Electrophilic phosphinidene

The most widely employed electrophilic phosphinidene complexes are generated from M(C0)5 (M=W, Mo, Cr) complexed 7-phosphanorbornadienes 7, which were reported by Marinetti et al. in 1982 [46]. They trapped the transient phosphinidene complex 8 at 110 °C (or at 55 °C if CuCl was used as catalyst) with olefins and alkynes to obtain three-membered phosphiranes and phosphirenes, respectively. 

Borst et al. <2005CEJ3631> conducted a study on the synthesis of strained bicyclic phosphirane and phosphirene iron-tetracarbonyl complexes (Scheme 11). It was shown that, depending on the ring size of the resulting heterocycle, electrophilic phosphinidene [Ri-PrNP=Fe(CO)4] could be trapped intramolecularly with both double and triple bonds (compounds 146-150). The phosphinidene addition was found to be reversible at room temperature and when using phenylacetylene as solvent, exchange between phenylacetylene and the phosphinidene group took place. Compound 151 was isolated as the dimer, compound 152. 

This process involves the formation of reactive electrophilic phosphinidene complex [(CO)sW <— PMe] and... 

Trapping electrophilic phosphinidene complexes with alkynes has been used in the synthesis of the new phosphirene systems (341) and (342). In the latter, the phosphirene rings are coplanar and conjugated. The diphosphinines (343) are formed unexpectedly in a head to head dimerisation of l.ff-phosphir-... 

Marinetti et Mathey have shown that the complexes of electrophilic phosphinidene, although they are not isolable, have a rich chemistry resembling that of carbenes ... 

Electrophilic and nucleophilic phosphinidene complexes have been related to the corresponding carbene complexes of which the Fischer-type is usually considered as a singlet-singlet combination and the Schrock-type as a triplet-triplet combination. However, both the strongly preferred triplet state of R-P and the M=P bond analysis suggest this schematic interpretation to be less appropriate for transition metal complexed phosphinidenes. 

The only other reaction with an aromatic substance is the C-H insertion into ferrocene [85], giving 41,which illustrates the highly electrophilic character of the phosphinidene complex. Other aromatic C-H insertions have been observed, but these likely occur by means of intermediate P,0- and P,N-ylids,such as the reaction of (0C)5W=PR withbenzophenone and azobenzene that give 42 and 43,respectively [56a, 86]. 

The following chapter concerns another kind of low-valent organophosphorus compounds, namely phosphinidenes. Little is known about free phos-phinidenes in contrast to the corresponding transition metal complexes. Many new reagents have been generated exhibiting either electrophilic or nucleophilic properties. The reactivity of these carbene-like reagents is evaluated (K. hammer tsma). 

These indices have been used to study the reactivity for a series of chlorobenzenes and a good correlation is observed, for example, between W and toxicity of chlorobenzene [41]. For a detail discussion of this concept and its applications, we refer the readers to a recent review [41,42]. For studying intramolecular reactivity, these philicity indices and local softness contain the same information as obtained from the Fukui functions, because they simply scale the Fukui functions. In some cases the relative electrophilicity and relative nucleophilicity may be used although they provide similar trends as s(r) and co(r) in most cases [43]. In the same vein, the spin-donicity and spin-philicity, which refer to the philicity of open-shell systems [44], could also be utilized to unravel the reactivity of high-spin species, such as the carbenes, nitrenes, and phosphinidenes [45]. 

The transient electrophilic terminal phosphinidene 188, which is readily accessible by thermolysis of 7-phospha-norbornadiene complex 187 (Scheme 59), is a powerful precursor to phospholenes. For example, it reacts with ethoxyacetylene to give phosphole 189, which upon hydrolysis affords the 2-phospholene complex 190 (Scheme 59)... 

Treatment of P3C3Bu 3 with [(CO)sW <—PMe], generated / si/u by thermal decomposition of 56b (R = Ph) at 110°C, furnished a 2 1 mixture of quadricyclane 58b and the tricyclic compound 59, which were separated by fractional crystallization as colorless or yellow crystals in 39% and 25% yield, respectively. The presence of a three-membered ring in 59 agrees with an initial attack of the phosphinidene complex at a P=C bond of the triphosphinine to give transient 60. An intramolecular electrophilic aromatic substitution furnished product 59, whereas rearrangement of 60 to tetraphosphanorbornadiene 57a and its intramolecular [2+2] cycloaddition would rationalize the formation of 58b (Scheme 22) <2001CEJ3545>. 

As we discovered that bulky electrophilic terminal phosphinidene tungsten complexes with CsMes or CH(SiMe3)2 at the phosphoms do not dimerize in the absence of trapping reagents [16, 17], we became interested in their fate. 

Past attempts to prepare terminal phosphinidenes indicate that these species are inherently electrophilic. To compensate, phosphinidenes were prepared that possessed intramolecular base stabilization, e.g., by means of a pyrazolyl borate derivative. The precursor, [HB(pz )3]PCl2, is combined with a metal anion to form the complex in 70% yield ... 

Although the chemistry of short-lived electrophilic terminal phosphinidene tungsten complexes [11, 12] has received increased attention during the recent years, partially because of the versatility of 2//-azaphosphirene complexes [13, 14], only a single example of a rearrangement yielding a P-Cl-substituted ri -phosphaalkene complex - via a 1,2-chlorine shift - has been reported so far [15]. 

It should be emphasized that the difference between silylenes and carbenes on the one hand and the phosphinidene complexes on the other hand is due to the nucleophilic or electrophilic, respectively, natures of these species. The former attack the carbon atom of a P/C double bond in the 1,3,5-triphosphinine, whereas the latter should preferentially attack the phosphorus atom. 

Sc-P bonds of a four-coordinate scandium phosphinidene complex has been determined (13JA14784). Reactions of electrophilic carbenes with white phosphorus in benzene afforded Pg clusters supported by four carbenes or a carbene—P4 adduct (13CC4486). A mechanistic insight into CO capture by amidophosphoranes which contain a highly reactive P—N bond within a four-membered ring, has been published (13CAJ3147). 

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