Metallacyclohexasulfanes: the crystal and molecular structures of ( r 1 5 - ~ s ~ s ) 2 ~ ~ s , M = Zr and Hf

ALAN SHAVER AND JAMES M. MCCALL Department of Chemistry, McGill University, 801 Sherbrooke St. W., Montreal, Que., Canada H3A 2K6

AND

VICTOR W. DAY AND SARAH VOLLMER The Crystalytics Company, Lincoln, NE 68501, U.S.A., and Department of Chemistry, University of Nebraska,

Lincoln, NE 68588, U.S.A.

Received August 25, 1986'

ALAN SHAVER, JAMES M. MCCALL, VICTOR W. DAY, and SARAH VOLLMER. Can. J . Chem. 65, 1676 (1987). The crystal and molecular structures of ( T ~ ~ - C ~ H ~ ) ~ Z ~ S ~ , 2, and ( q 5 - C 5 ~ 5 ) ~ f S 5 , 3, have been determined by single crystal

diffractometry methods. Both compounds crystallized with four molecules in a monoclinic unit cell of dimensions: a = 8.984(3)A, b = 13.336(4)A,c = 11.421(2)A, P = 93.10(2)"for2, and a = 9.012(2)A, b = 13.291(2)A, c = 11.381(2) A, p = 93.25(1)" for 3; the space group is P21 /n for both. These crystals of 2 and3 are thus isomorphous with those of (CSH5)2TiS5, 1 , studied by Epstein et al. (3a). The structures of all three complexes are very similar consisting of a cyclohexane-like six-membered MS5 ring with two C5H5 rings attached to the metals in an axial and equatorial position. The coordination spheres of 2 and 3 are less crowded than that of 1 . The consequences of this are discussed with respect to the barriers to ring inversion in these complexes.

ALAN SHAVER, JAMES M. MCCALL, VICTOR W. DAY et SARAH VOLLMER. Can. J . Chem. 65, 1676 (1987). Utilisant des mCthodes de diffractomktrie sur des cristaux uniques, on a dktermink les structures cristallines et molCculaires des

composCs (T5-C5~5),ZrS5 (2) et ( T ~ ~ - c ~ H ~ ) , H ~ S ~ (3). Chacun des compo$s cristallise avec quatre molCcules dans une cellule unitaire monoclinique avec a = 8,984(3), b = 13,336(4) et c = 11,421(2) Aet P = 93,10(2)"pour lecomposk 2et a = 9,012(2), b = 13,291(2) et c = 11,381(2) A et P = 93,25(1)" pour le composC 3; dans chacun des cas, le groupe d'espace est P2 , /n . Les cristaux des composCs 2 et 3 sont donc isomorphes avec ceux du composC (C5H5)2TiS5 (I) ktudiC par Epstein et ses collaborateurs (3a). Les structures de ces trois complexes sont trbs semblables; elles comportent chacune un cycle i six chainons de MS5 qui adopte une forme semblable i celle d'un cyclohexane ainsi que deux cycles de C5H5 qui sont attachks aux mCtaux dans les positions axiale et Cquatoriale. Les sphbres de coordination des composks 2 et 3 sont moins encombrkes que celles du composC 1. On discute de ces rksultats en fonction des barrikres a l'inversion de cycle dans ces complexes.

[Traduit par la revue]

Introduction Recently a general method for the preparation of metalla-

cyclosulfanes (i.e. species of the type MS,) was reported (1). Treatment of the appropriate dichloro precursors with non- aqueous solutions of Li2S,, prepared in situ, gave the series Cp2MS5 and C P * ~ M S ~ , where M = Ti, Zr, and Hf, Cp = C5H5, and Cp* = C5Me5. The complex Cp2TiS5, 1, had been reported previously (2) and had been shown (3) to have a cyclohexane- like six-membered ring with axial and equatorial Cp rings. At room temperature ring inversion is slow on the nrnr time scale for the titanium complex (4); however, only upon cooling the zirconium, 2, and hafnium, 3, analogues it was possible to resolve two signals for their Cp rings (1). The X-ray structures of the latter two complexes have been determined in order to compare their structures to that of 1 seeking an explanation for their relative ease of ring inversion. The availability of these three complexes also provided an opportunity to compare the structures for the complete series.

Experimental Crystal data C ~ ~ H ~ ~ S 5 Z r fw = 381.7 Monoclinic, P21/n, a = 8.984(3), b = 13.336(4), c = 11.421(2), P=93.10(2), V = 1 3 6 6 . 3 A 3 , Z = 4 , p , = 1.86gcm-3,(MoKah= 0.71073 A, CL = 1 .SO mm-' (6a)). CIOHI oS5Hf fw = 468.9 Monoclinic, P2 ' /n , a = 9.012(2), b = 13.291(2), c = 11.382(2), P = 93.25(1), V = 1360.9 A3, Z = 4, p, = 2.29 g cmP3, (MoK, = 0.71073 A, CL = 8.77 mm-I (6a)).

Large-well shaped single crystals of 2 and 3 suitable for X-ray diffraction studies were obtained as previously described (I). Both

'~evision received February 27, 1987.

compounds crystallize in the centrosymmetric monoclinic space group P2'/n (an alternate setting of P 2 1 / ~ - C 2 h , NO. 14) (5). Intensity measurements were made on a computer-controlled Nicolet P1 autodiffractometer for a spherical specimen of 2 which had a diameter of 0.69 mm (p,r = 0.52) and an irregularly shaped crystal of 3 . Intensity measurements for both compounds utilized graphite-mono- chromated MoKa radiation and full (1 .O0) wide w scans and gave a total of 5096 independent reflections having 2eMoKu < 71 .oO for 2 and 4663 reflections having 2eMoKa < 63.7O for 3. For all reflections of 2 a scanning rate of 3" min-' was employed for the scan between w settings 0.50" above and below the calculated K a doublet value (A = 0.71073 A). Similar scans for those reflections of 3 having 2eMoKa < 43" utilized a scanning rate of 4" min-I while a scanning rate of 3" min-' was used for all the other reflections. Each 1.0" scan of both compounds was divided into 19 equal time intervals, and those 13 contiguous intervals which had the h&hest single accumulated count at their mid~oint were used to calculate the net intensitv from scanning. ~ a c k ~ r o i n d counts, each lasting for one-half (2) or bne-fourth (3) of the total time used for the net scan (13119th~ of the total scan time), wefe measured at omega settings 1 .OO above and below the calculated K a doublet value for each reflection. Since the absorption of X-rays by a spherical crystal having p r = 0.90 is virtually independent of scattering angle (7), the data for 2 were not corrected for absorption. The intensity data of 3 were corrected empirically for variable absorption using x scans for five reflections having 20 values between 1 lo and 31".

The non-hydrogen atoms of 2 were located using Patterson and difference Fourier techniques, and those of the isomorphous hafnium compound, 3, were derived from the parameters of 2. Atomic positions were calculated for all hydrogens of both compounds assuming sp2 hybridized geometry for the cyclopentadienyl carbons and a C-H bond length of 0.95 A. The non-hydrogen parameters initially used for these calculations were those resulting from the full-matrix least-squares refined model (R, (8) (unweighted, based on F) = 0.029 and 0.035 for 2 and 3 respectively) which incorporated

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SHAVER ET AL.

TABLE 1. Atomic coordinates for non-hydrogen atoms in crystalline (CSH5)2ZrS5r 2, and (CsHs)2HfS5,3"

Fractional coordinates Equivalent isotropic tom^ thermal parameter,' tY Pe lo4 lo4 lo4 B, A'

"Numbers in parentheses are the estimated standard deviations in the last significant digit. *For each atom type, the coordinates are reported in two lines corresponding to complexes 2 and 3,

respectively. Atoms are labeled in agreement with Figs. 1 and 2. 'This is one-third of the trace of the orthogonalized B , tensor.

unit-weighting and anisotropic thermal parameters for all non-hydrogen atoms and reflections having 20,,,, < 43" and I > 3u(I) . They were periodically updated. The R values are defined as RI = C I IFoI - IFCII/CIF,l and R2 = {Zw(l FoI - l ~ , l ) ~ / C w l F , I ~ } ~ / ~ , where w is the weight given each reflection. The function minimized is Cw (IFo I - KI Fc I)2, where K is the scale factor. All structure factor calculations for both compounds employed recent tabulations of atomic form factors (66) and an anomalous dispersion correction (6c) to the scattering factors of the Hf, Zr, and sulfur atoms. A least-squares refinable extinction correction (8) of the form 1/(1 + glc)ll ' was employed for structure factors of 2. A careful examination of the final Fo and Fc values for 3 indicated the absence of extinction effects. The final cycles of empirically-weighted' full-matrix least-squares refinement which employed isotropic thermal parameters for fixed hydrogen atoms and anisotropic thermal parameters for all other atoms converged to values of 0.029 and 0.036 for Rl and R2 (weighted, based on F), respectively, for 4465 independent reflections of 2 having

2eMoKa < 71.0° and I > 3u(I ) . Similar refinement cycles for 3 gave RI = 0.037 and R2 = 0.045 for 3635 independent reflections having 2eMoKa < 63.7' and I > 3u(I ) . Hydrogen atom parameters were not varied for either 2 or 3.

Results and discussion The final atomic coordinates for the non-hydrogen atoms of 2

and 3 are presented with estimated standard deviations in Table 1 . 3 A perspective ORTEP drawing illustrating the numbering scheme is given in Fig. I . The crystals of 2 and 3 used in this study are isomorphous with the crystal of 1 studied by Epstein et al. ( 3 a ) . The volume of the unit cells follow the expected order Ti < Hf < Zr. The volumes for the isostructural and isomorphous indenyl series ( - q 5 - ~ 9 ~ 7 ) 2 M ( C H 3 ) 2 , M = Ti, Zr, and Hf followed the same order; this has been attributed to the lanthanide contraction effect (9).

7

2~mpirical weights were calculated from the equation p = ga,, I Fo I " = 0.548 - (2.23 X F,I + (1.00 x 10-4)IF,,l' for 2 and u = 3 za,,lFOln = 1.91 - (1.66 X I O - ~ ) I F ~ I + (2.36 X I O - ~ ) I F , I ' - (4.94 X 10-8)1~,13, the a,, being coefficients dfrived from the least-square fitting of the curve I l FoI - I FcI I = za,,l F0In, where Fc values were calculated from the fully refined model using unit weighting and an I > 3u(I) rejection criterion.

3~rystal structure analysis reports for 2 and 3, Fig. 2 (ORTEP drawing of 3), Table 2 (anisotropic thermal parameters for the non- hydrogen atoms of 2 and 3), Table 3 (hydrogen atom coordinates for 2 and 3), Table 5 (bond lengths and angles about the non-hydrogen atoms of the cyclopentadienyl rings in 2 and 3), Table 7 (structure factors for 2), Table 8 (structure factors for 3), (56 pages) may be purchased from the Depository of Unpublished Data, CISTI, National Research Council of Canada, Ottawa, Ont., Canada KIA OS2.

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CAN. J . CHEM. VOL. 65 , 1987

TABLE 4. Bond lengths (A) and angles (deg) subtended at the metal and sulfur atoms in crystalline (CsHs)2MSs, where M = Ti, 1; Zr, 2; and Hf, 3"

Typeb 1' 2 3

M-S I

M-SS M-S (averaged)

M-Cal M-C a2

M-C a3

M-Ca4 M-Cd M-Cbl M-Cb2 M-C b3 M-CM M-Cb5 M-C (averaged)

M-C,,' M-CEbe M-C, (averaged)

SI-S2 s2-s3

s3-s4

s4-ss S-S (averaged)

SI. . .SS s2 . . .s4

SlMSs

CgaMCgbe

MSlS2 MSsS4 MSS (average)

slS2s3 s2s3s4

S3S4S5 SSS (average)

Bond lengths, A 2.448 (1) 2.544 (1) 2.422 (1) 2.526 (1) 2.435(1, 13, 13,2) 2 .535(1 ,9 ,9 ,2)

2.376 (4) 2.514 (3) 2.374 (4) 2.502 (3) 2.367 (4) 2.489 (3) 2.388 (4) 2.515 (3) 2.398 (4) 2.523 (2) 2.392 (5) 2.513 (3) 2.380 (6) 2.503 (3) 2.348 (5) 2.472 (3) 2.341 (6) 2.467 (3) 2.370 (6) 2.487 (3) 2.373 (5, 14, 32, 10) 2.499(3, 16, 32, 10)

2.066 (-) 2.216 (-) 2.071 (-) 2.206 (-) 2.069(- ,3,3,2) 2.211(- ,5,5,2)

2.059 (2) 2.059 (1) 2.056 (2) 2.048 (1) 2.067 (2) 2.057 (1) 2.059 (2) 2.057 (1) 2.060 (2, 3, 7, 4) 2.055 (1, 4, 7, 4)

3.58 3.82 3.31 3.30

Angles, deg 94.6 (1) 97.8 (1)

133.7 (-) 131.3 (-1 107.4 (1) 102.7 (1) 108.6 (1) 103.7 (1) 108.0 (1, 6, 6, 2) 103.2 (1, 5, 5, 2)

105.2 (1) 106.7 (1) 106.7 (1) 107.0 (1) 102.7 (1) 104.2 (1) 104.9 (1, 14, 22, 3) 106.0 (1, 12, 18, 3)

110.7 (-1 111.7 (-) 11 0.7 (-) 111.2 (-)

100.5 (-) 100.2 (-) 99.6 (-) 99.1 (-)

"Numbers in parentheses following individual entries are the estimated standard deviations in the last significant digit.

bAtoms are labeled in agreement with Figs. 1 and 2. 'The data given for 1 were taken or calculated from ref. 3a. dSee footnote 4. 'The least-squares mean planes for the following groups of atoms in 2 and 3 are defined by the equation:

aX + bY + cZ = d where X, Y, and Z are orthogonal coordinates measured along a, b, and c * , respectively, ofthecrystalsystem: (a ) Gal, Ca2, Ca3, Ca4, andCaSfor2, a = 0.287; b = -0.707, c = 0.646, d = 1.947; (b) Cbl, Cbz, Cb3, C ~ J , andCbs f0r2, a = 0.505, b = 0.809, C = -0.302, d = 3.563; (c) C,,, Zr, andCgb, a = -0.402, b = 0.526, c = 0.749, d = 3.341; ( d ) S t , Zr, and Ss, a = 0.257, b = 0.856, c = -0.449, d = 1.128;(e)S1, SZ, S4, andS5for2, a = 0.624, b = -0.419, c = 0.660, d = -0.934;(f)S2, S3, andS4 for 2, a = 0.454, b = 0.830, c = -0.324, d = -0.987; ( g ) Gal, Ca2, Cn3, C,,, and CnS for 3, a = 0.282, b = -0.709, c = 0.646, d = 1.943; ( h ) C b l , Cb2, Cb3. Cb4, and Cbs for 3, a = 0.504, b=0.811 , c = -0.298, d = 3.548;(i)C,,,Hf,andCgb, a = -0.383, b =0.538, c =0.751, d = 3.355; ( j ) S I , Hf, and Ss, a = 0.257, b = 0.855, c = -0.450, d = 1.105; (k ) S , , S2, S4, and Ss for3, a = 0.622, b = - 0 . 4 2 2 , c = 0 . 6 6 0 , d = - 0 . 9 1 7 ; ( 1 ) S 2 , S 3 , a n d S 4 f o r 3 , a = 0 . 4 5 1 , b = 0 . 8 3 0 , c = - 0 . 3 2 7 , d = - 1.008; where C,, and Cgb refer to the center of gravity of the five membered rings of the cyclopentadienyl rings of a and b, respectively.

jThis is the dihedral angle between the least-square mean planes through the two groups of atoms listed.

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SHAVER ET AL. 1679

C

53 FIG. 1. A perspective ORTEP drawing of (r15-C5H5)2ZrSS, 2,

showing the atom labelling scheme used for 2 and 3. A similar drawing of 3 is shown in Fig. 2. (see footnote 3). All nonhydrogen atoms are represented by thermal vibration ellipsoids drawn to encompass 50% of the electron density; hydrogen atoms are represented by arbitrarily- sized spheres for purposes of clarity.

All three compounds 1, 2, and 3 are isostmctural being discrete, mononuclear Cp2MX2 species in which the metal ions adopt the familiar pseudotetrahedral "bent sandwich" configuration. The X groups in these cases are the terminal atoms of the bidentate pentasulfide chain thus forming a six-membered ring which adopts a chair conformation. The molecules approximate C,-m point symmetry with the idealized mirror plane passing through the two Cp ring centroids (C,, and Cgb), the metal atom and the central sulfur atom (S,). Selected bond lengths and angles about the metal and sulfur atoms in 1,2 , and 3 are given in Table 4. The bond lengths and angles for the non-hydrogen atoms of the cyclopentadienyl rings in 2 and 3 are given in Table 5.3 -

Parameters describing the Cp2M portion of the coordination spheres of 2 and 3 differ little from those of 1 and correspond well with other group IVB Cp2MX2 moieties. The average metal-to-carbon bond distances for 2 and 3 (2.499(3,16,32,10)~ A for 2 and 2.477(10,17,32,10) A for 3) are about 0.12 A larger than the average (2.376(1) A) for 1; this is consistent with the approximately 0.12 A smaller covalent radius of titanium. These distances correspond closely with other group IVB Cp2MX2 species for a variety of X ligands and cyclopentadienyl ligands (9) wherein the metal-to-carbon distances are remark- ably constant for each metal. In 2 and 3, the five carbon atoms o! the cyclopentadienyl ligands are coplanar to within 0.005 A and those carbon atoms nearest the sulfur atoms are slightly but significantly further from the metal atom. This was also

4 ~ h e first number in parentheses following an averaged value of a bond length or angle is the root-mean-square estimated standard deviation of an individual datum. The second and third numbers, when given, are the average and maximum deviations from the averaged value, respectively. The fourth number represents the number of individual measurements which are included in the average value.

TABLE 6. Intramolecular nonbonded contacts in crystalline ( C S H S ) ~ Z ~ S ~ , 2

Type" Distance, A Typea Distance, A

Zr . . .S3

"Atoms are labeled in agreement with Figs. 1 and 2 and Tables 1-3.

observed for 1 (3a) and probably reflects the steric bulk of the pentasulfido-ligand.

The plane determined by the metal atom and the two cyclopentadienyl ring centers intersects the plane of the metal, S , and S5 atoms in dihedral angles of 90.5", 90.6", and 90.8" for 1; 2, and 3, respectively. ow ever, the bidentate sulfur ligand is displaced from the "equatorial girdle" (the plane passing through the metal and bisecting the C,,-M-Cgb angle) towards the ring b such that the intramolecular contacts between ring b and S1 and S5 atoms are considerably shorter than those for ring a (Table 6). This distortion has been previously noted (3a) for 1 and was attributed to a combination of steric repulsions between the axial cyclopentadienyl ring (a) and the sulfur atoms S2 and S4 and attractive interactions between ring b and sulfur atoms S I and S5. These contacts provide a structural rationale for the novel migration of one of the cyclopentadienyl rings in 1 to the sulfur ligand as observed by Giolando and Rauchfuss (lo).

In 2 and 3 t h ~ sulfur atoms S, , S,, S4, and S5 are coplanar to within 0.01 A. The dihedral angles for the pairs of planes SIMS5/S1S2S4S5 and S1S2S4S5/S2S3S4 are similar (Table 4) and indicate similar MS5 ring shapes. The shortest S-S bond length is the S2-S3 bond in all three compounds. Although the S,-S, and S4-S5 bond lengths are equal within experimental error in 1 , 2 , and 3, the two M-S bonds and the central S2-S3 and S3-S4 bonds are unequal in length. In each case the longer M-S, bond is opposite the longer S,-S4 bond, and the shorter M-S5 bond lies opposite the shorter S2-S3 bond. Unequal Ti-S distances were also fqund for c ~ , T i ( s P h ) ~ (1 1) which are on average shorter (2.410 A) than the average Ti-S

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168G CAN. J . CHEM. 1 'OL. 65, 1987

distance in 1. The inequality of S-S bond lengths found in 1 ,2 , and 3 was also observed in Cp2VS5 (3b) and in Cp2WS4 (12). Thesalts M2'S5 (MI = NH4 (13), K (14), Rb (IS), Tl(16) which contain discrete S52- chains, also displayed a variation in bond lengths. For the rubidium salt the two inner bond lengths were 2.054(8) A and 2.109(7) A , and the two outer bond lengths were 2.019(7) A and 2.036(8) A with the longest S-S bond adjacent to the shortest S-S bond. The S-S bonds in the Cp2MS5 molecules, with the exception of the short S2-S3 bonds, are all longer than those found in Rb2S5. Cyclohexasulfur, S6, crystallizes in the chair ~onformation with all S-S bond lengths equal at 2.068(2) A (17). This distance is m!rginally greater than the average S-S distances of 2.060 A for 1, 2.055 A ( 1 , 4, 7, 4) for 2, and 2.059 A (3, 8, 17, 4) for 3, respectively. The S-S-S angles are larger in the Cp2MS5 molecules than those in S6 (102.61(6)") (17). The non-bonded trans-annular sulfur-sulfur distances S , . . .S5 follow the order Ti < Hf < Zr, consistent with the trend in the SI-M-S5

M =Ti, Zr, Hf

angles, and the M-S bond distances; however the S2. - .S4 distances are nearly the same. The "end-to-end" M. - .S3 distances in the 2 and 3 are only slightly shorter than for 1.

Clearly the structures of 1 ,2 , and 3 are quite similar with any significant differences being attributed to differences in the size of the metal atoms. Given this close similarity, the differences observed for their barriers to ring inversion (kJ mol- ' : 76.3, 1 (4b); 48.6, 2 (1); 58.0, 3 (1)) might initially seem surprising. However, while the coordination spheres of all three com- pounds are sterically quite conjested, that of 1 is more conjested than those for 2 and 3 due to the smaller covalent radius of titanium. If the non-bonded contacts between the cyclopentad- ienyl rings and the sulfur atoms were due, at least in part, to attractive forces, then the MS5 ring in 1 might be expected to have a higher barrier to ring inversion than those in 2 and 3. Consistent with this, it was found (1) that reducing the cyclopentadienyl ring - sulfur interaction by "tying-back" the C5 rings with a bridging methylene group in CH2(C5H4)2TiS5 lowered the barrier to 66.5 kJ mol- ' (the CgTiCg angle is 121"

in CH2(C5H4)2TiC12(18) and 13 1" in Cp2TiC12 (19)). Finally it is noted that the structures of 1, 2, and 3 are clearly different from that of (C5Me5)2ThS5 which contains a twist-boat confor- mation of the ThS5 ring with a 1,2,4,5-tetrahapto S5 ligand (20).

Acknowledgements This research was supported by grants from the Natural

Sciences and Engineering Research Council of Canada, the Quebec Department of Education, and Imperial Oil Co. of Canada. Predoctoral fellowships awarded to J.M.M. by NSERC and the Noranda Group of Companies are gratefully acknow- ledged.

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Chern. 26, 229 (1971); ( b ) E. G. MULLER, J . L. PETERSEN, and L. F. DAHL. J. Organornet. 111, 91 (1976).

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7 . International tables for X-ray crystallography. Kynoch Press. Birmingham, England. Vol. 11. 1967. p. 302.

8. H . H . ZACHARIASEN. Acta Crystallogr. 23, 558 (1967). 9 . ( a ) J . L. ATWOOD, W. E. HUNTER, D. C. HRNCIR, E. SAMUEL,

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