Phospholide Complexes

These complexes can be obtained by a route such as Equation 8.369 [12], 

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The half-sandwich and sandwich complexes of phospholides and phosphole tetramer are known even for the nontransition metals. The half-sandwich arrangement was studied for lithium tetramethylphospholide [89AG(E)1367] and sodium derivative 127 generated from the phospholide tetramer and sodium in the presence of 1,2-dimethoxyethane [94JA3306 96AG(E)1125]. Potassium and 1,2-dimethoxyethane in THE in these conditions give a full dianionic sandwich 128. 

The reaction of Ba[P(SiMe3)2]2(THF)2 with diphenylbutadiyne in toluene for 12 days induces a m-addition of the diyne to the phosphide, followed by a 1,3-silyl group shift and ring closure. The dinuclear complex 132 is then isolated in good yield.283 Its complex structure contains Ba-C a bonds (2.881(5), 2.899(5) A), side-on Ba-alkyne (3.003(6), 3.363(6) A) and arene interactions, and Ba-phospholide bonds (Ba-P = 3.487(2) A) (Figure 65). 

The sodium atoms are both bound rf to one phospholide ring and 171 to the phosphorus atom of the other phospholide ring of the dianion. Each Na atom is further coordinated by one of the phosphole phosphorus atoms and two oxygen atoms of the DME coligand. The potassium complex is quite different reduction of the phosphole tetramer with 4 equiv of potassium yields a tetraanion, which, after crystallization from DME containing 18-crown-6, gives the solvent sepa-... 

The synthesis, chemistry, and complexing behavior of phospholide (6, with 6a, 6b, and 6c resonance structures) and polyphospholide anions have been reviewed recently.The [C H Ps J series with n = 0—4 is a complete set of structures with a successive replacement of CH units by the same heteroelement, P. The counterions are alkaline metals (e.g., Ps K+, which, together with K2HP7, has been obtained from red P in refluxing DMF in a yield of... 

Phospholide ions can form metal complexes with different coordination numbers / -complexation is characteristic for their aromatic behavior. The first 7 -complex with Mn(CO)3 (7) was reported in 1976. The ring in some cases (e.g., in 7) is not strictly planar. In 7, the P atom is displaced by 0.041 A from the plane of the carbon atoms. The large number of... 

Structural data of phospholide ions themselves are scarce. The lithium salt of the tetramethylphospho-lide ion, which is in fact an y -complex, and the K salt of the 2,4,5-tri-terf-butyl-l,3-diphospholide an-ion have been reported. Also the structure of the Li salt of the 2,5-bis(ferf-butyl)-l,3,4-triphospholide ion has been obtained In all these structures the bond lengths are equalized (CC, 1.396—1.424 A CP, 1.690-1.752 A). 

The two-coordinate phosphorus atom of a phosphonio-phospholide moiety is generally a weaker Lewis-base than a tertiary phosphine as a consequence, the complexes are thermally less stable (this holds in particular for metal fragments with low back donation capability, e.g. Mn(CO)4Cl) [35, 43], benzophospholide ligands are easily displaced by tertiary phosphines such as PhsP [27, 44], and bidentate ligands comprising a phosphonio-ben-zophospholide and a phosphine site react with transition metal fragments preferentially at the phosphine site coordination of both phosphorus atoms is only observed if the substrate offers two vacant coordination sites [27, 47]. 

The related family of phosphonio-phospholides also belong to the five-membered aromatic heterocycles, as reviewed comprehensively in the recent work of Gudat [209] The aromaticity of the rings were concluded from stabilization in isodesmic reactions [210] and also from the structure of those rings characterized by X-ray diffraction, exhibiting equalized bond length distribution in the case of the cationic 59 [211] and also for the neutral zwitterionic 60 [212], and its r - and r 5-complexed forms [214] (Scheme 34)... 

Species with CN = 2 comprise phospholide anions 4 and 2H- and. 4//-phospholes 5 and 6, respectively. The chemistry of these compounds has experienced an extraordinary development in the last 10 years. Nowadays, they are key synthons for the synthesis of phosphole derivatives with CN = 3 or for a range of other P-heterocycles. Furthermore, phospholide anions 4 are versatile 7] -ligands affording a variety of phosphametallocene complexes such as mono- and di-phospho-ferrocenes 7 and 8. Chiral derivatives based on monophosphoferrocene units are powerful ligands in asymmetric catalysis. 

The cleavage of a P-Ph bond (method (1)) has been widely used to create a variety of phospholide salts. Notably, this methodology has been employed in the synthesis of group 13 phospholyl complexes, which have come to the fore in recent years as potential single source substrates for the preparation of the corresponding metal phosphides by chemical vapor deposition (CVD). This is exemplified by the reaction of lithium 2,5-di(tert-butyl)phospholide with GaBr to afford a Ga(l) polymer 297 (Scheme 101) <1999AGE1646>. Additionally, this synthesis nicely illustrates the use of bulky substituents in the position a to phosphorus to favor -coordination. 

The chemistry of phospholes and related phospholide anion complexes remains a very active area, which also continues to attract the attentions of the theoretical community. Among recent theoretical contributions are a consideration of the stability, structure and bonding in lithium- and beryl-lium-pentaphospholide systems, the aromaticity of the pentaphospholide anion (and its arsenic analogue) as probed by ring currents,the remarkable influence of fluorine-substitution (either at phosphorus or at a ring carbon) on the electronic and thermochemical properties of phospholes,and the effects of methyl and vinyl substitution at various positions on the geometries, relative stabilities and Diels-Alder reactivities of phospholes. An ab initio approach has been used to reinterprete some spectral and thermochemical properties of IH-phospholes. The synthesis and reactivity of phospholes of reduced... 

All known reactions of phospholide ions with electrophiles (R+, H+...) take place at phosphorus, probably as a result of the high concentration of negative charge at the heteroatom. With transition metal electrophiles (typically metal halides), three reaction pathways can lead either to the desired /f-complexes (Eq. 5), to -complexes (Eq. 6) or to l,l -biphospholes (Eq. 7) ... 

In a much more complex reaction, interaction of [K(PC4Me4)] with SmCl3 in toluene gives a complex supramolecular structure 7 built from two similar but crystallographically distinct eight-membered subunits linked through rf-potas-sium-phospholide bonds (Scheme 2) [21]. 

Attempts to produce the potassium-free complex [Sm(PC4Me4)3] failed. The toluene is much less strongly bound to the potassium center than the rf-coordinated phospholide, which also shows -coordination to a samarium center. A degree of oligomerization seems to persist in solution. 

Magnesium gives an alkenylphosphine-complex 8 [22], calcium and strontium produce / ,/T-bis(trimethylsilyl)phospholides 9 and 10 [11], and barium gives a dissymmetric phospholide bearing an enyne group 11 [22]. In every case... 

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