Diphosphines derivatives

Evaluation of trends in /pp coupling constants in solid-state 31P NMR spectra of P-phospholyl-NHPs allowed one to establish an inverse relation between the magnitude ofM and P-P bond distances [45], The distance dependence of. /pp is in line with the dominance of the Fermi contact contribution, and is presumably also of importance for other diphosphine derivatives. At the same time, large deviations between lJvv in solid-state and solution spectra of individual compounds and a temperature dependence of lJ77 in solution were also detected (Fig. 1) both effects... 

Diacylphosphines may be prepared by treatment of bis(trimethylsilyl)phenyl-phosphine (65) with acid chlorides.60 A diphosphine derivative (66) is formed with benzoyl chloride.60 A series of complex reactions occurs between nitrobenzenes and diphenyl(trimethylsilyl)phosphine (67).61 The oxides noted below were the only isolable products, and the yields were not high.61... 

Most successful of the diphosphine derivatives (e.g. 27, 28) are the cationic, edge-bridged dimers of type 28 developed by the Hofmann group, and described in a recent review.Routes to the neutral diphosphine complexes commonly utilize 22b as precursor (Scheme 4) 134-136 commercial availability, and consequent synthetic convenience, counterbalancing its slower rate of phosphine exchange, relative to 22a or 2 Vinylalkylidene... 

Preparative studies and luminescence studies have been conducted on the diphosphine derivative trans-02Re(dmppe)2+, including an X-ray crystal structure of this complex (dmppe is l,2-Ms(di-4-methylphenylphosphino)-ethane) [20]. The complex excited state emits both in the solid state and in CH3CN solution with a 1.1 us lifetime in the solid. The emission energy is... 

The subsequent stages involving tetraphosphine, triphosphine and diphosphine derivatives proceed rapidly owing to the high reactivity of the P-P bond. 

The reduction of trimethyl phosphite-borane by sodium naphthalide produces a new type of diphosphine derivative. The isomer which apparently explains all of the observed properties of the compound is (21). ... 

NHC-substituted monophosphine riienium hydrides [Re(Br)(H)(NO)(NHCs)2] (18 IMes, 19 SIMes, R = /Pr a, Cy b). As both IMes and SIMes ligands exhibit better electron-donating capabilities than alkylphosphines, complexes 18 and 19 are expected to be more active catalysts than the diphosphine derivatives 17 due to a labilized phosphine ligand trans to the NHC. 

Later, Hallam and Pauson prepared [Fe(CO)a- (CeHs) sP 2] by heating triphenylphosphine in an autoclave with an equimolecular amount of [Fe(CO)2CeH6]2 or [FeCl(CO)2C5H5], or by treating [Fel2(CO)j (C.Hs)aP ] with cyclopentadienylsodium in tetrahydrofuran. Recently, Cotton and Parish obtained the phosphine derivatives by heating triphenylphosphine and iron pentacarbonyl in a Carius tube. It has been found possible to prepare both mono- and diphosphine derivatives, as well as the corresponding arsines and stibines, much more simply by reaction in an appropriate solvent. ... 

Table 1.13 DPPBA and DPPA-based diphosphine derivatives.

Figure 5.1 Diphosphine-derived nickel PCP-pincer complexes.

Licandro, Froni, and coworkers have also employed the oxidative photocyclodehydrogenation approach for the synthesis of new enan-tiopure tetrathia-[7]-helicene diphosphine derivative 14 (05SL1137, 06S3670, 11EJ05649). A notable feature of this method lies in the fact that the key tetrathia-[7]-helicene scaffold can be easily and regioselectively... 

The initial reaction between lithium ethylphosphine and bromosilane (9.182) is followed by further reactions to give by-products (9.183) and (9.184). The monophosphine derivative from (9.182) slowly disproportionates on standing to give the diphosphine derivative which is relatively stable (9.185). ... 

A linear compound with both P-C and P-Si linkages is formed in reaction (9.248), while a diphosphine derivative is obtained (in small amounts) by reaction (9.249). 

Secondary phosphine sulphides can be obtained in a variety of reactions including the action of caustic soda on aliphatic diphosphine disulphides, or hydrogen sulphide on phosphinous amides. Secondary phosphine sulphides readily add more sulphur to give phosphino dithioic acids (6.79) -an excess produces diphosphine derivatives (below). 

A considerable amount of spectroscopic work has been done on various diphosphine derivatives to try and sort out the isomers which may be present under specified conditions. In contrast to the solid state, where only one isomer is usually present, the various forms are often in equilibrium in the liquid or in solution. In the case of the compound Me(CF3)P-P(CF3)Me, F and P NMR data indicate that d, l and meso forms of the molecule are aU present, the proportions depending on the temperature and other factors. In molecules of this kind, as the temperature is lowered the pyramidal inversions may cease, and only rotation or partial rotation takes place. According to spectroscopic data on R2N-PPhCl, the P atom inverts freely above 80°C, but only slowly at room temperature. At -80°C inversion ceases and only slow rotation about the P-N bond takes place. 

This method is not only restricted to dimethylphosphine boranes and sulfides. It has been also applied to cyclic diphosphine derivatives by deprotonation of one of the enantiotopic methylene groups a to the phosphorus atom (Scheme 5.3). In this case, a second stereogenic centre is created and therefore it is necessary to control also the diastereoselectivity of the reactions. 

More recently, diphosphine derivatives of the cyclic decapeptide gramicidin S were synthesized by SPPS and structurally characterized. In a first approach, the two ornithine residues included in the p-strand sequence were replaced by phosphine-containing amino acids (Figure 10.20). 

At -1 V (vs. AgjAgCl), this cation reduces protons to H2 with perfect Faradaic efficiency. The corresponding bis-phosphine complex, Fe2(SR)2(PMe3)2(CO)4 also exhibits good catalytic activity in the presence of excess protons [46]. Cyclic voltam-metric experiments indicate that the diphosphine derivatives are less catalytically active than the phosphine-cyanide complex [46, 50]. This difference is possibly attributable to the ability of the CN to convey a proton to the Fe-H-Fe group. 

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