Bis-phosphonium salts

The bis-phosphonium salt 56 in presence of Pd(OAc)2 leads to the formation of the neutral bis-ylide 57 which reacts with TICIO4 to give the dinuclear cationic complex 58 (Scheme 22) [89,90]. The bis-ylide part, which has potentially two carbons and one oxygen donor atoms, acts as a C,C-chelating ligand through its two soft ylidic carbons. 

A number of keto-carotenoids have been prepared from the bis-phosphonium salt (130) and substituted Cjs-aldehydes, the keto-functions... 

The bis-phosphonium salt (156) has been condensed with various dialdehydes to give potentially aromatic and anti-aromatic systems, while fully unsaturated 11- (158), 12- (159), and 13-membered (160) sulphur heterocycles have been prepared as shown. These showed no appreciable ring current and are presumably non-planar. 

Benzylphosphonates have been used in the synthesis of polymethoxy-stilbenes and of (174) and (175). The hydrocarbon (175) obtained in this way was much easier to purify than that prepared using the bis-phosphonium salt. 

The formation of the heterocycle 1 from the xylylene-bis-phosphonium salt 2 and PCI3 proceeds via a detectable intermediate 3 in a cascade of condensation reactions that is terminated by spontaneous heterolysis of the last remaining P-Cl bond in a cyclic bis-ylide-substituted chlorophosphine formed (Scheme 1) [15]. The reaction scheme is applicable to an arsenic analogue of 1 [15] and to bis-phosphonio-benzophospholides with different triaryl-, aryl-alkyl- and aryl-vinyl-phosphonio groups [16, 18, 19], but failed for trialkylphosphonio-substituted cations here, insufficient acidity prohibited obviously quantitative deprotonation of the phosphonium salts, and only mixtures of products with unreacted starting materials were obtained [19]. The cations were isolated as chloride or bromide salts, but conversion of the anions by complexation with Lewis-acids or metathesis was easily feasible [16, 18, 19] and even salts with organometallic anions ([Co(CO)4] , [CpM(CO)3] (M=Mo, W) were accessible [20]. 

Scheme 2 Products arising from base-induced condensation from PCI3 with xylylene-and butenylidene-bis-phosphonium salts (X=C1, Br)...

Reactions of butenylidene-bis-phosphonium salts with PCl3/triethyl-amine under similar conditions proceeded predominantly via base-induced fragmentation to triphenyl phosphine and polymeric products of unknown constitution (Scheme 2). Monocyclic bis-phosphonio-phospho-lides formed only as spectroscopically detectable but hardly isolable byproducts [18, 19]. 

Scheme 3 Proposed mechanism for the base-induced condensation of PCI3 with butenylidene-bis-phosphonium salts...

Treatment of the bis(phosphonium salt) 77 with PCI3 gives the salt 78 which may be trapped with nucleophiles to give stable benzophosphole bis(ylides) such as 79 and 80 <91AG(E)308>. 

Benzoxepin (27) has been synthesized from phthalaldehyde and a bis-phosphonium salt by a double Wittig condensation reaction as shown in equation (50) (66CB634). 

In the case of phosphonium salts substituted by an heteroaryl group, the furfuryl group is easily cleaved744 2,4-pyridindiyl bis(phosphonium) salts have been used as source of 2-pyridylphosphonio compounds745 (reaction 221). Clearly, the presence of... 

Lastly, mono- or bis-phosphonium salts can be cleaved to phosphines when a negative charge is created at a suitable position either with nucleophiles792,793 or using a base to abstract labile hydrogen atoms540,701,794-798 (reaction 243). In the case of 1.2-ethylene,... 

A Wittig style polymerization, shown in Scheme 33, is the result of condensation of dialdehyde monomers with bis(phosphonium) salts containing aromatic cores, and was reported for the first time in 1960 [134]. Unfortunately, due to low reactivity and conversion, the Wittig polymerization typically only affords materials with a DP of 10. Despite its limitation to forming low molecular... 

The bis-phosphonium salt (158) promotes the Lessen rearrangement of phenyl-hydroxamic acids and also brings about the Beckmann rearrangement of ketoximes under mild conditions. The salt (159), (formed from the reaction of 2-hydroxyethyl-triphenylphosphonium chloride with phosgene) has been employed as an amino-... 

The existence of U 42 -diphosphinines has not been firmly established. In 1967 Aguiar et al. published the acid-catalyzed dimerization of alkynyldiphenylphosphines (152) to the bis-phosphonium salts (153) <67JA3067, 67JA4235, 69JOC268l>. However, according to electrochemical studies only the formation of the radical cations (154) by one-electron transfer can be observed, and the neutral U 4A -diphosphinine species is not obtained (Scheme 28) <77JA6656>. 

In another attempt the bis-phosphonium salt (155) was treated with butyl and phenyl lithium, but ring opening rather than simple di-deprotonation was observed (Scheme 29) <66JA4090>. 

The diphosphinomethanes (70 R = Me, Ph) react with 1,2-xylylene dibromide to give the bis(phosphonium) salts (71 R = Me, Ph) <820M1266>. By stepwise deprotonation of the salts, the mono-, bis- <81CB1428>, and tris-ylides <820M1266> (72)-(74) have been prepared (74) has been used as a ligand for transition metal ions <820M1266,83AG(E)907>. 

Ring closure with bis(alkylidenephosphoranes) via bi(phosphonium salts)... 

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