Phobane

Alkyldiphosphines turned out to be very useful in a different reaction, namely the carbonylation/hydrogenation of ethylene oxide to give 1,3-propanediol also using cobalt catalysts. Interestingly, the ligand contains two phobane units bridged by 1,2-ethenediyl. The process was commercialised by Shell [18]. 

Recently, the reaction of the Phoban phosphine with precursor VIII was reported to give a very stable catalyst precursor XXVII (Equation 8.7) [60],... 

One of the latest compounds of this class is the phoban-indenylidene complex XXVII, synthesized by Forman et al. in 2006 [60]. This robust catalyst was tested in self-metathesis and ethenolysis reactions of methyl oleate, giving rise to significantly... 

For the further discussion of the catalytic applications it is important to note the acronym system which we apply to designate each ligand easily and unequivocally. According to the general label R/PR 2/PR", R denotes the substituent in the paro-position to the chiral a-chain (when R = H, it is omitted), PR 2 stands for the group in the ortho-position and finally PR" for the phosphino group in the a-chain itself (see Fig. 1.4.4). The abbreviations PbA and PbB refer to the regioisomeric phobane skeletons (PbA = phosphabicyclo[3.3.1]nonane, PbB = phosphabicyclo[4.2.1]nonane), Ind stands for indane and the (R,R)-2,5-dimethylphospholane unit is abbreviated to (R,R)-DMP . 

Eicosyl phobanes, HP-NMR and HP-IR studies, 1, 490-491 EIEs, see Equilibrium isotope effects Eighteen-electron complexes, ligand substitution in, 1, 96 Eighteen-electron rule... 

As already mentioned, the development of metathesis catalysts that can be easily accessed from simple precursors is necessary if a large-scale application is desired. With this in mind, Forman et al. developed a robust ruthenium-based phoban-indenylidene complex through a simple and relatively inexpensive procedure, if compared to the preparation of C3 [40]. This mthenium alkylidene was tested in the bulk SM of methyl oleate. As a result, they could reach up to 50% conversion with 0.005 mol% catalyst at 50°C. 

The bulk ethenolysis of methyl oleate was performed by Forman et al. using a phoban-indenylidene catalyst [38]. As for the SM of methyl oleate, this readily available catalyst demonstrated to be a suitable alternative to C3, affording the desired products in 64% conversion with a catalyst load of 0.005 mol%, at 50°C and 10 bar of ethylene. Using the same conditions, C3 led to a conversion of 43%. 

The radical addition of PH3 to limonene resulted in the formation of 2-phosphabicyclononane 177 which has been characterized by X-ray crystallographic analysis <2001TL2609>. Phobane is a mixture of the sym- and asym-bicyclic secondary phosphines 178 and 179, formed by the reaction of PH3 with 1,5-dicyclooctadiene. The mixture of phobanes may be separated efficiently by selective protonation of the syn isomer with HC1 <2005ASC1345>. 

Secondary phosphines can also be prepared by addition of P—H bonds across olefmic double bonds.40 For example, the industrially important bicyclic secondary phosphine phobane (43) can be synthesized from phosphine gas and cycloocta-1,5-diene, albeit as a mixture of two isomers (43a) and (43b) (Scheme 3). These isomers have recently been separated by an elegant sequence of hydrophosphination/dehydrophosphination steps, affording pure isomers which have been used in subsequent tertiary and ditertiary phosphine ligand syntheses.57... 

In a second report, the Bergman and Ellman groups improved on their original procedure for the arylation of heterocycles with aryl halides [103]. The key improvements over the previous method were three-fold (1) the use of the hindered tertiary amine base Pr.NBu in replacement of Et3N (2) microwave irradiation for rapid (<1 h), high temperature (250 °C) reactions in 1,2-dichlorobenzene (3) the use of bulky bicyclic trialkylphosphine ligands of the phobane family in replacement of PCy3 (Scheme 15). Under typical reaction conditions, the heterocycle... 

The scope of the reaction is broadened by the use of the tetrahydrophosphepine ligand. In addition to heterocycles that were reactive with PCy3 or cyclohexyl-phobane as ligands, 4,5-dimethylthiazole can be arylated. The scope with respect to the bromoarene partner is also broadened to include electron-rich bromoarenes and heteroaryl bromides such as 3-bromothiophene, 5-bromo-iV-methylindole, 5-bromobenzofuran, and 5-bromobenzothiophene. Functional groups including sulfoxides, chlorides, fluorides, ketones, esters, primary and secondary amides, phenols, anilines, and pyridines can be tolerated under these conditions. Sterically hindered and/or ortho substituted substrates are unreactive, but meta and para substituted substrates are well-tolerated. 

Secondary Phobanes were subjected to oxidation by air to result in the formation of one possible P-oxide or both isomers (Scheme 16). ... 

Transformation to phosphonium salts was used in a convenient procedure for the separation of sym and u ym-isomers of phobane (5-PhobPH and u-PhobPH, respectively). The investigation was prompted by... 

Figure 11.2 Bis-Phoban complex RuCl2(=CHPh)(Phoban)2 (29).

Shell was the first company to utilize cyclic trialkylphosphines for optimization of Co catalysts [13]. Meanwhile, these ligands are commercially available as a mixture under the collective chemical name phobanes. Bungu and Otto [14] evaluated various venues to phobanes by taking yields and safety issues into consideration. Differences in the methods consisted mainly in the employment of... 

A crucial problem of this short synthesis is certainly the use of the highly flammable, foul-smelling, and toxic PHg. Under the conditions described in Scheme 2.4, mainly 9-phosphabicyclo[3.3.1]nonane (syw-phobane) and its isomer 9-phosphabicyclo[4.2.1]nonane ( sytw-phobane) are formed in a ratio of about 3 2. The reaction has been conducted in >lkg scale. According to a protocol suggested by Pringle and coworkers [16], both isomers can be separated in a about 30 g scale via acidification in a biphasic system. After treatment with NaOH, the symmetric phobane could be isolated in 78% yield. 

In turn, Phobane-H may serve as starting material for the construction of a variety of tertiary phosphines (Scheme 2.5). Noteworthy, pathway (a) via the corresponding chlorophosphine and final alkylation also affords some undesired dimeric P-P coupling products. Alternatively, a chloro-free access has been suggested, which circumvents the Phobane-Cl (pathway b). A palladium-catalyzed P-C coupling reaction (with R = Ar) is less sensitive toward moisture and allows also the incorporation of a third P-substituent bearing functional... 

Scheme 2.5 Pathways to tertiary phobanes (in Ref. [14], exemplified with R = Ph) and typical...

Typical phobanes, which have been screened for hydroformylation as mixtures of isomers, are shown in Scheme 2.5. Isomeric [3.3.1]- and [4.2.1]-phobanes could also be separated at this level in a scale of 50-100 g by a similarly selective protonation protocol as outlined above with Phobane-H [17, 18]. Separation is likewise possible via selective oxidation or via the corresponding bis(hydroxymethyl)phosphonium salts [18]. The main difference between PBuj and phobanes consists in the cone angles differing from 132° for the former to 165° for individuals of the Phobane family. 

Besides the symmetric phobane s-PhobPR, nonsymmetric phobanes exist as two diastereomers, g-PhobPR and fly-PhobPR (Figure 2.5), which can be separated via their BHg adducts [19]. The donor strength decreases in the sequence Oy>s>a, but steric bulk follows the reverse order [20]. Highest reaction rates in the Co-catalyzed hydroformylation have been achieved with aj-PhobPR as ligand, but on the technical scale a mixture of all isomers is used. 

More stable and less volatile phosphines than simple trialkylphosphines are phosphabicyclononanes ( phobanes ) [43] or LIM hgands, which have been developed for the same purpose (Figure 5.11, see also Section 2.1) [44]. In addition, in 2014, Jiang and coworkers [45] suggested the use of alkylphosphines with polyethylene glycol chains for the transformation of Cj2 olefins into the corresponding alcohols in an aqueous biphasic system. 

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