Dithienophosphole

Two types of symmetric fused dithienophospholes exist, which differ according to the position of the S atoms as illustrated by compounds (53) [54] and (54) [50] (Scheme 15). The a A -dithieno[3,2-fo 2, 3 -d]phosphole (55) has recently been considered as a potential subunit for the construction of n-conjugated materials [55] (Scheme 15). Exploitation of the reactivity of the nucleophilic P-atom of (55) allows access to derivatives (56) and complexes (57) (Scheme 15). The absorption and emission behaviour of these species varies with the nature of the P-moieties. Upon oxidation of the P-centre of (55),bathochromic shifts of Ajnax Aejn were observed Aj ax 344 nm for (55) and ca. 373 nm for (56), and Agjn 422 nm for (55) and ca. 460 nm for (56) [55]. These results nicely illustrate... 

Mixed Oligomers and Polymers Based on Dibenzophosphole or Dithienophosphole... 

Dibenzophospholes A and dithienophospholes B and C (Fig. 4.7) do not display the typical electronic properties and reactivity patterns of phospholes, since the dienic system is engaged in the delocalized benzene or thiophene sextet [7, 10a, 51]. In fact, these building blocks have to be regarded as nonflexible diaryl-phosphines or as P-bridged diphenyl or dithienyl moieties. 

The dithienophospholes 74 are obtained in good yields by lithiation of dibromo-bithiophenes 73, followed by addition of dihalo (aryl) phosphines (Scheme 4.22) [57]. The Lewis basicity of the P center of 74 enables a broad range of facile chemical modifications to be undertaken, as exemplified with the synthesis of derivatives 75-77 (Scheme 4.22) [57]. 

Dithienophosphole units have been incorporated into polymers as either (i) side-chains or (ii) building block constituents of the extended polymer backbone itself. Polymers of the first type have been prepared by exploiting the ease with which a polymerizable styryl substituent may be introduced at the P atom of... 

It is clearly evident that the various series of conjugated polymeric systems based on dithienophospholes that have been prepared are promising candidates for optoelectronic applications since their optical properties can be easily varied in a variety of different ways (chemical modifications of the P center, variation of the Si and P substituents, etc.). Furthermore, their potential scope in a range of applications is broadened by the possibility of incorporating these conju-... 

Catalytic amounts of [Pd(PPh3)4] (chiffres ) and Cul were added to a solution of dithienophosphole 80 (1.73 g, 1.5 mmol) and l,4-diiodo-2,5-bis(octyloxy)benzene (0.88 g, 1.5 mmol) in N-methylpyrrolidinone (80 mL). The light-yellow reaction mixture was then stirred for 48 h at 200 °C, after which time the color changed to orange-red. The solution was then cooled to room temperature, the solvent evaporated under vacuum and the resulting amorphous solid taken up in a small amount of THF (ca. 5 mL). The suspension was filtered, precipitated into hexane and the residue dried under vacuum to yield 80 as a reddish brown pow-... 

One remarkable example of the reactivity of a phosphole P-substituent is the radical copolymerization of dithienophosphole 146 with styrene using 2,2,6,6-tetramethylpiperidinyl-l-oxy (TEMPO) as the initiator (Scheme 42) <2004AGE6197>. Copolymers 48 are high molecular weight materials with relatively narrow poly-dispersities. They have been characterized by H, and P NMR spectroscopy. 

A series of novel dithieno[3,2-A2, 3 -r7lphospholes 159 have been prepared in good yields by reacting 3,3 -dibromo-2,2 -dithiophene derivatives with butyllithium and subsequent addition of dichlorophosphines (Scheme 49) <2004AGE6197, 2005EJC4687>. Note that 5,5 -bis(pinacolboryl)-functionalized dithieno[3,2-A2, 3 -r7lphospholes 160 have been prepared by sequential lithiation and addition of isopropoxy(pinacol)borane to the unsubstituted dithienophosphole (Scheme 49) <20060L495>. 

Another interesting application of Jt-conjugated systems is their use as chemosensors. For example, a modified dithienophosphole oxide 160 (see Scheme 49 for the synthesis of its precursor) that incorporates boryl-end caps is a very sensitive and selective sensory material for the fluoride ion (Scheme 126). Treatment of this derivative by fluoride induces a red shift of the emission maximum (160, 452 nm 373, 485 nm) that is visible to the naked eye. This shift in the fluorescence emission can even be detected down to micromolar concentrations of fluoride ion notably, the addition of other halides (CP, Br, P) does not affect the fluorescence in any way <20060L495>. 

Little attention has been paid over the last decadeto the synthesis of fused phosphinines. However, in 2008, the preparation of a dithienophosphinine was reported. Compound 71 was obtained in three steps from dithienophosphole 70 by reaction successively with acetyl chloride, triethylamine and water [43], This transformation involves the transient formation of the oxide 69 (Scheme 17). DFT calculations reveal that the fused derivative is less aromatic than the parent compound C5H5P and suggest that a substantial electronic delocalization takes place within the three rings. Both the HOMO and the LUMO are localized on the P = C-Ph double bond and thus resemble those of a phosphaalkene derivative. 

Figure 12.2 Dithienophosphole (1) and related benzannelated phosphole systems (2).

Figure 12.3 HOMO (a) and LUMO (b) of dithienophosphole. Copyright 2007 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim [2b],...

Figure 12.11 Emission colors of representative dithienophosphole-based molecules. Reprinted with permission from Ref. [2c]. Copyright 2013 Georg Thieme Verlag Stuttgart New York.

Similar to the dithienophospholes, 24 (Figure 12.15) shows a blue emission but only weakly, as reported by Mathey and coworkers. While the properties of these molecules have not been extensively studied, their reactivity toward dienes has been investigated, leading to interest in homogeneous catalysis. 

Dithienophosphole oxides (a) Dienes, Y., Eggenstein, M., Karpati, T., Sutherland,... 

BINOL). Carbazole-containing dithienophosphole oxides were prepared in 1 1, 2 1 and 1 2 ratios by different variations of the Suzuki-Miyaura protocol (Scheme 61). ... 

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