1988 Inorganic Chemistry, Vol. 11,No. 9, 1972
HIPP, LINDOY, AND BUSCH
with T = 16,400 cm-I. Estimatess2 for the spinequilibrium complex Fe(o-phen)2(XCS)2 resulted in values of Dq(10w spin) = 16,300 cm-I and Dq (high spin) = 11,900 crn-l. The results of the earlier studies are in good agreement with those obtained from (52) E. Konig and K. Madeja, Inorg. C h e m . , 6, 48 (1967)
the spectral data of the [14]aneNd-Fe complexes. Acknowledgment. -This research was supported by Grant S o . GhI 10040 from the Xational Institute of General Medical Science of the U. S. Public Health Service. We wish t o acknowledge Dr. E. Gore of this department for helpful discussion concerning the pmr results.
CONTRIBUTION FROM THE EVANS CHEMICAL LABORATORIES, THEOHIO STATEUNIVERSITY, COLUMBUS, OHIO 43210
Synthesis of Metal Complexes with Macrocyclic Ligands Having Prescribed Patterns of Unsaturation. Oxidative Dehydrogenation of Fused-Ring Systems Involving Charged, Delocalized Six-Membered Chelate Rings BY CHRISTIAN J. HIPP, LEONARD F. LINDOY,
AND
DARYLE H. BUSCH*
Received January 4, 1972 Metal ion promoted oxidative dehydrogenation shares with coordination template effects the distinction of being a new synthetic technique uniquely suited t o the preparation of ligands that are difficult to produce by other means Oxidation of the chelate rings that arc formed by deprotonation of P-diimines produces a pattern of unsaturation that has not previously been achieved by this general class of reaction This pattern both places a localized C=C group in the six-membered ring and extends the unsaturation into the adjacent chelate ring This reaction has been effected by bromine oxidation of the macrocyclic nickeliI1) complexes ll,l3-dimethyl-l,4,7,10-tetraazacyclotrideca-l0,l2-dienatonickel(l I ) perchlorate and 12,14-dimethyl-1,4,8,ll-tetraazacyclotetradeca-ll,l3-dienatonickel(II) perchlorate (or hexafluorophosphate). The structures of the products were established throuqh conductivity and magnetic susceptibility measurements and visible, infrared, and nmr spectroscopy
Introduction The discovery that the complex having structure I
groups into azomethine linkages through the abstraction of 1 mol of hydrogen (eq 1). Such linkages have
I1 1
is formed by the reaction between ethylenediamine and acetone in the presence of nickel(I1) salts',* represented the initial example of the new synthetic macrocyclic ligands containing four nitrogen donors. Many such substances are known now3and they form an important new class of coordination compounds that have aroused much interest because of the fundamental structural relationship they bear to such critical natural products as heme proteins, chlorophyll, and vitamin B I ~ . ~ Two novel chemical reactions have figured in the synthesis of many of these new complexes-coordination template reactions3+ and oxidative dehydrogenation reaction^.^,^'^ The latter reactions have uniformly involved the conversion of secondary amine
been introduced into five-6 and six-membered chelate rings.' Goedken8 has shown that simple bidentate ligands, e . g . , ethylenediamine and o-phenylenediamine, in FeII (diamine) (CN)4*- can be oxidatively dehydrogenated to a-diimines while remaining coordinated. Also, the early work of Vassian and Murmanng showed that, when two a-diimine linkages are produced in one chelate ring, ionization of a proton may occur producing a p-diketonate-like chelate structure. The converse process, hydrogenation of coordinated imine groups, is well documented among complexes containing macrocyclic ligands.6j'0J1 Such processes have been observed both chemicallyfi~10~12 and electrochemically. l1l13 The mechanism of the oxidative dehydrogenation
(1) N. F. Curtis, J . C h e m . Soc., 4409 (1960). (2) N. F. Curtis and D. A . House, C h e m . Ind. (London), 1708 (1961). (3) L. F. Lindoy and D. H. Busch, "Preparative Inorganic Reactions," Vol. 6 , W . L . Jolly, E d . , Interscience, Kew York, N. Y . , 1971. (4) n. H. Busch, K. Farmery, V. Goedken, V. KatoviC, A . C. Melnyk, C. R. Sperati, and N . Tokel, AdvaTz. Chetn. Sei,., No. 100, 44 (1971). ( 5 ) D. H. Busch, Heln. Chinz. A cla, Fasciculus rxtvaordiizarius A l f r e d Wei.nev, 174 (19G7). ( 6 ) S. F. Curtis, Coord. Chein. Rev., 3 , 1 (1Q66). ( 7 ) E. K . Barefield and D. H. Busch, Inorg. C i w n . , 10, 108 (1971).
(8) V. L. Goedken, J . C h e m . Soc., C h e m . Commun., 207 (1972). (9) E. G. Vassian and R . K. Murmann, Iiiovg. C h e m , 6, 2043 (1967). (10) J. L. Karn and D. H. Busch, i b i d . , 8, 1189 (1969). (11) E. K. Barefield. F. V. Lovecchio, N. E. Tokel, E. Ochiai, and I ) . H. Busch, i b i d . , 11, 263 (1972). (12) V. Katovib. L. T. Taylor, F . L. Urbach, W . H. White, a n d D H. Busch, ibid.. 11, 479 (1972). (13) N. E. Tokel, V. Katovib, K. Farmery, L . B. Anderson, and D. H. Busch, J. Amev. C h e m . S o c . , 92, 400 (1970).
Inorganic Chemistry, Vol. 11, No. 9, 1972
METALCOMPLEXES WITH MACROCYCLIC LIGANDS
+
1989
/3-amino keto imine. The reaction produces both a C=C linkage and unsaturation in the adjacent fused chelate ring. This is shown schematically in eq 5.
Perhaps the structural relationships are more apparent if one thinks of the oxidation as involving the negatively charged nitrogen in one resonance form of the starting material (structure 11). Clearly this new rereaction is not thoroughly understood ; however, higher oxidation states of the metal seem almost certain to be involved.14-le The role of the metal ion is emphasized by the transition element specificity of the reaction. Iron promotes the reaction with mild oxidizing agents,15 while nickel and copper require progressively stronger oxidizing agentse-8p16aand cobalt does not appear to work a t all. Trivalent and nickelI4 appear to be active oxidizing agents in the reaction. For example, under appropriate conditions, solutions of the pure Fe(II1) complex will produce new azomethine linkages via oxidative dehydrogenation in the absence of other oxidizing agents.leb The metal ion specificity extends to the locations of the sites of unsaturation in the dehydrogenated ligands. For iron, the imine functions are produced in conjugated pairs (a-diimine groups)15 while the imines are produced in electronically isolated locations" in the case of nickel (eq 3 and 4).
H'
UH' II
action constitutes a major contribution toward the ultimate goal of learning how to synthesize any macrocyclic ligand having any desired degree of unsaturation. Ideal reactants for the characterization of this new reaction have recently become available.1*,19 These substances have structures I11 and IV.20
m
Tv Results
/
7L4
1 [O],M = NI (4)
We are concerned with solution of the general problem of generating any degree of saturation whatsoever in the structure of macrocyclic complexes Prior to this report there have been no instances in which carbon-carbon saturation has been produced in the macrocycle by metal ion promoted oxidative dehydrogenation We wish to report a new reaction in which the ring segment oxidized is the coordinated anion of a (14) N. F Curtis and D F Cook, Chem Commzln , 962 (1967) (15) J C Dabrowiak, F V Lovecchio, V. L Goedken, and D H Busch, Abstracts, 162nd Meeting of t h e American Chemical Society, Washington, D C , Sept 1971, No I N O R 140, J Amev Chem SOL,, in press, V L Goedken, P H Merrell, and D H Busch, r b r d , in press (16) (a) V L Goedken and D H Busch, l n o v g Chem , 10, 2679 (1971), ib) V L Goedken and D H Busch, J Amer Chem S O L ,in press (17) E S Gore and D H Busch, unpublished results
The complexes Ni( [13]dienoNd)+18 (111) and Ni( [14]dienoN4) + l 9 (IV) which contain uninegative macrocyclic Schiff base ligands with 13 and 14 ring members, respectively, are readily oxidized with bromine to produce, in each case, two isomeric substances (Scheme I ) . The structures of the resultant products have been deduced from analytical data, conductance and magnetic susceptibility measurements, and infrared, visible,
V
VI
(18) S. C . Cummings and R. E. Sievers, J . Amev. Chem. SOL., 92, 215 (1970); Inorg. Chem., 9, 1131 (1970). (19) S. C. Curnrnings, Abstracts, 3rd Central Regional Meeting of t h e American Chemical Society, Cincinnati, Ohio, 1970; also, private communication. (20) Structure 111-the name of the ligand is 11,13-dimethyI-1,4,7,10tetraazacyclotrideca-lO,l2-dienato, abbreviated 11,13-Me~[13]-10,12-dienoN4,or more simply just [13]dienoNc Structure IV-the name of the ligand is 12,14-dimethyl-1,4,8,ll-tetraazacyclotetradeca-ll,l3-dienato, abbreviated l2,14-Mez[141-11.13-dienoN~, or more simply [14]dienoN& For a summary of the system of abbreviations, see V. L. Goedken, P. H. Merrell, and D. H. Busch, J . Amer. Chem. Soc., in press.
HIPP, LINDOY, AND BUSCH
1990 Inorganic Chemistry, Vol. 11, No. 9, 1972 SCHEME Ia
-
OXIDATIONREACTIONS OF Ni( [13]dienoN4)ClOc AXD Ni( [14]dienoN4)X (XWITH BROMINEIN ACETONITRILE
Ni( [13]dieno&)ClO4
CHsCN
Brz
a- and
clod-, PFe-)
p-Ni( [13]trieneN4)BrC104.HzOb
.
I
G$HsOH
4,
J-
light brown insoluble powder a-Ni( [13]trieneNa)BrClOc*HzO
hot H20
=
dark brown-violet crystalline p-Ni( [13]trieneN4)BrClO4.H20
+Hf
-
yellow-orange crystals a-Ni( [13]trieneN4)(C104)2 *HzO Ni( [14]dienoN4)ClO4
CHsCN Bn
hot Hz0
a-Ni( [14]trieneN4)BrC1O4-HzOC brown powder
CHsCN
Ni( [14]dienoN4)PF~___t p-M([14]trieneN4)Brz Br2 dark brown powder
hot Hz0
+ H'
f"4PFa
+H+
+NaC104
yellow-orange crystals &Ni([13]trieneN4)(C104)~* H20 a-Ni( [14]trieneN4)(ClO4)a.H20 yellow-orange matted needles
p-Ni( [14]trieneN4)(PF&. H2O
yellow-green crystals
a The designations a and p refer to different isomers produced from t h e oxidation reactions. * T h e ligand has structure V and is named 11,13-dimethyl-l,4,7,1O-tetraazacyclotrideca-1,10,12-triene, abbreviated 11,13-Me2[ 131-lI1O,12-triene-l,4,7,10-i';a or [ 131trieneK4 C This ligand has structure I V and is named 12,14-dimethyl-1,4,8,ll-tetraazacyclotetradeca-l,ll,l3-triene, abbreviated 12,14-Mez[ 14]-1,11,13-triene-l,4,8,11-~~ or [ 141trieneN4.
and nmr spectra. The products of these reactions are assigned structures V and VI. 13-Membered Ring Derivatives.-The oxidation products derived from Ni( [13]dienoN4)C104are salts of the dipositive cations a-Ni( [13]trie11eN*)~+ and 0Ni( [13]trieneN4)2+ (Scheme I ) . Their electrolyte types have been established by conductance studies as shown in Table I. The bromoperchlorates have conTABLE 1" CONDUCTAXCE DATAFOR THE C O h l P L E X E S O F THE 13-MEMBERED MACROCYCLIC LIGANDS
A ~ (solvent) J
Complex
Ni( [13]dienoNc)C104 155 (CH3CK) a-Ki( [13]trieneru'4)BrC104.H20117 (CHaNOz) p-Ni( [13]trieneN4)BrClOa.HzO 68 (CH3N02) a-Ni( [13]trieneN4)(C104)z.H20176 (CHsNOz); 279 (CH3CN) p-Ni( [13]trieneN4)(C104)2.HzO 166 (CHaN02); 281 (CHICN) a Values reported for 1: 1 and 2 : 1 electrolytes in nitromethane are 80-95 and 160-190, respectively: T. D. DuBois and D. W. Meek, Inorg. Chem., 8, 146 (1969); values reported for 1: 1 and 2 : l electrolytes in acetonitrile are 136-155 and 250-310, respectively: M. Ciampolini and P. Paoletti, ibid.,6, 1261 (1967). See also W. J. Geary, Coord. Chem. Rev., 7, 81 (1971). Approximately (1-5) X M solutions; in cm2/(ohmmol).
ductance values in nitromethane solutions which are consistent with a five-coordinate species (0isomer) and the equilibrium between four- and five-coordinate species (a isomer)
e Ni([l3]trieneN\~4)*+ + Br-
Xi( [l3]trieneNr)Br+
Such an equilibrium behavior has also recently been reported for other Ni(I1) macrocyclic complexes with halide anions.21s22 The values given for the diperchlorate derivatives in acetonitrile and nitromethane are consistent with their formulation as 2 : 1 electrolytes as is required if oxidation of the Ni([l3]dienoNe)C104 complex to Ni( [13]trieneN4) + has occurred. This facile oxidizability was anticipated to some extent in view of preliminary reports on the electrochem(21) E. K. Barefield and D. H . Busch, Inovg. Chem., 10, 1216 (1971). (22) W.Rosen a n d D. H . Busch, J . Amev. Chem. Soc., 91, 4694 (1969).
ical behavior of these and related substance^.^^^^^ I t has been shown that Ni(II1) can be formed by oxidation of the complexes of structures I11 and I V a t exceptionally low potentials. 2 4 As indicated above, the intermediacy of Ni(II1) in closely related ligand oxidation processes seems to be established and the ease of attaining this intermediate may signal the ease of oxidative dehydrogenation. Since stable Ni(II1) complexes have been isolated, 2 6 , 2 6 the site of the oxidation required specific consideration. Ni(II1) is a d7 system and would ordinarily be expected to exhibit a t least one spin ( S = '/2 for low-spin form) , 2 5 , z 6 The oxidation products are uniformly diamagnetic, supporting the assumption that the central metal ion is Ni(I1) and that the ligand, not the metal, remains oxidized in these final products. The simplest interpretation that could be applied to account for the change in charge of the macrocyclic complex from 1+ to 2+ would not involve oxidation. These and most related structures are readily protonated (eq 6).19s27The structure of the resultant
V
m
complex contains two equivalent imine groups separated by a methylene group (eq 6). This can be distinguished from structure V very readily; i.e., the former contains a symmetry plane and equivalent methyl groups. Nmr has been used for this purpose (see below). The results conclusively show that ligand oxidation, not protonation, h,as occurred. Changes in the infrared spectra also support the (23) D. C. Olson and J. Vasilevskis, I?torg. Chem., 8 , 1611 (1969). (24) D. P. Rillima, J. F. Endicott, and E. Papaconstantinou, ibid., 10, 1739 (1971). (25) E. K. Barefield and D. H. Busch, Chem. Commun., 522 (1970). (26) E. S. Gore and D. H. Busch, Inovg. Chem., in press. (27) C. J. Hipp and D. H. Busch, unpublished results.
Inorganic Chemistry,Vol. 11, No.9, 1972
METALCOMPLEXES WITH MACROCYCLIC LIGANDS
1991
that the delocalized anionic ring has been oxidized. The distinction between the C=N modes for the a and /3 isomers is useful in monitoring the isomeric purity of samples. The nmr spectra of a- and P-Ni([13]trieneN4)(PF&.HzO are given in Figure 2. The limited solubility of these materials in appropriate solvents, along with the complexity observed for the methylene resonances, precluded a detailed analysis of these pmr spectra. The most notable features are the methyl singlets a t 2.20 and 2.25 ppm (a isomer) and the broadened methyl singlet a t 2.36 (@isomer) and a singlet, in both cases, a t -5 ppm which is assigned to the vinyl proton in the six-membered ring (structure V). Observation of two methyl resonances for the a isomer eliminates the possibility of ring protonation, while the p isomer clearly is not the protonation product (VII) whose spectrum is also shown in Figure 2. A consequence of this inequivalence of the methyl groups in the oxidation products is that either the two Figure 1,-Infrared spectra of the 13-membered ring derivafive-membered chelate rings adjacent to the acetylacetives: (i) Ni( [13]dienoN4)C104; (ii) ~~Ni([l3]trieneN4)(Cl04)~* tone residue are nonequivalent or the remote fiveH20; (iii) p-Ni( [13]trieneN4)(ClOa)~.HzO. Samples prepared in membered ring is unsymmetrical. halo oil mulls. The likelihood of an isolated imine linkage being generated by oxidative dehydrogenation in this system is remote. The ir and nmr characteristics of such an azomethine proton in a five-membered chelate ring of a nickel(I1) complex with a macrocyclic ligand are known. The C-H stretch for this type of proton has been assigned to the region -3070 cm-1,28 while the nmr resonance expected for such a proton is found a t 4 3 ppm.29 The additional unsaturation must then be located directly adjacent to one of the nitrogens comprising the formerly charged chelate ring as shown in structure V. 5.0 4.0 3.0 a. 0 PPM (0) I This is consistent with the absence of a C-H stretching band a t -3070 cm-' in the ir spectra of the oxidation products and the absence of nmr signals below -5 ppm for these complexes. The oxidation reaction can then be viewed as the formal result of hydride abstraction from Ni( [13]dienoN4)C104 to produce the observed complexes (eq 7). E i n cm-1
5500
3000
1700
1600
1500
3
H3cYYcH3+ H3Cwc C
5.0
4.0
3.0
2.0
1.0
0.0
PPM (a)
Figure 2.-Nmr spectra of the 13-membered ring derivatives : (i) Ni( [13]dienoN4)ClOa (CDsCN); (ii) Ni ([131dieneN4)(PF&. HzO (CDaCN); (iii) ol-Ni([l3]trieneNr)(PFe)~.HzO(CDaCN); (iv) p-Ni( [13]trieneN4)(PFe)~.HzO (CDsNOn). Tetramethylsilane, internal standard; solvent given in parentheses; 60-MHz spectra in i and ii and 100-MHz spectra in iii and iv. The ligand in ii has structure VI1 and is named ll,l3-dimethyl1,4,7,10-tetraazacyclotrideca-10,13-diene,1g abbreviated 11,13Me,[13]-10,13-dieneN4or [13]dieneN4.
interpretation given here (Figure 1). The conjugated C=N and C=C bands that are found in the 15001600-cm-' region for Ni( [13]dienoN4)+ do not appear in the infrared spectra of the oxidation product. These characteristic modes are replaced by a sharp imine stretch a t 1670 cm-' (a isomer) or 1650 cm-' (p isomer). These changes clearly support the suggestion
II
V
The visible absorption spectra of the two isomers (Table 11)indicate that both are stable in deoxygenated acetonitrile in the presence of water and that, when the water has been removed (by recrystallization from acetonitrile), the p fraction remains unaffected in solution while the spectrum of the a isomer changes with time. With both isomers, the region below 16,000 cm-I is transparent and they do not display distinct d-d transitions although they both have low-energy shoulders on the charge-transfer bands whose intensities are in the range expected for d-d transitions (28) N. F. Curtis, Chem. Commun., 881 (1966). (29) V. L. Goedken and D. H . Busch, Inovg. Chem., in press.
1992 Inorganic Chemistry, Vol. 11, No. 9, 1972
HIPP, LINDOY, AND BUSCH
TABLE I1 SPECTRAL DATAIK DEOXYGENATED ACETONITRILE FOR Complex
TABLE 111 DATAFOR 14-RIEMBERED RING DERIVATIVES IN ACETONITRILE
COSDUCTANCE
Ni( [13]trieneN4)X~ YmsXa
(4
~-Ni([l3]trienel\T4)(ClO4)z~HzO 27,400 (1790) 27,300 (1780) 27,300 (1790) 27,000 (1760) P-Ni( [13]trieneN4)(C104)2.H~O 27,500 27,400 27,500 27,400
(1880) (1840) (1870) (1860)
a-Ni( [13]trieneN4)(PFs)~.CH1CK 27,300 (1870) 27,400 (1970) 27,400 (1990) 27,400 (2030) 27,500 (2070)
Elapsed hr
0 12 23 105 0 12 23 105
Complex
Axa
Xi( [ 141dienoN4)C104 162 Xi( [14]dienoN4)PF6 142 a-Xi( [14]trieneNa)(Cl04)~. HzO 266 /3-Ki( [ 141trieneNd)(PF~)z .HzO 3 18 a Approximately (1-5) X M solutions; in units of cmz/ (ohm mol). E in cm-1
3500 I
#
I
1100
3000 I
I
I
I
I
*
J
I
1500
1600 *
I
I
1
0 1.5 12 24 36
&Xi( [13]trieneN4)(PF6)~.CHsCN 27,400 (2150) 0 27,500 (2190) 12 27,500 (2170) 40 a vmax in em-'; B in parentheses in l./(mol cm). The initial measurement necessarily entailed a -20-minute delay following sample preparation.
The first charge-transfer band, present in both isomers a t 27,400 cm-' ( e -2150, (3 isomer; e
