dimeric, tetrameric, or hexameric aggregates generally adopted by lithium enolates.izl
T H F solvation proved to be the key to capturing the
dilithioacetylacetone in a crystalline form suitable for X-ray
diffraction study. However, despite the availability of excess
T H F in the reaction solution, solvation is incomplete with only
eight of the twelve Li+ ions carrying a T H F ligand.
The implication of the THF-deficiency. that the doubly
charged acac anions form a robust aggregate with the Li' ions,
is confirmed by the crystal structure (Fig. 1 a).[31Possessing
Fig. 1. a) Crystal strncture of 1 (excluding hydrogen atoms). Principal distances
L i l - 0 1 1.947(7), L i l - 0 3 1.883(7), Lil-05a 2.071(7). L i l - 0 9 2.009(7),
Li2-02 1.969(7). Li2-03 1.961(7), Li2--04 2.003(7), Liz-08 2.037(7), Li3-02
1.915(7). Li3-04 1 853(7). Li3-07 1.924(7), Li3-CI5 2.429(8), Li4-03 2.015(6),
L i 4 - 0 4 1.984(7), Li4-06 1.912(6), Li4-010 1.945(7), L i 5 - - 0 1 1.920(7), Li5-02
1.906(6), Li5--05 2.049(6), LiS-06 1.980(7), Li6-05 2.011(5), Li6-06 1.912(3),
Li7-01 1.853(3), Li7-05 2.165(9); angles at Li atoms in range 86.1(3)-159.7(8)".
h) Line drawing of the quintuple-decker sandwich core of 1 showing the L i - 0
rhomboid and six-membered boat layers with solid lines and connections between
these layers as dashed lines; the view direction is as for a ) .
[A]:
-
crystallographic C , symmetry about the Li6. ' . Li7 axis, the
molecule's irregular appearance can be made more intelligible if
its Li-O(acac) core is viewed as a quintuple-decker sandwich
(Fig. 1 b): a central unique rhomboid Li6-05-Li7-05a sits beI
tween two identical, distorted boats Li4-03-Lil -03 -Li5-06
and its symmetry equivalent. Two identical. rhomboids
Li2-02-Li3-04 and its symmetry equivalent form the outer
layers. The unique "bridging" rhomboid forms y4-contacts with
the boats on either side, while the other rhomboids bind to them
in a "terminal" y3 manner. These latter rhomboids additionally
interact with a terminal carbon atom of acac (C15jCISa).
Two of the three crystallographically distinct acac dianions A
and B each participate in six L i - 0 contacts in total (three per
0 atom; Fig. 2). Such p,O-Li bonding is commonplace in
higher aggregates, for example, the hexameric enolate derived
from p i n a ~ o l o n e . [In
~ ]contrast, the third dianion C takes part in
seven L i - 0 contacts, the odd number stemming from a novel
p,-bonding stance assumed by 0 5 . This extra coordination
leads to long Li-05 bonds (2.011 -2.165 A; mean 2.074 A). In
comparison, other Li-O(anionic) bonds have mean lengths below 2 A (range of mean lengths, 1.907-2.953 A). Figure 2
shows how the attached Li+ centers are oriented with respect to
-
1
0
0
2
[*IDr. R. E. Mulvey, M . J. Ross
Department of Pure and Applied Chemistry, University of Strathclyde
GB-Glasgow GI 1XL (UK)
Telefax: Int. code (141) 552 OX76
Prof. W. Clegg, L. Horshurgh
Department of Chemistry, University of Newcastle (UK)
+
[**I
This work was supported by the UK Engineering and Physical Science
Research Council.
A n ~ v i i . Chcvn.
.
in/
Ed. Engl. 1995. 34, No. I 1
(i;~ VCH Verkrgsgrwllschufr mhH. 0-69451 Weinhein?, 1995
0570-0833!95,'111i-1233
$
10.00L . ? j ; O
1233
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pentafluorophenyl, exchanger, example, reaction, competing, cyclopentadienyl, elimination, methylцhydride, dimethylzirconium, versus, bis, pentacoordinate, boranes, pathways, carbon, methane
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