Diphosphanes

However, we can deduce from Fig. 5.27 that the phosphino groups of a diphos-phane usually resonate slightly upheld from their parent phosphanes. This is particnlarly prononnced in the case of tcrt-butyl groups. Whereas PBu 3 has a chemical shift value of typ=63ppm, the corresponding diphosphane P Bu resonates at 

Primary phosphanes usually resonate upheld from HCF3PPHCF3 whereas secondary phosphanes are seen downheld. The most remarkable feature of the two examples in Fig. 5.28 is the chemical shift distribution in Me PPCCFj). The PMe gronp in Me2PP(CF3)3 has almost the same phosphorus resonance as in P Me, althongh the respective counter groups resonate at p=-58.5 ppm (Me P in P Me ) and Ap= 10.8 (P(CF3)3 in Me PPCCFj) ). 

We note that Me2PP(S)Mej features a chemical shift of -58.7 ppm virtually identical to that of P Me at p=-58.5 ppm. The same holds true for the PMe part of Me2PP(Se)Me2 at -57.5 ppm, and to a lesser extent for Me2PP(S)Ph2 

We would have expected a downfleld shift for both phosphorus atoms even if only one phosphorus atom is oxidized. The reason seems simple oxidizing a phosphorus atom decreases the electron density on this atom. The oxidized phosphorus atom would then pull stronger on the electrons of the P-P single bond, causing a downfleld shift in the resonance of the unoxidized phosphorus atom. In reality, we witness anything from a A =10ppm downfleld to a A =-7ppm upfleld shift. 

The NPPN compounds featuring an iminophosphorane and a phosphinoamido group depicted in Figs. 5.32-5.34 challenge our understanding of phosphorus chemical shifts. First, we need to determine which phosphorus atom gives rise to which 

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The phosphine produced is impure and contains small quantities of diphosphane, P2H4 (p. 227). 

Nitrogen, phosphorus and arsenic form more than one hydride. Nitrogen forms several but of these only ammonia, NHj, hydrazine, N2H4 and hydrogen azide N3H (and the ammonia derivative hydroxylamine) will be considered. Phosphorus and arsenic form the hydrides diphosphane P2H4 and diarsane AS2H4 respectively, but both of these hydrides are very unstable. 

This reaction gives an impure product containing hydrogen and another hydride, diphosphane, P2H4. 

This can be extracted from impure phosphine prepared by the action of sodium hydroxide on phosphorus. Unlike hydrazine, it has no basic properties. It is a powerful reducing agent and burns spontaneously in air, this reaction explaining why impure phosphine containing traces of diphosphane ignites spontaneously in air. 

Ruthenium hydride complexes, e.g., the dimer 34, have been used by Hofmann et al. for the preparation of ruthenium carbene complexes [19]. Reaction of 34 with two equivalents of propargyl chloride 35 gives carbene complex 36 with a chelating diphosphane ligand (Eq. 3). Complex 36 is a remarkable example because its phosphine ligands are, in contrast to the other ruthenium carbene complexes described so far, arranged in a fixed cis stereochemistry. Although 36 was found to be less active than conventional metathesis catalysts, it catalyzes the ROMP of norbornene or cyclopentene. 

With diphosphanes recently Stephan et al. reported an intriguing Al and P based macrocyclic structure [37]. A zirconium based catalyst precursor first was employed in the catalytic dehydrocoupling of the primary bidentate phosphane to give the tetraphosphane 6, (Scheme 4). The function of 6 as a molecular building block has been demonstrated by its reaction with MMe3(M = Al, Ga). Although, the gallium derivative 7 has not been... 

Fig. 4. Push-pull substituted diphosphanes, bonding parameters in Angstroms and degrees...

These phosphinous amide anions are presumably responsible for the formation of the by-products AT-phosphino phosphinous amides 11 and mono-phosphazenes derived from diphosphanes 12 in the sequential treatment of primary amines with n-BuLi and chlorophosphanes for preparing NH phosphinous amides [75,88] (Scheme 14). Compounds 11 and 12 are presumably derived from anions 9 and 10, respectively, generated by deprotonation of the newly formed phosphinous amide with the lithiated amine R NHLi. In solution, 9 can establish a metallotropic equilibrium with 10. 

Occasionally, attempts at introducing a new PR2 group on the nitrogen atom of an NH phosphinous amide, with the aim of preparing Ar,AT-bis(phosphino) phosphinous amides, result in the generation of monophosphazenes derived from diphosphanes, as seen in the preparation of 20 which occurs by P-P bond formation [74] (Scheme 20). The authors of this work claimed that the electron-... 

The hydrolysis of phosphinous amides leading to their constituents, amine and phosphinous acid, is an easy process that is usually followed by the selfcondensation of the acid to yield the diphosphane monoxides 21 [117, 118] (Scheme 21). 

An unprecedented stereoselective procedure to obtain enantiomerically pure transition cluster M3Q4 complexes consists of the direct excision of the M3Q7X4 n polymers using chiral diphosphanes, namely (+)-l,2-bis[(2J ,5R)-2,5-(dimethylphospholano)]ethane [(R,R)-Me-BPE] and its respective enantiomer [(S,S)-Me-BPE] to afford the trinuclear complexes (P)-[Mo3S4Cl3(J ,J -Me-BPE)3] and (Af)-[Mo3S4Cl3(S,S-Me-BPE)3] , respectively [30]. The structures of both enantiomers are shown in Fig. 7.3. The symbols (P) and (M) refer to the rotation of the chlorine atoms around the C3 axis, with the capping sulfur pointing towards the viewer. 

Calcium and other phosphides on contact with water liberate phosphine, which usualy ignites in air, owing to the diphosphane content. 

This material (possibly phosphine adsorbed on phosphorus, and produced by decomposition of diphosphane in light) ignites in air, on impact, or on sudden heating to 100°C [1,2]. 

Asymmetric synthesis of tricyclic nitro ergoline synthon (up to 70% ee) is accomplished by intramolecular cyclization of nitro compound Pd(0)-catalyzed complexes with classical C2 symmetry diphosphanes.94 Palladium complexes of 4,5-dihydrooxazoles are better chiral ligands to promote asymmetric allylic alkylation than classical catalysts. For example, allylic substitution with nitromethane gives enantioselectivity exceeding 99% ee (Eq. 5.62).95 Phosphi-noxazolines can induce very high enatioselectivity in other transition metal-catalyzed reactions.96 Diastereo- and enantioselective allylation of substituted nitroalkanes has also been reported.9513... 

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