3578 Inorganic Chemistry, Vol. 17, No. 12, I978
Gordon, Peng, and Goedken
Contribution from the Departments of Chemistry, The Florida State University, Tallahassee, Florida 32306. and The University of Chicago, Chicago, Illinois 60637
Oxidation of Octaaza Macrocyclic Complexes of Nickel(I1): Structures Containing the New P-Diazonato Chelate Ring G U Y C. G O R D O N , S H I E - M I N G P E N G , and VIRGIL L. GOEDKEY*l Receiued July 26, 1978
.
The octaaza bis-a-diimine macrocyclic complex [Ni(CloH2,N,)]*', 1, readily undergoes a variety of reactions involving the macrocyclic ligand. Complex I reacts with hydrazine and dioxygen via nucleophilic attack of hydrazine on an imine carbon of each five-membered ring and oxidative dehydrogenation of the six-membered rings to yield the dodecaaza complex [Ni(CloHzoN12)], 111. The reaction of I with borohydride, followed by aerial oxidation, yields an isomer of [Ni(CloH18N8)], 11, in which the a-diimine functions have been reduced and double bonds introduced into the six-membered rings. Initial attempts to oxidize this species to the dihydrooctaaza[ 14lannulene complex using the trityl cation led instead to electrophilic substitution on the six-membered rings to yield [Ni(CloHl,N8(CPh3)2)],V. Complex V can be oxidized to the ditrityldihydrooctaaza[ 14lannulene VII, which is monomeric unlike the unsubstituted Ni-Ni bonded dimer 161. Methyl groups on the methine carbons of the six-membered rings, as in IX, block electrophilic attack by the trityl cation allowing oxidation to the dimethyldihydrooctaaza[14]annulene XI. Spectroscopic and electrochemical evidence show that the Nil' ion and the trityl substituents in VI1 stabilize a different resonance isomer of the macrocycle than does the cobalt(II1) alkyl in XIV. X-ray crystal structures of I1 and I11 have been determined to fully elucidate the delocalization patterns in the altered macrocyclic ligands. Crystal data for 111, [Ni(C10H20N12)]:space group P 2 , / c , a = 9.287 (2) A, b = 13.608 (4) A, c = 12.565 (4) A, = 106.09 (2)", pexptl= 1.59 g/cm3, p&d = 1.55 g/cm3, Z = 4. Crystal data for 11, [Ni(CloH18N8)]: space group P ~ , / c ,a = 6.954 (2) A, b = 12.594 (3) A, c = 8.516 (2) A, B = 108.43 (Z)', pexptl= 1.46 g/cm3, pcalcd = 1.46 g/cm3, 2 = 2. The structure of I1 contains two saturated five-membered chelate rings and two fully delocalized, anionic six-membered chelate rings of the previously unknown P-diazonato type. The average NikN distance is 1.790 (3) A and the nickel atom is crystallographically required to be in the N 4 plane. Structure I11 has a hydrazine adduct attached to a carbon atom of each five-membered chelate ring. Both hydrazines are located on the same side of the macrocyclic ligand plane. Two patterns of delocalization are observed in the complex. One is a fully delocalized six-membered ring of the P-diazonato type observed in structure 11. The other consists of a seven-atom system extending through a delocalized allylic-like anion in the six-membered ring and an imine function in each five-membered ring. By the chemical transformations presented, three oxidation states of the octaaza macrocycle show eight patterns of unsaturation.
Introduction One of the more intriguing aspects of macrocyclic ligand complexes of transition metals is the extent to which the ligand can be modified. In principle the ligands may be subjected to any modification within the limits of the functional groups from which they are constituted. However, the coordinated metal ions significantly alter both the course and the ease of these reactions. The most common type of reaction studied has been oxidative dehydrogenation of saturated C-I% linkages2-10 Other reaction types that have been reported include (1) oxidative dehydrogenation of C-C bonds,' (2) simple deprotonation of the ligand," (3) reduction of imine bonds," (4) attack of nucleophiles on coordinated imine bond^,'^^'^ and (5) electrophilic substitutions on unsaturated six-membered rings.15 Most of these reactions have counterparts with metal complexes of simpler nonmacrocyclic chelate ligands.16-22 However, the robust constitution of most synthetic macrocyclic ligands permits the above reactions to occur with greater facility than with noncyclic counterparts because these complexes may be subjected to much harsher reaction conditions. The octaaza macrocyclic complex 1 is remarkable with respect to the variety of reactions which it undergoes. The nature of some of these reactions is illustrated in Scheme I. Some of these and other reactions have been described in previous publication^.^^-*^ This paper presents an account of the synthesis and structural characterization of the nickel(I1) complexes shown in the scheme. Experimental Section All solvents and chemicals were obtained conimercially and were reagent grade. Solvents were used without further purification other than drying over 3A molecular sieves. Infrared spectra were recorded on a Beckman IR-IO or a Perkin-Elmer 521 spectrophotometer in the range 4000-500 cm..'. Samples were prepared as Nujol mulls and were calibrated with the 2851 .5- and 1601.3-cm-' absorptions of polystyrene film. Ultraviolet and visible spectra were obtained using a Cary Model 14 recording spectrophotometer within the range 1000-270 nm. Proton magnetic resonance spectra were recorded on either Varian A-60 or Bruker 270-MHz instruments. Elemental
0020-1669/78/1317-3578$01 .OO/O
analyses were determined commercially by Galbraith Laboratories, Inc., Knoxville, Tenn. Electron paramagnetic resonance was performed on a Varian E12 spectrometer. Electrochemical measurements were performed using a Princeton Applied Research Model 175 universal programmer and Model 173 potentiostat. The experiments were performed in a three-compartment glass cell with fritted-glass dividers. The central compartment was kept under a nitrogen or argon atmosphere and contained a platinum electrode. The reference electrode was a silver foil in 0.100 M AgC104 in acetonitrile connected to the reference compartment by an asbestos wick. All measurements were made in reagent grade acetonitrile dried over 3A molecular sieves, made 0.1 I\.I in tetraethylammonium perchlorate, and deaerated with nitrogen. Syntheses. [Ni(CloHzoNlz)],111. A solution of 2 g of [Ni(CloI, was kept under 2 atm of 02.Hydrazine, 0.3 HzoNs)](C104)2,24 mL, was injected and the color of the solution became orange-red. The cherry red product started precipitating in 30 min. The product was filtered after standing overnight, washed with methanol, and dried in air. The yield was 40%. Anal. Calcd: C, 32.72; H , 5.45; N , 45.81. Found: C , 33.59; H, 5.41; T,43.06. [Ni(Cl0Hl8Ns)],11. To a deaerated suspension of 510 mg (1 mmol) of I in 25 m L of methanol was added 155 mg (4 mmol) of NaBH4. Within 2 min everything dissolved and gas evolution ceased. Oxygen was bubbled through the solution for about 1 min until no more heat was evolved and the color turned deep blue. Water was added dropwise until the product precipitated. The yield was 70%. The product was recrystallized from diethyl ether by the addition of methanol and water. Anal. Calcd: C , 38.87; H, 5.83; N, 36.28. Found: C. 38.99; H, 5.94; N,36.21. [Ni(C10H16N8(CPh3)2)], V. To a solution of 1.2 g (4 mmol) of I1 in 15 m L of C H 3 C N was added 2.6 g (8 mmol) of Ph3CBF4. The solution became blue-green and the product started crystallizing within a few minutes. After 0.5 h, the product was filtered, washed with methanol, and air-dried. The yield was 70%. Anal. Calcd: C, 72.63; H , 5.80; K, 14.12. Found: C: 73.49; H, 5.85; N , 14.37. [Ni(CloH12N8(CPh3)2)], VII. Oxygen was bubbled slowly through a boiling solution of 200 mg of V in 15 m L of toluene. After 12 h, the solution had changed color from blue-green to deep emerald green. Methanol (5 mL) was added, and, on cooling, the product crystallized as large dark green needles. The yield was 85%. Reduction of VI1 to V. A deaerated solution of VI1 in tetrahydrofuran was treated with a large excess of NaBH, and refluxed under nitrogen until the green solution turned violet (5 min). At this
0 1978 American Chemical Society
Inorganic Chemistry, Vol. 17, No. 12, 1978 3519
Octaaza Macrocyclic Ni(I1) C o m p l e x e s Scheme I
I
Tp
I
CPh;
c P t' 3
I
NoBH4
/
j
'
2
H'
r
Y
CPh
A
L
Y
D e t a i l s of t h e X - r a y S t r u c t u r e D e t e r m i n a t i o n Crystal Examination and Data Collection. X-ray precession photographs of [ N i ( C I O H I 8 N 8 )and l [Ni(CloH20N12)Iexhibited monoclinic symmetry with systematic absences consistent with the unique space group P & / c . ~ ' Lattice constants and their estimated
rn
I
ix
point oxygen will regenerate the green VII. Deaerated 60% HC10, was cautiously added dropwise until the color changed to blue-green. Water was added dropwise until the product, V, crystallized as blue-green needles. The yield was quantitative. [Ni(CIOH16N8(Me)2)], IX. To a deaerated solution of 538 mg (1 VIII, in 100 mL Of mmol) Of [Ni(CloHi8N8(Me)2)](C104)2,24 methanol was added 155 mg (4 mmol) of NaBH,. The solution was warmed slightly to ensure complete reaction as indicated by the change in color from dark brown to light brown. Oxygen was bubbled through the warm solution until no more heat was generated. The color of the solution turned burgundy red. Water (50 mL) was added and the solution was warmed again, turning green in color. The product precipitated as blue-green flakes. The crude product was extracted into diethyl ether. The ether layer was washed twice with water and once with brine and then predried over CaCI,. Acetonitrile (50 mL) was added to the solution and the ether was removed on a rotary evaporator. This solution was dried over 3A molecular sieves for 24 h. The volume of the solution was then reduced on a rotary evaporator until crystals formed. The yield was 40%. [Ni(C10Hi4N8(Me)2)], X. To a solution of 169 mg (0.5 mmol) of IX in 25 m L of CH3CN was added 180 mg (0.5 mmol) of Ph3CBF4 giving a brown solution. After 5 min, 5 mL of methanol was added to remove any unreacted Ph3CBF4. The solution was heated allowing 10 m L of the solvent to boil off. Diethyl ether (1 50 mL) was added, and the ether solution was washed with water until the water layer was no longer brown leaving a bright green solution. This solution was worked up in the same manner as X above. The yield was 30%. [Ni(CloHlzN8(Me)2)]2,XI. Air was allowed to slowly diffuse into a solution of 200 mg of VI11 in deaerated C H 3 C N and 0.5 m L of N E t 3 . The product precipitated as black microcrystals. The yield was 50%. Alternately, IX or X may be oxidized by excess Ph3CBF4 or air. Growth of Single Crystals for Structural Investigation. Ruby red crystals of [Ni(CloH20N,2)],pseudooctahedrally shaped and suitable for X-ray investigation, were obtained after numerous recrystallizations of the compound from trifluoroethanol. Long, thin, blue-black needle-like crystals of [Ni(C10H18NB)] having highly reflective faces were grown by slow diffusion of water into an acetonitrile solution of the compound.
CPh3
PI
P
rn
l-
CPh3
CPh3
X Table I. Crystal Data and Data Collection Details compd mol wt space group a, A b, A c, '4 a,deg P, deg 7, deg Z
no. of reflections used to determine cell constants 28 limits, deg dcalcd?g/cm3
dexpt13 p/cm3
absorption coeff, cm-' crystal dimension, mm absorption cor diffractometer monochromater (Bragg angle) (K4,A Takeoff angle, deg method scan speed, deg/min scan width, deg bkgd time standards av med dev of standards, 96 28 limits of data, deg no. of data collected no. of data used in final refinement
[Ni(CloH,oNl,)lo 376.06 P2,lC 9.287 (2) 13.608 (4) 12.565 (4) 90.0 ( 0 ) 106.09 (2) 90.0 (0) 4 24
309.02 P2,lc 6.954 (2) 12.594 (3) 8.516 (2) 90.00 (0) 108.43 (2) 90.00 ( 0 ) 2 25
60 4 28 G 70 (Cu KLY) 1.59 1.55 19.61
30 4 28 4 40 (Ma KCY) 1.46 1.46 13.75
0.25 X 0.25 X 0.25
0.09 X 0.09 X 0.5
NO Picker-FACS-1 NO
NO Picker-FACS-1 graphite (6.093)
1.5418 (Cu) 0 8-28 1.0 2.0 20x 2 3
0.710 69 (Mo) 3.0 8-28 2.0 1.8 20x 2 3 2 (random)
1
o 4 28 4
130
2868 (non-std) 2570 (unique) 2109 ( F > 3u(F))
[Ni(C,,H,,N,)
lo
o 4 28 4 55 1856 (non-std) 1394 ( F > 3u(F))
standard deviations, together with other pertinent crystal data, are given in Table I. The details of the data collection for both complexes are also presented in Table I.28 The data were reduced in the conventional manner with corrections applied for Lorentz and po-
3580 Inorganic Chemistry, Vol. 17, No. 12, 1978
Gordon, Peng, and Goedken
a(F) = u(I)/2F(Lp)’!2
by full-matrix least-squares technique^.^^ Scattering factors of neutral atoms were taken from standard ~ o u r c e s . ~Corrections I for anomalous dispersion were applied to the nickel atom of each structure from the values of A y and .If”tabulated by Cromer. The details of the solution and refinement of the structures are summarized in Table 11. The solution and refinement of [ ~ i ( C 1 0 H 1 8 N 8were ) ] straightforward. The initial solution for the structure of [Ni(C,oH,oNlz)]appeared straightforward with all of the atoms being located on the first Fourier map. Two cycles of refinement employing anisotropic temperature factors for the nickel atom and isotropic temperature factors for the nonhydrogen atoms yielded R , = 6.8% and R2 = 8.1% for the 1033 most intense data. Although the bond distances and angles involving the nickel atom and the 14 atoms of the macrocyclic ring were consistent with those expected at this degree of refinement, those of the substituents (methyl groups and hydrazine moieties) of C3 and C5 were chemically unreasonable. Careful examination of a difference Fourier map obtained at this point revealed disorder between the meso and d,l configurations of atoms C 3 and C 5 as determined by the orientation of the methyl and hydrazine substituents. One cycle of full-matrix refinement in which the minor fragments of the disordered hydrazines (DN9, DN10, DNI 1. and DN12) were included, varying the multiplicities in addition to the isotropic temperature factors and the positional parameters, yielded residuals of R1 = 4.8% and R2 = 5.1% using the most intense 1033 data. Eight hydrogen atoms attached to C1, C4, C7: and C10 were located from a difference Fourier map; their positions were optimized to normal geometry for these systems and were then included as fixed contributions in the remaining cycles of refinement. Hydrogen atoms in the disordered portions of the structure could not be located. Continued refinement with 2109 data having IF1 2 3u(F) and using anisotropic thermal parameters for all atoms was unsuccessful because some temperature factor terms of the disordered hydrazine atoms Dh-9 and DN11 became negative. However, a difference Fourier map indicated that the electron density of these atoms was well accounted for by the anisotropic thermal motions of C8, C9, N9, and N 1 1. The final model included only atoms DNlO and DN12 from the disordered portion, The positional parameters and anisotropic thermal parameters of all nonhydrogen atoms were varied, in addition to the multiplicities of all atoms involved in the regions of disorder. At convergence, R1 = 5.9% and R2 = 4.7%. The highest peak on the final difference Fourier map corresponded to 0.7 e/A3 and was located in the vicinity of the disordered atoms. The multiplicities of the disordered fragments were not equal for the two halves of the molecule: the multiplicity of DNlO was 0.36 and that of DN12 was 0.13. Since the major interests in this structure pertain to the patterns of delocalization in the macrocyclic ligand, the disorder of the hydrazine and methyl substituents, though unfortunate. does not seriously affect the sought after structural results. The final positional and thermal parameters of the nonhydrogen atoms for [Ni(CI0Hl8N8)]are listed in Table 111 and those for [Ni(CioHzoNl2)]are listed in Table IV. Hydrogen atom positions for the two structures are listed in Tables V and VI.
A total of 2129 independent reflections with F 1 2u(F) was used in the refinement of [Ni(CloH20h~12)] and 1394 data wlith IF/ > 3u(F) were used for [Ni(CloH,,N,)]. The effects of absorption ( p = 19.61 and 13.75 cm-I for [Ni(CIOHZON12)] and [Ni(C,oH18T\;8)],respectively) were judged to be minimal for the particular crystals used and were not compensated for. Structural Solution and Refinement of the Structures. Both structures were solved by standard heavy-atom methods and refined
Results and Discussion The octaaza macrocyclic complex I is particularly susceptible to oxidation reactions involving the N-N and C-N linkages, to nucleophilic attack on the a-diimine functions, and to hydrogenation of the imine linkages. Under certain conditions, a number of transformations occur sequentially. For example, a complicated series of reactions occur when excess
Table 11. Summary of the Details of the Solution and Refinement of the Structures compd
[Ni(C,OH1 8NB) 1
“,OH,”N,,)l0
method heavy atom position from Patterson synthesis problem in refinements no. of cycles used in refinements model for final cycle of refinement
final R final R , highest peak (e/A’) in final difference Fourier map noise level of final Fourier map, e / A 3 ratio of observations to variables
heavy-atom techniques general position: x = 0.195, y = 0.114, t = 0.103 yesa
heavy-atom techniques special position: x = 0.0, y = 0.0,
8
5
all nonhydrogen atoms positional and anisotropic thermal parameters varied; hydrogen atoms included as fixed contributions 5.9 4.7 0.7 around disordered portion
all nonhydrogen atoms positional and anisotropic thermal parameters varied; hydrogen atoms included as fixed contributions 3.5 3.8 0.4 around Ni
