Metal complexes of furfurylamine derivatives

J. inorg, nucl. Chem.. 1967, Vol. 29, pp. 1421 to 1426. Pergamon Press Ltd. Printed in Northern Ireland

METAL COMPLEXES OF F U R F U R Y L A M I N E DERIVATIVES* M . D. JOESTEN,t K . G . CLAUS~ a n d K . P. LANNERT§ Department of Chemistry, Southern Illinois University, Carbondale, Illinois (First received 21 October 1966; in revised form 9 January 1967) Abstract---Complexes of Ni(II), Co(II), and Cu(II) with furfurylamine, tetrahydrofurfurylamine, and N-methyltetrahydrofurfurylamine have been isolated. The first ligand coordinates as a monodentate ligand while the second and third coordinate as bidentate ligands. The complexes of COC12 and CuCI~ are initially non-electrolytes in nitromethane but become 1 : 1 electrolytes after the complexes have been in solution for 1 day. The spectral data for solutions of these complexes in nitromethane and aeetonitrile are in agreement with those reported for solvolyzed tetraehlorometallate species. INTRODUCTION

THEFURVURYLAMINES(I,II,III)have two donor sites which may coordinate to H

H

N~ H

(I) H

furfurylamine(FA)

C--N\ H

(II) H

tetrahydrofurfurylamine(TFA)

--C--N\ H

(IIt) CHa

N-methyltetrahydrofurfurylamine(MTFA)

metal ions. Previous attempts at the isolation of complexes of furfurylamine from aqueous solution resulted in hydrolysis of the ligand and precipitation of metal hydroxides. (1) Since complexes of tetrahydrofuran have been isolated) 2) we felt tlmt an investigation o f the c o o r d i n a t i n g a b i l i t y o f I, II, a n d I I I w o u l d be o f interest. * Presented in part at the 150th Meeting of the American Chemical Society, Atlantic City, N.J., September, 1965. t To whom correspondence may be addressed at the Department of Chemistry, Vanderbilt University, Nashville, Tenn. 37203. :~ Abstracted in part from the M.A. Thesis of K. G. Claus, 1965. § Undergraduate NSF Research Participant, 1966. (tl E. GONICK, W. C. FERNELIUSand B. E. DOUGLAS, J. Am. chem. Soc. 76, 5253 (1954). t~ R. J. KERN, J. inorg, nucL Chem. 24, 1105 (1962). 1421

1422

M . D . JOESTEN, K. G, CLAUS and K. P. LANNERT EXPERIMENTAL

Chemicals. Research samples of the furfurylamines were supplied by Miles Chemical Co. Additional quantities of the ligands were obtained from Aldrich Chemical Co. Tetrahydrofurfurylamine and N-methyltetrahydrofurfurylamine were used without further purification. Furfurylamine decomposes upon standing and must be purified before use. The fraction boiling at 50-52°C at 20 mm pressure was used for reactions with metal ions. Fisher reagent grade acetonitrile and nitromethane were used for conductance and spectral measurements. Conductance measurements. Molar conductivities of the complexes in nitromethane were measured with a conductance bridge manufactured by Industrial Instruments, Inc. A cell with platinum electrodes and a constant of 0.096 was used. Spectral measurements. I.R. spectra of Nujol mulls were obtained with a Beckman Model IR 5-A. Visible and u.v. spectra were recorded on a Cary Model 11 and near-i.r, spectra were recorded on a Beckman DK-1A. ,analyses. Carbon, hydrogen, and nitrogen analyses were performed by Weiler and Strauss, Microanalytical Laboratory, Oxford, England and Alfred Bernhardt, Max Planck Institute, Mulheim, Germany. Preparation of complexes Method.4. All of the complexes with metal perchlorates were prepared by this method. Approx. 0"004 moles of hydrated metal perchlorate were dissolved in 6 ml of 2,2-dimethoxypropane and stirred for a minimum of 1 hr. This served to dehydrate the metal perchlorates. ~8~ After this period of time, a 6: I mole ratio of ligand to metal ion was added to the resulting solution. If no crystals formed after the mixture was left standing for 1 hr, ether was added to precipitate the complex. Method B. This method was used for all metal chlorides except for the reaction of copper(II) chloride with furfurylamine and tetrahydrofurfurylamine. Approx. 0'002 mole of the anhydrous metal chloride were added directly to the ligand. In most cases, the salts were slightly soluble in the ligand. However, many reactions took place directly at the surface of the metal salt. Whenever possible, the liquid phase was filtered offand flushed with anhydrous ether to give a precipitate. In no instance did this product prove to be any different than the solid which remained in the reaction flask. CuC12.2MTFA

Method C. This compound was prepared by Method B and also by the following procedure. Anhydrous CuCI~(0-008 mole) was dissolved in 100 ml of acetonitrile. N-Methyltetrahydrofurfurylamine (0.016 mole) was added to the resulting solution, and then the excess acetonitrile was drawn off using a water aspirator. As the volume decreased, blue crystals precipitated from solution. These crystals were collected by filtration, washed with ether, and dried under vacuum. RESULTS

AND DISCUSSION

Tables 1-4 are tabulations of analytical data, i.r. spectral data, conductance data, and visible spectra data for the complexes isolated in this studv. The complexes were insoluble in most organic solvents and dissolved with decomposition in water. The amounts required for spectral and conductance measurements could be dissolved in nitromethane and acetonitrile. Furfurflamine complexes. Attempts to isolate complexes of metal perchlorate salts with furfurylamine were not successful. The chloride salts of Ni(II), Cu(II), and Co(If) reacted to give NiC12"4FA, CoC12"4FA, and CuC12.3FA. Both of the N-H stretching frequencies of furfurylamine are shifted to lower frequencies in the complexes (Table 2). This is evidence for coordination of the nitrogen donor site with the metal ion. The bands at 1155 and 1010cm -1 are tentatively assigned as C-O-C stretching vibrations, t4) The band at 1155 cm-1 is shifted 5-15 t3~ K. STARKE,J. inorg, nucl. Chem. 11, 77 (1959). t4~ A. R. KATRITZKYand J. M. LA~OWSrd, J. chem. Soc. 657 (1959).

Metal complexes of furfurylamine derivatives

1423

TABLE 1 . - - A N A L Y T I C A L DATA FOR COMPLEXES OF FURFURYLAMINE DERIVATIVES

Compound

ZC Calcd. Found

ZH Calcd. Found

%N Calcd. Found

NiC12.4FA CoCI~-4FA CuC12.3FA

46.3 46.3 42.3

46.4 45.5 42.2

5.40 5.39 4.92

5.73 5.62 4.99

10.8 10.8 9.87

10-3 10.9 9.86

Ni(CIO4)2"4TFA CuCI2"2TFA Ni(CIO4)2"3MTFA

36-3 36.2 35"8

36"3 35'5 35"4

6.65 6.65 6"48

7"06 6.59 6'56

8.46 8-47 6"98

8"50 8"67 6"97

CoCI~.2MTFA CuC12"2MTFA CuClz.2MTFA

39.9 39-5 39.5

40-0 40.0 39.5

7.23 7.13 7.13

7.32 6-93 7.19

7-77 7-68 7.68

7.99 7.86 7.76

TABLE 2.--I.R.

Color

Method of Preparation

green violet bluegreen blue blue bluegreen violet blue blue

B B

A A A A B B

C

SPECTRAL DATA FOR COMPLEXES OF FURFURYLAMINE DERIVATIVES* ~N-H sym.

~C-O-C

Compound

7)N H asym.

(cm -~)

(cm -i)

(cm -1)

FA NiCI2.4FA CoC12"4FA CuCI2"3FA TFA Ni(C104)2"4TFA CuC12.2TFA MTFA Ni(C104)2-3MTFA CoC12-2MTFA CuCIf2MTFA

3400 (m) 3300 (w) 3210 (m) 3280 (m) 3380 (m) 3300 (m) 3270 (m) 3300 (m) 3225 (m) 3200 (s) 3200 (s)

3300 (m) 3200 (w) 3130 (m) 3140 (m) 3300 (m) 3250 (m) 3150 (In) -----

1155 (s), 1010 (s) 1145 (m), 1010 (m) 1145 (m), 1010 (m) 1140 (m), 1010 (m) 1060 (s) -- f 1020 (m) 1070 (s), 920 (m) 1050 (sh), 1021 (s), 920 (s) 1049 (s), 1011 (s), 943 (s), 928 (s) 1060 (s), 1028 (s), 953 (s) 929 (s)

* Relative intensities are indicated in parentheses; strong (s), medium (m), and weak (w). t Solvent absorption.

TABLE 3 . - - C O N D U C T A N C E

DATA FOR COMPLEXES OF FURFURYLAMINE DERIVATIVES*

Compound

C~t × 10 a (mole/l)

NiCI~'4FA CoClf4FA CuC12-3FA Ni(C104)~'4TFA CuCIf2TFA Ni(C104)~.3MTFA CoClz.2MTFA CuCI3.2MTFA

0"80 1"75 0"98 0.98 1"79 0.84 1"07 0"91

* In nitromethane at 25 °C.

AM initial (cm 2 ~ - i mole-i) 18 16 16 174 14 180 29 18

Am final (cm 2 ~)-1 mole-i) 18 50 (4 days) 59 (2 days) 174 63 (1 day) 180 55 (2 days) 67 (1 day)

1424

M.D. JOEST~r¢,K. G. CLAUSand K. P. LANNERT TABLE 4.INVISIBLE SPECTRAL DATA FOR COMPLEXES OF FURFURYLAMINE DERIVATIVES

Compound NiCI2.4FA CoCI,.4FA CuC12"3FA (after 1 day)* Ni(CIO4)~.4TFA CuCIz'2TFA (after 1 day)* Ni(CIO~)~.3MTFA CoCI2.2MTFA CuC12.2MTFA (after 15 rain)*

2max (mp)

e

583 660 595 605 630 700 270 393 615 700 271 385 628 1075 590 620 650 705 273 305 (sh)

50 50 292 303 350 66 3300 69 12 94 5400 33 15 11 324 358 386 71 8900 3200

Solvent nitromethane nitromethane acetonitrile nitromethane acetonitrile nitromethane nitromethane acetonitrile

* From time of mixing. Initial spectra were run immediately after mixing. cm -1 in the complexes while the band at 1010 cm -1 is not affected. The slight shift of the 1155 cm -1 band may be due to a weak interaction of the metal with the oxygen donor site or with the unsaturated ring. The C - N stretching frequency which occurs at 1070 cm -1 in furfurylamine is split in the complexes to give two bands at 1070 and 1035 cm -1. This decrease is caused by the withdrawal o f electron density from the C - N bond when the nitrogen becomes coordinated to the metal ion. Initially, the complexes of furfurylamine are non-electrolytes in nitromethane. However, the resistance of solutions o f CoCI~.4FA and CuCI~.3FA decrease with time. The initial and final values of the molar conductances of these complexes are given in Table 3. The conductance data can be interpreted in two ways, as shown by Equations (1) and (2). 2MC12"4FA

CHaN02

~- [M(FA)4] 2+ + [MCI~] 2-

MC12"4FA CHsNO~~" [M(FA)4C1]+ + C1- M = Cu(II), Co(II)

(1) (2)

The solvent may also replace either FA or C1- to give solvolyzed species such as [M(FA)aSa] *+ or [MClaS]- where S is nitromethane in this case. The color of CoC12"4FA changes immediately from light violet to dark blue when the complex is dissolved in nitromethane. The spectrum is similar to that reported for tetrahedral Co(II) in the form of [CoC14]*-. tS~ However, the differences in spectral properties of tetrahedral Co(II) in various solvolyzed forms such as [CoCI3S]- and [CoCI(S)a]+ are not sufficient to enable us to choose between (1) and (2). It is likely that both are important. All conductivities were calculated on the basis of Equation (2). The fact ts) C. FURLANIand G.

MORPURGO,

Theor. ehim. Acta 1, 102 (1963).

Metal complexes of furfurylamine derivatives

1425

that some of the values are low for 1 : 1 electrolytes can be attributed to the presence of some [CoC1,] 2- and [CoC13S]- in solution. The initial spectrum of CuC12.3FA in acetonitrile is characteristic of tetragonal Cu(II). c6) In the solid state CuCI2"3FA may be polymeric with chloride bridging or an example of five-coordinate Cu(II). The spectrum of the acetonitrile solution of CuC12"3FA changes to that characteristic of [CuC1]+.(7) This indicates the importance of the reaction of type (2) above. Tetrahydrofurfurylamine complexes. Complexes of this ligand were very difficult to isolate and characterize. Only CuCI~.2TFA and Ni(CIO4)2"4TFA were characterized. Other solids were isolated from reaction mixtures, but the i.r. spectrum indicated that the ligand had undergone decomposition during the course of the reaction. The conductance and spectral data for CuCI~-2TFA in acetonitrile are similar to those obtained for CuC12"3FA. Thus, these compounds are also solvolyzed in solution. The decrease in the N - H and C-O-C stretching frequencies are support for both the nitrogen and the oxygen donor sites coordinating to the metal ion. The stoicheiometry of the Cu(II) complex is that expected if TFA is a bidentate ligand. However, one would expect the Ni(II) complex to have a 3 : 1 ligand-to-metal ratio if the TFA were coordinating as a bidentate ligand. Since the perchlorate anion absorbs in the 1090 cm -1 region, it is not possible to determine whether some of the ligands are monodentate and some bidentate or whether all are monodentate. However, the visible spectrum is that expected for octahedral Ni(II) since the two peaks in the visible region have very low molar absorptivities. Therefore, at least two ligand molecules are coordinating as bidentate molecules. Complexes of tetrahydrofuran have been isolated <2)so the coordination of the oxygen in TFA to the metal ion is not unexpected. N-Methyltetrahydrofurfurylaminecomplexes. These complexes were the most stable of all those isolated in this study. As in the other complexes a decrease in the N - H stretching frequency is observed when the ligand is coordinated to the metal ion. In the C-O-C region several of the bands are split and broadened. The C-O-C band at 1070 cm -1 shifts to lower frequencies and is split into two bands. One of the lower bands is probably due to the C - N stretching frequency which occurs in the same region as the C-O-C band (1070 c m -1) and would be expected to decrease as coordination to the metal ion occurs. The C-O-C band at 920 cm-1 is broadened in the complexes with new bands appearing at higher frequencies. In complexes of tetrahydrofuran a decrease in both C-O-C stretching frequencies was observed. (~) The i.r. data for the complexes isolated in this study are difficult to interpret. The complexity of the i.r. spectra may be interpreted as evidence that the N-methyltetrahydrofurfurylamine molecules exist in more than one type of chemical environment. However, the ease of isolation of these complexes as well as the similarity of CuC12.2MTFA and CuC12"2TFA are support for the presence of N-methyltetrahydrofurfurylamine as a bidentate ligand. Additional support for the contention that N-methyltetrahydrofurfurylamine is behaving as a bidentate ligand is the presence of octahedral Ni(II) in a nitromethane Ca! j. BJERRUM,C. J. BALLI-IAUSENand C. K. JORGENSEN,.4CtQ chem. scand. 8, 1275 (1954). ~?) S. "1~.MANAHANand R. T. ]WAMOTO,Inor~. Chem. 4, 1409 (1965). 3

1426

M . D . JOESTEN, K. G. CLAUS and K. P. LANNERT

solution of Ni(C104)2.3MTFA. The molar conductance of this complex is in the range expected for 2:1 electrolytes (130-180). The visible and near-i.r, spectrum of Ni(C104)z'3MTFA has three weak peaks at 385 m/z (26,000 cm-X), 628 m# (15,900 cm-1), and 1075 nap (9300 cm-1) which are characteristic of octahedral Ni(II). ~s~ The band assignments for these three peaks are 3A2--~3Tl~p~, 3A2--~3Tl, cp~, and 3A2, ~ ZT2gcr~, respectively. Ligand field parameters were calculated according to the procedure outlined by DRA¢O.~s) The Dq value calculated for N-methyltetrahydrofurfurylamine is 930 cm-1. This is lower than the Dq value for ammonia (1080) and methylamine (993) but higher than the Dq value for water (850). The lowering of the ap energy is often used for estimating covalent contributions to the metal-ligand bond. The parameter/~ is defined as B'/B where B' is the value calculated for 3p in free gaseous Ni(II). (s) The/~ value for N-methyltetrahydrofurfurylamine is 0.84 which is in the range reported for other amines. ~9) The calculated value for the aA2, ~ 3T~g~r' band is 15,242 cm-1 which is in fair agreement with the experimental value of 15,900 cm-1. The conductances of CoCI2"2MTFA and CuCI2"2MTFA undergo the same change observed for complexes of furfurylamine and tetrahydrofurfurylamine. Both complexes show an increase in conductance with time to values which are slightly low for 1:1 electrolytes. MANAHAMand IWAMOTO(7) have published the spectral characteristics for [CuC1]+, [CuC13]-, and [CuC14]2- species in acetonitrile. All three species have an intense peak near 300 m/z. However, the [CuC13]- and [CuC14]~ species also have intense peaks between 400 and 470 m~. In the present study, the spectrum of CuC12.2MTFA in acetonitrile which was obtained 15 rain after the compound was dissolved has only one intense peak at 273 mg with a shoulder at 305 m/~ (Table 4). This is support for the presence of mainly [CuC1]+ with the remaining coordination positions occupied by MTFA and acetonitrile. This conclusion can also account for the fact that the conductivity of the solution is near that of 1 : 1 electrolyte. CONCLUSION

The difficulty of the oxygen site in furfurylamine to coordinate to metal ions is illustrated in this study. Saturation of the furan ring of furfurylamine gives a ligand which can coordinate to metal ions by using both the oxygen and the nitrogen donor sites. However, these complexes are not stable and are difficult to characterize. The stability of the complexes of N-methyltetrahydrofurfurylaminemay be caused by the steric requirements of the methyl group which allow the oxygen donor sites of all ligand molecules present to coordinate to the metal ion. ~8~R. S. DRAGO, Physical Methods in Inorganic Chemistry, pp. 167-170. Reinhold, New York (1965). ¢9~R. S. DRAGO,D. W. MEEK,R. LONGHIand M. D. JOESTEN,Inorg. Chem. 2, 1056 (1963).