Phosphorus fragmentation

Conceptually and synthetically more straightforward molecules can be prepared through incorporation of chromophores onto simple phosphine moieties. The phosphorus fragment can be used either to influence or to organise the n-con-jugated systems. This section will focus only on derivatives tailored in order to exhibit specific properties related to applications in NLO,opto-electronics or as sensors. 

Chromophores based on aryl moieties can be easily grafted on to halophosphines via simple nucleophilic substitutions, as illustrated by the synthesis of 114 (Scheme 4.34). As a result, numerous phosphines bearing extended jt-conjugated substituents have been prepared. The aim of this section is not to give a comprehensive account of all derivatives that have been synthesized, but rather to illustrate how phosphorus fragments can be used either to influence or to organize the Jt-conjugated systems, with special emphasis upon fluorescence and NLO properties. 

Homonuclear aggregates of phosphorus atoms exist in many forms discrete molecules, covalent networks in crystals, polyphosphide anions, and phosphorus fragments in molecular compounds. 

CU2P3I2, that is, (CuI)8Pi2. Also, the compounds (CuI)3Pi2 and (CuI)2Pi4 with phosphorus strands similar to Hittorf s phosphorus have been reported.All of these structures can be considered as neutral phosphorus substructures that are embedded in a copper halide matrix. Some of the neutral phosphorus fragments are presented in Figure 12. As an example for the packing of the 1-D phosphorus units in the copper halide matrix, the structure of (Cul)2 Pi4 is... 

Three-membered heterocyclic compounds are available when one atom fragments like carbenes [108 or phosphorus compounds [109] add to C=0 ot C=N bonds (equation 26)... 

Plasticized white phosphorus (PWP) was found to be the most promising development for control of the fragmentation of P and pillaring of die smoke. It consists of an intimate mixt of granulated WF in a viscous rubber soin. The material burns more slowly and the particles... 

The final possible mode of action for an antioxidant is as a peroxide decomposer. In the sequences that lead to photodegradation of a polymer the ready fragmentation of the hydroperoxide groups to free radicals is the important step. If this step is interfered with because the peroxide has undergone an alternative decomposition this major source of initiation is removed. The additives which act by decomposing hydroperoxide groups include compounds containing either divalent sulfur or trivalent phosphorus. The mechanism involves... 

The displacement of a ligand L from the phosphorus atom of a phosphoranyl radical can easily occur via a-scission of the L-P bond (Scheme 23). The fragmentation is a regiospecific process, i.e., the leaving group must be apical (Scheme 23) and it occurs via an intermediate o" structure (Fig. 5). 

During the last two decades, Bentrude et al. [70] has shown that phosphoranyl radicals exhibiting very slow a- and P-fragmentations react with alkyl disulfides via Sh2 homolytic substitution (Scheme 35) [70b]. The reactivity of phosphoranyl radicals in these Sh2 reactions depends strongly on the substituents attached to the phosphorus atom and on the structure of the disulfides [70c]. 

As an illustration of the phosphorus-carbon analogy, consider the result of replacing a carbon fragment (CR2) by a phosphorus moiety (PR) in each of the common low-coordinate organic compounds (1C-4C) shown in Fig. 1. For example, the replacement of a single carbon in an alkene (1C) results in a phos-phaalkene (IP). Similarly, the phosphaalkynes (2P) are isolobal relatives of the alkynes (2C), and terminal phosphinidene complexes (3P) can be related to the... 

Like the C NMR chemical shifts for the central carbon of heteroallenes. changing the composition of the allene fragment can have as much of an effect (if not more) on the Si chemical shift as does changing a substituent. Switching the carbon at position 3 to a phosphorus (silaphosphaallene 122) moves the " Si chemical shift downheld to 75.7 ppm, which is the most deshiclded " Si shift fora silaallene to date, even though it has two aryl groups on silicon, which should keep the shift uplield. 

Thermal decomposition of 1-methyl-A -phospholen in toluene at 356-444 °C yielded butadiene as the primary product. The activation parameters are in agreement with a mechanism involving ring opening to a biradical followed by fragmentation into butadiene, phosphorus, and methyl radicals. ... 

The phosphorus atom of the cyclophosphazene ring can also be involved in interaction with transition metal atoms either by a coordinate or by a covalent linkage. The former occurs with hydridocyclo-phosphazenes by a tautomerization of the P-H to result in a P(III) center (222). The covalent mode of linkage occurs by the reaction of the appropriate organometallic or metal fragment with the halo-genocyclophosphazenes (223). 

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