Organometallics 1995, 14, 4776-4780
4776
Crystal Structures of Chiral Halo{24 l-(S)-(dimethylamino)ethyl]phenyl-C1~mercury(II) Complexes Saeed Attar and John H. Nelson* Department of Chemistry, University of Nevada, Reno, Nevada 89557-0020
Jean Fischer Cristallochimie et de Chimie Structurale (URA424 CNRS), Universiti Louis Pasteur, F-67070 Strasbourg Cedex, France Received January 11, 1995@
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The reaction of HgClz with enantiomerically pure o-lithio-(S)-(-)-dimethyl(l-phenylethy1)n amine, (S)-ArLi, results in good yields of (S)-{H~C~[C~H~CH(M~)NM~Z~}, 2a. The bromide
(2b) and iodide (2c) analogs were prepared by metathetic reactions of 2a with NaBr and NaI, respectively. Single-crystal X-ray crystallographic data on all three complexes show that the Hg atom in each is nonplanar with three different groups bonded to it, making it a stereocenter. Thus, with the chiral benzylic carbon of the chelating amine ligand having the (S)absolute configuration, these complexes form as only the (S)C(R)H,diastereomers. Introduction Organomercury(I1) compounds of the type RHgX or h H g (R = alkyl or aryl; X = halide) have received a lot of attention for the past two decades, and a large number of them are kn0wn.l Among the reasons for this attention are the continuing search for pharmacologically active drugs and simple preparations of organomercury compounds, the latter being related to their remarkable stability to air and water which in turn engenders them with utility as versatile synthetic agents. We have utilized the mercury(I1)chloride complex 2a, designated (S)-ArHgCl, as a very convenient starting material in the syntheses of chiral ruthenium halfsandwich compounds.2 Van Koten and co-workers3 proposed structures 1 and 2a for CDCl3 solutions of this
N
/
'3
'CH3
compound a t room temperature and -70 "C, respectively. Compounds 2a-c are among the few examples of three-coordinate Hg in organometallic complexes. In this note, we raise the possibility, for the first time, that Hg may be considered a stereocenter in the solid state @
Abstract published in Advance ACS Abstracts, September 15,1995.
(1)(a) Brodersen, K.; Hummel, H.-U. In Comprehensive Coordina-
tion Chemistry; Wilkinson, G., Gillard, R., McCleverty, J. A,, Eds.; Pergamon Press: Oxford, 1987; Vol. 5, pp 1047-1097. (b) Wardell, J. L. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 2, pp 863-978. (c) Wardell, J . L., Ed. Organometallic Compounds of Zinc, Cadmium and Mercury; Chapman and Hall New York, 1985; pp 11130. (d) Eller, P. G.; Bradley, D. C.; Hursthouse, M. B.; Meek, D. W. Coord. Chem. Rev. 1977,24, 1. (e) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon Press: Oxford, 1984; p 1408. (2)Abbenhuis, H. C. L.; Pfeffer, M.; Sutter, J.-P.;de Cian, A.; Fischer, J.; Ji, H.-L.; Nelson, J. H. Organometallics 1993, 12, 4464. (3) Van der Ploeg, A. F. M. J.;van der Kolk, C. E. M.; van Koten, G. J. Organomet. Chem. 1981,212, 283.
on the basis of the X-ray crystallographic evidence presented below.
Results and Discussion Complex 2a was obtained in 81% yield via a slight modification of the procedure reported by Osman et aL4" for the preparation of RzM and RMCl compounds (R = NJV-dimethylbenzylamine; M = Zn, Cd). We have consistently obtained yields of 75%-81% in our preparations of 2a and its (R)-(+)-analog. By way of comparison, van Koten and co-workers report3 that treatment of (SI-ArLi with HgClz gave metallic mercury, but pure 2a was obtained from the reaction of HgClz with (SI-ArCu. It should be noted that attempts to prepare 2a via the reaction of (S)-(-)-dimethyl(1-phenylethy1)amine with mercury(I1) acetate in the presence of LiCl, as reported by Huo et al.,5c,d yielded only trace amounts of 2a. The bromide (2b) and iodide (2c) analogs were prepared in similar yields (280%) by metathetic reactions of 2a with NaBr and NaI, respectively. X-ray crystal structures of the three halide complexes 2a-c show similar features (Tables 1 and 2). The structure of the chloride analog 2a (Figure 1)is repre(4) (a) Osman, A.; Steevensz, R. G.; Tuck, D. G.; Meinema, H. A.; Noltes, J. G. Can. J. Chem. 1984, 62, 1698. (b) (S)-(-)-Dimethyl(1phenylethyllamine, (SI-ArH, was obtained via the Eschweilermethylation of the commercially available (S)-(-)-l-phenylethylamine. ( c )Cope, C. A.; Ciganek, E.; Fleckenstein, L. J.;Meisinger, M. A. P. J.A m . Chem. Soc. 1960,82,4651. (d) Clarke, H. T.; Gillespie, H. B.; Weisshaus, S. Z. J. Am. Chem. SOC.1933, 55, 4571. (5) (a) Huheey, J. E. Inorganic Chemistry, 3rd ed.; Harper & Row: New York, 1983; pp 258-259. (b) Pakhomov, V. I. J. Struct. Chem. (Engl. Transl.) 1963,4, 540. (c) Huo, S. Q.;Wu, Y. J.; Zhu, Y.; Yang, L. J. Organomet. Chem. 1994, 470, 17. (d) Ibid. 1994,481, 235. (e) Hawkins, C. J. Absolute Configuration ofMetal Complexes; Wiley: New York, 1971; Chapter 1. (0 For pertinent discussions see: van der Schaaf, P. A.; Boersma, J.; Kooijman, H.; Spek, A. L.; van Koten, G. Organometallics 1993, 12, 4334. Jiang, Q.;Ruegger, H.; Venanzi, L. M. J. Organomet. Chem. 1996,488, 233. (g) Atwood, J. L.; Berry, D. E.; Stobart, S. R.; Zaworotko, M. J . Inorg. Chem. 1983,22, 3480. (h) Canty, A. J.; Deacon, G. B. Inorg. Chim. Acta. 1980, 45, L225. (i) Canty, A. J.; Gatehouse, B. M. J.Chem. Soc., Dalton Trans. 1976,2018. (j) Canty, A. J.; Marker, A.; Barron, P.; Healy, P. C. J. Organomet. Chem. 1978, 144, 371.
0276-7333/95/2314-4776$Q9.0Q/Q0 1995 American Chemical Society
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Organometallics, Vol. 14, No. 10, 1995 4777
and HgBrz (2.48 &.le The Hg-I distance of 2.622(1)A in 2c may be compared with that reported for HgIz (2.78 &,le although the latter distance corresponds t o sixX = Cl(2a) X = Br (2b) X = I (2c) coordinate Hg(I1); this distance has not been reported formula CloH14NClHg CloHlrNBrHg CloH14NIHg for PhHgI.5b The YHg-X values for 2a-c (322,234, and fw 384.29 428.74 475.74 cryst syst orthorhombic orthorhombic orthorhombic 170 cm-l, respectively)are comparable to those reported 5.880(1) 5.892(1) 5.937(1) a (A) for the PhHgX complexes (320, 259, and 170 cm-l, 13.318(4) 13.410(4) b (A) 13.344(4) respectively,6 indicating similar Hg-X bond strengths 14.905(4) 15.209(4) c (A, 14.716(4) in the two series. The Hg-C1 distances in 2a-c are 1169.5 1210.9 v (A3) 1154.6 similar [2.04(1),2.07(1), and 2.02(1)A, respectively], are z 4 4 4 p212121 P212121 P212121 all slightly shorter than the normal range for a mercury0.7107 0.7107 0.7107 *OUP carbon bond(2.05-2.10 A),1a and may be compared to 2.435 2.609 ecalcd (g cm-9 2.210 those reported for { [(PhCH2NMe~)-C1,i'VlzHg}(2.10(2) y (cm-l) 135.2 165.0 151.95 AI59 and for the (ferrocenylimine)mercury(II)chloride abs m i d m a x 0.48/1.00 0.63/1.00 0.49l0.99 complexes mentioned above (2.016 8, for R = H5cand R(F)" 0.028 0.036 0.033 RW(mb 0.042 0.051 0.049 2.037 A for R = CH35d).The Hg-C1 distance in 2b L2.07(1)AI may be compared with that reported for PhHgBr " R O = U F o I - l F c l ) E ( l F o l ) . * R w O = [ k ~ ( l F o l - IFcl)2/ (2.08 A).5b The similar Hg-N distances in 2a-c [2.65CwIFc12]1'2; w = l/u2(F)2 = &counts) + (pn2. (l), 2.64(2), and 2.63(1)A, respectively) are considerably sentative. For 2a-c, four molecules are packed in an shorter than the sum of the van der Waals radii for Hg orthorhombicunit cell, in the noncentrosymmetric space (1.50 &"9gsh and N (1.55 A)5a,iand may be compared to group P212121. The intermolecular interactions in the such values as 2.89 A reported for {[(PhCHzNMedlattice are those of Hg-X between two adjacent molC1JVl~Hg}5gand 2.897 A (R = HPc and 2.766 A (R = ecules a t 3.1 (X = Cl), 3.4 (X = Br), and 3.8 A (X = I). CH3)5dfor the ferrocenylimine compounds. According These distances are not significantly different from the to the criteria suggested by Canty et al.,5h1ithe Hg-N sum of the van der Waals radii5" for Hg (1.50 A) and distances in 2a-c certainly constitute bonding (albeit that for each of the three halide atoms: C1 (1.70-1.90 weak) interactions. A), Br (1.80-2.00 A), and I (1.95-2.12 A). Thus, no The lability of the Hg-N bond is indicated by the intermolecular Hg.0.X bonding interaction may be contemperature dependence of the NMez resonances in the stituted here. The intermolecular Hg-X distances lH- and 13C-NMRspectra of (CD3)zCO solutions of 2aobtained in our work compare well with those calculated c. At 25 "C, only one resonance is observed for the C (6 for the three PhHgX complexes from their powder 42.6) and H (6 2.29) nuclei of the NMez group which is diffraction patterns:5b 3.4 (X = Cl), 3.5 (X = Br), and possible only if the Hg-N bond is cleaved (structure 1) 3.6 8, (X= I). in solution at ambient temperatures so that the two Me Selected structural parameters for the three comgroups become equivalent through rotation about the plexes are presented in Table 2. A literature search1 N-C7 bond, leading to pyramidal inversion of the N reveals that the structures of 2a-c represent the first atom. However, a t temperatures below -70 "C, two examples of diastereomeric Hg(I1) complexes (vide inequally intense resonances are observed for both nuclei fra). The coordination geometry around Hg is best (13C 6 40.9, 44.5; 'H 6 2.16, 2.53), indicating the described as T-shaped, the preferred geometry in almost nonequivalence of the two N-methyl groups due to all cases where such three-coordination has been blocked inversion of the N atom which results from its observed.ld The five-membered chelate ring consisting coordination t o Hg.3 The lg9Hg6 values (neat MezHg of atoms Hg-N-C7-C6-C1 has the expected envelope ref) for 2a-c are -948.9, -1058.7, and -1246.6 ppm, (puckered) c~nformation.~" Of the two enantiomeric respectively. The increased shielding of this signal (2a envelope conformations that arise from the folding along 2b < 2c) may be explained in terms of decreased the Hg.*.C7 line for molecules such as these, only the electronegativity of the halide (C1 Br > I), making one that minimizes the interactions between the two the Hg-X bond more covalent. In the variable temperN-methyl groups and the C-methyl group is observed. ature (VT)lg9Hg NMR spectra of compound 2a (in For the three compounds, the dihedral angles between acetone-d6) only a single, broad resonance is observed, the Hg-Cl-C6-C7 and Hg-N-C7 planes are 137.0which progressively shifts upfield with decreasing tem(6) (2a), 138.2(9) (2b),and 134.2(9)" (2c). In all three perature (from -948.9 ppm a t 25 "C to -1009.5 ppm at compounds the a-methyl group is located equatorially -90 "C). This result is in agreement with a previous nearly in the plane of the phenyl ring. This methyl observation5Jthat for unidentate and bidentate ligands group orientation has been observed for about half the for similar basicity (e.g., pyridine and bipyridine), compounds containingthe {M-o-aryl-CH(Me)NMez}fragchelation with bidentate ligands to give three-coordinate ment found in the Cambridge Structural Data Base.5f Hg results in upfield shifts of lg9Hg6 relative to those The Hg-C1 distance of 2.323(3) A in 2a is comparable of linear complexes, indicating increased shielding of the to others reported, e.g., 2.25 A in HgClz,le 2.364 8, in Hg center. The broadness of the lg9Hgresonances (AWZ dichloronicotinemercury(II),laand 2.296 and 2.390 A for = 100 Hz) may, however, be indicative of a very lowthe recently reported mercury(I1) chloride complexes of energy dynamic process attributable to the pyramidal n inversion of the Hg atom as a stereocenter in 2a-c. It ferrocenylimines { (C~H~)Fe[C~H4C(R)=NArHgCll} (R = should be noted, however, that it is difficult t o draw I conclusions since lg9Hg chemical shifts are H, Ar = O - C ~ H ~ O C and HR ~~ =~Me, Ar = o - C ~ H ~ C ~ ~definite ~), respectively. The Hg-C1 distance in PhHgCl has not (6)(a) Barraclough, C. G.; Berkovic, G. E.;Deacon, G. B. Aust. J. been reported, as the authors faced difficulty r o w i n g Chem. 1977,30, 1905. (b) Green, J. H. S. Spectrochim. Acta 1968, crystals.5b The Hg-Br distance of 2.451(2) in 2b 24A,863. (c) Goggin, P. L.; McEwan, D. M. J.Chem. Res., Syrwp. 1978, 171. compares well with those reported for PhHgBr (2.43A)5b
Table 1. Crystallographic Data for [(S)-ArHgXl Complexes 2a-c
ET;
4778 Organometallics, Vol. 14, No. 10,1995
Attar et al.
Table 2. Selected Structural Parameters for Complexes 2a-c bond lengths Hg-X Hg-Cl
X C1
2.323(3) 2.451(2) 2.622(1)
Br I
2.04(1) 2.07(1) 2.02(1) 2.04(2)
av
(A) Hg-N
X-Hg-CI
2.65(1) 2.64(2) 2.63(1) 2.64(2)
174.2(3) 173.8(4) 174.0(3) 174.0(4)
bond angles (deg) X-Hg-N Cl-Hg-N 106.0(3) 104.9(3) 104.1(3) 105.0(3)
C4
C8
c10
I/
c1
Figure 1. ORTEP drawing of [(S)-ArHgClI(2a),showing the atom-numberingscheme (50%probability ellipsoids). highly temperature and medium dependent, even for compounds that are inert toward coordination by donor molecules. The optical activities of 2a-c were determined by obtaining their room-temperature W-vis and CD spectra (in EtOH) in the 200-300 nm region, which corresponds t o n-n* transitions of the aryl (benzene) chr~mophore.~" With respect to W-vis spectra, all three complexes show absorption maxima with comparable ,A values but different E values; compared to the E values of the free ligand (SI-ArH, those of 2a-c are much greater. Compounds 2a-c show CD spectra with the same rotational sense, i.e., positive Cotton effects are observed at the longest wavelength (by convention)% where any such effect is detectable (-273 nm). However, the positions of the absorption maxima and their corresponding values of molecular ellipticity [ell are different for each compound. The CD spectrum of 2a (Figure 2, curve 3)is representative; the [OIL values for all three compounds are summarized in the Experimental Section. For comparison, the CD spectra of the free (7)(a)Cymerman, C. J.; Chan, R. P. K.; Roy, S. K Tetrahedron 1967, 23,3573.(b) Djerassi, C.; Bunnenberg, E. Proc. Chem. SOC.1963,299.
74.5(4) 74.9(5) 74.96) 74.8(4)
sum of angles around Hg (deg)
distance of Hg from the C1-N-X plane (A)
354.7 353.6 353.0 353.8
0.1087(4) 0.1209(5) 0.1190(5) 0.1162(5)
ligand (SI-ArH (curve 11,its enantiomer (R)-ArH(curve 2),and the enantiomer of complex 2a, i.e., (R)-ArHgCl (curve 4), have also been included in Figure 2. Both the free ligands and their corresponding complexes show CD spectra with the same rotational sense, e.g., the CD spectra of both (SI-ArH (curve 1)and (S)-ArHgCl(curve 3) are positive at -270 nm. However, from about 240 down to 200 nm, the curves corresponding to the two enantiomeric complexes (curves 3 and 4) are much enhanced and are of opposite rotational sense of those of their corresponding free ligands (curve 1 and 2, respectively). Since the lack of N-coordination at room temperature is established for these complexes (vide supra), the substantial changes in both the value and the sense of each CD curve can be accounted for only by the asymmetric perturbation in the electronic transitions of the aryl chromophore caused by Hg coordination to the ring carbon. Finally, we raise the question of whether Hg can be considered a stereocenter in compounds 2a-c. Our rationale is as follows. In the solid-state structures of 2a-c (Table 2),the Hg atom deviates by an average of 0.12A from the mean plane defined by the X (= C1, Br, I), N, and C1 atoms. The average value for the sum of the three angles around Hg [353.7(5)"1is less than 360" (the value expected for a planar structure). Thus, the molecules are pyramidal, with Hg located at the apex of each pyramid and connected to three different groups. This is a situation similar t o that in chiral tertiary amines or phosphines. The absolute configuration of the chiral benzylic carbon in 2a-c, i.e., (S),7a98a is not affected by coordination of Hg to the aryl ring. Thus, we propose that the title compounds 2a-c, and their (R)c enantiomers, be considered diastereomeric complexes as they each contain two stereocenters in the solid state. The absolute configuration at Hg in each of the 2a-c complexes is (R)assuming the following priority numbers:8 1 (X= C1, Br, I), 2 (N), 3 (Cl), and 4 (the apex of the pyramid). Therefore, one may designate 2a-c as the "(S)C(R)Hg" diastereomers. This is another demonstration of how a single stereogenic center (Le., the benzylic C atom) can determine the absolute configuration of a metal center (i.e., the Hg atom) in a cyclometalated chelate ringqgaThe single, broad resonance in the lg9Hg NMR spectrum of 2a may be an average signal of two species, (S)C(R)H,and ( s ) C ( s ) H g , rapidly equilibrating through a pyramidal-like inversion a t Hg with an activation barrier so low that the exchange can not be stopped (even at -90 "C). A similar dynamic process, reportedgbfor the mercury(11)chloride (where complex of N,iV,",iV'-tetxamethylethylenediamhe the Hg atom is part of a five-membered ring), has a barrier of about 5-7 kcaYmo1. (8) (a) Cahn, R. S.; Ingold, C.; Prelog, V. Angew. Chem., Int. Ed. Engl. 1966,5 , 385. (b) Stanley, K.;Baird, M. C. J.Am. Chem. SOC. 1976,97,6598. ( c ) Sloan, T.E. Top. Stereochem. 1981,12,1. (9)(a) Jastrzebski, J. T. B. H.; van Koten,G.Adu. Orgunomet. Chem. 1993,35, 241. (b) Caulton, K. G . Inorg. Nucl. Chem. Lett. 1973,9, 533.
Chiral Mercury(II) Complexes
Organometallics, Vol. 14,No.10, 1995 4779
8.80
-8.80
/ .' 1
200
)i
(nm)
300
Figure 2. Circular dichroism (CD) curves of EtOH solutions of (6')-(-1-dimethyl(1-phenylethyllamine, (S)-ArH(1, - - -), its enantiomer (RI-ArH (2, the (S)-ArHgCl com-.-e-),
plex 2a (3, -1, and its enantiomer (R)-ArHgCI (4,
- - -).
Experimental Section k Physical Measurements. NMR spectra were recorded on a Varian Unity Plus-500 spectrometer operating at 500 MHz for 'H, 125 MHz for 13C, and 89.4 MHz for l*Hg. Infrared spectra were recorded on a Perkin-Elmer PE-1800 FT spectrometer for the far IR region (below 400 cm-l) and a Perkin-Elmer Paragon 1000 PC FT spectrometer for the region 400-4000 cm-'. W-visible spectra were recorded on a Perkin-Elmer Lambda-11 UVNIS spectrophotometer. CD spectra were recorded on JASCO 5-600 and/or 5-40 spectropolarimeters. B. Preparation of o-Lithio-(S)-(-)-dimethyl(1-phenylethyl)amine,(S)-ArLi.'O Under a dry dinitrogen atmosphere and utilizing standard Schlenk techniques, tert-butyllithium (125 mL of 1.7 M solution in pentane, 212 mmol) was added slowly via a n addition funnel to (SI-(-)-dimethyl(1-phenylethyllamine, (S)-ArH4b(32 mL, 28.8 g, 193 mmol) in freshlydistilled hexane (40 mL), all at room temperature. A white solid was formed within 1h. The reaction mixture was stirred for at least 15 h, after which the (SI-ArLi product was collected on a filter stick under high vacuum. It was then washed with several portions of freshly-distilled hexane t o remove unreacted t-BuLi (until the pink filtrate became colorless), dried under vacuum, and transferred t o a glovebox for further preparative work: yield 25.2 g (84.1%). C. Preparationof (S)-ArHgCl,2a. Powdered HgClz (43.2 g, 159 mmol) was slowly added over 1 h to a cooled (-77 "C) suspension of (SI-ArLi (25.2 g, 162 mmol) in anhydrous Et20 (250 mL) under a dry dinitrogen atmosphere. After the addition of HgClz was complete, the mixture was gradually warmed up to room temperature and was stirred for an additional 5 h. The removal of LiCl by filtration through Celite and reduction of the colorless Et20 filtrate under reduced pressure afforded the white microcrystalline product; this was recrystallized by rapid cooling of its hot hexane solution: yield 49.3 g (80.6%); mp 77-78 "C (lit.3 70 "C). NMR data: all spectra were obtained on acetone46 solutions; 'H (25 "C, TMS ~ Hz, 3H, C-CH3), 2.29 [s, 6H, ref) 6 1.33 (d, 3 J =~ 6.5 N(CH3)21, 3.53 (9, 3 5 H H = 6.5 Hz, 1H, C-H), 7.1-7.7 (m, 4H, 'H (-77 "C) (spectrum similar t o that at 25 "C except that the singlet at 6 2.29 due to NMez is split into two singlets at 6 2.16 and 2.53 (3H each)); I3C (25 "C, TMS ref) (numbering of C atoms follows that in the X-ray crystal structure, Figure la) 6 21.5 (C8), 42.6 (c9, C10 av), 66.6 (c7, 3 J H g - C = 93 Hz), 127.7 (C3, 3 J H g - C = 213 HZ), 129.1 (C5, 3 J H g - C = 169 HZ), 129.2 (C4, 4 J H g - C = 33 HZ), 138.3 (C2, 2 J ~ g -=~ 136 HZ), 148.7 (CI, ' J H ~ -=c 2541 Hz), 151.6 (C6, 2 J ~ g=- 52 ~ Hz); 13C (-77 "C) (spectrum similar to that a t 25 "C except for two singlets at 6 40.9 and 44.5 (C9 and C10) due t o splitting of the NMez singlet (10)Van Koten, G.; Jastrzebski, J . T. B. H. Tetrahedron 1989,45, 569.
at 6 42.6); VT '*Hg (neat MezHg ref) 6 -948.9 (25 "C, Av112 = 100 Hz), -952.4 (0 "C), -955.6 (-15 "C), -957.7 (-40 "C), -1009.5 (-70 "C) and constant at this value from -70 to -90 "C. IR Data: YHg-Cl322 cm-' (strong and very sharp) with a shoulder at 307 cm-' due to the Hg-37Cl stretch (Nujol mull on polyethylene sheet); Y H ~ - N 491 cm-' (weak: Nujol mull between NaCl plates). UV-vis data: for the free ligand (S)ArH (c = 1.1 x lo-* M in EtOH, 25 "C)'A,, (nm)/E (L mol-' cm-'), 272/0.80, 267/2.4, 264/3.2, 2W6.3, 252/7.9, 207h.3 x lo3; for 2a (c = 8.1 x M in EtOH, 25 "C) A, (nm)/E (L mol-' cm-I), 27312.4 x lo3, 25715.0 x lo3, 246/7.6 x lo3, 229/ 1.7 x lo4, 201/7.8 x lo5. CD data: since CD curves of enantiometric pairs agreed t o within 5%(Figure 2), only that of the (6')-enantiomer of the ligand [(S)-ArH] and its corresponding complex [(S)-ArHgClI, 2a, are described here as molecular ellipticity [elk (in units of deg cm2/dmol),where [eli = 3300 x (A€), and ( A E )is ~ the measured CD quantity (in units of L mol-' cm-') at a given wavelength; c = 0.011 M in EtOH at 25 "C for both (S)-ArH and (6')-ArHgCl. For (Sl-ArH: [el290 = 0, = +254, = -190, = 0, [eiZs8 = +508, [@I261 = +762, [el256 = $635, [el250 = +888, [elzu = $698, [el241 = -825, = -1320, = -1206, = -2665, [elzz3 = -3427, [81216 = -7260. For (S)-ArHgCl(2a), [8lzs0= 0, [el273 = +2723, = +3960, = $4208, [eizs0= +6930, = +ii 138, = +27 638, [eiZz6 = $14 438, [elzz3= +7343, [el216 = $2723. D. Preparation of (5')-ArHgX Compounds 2b,c. (i) Synthesis and Characterization of 2b (X = Br). To a stirred solution of 2a (1.0 g, 2.6 mmol) in 95% EtOH (100 mL) was added solid NaBr (2.68 g, 26 mmol), and the resulting cloudy, white mixture was stirred for 1 h at room temperature. The mixture was then taken to dryness under reduced pressure, and the product was extracted with CH2C12. Volume reduction of this extract afforded 2b as a white microcrystalline solid: yield 0.95 g (85.6%); mp 89-90 "C. NMR data: all spectra were obtained on acetone-& solutions; 'H (25 and -70 "C) (these spectra were identical in shape and 6 values to those described for 2a above); I3C (25 "C) (numbering of C atom follows that in the X-ray crystal structure for 2a, Figure l a 6 21.6 (C8), 42.6 (c9, c10 av), 66.9 (c7, 3 J ~ g -= c 92 Hz), 127.8 ((23, 3 J H g - C = 211 HZ), 129.1 (C5, 3 J H g - C = 168 HZ), 129.2 (C4, 4 J ~ g - c = 31 Hz), 138.2 (c2, 2 J ~ g =-138 ~ Hz), 152.5 (c1, ' J H ~ - C = 2462 Hz), 151.9 (C6, 2 J ~ g=-52 ~ Hz); I3C (-77 "C) (spectrum similar to that of 2a at this temp); VT 199Hg6 -1058.7 (25 "C), similar behavior to that of 2a from 25 to -90 "C. IR data: Y H ~ - B ? = 234 cm-l (strong and sharp; Nujol mull on polyethylene sheet); Y H ~ - N = 490 cm-' (weak; Nujol mull between NaCl plates). UV-vis data (c = 8.1 x M in (nm)/E (L mol-' cm-'1: 230/8.1 x lo3, 201/ EtOH, 25 "C) A,, 1.3 x lo5. CD data (c = 8.1 x M in EtOH, 25 "C) [el2 (in units of deg cm2/dmol), [el290 = 0, [@I273 = +2000, [e1266 = +3ooo, =+mo, = + i 6 250, = +E 500, [eizZs = + i 6 500, [eiZz8 = +i3 500, [elzz7 = $12 250, [elzz2 = -1000, reizz1= -3000, reizl8= +GOO, reizl4= $1500, rei212 = +i250, = $3750, [elzo4= $5000, [eizo2= +750. = 0, (ii) Synthesis and Characterization of 2c (X = I). A procedure similar to that for the preparation of 2b was followed, except that NaBr was replaced with NaI. Compound 2c was obtained as a beige microcrystalline solid: yield 0.97 g (78.3%);mp 81-83 "C. NMR Data: all spectra were obtained on acetone& solutions; 'H (25 and -70 "C) (these spectra were identical in shape and 6 values to those described for both 2a (25 "C) (numbering of C atoms follows that and 2b above); in the X-ray crystal structure for 2a, Figure la) 6 21.8 (C8), 42.6 (c9, c10 av), 66.7 (c7, 3 J ~ g - c = 88 HZ), 127.7 (c3,3 J ~ g - c = 204 HZ), 129.1 (C5, 3 J H g - C = 161 HZ), 129.1 (C4, 4 J H g - C = 29 Hz), 138.1 (C2, ' J H ~ -= C 137 Hz), 159.2 (Cl, 'JH~-c = 2347 ~ Hz); 13C (-77 "C) (not obtainable Hz), 152.3 (C6, 2 J ~ g=-50 due to precipitation of 2c at temperatures below 0 "C); lg9Hg (25 "C) 6 -1246.6. IR data: Y H ~ - I = 170 cm-l (weak; Nujol mull on polyethylene sheet); V H ~ - N = 489 cm-' (weak; Nujol mull between NaCl plates). W - v i s Data: (c = 8.1 x M
Attar et al.
4780 Organometallics, Vol. 14,No. 10,1995 in EtOH, 25 "C), ,A (nm)/c (L mol-' cm-l): 233h.6 x lo4, M in EtOH, 25 "C), 201A.3 x lo5. CD data: (c = 8.1 x [OIL (in units of deg cm2/dmol)[ ~ I Z S O= 0, [el273 = +4000, [el267 = +5ooo, = +6ooo, = +io 000, = +ii 000, = $13 000, = 0, = -4000, = -5250, = -6000,[elzz8= -3500, [elzz5 = -2000, = +3ooo, = +gooo, = + i 3 500, [elzl3= + i 5 000,[e1209= -18 500, = +12 000,[elzo6 = +GOO, [elzo4 = +3ooo, [eiZol = -10 000. E. X-ray Data Collection and Processing. Colorless needles of 2a-c were obtained by slow evaporation of hexane solutions of each. Crystal data and details of data collection are given in Table 1. The samples were studied on an EnrafNonius CAD4F diffractometer with graphite-monochromated Mo Ka radiation. Quantitative data were obtained at 293 K in the 8-26 mode. The resulting data sets were transferred t o a VAX computer, and for all subsequent calculations the Enraf-Nonius SDPNAX package1' was used. Three standard reflections measured every 1h during the entire data collection period showed no significant trends. The raw data were converted to intensities and corrected for Lorentz, polarization, and absorption effects using b,t scans of four reflections (14 < 8 < 16"). The structures were solved by the heavy-atom method. After refinement of the heavy atoms, difference(11)Frenz, B. A. The Enraf-Nonius CADI-SPD in Computing in
Crystallography; Shenk, H., Olthof-Hazekamp, H., van Koningsveld, H., Bassi, G. C., Eds.; Delft University Press: Delft, The Netherlands, 1978; pp 64-71.
Fourier maps revealed maximas of residual electronic density close to the positions expected for hydrogen atoms. They were introduced in the structure calculations by their computed coordinates (C-H = 0.95 A) with isotropic temperature factors such as B(H) = 1.38B,(C) A2 but not refined. The atomic positional and thermal parameters and the extinction parameters were refined by full-matrix least-squares methods. The scattering factor coefficients and anomalous dispersion coefficients come, respectively, from parts a and b of ref 12.
Acknowledgment. We would like to thank Prof. David A. Lightner for his generous permission to use the JASCO spectropolarimeters and also Dr. Stefan Boiadjiev for helpful discussions on CD techniques and spectra. The financial support of the Petroleum Research Fund, administered by the American Chemical Society, is gratefully acknowledged. Supporting Information Available: Tables of X-ray crystallographic data, including atomic coordinates, interatomic distances and angles, and anisotropic thermal parameters for compounds 2a-c (12 pages). Ordering information is given on any current masthead page. OM950021F (12) (a) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. IV, Table 2.2b; (b) Table 2.3.1.
