2800 Organometallics 1989, 8, 2800-2804

the Petroleum Research Fund, administered by the Am- erican Chemical Society.

Supplementary Material Available: Listings of mass spectrometric data (Table S-1) and IR absorptions (Table S-2) of I11 and IV, an additional table of bond lengths, bond angles, and torsion angles for I11 (Table S-3), a table of anisotropic

displacement coefficients of I11 (Table S-4, a table of H-atom coordinates and isotropic displacement coefficients of I11 (Table S-5), a table of calculated bond distances of I11 and IV.(Cl5HI1N3) (Table S-6), and a listing of one- and two-center terms and op- timized dihedral angles for IV~(Cl5HI1NB) (Table S-7) (23 pages); a listing of structure factors of III (Table S-8) (41 pages). Ordering information is given on any current masthead page.

Synthesis of Transition-Metal-Substituted Diarsenes. X-ray Structure Analysis of ($-C,Me,) (CO),FeAs[Cr(CO),] =AsR

(R = 2,4,6-t-B~SCeH,)

Lothar Weber," Dagmar Bungardt, Achim Muller, and Hartmut Bogge

Fakuffat fur Chemie der Universitat Biele feM, 0-4800 BielefeM 1, Germany

Received April 3, 1989

The reaction of (q5-C5Me5)(CO)zFeAs(SiMe,)z with RAsC1, (R = 2,4,6-t-Bu3C6Hz) in THF afforded the twice metalated cyclotetraarsine [ (q5-C5Me5)(C0)2FeAsAsR]2. However, if the freshly prepared reaction mixture was treated with ((Z)-cycl~octene)Cr(CO)~, the metal-functionalized diarsene was intercepted as its Cr(CO)5 adduct (q5-C5Me5)(CO)2FeAs[Cr(CO)5]=A~R. Similarly the complex (q5-C5H5)(CO)(PPh3)- FeAs[ Cr(CO)5]=AsR was prepared. The novel compounds were characterized by elemental analyses and spectroscopic methods (IR, 'H and 13C NMR, and mass spectroscopy). The molecular structure of the diarsene derivative (q5-C5Me5)(CO)2FeAs[Cr(CO)5]=AsR was established by a singlecrystal X-ray diffraction study [Pl space group; 2 = 2, a = 1057.0 (4) pm, b = 1246.6 (5) pm, c = 1577.2 (7) pm; a = 88.08 (3)O, 0 = 86.20 (3)O, y = 82.37 (3)OI.

There is a great current interest in the chemistry of compounds of main-group elements in low coordination numbers.'p2 In contrast to a considerable number of di- phosphenes, featuring P=P double bonds, there are only few examples of the corresponding diarsenes (A-C) de- scribed in the literature. The same is true for coordination compounds involving diphosphene and diarsene ligands (D-G) .

Me,Si

Me3Si-C I

As=As, ,H Me,Si' 'As=As, ,SiMe, F-SiMe, Y-SiMe, I

SiMe3 A3

SiMe,

(1) Cowley, A. H. Polyhedron 1984,3, 389. Cowley, A. H.; Norman,

(2) Scherer, 0. J. Angew. Chem. 1985,97,905; Angew. Chem., Int. Ed.

(3) Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. J. Am.

(4) Couret, C.; Escudi6, J.; Madule, Y.; Ranaivonjatovo, H.; Wolf, J.-G.

N. C. h o g . Inorg. Chem. 1986,34,1.

Engl. 1985, 24, 924.

Chem. SOC. 1983, 103, 5506.

Tetrahedron Lett . 1983, 24, 2769.

Recently we developed a synthetic procedure for tran- sition-metal-substituted diphosphenes (diphosphenyl complexes):

[MI :As=ER (1) 2

1, 2, E = P; 3, E = As; [MI = (v5-C5Me5) (C0)2Fe,1" ( V ~ - C ~ M ~ ~ ) ( C O ) ~ R U , ~ ~ (V~-C~M~~) (CO)~OS, ' " (V~-C,M~~)(CO)(NO)M~," (v5-C5Me5)(CO)(NO)Re,12 (v5-C5H5)(CO)(PPh3)Fe1"

Similarly the isomeric metalated phosphaarsenes (phos- phaarsenyl complexes) 213 and 35 were generated.

Independently Jutzi et al. presented an alternative pathway to diphosphenyl- and phosphaarsenyl complexes of chromium and m01ybdenum.l~ It was of interest to find

(5) (a) Weber, L.; Bungardt, D.; Sonnenberg, U.; Boese, R. Angew. Chem. 1988,100,1595; Angew. Chem., Znt. Ed. Engl. 1988,27,1537. (b) Weber, L.; Bungardt, D.; Boese, R. 2. Anorg. Allg. Chem., in press.

(6) Elmes, P. S.; Leverett, P.; West, B. 0. J. Chem. Soc., Chem. Com- mun. 1971, 747.

(7) Elmes, P. S.; Scudder, M. L.; West, B. 0. J. Organomet. Chem. 1976,122, 281.

(8) Cowley, A. H.; Kilduff, J. E.; Lasch, J. G.; Norman, N. C.; Pa- kulsky, M.; Ando, F.; Wright, T. C. Organometallics 1984, 3, 1044.

(9) Huttner, G.; Schmid, H. G.; Frank, A.; Orama, 0. Angew Chem. 1976,88, 255; Angew. Chem., Int. Ed. Engl. 1976, 15, 234. (10) Weber, L.; Reizig, K.; Boese, R. Organometallics 1987, 6, 110. (11) Weber, L.; Meine, G. Chem. Ber. 1987, 120, 457. (12) Weber, L.; Meine, G.; Boese, R.; Bliiser, D. Chem. Ber. 1988,121,

(13) Weber, L.; Bungardt, D.; Boese, R.; BlLer, D. Chem. Ber. 1988,

(14) Jutzi, P.; Meyer, U. Chem. Ber. 1988, 121, 559.

853.

121, 1033.

0276-7333/89/2308-2800$01.50/0 0 1989 American Chemical Society

Synthesis of Transi t ion-Metal-Subst i tuted Diarsenes

out if the synthetic approach of eq 1 is useful for the preparation of transition-metal-substituted diarsenes (diarsenyl complexes) as well. Parts of our results have been reported in a preliminary comm~nication.'~

Experimental Section General Information. Standard inert-atmosphere techniques

were used for the manipulation of reagents and reaction products. Infrared spectra were recorded on a Perkin-Elmer Model 597 spectrometer. The 'H and 13C NMR spectra were taken on a Varian XL 200 NMR spectrometer in C6D6 solution a t ambient temperature. Electron-impact mass spectra were recorded on a Varian MAT 312 spectrometer.

Materials. The disilylarsenido complexes (v5-C5Me5)- (C0)zFeAs(SiMe3)z (4a)16 and (q5-C5H5)(CO)(PPh3)FeAs(SiMe3)2 (4b),lS a hexane solution of ((Z)-cycl~octene)Cr(CO)~,~~ and the dichloroarsine 2,4,6-t-Bu3C6H2AsClz (= R A S C ~ ~ ) ~ were prepared as described in the literature. All solvents were rigourously dried with an appropriate drying agent and distilled before use. Alumina (TSC Woelm, Eschwege, Germany) was used for column chro- matography.

Preparation of Compounds. [ (q5-C5Me5)(CO)zFeAsAsR]z (6a). To a solution of 1.36 g (2.90 mmol) of (v5-C5Me5)- (C0)zFeAs(SiMe3)2 (4a) in 30 mL of T H F was added 1.13 g (2.90 mmol) of solid 2,4,6-t-Bu3C6H2&Clz a t 0 "C, and the mixture was stirred for 30 min a t 20 "C. All volatiles were removed in vacuo. The residue was dissolved in 20 mL of ether and filtered. The red-brown filtrate was stored a t -28 "C to give red-violet mi- crocrystalline tetracarbonyl(p-3,4-disupermesitylcyclotetra- arsine-l,2-diyl)bis(pentamethylcyclopentadienyl)diiron (6a), which was recrystallized from ether a t 4 "C: yield: 0.55 g (30%); mp 149 "C dec; IR (cyclopentane) 1981 (vs), 1944 (s), 1928 (m) cm-' [v(CO)]; IR (Nujol) 1975 (vs), 1973 (vs), 1956 (w), 1938 (s), 1927 (w), 1918 (m) [v(CO)], 1587 (w) [u(c=c)], 1363 (m), 1262 (w), 1245 (w), 1121 (m), 1071 (m), 1033 (m), 871 (s), 803 (s), 740 (s), 636 (m) cm-'; 'H NMR 6 1.36 (s, 18 H, p-t-Bu), 1.42 (s, 30 H, C5Me5), 1.88 (s, 18 H, o-t-Bu), 2.09 (s, 18 H, o-t-Bu), 7.36 (d, J = 2 Hz, 2 H, aryl-H), 7.53 (d, J = 2 Hz, aryl-H); 13C{1HJ NMR 6 9.80 (s, C,(CH,),), 31.56 (s, p-C(CH,)S), 34.65 (s, p-C(CHJ, ) , 34.69 (s, o - C ( C H ~ ) ~ ) , 36.59 (5, o - C ( C H ~ ) ~ ) , 39.57 (s, o - C ( C H ~ ) ~ ) , 41.00 (s, o-C(CH,),), 95.00 (s, C,(CH,),), 120.42 (s), 124.42 (s), 145.46 (s), 147.61 (s), 157.97 (s, aryl-C), 217.26 (s, Fe(CO)), 218.50 (s, Fe(C0)); MS/FD, m/e 1286 (M'). Anal. Calcd for CWHM- As4Fe204 (1284.9): C, 56.08; H, 6.92; Fe, 8.69. Found: C, 56.37; H, 6.81; Fe, 9.16. (q5-C5Me5)(CO)zFeAs[Cr(CO)5]=AsR (7a). A mixture of

1.36 g (2.90 mmol) of 4a and 1.13 g (2.90 mmol) of 2,4,6-t- Bu3C6H2AsC1, in 30 mL of T H F was allowed to react for 30 min and was then treated with 150 mL of a photochemically prepared solution of ((Z)-C8Hl4)Cr(CO), (3.60 mmol) in hexane. The re- sulting solution was stirred for 1 h a t 20 "C and was then freed from solvent. The red-brown residue was chromatographed on alumina. Development with petroleum ether gave two orange- yellow bands. From the first band 0.09 g (10%) of crystalline orange-yellow [ 2 , 4 , 6 - t - B ~ ~ C ~ H ~ A s ] ~ was i s ~ l a t e d . ~ The eluate of the second band was discarded. The elution was continued with a mixture of petroleum ether and ether (5:1), resulting in the development of a red-violet and a dark red band. From the red-violet band 0.21 g of 6a was obtained, whereas the following red band furnished 0.46 (19%) of dark red crystalline (v5- C5Me5)(CO)2FeAs[Cr(C0)5]=A~R (7a); mp 170 "C dec; IR (cy- clopentane) 2014 ($, 1969 (s) cm-' [u(Fe(CO))], 2059 (s), 1985 (s), 1945 (vs), 1936 (s), 1925 [v(Cr(CO),)] cm-'; IR (Nujol) 2054 (s), 2012 (s), 1973 (s), 1944 (s), 1930 (s), 1927 (s), 1914 (s) [v(CO)], 1598 (w) [v(C=C)], 1368 (w), 1216 (w), 1126 (w), 1027 (w), 880 (w), 728 (w), 665 (m), 650 (m) cm-'; 'H NMR 6 1.39 (s, 9 H, p-t-Bu),

m-aryl-H); '%{'H) NMR 6 10.09 (8, C5(CHJ5), 31.46 (9, p-C(CHJ,), 1.46 (9, 15 H, C5(CH3)5), 1.65 (9, 18 H, 0-t-Bu), 7.66 (8, 2 H,

33.53 (s, o-C(CH,),), 35.17 (s, p-C(CH,),), 39.21 (9, o-C(CH,),),

Organometallics, Vol. 8, No. 12, 1989 2801

97.43 (s, C5(CH3)5), 122.99 (s), 150.92 (s), 152.31 (e), 155.64 (8, aryl-C), 214.87 (s, Fe(CO)), 216.06 (s, Cr(CO),), 226.53 (s, Cr- (CO)bm); MS/EI (70 eV, 70 "C), m/e 835 (M+). Anal. Calcd for C&144As2CrFe07 (834.5): C, 50.37; H, 5.33; Cr, 6.23; Fe, 6.69. Found C, 50.30; H, 5.33; Cr, 6.16; Fe, 6.63. (q5-C5H5)(CO)(PPh3)FeAs[Cr(CO)5]=AsR (7b). To a so-

lution of 1.77 g (2.80 "01) of (q5-C5H5)(CO)(PPh3)Feks(SiMe3)z (4b) in 40 mL of T H F was added 1.09 g (2.80 mmol) of 2,4,6-t- Bu3C6H2AsClz (RAsCl2) a t 0 "C. A color change from green to browh was observed. After the mixture was stirred for 10 min a t 20 "C, a solution of 3.2 mmol of photochemically freshly prepared ((z)-cy~looctene)Cr(CO)~ in 40 mL of hexane was added. Stirring a t room temperature was continued for another hour. Then the red-brown solution was freed from volatiles. The residue was subsequently chromatographed. With petroleum ether an orange band was separated from a yellow zone. From the eluate of the orange band 0.02 g (2%) of orange-yellow RAs=AsR (C) was isolated. The eluate of the yellow band was discarded. Then with T H F a red-brown fraction was taken, which was brought to dryness in vacuo. The remaining red-brown solid was triturated with ether, filtered, and dried in vacuo to yield 1.13 g (40%) of 7b: IR (cyclopentane) 2054 (s), 1977 (w), 1936 (s), 1931 (s), 1923 (s) [u(Cr(CO))], 1962 (s) [u(Fe(CO))] cm-'; IR (Nujol) 2052 (s), 1982 (w), 1958 (w), 1938 (sh), 1931 (s), 1919 (w), 1913 (w) [u(CO)], 1585 (w) [v(C==C)], 1090 (w), 976 (m), 870 (w), 842 (w), 820 (w), 740 (w), 690 (m), 665 (s), 648 (s) cm-'; 'H NMR 6 1.28 (s, 9 H,

= 1.2 Hz, 5 H, C5H5), 7.00 (m), 7.42 (m, 15 H, Ph), 7.66 (s, 2 H, m-aryl-H); l3C('H) NMR 6 31.62 (9, p-C(CHS)J, 34.21 (s, 0-C-

p-t-Bu), 1.48 (9, 9 H, 0-t-Bu), 1.59 (9, 9 H, 0-t-Bu), 4.54 (d, 3JpH

(CH3)3), 34.27 (9, o-C(CH~)~) , 35.44 (8, p-C(CH,),), 39.25 (8, 0-C- (CH3)3), 39.54 (8, o-C(CH,),), 84.41 (9, C5H5), 123.21 (s), 123.66 (s), 129.42 (d, Jpc = 9.5 Hz), 131.26 (s), 134.37 (d, Jpc = 11.1 Hz), 148.96 (s), 150.89 (s), 151.58 (s), 157.48 (s, aryl-C and phenyl-C), 217.50 (s, Cr(CO),,), 219.48 (d, VPc = 31.8 Hz, Fe(CO)), 227.37 (s, Cr(CO),,); 31P{1H) NMR 6 71.5 (s); MS/FD, m/e 998 (M+). Anal. Calcd for CI7H&szCrFeO8 (998.6): C, 56.53; H, 4.96; Cr, 5.21; Fe, 5.59. Found C, 56.54; H, 5.09; Cr, 5.13; Fe, 5.79.

X-ray Structure Determination of (q5-C5Me5)(CO)2FeAs[Cr(C0)5]=AsR 0.5C4HlOO

(7a 0.5C4H100) Crystals of 7a.0.5C4H100 were grown from diethyl ether a t 4

"C. The structure of 7a was determined a t 21 "C from a suitable single crystal (crystal dimensions 0.65 x 0.5 X 0.15 mm) by using a Syntex P2, four-circle diffractometer (graphite-monochromated Mo Ka radiation, X = 71.069 pm, w-scan, 4.5-29.3"/min). Unit-cell parameters were obtained by refinement of the angular settings of 15 reflections (20" < 20 < 30"). 7a crystallizes triclinic (PI, a = 1057.0 (4) pm b = 1246.6 (5) pm, c = 1577.2 (7) pm; a = 88.08 (3)", 6 = 86.20 (3)", y = 82.37 (3)"; V = 2054.5 X lo6 pm3; D,, = 1.41 gem-,; = 22.18 cm-'; Z = 2). Three periodically monitored reflections showed a decay in their intensity (to a value of 0.84 of the starting intensity) due to slow decomposition of the crystal. The intensity data were corrected for this effect. Lp and empirical absorption corrections were applied, too. The structure was solved by direct methods (SHELXTL18 program package). The final refinements (all atoms except a disordered E h O molecule a t 0, 1, l/z were refined anisotropically) converged to R = 0.072 and

0.0001F2) for 5448 independent data (F, > 3.92a(F0), 4" < 219 < 54", +h,fk,fl octands). The maximum residual electron density was 0.91 x 104/e.pm-? The atomic scattering factors for d atoms were taken from standard source^.'^

R, = ( C U ~ ( ~ F ~ I - ~ F , . ~ ) 2 / ~ ~ ~ F o ~ 2 ) ' ~ 2 = 0.070 ( l / ~ = 02(F) +

Results and Discussion The disilylarsenido iron complex 4a smoothly reads with

an equimolar amount of 2,4,6-t-Bu3C6H2AsC1, (RAsC12) in THF to give the red-violet cyclotetraarsine 6a in 30% yield. Presumably under these conditions the expected

(15) Weber, L.; Bungardt, D. J. Organomet. Chem. 1988, 354, C1. (16) Weber, L.; Meine, G.; Bungardt, D.; Boese, R. 2. Anorg. Allg.

(17) Grevels, F.-W.; Skibbe, V. J. Chem. Soc., Chem. Commun. 1984, Chem. 1987,549, 73.

681.

(18) Nicolet Analytical Instruments: "SHELXTL" by G. M. Shel-

(19) Internotional Tables for X-ray Crystallography; Kynoch Press: drick, Revision 5.1, December 1985.

Birmingham, England, 1974; Vol. IV.

2802 Organometallics, Vol. 8, No. 12, 1989 Weber et al.

+ R -As=As -R

lFe1 >As = A s 0 (CO)5Cr 'R

7a,b

a, [Fe] = (C5Me5)(C0)2Fe; b, [Fe] = (C5H5)(CO)(PPh3)Fe; R = 2,4,6-t-Bu3C6H2; L = (Z)-cyclooctene

diarsenyl complex 5a undergoes head to head dimerization to the four-membered ring 6a. If, however, the reaction mixture is treated with a freshly prepared hexane solution of ((z)-cyclooctene)Cr(CO)5, the transient diarsenyl com- plex 5a is trapped as the stable (CO),Cr adduct 7a in 19% yield. The red, crystalline 7a is separated from the or- ange-yellow diarsene 8 (10%) and from the ring compound 6a (11 70) by column chromatography. Similarily the red-brown diarsenyl complex 7b is obtained in 40% yield. The products 6a, 7a, and 7b were initially characterized by elemental analyses and spectroscopic methods (IR, 'H and 13C NMR, and MS). The IR spectrum of 7a (cyclo- pentane solution) displays more v(C0) bands as expected for the nonperturbed Clv symmetry of the Cr(C0)5 frag- ment. The frequencies, number, and intensities of the v(C0) bands of the Cr(C0)5 group and the Fe(C0)2 moiety in 7a are nearly identical with those registered for the analogous diphosphenyl complex (q5-C5Me5)(C0)2FeP- [Cr(CO),]=PR (9) (2059 (m), 1985 (w), 1947 (vs), 1939 (s), 1924 (s) [v(Cr(CO),)]; 2016 (ms), 1972 (m) cm-' [v(Fe- (CO)2)])'2 and the two isomeric phosphaarsenyl complexes (q5-C5Me5) ( CO)2FeAs [ Cr (CO),]=PR ( (2060 (s), 1986 (w), 1947 (m), 1939 (s), 1924 (s) [v(Cr(CO),)], 2016 (s), 1971 (s) cm-' [ ~ ( F e ( C 0 ) ~ ) 1 ) and (q5-C5Me5)(C0)2FeP[Cr- (CO),]=AsR (11) (2061 (s), 1986 (w), 1946 (vs), 1938 (s), 1925 (s) [v(Cr(CO),)], 2018 (s), 1973 (s) cm-l [v(Fe(CO)J])? This finding indicates a comparable u donor ?r acceptor

P, As) in the Cr(CO), adducts and analogous structures of these molecules. Consequently the Cr(C0)5 moiety in 7a should be attached to the metalated arsenic atom of the As=As double bond. The same is true for 7b and the analogous complexes (C,H,)(CO)(PP~,)F~AS[C~(CO)~]= PR (2054 (s), 1976 (m) 1937 (vs), 1931 (vs), 1924 (vs) [Y- (Cr(CO),)]; 1962 (vs) [V(F~(CO)~)] cm-lP0 and (C5H5)- (CO)(PPh3)FeP[Cr(C0)5]=AsR (2054 (m), 1978 (s), 1938 (s), 1930 (s), 1924 (s), [v(Cr(CO),)]; 1964 (s) cm-l [v- (FeCO)2)]).5b The mass spectrum (FD) of 6a displays the molecular ion of the cyclotetraarsine with 17% intensity relative to the peak of the monomer 5a at m / e (100%). The easy fragmentation of the four-membered ring may be caused by the bulky substituents. The cyclo- dimerization of 5a can principally lead to the isomeric cyclotetraarsines 6a and 6a'. The observation of two 'H

ratio of the ligands (q5-C5Me5)(C0)2FeE1=E Li R (El, E2 =

6a 6a* 12

NMR resonances for the four o-butyl groups and for the four m-aryl protons, respectively, as well as the registration of two 13C NMR absorptions for the o-tert-butyl substit- uents is in agreement with the dissymmetric structure 6a. It is conceivable, however, that hindered rotation of the

Table I. Atomic Coordinates and Equivalent Isotropic Thermal Parameters ( lo4 pm') for 7a

atom X Y 2 U As(1) 0.4882 (1) As(2) 0.4286 (1) Fe 0.3182 (1) Cr 0.6946 (1) O(1) 0.3444 (7) O(2) 0.4926 (6) O(3) 0.8294 (6) O(4) 0.7632 (7) O(5) 0.9476 (7) O(6) 0.6133 (8) O(7) 0.5917 (8) C(1) 0.3365 (8) C(2) 0.4256 (7) C(3) 0.7716 (8) C(4) 0.7368 (8) C(5) 0.8501 (9) C(6) 0.6435 (9) C(7) 0.6282 (9) C(8) 0.5665 (8) C(9) 0.5759 (7) C(l0) 0.6774 (9) C(l1) 0.7630 (9) C(l2) 0.7511 (8) C(13) 0.6525 (7) C(14) 0.4832 (8) C(15) 0.4970 (10) C(l6) 0.3389 (9) C(17) 0.5106 (11) C(18) 0.8722 (10) C(19) 0.8528 (14) C(20) 0.8608 (14) C(21) 1.oO01 (11) C(22) 0.6410 (8) C(23) 0.6799 (9) C(24) 0.7349 (10) C(25) 0.5046 (9) C(26) 0.1850 (8) C(27) 0.1270 (8) C(28) 0.1343 (9) C(29) 0.1936 (9) C(30) 0.2262 (8) C(31) 0.1816 (11) C(32) 0.0650 (11) C(33) 0.0760 (11) C(34) 0.2094 (12) C(35) 0.2804 (11) Et(1) -0.1096 (46) Et(2) -0.1017 (39) Et(3) -0.0524 (45) Et(4) -0.0141 (29) Et(5) 0.0405 (58)

" U defined as one-th tensor.

0.6587 (1) 0.8107 (1) 0.5553 (1) 0.5899 (1) 0.5930 (5) 0.3559 (4) 0.7784 (5) 0.4668 (5) 0.4995 (7) 0.7036 (5) 0.3946 (5) 0.5797 (6) 0.4358 (6) 0.7095 (7) 0.5142 (6) 0.5335 (8) 0.6627 (7) 0.4703 (7) 0.9043 (5) 0.9856 (5) 1.0492 (6) 1.0371 (6) 0.9592 (6) 0.8946 (5) 1.0138 (6) 0.9217 (6) 1.0370 (7) 1.1183 (7) 1.1077 (7) 1.1725 (10) 1.1950 (11) 1.0389 (10) 0.8193 (6) 0.6974 (6) 0.8434 (7) 0.8357 (7) 0.6577 (6) 0.6305 (7) 0.5131 (8) 0.4712 (7) 0.5572 (7) 0.7712 (7) 0.7111 (10) 0.4517 (12) 0.3544 (8) 0.5514 (10) 0.9144 (39) 0.8654 (32) 0.7787 (38) 1.0695 (20) 0.9931 (64)

iird of the trac

0.7569 (1) 0.8313 (1) 0.7971 (1) 0.6793 (1) 0.9751 (4) 0.8026 (4) 0.7226 (4) 0.8415 (4) 0.5983 (5) 0.5164 (4) 0.6135 (5) 0.9038 (5) 0.7997 (5) 0.7088 (5) 0.7812 (5) 0.6280 (6) 0.5798 (6) 0.6409 (5) 0.8265 (5) 0.7617 (5) 0.7644 (5) 0.8241 (6) 0.8908 (5) 0.8929 (5) 0.6920 (5) 0.6250 (5) 0.7288 (6) 0.6395 (6) 0.8275 (7) 0.9125 (9) 0.7539 (10) 0.8228 (12) 0.9751 (5) 0.9524 (6) 1.0419 (6) 1.0199 (5) 0.7262 (5) 0.8057 (6) 0.8115 (7) 0.7367 (7) 0.6820 (5) 0.6875 (8) 0.8713 (7) 0.8889 (8) 0.7097 (9) 0.5908 (6) 0.5120 (30) 0.4843 (25) 0.4891 (29) 0.5092 (18) 0.5038 (50)

:e of the orthc

0.038 (1)' 0.043 (1)" 0.040 (1)' 0.046 (1)" 0.086 (3)' 0.078 (3)" 0.082 (3)" 0.088 (3)" 0.117 (4)" 0.105 (4)" 0.097 (3)" 0.057 (3)" 0.049 (3)" 0.059 (3)" 0.052 (3)" 0.070 (4)" 0.065 (4)" 0.061 (3)" 0.042 (3)" 0.041 (3)" 0.050 (3)" 0.056 (3)" 0.049 (3)' 0.039 (3)" 0.051 (3)" 0.070 (4)" 0.071 (4)" 0.084 (5)" 0.074 (4)" 0.138 (7)" 0.150 (8)" 0.159 (9)" 0.050 (3)O 0.063 (4)" 0.072 (4)" 0.064 (4)" 0.055 (3)" 0.063 (4)" 0.074 (4)" 0.067 (4)" 0.059 (3)" 0.102 (5)" 0.118 (6)" 0.141 (7)" 0.120 (6)" 0.103 (5)" 0.188 (20) 0.158 (16) 0.228 (20) 0.129 (10) 0.247 (22)

)gonalized Uij

aryl groups of structure 6a' may lead to similar spectra. Unfortunately solutions of the ring begin to decompose at about 45 "C. The constitution of the compound can be derived by comparison with the dissymmetic 1,Zdiphos- pha-3,4-diarsetane 12.5b

The 'H NMR spectra of 6a and 12 are nearly identical. The molecular structure of 12 is known, and therefore the cyclotetraarsine most likely has structure 6a. Structure 6a' with a hindered rotation can be excluded. Repeated attempts to grow crystals of 6a suitable for an X-ray diffraction analysis, failed. Crystallization of 6a from various solvents always resulted in the formation of very fine needles.

X-ray Structure Analysis of 7a 0.5C4Hlo0 The X-ray structure analysis of 7a fully confirms the

conclusions derived from analysis and spectroscopic data. The results of the structural determinations are shown in

Synthesis of Transition-Metal-Substituted Diarsenes

oc32 Ci6

b o 5

Figure 1. Molecular structure of 7a in the crystal.

Table 11. Selected Bond Lengths (pm) of 7a As(l)-As(2) 225.9 (1) Cr-C(4) 188.5 (8) As(1)-Fe 238.7 (1) Cr-C(5) 184.5 (9) As(1)-Cr 249.2 (1) Cr-C(6) 186.1 (9) As(2)-C(8) 198.0 (8) Cr-C(7) 186.4 (9) Fe-C(l) 174.9 (9) O-(l)-C(l) 115.1 (10) Fe-C(2) 175.0 (7) 0(2)-C(2) 114.4 (9) Fe-C(26) 212.1 (8) 0(3)-C(3) 115.2 (11) Fe-C(27) 211.0 (8) 0(4)-C(4) 113.4 (10) Fe-C(28) 207.7 (10) 0(5)-C(5) 113.9 (11) Fe-C(29) 208.3 (10) 0(6)-C(6) 115.2 (11) Fe-C(30) 211.4 (9) 0(7)-C(7) 117.2 (12) Cr-C(3) 187.6 (9)

Table 111. Selected Bond Angles (deg) of 7a0 As(2)-As(l)-Fe 101.6 (1) C(4)-Cr-C(5) 90.2 (4) As(B)-As(l)-Cr 131.1 (1) C(4)-Cr-C(6) 176.7 (4) Fe-As( 1)-Cr 125.9 (1) C(4)-Cr-C(7) 90.5 (4) As(l)-As(Z)-C(8) 111.4 (2) C(5)-Cr-C(6) 92.3 (4) As(1)-Fe-C(1) 89.5 (3) C(5)-Cr-C(7) 87.5 (4) As(l)-Fe-C(2) 91.1 (3) C(6)-Cr-C(7) 87.5 (4) C(l)-Fe-C(2) 92.1 (4) Fe-C(l)-O(I) 177.0 (8) As(l)-Cr-C(3) 92.4 (3) Fe-C(2)-0(2) 177.7 (7) As(l)-Cr-C(4) 86.1 (2) Cr-C(3)-0(3) 173.4 (7) As(l)-Cr-C(5) 176.3 (3) Cr-C(4)-0(4) 178.5 (7) As(l)-Cr-C(6) 91.4 (3) Cr-C(5)-0(5) 178.2 (9) As(l)-Cr-C(7) 92.3 (3) Cr-C(6)-0(6) 177.0 (7) C (3) -Cr-C (4) 92.4 (4) Cr-C(7)-0(7) 176.4 (8) C(3)-Cr-C(5) 88.0 (4) As(1)-Fe-Cp* 126.2 C(3)-Cr-C(6) 89.8 (4) C(1)-Fe-Cp* 124.1 C(3)-Cr-C(7) 174.7 (4) C(2)-Fe-Cp* 123.7

OCp* describes the center of the ring.

Figure 1. Positional parameters for the complex are given in Table I, and derived distances and angles are presented in Tables I1 and 111, respectively. Compound 7a crystal- lizes isostructurally to the congeneric diphosphene (v5- C5Me5)(CO)2FeP[Cr(C0)5]=PR (9)12 and phosphaarsene (v5-C5Me5) ( CO)2FeAs[ Cr( CO)5]=PR ( Compound 7a features a transition-metal-substituted diarsene with an unsupported As=As double bond, which is coordinated to a Cr(CO)5 fragment via the lone pair a t the distorted trigonal-planar configurated Asl. The bond length Asl- As2 (225.9 (1) pm) is well comparable with the respective distances in 2,4,6-t-B~~C~H~As=As[Cr(C0)~] [CH(SiMe3),] (224.6 (1) pmIs and 2,4,6-t-Bu3C,H2As=AsCH(SiMe,), (222.4 (2) ~ m ) ~ and close to the sum of double bond co- valent radii (222 pm).21 Bond lengths for metal complexes of As2 fall in the range 227-232 pm.22 The As-As bond

(20) Weber, L.; Bungardt, D.; Boese, R. Chem. Ber. 1988,121, 1535. (21) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornel1

University Press: Ithaca, NY, 1960.

Organometallics, Vol. 8, No. 12, 1989 2803

distances in cyclic arsines varies from 240 to 246 pm, whereas in cluster ions bond lengths of 236-250 pm are observed.23 The arsenic atom As1 is one vertex of a distorted octaedron with a central Cr atom. The steric congestion of the Cr(C0)5 group leads to a decrease of the angle Fe-&-As (101.6 (1)'). In 9 and 10 the corresponding angles Fe-As-P (102.2 (1)') and Fe-P-P (102.7 (1)') are similar. The same is true for the angles Asl-As2-C8 in 7a (111.4 (2)'), As-P-C8 (112.1 (1)') in 9, and Pl-P2-C8 (113.3 (1)') in 10. The Fe-As-distances in 7a (238.7 (1) pm) and 9 (238.9 (1) pm) are slightly smaller than in (q5-C5Me5) (CO) ,FeAs=C ( OSiMe3) (t-Bu) (240.7 (1) pm) ,16 and are regarded as a Fe-As-single bond. The Fe-As bonds in low-valent carbonyliron complexes fall in the range 225-247 pm.24 The Cr-As bonds in 7a (249.2 (1) pm) and 9 (249.4 (1) pm) are considerably shorter than the calculated Cr-As single bond distance of 269 pm which results from the sum of the covalent radii of Cr(0) (148 pm)25 and As (121 pm).21 They are well comparable with Cr-As bond distances in RAS=AS[C~(C~)~]CH(S~M~~)~ (245.4 (1) pm)s and 13 (249 (1) pm).26

(CO)5Cr, As Ph

Cr(CO), Ph' oc, 1 ,co '

oc /"i W M e h

13

Like in 9 and 10 the steric requirement of the diarsene ligand causes a distortion of the Cr(C0)5 group. Two of the four cis oriented CO ligands are bended toward the trans carbonyl group, which is obvious from the angles As-Cr-C3 (92.4 (3)') and As42147 (92.3 (3)"). The atoms Fe, Asl, As2, and C8 are not arranged in the same plane. The ipso-carbon atom C8 is located 30.8 pm above the plane defined by Fe, Asl, and As2, whereas the Cr atom is found 41.9 pm above this plane. The C5Me5 ring is located at the opposite side of the plane. The center of the five-membered ring Cp* is separated from Fe by 171.7 pm. The bond angles including Cp* and Fe are similar (Cp*-Fe-As1 = 126.2'; Cp*-Fe-C1 = 124.1'; Cp*-Fe-C2 = 123.7'). The arene ring is orthogonally oriented with respect to the plane Fe-Asl-As2 (84.7'). The plane Fe- Asl-As2 and the mean plane of Cr-C7-C3-C5-Asl form an interplanar angle of 15.0'. The torsion angles Fe- Asl-As2-C8 and Cr-Asl-AsB-C8 are 170.4' and 3.3', re- spectively.

Acknowledgment. This work has been supported by the Deutsche Forschungsgemeinschaft, Bonn, Fonds der

(22) (a) Foust, A. S.; Foster, M. S.; Dahl, L. F. J. Am. Chem. SOC. 1969, 91, 5633. (b) Foust, A. S.; Campana, C. F.; Sinclair, J. D.; Dahl, L. F. Inorg. Chem. 1979, 18, 3047. (c) Sigwarth, B.; Zsolnai, L.; Berke, H.; Huttner, G. J. Organomet. Chem. 1982, 226, C5. (d) Sullivan, P. J.; Rheingold, A. L. Organometallics 1982, 1, 1547.

(23) (a) Maxwell, L. K.; Hendricks, S. B.; Mosely, V. M. J. Chem. Phys. 1935,3,699. (b) Burns, J. H.; Waser, J. J. Am. Chem. SOC. 1957, 79,859. (c) Hedberg, K.; Hughes, E. W.; Waser, J. Acta Crystallogr. 1961, 14,369. (d) Rheingold, A. L.; Sullivan, F. J. Organometallics 1983,2,327. (e) Mundt, 0.; Becker, G.; Wessely, H.-J.; Breunig, H. J.; Kischkel, H. 2. Anorg. Allg. Chem. 1982,486,70. (f) Review: FrBhlich, R.; Tebbe, K.-F. 2. Kristallogr. 1982, 158, 255.

(24) (a) Rheingold, A. L.; Foley, M. J.; Sullivan, J. P. Organometallics 1982,1,1429. (b) Lang, H.; Huttner, G.; Sigwarth, B. Weber, U.; Zsolnai, L.; Jibril, I.; Orama, 0. 2. Naturforsch., B: Anorg. Chem., Org. Chem. 1986, B41, 191. (c) Huttner, G.; Mohr, G.; Frank, A.; Schubert, U. J. Organomet. Chem. 1976,118, C73. (d) Winter, A.; Zsolnai, L.; Huttner, G. J. Organomet. Chem. 1982,234, 337.

(25) Cotton, F. A,; Richardson, D. C. Inorg. Chem. 1966, 5, 1851. (26) Huttner, G.; Jibril, I. Angew. Chem. 1984,96,709; Angew. Chem.,

Int. Ed. Engl. 1984, 23, 740.

2804 Organometallics 1989,8, 2804-2808

Chemischen Industrie, Frankfurt, and the BASF AG, Ludwigschafen, Germany, which is gratefully acknowl- edged. We thank Dr. K. Steinbach, University of Marburg, for FD-mass spectra. Registry No. 4a, 112681-58-0; 4b, 112681-557; 6a, 122474-90-2;

7a, 122474-91-3; 7a.0.5C4Hlo0, 123122-66-7; 7b, 123053-96-3;

2,4,6-t-Bu,C6H2AsCl2, 117184-75-5; ((Z)-C8H14)Cr(CO)5, 92889- 73-1; [2,4,6-t-Bu,CsH,As]z, 117184-76-6.

Supplementary Material Available: A table of anisotropic thermal parameters (1 page); a listing of observed and calculated structure factors (53 pages). Ordering information is given on any current masthead page.

Effective Electronegativities of Phosphorus, Arsenic, and

Dichroism Antimony in a 7r System. Evidence from Magnetic Circular

Jacek Waluk,laVb Heinz-Peter Klein,la Arthur J. Ashe 111,'' and Josef Michl*-la

Center for Structure and Reactivity, Department of Chemistty, The University of Texas at Austin, Austin, Texas 78712-1167,

and Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48 109

Received April 20, 1989

The UV absorption and magnetic circular dichroism of phosphabenzene, arsabenzene, and stibabenzene are reported and analyzed. In each molecule, the lowest energy transition is attributed to an na* state. Three aa* states are also assigned and related to the Lb, La, and Bb states of the aromatic six-electron perimeter. The analysis of orbital splitting5 indicates that the effective a-orbital electronegativities of P, As, and Sb are higher than that of carbon.

Introduction Since their synthesis in the seventies,2-6 heterocyclic

derivatives of benzene containing the heavier heteroatoms of the group 15, P, As, Sb, and Bi, have been investigated by electron diffra~tion,~J NMR,8 photoelectron (PE)? electron transmission (ETS),l0 and m i c r o ~ a v e ~ J ~ - ' ~ spectroscopy. It was found that the "aromatic character" of benzene and benzene-like molecules such as pyridine (1) is qualitatively preserved in these heterocycles, even in the antimony and bismuth derivatives.14-16 These molecules can be viewed as the prototypes of a large class of heteroaromatic systems. It is of interest to ascertain the basic characteristics of these heavier heteroatoms with respect to participation in a conjugation.

The two main factors to be established are (i) changes

(1) (a) The University of Texas. This project was initiated at the University of Utah. (b) On leave from The Institute of Physical Chem- istry, Polish Academy of Sciences, Kaspnaka 44,Ol-224, Warsaw, Poland. (c) The University of Michigan.

(2) Ashe, A. J. 111 J. Am. Chem. SOC. 1971, 93, 3293. (3) Ashe, A. J. 111, J. Am. Chem. SOC. 1971, 93, 6690. (4) Ashe, A. J. 111, Tetrahedron Lett. 1976, 415. (5) Ashe, A. J., 111; Gordon, M. D. J. Am. Chem. SOC. 1972,94,7596. (6) Wong, T. C.; Bartell, L. S. J. Chem. Phys. 1974, 61, 2840. (7) Wong, T. C.; Ashe, A. J., 11% Bartell, L. S. J. Mol. Struct. 1975,25,

65. (8) Ashe, A. J., 111; Sharp, R. R.; Tolan, J. W. J. Am. Chem. SOC. 1976,

98, 5451. (9) Batich, C.; Heilbronner, E.; Hornung, V.; Ashe, A. J., 111; Clark, D.

T.: Cobley, U. T.; Kilcast, D.; Sanlan, I. J. Am. Chem. SOC. 1973,98,928. (10) Burrow, P. D.; Ashe, A. J., 111; Bellville, D. J.; Jordan, K. D. J .

Am. Chem. SOC. 1982, 104, 425. (11) Kuczkoweki, R. L.; Ashe, A. J., 111 J. Mol. Spectrosc. 1972,42,457. (12) Lattimer, R. P.; Kuczkowski. R. L.: Ashe. A. J.. 111: Meinzer, A.

L. J. Mol. Spectrosc. 1975, 57, 428.

1978, 70, 197. (13) Kuczkowski, R. L.; Fong, G.; Ashe, A. J., 111 J. Mol. Spectrosc.

(14) Ashe, A. J. 111 Acc. Chem. Res. 1978, 11, 153. (15) Ashe, A. J. I11 Top. Curr. Chem. 1982, 105, 125. (16) Ashe, A. J., III; Diephouse, T. R.; El-Sheikh, M. Y. J. Am. Chem.

SOC. 1982,104,5693.

Table I. Valence State Ionization Potentials (ZX) and Electron Affinities (E,) for the T OrbitallSm a6 a Function oP the

Valence Ande a (C-XC) a = 1200 (trstrtrr) a = goo (s2ppr) Ix Ex Ix + Ex Ix + Ex a,Odeg Ix Ex IX + Ex

Cb 11.16 0.17 11.33 11.33 120 11.27 0.34 11.60 N 14.12 1.78 15.90 15.83 117 13.94 0.84 14.78 P 11.64 1.78 13.42 12.75 101 10.73 1.40 12.13 As 11.24 2.80 14.04 11.89 97 9.36 1.49 10.85 Sb 10.51 2.74 13.25 10.40 93 8.75 1.15 9.90

"The experimental valence angles for 1-4.'' The IX + EX values were interpolated from those at a = 120° (trqrtrr) and a = 90' (s$p~) using [(tan-' ( ~ x / 2 ) ) ~ - (tan-' 60°)2]/[(tan-' 45°)2 - (tan-' 60°)2] as a fraction of the sZppr configuration. *In this case, the atomic configu- rations are trtrtrr and sppr.

in the carbon-heteroatom resonance integral Pcx relative to pCc and (ii) differences in the effective heteroatom electronegativities, xx = (IFx + EAx)/2. Here, IPX stands for the ionization potential and EAx for the electron af- finity of the a-symmetry atomic p orbital of element X in its valence state. PE9 and ETS'O studies of the energies and ordering of a orbitals in the P, As, and Sb derivatives leave little doubt that the resonance integrals PCX are substantially less negative than PCc as might be surmised from the greatly increased bond lengths. Due to its low stability, bismabenzene has received less attention. In these studies, the a-orbital electronegativities of the het- eroatoms were assumed to be larger than that of carbon for N but smaller for P, As, and Sb. This may have been natural in view of the low Pauling electronegativities of these elements,17 but we now provide evidence that it is not correct.

One indication that a t least the effective a electroneg- ativities of P and As are higher than that of C has been

(17) Pauling, L. in The Nature of the Chemical Bond; Cornell Univ- ersity Press: Ithaca, NY; 1960.

0276-7333/89/2308-2804$01.50/0 0 1989 American Chemical Society