Catalysis in Polymer Synthesis - American Chemical Society

Chapter 2

New Applications of "Carbonylbis(triphenylphosphine)ruthenium" Catalysis in Polymer Synthesis Downloaded by NORTH CAROLINA STATE UNIV on May 3, 2015 | http://pubs.acs.org Publication Date: August 10, 2000 | doi: 10.1021/bk-2000-0760.ch002

William P. Weber, Jyri K. Paulasaari, Diyun Huang, Shashi Gupta, Timothy M. Londergan, Jonathan R. Sargent, and Joseph M. Mabry D. P. and K. B. Loker Hydrocarbon Research Institute, Department of Chemistry, University of Southern California, Los Angeles, CA 90019-1661 (e-mail: [email protected])

A novel 1:1 complex of divinyldimethylsilane and (PPh ) RuCO, catalyzes the step-growth copolymerization of aromatic ketones and sym-divinyltetramethyldisiloxane (I). The X-ray structure as well as the dynamic NMR behavior of this material is reported. "(Ph P) RuCO" catalyzed reaction of thioxanthen-9-one with I fails to give copoly(1,8-thioxanthen-9-onylene/3,3,5,5-tetetra methyl-4-oxa-3,5-disila-1,7-heptanylene (II). Nevertheless, a reac tive α,α'-difunctional aryl ketone monomer, 1,8-bis-(3,3,5,5,5pentamethyl-4-oxa-3,5-disilahexanyl)thioxanthen-9-one (III), has been prepared by "(Ph P) RuCO" catalyzed reaction of thioxanthen-9-one with excess vinylpentamethyldisiloxane (IV). III undergoes acid catalyzed siloxane equilibration polymerization to yield II. This approach, in which "(Ph P) RuCO" catalyzed reaction of less reactive aryl ketones with an excess of IV to yield reactive α,α-difunctional monomers which undergo acid catalyzed siloxane equilibration polymerization, has been explored. Copolymers based on acetyl thiophene systems and I have been prepared by direct "(Ph P) RuCO" catalyzed copolymerization and by acid catalyzed siloxane equilibration polymerization. Finally, "(Ph P) RuCO" catalysis permits hydrosilylation copolymerization between aromatic α,ω)-diketones and α,ω -dihydrido siloxanes to yield aromatic poly(silyl ethers). 3

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Introduction Murai has reported that dihydridocarbonyltris(triphenylphosphine)ruthenium (V) [1] will catalyze the ortho-alkylation reaction of acetophenone with vinyltri-

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© 2000 American Chemical Society

In Transition Metal Catalysis in Macromolecular Design; Boffa, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

Downloaded by NORTH CAROLINA STATE UNIV on May 3, 2015 | http://pubs.acs.org Publication Date: August 10, 2000 | doi: 10.1021/bk-2000-0760.ch002

25 methylsilane [2,3]. This catalytic C-H activation reaction involves the regioselective anti-Markovnikov addition of an ortho C-H bond of acetophenone across the C-C double bond of vinyltrimethylsilane. We have used this reaction to synthesize copolymers in which carbosilane or carbosilane/siloxane units alternate with aromatic ketone groups. For example, copolymerization of acetophenone and I catalyzed by V yields copoly(3,3,5,5-tetramethyl-4-oxa-3,5-disilaheptanylene/2-acetyl-l,3-phenylene) [4]. Initially, molecular weight of the copolymers was quite low. Exact balance of stoichiometry is essential to achieve high molecular weight in step-growth polymerizations [5]. The observation of Si-ethyl groups by NMR end group analysis suggested a stoichiometric imbalance due to hydrogenation of one of the C-C double bonds of I. This converts a (Afunctional monomer into a monofunctional end group. We have suggested that the hydrogen for this reduction came from the catalyst [6]. Prior treatment of V with a stoichiometric amount of styrene for a few min at 130 °C leads to a quantitative yield of ethyl benzene and an active catalyst. Loss of hydrogen from the catalyst is probably essential to create a site of coordinate unsaturation. The P NMR of solutions of this catalyst show that only two of the three triphenylphosphine ligands are still bound to the ruthenium center. While, ruthenium carbonyl species are known to form carbonyl bridged dimers and trimers, we suggest that the active form of the catalyst may be the highly coordinately unsaturated species "(Ph P) RuCO". Addition of a 1:1 mixture of acetophenone and I to this activated catalyst leads to higher molecular weight copolymers [7]. Addition of ortho-acetylstyrene to a soluiton of V which has beeen activated with styrene gives a 1:1 complex of ortho-acetylstyrene and (Ph P) RuCO whose structure has been determined by X-ray crystallography [8]. The ligand is coordinated to the Ru center via an O-Ru as well as by a 7i-bond between the vinyl group and Ru. Heating a solution of this complex with acetophenone and I results in high molecular weight copolymer. Recently, 1:1 complexes of (Ph P) RuCO with 2phenylpyridine or N-benzylideneaniline have been reported [9]. 31

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1:1 Complex of divinyldimethylsilane and (Ph P)2RuCO. 3

We should like to report that addition of divinyldimethylsilane to a solution of "(Ph P) RuCO" yields a 1:1 complex whose X-ray structure has been determined at -100 °C. See figure 1 and table 1 for bond lengths and angles. The structure is unsymmetrical. Both the P h ^ ligands and the C-C double bonds of the divinyl dimethylsilane ligand are different. Bond lengths Ru-C and Ru-C are shorter 2.21 and 2.22 A while Ru-C and Ru-C i are longer 2.29 and 2.31 A. The C - C double bond is more tightly bonded to Ru than the C - C i double bond. Consistent with this, the C 9-C o bond 1.41 A is longer than the C o-C i bond 1.37 A. The *H and P solution NMR of this complex change with temperature. At low temperature, two signals, which are coupled to one another, are detected in the P NMR, while at higher temperature these resonances broaden, coalesce and finally 3

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26 !

sharpen to a single line (figure 2). Likewise at 20 °C in the H NMR, the two Si-CH groups give rise to two sharp singlets. At higher temperature, these broaden, collesce and finally sharpen to a single resonance. Similar dynamic behavior is observed in the *H NMR for the vinyl hydrogens. The H NMR chemical shifts for the Ru complexed vinyl protons are at high field. Analysis based on exchange of two nonequivalent sites gives AG = 12.7 kcal/mol [10]. Addition acetophenone and I (1:1) to a solution of this 1:1 complex at 135 °C gives high molecular weight copolymer. Murai has suggested that coordination of the carbonyl oxygen to Ru followed by insertion of the coordinated Ru into an ortho C-H bond of acetophenone is critical for reaction. The fact that divinyldimethylsilane can be copoiymerized with acetophenone and also form a 1:1 complex with (PlbP^RuCO suggests that 7t-complexation of the C-C double bonds of vinylsilane or vinyldisiloxane to Ru center may be important in the catalytic cycle. 3


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^

Space group

P2i/n

a

10.368(3) A

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20.748(2) A

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16.849(2) A

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98.29(2)°

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3586.6 A

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Figure 1. X-ray structure and dimensions of the complex, phenyl rings omitted. Table 1. Bond distances (A) and angles (deg) for the complex. Bond Distances Ru-Ci Ru-C Ru-C Ru-C Ru-Gu RU-P! Ru-P Si-C i Si-C C -C o 29

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C40-C41

1.848(12) 2.208(12) 2.220(11) 2.285(12) 2.308(12) 2.401(3) 2.353(3) 1.838(12) 1.846(12) 1.41(2) 1.37(2)

Bond Angles Ci-Ru-Pi C Ru-P r

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Ci -RU-C40

Ci-Ru-Ci C Ru-C C Ru-C Pi-Ru-Co Pi-Ru-Ci P Ru-C P Ru-C P -Ru-C P -Ru-C i P -Ru-C P -Ru-C r

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104.8(4) 87.1(4) 96.6(5) 80.1(5) 157.8(5) 120.8(5) 81.6(3) 115.2(3) 97.3(3) 134.4(3) 176.0(3) 145.5(3) 91.1(3) 85.0(3)

P Ru-P C -Ru-C o r

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C40-RU-C41

C -Ru-C4o C -Ru-C i C -Ru-C4i C o-Ru-C o C o~Si-C i C^-C^-Si C o-C i-Si Ru-C -Si Ru-C i-Si 29

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C 6-Si-C 7 2

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98.93(12) 37.1(4) 34.7(4) 84.9(4) 74.7(4) 89.1(4) 91.8(4) 96.5(5) 119.2(9) 125.3(9) 94.7(5) 92.0(5) 108.1(7)



"(Ph P)2RuCO" synthesis of reactive o^a'-monomers for acid catalyzed siloxane equilibration polymerization. 3

The copolymerization reaction is successful with various substituted aromatic ketones [11-13] as well as with fluorenone, xanthone and anthrone [6]. Neverthe less, with "(Ph P) RuCO", benzophenone and I yield a mixture of irregular polymer and cyclic disiloxane monomer. Fortunately, acid catalyzed ring opening polymeri zation of cyclic disiloxane monomer gave regular copolymer whose T is higher [14]. This observation suggested that acid catalyzed siloxane equilibration polymeri zation might permit preparation of copolymers of aryl ketones and I for systems which do not undergo direct "(Ph P) RuCO" catalyzed copolymerization. For example, the "(Ph P) RuCCT catalyzed reaction of I with thioxanthen-9-one (1:1) fails. On the other hand, "(Ph P) RuCO" catalyzed reaction of thioxanthen-9-one 3

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Figure 3. Acid catalyzed siloxane equilibration polymerization ofIII.


28 with an excess of IV gives III, which can undergo acid catalyzed siloxane equilibration polymerization to yield II (figure 3) [15]. We have been able to copolymerize l,4-bis(5'-acetyl-2-thiophenyl) benzene (VI) and I to yield a//

Catalysis in Polymer Synthesis - American Chemical Society

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