Organometallics 1995, 14, 1870-1874
1870
Five-Membered-NiobacycleFormation from an Allyl-Alkyne Coupling Reaction Fabienne Biasotto, Michel Etienne,* and Franqoise Dahan Laboratoire de Chimie de Coordination du CNRS, UPR 8241,205route de Narbonne, 31 077 Toulouse Cedex, France Received December 28, 1994@ Reaction of Tp*NbClz(PhC=CR) (R = CH3, Ph) with 1 equiv of allyl Grignard gives I
I
moderate yield of five-membered niobacycles Tp*(Cl)Nb[C(Ph)C(R)CHCH(CHdI resulting from a n allyl-alkyne coupling reaction accompanied by a 1,3-hydrogen shift in the allyl moiety. Both the spectroscopic and X-ray crystal data indicate a n q4-butadienyl formulation is appropriate for the new ligand.
Introduction We have recently discovered rare cases of roomtemperature stable n-alkyl- (ethyl and n-propyl) niobium alkyne complexes Tp*Nb(Cl)(CHzCHzRXPhCICR') (R = H, CH3; Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) where an a-agostic interaction is preferred over a more commonly observed P-agostic intera~tion.l-~ This is more likely due t o the use of the bulky Tp* ligand which prevents the sterically demanding bending of the alkyl group that would be necessary for the P-agostic interaction to occur.l,4 Upon heating, an intramolecular exchange of the niobium-bound alkyl group with the alkyne substituent is observed, the a-agostic interaction assisting the r e a ~ t i o n .A~ benzyl complex, shown to be nonagostic, merely decomposes upon thermolysi~.~ In order to understand more in depth the occurrence of such a-agostic interactions and rearrangements, we are studying the effects of substitution a t Ca. In this note, we report on the allyl-alkyne coupling reaction that results from allyl Grignard addition to the dichloro alkyne complexes Tp*NbClz(PhCWR). We present first spectroscopic and crystallographic data on the fivemembered niobacycles which are formed, and then we briefly discuss a possible reaction pathway.
Results and Discussion Synthesis and Spectroscopic Data. The treatment of a red-purple toluene solution of Tp*NbClz(PhC=CCH3) (la)5with 1 equiv of allylmagnesium chloride between -30 "C and room temperature leads to an orange-brown slurry shown by IH NMR to contain a single organoniobium complex apart from ill-defined signals due to unknown decomposition products. The orange crystalline compound is isolated in 25% yield after chromatographic workup and crystallization. It ~
~ _ _ _
Abstract published in Advance ACS Abstracts, March 15, 1995. (1)Brookhart, M.; Green, M. L.H.; Wong, L.-L.Prog. Inorg. Chem. 1988,36,1. (2)Etienne, M.Organometallics 1994,13,410. (3)Etienne, M.; Biasotto, F.; Mathieu, R. J. Chem. Sac., Chem. Commun. 1994,1661. (4)A similar preference, also proposed to lie to steric grounds, has appeared in cationic hafnocene complexes: Guo, Z.; Swenson, D. C.; Jordan, R. F. Organometallics 1994,13,1424. (5)Etienne, M.; White, P. S.;Templeton, J. L.Organometallics 1991, 10,3801. @
0276-7333/95/2314-1870$09.00/0
r
has been characterized as the niobacycle Tp*(Cl)NbI
[C(Ph)C(CH3)C(H)CH(CH3)](2a)on the basis of elemental analysis and 'H and 13CNMR data. Starting from the diphenylacetylene complex Tp*NbClz(PhCrCPh) (lb),a similar compound Tp*(Cl)Nb[C(Ph)C(Ph)C(H)1
CH(CHd1 (2b) has been obtained and fully identified by an X-ray crystallographic analysis. These events are summarized in Scheme 1. Thus, compounds 2a,b result from the coupling of the 4e-donor alkyne in la,b with a rearranged allyl group. This rearrangement involves a 1,3-hydrogen shift. In the IH and 13C NMR in benzene-de of 2a,b each set of the Tp* hydrogens and carbons appears in a 1:l:l ratio in accord with the lack of plane of symmetry in these niobacycles. For 2a, the rearranged allyl group is identified by a doublet integrating for one proton at 6 5.49 attributed t o Hy (we assign the a position to the phenyl attached carbon; see Scheme 11, coupled ( 3 ~ H H = 12.4 Hz) to a shielded anti proton H6 (6 1.62). H6 shows additional coupling ( 3 ~ H H= 5.5 Hz) with a methyl group (6 2.42) bound to the same C6 carbon. The Cy and C6 carbons give 13CNMR signals at 6 112.2 (d, ~ J C H = 150 Hz) and 6 93.4 (d, ~ J C=H133 Hz), respectively. The latter coupling constant indicate substantial sp3 hybridation for C6, which is furthermore slightly broadened by the niobium nucleus. The formerly phenylpropyne ligand is now identified by a niobium-broadened carbene-like resonance assigned to Ca (6 240.0) and by a second quaternary signal at 6 105.8 attributed to CP. Similar key spectral data have been obtained for 2b. Solid State Molecular Structure of 2b. An ORTEP drawing resulting from an X-ray diffraction analysis on a single crystal of 2b is shown in Figure 1. Table 1 summarizes the crystallographic and solution and refinement data, and atomic coordinates are to be found in Table 2. Table 3 provides relevant bond lengths and angles. The overall geometry around the niobium center is that of a distorted octahedron if C(2) and C(3) are neglected in defining the metal coordination sphere, or a capped octahedron may be visualized when considering the interaction of the C(2)-C(3) bond with the niobium center. The almost planar four-carbon chain (torsional angle C(I)-C(2)-C(3)-C(4) = -5.7(7)") is r4bound to the niobium center via a double bond with C(1)
0 1995 American Chemical Society
Five-Membered-NiobacycleFormation
Organometallics, Vol. 14, No. 4, 1995 1871
Scheme 1
:, -30°C to r.t.
CI’ CH3’
YRt
H
-
R’= CH3 (la), Ph (lb)
R = CH3 (2a), Ph (2b)
Table 1. Experimental Data for the X-ray Study of
Tp*(Cl)Nb[C(Ph)C(Ph)CHCH(CH~)]4)SCd-I~~ (2b) formula fw
cryst system space group a,
A
b, A c, A deg
PP
v,A’
Z
F(0W g“’ temp, K radiation
gcalcd.
cryst size, mm p, mm-l
v
c9
Y6 0 c19
Figure 1. ORTEP plot of 2b.
A;
A
[Nb-C(l) = 1.993(4) Nb=C = 2.026 in Cp*Nb(=CHPh)(NR)(PMe3)61,a single bond with C(4) CNbC(4) = 2.277(5) A; Nb-C = 2.316(8) A in Cp2Nb(CH2CH3)(C2H4)71,and with C(2) and C(3) unsymmetrically interacting with the metal center (Nb-C(2) = 2.334(4); Nb-C(3) = 2.370(5) A). The five-membered niobacycle is folded about the C(l)-C(4) axis (109.4(2)”).There is appreciable electron delocalization over the four-carbon chain although C(l)-C(2) is slightly longer than C(3)C(4) (1.439(7), 1.392(7) respectively). C(2)-C(3) (1.418(6)A) is, within 3a, similar to the two other C-C bond lengths. All of these carbons are sp2-hybridized but, taking also into account the reduced ~ J C of H 136 Hz,C(4) (Cd) retains some sp3 character. The bonding at C(4) is reminiscent of that in diene- (butenediyl) niobium complexes.8 Structural Discussion. Both the spectroscopic data for 2a,b and the crystallographic data for 2b are characteristic of a now well-known family of y4-butadi-
A,
(6) Cockcroft, J. K.; Gibson, V. C.; Howard, J. A. K.; Pool, A. D.; Siemeling, U.;Wilson, C. J. Chem. Soc., Chem. Commun. 1992, 1668. (7) Guggenberger, L. J.; Meakin, P.; Tebbe, F. N. J . Am. Chem. SOC. 1974,96, 5420. (8) Okamoto, T.; Yasuda, H.; Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N. J . Am. Chem. SOC.1988,110, 5008.
scan mode 28 m a , deg scan range, deg no. of rflns measd no of indep mns final no. of variables R” RWb
goodness of fit
“ R= X
HFoI
C35bBN6ClNb 687.94 monoclinic P24n (No. 14) 10.640(1) 14.539(2) 23.031(2) 102.38(1) 3480.0(8) 4 1436 1.313 293 graphite monochromated, A(Mo Ka) = 0.710 73 8, 0.40 x 0.40 x 0.30 0.42 w-28 48 0.80 0.35 tan e 5769 (0 5 h 5 12,O 5 k 5 16, -26 5 1s 26) 5455 (Ray= 0.025 on Z) 392 0.033 [3747 rflns with F2 > 3u(Fo2)1 0.034 (with unit weights) 1.175
+
- IFclIICIFoI. b R w = [ X W ( ~ I F ~ I - I ~ ~ I ~ ) ~ ~ ~ W / ~ ~ I ~
enyl (y4-C4R5)group 6 metal complexes as exemplified by the work of D a v i d ~ o n Green,lo ,~ Templeton,’l and their co-workers. Somewhat related (v3-butadienyl)niobium complexes have also been fully characterized.12 The three resonance forms shown in Scheme 2 nicely account for all of the data. The carbene-like Ca, the single bond between Nb and Cd, and sp3 character a t Cd are noteworthy. However, the data also fit with an heteroatomcontaining class of group 5 metal complexes as described more recently by Curtis and co-workers13and by some of us.14 These complexes are oxa- or azametallacycles (9) Carlton, L.; Davidson, J. L.; Ewing, P.; Manojlovic-Muir,L.; Muir, K. W. J. Chem. Soc., Chem. Commun. 1986, 1474. (10) (a) Conole, G. C.; Green, M.; McPartlin, M.; Reeve, C.; Woolhouse, C. M. J . Chem. Soc., Chem. Commun. 1988, 1310. (b) Green, M.; Mahon, M. F.; Molloy, K. C.; Nation, C. B. M.; Woolhouse, C. M. J .
Chem. SOC.,Chem. Commun. 1991, 1587. (11) (a) Morrow, J. R.; Tonker, T. L.; Templeton, J. L. J . A m . Chem. SOC.1986,107, 5004. (b) Feng, S. G.; Gamble, A. S.; Templeton, J. L. Organometallics 1989, 8, 2024. (12)(a) Herberich, G. E.; Hessner, B.; Mayer, H. J . Organomet. Chem. 1986,314, 123. (b) Herberich, G. E.; Mayer, H. Organometallics 1990, 9, 2655. (13) (a) Curtis, M. D.; Real, J. J . Am. Chem. SOC.1986, 108, 4668.
(b) Curtis, M. D.; Real, J.;Hirpo, W.; Butler, W. M. Organometallics 1990, 9, 66. (c) Hirpo, W.; Curtis, M. D. Organometallics 1994, 13, 2706. (14) Etienne, M.; White, P. S.; Templeton, J. L. Organometallics 1993,12,4010.
1872 Organometallics, Vol. 14, No. 4, 1995
Biasotto et al.
Scheme 2
Table 2. Fractional Atomic Coordinates and Isotropic or Equivalent Isotropic Temperature Factors (A2x 100) with Esd’s in Darentheses for 2b atomb
xla
Ylb
dC
Uq”l Uiw
0.58326(4) 0.6192(1) 0.4478(4) 0.5306(4) 0.6649(4) 0.7272(4) 0.8667(5) 0.4481(3) 0.5549(3) 0.7336(3) 0.4732(3) 0.5528(3) 0.7095(3) 0.5765(5) 0.3905(4) 0.3108(5) 0.3474(4) 0.3933(5) 0.2894(5) 0.5286(5) 0.5139(5) 0.5316(5) 0.5155(6) 0.5267(5) 0.8137(4) 0.9063(4) 0.8538(4) 0.8172(5) 0.9167(5) 0.3233(4) 0.2494(4) 0.1358(5) 0.0905(5) 0.1601(5) 0.2765(5) 0.4837(4) 0.5596(6) 0.5166(6) 0.3984(6) 0.3215(5) 0.3634(5) 0.5321(8) 0.7 118(8) 0.6707(5) 0.5849(13)
0.55177(33 0.39218i8j 0.5612(3) 0.5001(3) 0.5 173(4) 0.5932(4) 0.61 16(5) 0.5574(3) 0.7104(2) 0.5812(2) 0.61 lO(3) 0.7463(3) 0.6416(2) 0.6865(4) 0.5889(3) 0.5214(3) 0.5038(3) 0.6326(4) 0.4360(4) 0.8373(3) 0.8611(3) 0.7821(3) 0.8964(4) 0.7782(4) 0.6496(3) 0.5927(3) 0.5507(3) 0.71 17(4) 0.4803(4) 0.5983(3) 0.6470(3) 0.6879(4) 0.6792(4) 0.6300(4) 0.5902(3) 0.41 14(3) 0.3644(4) 0.2843(4) 0.2508(4) 0.2959(4) 0.3752(3) 0.5448(4) 0.6296(8) 0.5417(9) 0.5839(11)
0.80503(21 0.~2883(5 j 0.7307(2) 0.7068(2) 0.7195(2) 0.7495(2) 0.7580(3) 0.8680(1) 0.8146(2) 0.8932(2) 0.9 184(2) 0.8701(2) 0.9351(2) 0.9260(2) 0.9536(2) 0.925l(2) 0.8722(2) 1.0122(2) 0.8249(2) 0.8661(3) 0.8078(3) 0.7766(2) 0.9176(3) 0.7118(2) 0.9803(2) 0.9674(2) 0.9138(2) 1.0314(2) 0.8823(2) 0.7008(2) 0.7332(2) 0.7058(3) 0.6455(3) 0.6127(2) 0.6400(2) 0.6758(2) 0.6434(2) 0.6138(3) 0.6149(3) 0.6459(2) 0.6760(2) 0.4985(3) 0.5603(5) 0.5275(9) 0.5581(5)
4.06(21* 6.1 ii8 j* 4.6(3)* 4.8(3)* 5.5(3)* 5.5(3)* 9.4(5)* 4.5(2)* 4.7(2)* 4.6(2)* 4.6(2)* 4.8(2)* 4.3(2)* 4.7(3)* 5.3(3)* 5.9(3)* 4.9(3)* 7.6(4)* 6.8(3)* 5.9(3)* 6.7(4)* 5.7(3)* 9.1(5)* 7.6(4)* 4.4(3)* 4.9(3)* 4.9(3)* 6.3(3)* 7.7(4)* 4.6(3)* 5.4(3)* 6.8(4)* 6.7(4)* 6.3(3)* 5.6(3)* 4.9(3)* 7.1(4)* 8.6(5)* 7.9(4)* 6.8(4)* 5.7(3)* 20.7(7) 2 1.8(5) 19.7(9) 17.6(8)
“ Asterisk indicates Ue4= ’/i[UlI an occupancy factor of 0.5.
+ U22 +
431.
C(3s) and C(4s) have
where -0- or -NR- groups replace the -CH(CH3)group at the 6 position. Curtis has carefully analyzed this situation,13 and he has proposed a metallacyclopentatriene formulation akin to that found in some more symmetrical group 613bJ5and group 5 metal complexes.16 In this case, two resonance forms may be drawn as in Scheme 3.13 As we mentioned just above, the oxa- and azametallacycles may be viewed through both the y4-butadienyl (15) (a)Hirpo, W.; Curtis, M. D. J . A m . Chem. SOC.1988,110,5218. (b) Kerschner, J. L.; Fanwick, P. E.; Rothwell, I. P. J . A m . Chem. SOC.
1988,110,8235. (c) Kriley, C.E.; Kerschner, J. L.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1993,12,2051.
-
Table 3. Selected Bond Lengths (A) and Angles (deg) for Complex Tp*(Cl)Nb[C(Ph)C(Ph)CHCH(CHs)](2b) Nb-N(1) Nb-N(2) Nb-N(3) Nb-Cl Nb-C(1) Nb-C(2) Nb-C(3) Nb-C(4)
Bond Lengths 2.252(4) C(l)-C(2) 2.343(4) C( 1)-C(21) 2.339(4) C(2)-C(3) 2.396( 1) C(2)-C(27) 1.993(4) C(3)-C(4) 2.334(4) C(4k-W) 2.370(5) C(3)-H(C3) 2.277(5) C(4)-H(C4)
C( l)-Nb-C(2) C(l)-Nb-C(3) C( l)-Nb-C(4) C(2)-Nb-C(3) C(2)-Nb-C(4) C(3)-Nb-C(4) Nb-C( 1)-C(2) Nb-C(2)-C( 1) Nb-C(2)-C(3) C(l)-C(2)-C(3) Nb-C(3)-C(2)
Bond Angles 37.8(2) Nb-C(3)-C(4) 68.1(2) C(2)-C(3)-C(4) 87.0(2) C(2)-C(3)-H(C3) 35.1(2) C(4)-C(3)-H(C3) 65.9(2) Nb-C(3)-H(C3) 34.8(2) Nb-C(4)-C(3) 84.0(2) Nb-C(4)-C(5) 58.1(2) Nb-C(4)-H(C4) 73.9(3) C(3)-C(4)-C(5) 119.1(4) C(3)-C(4)-H(C4) 7 1.1(3) C(5)-C(4)-H(C4)
1.439(7) 1.459(6) 1.418(6) 1.508(6) 1.392(7) 1.479(7) 0.97(3) 0.97(3) 69.0(3) 126.4(5) 118(2) 114(2) 124(3) 76.3(3) 138.6(4) 83U) 124.5(5) 119(2) 109(2)
Scheme 3
and the metallacyclopentatrieneformulations. Actually, we propose that these heteroatom-containing complexes are bridges between the two descriptions, but again the data for 2a,b clearly point to the v4-butadienylformulation (Scheme 2). To our knowledge, 2a,b are the first compounds of this kind in niobium chemistry. The niobium has 16 valence electrons and, formally, the oxidation state is +3 (d2)or +5 (do)with the v4-butadienyl ligand giving 6 (monoanionicligand) or 8 (trianionic ligand) electrons. v3-Butadienyl complexes in the bent niobiocene series have been described by Herberich and co-workers:12the electron count for the metal is 18 with no interaction of the Cp-Cy bond with the niobium center (Nb-C = 2.78 and 2.79 A in a typical example,lZb(CpzNb[C(Et)C(Et)I
C(CO2Me)CH(COzMe)l. Mechanistic Consideration. Finally, we would like to briefly discuss a possible pathway for this “allylalkyne” coupling reaction. Recall first that (+allyl)niobium complexes are k 1 1 0 ~ n . l ~Although it is wellknown that allylic hydrogens are quite mobile via acidbase catalysis, rearrangement of an +allyl complex to (16)(a) Hessen, B.; Teuben, J. H. J . Organomet. Chem. 1989,367, Cl8. (b) Hessen, B.; Meetsma, A.; Van Bolhuis, F.; Teuben, J. H. Organometallics 1990,9, 1925. (17)For a recent example, see: Chemega, A. N.; Green, M. L. H.; Suarez, A. G. J . Chem. Soc., Dalton Trans. 1993,3031.
Five-Membered-Niobacycle Formation
Organometallics, Vol. Scheme 4
L
[Nb] = Tp*NbCI
1,3-H shift
H
an +vinyl complex (rearrangement of an vl-prop-2-ene complex to an 7'-prop-1-ene complex) prior to alkyne coupling is unlikely in this system since we have recently isolated18 the thermally stable (up to 353 K) complex Tp*Nb(Cl)(CPh=CEtz)(PhC=CCHg), containing 4e-donor alkyne and +vinyl ligands. In niobiocene complexes, coupling of Vl-vinyls with 2e-donor alkynes is known,12whereas v2-vinylscouple to 4e-donor alkynes in group 6 metal complexes.lg The required 1,3hydrogen shift could occur after allyl-alkyne coupling via C a attack at the coordinated alkyne carbon. In support of this proposal, we recently described a similar mechanism which accounts for alkyl group exchange between the alkyne and the niobium enter.^ A possible sequence of events is depicted in Scheme 4. The driving force for the 1,3-shift in a putative allyl-substituted q2vinyl intermediate would be the formation of a conjugated carbon chain.
Experimental Section General Methods. All reactions and workup procedures were performed under an atmosphere of dried dinitrogen using conventional vacuum line and Schlenck tube techniques. Toluene was dried and distilled by refluxing over sodiumbenzophenone under argon. n-Hexane was dried and distilled over CaHx under argon. These solvents were then stored over molecular sieves under a dinitrogen atmosphere. Column chromatography was performed on silica gel. Allylmagnesium chloride (2.0 M in tetrahydrofuran) was purchased. Benzeneds was stored over molecular sieves. IH NMR data were acquirred at 200 or 250 MHz, and 13C NMR data at 50.3 or 62.9 MHz. Elemental analyses were performed in the Analytical Service of our laboratory. Complexes Tp*h(Cl)[C(Ph)C(R)C(H)CHCH3] (2a,b) are synthesized according to the same procedure described in detail for 2a starting from the appropriate alkyne ~ o m p l e x . ~
Tp*~(Cl)[C(Ph)C(CH)C(H)CH(CHs)](2a). A vigorously stirred toluene (50 mL) solution of Tp*NbClz(PhC=CCHd (la)(0.580 g, 1.0 mmol) cooled to -30 "C is treated dropwise with allylmagnesium chloride (0.50 mL, 1.0 mmol). Slow warming to room temperature over 4 h gives an orange brown slurry. Concentration t o ca. 25 mL, addition of hexane (10 (18)Etienne, M.Unpublished result. (19) Templeton, J. L.Adu. Organomet. Chem. 1989,29, 1.
L
.H
I
mL), and filtration through Celite (subsequently rinsed with hexane three times) leads to an oil which is further purified by column chromatography. Elution with a 1:l (v) toluene/ hexane mixture gives a n orange solution, from which, after evaporation to dryness and recrystallization from a toluene/ hexane mixture at +5 "C, compound 2a is obtained as orange microcrystals in 25% yield (0.150 g; 0.25 mmol). lH NMR: S = 6.98-6.56 (m, 5H, C&), 5.76, 5.74,5.21(1H each, Tp*CH), 5.49 (d, J = 12.4 Hz, l H , CHCHCH3), 2.42 (d, J = 5.5 Hz, 3H, CHCHCHs), 2.80, 2.30, 2.22, 2.19, 2.18, 2.00, 1.17 (3H each, Tp*CH3 and 1.62 (pseudosextet, J = 12.3, 5.5 Hz, lH, CHCHCH3). 13CNMR (except phenyl resonances): 6 = 240.0 (NbC), 152.7, 152.2, 152.0, 144.6, 144.5, 140.5 (Tp*CCHd, 112.2 (d, JCH = 150 Hz, CHCHCH31, 108.7, 108.3; 108.0 (Tp*CH), 105.8 (NbCPhCCHs), 93.4 (d, JCH = 133 Hz, CHCHCHB), 20.8, 19.0, 17.4, 16.9, 16.8, 13.7, 13.3, 13.1 (CHCHCH3, p-CH3 and Tp*CH3). Anal. Calcd for C27H35BCINsNb: C, 55.7; H, 6.00; N, 14.4. Found: C, 55.8; H, 5.9; N, 14.9. 2b. 'H NMR: 6 = 8.18 (d, J = 7 Hz, 2H, NbCPhC-o-Cas), , (t, J = 7 Hz, 7.36 (t, J = 7 Hz, 2H, N b c P h C - m - C a ~ )7.21 lH, NbCPhC-p-C*5), 6.81-6.45 (m, 5H, NbCC&,), 5.86 (d, J = 12.5 Hz, l H , CHCHCH3), 5.75 (9, 2H, Tp*CH), 5.24 (s, lH, Tp*CH), 2.64, 2.30, 2.21, 2.09, 2.01, 1.18 (s, 3H each, Tp*CH3), 2.37 (d, J = 5.5 Hz, 3H, CHCHCHd, 1.75 (pseudosextet, J = 12.4,5.8 Hz, l H , CHCHCH3). 13CNMR (except phenyl resonances): 6 = 235.7 (NbC), 114.2 (NbCPhCPh), 153.2, 152.0, 151.9, 146.2, 142.4, 140.9 (Tp*CCH3), 108.8, 108.5, 108.2 (Tp*CH), 95.6 (d, J = 136 Hz, CHCHCH3), 20.7 (d, J = 127 Hz, CHCHCHd, 17.6, 17.1, 17.1, 13.6, 13.4, 13.0 (Tp"CH3). Anal. Calcd for C ~ Z H ~ ~ B C ~ N ~ N ~c. ,O61.1; .~C~H~~: H, 6.45; N, 12.2. Found: C, 61.7; H, 6.6; N, 11.8. One ofthese crystals was selected for the X-ray crystal study. X-ray Diffraction Study. Data collection, crystal, and refinement parameters are collected in Table 1. Diffraction measurements were made on a n Enraf-Nonius CAD4 diffractometer. The unit cell parameters were obtained from a leastsquares fit of 25 reflections (with 0 between 12.5 and 16").Data were collected with the 0-28 scan technique and a variable scan rate with a maximum scan time of 60 s per reflection. The intensities of three standard reflections were monitored every 2 h. No significant variations were observed. Lorentz and polarization corrections and empirical absorption corrections2O from yj scans were applied using the MolEN package,21 (20)North, A.C.T.; Phillips, D.'C.; Mathews, F. S. Acta Crystallogr., Sect. A, 1988, A21, 351. (21)Fair, C . K. MolEN. Structure Solution Procedures; EnrafNonius: Delft, Holland, 1990.
Biasotto et al.
1874 Organometallics, Vol. 14, No. 4, 1995 and the data were reduced to lFol values. The structure was solved by Patterson methods using the program SHEZXS86.22 Full-matrix least-squares refinement was made with the SHELX76 program.23 All non-H atoms of the complex were refined anisotropically. A disordered half solvent molecule (i.e. hexane) was found and refined isotropically. Solvent H atoms were not calculated. All other H atoms were geometrically placed, except those bonded t o C(3) and C(4) atoms which were isotropically refined. H isotropic thermal parameters were first refined and then kept fmed. The maximum shifts to esd ratio in the last full-matrix least-squares cycle were 0.129 for solvent and 0.004 for other parameters. The final difference Fourier map showed no peaks higher than 0.76 e A-3 near the (22) Sheldrick, G. M. SHELXS86. Program for Crystal Structure Solution; University o f Gottingen: Gottingen, FRG, 1986. (23) Sheldrick, G. M. SHEwT76. Program for Crystal Structure Determination; University of Cambridge: Cambridge, U.K., 1976.
disordered CeH14, nor any deeper than -0.57 e A-3. Atomic scattering factors were taken from ref 24. Crystallographic plot was made with ORTEP.25All calculations were performed on a MicroVax 3400.
Supplementary Material Available: Crystal structure data for 2b, including tables of hydrogen positional and thermal parameters, anisotropic thermal parameters, bond distances, bond angles, torsion angles, and least-squares plane equations (5 pages). Ordering information is given on any current masthead page. OM940992F (24) International Tables for X-Ray Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV. (25) Johnson, C. K. ORTEP. Report ORNL-3794; Oak Ridge National Laboratory: Oak Ridge, TN, 1965.
