Organometallics 1996, 14, 4944-4947
4944
Ferrocenylenegermane Polymers and Copolymers Ramesh N. Kapoor,? Guy M. Crawford,? Jawad Mahmoud,? Vyacheslav V. Dementiev,? My T. Nguyen,$ Arthur F. Diaz,$ and Keith H. Pannell* Department of Chemistry, University of Texas a t El Paso, El Paso, Texas 79968-0513,and IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120 Received February 8,1995@ Ferrocenylenegermane polymers and copolymers (1)have been prepared, in situ, by thermal treatment of the product from the reaction between dilithioferrocene and the corresponding RzGeClz, R = methyl (la), ethyl (lb), n-butyl (IC),or their mixtures, MezGeClz n-BuzGeC12 (Id) and EtzGeClz n-BuzGeClz (le). Thin films of the polymers can exhibit both semicrystalline or amorphous morphology dependent upon the nature of the alkyl group and/or mode of casting. When cast from THF, ICwas observed as a n amorphous material; however, after time a crystalline form was obtained. Films of mixed polymer systems, l b IC,cast from THF immediately resulted in crystalline forms for both polymers, i.e., a seeding of IC by l b occurred. The diethylldi-n-butyl copolymer was amorphous and elastomeric as was the dimethylldi-n-butyl analog. Cyclic voltammetry indicated the presence of two reversible redox couples in solution with potentials slightly higher than the Si analogs. The copolymers also exhibited distinctive electrochemistry and not a combination of the two individual components.
+
+
+
Introduction The study of inorganidorganometallic compounds as new materials, or as prematerial systems, is developing rapidly in the hope that the metallic component can bring new and unusual properties to the resulting materia1s.l Electrical, optical, and high-temperature conversions are among the potential properties of interest in this class of chemicals. There has long been interest in the area of organometallic polymers containing ferrocene groups both as pendant and backbone units,2including silicon-based systems which have been shown to possess interesting electrochemical, thermal, conducting, and electrooptical proper tie^.^-^ Foucher et al. recently reported the preparation of the related ferrocenylenegermane analogs, [FCGeR&, FC = (v5C5H4)Fe(v5-C5H4),R = Me, Et, Ph,' which prompted us t o report our own studies on such compounds including the di-n-butylgermyl polymer and a copolymer with dimethylldi-n-butylgermane and diethylldi-n-butylgermane units, a new type of ferrocenylene polymer. Wide-angle X-ray diffraction and cyclic voltammetric electrochemical studies are reported on the ferrocenylenegermane polymers for the first time. +Universityof Texas a t El Paso. IBM Almaden Research Center. Abstract published in Advance ACSAbstracts, September 1, 1995. (1)(a)Inorganic and Organometallic Polymers; Zeldin, M., Wynne, K. J., Allcock, H. R., Eds. ACS Symposium Series 360; American Chemical Society: Washington, DC, 1988. (b) Mark, J. E.; Allcock, H. R.; West, R. Inorganic Polymers; Prentice Hall Polymer Science and Engineering Series; Prentice Hall: Englewood Cliffs, NJ, 1992. (2)(a) Gonsalves, K.E.; Rausch, M. D. In ref la, Chapter 36. (b) Hayes, G. F.; George, M. H. In Organometallics Polymers; Carraher, C. E., Sheats, J. E., Pittman, C. U., Eds.; Academic Press: New York, 1978;p 13. (3)(a) Zuaodung, D.; Xiaoyao, W.; Jing, L. Shandong DuxueXuebao 1987, 22, 115. (b) Pannell, K. H.; Rozell, J. M.; Zeigler, J . M. Macromolecules 1988, 21, 278. (c) Pannell, K. H.; Rozell, J. M.; Vincenti, S. In Silicon-Based Polymer Science: A Comprehensive Resource; Zeigler, J. M., Fearon, F. W. G., Eds.; Advances in Chemistry Series 224; American Chemical Society: Washington, DC, 1990; Chapter 20. (d) Diaz, A.; Seymour, M.; Pannell, K. H.; Rozell, J. M. J . Electrochem. SOC.1990,137,503. @
Experimental Section Organogermanium compounds were synthesized by published proceduress or purchased from Gelest Inc. Wide-angle X-ray scattering and electrochemical properties were investigated using previously described experimental conditions and equipment.6 Analyses were performed by Galbraith Laboratories Inc. Synthesis of FerrocenylenediethylgermanePolymer, lb. To a mixture of ferrocene (3.0 g, 16 mmol) and TMEDA (5 mL, 33 mmol) dissolved in hexane (60 mL) was added slowly a solution of n-butyllithium in hexanes (22 mL of a 1.6 M solution). After about 2 h, an orange precipitate formed, and the system was stirred for 12 h. The precipitate was washed with hexane until essentially colorless, and 50 mL of hexane was added. The resulting sluny was stirred and cooled to -78 "C. To this stirred system was added EtzGeClz (3.23 g, 16 mmol in 5 mL hexane) over a 2 h period. The solution was warmed to room temperature and stirred overnight. The reaction mixture was filtered, and the solvent was removed under vacuum to leave red-orange crystals. I3C NMR confirmed the presence of the ferrocenophane by observation of (4)(a) Foucher, D. A.; Tang, B.-Z.; Manners, I. J . Am. Chem. SOC. 1992,114,6246.(b) Tang, B.-Z.; Foucher, D. A.; Lough, A.; Coombs, Chem. Commun. 1993,523. N.; Sodhi, R.; Manners, I. J . Chem. SOC., (c) Foucher, D. A,; Ziembinski, R.; Tang, B.-Z.; Macdonald, P. M.; Massey, J.; Jaeger, C. R.; Vancso, G. J.; Manners, I. Macromolecules 1993,26,2878. (d) Foucher, D. A.; Honeyman, C. H.; Nelson, J . M.; Tang, B.-Z. Manners, I. Angew. Chem., Int. Ed. Engl. 1993,32,1709. (e) Foucher, D. A,; Ziembinski, R.; Peterson, R.; Pudelski, J.; Edwards, M.; Ni, Y.; Massey, J.; Jaeger, C. R.; Vancso, C. J.; Manners, I. Macromolecules 1994,27,3992.(0 Rulkens, R.; Lough, A. J.; Manners, I. J . Am. Chem. SOC.1994,116,797. (5) (a) Nguyen, M. T.; Diaz, A. F.; Dementiev, V. V.; Sharma, H. K.; Pannell, K. H. Proc., SPIE-Int. SOC. Opt. Eng. 1993,1910, 230. (b) Nguyen, M. T.; Diaz, A. F.; Dementiev, V. V.; Pannell, K. H. Chem. Mater. 1993,5,1389. (c) Nguyen, M. T.; Diaz, A. F.; Dementiev, V. V.; Pannell, K. H. Chem. Mater. 1994, 6,952. (d) Pannell, K. H.; Dementiev, V. V.; Li, H.; Cervantes-Lee, F.; Nguyen, M. T.; Diaz, A. F. Organometallics 1994,13,3644. (6)Tanaka, M.; Hayashi, H. Bull. Chem. SOC.Jpn. 1993,66,334. (7)(a) Foucher, D. A,; Manners, I. Makromol. Chem., Rapid Commun. 1993,14,63. (b) Foucher, D. A.; Edwards, M.; Burrow, R. A.; Lough, A. J.; Manners, I. Organometallics 1994,13,4959. (8)Lee, M. E.; Bobbitt, K. L.; Lei, D.; Gaspar, P. P. Synth. React. Inorg. Met.-Org. Chem. 1990,20, 77.
0276-7333/95/2314-4944$09.00/0 0 1995 American Chemical Society
Ferrocenylenegermane Polymers and Copolymers the ipso-C resonance at 31 ppm. No attempt was made to further purify this material, which was then dissolved in 20 mL of toluene and heated in a sealed tube to 105 "C for 10 day. The toluene was removed under vacuum, and the polymeric residue was dissolved in THF (10 mL), filtered, and precipitated by addition of methanol (300 mL) to form the polymer, lb, as a yellow solid (1.5 g, 4.7 mmol, 29%). Gel permeation chromatographyusing polystyrene standards gave molecular weights in the range 40 000-80 000 from different syntheses. All polymer products exhibited monomodal molecular weight distributions. Anal. for Cl4HlaFeGe, calcd (found): C, 53.43 (52.82);H, 5.76 (5.81). In a similar manner we produced the previously reported polyferrocenylenedimethylgermane (la, 30%-40%) and the new dibutyl analog (IC,40%-50%. Anal. for ClsHzPeGe,calcd (found): C, 58.30 (57.48);H, 7.07 (7.16)). Polymerization by heating the crude ferrocenophanematerials, or their mixtures, in a sealed tube for 3 h gave similar products. Spectral and other related data are listed in Table 1. Preparation of Ferrocenylenediethylgermane-co-ferrocenylenedi-n-butylgemane.To a slurry of dilithioferrocene prepared as above from 3.0 g (16 mmol) of ferrocene was added at -78 "C an equimolar mixture of EtzGeClz (1.62 g, 8 mmol) and n-BuzGeClz (2.06 g, 8 mmol), and the mixture was stirred for 1 h, warmed to room temperature, and stirred for 12 h. The solvent was removed under reduced pressure, and I3C NMR spectroscopy indicated the presence of the two ferrocenophane complexes in the residue, with ipso-C at 29.6 ppm (n-BuzGe) and at 31.0 ppm (EtzGe). The residue was placed in a sealed tube and heated to 140 "C for 3 h. Workup as above yielded 1.4 g (2.1 mmol, 26%)of polymer as a thick orangelred gum which was analyzed to yield the data in Table 1. Dissolution in THF and sequential precipitation by methanol produced six fractions, a-f. NMR data from the fractions could not be distinguished, nor could their WAXS data; all were amorphous materials with a very broad signal between 6.48.5 A. Anal. for C32H44FezGe2,calcd (found): C, 56.06 (54.86); H, 6.47 (5.71). Wide-Angle Scattering X-ray Diffraction. The experiments were performed with thin films cast from toluene or THF solutions onto microscope glass slides using previously described equipment. The experiments were repeated under identical conditions after several hours and/or weeks to note changes. Electrochemistry. The electrochemical measurements5 were carried out in a one-compartment cell equipped with a platinum disk working electrode (surface area = 0.2 cm2, a gold wire counter electrode, and an AglAgC1 (3.8 N KCI) double-junction reference electrode. The cyclic voltammograms were recorded using a EG&G PAR potentiostatJga1vanostat (model 273) connected to an IBM x-y-z plotter (model 7424 MT). Dichloromethane solutions containing0.1 M n-BuNBF4 were used for measurements.
Results and Discussion Synthesis. The homopolymers were readily synthesized by heating t h e hexane-extracted products of the reaction of dilithioferrocene and t h e corresponding dichlorogermane, without the isolation of the parent [1lgermylferrocenophane,in overall good to moderate yields, eq 1. Molecular weights in the range 40 000100 000 were obtained, permitting ready analysis of their polymer properties. This method is similar to that originally reported by Rosenberg for t h e formation of t h e ferrocenylenesilane polymer^.^ Solution or melt polymerization did not produce polymers with significantly differing molecular weights (9) Rosenberg, H.U.S.Patent 3,426,053,Appl. August 1966, granted February 1969; Chem. Abstr. 1969,70, 78551~.
Organometallics, Vol. 14, No. 10,1995 4945
R = Me (la), Et (1b), n-Bu (IC), in these experiments. Indeed, the molecular weights from different experiments with t h e same technique, i.e., melt or solution, covered a range similar to that between t h e two techniques. The values presented here are typical, and all are lower than those reported by thermal treatment of pure isolated germylferrocenophanes. This is probably due to the presence of impurities during the thermal treatment; however, we feel that t h e nature of the polymers obtained is justification for t h e process used. If higher molecular weights a r e needed, then perhaps isolation of t h e intermediate ferrocenophanes would be appropriate; however, during this isolation process, which can involve sublimation, polymerization often occurs at t h e same time. Ferrocenylenegermane copolymers were obtained by heating the extracted product from the reaction of dilithioferrocene and 1 equiv of a 50:50 mixture of t h e two appropriate dichlorodialkylgermanes, eq 2.
In a similar fashion we obtained t h e dimethylgermaneco-di-n-butylgermanepolymer (10. Structure. "he spectroscopic properties of t h e polymers are in expectation with their proposed structures, and all data a r e presented in Table 1. The data for t h e dimethylgermane polymer are in agreement with those reported for the high molecular weight form, M , = 2 x lo5 to 2 x 106.7 There appears to be little change in t h e spectral properties of t h e polymers as a function of molecular weight. In t h e case of the copolymers we could distinguish t h e two components via 'H and 13C NMR spectroscopy. In each case the germanium copolymers contained, within experimental error, t h e same relative amounts of t h e two starting components. All polymers exhibit a W/visible spectrum with bands centered at 215 and 275 n m (sh) and at 450 nm, typical of t h e ferrocenyl group when recorded in THF. To determine possible heterogeneity in the copolymers we performed a successive precipitation-fractionation of copolymer l e by slow titration of a THF solution with methanol, collecting six individual fractions, a-f. Each fraction was investigated with respect to its NMR, molecular weight, and wide-angle X-ray scattering, WAXS (vide infra), properties. For each fraction we were unable to detect a n y significant spectroscopic
4946 Organometallics, Vol. 14, No. 10,1995
Kapoor et al.
Table 1. Analytical and Spectral Data and Some Properties for Poly(ferroceny1enegermanes): [-FC-G&'a-FC-GeR"z-I, mol wt!
cyclic voltammetry
la
Me
Me
37
36
82.7 74.0 0.68(Me); 4.01;4.13(FC)
450 (140) 0.60 0.72 0.67 0.55
lb
Et
Et
21
29
45.0 39.0
451 (140) 0.42 0.28 0.69 0.62
IC
n-Bu n-Bu -23
Id
Me
n-Bu
28 33
96.4 58.7
le
Et
n-Bu
'9 26
79.5 64.2
a
37 47.8 43.9
-1.12 (Me); 71.4;73.2 (FC); 74.9(ipso-FC) 7.41 (CH2);9.88(CH3);71.1; 1.10(CH3);1.30(CHz); 72.8 (FC);73.3 (ipso-FC) 4.15;4.32(FC) 1.04;1.36;1.51;1.71 (n-Bu); 14.2;15.5;27.1;28.3 (n-Bu);71.2; 74.4 (FC);74.3 (ipso-FC) 4.22;4.36 (FC) 0.65 (Me);0.88;0.91;0.96; -1.1 (Me); 14.2;15.5;27.1;28.2 (n-Bu);71.0;74.5 (FC);72.9 1.23 (n-Bu);4.12;4.18; (ipso-FC) 4.27;4.31 (FC) 1.05;1.08;1.30;1.50;1.58; 7.38(CHa);9.85(CH3);14.1;15.5; 27.0;28.2 (n-Bu); 71.0;73.3 (FC); 1.71 (Et + ~-Bu); 4.16; 4.32 (FC) 72.83(ipso-FC)
DSC: Perkin-Elmer DSC-7, 30 "C/min. b GPC: Styragel column, polystyrene standards,
17.66 215.0 '
8.84
,
2.98 LIOO
3.56
I
17.66
448 (130) 0.52 0.35 0.83 0.68 442 (380) 0.54 0.45 0.73 0.69 451 (380) 0.54 0.40 0.80 0.73
THF.
8.84
d(A)
,
,
2.98
3.56
275.0'
LIO(
-90
la
220.0 -
-80
-90
- 70
165.0 -
-60
-
55.0
-
-40
165.0.
110.0-
-30 -20
0.0-
I
*
I
I
I
I
5
10
11.66
8.84
I
I
,
, 15 ,
275.0
S . 0 - A
- 10 I
I
I
I
I
I
I
1
I
d ( h
I
8
I
I
25
20
20 (3
I
o.o-, ,
30 2.98
3.56
,
*-0 blOO
IC
-80
, , I , , ,
17.66 275.0A '
8.84
-
-60
6.7
.40
-60 -50
5.0
-40
-30 -20
- 10 I
,
,
,
, ,
2 0 (") d(4
I
,
,
20
, ,
I
,
3.56
-
o.o-, 5
-20
1d 6.4
165.0.
,
10
,
I , , ,
15
20 PI
I
I
20
I
I
I
I
I
25
I
I
I
1
f
0
30
30
2.98 L1O -80
- 70 -60
-50
6.7
-4
110.0-
-30
=o-/
-20
- 10 , , ,
, ,>r
-90
11.2
-30
55.0
,
25
220.0-
-50
110.0 -
-80
- 70
15
.70
165.0
,
10
5
-90
220.0 -
1b
6.4
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110.0
-
220.0- 11.2
- 10 o.o-, 5
, , , I , ,
10
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30
Figure 1. WAXS spectra of dialkylgermaneferrocenylenepolymers: (a) di-n-butyl,t = 0; (b) di-n-butyl, t = 7 days; (c) diethyl; (d) 5050 mixture of di-n-butylldiethyl,t = 0.
differences; the lH and 13C NMR data, chemical shifts, and approximate integrations were in accord with 1:l monomer unit incorporation for all fractions, suggesting that we formed copolymers, the first example of the ferrocenylene systems. The molecular weight distributions in fractions a-f changed regularly as would be expected. (Mw,M,, polydispersity): (a)95 000 (76 8001, 1.24; ( b ) 60 000 (51 400), 1.35; (c) 50 000 (40 200) 1.21; ( d ) 35 000 (29 500) 1.21; (e) 20 000 (14 800) 1,36; cf, 15 000 (12 100) 1.30. The polymers were investigated by WAXS. Each of the homopolymers, R = Me, Et, and n-Bu, possess a partial crystallinity, with different spacings noted for the three distinct alkyl groups, Figure 1. Immediate
WAXS examination of a film of the di-n-butylgermane homopolymer cast from THF revealed little crystalline character, Figure la; however, afier several hours a crystalline form was observed, Figure lb. In our hands the diethylgermane analog always produced a partially crystalline material upon film casting, Figure IC.Casting a mixture of the ferrocenylenediethylgermane and -di-n-butylgermane homopolymers always produced a mixture of the two crystalline polymers, i.e., l b seeded the crystallization of IC,Figure Id. This'latter observation strongly suggests a similar crystalline form for the two polymers, and the slow recrystallization of the n-butyl analog reflects the ordering of the longer chain n-butyl group needed prior t o crystallization. The
FerrocenylenegermanePolymers and Copolymers degree of crystallinity, to the extent that it can be measured by inspection of these diffraction patterns, increases the order Me < Et .C n-Bu. Furthermore, the spacings observed are almost identical with those reported for the corresponding silicon analogs under identical conditions. The diethyl and di-n-butyl polymers exhibited strong sharp reflections at 6.7 and 6.4 A, respectively. These distances are reminiscent of the Fe- *Fedistance along the polymer chain obtained from oligomer structures and MMX calculations, which were shown to be dependent upon the conformation of the backbones.5d The homo-di-n-butylgermanepolymer also exhibited an extra, intense, well-defined peak at 11.2 A. It is tempting to assign this to an interchain distance implying an ordering of the ferrocenylene chains. The reason for this extra ordering of the polymers containing the butyl chain (also noted for the silicon analog)5bis unclear. However, interchain butyl-butyl group hydrophobic interactions could be responsible. For the shorter alkyl chains the interaction distance may not be close enough for significant ordering, whereas for the longer dihexyl-substituted polymer (only reported for the Si system) it is lost, probably due to entropic reasons. The copolymers exhibited a predominantly noncrystalline character. Partial ordering was observed via a broad envelope of reflections in the general region between 6.1 and 8.0 A. The WAXS spectrum of the copolymer involving both the Et and n-Bu groups, le, lacked all traces of the previously well-resolved crystallinity of the related homopolymers. These data reinforce our assertion that we are dealing with true copolymers and not simple mixtures of the two homopolymers since, as noted above, mixtures of lb,c provided a crystalline material under all the conditions we employed. We are unable to completely address the question as to whether ld,e are random or block copolymers. The 13CNMR of the copolymers are remarkably clean, which could signify that they could be very regular ABABAB systems; however, we think this unlikely. The physical properties of the copolymers are very distinctive. They tend to form considerably more elastic materials and tend to form gels in solution to a larger extent than the homopolymer analogs. This is particularly true for methyl-containing polymers which tend to form insoluble rubber materials after a time, whereas samples of the diethylgermaneco-di-n-butylgermanepolymer have been stored in our laboratory for many months without noticeable change in properties. The Tgdata for polymers ld,e (recorded in Table 1) exhibited a single Tg,supporting their designation as random copolymers and not block copolymers or blends. Electrochemistry. Solutions of the homopolymers in CHzClz were investigated using cyclic voltammetry. Two distinct oxidation processes were observed, the first, Epal,between 0.45 and 0.6 V, and the second, Epaa,
Organometallics, Vol. 14, No. 10, 1995 4947 between 0.55 and 0.83 V, and two corresponding reduction processes, Epc1and Epcz,Table 1. The behavior is similar to that observed for the polymeric and oligomeric silicon analogs and reflects the coulombic effect of the first oxidized FC cations upon the potential required to oxidize a neighboring ferrocenylene unit.435J0J1 The Ge polymers exhibit slightly higher oxidation potentials than the Si analogs. For both the Si and Ge polymers, the introduction of the n-butyl group onto the group 14 bridge significantly increases the difference between the first and second oxidation potentials. It seems that the increased hydrophobicity of the butyl groups effectively decreases solvation a t the first oxidized site, thereby increasing its effective charge, which further translates into a greater coulombic effect upon the neighboring ferrocenyl unit. The shape of the cyclic voltammograms of the Ge polymers also differs from those of the Si polymers in that the initial oxidation appears as a much broader peak, reflecting slower electron exchange of the Ge polymer with the working electrode. The copolymers exhibit similar electrochemical behavior. For polymer l e the oxidations at 0.54 and 0.80 V are close to those of the di-n-butyl polymer at 0.52 and 0.83 V. The first oxidation and reduction waves are significantly broader than those of the homopolymers, indicating the possibility of multiple peaks resulting from gross structural variations among those ferocenylene units undergoing oxidation-reduction. The voltammograms of ld,e are distinctly different to those of the appropriate mixture of la-c in which two sets of redox behavior may be observed representing each homopolymer.
Conclusions We have used the simplified synthetic procedure of thermal treatment of nonisolated ferrocenophanes, first reported by Rosenberg for ferrocenylenesilane polym e r ~ to , ~form germanium analogs. The study concerned the following: (a) report and discussion of WAXS structural data and seeding of polymers, including the slow amorphous to crystal polymer transformation; (b) the first copolymerization of ferrocenophanes and characterization of copolymers which contrasted mixtures of homopolymers; (c) electrochemical study on the polymers; (d) the effect of the n-butyl group upon structure and electrochemistry of the polymers. Acknowledgment. Support of this research by the NSF, Grant No. RII-88-02973, and the Robert A. Welch Foundation, Houston, TX,Grant No. AH-546, is gratefully acknowledged. OM9501079 (10)Dementiev, V. V.; Cervantes-Lee, F.; PBrkAnyi, L.; Sharma, H.; Pannell, K. H.; Nguyen, M. T.; Diaz, A. F. Organometallics 1993,12, 1983. (11)Brandt, P. F.; Rauchfuss, T.B.J.Am. Chem. Soc. 1992, 114, 1926.
