YNTHESIS AND PHYSICOCHEMICAL PROPERTIES

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The interaction of the cyclic amines (L) 1,4,8,11-tetraazacyclotetradecane ... The following aliphatic tetraamines (L) were selected as ligands: 1,4,8,11-tetraaza-.
YNTHESIS AND PHYSICOCHEMICAL PROPERTIES OF ERIVATIVES OF COPPER(II) TETRAHYDROBORATE HTH CYCLIC AMINES V. D. M akhaev, A. P. Borisov, B. I. Saidov, N. S. Kedrova, A. S. Antsyshkina, N. N. Mal'tseva, and Yu. M. Shul'ga

UDC 546.562:546.271:547.898

The interaction o f the cyclic amines (L) 1,4,8,11-tetraazacyclotetradecane a n d 5,7,12,14-tetram ethyl-1,4,8,11-tetraazacyclotetradecane with [(RO )3P]C uBH 4 (R = C2H 5 or C J i g) in ethanol gives com plex com pounds o f the type C u (B H J2 L. The com pounds synthesized have been characterized by data fro m chem ical analysis, DTA, x-ray photoelectron spectroscopy, and IR spectroscopy. The interest in the tetrahydroborato complexes of copper is due to the possibility o f their employment as elective reducing agents in inorganic and organic synthesis, as light-sensitive substances in silver-free photograny, etc. In addition, the investigation of derivatives of copper tetrahydroborate is o f interest for the chemistry f hydrides, since the monodentate coordination of a B H4 group to a metal atom was first structurally characnzed and the dependence o f the type o f bonding (mono- and bidentate) on the nature of the ligand was first ;tablished in just these compounds [1-3], Alkali-metal tetrahvdroboratcs reduce compounds of Cu(ll) to Cu(I) or elemental copper [4J. In the case of u(II), the literature offers only a description of the synthesis of Cu(NH3)4(BH4)2 (without its characteristics), hich decomposes at -4 0°C [5], Although coppcr(l) tetrahydroborate was described in a number of publications 7], it was isolated only in the form o f the complex (LiCl)x-CuBH4 according to the reaction CuCl2 + 2 L i BH4

(LiCl)v C uB H 4 + 0.5B2H6 + 0.5H2 ■+ (2 - jc)LiCl.

he compound is obtained in the form o f a white, nonvolatile substance, which is poorly soluble in diethyl ether ind thermally unstable. The compounds C uBH4-«L, where L is a Lewis base, for example, an alkvl(aryl)ihosphine(arsine, stibine) or a phosphite, are more stable [8-11], In this communication we shall describe the synthesis and properties of derivatives o f copper(II) tetrahvdro'orate with cyclic amines. E X P E R IM E N T A L Trialkyl phosphite complexes of coppcr(I) tetrahydroborate obtained according to the method described in ?] were used in the work. The following aliphatic tetraamines (L) were selected as ligands: 1,4,8,11-tetraaza:vclotetradecane (C 10H24N 4, cyclam) from Fluka and 5,7,12-14-tetramethyl-1,4,8,11-tetraazacyclotetradecane C 14H32N 4, tmc).* The thermograms o f the samples were recorded with the aid o f an NTR-75 pyrometer, and the IR absorption spectra were recorded on UR-20 and Specord M-80 spectrometers with the use o f suspensions o f the compounds

•The specimen o f tmc was obtained from Yu. N. Shevchenko, whom we sincerely thank. N. S. Kumakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences. Translated from Koordinatsionnaya Khimiya. Vol. 18, No. 5, pp. 469-473, May, 1992. Original article submitted January 31, 1992.

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0364-4626/92/1805-0406$ 12.50 ©1992 Plenum Publishing Corporation

in liquid petrolatum. The ESR spectra were recorded on a Radiopan Ex-2542 spectrometer. The electronic spectra were recorded on a Specord UV VIS spectrometer. The x-ray photoelectron spectra were recorded on an IEE-15 spectrometer with a magnesium anode (£v =1253.6 eV) and a residual pressure equal to MO™6 mm Hg. The spectra were calibrated with respect to the C Is peak (285.0 eV) from the oil vapor. The measurements of the electrical conductivity o f 1 0'3 M aqueous solutions were performed on a Radelkis OK-102/1 conductometer. The chemical analysis o f the substances for C, H, and N was carried out on an EA 1108 Elemental Analyzer. In the analysis for Cu and B the compound was decomposed by concentrated nitric acid with heating followed by the addition o f concentrated sulfuric acid, and then the copper content in the solution obtained was determined trilonometrically, and the boron content was determined by titration with sodium hydroxide in the presence of mannitol with naphtholphthalein as an indicator. Synthesis of C u (B H 4)2 cyclam. A solution of 0.3 g (1.5 mmole) o f cyclam in 10 ml o f 95% ethanol was given an addition of 0.9 g (1.56 mmole) of [P(OEt)3]3C uBH4. The mixture was vigorously stirred in the presence o f atmospheric oxygen. The instantaneous appearance of a blue color, which changed to a lilac-pink color, was observed. The reaction mixture was left to stand for 24 h for the crystals to grow. They were filtered out, washed with ethanol, and dried in a vacuum at room temperature. This gave 0.17 g of the substance (the yield was -40%). Found, %: C, 40.96; H, 11.06; N, 18.84; Cu, 21.20; B, 7.30. Calculated for Cu(BH4)3C 10H 24N 4, %: C, 40.92; H, 10.99; N, 19.08; Cu, 21.65; B, 7.36. Synthesis of C u (B H 4)2 tmc. A 0.3-g portion (1.17 mmole) o f tmc was given an addition o f 1.93 g (2.33 mmole) of [P(OBu)3]3C uBH 4. The mixture was stirred for 20 h and then given an addition o f 5 ml o f pentane. The precipitate formed was filtered out, washed with ethanol and dried in a vacuum at room temperature. The yield was -50%. Found, %: C, 48.0; H, 11.44; N, 15.55; Cu, 17.88; B, 6.20. Calculated for Cu(BH4)2C 14H32N 4, %: C, 48.07; H, 11.54; N, 16.03; Cu, 18.18; B, 6.18. R E S U L T S AND DISC U SSIO N An attempt to obtain the complexes of copper(II) tetrahydroborate with the macrocyclic amines cyclam and tmc with the aid of the general synthesis method, i.e., by reacting copper(II) chloride (bromide) with lithium tetrahydroborate in the presence of the ligand in an organic solvent, was initially made. The compounds sought could not be obtained. The attempt to synthesize the copper(II) derivatives by means o f an exchange reaction of Zn(BH4)2 L with CuCl2 (or C u S 0 4) in an aqueous medium likewise did not yield positive results. Success was achieved in the case of the reaction o f [P(OR)3]3C uBH4 (R = C2H 5, C4H9) with L in ethanol: [P(OR)3]3CuBH4 + L

C A° aC>1 > Cu(BH4)2 L.

The reaction takes place at room temperature. The complex formed precipitates, and the excess o f tris(trialkyl phosphite)copper(I) tetrahydroborate remains in the solution. One necessary condition for the occurrence o f the the reaction is the presence o f oxygen. When the synthesis is carried out in an atmosphere o f an inert gas after the thorough removal o f the traces o f oxygen, no reaction takes place. When the reagents are mixed, the appearance o f a blue color is observed, and then a lilac-colored precipitate forms, i.e., Cu(I) is oxidized to Cu(II). It might have been expected that disproportionation according to the scheme Cu(I) -» Cu(II) + Cu(0) would take place, but the reaction does not occur in the absence o f oxygen, and the results o f the investigation o f the compound obtained indicate the formation o f only Cu(II). When the reaction is carried out in the presence of sodium tetrahydroborate, the yield o f the complexes is nearly quantitative. These data attest to the fact that the formation o f Cu(II) occurs as a result o f the oxidation o f Cu(I), rather than as a result of disproportionation. The formation o f complex compounds o f Cu(II) is also confirmed by the results o f the spectroscopic investigation o f the complexes. The ESR spectra are characterized by the parameters g = 2.095 and A Cu = 86 Oe. As in the case o f other complex compounds o f Cu(II) with tetraaza ligands, the electronic spectra display a broad band with a maximum at -23,000 c m '1 (Fig. 1). The x-ray photoelectron spectrum o f Cu(BH4)2-tmc contains a peak assigned to Cu 2p 3/ at 934.0 eV and an intense satellite on the high-binding-energy side.

407

30

28

Z2

18

v-103. cnV1

Fig. 1. Electronic absorption spectra of Cu(BH4)2 cyclam in water (1). liquid petrolatum (2), and glycerol (3). According to the data from chemical analysis, the compounds obtained have the general formula C'u(BH4),-L. and are obtained in the form o f crystalline substances o f lilac color, which arc soluble in chloroform. methylene chloride (ethylene), glycerol, liquid petrolatum, and water (with slow decomposition) The values of the molar conductivity o f aqueous solutions o f the complexes are similar (|i = 137 O ’cnVmoIc ' ) and attest to dissociation of the compounds in water The compounds Cu(BH4)2-L arc thermally stable: according to the DTA data they decompose in an inert atmosphere at 110°C. The heating curves are characterized by an exothermic effect accompanied by the evolution of gas In addition, as in the case o f the complexes of zinc with amines [12], sublimation of the aminoborane is observed. According to the data from the x-ray structural investigation in [13], in both structures the copper atoms are located at the center of a square formed by the four nitrogen atoms o f the macrocycle (C u-N ~ 2.02 A) The configuration o f the copper atom is brought up to a bipyramidal configuration by two tetrahydroborato groups (C u-H B H j ~ 2.2-2.3 A). The absorption bands for the B H4 group in the IR spectra are known to be characteristic, and their position and intensity depend on the type of bonding between the tetrahydroborato group and the metal (ionic or by means of single, double, or tnplet hydrogen bridges). For example, it was established by x-ray diffraction analysis that in the complexes C uL3B H 4 (L = M ePh2P [1, 11], P(OPr-z)2Ph, and PDPh2 [3]} the copper atom is bonded to the B H 4 group by means of a single bridge o f the C u - H - B H 3 type, while in C uL2BH4 {L = (C6H 5)3P [9], P(OEt)3, H

P(OPr-/)3, PPh3, PBuPh2, P(NM e2)3 [3]} it is bonded by a double bridge of the Z\i

^BH, type.

In each case

XXHZ

the IR spectrum displays a system of bands at 2000-2500 cm ': in the case o f B H4 groups bonded as monodcntate ligands v (B -H )b = -2000 and v(B-H), = 2300-2450 cm "1, and in the case of groups bonded as bidcntate ligands v (B -H )b = 1650-2150, v(B-H), = 2400-2600 cm 1 [14], The IR spectra o f the complex compounds o f the type Cu(BH4)2-L that we synthesized (Fig 2 and Table 1) display only one broad absorption band in the 2100-2400-cm*1 region, which is similar to the band of the BH4 anion in the spectra of alkali metal tetrahydroborates [14] and is apparently associated with the transfer of electron density from the nitrogen atoms to the copper atoms and then to the boron atoms. The IR-spectroscopic data are in good agreement with the results from x-ray photoelcctron spectroscopy: the value o f E o f the N Is level in the free amine tmc is equal to 398.8 eV, while its value in the complex Cu(BH4)2 tmc is equal to 399.6 eV, and the value o f E of the B Is level in the complex Cu(BH4)2 tmc is equal

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--------------------------------------------------1 ____ I____ 1

7

11

15

19

Zl

I

I

ZS

I____ I

30

1

v-105, c m 1

Fig. 2. IR absorption spectra of Cu(BH4)2-cyclam (1), [(RO)3P]2C uB H 4 (2), and Cu(BH4)2-tmc (3) T A B L E 1. Absorption Bands in the IR Spectra of the Complexes Com pound

[I-(O E t)3]2C u B ll4 C u (B H ,)y c y d a m

C u (B H 4) 2lm c

v (» HX

v (B -H )

2397 s 2360 sh

6 { B -H )

1994 s 1933 s

2156 2227 2315 2160 2221 2333 2377

v(N It)

1137 1104

3186

1118

3177

3185 3265 3234 3260

cyclam

to 187.2 eV, while its value in NaBH4 is equal to 188.0 eV, and its value in the complex 2Zn(BH4)2-tmc [12] in which the tetrahydroborato groups are covalently bonded to the metal, is equal to 188.6 eV. L IT E R A T U R E C IT E D 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

J. L. Atwood, R. D. Rogers, C. Kutal, and P. A. Grutsch, J. Chem. Soc., Chem. Commun., No. 17, 59! (1977). C Kutal, P. A Grutsch, J. L. Atwood, and R. D. Rogers, Inorg. Chem., 17, No. 12, 3558 (1978). V. D. Makhaev, A. P. Borisov, E. B. Lobkovskii, et al., Izv. Akad. Nauk SSSR, Ser. Khim., No. 8, 188^ (1985). N. N. Mal'tseva and V. S. Khain, Sodium Borohydride [in Russian], Nauka, Moscow (1985). P. W. Schenk and W. Muller, Chem. Ber., 97, No. 8, 2400 (1964). E. Wiberg and W. Henle, Z. Naturorsch., 7b, No. 10, 582 (1952). R. J Spokas and B. D. James, Inorg. Chim. Acta, 118, No. 2, 99 (1986). J. M. Davidson, Chem. Ind., No. 49, 2021 (1964). S. J. Lippard and D. A. Ucko, Inorg. Chem., 7, No. 4, 1051 (1968). F. Cariati and L. Naldini, J. Inorg. Nucl. Chem., 28, No. 10. 2243 (1966). J. C. Bommer and K. W. Morse, Inorg. Chem., 19, No. 3, 587 (1980). N. T . Kuznetsov, B. I. Saidov, N. S. Kedrova, et al., Koord. Khim., 17, No. 3, 411 (1991). 409