Inorganic Chemisfry
1386 MELVYN R. CHURCIIILL AND TITOMAS A. O%RTF,N COXTRIBUTION FROM
MALLINCKRODT LABORATORY, DEPARTMENT OF CHEMISTRY, HARVARD USIVERSITY,CAMBRIDGE, MASSACHUSETTS 02138
THE
The Crystal and Molecular Structure of Dimeric 2-Carboxyethyl-~-allylnickel Bromide BY MELYYK R. CHURCHILL AND THOMAS A. O'BRIEN
Received December 14, 1966 Dimeric 2-carboxyethyl-rr-allylnickel bromide, [ rr-CHaC(C02C2Hb)CH2NiBr]?, crystallizes in the triclinic space group P i witha = 7.17 =t0 0 1 A, b = 12.73 =t0.02 A , c = 4.83 zk 0.01 A , CY = 77.4 zI= 0.2", 0 = 97.6 f 0 . Z o , y = 1050 I 0.2', 2 = 1. Despite the abnormally large mosaic spread of the crystal diffraction data, an X-ray structural analysis of the complex has been completed. The final discrepancy index is 14.2% for complete three-dimensional counter data collected with Mo KCY radiation (sin Omax = 0.41). The molecule possesses a crystallographic center of symmetry, the over-all metal coordination scheme being similar to that established for rr-allylpalladium chloride. The rr-allyl and carboxylate groups are coplanar, the dihedral angle between this plane and the nickel coordination plane being 106.2°-a value in the range predicted from orbital overlap considerations.
Introduction C3HSPdXIz does not have the expected value of 90°, but is typically about l10-120°.18,19 This last result has Many n-allyl-transition metal complexes are known, been explainedlg in terms of the various n-allyl-metal and the crystal structures of a number of palladium2-5 overlap integrals, which also indicate that the correand n i c k e P 7 derivatives have been determined, Cryssponding w-allyl-nickel complexes (which have distallographic studies have also confirmed the existence tinctly different chemical properties) should have the of r-allyl-metal bonding in molecules containing such organic ligands as : azulene [in CloHBFe2(CO)j],8 n-allyl group inclined a t a similar angle t o the metal coordination plane. cyclooctatetraene [CsH8Fe2(C0)6], bicyclo [3.2.1 IoctaIn order t o determine the dihedral angle between the dienyl [CsH9Fe(CO) 3+BF4-], lo perfluorocyclopentadirr-allyl ligand and the nickel coordination plane, a ene [CjF&o2(C0)7],l1 and cycloocta-2,4-dienyl [CsH11crystallographic determination of the structure of Pd(acac)].12 The n-allyl system often occurs in organodimeric 2-carboxyethyl-~-allylnickelbromide was untransition metal species formed as intermediates in the dertaken, oligomerization (or cyclooligomerization) of unsaturated organic molecules-the complexes R U C I ~ ( C ~3 H , 1 3~ ) Experimental Section CO*(CO)~(HC~(~-C~H~))~(HC~H),~~ and (isoprene)*Dimeric 2-~arboxyethyl-~-allylnickel bromide, [CH2C(C02RuC1315have been shown to contain a,w-diallyls. FiC2Hj)CH2NiBr] 2, was preparedZofrom the reaction of 2-carboxynally, the complexes (C6HjC2H)3COFe2(CO)j16 and ethylallyl bromide and nickel tetracarbonyl. The complex was isolated as extremely air-sensitive red plates and needles which trans- (cyclododeca-lf6-dienyl)Rh (en)ClZ1 have also decompose by an apparently autocatalytic route. For the crysbeen found t o contain n-allyl-metal linkages. tallographic analysis, crystals mere inserted into 0.2-mm thinAlthough the delocalized n-allyl ligands are parallel walled capillary tubes, under an argon atmosphere. Of some 30 in such species as [CH2C(CH3)CH212Nij6 the dihedral specimens examined, only one (an irregular needle of dimension angle between the metal coordination plane and the n0.10 X 0.12 X 0.72 mm) was found t o give an acceptable pattern, allyl ligand in palladium complexes of the type [n- and even this showed an abnormally large mosaic spread. The (1) M. L. H. Green and P. L. I. S a g y , Advan. Ovganometal. Chem., 2, 325 (1964). Chem. Soc., 6 6 (1962); (b) 1 ' . F. Sevdik and M . (2) (a) J. M . Rowe, PYOC. A. Porai-Koshits, Zh. Slrukt. K h i m . , 3 , 472 (1962); ( c ) W. E. Oberhansli and L. F. Dahl, J . Organomefal. Chem. (Amsterdam), 3, 43 (1965); (d) A. E. Smith, Acta Cryst., 18,331 (1965). (3) M. R. Churchill and R. Mason, Nature, 204, 777 (1964). (4) L. F. Dahl and W. E. Oberhansli, Inovg. Chem., 4, 629 (1966). ( 5 ) R. Mason and D. R. Russell, Chem. Comman., 26 (1966). (6) H. Dietrich and R. Uttech, N a t u v v i s s e ~ ~ s c h a j t e6n0,, 613 (1963). (7) W. E. Oberhansli and L. F. Dahl, Inorg. Chem., 4, 150 (1965). ( 8 ) (a) M. R. Churchill, Chem. Conzmztrz., 450 (1966); (b) M. R. Churchill, Inoug. Chem., 6, 190 (1967). (9) E. B. Fleischer, A . L. Stone, R. B. K. Dewar, J. D. Wright, C. E. Keller, and R. Pettit, J . A m . Chem. Soc., 83,3158 (1966). (10) T. N. Margulis, L. Schiff, and S . Kosenblum, ibid., 81, 3269 (1965). (11) P. B. Hitchock and R. Mason, Chem. Commun., 503 (1966). (12) (a) M. R. Churchill, ibid., 625 (1965); (b) AI. R. Churchill, Inoig. Chent., 5, 1608 (1966). (13) J. E. Lydon, J. K. Xicholson, B. L. Shaw, and M . R. Truter, Pvoc. Chem. Soc., 421 (1964). (14) 0. S. Mills and G. Robinson, ibid., 187 (1964). (15) L. Porri, M. G. Gallazzi, A . Colombo, and G. Allegra, Tetvahedron L e l t e v s , 4187 (1965). (16) G. S. D. King, Acta Cryst., 1 5 , 243 (1962). (17) G. Paiaro, A. Musco, and G. Diana, .I. Organomrlal. C h e m . (Amsterd a m ) , 4, 466 (1965).
compound appeared t o crystallize in the triclinic habit; since a survey of the reciprocal lattice failed to indicate any diffraction symmetry other than that imposed by the Friedel condition (i), the crystals were assumed to be truly triclinic. Unit-cell parameters, obtained from zero-layer Weissenberg (hkO) and precession (Okl and h0l) photographs taken with Mo K a rqdiation (A 0.7107 A4)and calibrated with sodium chloride (ayacl = 5.640 A ) are: a = 7 . 1 7 2 ~ 0 . 0 1 A , b =1 2 . 7 3 2 ~ 0 ~ 0 2 4 , c = 4 , 8 3 i O . O l A , cr = 77.4 & 0.2', p = 97.6 I 0.2", y = 105.0 rt 0.2". There are no systematic absences, and the unit-cell volume is 414.5 A3. The calculated densityz1is 2.016 g for M = 503.3 a n d 2 = 1. Of the possible space groups P l (KO.1)and P i (No. 2), the latter was considered the more likely due to its greater frequency of occurrence and to the likelihood that the molecule might contain a center of symmetry. The linear absorption coefficient ( p ) is 73.7 cm-1. To a first approximation the specimen may be treated (18) M . R. Churchill and R. Mason, Advan. Orpanometal. Chem., 5 , 9 3 (1967). (19) S. F. A. Kettle and R. Mason, J . Ovganometal. Chem. (Amsterdam), 5 , 573 (1966). (20) M . Semmelhack, personal communication. (21) No experimental density was obtained due to the great air sensitivity of the complex.
Vol. 6, No. 7, July 1967
CRYSTAL STRUCTURE O F A
as a cylinder of radius 0.055 mm; hence F R = 0.405. Since the no correction variation of transmission factor with 6 is for absorption was applied. Data were collected with a 0.01’ incrementing Buerger automated diffractometer in conjunction with a fully-stabilized Phillips X-ray generator (operated a t 45 kv/17 ma), a Phillips transistorized scintillation counter, and a Phillips electronics panel. Within a given zone, the over-all stability of the entire system was monitored by remeasuring a carefully-selected check reflection after every 20 reflections had been collected. No variation greater than 3l/count was detected. The scintillation count 0.7107 A ) , the Mo Kp was adjusted to receive Mo Ka radiation radiation being virtually eliminated by the use of a 0.003-in. Zirconium filter a t the X-ray source. The base line of the pulseheight analyzer, the window voltage, and the counter voltage were maintained a t constant values throughout the analysis. The diffractometer was programmedzs to collect all data in a given Weissenberg zone, using a stationary background, w scan, stationary background counting sequence. Owing to the unusually large mosaic spread of the diffraction peaks, the angle l / L ) O ] ,where scanned ( w ) was greater than usual [w = (3.0 1 / L is the Lorentz factor. (The inclusion of the term involving the Lorentz factor allows for the divergence of the X-ray beam which is usually associated with distorted low-order reflections on upper-level I(hkZ), the intensity of a reflection hkZ (hav) , reing the Weissenberg coordinates To(hkZ) and @ 0 ( h k 1 ) ~ ~was corded in the following way: (i) The counter was positioned to To(hkZ), where it remained during the subsequent steps. (ii) The crystal was rotated to *I [=%(hkZ) - w(hk1)/2]and the first background (B1) counted for t seconds. (iii) The crystal was slowly rotated by w(hkZ) degrees a t a constant rate of 2”/min to @Z [ = %(hkZ) w ( h k l ) / 2 ] The entire scan took Pt seconds, the integrated count being C. (iv) The second background (Bg) was measured for t seconds a t +z. Reflections for which I(hkZ) [ = C - ( B I B z ) ]were negative or zero were removed from the analysis. Observed reflections were weighted according to the scheme
(x
+
+
.
+
(The large mosaic spread of the diffraction peaks resulted in an overlap problem; the weighting scheme adopted is sensitive to any asymmetry between the background counts B1 and Bz and gives a low weight to any reflection showing a significant asymmetry. While this is not a very satisfactory state of affairs, the quality of the crystals which could be obtained was such as to preclude a more accurate analysis.) The zones hkO through hk5, representing complete three-dimensional data to sin 0 = 0.41, were collected, corrected for Lorenta and polarization effects, and placed on an absolute scale by means of a Wilson plot.
The Solution of the Structure The positions of the nickel (X = 0.143, Y = 0.097, 2 = 0.148) and bromine ( X = 0.190, Y = -0.060,Z = 0.019) atoms were quickly and unambiguously determined from a three-dimensional Pattersonz6synthesis, which had been sharpened so that the average intensity was independent of sin 6, and which had the origin peak reduced t o the size of a single N i . . . N i interaction. A structure-factor calculationz7based only on the con(22) “International Tables for X-Ray Crystallography,” Vol. 2, The Kynoch Press, Birmingham, England, 1959, p 295. (23) Using the program PREPAR by G. N. Reeke. (24) D. C. Phillips, Acta Cryst., 7 , 746 (1954). (25) C. T. Prewitt, Z. Krist., 18, 355 (1960). (26) Patterson and Fourier syntheses were calculated using ERFR-2, a two- and three-dimensional Fourier program for the I B M 709/7090 by W. G. Sly, D. P. Shoemaker, and J. H. van der Hende. (27) Structure-factor calculations and full-matrix least-squares refinement of positional and thermal parameters were performed using ORFLS,a Fortran crystallographic least-squares program by W. R. Busing, K . 0. Martin, and H. A. Levy.
T-ALLYLNICKEL COMPLEX 1387
tributions from nickel and bromine atoms (RF= 211F01 - FolI/2Fo = 0.374) was used to phase a three-dimensional Fourier synthesis, from which i t was possible to locate each of the carbon and oxygen atoms in the molecule. Structure-factor calculations, phased by one nickel, one bromine, two oxygen, and six carbon atoms, had an initial discrepancy index (RF) of 0.35, which converted to a value of 0.179 after four cycles of positional and isotropic thermal parameter refinement. A survey of a difference Fourier a t this stage showed signs of anisotropic motion associated with the heavy atoms, and refinement was continued using anisotropic thermal parameters, which were of the form
T = exp[-bllh2
- bzzk2 - b&
- 2blzhk 2b13hZ - Zbzskl]
Three cycles of refinement of the 90 positional and anisotropic thermal parameters led to a final residual RF = 0.142 for the 1140 independent reflections, a t which stage refinement was judged to be complete, since the maximum suggested coordinate shifts were less than 10% of the standard deviation for the parameter considered. [The rather high value of R F is attributable to the overlap of adjacent reflections (vide S U ~ Y U ) . ] Contributions from the nine hydrogen atoms were not included in the analysis, nor were their positions detected from a final difference Fourier. During the analysis the scattering factors for neutral nickel, bromine, oxygen, and carbon were used.28 No corrections were made for dispersion. The residual minimized was Zw[ - lFclzlz. Final observed and calculated structure factors are shown in Table I ; atomic coordinates are given in Table 11, and thermal parameters in Table 111. Molecular Structure The successful determination of the crystal structure confirmed that the true space group is P i (No. 2 ) , with the dimeric molecule possessing a crystallographic center of symmetry. As such, the situation is analogous to that of [r-C3HgPdCl]zwhich has two molecules in space group P%/n. 2d The stereochemistry of dimeric 2-carboxyethyl-nallylnickel bromide is shown in Figure 1; the packing of molecules in the unit cell is illustrated by Figure 2 . Interatomic distancesz9 are collected in Table IV; bond angleszgare shown in Table V. Each of the (equivalent) ds Ni(I1) cations in the molecule is in a formally square-planar environment; the donation of two electrons from each bromine and four electrons from the substituted 7r-allyl anion results in the stable 16-electron configuration for each of the nickel ions, in keeping with the observed diamagnetism of such d8 square-planar complexes. The NiBrzNi bridge is accurately planar and approximately sym(28) “International Tables for X-Ray Crystallography,” Vol. 3, T h e Kynoch Press, Birmingham, England. Values for nickel and bromine are taken from p 211; those for oxygen and carbon from p 202. (29) Interatomic distances and angles were calculated using ORFFE, a crystallographic function and error program by W. B. Busing and H. A. Levy.
1388 MELV Y N K. CHURCHILL AND THOM AS A. O'BRIEN
.
Inorgunic Chemistry
TABLE I
[ a-CH2C(COZC~H6)CH~i\jiBr] Z: FINALOBSERVE :D k
... . L
51c
5 K
5FC
K
-5
..
0
69
-6
I+>
-1 7
- 76
- I - 2 3 1 -2U I -381 -392
4 5 5
1 -1c2 -1 34 1 122
6 b 7 7
-I
I
2
2 2 3
-2
I
.
-22
-16
3
-7
187
196
-1
-I
3
191 174
16.
-3
I57 33
1 -1
-1
28
- 3
.5
I
I
5 b d
-7
1r
-2
-12
2 2 -2
-15
-!e
-:1
117
2
IC1 -3' IC
3
2f IO I,! l l b
2 -2
9 i 1
-2
2
2 3
3
-.o
-178 ti 51
-? -8. -61 3 -! 9 7
62
L
1
-6
3 -3
lCl
2
-2
I.
7,
b
->
-78
-w
8
c I
1 2
3 ! 4 5 5 6 6
7 7
.. . -.-.,
IL
-25c
-,- 21 c3 tb , -+ le1
-
