238 Organometallics 1996, 14, 238-244

[ C ~ S , C ~ S , tr~n~-RuCl2( C0)2{ Ph2P(CH2CH20),CH2CH2PPh2-PP '} 1, (n = 4, 5; m = 1, 2, ...) Metallacrown Ethers. X-ray

Crystal Structures of

a Complex Which Exhibits Rotational Isomers in the Solid State, and [cis,cis,truns-RuCl~(CO)~=

{pPh2P(CH2CH20)4CH2CH2PPh2=P,P '}12, an Unusual Dimetallacrown Ether

cis,cis,tr~n~-R~C12( C0)2{ P~~P(CH~CH~O)~CHZCH~PP~~-PP '}

Gary M. Gray,* Ashima Varshney, and Christina H. Duffey Department of Chemistry, The University of Alabama at Birmingham, 242-OB15 UAB Station,

Birmingham, Alabama 35294, and Department of Chemistry, Samford University, Birmingham, Alabama 35229

Received August 16, 1994@

The reactions of Ph2P(CH2CH20),CH2CH2PPh2 (n = 4, 5 ) ligands with RuC12(C0)3(THF) give a variety of complexes of the type [c~s,c~s,~~u~s-RuC~~(CO)~{P~~P(CH~CH~~),CH~CH~- PPhz-PQ '}Im. Multinuclear NMR and IR spectroscopic studies indicate that the major product in each reaction is the mononuclear (m = 1) complex in which the P~~P(CH~CHZO),- CH2CH2PPh2 ligand spans two trans positions. The minor products are polynuclear (m = 2, 3, ...I complexes in which each P ~ ~ P ( C H ~ C H Z O ) , C H ~ C H ~ P P ~ ~ ligand bridges two rutheniums. X-ray crystal structures of cis,cis,truns-RuC12(C0)2{Ph2P(CH2CH20)4CH2CH2- PPhz-PQ '}, 4a, (monoclinic space group P2l/n, a = 10.194(1), b = 22.907(3), c = 15.259(2) A; p = 92.46(1)"; V = 3560.0(8) A3; 2 = 4) and [cis,cis,trans-RuCl2(CO)2{~-Ph2P(CH2CH20)4- CH2CH2PPh2-PQ '}12*(CH&CO, 4b.(CH&CO, (monoclinic space group P21/a, a = 18.976(3), b = 22.076(5), c = 10.426(8) A; /3 = 111.64(1)"; V = 4060(1) A3; 2 = 4) confirm these conclusions. The monomeric 4a is a rare example of an octahedral complex with a trans- spanning bis(phosphine) ligand. Two different rotamers of 4a are observed in the solid state. In the major rotamer the trans-spanning ligand passes between one chloride and one carbonyl while in the minor rotamer the trans-spanning ligand passes between the two chlorides. The dimeric 4b is the first example of a dimetallacrown ether. The trans phosphines in 4b cause the formation of two, distinct metallacrown ether sites separated by a chloride and a carbonyl ligand on each ruthenium.

Introduction

One of the most interesting classes of metallomacro- cycles1 are the metallacrown ethers, formed by chelation of R2PX(CH2CH20),CH2CH=R2 (R = Ph, 0-alkyl; X = -, 0; n 1 3) ligands to transition These metallacrown ethers readily coordinate hard metal

* To whom correspondence should be addressed at The University

@ Abstract published in Advance ACS Abstracts, November 1,1994. (1) This class of complexes has recently been reviewed van Veggel,

F. C. J. M.; Werbloom, W.; Reinhoudt, D. N. Chem. Reviews 1994,94, 279. (2) (a) Powell, J.; Kuksis, A,; May, C. J.; Nyberg, S. C.; Smith, S. J.

J. Am. Chem. SOC. 1981,103,5941. (b) Powell, J.; Nyberg, S. C.; Smith, S. J. Inorg. Chim. Acta 1983, 76, L75. ( c ) Powell, J.; Ng, K. S.; Ng, W. W.; Nyberg, S. C. J. Organomet. Chem. 1983,243, C1. (d) Powell, J.; Gregg, M.; Kuskis, A.; Meindl, P. J. Am. Chem. SOC. 1983,105, 1064. (e) Powell, J.; Gregg, M. R.; Kuksis, A.; May, C. J.; Smith, S. J. Organometallics 1989, 8, 2918. (0 Powell, J.; Kuskis, A.; May, C. J.; Meindl, P. E.; Smith, S. J. Organometallics 1989,8, 2933. (g) Powell, J.; Gregg, M. R.; Meindl, P. E. Organometallics 1989, 8, 2942. (h) Powell, J.; Lough, A.; Wang, F. Organometallics 1992, 11, 2289.

(3) (a) Alcock, N. W.; Brown, J . M.; Jeffery, J. C. J . Chem. SOC., Chem. Commun. 1974, 829. (b) Alcock, N. W.; Brown, J . M.; Jeffery, J . C. J . Chem. Soc., Dalton Trans. 1976,583. ( c ) Thewissen, D. H. W.; Timmer, K.; Noltes, J. G.; Marsman, J. W.; Laine, R. M. Inorg. Chim. Acta 1986,97, 143. (d) Timmer, K.; Thewissen, D. H. W. Inorg. Chim. Acta 1986, 100, 235. (e) Timmer, K., Thewissen, H. M. D.; Marsman, J. W. Recl. Trav. Chim. Pays-Bas 1988, 107, 248.

of Alabama at Birmingham.

0276-7333195123 14-O238$O9.OOIO

cations, and the stabilities of the alkali metal cation complexes depend upon the relative sizes of the cation and the metallacrown ether ~ a v i t y . ~ , ~ , ~ Cations bound to the metallacrown ethers can interact with the oxygen lone pairs of the carbonyl ligands in cis-Mo(CO)4{Rz- PX(CH~CH~~),CHZCH~XPR~-PQ '} metallacrown ethers. Coordination of Li+ activates the carbonyl ligands of cis- MO(C~)~{RZPO(CHZCH~O)~CH~CH~OPR~-PQ '] met- allacrown ethers toward nucleophilic attack by alkyl- and aryllithium reagents.2 Coordination of Hg2+ cata- lyzes the cis to trans isomerization of the cis-Mo(CO)r- { Ph2P(CH2CH20)4CH&H2PPh2-P,P '} metallacrown ether.6 These results suggest that hard metal ion complexes of metallacrown ethers could be used to activate a variety of bifunctional ligands, such as carbonyls, that can coordinate to both metal centers. This property could be quite useful in the design of catalysts for reactions involving such ligands.

The phosphorus-donor groups are cis coordinated iq all reported metallacrown ethers except trans-Mo(CO)4- {Ph2P(CH2CH20)4CH2CH2PPh2-PQ '}, l.5 The chelate (4) (a) Varshney, A,; Gray, G. M. Inorg. Chem. 1991, 30, 1748. (b)

Varshney, A.; Webster, M. L.; Gray, G. M. Inorg. Chem. 1992,31,2580. ( 5 ) Gray, G, M.; Duffey, C. H. Organometallics 1994, 13, 1542. (6) Gray, G, M.; Duffey, C. H. Organometallics, in press.

0 1995 American Chemical Society

Ruthenium Metallacrown Ethers Organometallics, Vol. 14, No. 1, 1995 239

Table 1. 31P and Phenyl 13C NMR Data"

para P ipso ortho meta

no. 6 ( W (ppm) W3C) (ppm) lJ(PC)I (Hz) 613C (ppm) IJ(PC)I (Hz) W3C) (ppm) IJ(PC)I (Hz) W3C) (ppm) l b 32.57 s 139.48 aq 34d 131.70 aq 1 lf 128.28 bs 129.16 s 2 e -21.68 s 138.17 d 12e 132.68 d 188 128.56 d 12h 128.41 s 3' -21.69 s 138.29 d 12' 132.71 d 178 128.58 d loh 128.41 s 4a 9.74 s 132.74 aq 47d 132.55 aq 8f 128.74 aq 8' 130.79 s 4b 13.43 s 131.02 aq 45d 132.85 aq sf 128.52 bs 130.71 s 4d 14.77 s i 132.93 bs 128.43 bs 130.70 s Sa 11.16 s 131.85 aq 46d 132.63 aq 1N 128.71 bs 130.81 s

Ob = broad, s = singlet, d = doublet, aq = apparent quintet. *Data from ref 5 . Data from ref 3a. IIJ(PC) + 3J(PC)I. e IIJ(PC)/. f I2J(PC) + 4J(PC)l. g 12J(PC)I. 13J(PC)I. 13J(PC) + 5J(OC)I. j Not observed.

Table 2. AliDhatic and Carbonyl 13C NMR Data"

C3, C4, C5, C6 W3C) (ppm)

l b 34.38 aq 22d 66.96 aq 1 2 71.07 s, 71.03 s, 70.24 s 210.59 t 8 2' 28.73 d 12e 68.53 d 268 70.58 s, 70.53 s, 70.10 s 3c 28.73 d 13' 68.49 d 258 70.55 s, 70.51 s, 70.51 s, 70.07 s 4a 27.05 aq 2gd 65.18 s 70.46 s, 69.98 s, 69.07 s 191.67 t 11 4b 24.54 aq 27d 66.01 s 70.61 s, 70.44 s, 69.95 s 192.23 t 11 4d 24.13 aq 27d 66.05 s 70.43 s, 70.36 s, 69.86 s 192.25 t 11 Sa 25.47 aq 2gd 65.54 s 70.97 s, 70.69 s, 69.89 s, 69.69 s 191.94 t 11

r? b = broad, s = singlet, d = doublet, t = triplet, aq = apparent quintet. Data from ref 5. Data from ref 3a. I*J(PC) + 3J(PC)I. e IIJ(PC)I. f I2J(PC) + 4J(PC)I. IZJ(PC)I.

ring in 1 has very different solution and solid state conformations from those of the chelate rings in the metallacrown ethers with cis phosphorus-donor groups. In addition, the Mo(C0)4 group in 1 freely rotates within the chelate ring making this complex a 'molecular gyroscope'. Both these properties suggest that metal- lacrown ethers with trans-coordinated phosphorus- donor groups (trans-metallacrown ethers) could exhibit properties that are quite different from those with cis- coordinated phosphorus-donor groups (cis-metallacrown ethers).

In this paper, we report the results of our studies of the reactions of RuC12(CO)&THF') with Ph2P(CH2CH20),- CH2CH2PPh2 (n = 4 (2),5 (3)). These reactions yield a variety of trans-metallacrown ethers, and these have been characterized by multinuclear NMR and IR spec- troscopy. The insights that these spectroscopic studies provide into the solution structures of these metalla- crown ethers are discussed. X-ray structures of the major product and one of the minor products from the reaction of RuC12(CO)3(THF) with Ph2P(CH2CH20)4CH2- CH2PPh2 have also been determined and are presented.

Experimental Section

The 31P{ lH} and 13C{ 'H} NMR spectra were recorded on a GE NT-300, multinuclear NMR spectrometer. The 31P NMR spectra were referenced to external 85% H3P04, and the 13C NMR spectra were referenced to internal SiMe4. The 31P and 13C NMR data for the complexes are given in Tables 1 and 2 with positive chemical shifts downfield from those of the references. Infrared spectra of KBr disks of the complexes were run on a Nicolet IR44 spectrometer. Elemental analyses were carried out by Atlantic Microlab, Inc., Norcross, GA.

All free ligands, tetrahydrofuran (THF) and diethyl ether were handled under high purity nitrogen, and all reactions and recrystallizations were carried out under high purity nitrogen. The solid products were air stable. All solvents were of reagent grade and were used as received except for diethyl ether and THF which were distilled from sodium-benzophe- none. All starting materials were reagent grade and were used as received. The deuterated solvents were opened and handled under a nitrogen atmosphere at all times. The PhzP(CH2-

CH20),CH2CHzPPh2 (n = 4 (2), 5 (3)) ligands4* and RuClz(C0)3- (THF)' were prepared using literature procedures.

PQ '}Im (4). Solutions of 1.00 g (3.05 mmol) of RuC12(CO)3- (THF) in 500 mL of dichloromethane and 1.85 g (3.23 mmol) of 2 in 500 mL of dichloromethane were added dropwise and simultaneously to 1000 mL of dichloromethane over a period of 5 h. The reaction mixture was then stirred for an additional 18 h after which it was evaporated to dryness to yield 2.56 g (100%) of crude 4 as a white foam. The 31P NMR (chloroform- d l ) of the material contained four singlets at 9.71 (4a, major), 13.42 (4b, minor), 14.35 (4c, very minor) and 14.77 (4d, minor) ppm. A portion of the material (0.80 g) was chromatographed on silica gel. Elution with a 3:l mixture of ethyl acetate- hexanes yielded 4a (0.46 g, 58%). Next, elution with a 4:l mixture of ethyl acetate-hexanes initially yielded 4b (0.13 g, 16%) and then a mixture of 4b, 4c and 4d. Finally, elution with a 1 O : l mixture of ethyl acetate-methanol yielded pure 4d (0.07 g, 9%). Each fraction that contained a single component was triturated with hexanes to give the compounds as analytically pure white powders (mp 203-205 "C for 4a, 192-195 "C for 4b, 90-95 "C for 4d). Anal. Calcd for C ~ ~ H ~ ~ C ~ Z O ~ P ~ R U : C, 53.86; H, 4.99%. Found for 4a: C, 53.65; H, 5.09%. Found for 4b: C, 53.56; H, 5.06%. Found for 4d: C, 53.62: H, 5.13%. IR (KBr): v(C0) 2058, 1995 cm-l, 4a; 2058, 1995 cm-l, 4b; 2058, 1995 cm-l, 4d.

PQ '}I,,, (5). Using the procedure for the preparation of crude 4, 0.10 g (0.32 mmol) of 3 and 0.10 g (0.30 mmol) of RuC12- (C0)3(THF) were reacted to yield a white waxy residue. A 31P NMR spectrum of the material in chloroform-dl had singlets at 11.17 (Sa, major), 13.99 (Sb, minor) and 14.75 (Sc, minor). The residue was chromatographed on silica gel. Elution with a 2:l mixture of ethyl acetate-hexanes yielded 0.20 g (74%) of analytically pure Sa (mp 280 "C). Anal. Calcd for C38H44C1207P2R~: C, 53.91; H, 5.24%. Found: C, 54.49; H, 5.32%. IR (KBr): v(C0) 2058, 1997 cm-l.

[ ~ i s p i s a m - R ~ ( C O ) & l 2 { Phap(CHzCH20)4CHzCHapph2

[C~&S&YJIW-RU(CO)~C~Z{ PhaP(CHzCH2O)&HzCI&PPhr

(7) We originally reported that this complex was [Ru(C0)&121. 0.75THF based upon analytical results. (Reddy, V. V. S.; Whitten, J. E.; Redmill, K. A.; Varshney, A.; Gray, G. M. J. Organomet. Chem. 1989, 372, 207). We have now obtained a crystal structure of this complex (Duffey, C. H.; Gray, G. M. Unpublished results) which indicates that the correct formula is as shown in the text. The difference in formulas most likely is due to loss of THF during drying of the analytical sample.

240 Organometallics, Vol. 14, No. 1, 1995

X-ray Structure Determination of 4a and 4b(C&)&O. A colorless, needlelike crystal of 4a was grown by slowly diffusing hexanes into a dichloromethane/methanol solution of the complex. A colorless, blocky crystal of 4b.(CH&CO was grown by slowly diffusing acetone into a dichloromethane solution of 4b. The crystals were mounted on glass fibers with epoxy cement, and the cell constants were obtained from least- squares refinement of 25 reflections with 25 5 8 5 35" for 4a and 12 5 8 5 16" for 4b.(CH&CO. All measurements were carried out on an Enraf-Nonius CAD4 diffractometer at 23 "C using graphite-monochromated Cu Ka radiation (A = 1.5418 A) for 4a and at 22 "C usin graphite-monochromated Mo Ka

collected by 0-20 scans for both crystals. No decay correction was applied to the data for 4a, but an empirical absorption correction was applied. Both linear decay and empirical absorption corrections were applied to the data for 4b.(CH& co.

Both structures were solved by heavy-atom methods and refined by a full-matrix least squares procedure that mini- mized w(lFol - lFc1)2 where w = l/u2(Fo) using the Crystals programs in the MolEN package of programs from Enraf- Nonius. The structure of 4a was disordered due to rotational isomerism that exchanged one carbonyl and one chloride ligand. The sum of the occupancies of the chloride and carbonyls in the two sites were set equal to one, the occupancy of the chloride in one site was linked to that of the carbonyl in the other site and the occupancies were refined. The polyether chains in 4b.(CH&CO were quite mobile and gave poor bond lengths when freely refined. In order to obtain a reasonable structure, the C-C bond lengths were restrained to 1.54 A and the C-0 bond lengths were restrained to 1.43 A during the refinement. This did not materially affect the R factors and did result in reasonable bond angles. All hydrogen atoms in both structures were placed in calculated positions (C-H = 0.96 A, UISO(H) = 1.3U1so(C)) and were ridden on the heavy atoms to which they were attached. Both data sets were weighed using a non-Poisson scheme. A secondary extinction correction was applied to each set of data: and the extinction coefficients were refined. In the last stage of the refinement for each structure, no parameter varied by more than 0.01 of its standard deviation, and the final difference Fourier map had no interpretable peaks. Heavy atom scattering factors were taken from the compilations of Cromer and Weber,g and those for hydrogen were taken from the International Tables for X-Ray Crystallography, Vol. W.lo Corrections for anomalous dispersion were taken from the compilations of Cromer and Liebermanl' and applied to chlorine, phosphorus and ruthe- nium. Data for the X-ray structure analyses are given in Table 3. Positional parameters for 4a are given in Table 4, and those for 4b.(CH&CO are given in Table 5. Values of selected bond lengths for 4a are given in Table 6, and those for 4b.(CH&- CO are given in Table 7. Values of selected bond angles for 4a are given in Table 8, and those for 4b.(CH&CO are given in Table 9. Values of selected torsion angles for both struc- tures and for 1 are given in Table 10. Tables of hydrogen atomic positional parameters, thermal parameters, torsion angles and least squares planes for 4a and 4b are available as supplementary material. ORTEP12 drawings of the major and minor rotamers of 4a are given in Figures 1 and 2, and that for 4b.(CH&CO is given in Figure 3.

radiation (A = 0.710 73 1 ) for 4b.(CH&CO. Data were

Results and Discussion Syntheses and Solution Conformations of the

RUC~~(C~)~{P~~P(CH~CH~O)~CH~CH~PP~~} Com-

Gray et al.

(8) Zachariasen, W. H. Acta Crystallogr. 1963, 16, 1139. (9) Cromer, D. T.; Waber, D. T. Acta Crystallogr. 1966,18, 104. (10) International Tables for Crystallography; Hahn, T., Ed.; The

(11) Cromer, D. T.; Lieberman, D. J. J. Chem. Phys. 1970,53,1891. (12) Johnson, C. K. ORTEPII. Report ORNL-5138. Oak Ridge

Kynoch Press: Birmingham, U.K., 1974; Vol. IV, p 72.

National Laboratory: Oak Ridge, TN, 1976.

Table 3. Data Collection and Structure Solution and Refinement Parameters for 4a and 4b

Z

cryst dimens, mm dCdc (g/cm3)

h m a , hmin kmax, kmin &I" radiation (A (A)) temp ("C) abs coeff (cm-I) 8 (limits (deg) decay corr decay (%) abs corr Tma. Tmm (%) refl measd scan width (deg) refl with I ? nu(l) no. of variables function minimized weighing scheme

instrumental uncertainty factor secondary extinction corr type minimized extinction coeff R, %" Rw GOFC max, min resid electron

max shifuerror density (e/A3)

4a

P21/n 10.194( 1) 22.907(3) 15.259(2) 92.46( 1) 3560.0(8) 4 1.497 0.11 x 0.10 x 0.21 12, 0 28,O 19, -19 Cu Ka (1.541 84) 23 62.890

none

empirical 99.6, 84.8 8036 1.34 4310 ( n = 3) 423

non-Poisson

0.03 Zachariesen 7.608 x lo-* 7.13 8.68 1.324 1.057, -0.287

0.01

0.1-74

W(lF0I - IFcl)2

(w = l/u2(Fo))

P21/a 18.976(3) 22.076(5) 10.426(8) 11 1.64(1) 4060.(1) 4 1.408 0.37 x 0.34 x 0.50 24, -24 0, -28 13,O Mo Ka (0.710 73) 22 6.324 0.1 -27.5 linear 6.9 empirical 99.9,94.6 10 073 1.35 4305 (n = 2) 46 1

non-Poisson

0.02 Zachariesen 2.867 x lo-* 5.58 6.04 1.972 0.721, -0.140

0.01

W(lF0l - IFCIY

(w = l/u2(Fo))

R = E(IF0I - lFcl ) /z lFo l ) . R, = Ew(lF0l - lFcl)2/XIFo12)o~5. GOF = [Zw(llFoi - IFcl)2/n - mlO.5.

plexes. I n contrast to t h e reactions of the PhzP(CH2- CH20),CHzCH2PPhz (n = 4 (2), 5 (3)) ligands with Mo(C0)4(norbornadiene) and PtC1~(1,5-cyclooctadiene) in 1:l ratios, which yield single product^,^ the reactions of these ligands with RuClz(C0)3(THF) in 1:l ratios under similar conditions yield a variety of products (eq 1). Elemental analyses of the crude reaction mixtures

RuCl,(CO),(THF) + Ph2P(CHzCHzO),CH2CHzPPh2 -

2 (n = 4), 3 (n = 5 ) RuC1,(C0),{Ph2P(CH2CH,0),CH,CH,PPh,1 (1)

4 (n = 4), 5 (n = 5 )

indicate that all of these products have empirical formulas of the type RuCl2(CO)z{PhzP(CHzCHzO),CH2- CHzPPhz} (n = 4 (41, 5 (5)). The various products do not interconvert as indicated by the fact that t h e 31P NMR spectra of t h e mixture did not vary with either temperature or concentration and by t h e fact that the major components and some of the minor components could be separated by column chromatography on silica gel.

Each of the RuCl~(CO)~{Ph2P(CH2CH~O)~CH~CH2- PPhz} complexes have identical ruthenium coordination geometries with cis carbonyls, cis chlorides and trans phosphines as shown by their IR and 31P and I3C NMR spectra (Tables 1 and 21. The IR spectrum of each

Ruthenium Metallacrown Ethers Organometallics, Vol. 14, No. 1, 1995 241

Table 5. Positional Parameters and Isotropic Thermal Factors (Az) for 4b.(CH3)zCO"

atom X Y Z B O

Table 4. Positional Parameters and Isotropic Thermal Factors (Az) for 4a'

atom X Y Z B" Ru c11 c12 C12' P1 P2 0 1 0 2 0 3 0 4 0 5 0 6 06' c 1 c 2 c 3 c 4 c 5 C6 c 7 C8 c 9 c10 c11 c12 C13 C14 C15 C16 C17 C18 C19 c20 c 2 1 c22 C23 C24 C25 C26 C27 C28 C29 C30 C3 1 C32 c33 c34 c35 C36 C36'

0.58941(6) 0.7932(2) 0.6528(4) 0.4986(7) 0.4982(2) 0.6808(2) 0.5492(7) 0.772 l(8) 0.835(1) 0.8076(7) 0.3393(7) 0.503( 1) 0.695(3) 0.4672(9) 0.5882(9) 0.637( 1) 0.768( 1) 0.767( 1) 0.798( 1) 0.851(1) 0.9025(9) 0.800( 1) 0.6977(9) 0.3376(8) 0.3280(9) 0.207( 1) 0.093( 1) 0.1011(9) 0.2208(9) 0.5887(8) 0.5282(9) 0.599( 1) 0.725( 1) 0.783( 1) 0.719( 1) 0.841 l(9) 0.888( 1) 1.008(1) 1.084(1) 1.040(1) 0.9 192(9) 0.5757(8) 0.507( 1) 0.426( 1) 0.412(1) 0.479( 1) 0.559( 1) 0.432( 1) 0.533( 1) 0.659(3)

0.52967(3) 0.571 8( 1) 0.5260(2) 0.5273(3) 0.62620(9) 0.43447(9) 0.7107(3) 0.6840(3) 0.5342(4) 0.4133(3) 0.474% 3) 0.5382(5) 0.532( 1) 0.6670(4) 0.6885(4) 0.7495(5) 0.7264(5) 0.6275(5) 0.5854(5) 0.4837(5) 0.4356(5) 0.4443(4) 0.4128(4) 0.6239(4) 0.6023(5) 0.5942(5) 0.6087(5) 0.6290(5) 0.6361(5) 0.6788(4) 0.7317(4) 0.7727(4) 0.7600(4) 0.7084(5) 0.6681(4) 0.4 176(3) 0.3593(4) 0.3460(5) 0.3873(5) 0.4440(5) 0.4591(4) 0.3766(4) 0.3375(5) 0.2960(5) 0.2919(5) 0.3314(5) 0.3734(5) 0.4957(4) 0.5351(6) 0.531(1)

0.75769(4) 0.7086(2) 0.9125(3) 0.6141(5) 0.7759( 1) 0.7334(2) 0.5487(5) 0.4291(5) 0.4268(5) 0.4880(4) 0.8153(5) 0.5705(8) 0.955(2) 0.674 l(5) 0.6309(6) 0.5 130(9) 0.497 l(9) 0.4554(8) 0.3850(8) 0.3722(7) 0.4306(6) 0.5680(6) 0.6195(6) 0.8238(6) 0.9091(6) 0.9443(6) 0.8975(8) 0.8131(8) 0.7773(7) 0.8449(6) 0.8658(6) 0.9174(6) 0.9479(7) 0.9287(8) 0.8747(7) 0.7868(6) 0.7814(7) 0.8231(9) 0.8635(8) 0.8690(8) 0.8299(7) 0.7739(6) 0.7 192(7) 0.7570(9) 0.8437(8) 0.8982(7) 0.8629(6) 0.7932(6) 0.6307(9) 0.884(2)

2.15(1) 3.34(4) 4.29(7)* 3.2(1)* 2.16(4) 2.49(4) 4.5(2) 5.1(2) 6.1(2) 3.7(1) 4.3(2) 5.1(3)* 5.1(6)* 2.7(2) 3.4(2) 5.5(3) 5 3 3 ) 6.0(3) 5.3(3) 4.1(2) 3.4(2) 3.5(2) 3.0(2) 2.5(2) 3.6(2) 3.6(2) 4.3(2) 4.6(3) 3.5(2) 2.6(2) 3.1(2) 3.2(2) 3.6(2) 4.2(2) 3.8(2) 2.7(2) 3.9(2) 5.1(3) 4.8(3) 4.5(2) 3.5(2) 2.5(2) 5.0(3) 6.8(3) 5.3(3) 4.6(2) 3.9(2) 3.2(2) 3.3(2)* 3.0(5)*

a Starred B values are for atoms that were refined isotropically. Anisotropically refined atoms are given in the form of the isotropic equivalent displacement parameter defined as (4/3)[a2B(l,l) + b(2,2) + c2B(3,3) + &cos y)B(1,2) + ac(cos Pp(1.3) + bc(cos a)B(2,3)].

complex has two equally intense bands at approximately 1995 and 2058 cm-' indicating that the carbonyls in each of the complexes are cis-coordinated.13 The 13C NMR spectrum of each complex has a single 1:2:1 triplet for the two carbonyls at approximately 192 ppm with a relatively small 12J(PC)I of approximately 11 Hz. This demonstrates that the carbonyls are chemically equiva- lent and are cis to both phosphines.13 Each complex also has a single 31P NMR resonance indicating that the phosphines are chemically equivalent.

The above data suggests that the reactions shown in

(13) (a) Lindner, E.; Schober, U.; Fawzi, R.; Hiller, W.; Englert, U.; Wegner, P. Chem. Ber. 1987,120,1621. (b) Reddy, V. V. S. R.; Whitten, J. E.; Redmill, K. A,; Varshney, A.; Gray, G. M. J. Organomet. Chem. 1989,372, 207. (c) Lindner, E.; Karle, B. Chem. Ber. 1990,123, 1469. (d) Lindner, E.; Mockel, A.; Mayer, H. A.; Fawzi, R. Chem. Ber. 1992, 125, 1363. (e) Lindner, E.; Mockel, A.; Mayer, H. A.; Kuhlbauch, H.; Fawzi, R.; Steimann, M. h o g . Chem. 1993, 32, 1266.

Ru c11 c12 P1 P2 0 1 0 2 0 3 0 4 0 5 0 6 c 1 c 2 c 3 c 4 c 5 C6 c 7 C8 c 9 c10 c11 c12 C13 C14 C15 C16 C17 C18 C19 c20 c 2 1 c22 C23 C24 C25 C26 C27 C28 C29 C30 C3 1 C32 c33 c34 c35 C36 0 7 c37 C38 c39

0.22681(3) 0.2518(1) 0.1715(1) 0.10206(9)

-0.3453( 1) -0.0708(3) -0.1664(4) -0.2993(3) -0.4267(3)

0.2964(3) 0.1903(3) 0.0565(4)

-0.0155(5) -0.1389(5) -0.1960(5) -0.1748(6) -0.2544(5) -0.3734(5) -0.4182(4) -0.4344(4) -0.3576(4)

0.0454(3) 0.0006(4)

-0.0346(4) -0.0247(5)

0.0195(5) 0.0544(4) 0.0936(3) 0.0288(4) 0.0215(4) 0.0798(4) 0.145 l(4) 0.1530(4) 0.4309(3) 0.4339(4) 0.5009(4) 0.5653(4) 0.5638(4) 0.4972(4) 0.3541(3) 0.3423(4) 0.3452(4) 0.3615(4) 0.3719(4) 0.3680(4) 0.2694(4) 0.2042(4) 0.8469(4) 0.7521 (7) 0.7936(5) 0.7673(8)

0.07645(3) 0.00032(9) 0.0017(1) 0.08849(9)

-O.O498( 1) 0.0502(3) 0.1474(3) 0.1729(3) 0.1013(3) 0.1737(3) 0.1646(3) 0.0154(3) 0.0077(4) 0.045 l(4) 0.0881(4) 0.1877(5) 0.2158(5) 0.1968(4) 0.1548(4) 0.05 16(4) 0.0314(4) 0.1378(3) 0.1161(4) 0.1561(5) 0.2183(4) 0.2394(5) 0.1994(4) 0.1209(3) 0.1498(3) 0.1705(3) 0.1643(4) 0.1352(3) 0.1 140(3) 0.0736(3) 0.0699(4) 0.0809(4) 0.0972(4) 0.1010(4) 0.0898(4) 0.0792(4) O.O415(4) 0.0679(5) 0.1279(5) 0.1642(5) 0.1388(4) 0.1372(3) 0.1305(4) 0.2328(4) 0.1752(6) 0.1977(5) 0.18 12(7)

0.00749(6) 4.08(1) -0.1402(2)

0.1115(2) -0.1677(2) -0.1860(2) -0.3333(8) -0.4275(7) -0.3448(7) -0.3953(6) -0.1051(6)

0.1933(6) -0.2078(8) -0.337( 1) -0.453( 1) -0.426( 1) -0.327( 1) -0.384( 1) -0.374( 1) -0.3 14( 1) -0.3 140(8) -0.2071(8) -0.105 l(7) -0.0375(8)

0.0227(8) 0.0178(9)

-0.0490(8) -0.1090(9) -0.333 l(6) -0.4163(7) -0.5449(7) -0.5911(7) -0.5108(7) -0.3809(6)

0.1624(7) 0.0314(7) 0.0113(9) 0.1 193(9) 0.2509(9) 0.2712(8) 0.3558(6) 0.4531(7) 0.5785(8) 0.6040(8) 0.5064(8) 0.3835(8)

-0.0630(7) 0.1217(8) 0.1868(8) 0.022( 1) 0.151(1) 0.253( 1)

5.46(5) 7.86(6) 3.96(4) 4.48(5) 8.9(2)

11.5(3) 8.3(2) 8.5(2) 6.9(2) 8.9(2) 5.7(2) 9.4(3) 9.4(4)

12.5(4) 12.8(5) 10.9(4) 10.3(4) 9.4(3) 6.8(2) 5.8(2) 4.3(2) 6.5(2) 9.2(3) 8.9(3) 8.2(3) 6.2(2) 3.7(2) 4.6(2) 5.4(2) 6.0(2) 5.0(2) 4.1(2) 4.5(2) 5.5(2) 7.3(2) 7 3 3 ) 7.2(3) 5.8(2) 4.8(2) 6.8(2) 7.8(3) 8.4(3) 7.6(3) 6.2(2) 4.3(2) 6.2(2)

12.1(3) 17.9(6) 9.6(3)

25.9(7)

Anisotropically refined atoms are given in the form of the isotropic equivalent displacement parameter defined as (4/3)[a2B(l,l) + b2B(2,2) + c2B(3,3) + ab(cos y)B(1,2) + ac(cos P)B(1,3) + bc(cos a)B(2,3)].

Table 6. Selected Bond Lengths (A) for 4a Ru-Cl1 2.438(2) 01-C3 1.39(1) Ru-C12 2.424(4) 02-C4 1.42(2) Ru-C12' 2.343(7) 02-C5 1.36(1) Ru-P1 2.420(2) 03-C6 1.38(1) Ru-P2 2.406(2) 03-C7 1.44( 1) Ru-C35 1.88(1) 04-C8 1.43(1) Ru-C36 2.00(1) 04-C9 1.42(1) Ru-C36' 2.02(3) 05-C35 1.13( 1) P1-c1 1.829(9) 06-C36 0.96(2) P1-c11 1.822(8) 06'-C36' 1.14(4) P1-C17 1.824(9) Cl-C2 1.51(1) P2-c10 1.82(1) c3-c4 1.47(2) P2-C23 1.836(9) C5-C6 1.49(2) F'2-C29 1.828(9) C7-C8 1.50(1) 01-c2 1.39(1) C9-C10 1.51(1)

eq 1 yield mixtures of monomers and oligomers. The minor products of each reaction appear to be oligomers as demonstrated by the fact that their 31P NMR

242 Organometallics, Vol. 14, No. 1, 1995

Table 7. Selected Bond Lengths (A, for 4bKHdCO

Gray et al.

Ru-Cl1 2.440(2) 02-C4 1.43( 1)n Ru-C12 2.417(3) 02-C5 1.43(1)” Ru-P1 2.413(2) 03-C6 1.43( 1)” Ru-PI 2.404(3) 03-C7 1.43( 1)” Ru-C35 1.853(8) 04-C8 1.43( 1)“ Ru-C36 1.843( 9) 04-C9 1.43(1)” P1-c1 1.807(7) 05-C35 1.13( 1) P1-c11 1.8 1 1 (8) 06-C36 1.16( 1) P1-C17 1.8 19(7) Cl-C2 1.53( l)b P2-c10 1.81 l(8) c3-c4 1.54( l)b P2-C23 1.809(8) C5-C6 1.54( l)b P2-C29 1.834(7) C7-CS 1.54(l)b 01-c2 1.42(1)n C9-C10 1.538(9)b 01-C3 1.431(9)”

a C-0 distances were constrained to 1.43 A. C-C distances were constrained to 1.54 A.

Table 8. Selected Bond Angles (deg) for 4a Cll-Ru-Cl2 96.8(1) C35-Ru-C36 95.3(5) C11 -Ru-C12’ 91.7(2) C35-Ru-C36’ 90.0(9) C11-Ru-P1 90.58(8) Ru-P1-C1 115.0(3) Cll-Ru-P2 88.34(8) Ru-P1-C11 112.1(3) Cll-Ru-C35 178.5(3) Ru-Pl-Cl7 118.8(3) Cll-Ru-C36 83.7(4) Ru-P2-C 10 116.6(3) Cll-Ru-C36’ 91.1(9) Ru-P2-C23 117.8(3) C12-Ru-Pl 90.4(1) Ru-P2-C29 11 1.6(3) C12-Ru-P2 91.7(1) C2-01-C3 115.0(8) C12-Ru-C35 84.3(3) C4-02-C5 115.6(9) C12-Ru-C36 178.0(4) C6-03-C7 116.9(9) C12’-Ru-P1 89.4(2) C8-04-C9 114.3(7) C12’-Ru-P2 88.6(2) P1 -Cl-C2 115.1(6) C12’-Ru-C35 87.3(3) 01-c2-c1 107.8(7) C12’-R~-C36’ 177.2(9) 01-C3-C4 116(1) P 1 - Ru - P2 177.70(8) 02-C4-C3 115(1) Pl-Ru-C35 90.5(3) 02-C5 -C6 113(1) Pl-Ru-C36 87.6(4) 03-C6-C5 106(1) Pl-Ru-C36’ 90.2(9) 03-C7-C8 107.0(8) P2-Ru-C35 90.6( 3) 04-C8-C7 113.6(8) P2-Ru-C36 90.2(4) 04-C9-C 10 105.8(8) P2-Ru-C36’ 91.9(9) P2-ClO-C9 117.4(6)

Table 9. Selected Bond Angles (deg) for 4b.(CH&CO Cll-Ru-C12 91.74(8) Ru-P2-C10 112.2(2) C11-Ru-P1 87.88(7) Ru-P2-C23 117.0(2) Cll-Ru-P2 88.62(7) Ru-P2-C29 112.8(2) Cll-Ru-C35 91.9(2) C2-01-C3 11 1.4(7) Cll-Ru-C36 176.5(3) C4-02-C5 114.4(9) C12 - RU - P 1 87.01(7) C6-03-C7 109.8(7) C12-Ru-P2 85.52(7) C8-04-C9 107.3(7) C12-Ru-C35 176.3(2) Pl-Cl-C2 1 1 9.8( 6) C12-Ru-C36 84.8(3) 01-c2-c1 109.4( 8) P1 -Ru-P2 171.65(8) 01-C3-C4 105.4(8) Pl-Ru-C35 94.0(2) 02-C4-C3 104.9(8) Pl-Ru-C36 91.2(2) 02-C5-C6 109.3(8) P2-Ru-C35 93.7(2) 03-C6-C5 103.2(8) P2-Ru-C36 91.8(2) 03-C7-C8 109.8(7) C35-Ru-C36 91.6(4) 04-C8-C7 102.4(8) Ru-P1-C1 109.2(2) 04-C9-C10 112.1(6) Ru-P1-C11 109.9(2) P2-ClO-C9 114.9(5) Ru-PI-Cl7 118.7(2)

coordination chemical shifts (d31P complex - d31P ligand) (4b, 35.11 ppm; 4c, 36.03 ppm; 4d, 36.45 ppm; 5b, 35.68 ppm; 5c, 36.44 ppm) are similar to those of cis,cis,trans-Ru(CO)~C12{Ph2P(CH2CH~O)~CH3-P}2 (6, 36.00 ~ p m 1 . l ~ ~ This similarity is due to the fact that bridging bis(phosphine1 ligands in oligomeric complexes can adopt conformations similar to those of monodentate phosphine ligands.14 The major products for each reaction appear to be monomers with trans-spanning P~Z.P(CH~CH~O),CH~CH~PP~~ ligands as demonstrated by the fact that their 31P NMR coordination chemical

(14) Hill, W. E.; Minahan, D. M. A.; Taylor, J. G.; McAuliffe, C. A. J. Am. Chem. SOC. 1982,104, 6001.

Table 10. Selected Torsion Angles (deg) for 4a, 4b*(CH&CO, and 1

4a 4b(CH3)zCO 1‘

C11-Ru-P1-C1 67.3(3) 5 3 3 3 ) C11 -Ru-P2-C10 -7 1.1(3) -46.1(3) Ru-Pl-Cl -C2 -71.7(7) -166.5(6) 65.5(4) Ru-P2-ClO-C9 69.4(7) 176.6(5) -65.3(4) C3-01-C2-C1 158.8(8) 179.6(7) -166.4(5) C2-01-C3-C4 61U) 173.5(7) -61.5(8) C5-02-C4-C3 -95(1) - 141.2(9) 157.9(7) C4-02-C5-C6 -169(1) -83(1) -177.8(6) C7-03-C6-C5 171(1) 172.2(8) 168.9(6) C6-03-C7-C8 175(1) -172.1(8) 173.9(5) C9-04-C8-C7 -86(1) 153.5(7) 82.8(5) C8-04-C9-C10 -178.3(7) -78.8(8) 178.4(4) Pl-Cl-C2-01 171.2(6) -55.3(9) -173.4(3) 01-C3-C4-02 6 W ) 67(1) -50.5(9) 02-C5-C6-03 159(1) 8 W ) 142.4(6) 03-C7-C8-04 71(1) -66.7(9) -79.6(5) 04-C9-ClO-P2 170.8(6) -139.4(6) -173.5(3)

a Data from ref 5 . Numbering is identical except Ru should be replaced with Mo.

c3

0 4 01

7

C26 cloL

C15

14

Figure 1. ORTEP12 drawing of the molecular structure of the major rotamer of 4a. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity.

shifts (4a, 31.42 ppm; 5a, 32.85 ppm), are smaller than that of 6. This difference is due to the fact that trans- spanning bis(phosphine) ligands cannot adopt confor- mations similar to those of monodentate phosphine ligands.14 These conclusions are supported by the X-ray crystal structures of 4a and 4b discussed below, and by the fact that the longer ligand, 3, gives a higher yield of the monomeric product, 5a.

The variations in chemical shifts of the ipso, ortho, meta, and pura phenyl and the C1 and C2 methylene 13C NMR resonances are also consistent with the assignment of the solution structures of the RuC12- (CO)~{P~~P(CHBCH~O),CH~CH~PP~~} complexes made in the previous paragraph. The chemical shifts of these resonances are similar for 4b and 4d, in which the Ph2P(CH2CH20)&H2CH2PPh2 ligands are bridging, but are significantly different from those for 4a, in which the same ligand is trans-spanning. The chemical shifts of these resonances for Sa, in which the longer Ph2P(CH2- CH20)&H2CH2PPh2 ligand is trans-spanning, are in-

Ruthenium Metallacrown Ethers Organometallics, Vol. 14, No. 1, 1995 243

coordination chemical shifts is quite different for the two types of complexes. In the square planar complexes, the coordination chemical shifts from trans-coordination of bidentate ligands increase as the length of the ligand decreases,14 but the opposite trend is observed for 4a and Sa. This suggests that the additional cis ligands in octahedral complexes cause the conformations of trans-spanning ligands in these complexes to be differ- ent from those of trans-spanning ligands in square planar complexes.

NMR resonance is observed for the carbonyl ligands in both 4a and 5a. This suggests that the RuC12(CO)2 group moves freely within the chelate ring to average the environments of the two carbonyl ligands because the chemical shifts of carbonyl resonances in transition metal complexes are quite sensitive to asymmetry in the phosphine ligands.15 The rotation of the RuC12(C0)2 around the P-Ru-P axis is strongly supported by the fact that two rotamers of 4a are observed in the solid state, as discussed below. The carbonyl 13C NMR resonance of 4a does not broaden as much as does that of ~~~~~-Mo(CO)~{P~~P(CH~CH~O).&H~CH~PP~~-P,P '1, 1: as the temperature is lowered from 21 "C to -80 "C. This suggests that the barrier to rotation about the P-M-P axis is somewhat lower in 4a than in 1. The lower rotation barrier in 4a could be due to the fact that the carbonyl ligands in 4a can be averaged by rotating the RuC12(CO)2 group so that the trans-spanning ligand moves over the smaller chlorides but not over the larger carbonyl ligands. This is not possible in 1.

X-ray Crystal Structure of cis,cis,truns-RuCl~- (CO>~{P~&'(CH&HZO>&HZCHZ~P~~-P~ '1,4a. The X-ray crystal structure of 4a has been determined. The ruthenium has an octahedral coordination geometry with a trans-spanning Ph2P(CH2CH20)4CH2CH2PPhz ligand, cis carbonyl ligands and cis chloride ligands consistent with the NMR data. Two rotamers of the RuCl2(C0)2 group relative to the trans-spanning ligand are observed, and ORTEP drawings of the major and minor rotamers Of 4a are shown in Figures 1 and 2. In the major rotamer (-70%), the trans-spanning ligand passes between one carbonyl and one chloride while in the minor rotamer (-30%), the trans-spanning ligand passes between the two chlorides. There is no evidence of the third rotamer in which the trans-spanning ligand would pass between the two carbonyls. The relative abundances of the two rotamers are consistent with a statistical occupancy of the sites.

The presence of rotamers in the crystal structure of 4a may be due to the fact that rotation about the P-Ru-P bond to generate the two different rotamers does not affect the orientation of the phenyls and the trans-spanning polyether chain. Because these are the outermost portions of the molecule, the rotamers would have the same shapes and could cocrystallize. However, if this is the case, it is somewhat surprising that the third rotamer, in which the trans-spanning ligand passes between the two carbonyls, is not observed. It is possible that this rotamer is not observed because, when the trans-spanning ligand is between two larger carbonyl ligands, it adopts a different and less stable conformation that prevents cocrystallization with the other two rotamers. This hypothesis is supported by the fact that conformation of the trans-spanning ligand

A final point of interest is that a single

c3

04hc9

I gb cll

f o l

I c19

W

Figure 2. ORTEPI2 drawing of the molecular structure of the minor rotamer of 4a. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity.

Figure 3. 0RTEPl2 drawing of the molecular structure of 4b. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity.

termediate between those for 4a, on the one hand, and those for 4b and 4d, on the other.

Although the complexes in this study are the first octahedral complexes observed to form both monomers with trans-spanning bis(phosphine) ligands and oligo- mers with bridging bis(phosphine) ligands, it is well established that such mixtures are formed when bis- (phosphine) ligands react with square-planar platinum- group metal (Rh(I), Ir(I), Pd(II), and Pt(I1)) precur- s o r ~ . ~ ~ , ~ ~ However, the behavior of the 31P NMR

(15) (a) March, F. C.; Mason, R.; Thomas, K. M.; Shaw, B. L. J. Chem. SOC., Chem. Commun. 1976, 584. (b) Pryde, A.: Shaw, B. L.; Weeks, B. J. Chem. SOC., Dalton Trans. 1976,322. (c) Appleton, T. G.: Bennett, M. A.; Tompkins, B. I. J. Chem. Soc., Dalton Trans. 1976, 439. (d) Sanger, A. R. J. Chem. Soc., Dalton Trans. 1977, 120. (e) Alcock, N. W., Brown, J. M.; Jeffery, J. C. J . Chem. Soc., Dalton Trans. 1977,888. (0 Sanger, A. R. J. Chem. SOC., Dalton Trans. 1977,1971. (g) Al-Salem, N. A.; Empsall, H. D.; Markham, R.; Shaw, B. L.; Weeks, B. J. Chem. SOC., Dalton Trans. 1979,1972. (h) Hill, W. E.; McAuliffe, C. A.; Niven, I. E.; Parrish, R. V. Inorg. Chim. Acta 1980,38,273. (i) Crocker, C.; Errington, J.; Markham, R.; Moulton, C. J.; Odell, K. J.; Shaw, B. L. J. Am. Chem. SOC. 1980,102,4373. (i) Hill, W. E.; Minahan, D. M. A.; McAuliffe, C. A. Inorg. Chem. 1983,22, 3382. (16) Gray, G. M.; Redmill, K. A. Inorg. Chem. 1985,24, 1279.

244 Organometallics, Vol. 14, No. 1, 1995

in 4a is quite different from that of the identical ligand in 1 as indicated by torsion angles (Table 10) that differ by as much as 60". X-ray Crystal Structure of [cis,cis,truns-RuCl2-

(CO)2(C1-Ph2P(CH2CH20)4CH2CH2PPh2PQ '}, 4b. The X-ray crystal structure of 4b has been determined and shown to be a cyclic dimer. A n ORTEP drawing of the structure is shown in Figure 3. Consistent with the NMR data, each Ru has an octahedral coordination geometry with trans, bridging Ph2P(CH&H20)4CH2- CH2PPh2 ligands, cis carbonyl ligands and cis chloride ligands. The bond lengths and angles about the Ru are similar to those observed in 4a with the largest differ- ence in the P-Ru-P angles (4b: 171.65(8)"; 4a: 177.70- (8)"). This is consistent with the fact that the 31P NMR coordination chemical shift of 4b was larger than that of 4a which suggested that the phosphorus environ- ments were different in the two complexes.

The most interesting feature of this structure is that the trans coordination of the bridging bidphosphine) ligands results in two, separate metallacrown ether sites. Because each ruthenium is octahedral and the molecule crystallizes around an inversion center, both a chloride and a carbonyl ligand stick into the cavity and separate these two sites. This results in a Ru-Ru distance of 9.1961(9) A indicating that there is no interaction between the two ruthenium centers. These

Gray et al.

cavities are enclosed by the phenyl groups on P1 and P2 that are located above and below the cavities. This conformation suggests that it may be possible to coor- dinate a hard metal cation to each of these sites to form tetrametallic complexes. It may also be possible to bridge a bidentate ligand between the two rutheniums to generate a more rigid dimetallacrown ether. Such complexes could exhibit unusual catalytic activities and selectivities.

Acknowledgment. The authors thank the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research, Johnson Mathey for a generous loan of RuCl3-nH20, and Dale C. Smith, Jr., for helpful discus- sions. A.V. thanks the Graduate School of the Univer- sity of Alabama at Birmingham for a Graduate Fellow- ship.

Supplementary Material Available: Tables of X-ray crystallographic data for 4a and 4b including hydrogen coordinates and B values, anisotropic thermal parameters, complete bond lengths and angles, torsion angles, and least squares planes (16 pages). Ordering information is given on any current masthead page.

0M940650+