1408 J. E. PARKS AND R. H. HOLM COXTRIBUTION FROM
Inorganic Chemistry THE
DEPARTMENTS O F CHEMISTRY, UNIVERSITY O F WISCONSIS, MADISON, WISCONSIN, AND MASSACHUSETTS INSTITUTE OF TECHSOLOGY, CAMBRIDGE, MASSACHUSETTS
The Synthesis, Solution Stereochemistry, and Electron Delocalization Properties of Bis(p-iminoamino)nickel(II)Complexes BY J. E. PARKS
AND
R. H . HOLM]
Received February 2, 1968 Reaction of &ketoamines with primary amine hydrochlorides yields a series of P-iminoamines R,C(NR)=CHC(NHR)R, (R, = H , CHs; R = benzyl, aryl). These compounds react with nickel(I1) salts under nonaqueous conditions to form bischelate complexes of the general type ~ i [ R , C ( N R ) C H C ( S R ) R , ] ~ . Magnetic, spectral, and proton resonance properties of these complexes indicate that they adopt a pseudo-tetrahedral structure with a spin-triplet ground state in chloroform solution and that no diamagnetic planar stereoisomer is present in any case. All complexes manifest large isotropic proton contact shifts in solution which have been interpreted in terms of a n effective r-delocalization mechanism involving ligand+ metal antiparallel spin transfer. The mode of spin transfer is considered in some detail, and experimental spin densities at several ligand positions evaluated from contact shift measurements are shown to be consistent with -1/13 unit of free spin in the highest filled 7 MO of the ligand anion. Two or more of the four possible diastereoisomers of the R, = CHs, R = otolyl complex have been detected by proton resonance. Proton resonance spectra of the free ligands indicate that, a t least on the time scale of the measurements, they exist as symmetrical hydrogen-bonded species or undergo rapid intramolecular proton transfer between the two nitrogens
Introduction The conjugated, monoanionic, P-difunctional ligand shown in general form 1 is among the most fundamental
C}@
R1
R2 1
chelating systems in coordination chemistry. One of its principal advantages is found in the flexibility of synthesis such that a wide variety of terminal substituents R1 and Rz (usually H, alkyl, aryl) and donor atoms or groups X and Y may be incorporated in various combinations. In the past few years we have been engaged in a general investigation of the synthesis and solution stereochemistry of bis-chelate complexes derived from 1. An integral part of this work has been a study of the configurational equilibria and electron delocalization of Ni(I1) complexes. Consideration of steric and electronic factors, supported by some published information, indicates that in strictly four-coordinate, bis-chelate complexes variation of the donors X and Y will generally have a more pronounced effect on stereochemistry, electronic structures, and attendant electron delocalization than will variation of the groups R1 and Rz. For this reason investigations of these properties as a function of X and Y are of particular significance. Commonly X and Y are 0, S,and NR (R = H, alkyl, aryl), generating six possible sets of donor atoms in a bis-chelate system. Substantial progress has recently been made in elucidating some of the aforementioned properties of complexes with X = Y = 0,2in particular, and those with X = 0, Y = S3and X = 0, Y = NR.4 The chemistry of these groups of complexes derived from 1 is (1) Massachusetts Institute of Technology. (2) For a review of 0-ketoenolate complexes see J. P. Fackler, Jr., Progr. Inorg. Chem., 7, 361 (1966).
rather well developed. On the other hand, complexes having X = Y = S5 and X = S,U = NR6 have been prepared only recently and little has been reported thus far on their structural and electronic properties. Even less is known about the remaining group of complexes, characterized by X = Y = S R , which may be considered to be derived from a$-unsaturated P-iminoamines. Brief reports of the synthesis of Ni(II), Cu(I1) and Co(I1) derivatives of malondialdehyde dianil and methylmalondialdehyde diani17 and of a unique, completely encycled Ni(I1) complex obtained by a metal template condensation of 3-formylacetylacetone and o-phenylenediamines have been published. The only other example of a P-iminoamine chelate ring occurs in the aromatized derivative of 2,2'-( 1,3-diaminopropane) bis(2 -methyl - 3 - butanone)dioximinenickel(II) cation. By way of furthering the systematic investigation of bis-chelate complexes derived from the @-difunctional ~
(3) 0-Thioxoketone complexes:
E . Uhlemann, G. Klose, and H. Muller,
2. Naturforsch., 19b,962 (1964); S. H. H. Chaston, S . E. Livingstone, T. N. Lockyer, 1'. A. Pickles, and J. S. Shannon, A t r s t i a l i a ~J . Chem., 18, 673 (1965); R. K. Y. Ho, S . E . Livingstone, and T. N. Lockyer, i b i d . , 18, 1927 (1965); 19, 1179 (1966); S.H. H. Chaston, S . E. Livingstone, a n d T. N. Lockyer, ibid., 19, 1401 (1966); S.H. H . Chaston and S. E . Livingstone, ibid., 19, 2035 (1966); E . Uhlemann and W. W. Suchan, Z. Anorg. Allpem. Chern., 342, 41 (1966); E. Uhlemann and P. Thomas, J. Piakt. Chem., 34, 180 (1966); A. Yokoyama, S . Kawanishi, M. Chikuma, and H. Tanaka, Chem. Pharm. Bull. (Tokyo), 15, 540 (1967); S. H. H. Chaston and S. E. Livingstone, Auslraliaiz J . Chem., 20, 1065, 1079 (1967). (4) @-Ketoamine complexes: (a) G. W. Everett, Jr., and R . H. Holm, J . A m . Chem. SOL.,87, 2117 (1965); (b) E.-G. Jager, Z . Anorg. Allgem. Chem., 337, 80 (1965); (c) S . Yamada, H. Nishikawa, and E. Yoshida, Bzcll. Chem. Soc. J a p a n , 89, 994 (1966); (d) G. W. Everett, Jr., and R . H. Holm, J . A m . Chem. SOC.,88, 2442 (1966); Inow. Chem., 7, 776 (1968); (e) S . Yamada and E. Yoshida, Bzdl. Chem. Soc. J a p a n , 40, 1884 (1967); (f) K. E. Ernst, M. J. O'Connor, and R . H. Holm, J . A m . Chem. Soc., 89,6104 (1967). (5) R. L. Martin and I. M. Stewart, Nuttrue, 210, 562 (1966); R. Beckett and B. F. Hoskins, Chem. Commun., 909 (1967); K. Knauer, P. Hemmerich, and J. D. W. van Voorst, Angew. Chem. I?zteviz. Ed., Eagl., 6, 262 (1967); G. Barnikow a n d H. Kunzek, 2. Chem., 6, 343 (1966). (6) E. Uhlemann, Z. ~'Qtur.fo~~oi.sch.,2lb, 692 (1966); D. H. Gerlach and K. H. Holm, unpublished work. ( 7 ) N, M.Tsybina, V. G . Vinokurov, T. V. Protopova, and A . P. Skoldinov, J . Gen. Chem. U S S R , 36, 1383 (1966). (8) E.-G. Jager, 2 . Chem., 4, 437 (1961). (9) E. G. Vassian and R. K. Murmann, Ixovg. Chem., 6, 2043 (1967).
Vol. 7, No. 7 , July 1968
B IS(@-IMINO AMINO) NICKEL (I I) COMPLEXES1409 TABLE I
CHARACTERIZATION OF 2-N-ARYLAMINO-4-N-ARYLIMINO-2-PENTENES AND THEIRBIS-CHELATENi(I1) COMPLEXES
-----c C
___
-yoligandalcd---H
7
c-----Found--
N
C
H
N
-----
yo complex--
7-7---
Calcd---H
-FoundH
N 162-163 73.26 6 . 1 5 10.05 73.20 6 . 0 4 9 . 7 7 282-284 74.39 6.90 9 . 1 3 74.07 6.80 8.91 143-144 74.39 6.90 9.13 73.83 6.92 8.61 186-187 74.39 6.90 9.13 74.05 7.05 8.49 2 15-2 16 80.84 5 . 8 5 6.50 79.36 6 . 0 7 6 . 1 8 134-136 74.39 6.90 9 . 1 3 74.74 7.06 9 . 1 4 g h 313-316 71.88 5.23 11.18 71.95 5.19 11.22 a Uncorrected. Ligand recrystallized from 1: 1 tetrahydrofuran-n-heptane. Complex extracted from reaction mixture with nheptane and recrystallized from n-heptane. Final purification of complex by vacuum sublimation. e Complex extracted with 1: 1 nheptane-toluene and recrystallized from 5: 1n-heptane-toluene. 1 Extracted and purified by Soxhlet extraction with benzene. 0 Ligand previously ~haracterized.'~ 1-Phenylamino-3-phenyliminopropene ; previously characterized. l 4 * I 6
81.56 81.97 81.97 81.97 86.53
7.25 7.97 7.97 7.97 6.51
11.19 10.06 10.06 10.06 6.96
81.58 82.02 81.92 81.74 86.59
7.15 7.89 8.04 7.85 6.54
ligand 1, we have prepared a new series of bis(0-iminoamino)nickel(II) complexes 2. These have R = aryl or
2
benzyl and are designated throughout as Ni(R2-RaR,Ra)2,10using a notation of ligand positions consistent with that for P-ketoamine complexes.4a,d,f The complexes have been characterized by magnetic, spectral, and proton resonance measurements. Large isotropic hyperfine contact shifts have been observed whose signs and magnitudes are consistent with unpaired electron delocalization effected by ligand-to-metal antiparallel spin transfer. The complete body of results and conclusions from these investigations is reported here. Experimental Section Preparation of Ligands.-Among the ligands utilized in this study, all of t h e N,N'-diaryl-@-iminoamines derived from acetylacetone are reported for the first time. The hydrochlorides of 2phenylamin0-4-phenylimino-2-pentene~~~'~ and 2-p-tolylamino-4p-tolylimino-2-pentene" have been previously reported, as have and the free bases 2-benzylamino-4-benzylimino-2-pentene13 malondialdehyde dianil14q15and their hydrochlorides. The 2-N-arylamino-4-N-arylimino-2-pentenehydrochlorides were prepared by a method reported by Schiebe." The @-ketoamines were first obtained by reaction of acetylacetone and the appropriate amine4*and purified by distillation or recrystallization. Equimolar quantities of the P-ketoamine and amine hydrochloride were refluxed for 1 hr with enough absolute ethanol to dissolve them. The first crop of crystals was obtained by cooling of the reaction mixture; reduction of solution volume followed by cooling yielded a second crop. The @-iminoamine hydrochlorides were deprotonated by refluxing them with a twofold molar excess of triethylamine in enough dry ether to make up a thin slurry, followed by filtration to remove triethylammonium chloride, evaporation of ether, and removal of the remaining triethylamine in BUCUO. The resultant oils were re(10) R = Bz, benzyl; P h P h , p-biphenylyl; o-tal, o-tolyl; m-tal, m-tolyl: +-tal, $-tolyl. (11) G . Schiebe, Ber., 66, 137 (1923). (12) M. Julia, A n n . Chim. (Paris), (12) 5, 595 (1950). (13) L. C. Dorman, Tetrahedron L e t l e v s , 4, 459 (1966). (14) F. Reitzenstein a n d G. BBnitsch, J. Pvakl. Chem., 86, 1 (1912): T. V. Protopova a n d A. P. Skoldinov, J. Gen. Chem. USSR, 26, 3733 (1956). (15) W. J. Barry, I. L. F:nar, and E. F. Mooney, Spectrochim. Acta, 21, 1095 (1965).
MP,~ 'C
C
N
C
11.36 10.05 9.85 10.16 6.92
crystallized from dry pentane, unless otherwise indicated in Table I, until a constant melting point was achieved. Compounds so obtained were analytically pure. Characterization data are given in Table I (chemical shift values are set out in Table V) . Malondialdehyde dianil monohydrochloride was obtained from Aldrich Chemical Co. and used directly. Dorman's procedure13 was used to prepare 2-benzylamino-4-benzylimino-2-pentene. Preparation of Complexes.-The sensitivity of the 8-iminoamine complexes to hydrolytic decomposition required the use of nonaqueous chelation reactions for their preparation. Thoroughly dried solvents were employed in the extraction and recrystallization steps referred to below. Toluene and n-heptane were dried by refluxing them over sodium and phosphorus pentoxide, respectively. Ni(Rz-CHaHCH3)2 ( R = C B H ~Bz) , and N ~ [ ( C B H ~ ) Z - H H H ] ~ were prepared in t-butyl alcohol by use of the nonaqueous chelation procedure described p r e v i o ~ s l y . ~After ~ removal of the tbutyl alcohol in vacuo, the complexes were extracted from the solid residue using n-heptane alone or mixed with toluene, as indicated in Table I . Ni(R2-CHzHCH3)2( R = PhPh, nz-tol, ptol) complexes were obtained by reaction of the ligand with nbutyllithiurn in tetrahydrofuran in a manner analogous to t h a t recently employed in the synthesis of iron( 11) aminotroponeiminates.I6 The ligand (0.02 mol) was dissolved in 20 ml of tetrahydrofuran (distilled from lithium aluminum hydride) and the solution was cooled to -78" under nitrogen. Then 13 ml of n-butyllithium in hexane (1.6 N , 0.021 mol) was added during 2 min, followed by warming of the mixture to room temperature and the addition of 7.0 ml (0.011 mol) of tetraethylammonium tetrabromonickelate." The mixture was stirred vigorously under nitrogen for 2-3 hr while a greenish brown color developed. The solvent was then removed in vacuo and the residue was extracted by use of the solvents indicated in Table I. I n both methods the complexes were first isolated by volume reduction of extract solution followed by recrystallization from the solvents noted in this table. To indicate the efficacy of either preparative method for a given complex, N ~ [ ( O - ~ O ~ ) ~ - C H ~ H C H ~ ] ~ was prepared in equally good yield and purity by both methods. Yields ranged between 50 and 70y0 except in the case of Ni( ( C ~ H ~ ) Z - H H H which )Z, was obtained in 83% yield. I n several cases cocrystallization of the complex and free ligand or its lithium salt, which could not be completely avoided despite several recrystallizations, led to slightly high analytical results; the presence of small amounts of ligand or its salt was indicated by the pmr spectra of these complexes. Characterization data for the complexes are found in Table I . The complexes Ni( R z - C H ~ H C H form ~ ) ~ greenish black crystals which are readily soluble in common, weakly polar organic solvents giving very deep green solutions. The dissolved complexes are decomposed by small amounts of water or by prolonged (16) W. R. McClellan and R. E. Benson, J . A m . Chem. Soc., 88, 5165 (1966). (17) N. S. Gill a n d R. S. Nyholm, J. Chem. Soc., 3997 (1959).
Tnorganir Chemistry
AND R. H. HOT,M 1410 J. E.PARKS
heating above -60’. Xi(( C6Hj)a-HHH)2 is a reddish violet solid which is only slightly soluble in organic solvents to yield reddish orange solutions. Magnetic Susceptibility Measurements.-Measurements of solids and solutions were made by the Gouy method using aqueous nickel chloride solutions or HgCo( S C S ) 3 and distilled water, respectively, as calibrants. Solutions were prepared in the absence of air and moisture by admission of chloroform, previously distilled from phosphorus pentoxide under nitrogen, to an evacuated sample tube containing tile comples. Molecular Weights .-The molecular weight of a representative complex, Ni[(CGH,),-CH3HCH3In, was measured by a Mechrolab osmometer in fresh, dry carbon tetrachloride solution; found, 532 (average of four determinations, 3 . 5 - 4 i mm); calcd, 557. The slightly low result may indicate a small amount of decomposition to which molecular weight measurements by this method are quite sensitive. Electronic Spectra.-Solutions were prepared using dry chloroform and were recorded immediately o n a Cary 14 spectrophotometer. Proton Resonance Measurements.-Spectra of ligands and complexes were obtained on Varian 4-60 and HA-100 spectrorneters, respectively, equipped with a constant-temperature probe assembly. All spectra were recorded usiug CDCIDsolutions coritaiuing T M S as an internal reference, Chemical shifts were measured using the usual side-band technique. Concentrations used were -0.1 dd except in the case of Si((CeH:)1HHH), for which a saturated solution AI) and repetitive scan technique were required owing to low solubility.
Results and Discussion The majority of p-iminoamines and their nickel(I1) complexes 2 investigated in this work have R, = CHI and R = aryl. All of these complexes have been prepared for the first time, as have the corresponding free ligands. Of the substitutional variants of 2 with R = alkyl, only Ni(Bz2-CH3HCH3)2 has been prepared; no complexes with R = H are presently known. The nonaqueous chelation methods described here and e l ~ e w h e r ewould ~ ~ , ~ almost ~ certainly be applicable t o the synthesis of these complexes. In this connection it is noted that H [ (C2H5)2-CHIHCH3] . HC10418as well as H ( H ~ - C ~ H ~ H C ~ H and S ) ,H(H2-C6H:HCH3)1g have been reported. Their ligand properties have yet to be investigated. Although the present investigation of four-coordinate, bis-chelate p-iminoamine complexes has been preceded by only one study of such complexes, which was restricted in scopej7six-membered chelate rings of a symmetrical, unsaturated nature with a pair of nitrogen-donor atoms are well recognized in other groups of complexes, These include the bis[N ’-(perfluoroacylimidoyl)perfluoroalkylamidine],2o bis(pyrromethene),2 1 , 2 2 b i s ( f o r m a ~ a n ) , * ~and - ~ ~ deprotonated bis(dipyridy1methane) and bis(dipyridy1(18) G. Schwarzenbach and K. Lutz, H e h . Chiin. A c t a , 23, 1139 (1940). (19) A. Quilico, G. Gaudiano, and L. Merlini, Gam. Chi?n. ItaZ., 89, 571 (1959). (20) H. C. Brown and P. D. Schuman, J . Ovg. C k e m . , 28, 1122 (1963). (21) (a) D. P. ?vIellor and W. €1. Lockwood, Pvoc. R o y . Soc. A’. S.Wder, 74, 141 (1940); (b) J. E. Fergusson and C. A. Ramsey, J . Chem. SOL.,5222 (1965); (c) J . Ferguson and B. 0. West, i b i d . , A , 1565 (1966). (22) D. R . Eaton and E. A, LaLancette, J . C h e r n P k y s . , 41, 3534 (1964). (23) L. Hunter and C. B. Roberts, J . C k e m . Soc., 823 (1941); B. Hirsch, A n n , , 637,167, 173, 189 (1960); i b i d . , 648, 151 (1961); B. Hirsch and E . - A . Jager, i b i d . , 683,99 (1965). (24) H. Irving, J. B. Gill, and W. R . Cross, J . Chem. Soc., 2087 (1960). (25) M. I. Ermakova, E. I. Krylov, and I . Ya. Postovskii, J . Gen. CkPnz. U S S R , 30, 863 (1960). (26) D. Dale, J . Chem. S o c . , A , 278 (1967).
amine) complexes.27 Of these, the bis(formazan) complexes (3) are the most closely related to the p/R N= N,
N-N ‘R’ 3
iminoamines and the structures of the two groups of complexes will be compared. Stereochemistry in Solution.-When R is a particularly large group such as phenyl, complexes 2 cannot have a structure in which the two chelate rings and the metal are coplanar without seriously disturbing the expected trigonal-coplanar arrangement of bonds around the donor nitrogens This situation is also encountered in the bis(formazans) 3 with R, R‘ = aryl, and in bis(P-ketoamine) and bis(salicyla1dimine) complexes which possess two sterically active nitrogen substituents. On the basis of the considerable amount of X-ray structural information now a t hand for bis-chelate Ni(I1) complexes, two general distortions from coplanarity of the metal and chelate rings, both of which preserve the approximate planarity of the individual chelate rings (excluding the metal), may be recognized. The first of these is a simple torsional distortion so as to produce a nonzero dihedral angle between the rings. Such a structure is well established for several sterically hindered, paramagnetic, bis(salicyla1dimino) comp1exesz8; in these cases the dihedral angle exceeds 80”. The second distortion takes the form of a “stepped” structure in which the coordination sphere of the metal is planar and the two chelate rings are approximately planar but are offset from each other in parallel planes separated by -1-2 A. This structure ha5 been found for bis(K-phenyl-N’-p-tolyl-C-methy1formazan)nickel(11)26 and is illustrated by 4. At present it is not at all
4
certain which distortion a given sterically crowded Ni(I1) complex will assume inasmuch as both have been found for the bis(N-substituted salicylaldimino) comp l e ~ e s . ~ a , The ~ g two structures should be distinguishable by magnetic measurements because 4 will be diamagnetic n-hereas the torsionally distorted (pseudo(27) J. F . G e l d a r d a n d F . Lions, J . A m . C h e m . Soc., 84, 2262 (1962); H . C. Freeman and M . R . Snow, A c l a Cvysl., 18,845 (1965), T. J. Hurley and &I. A. Robinson, Iwovg. C k e m . , 7 , 33 (1968). (28) hI. R.F o x , E. C. Lingafelter, and L. Sacconi, Acta Crysl., 17, 1159 (1964) [bis(N-isopropylsalicylaIdimino)nickel(II)];R. L. Braun and E. C. Lingafelter, i b i d . , 22, 780 (1967) [bis(3-ethyl-N-isopropylsalicylaldimino). nickcl(I1) I. (29) L . M. Shkolnikova, A. N . Knyazeva, and V. A. Voblikova, Z h . S ; r d d , K h i m . , 8, 94 (1967) [bis(S-ethylsalicylaldimino)nickel(lI) 1; R. L. Braun and E. C. Lingafelter, Acta Cvyst., 21, 546 (1968) jbis(3-methyl-Nisopmpylsalicylaldimino) nickel(I1) 1.
Vol. 7, No. 7 , July 1968
BIS(~-IMINOAMINO)NICKEL(~~) COMPLEXES1411
TABLE I1 tetrahedral) structure will be paramagnetic provided MAGNETIC MOMENTS AND LIGANDFIELD the dihedral angle is sufficiently large. SPECTRA OF NICKEL(II)COMPLEXES Magnetic moments for complexes 2, given in Table 11, --Peff. a BMreveal a triplet ground state in both solid and solution CHCls Complex Solid s o h b -----Amax, cm-1 (enic))-phases and are consistent with a pseudo-tetrahedral K~[(C~H~)Z-HHH 3.17 ]Z d 7140 (29), 9100 (28), 10,200 structure. However, several lines of evidence indicate (19) that the degree of distortion of the Ni-N4 unit from N ~ ( B Z ~ - C H ~ H C3H. 0~6) ~ 3.04 7940 (32), 9440 (31), 10,400 planarity, while sufficient to stabilize a triplet ground (23), 17,220 (170) state, does not result in the highest possible symmetry Ni[(ceH&-CH3H3.10 3 . 0 8 7250 (63), -85006 (56), (Dzd) of the complex. The Curie magnetic moments of CH31zf 10,000 (38),15,870 (500) Ni[(PhPh)z-CH3H- 3.11 2.97 7220 (76), 8510 (66), 10,100 Ni(I1) in a perfect or effective tetrahedral environment CHdz (44), 15,870 (450) should fall in the 3.6-4.0-BM range a t room temperNi[(p-tol)z-CH3H- 3 . 0 7 3 . 0 8 7300 (66), -85006 (58), ature and decrease markedly with decreasing temper10,000 (39), 15,390 (400) CHB]z at~re.~O Moments in this range are not usually found Ni[(m-tol)z-CH3H- 3 . 1 3 3.05 7270 (67), -8500" (55), CH31z 10,000 (36), 15,870 (380) for bis-chelate Ni(I1) complexes, although those comNi[ (o-tol)z-CH~H- 3 . 1 6 3 , 0 5 7010 (80), -79OOe (70), plexes which like 2 possess an N4 coordination sphere CHslz 10,150 (42), 15,730 (570) and potential Dzd symmetry, viz., the bis(pyrrometha Calculated from the Curie law, peff = * Conenes) 21c and bis(aminotroponeimines), 3 1 usually have centration range 0.045-0.14 M. Apparent values in 1. mole-1 room-temperature moments in excess of -3.30 BM. cm-', uncorrected for overlapping absorption; chloroform soluAdditionally, the observed moments of 2 fall below tion. Insufficiently soluble for measurement. e Shoulder on lower energy peak. f Spectrum in 5000-13,000-~m-~region those of bis(0-ketoamin0)- and bis(salicyla1dimino)shown in Figure 1. nickel(I1) complexes ( 23.25 BM) whose pseudo-tetrahedral structures have been established in both solution4 and crystallinez8phases and whose ligand field microsymmetry is ostensibly lower than that in the p-iminoamines. The Curie dependence of the proton contact shifts (vide infra) rules out the possibility that magnetic moments result from a significant fraction of singlet-state complexes which might arise as a consequence of a planar tetrahedral or monomer e polymer (paramagnetic) equilibrium. Molecular weight measurements have shown that N ~ [ ( C ~ H G ) Z - C H & C H ~ ] Z is monomeric in solution. Spectral measurements in the ligand field region are also indicative of low symmetry distortions. Data are presented in Table I1 and the spectrum of a typical complex is shown in Figure 1. Absorptions in the 6000-11,000-~m-~region are diagnostic of pseudo-tetrahedral structures of Ni-O2NZ4and Ni-N421 complexes but do not usually 5 7 9 II 13 take the form of three closely spaced, clearly observable frequency, crn-1x10-3 bands. Indeed, only two are expected in this r e g i ~ n , ~ Figure 1.-Ligand field spectrum of Ni[(CsH5)2-CH3HCHs]2 in viz., v 2 and the first singlet-triplet transition of tetrachloroform solution in the near-infrared region. hedral Ni(I1). The lowest energy feature is presumably associated with V Z , ~whose upper state (3A2)cannot be split by lower symmetry distortions. The remaining coordinating solvents although they are different in the bands cannot be assigned with any certainty, but their solid phases. Indeed, a pseudo-tetrahedral structure presence, together with the small orbital contributions was proposed for bis(N-phenyl-N'-$-tolyl-C-methylto the magnetic moments, must imply a grossly formazan)nickel(II) on the basis of its partial resolution distorted pseudo-tetrahedral structure for the 0- on (+)-quartz.24 However, as Dalez6has pointed out, iminoamine-nickel(I1) complexes. structure 4 with identical aryl groups cis to each other The bis(formazan)nickel(II) complexes 3 (R, R' = is also enantiomeric. We have obtained the proton aryl, R" = CH3, aryl) have been found to be diamagresonance spectrum of this compound in a saturated netic in the solid a behavior consistent with solution in deuteriochloroform. At 60 Mc the N-p-tolyl structure 4. The possible similarity of steric intermethyl and C-methyl shifts are -135 and -173 cps; actions between the same set of aryl groups in 2 and 3 corresponding signals in the free ligand occur a t - 137 suggests that the structures of the two groups of nickel and - 143 cps, respectively. This complex exhibits no complexes might be closely related in solutions of nonproton hyperfine contact shifts, in contrast t o the p-iminoamines (vide infra), and therefore remains (30) B. N. Figgis a n d J. Lewis, Progr. I n o v g . Chem., 6 , 3 7 (1964). diamagnetic in solution. It is concluded that the (31) D. R. Eaton, W. D . Phillips, a n d D. J. Caldwell, J . A m . Chem. Soc., formazan complex undergoes no significant torsional 85, 397 (1963).
1412 J. E.PARKS AND I
