1,4-Diphosphines

PhzP PPh2 PhaP PPh2 PhaP PPha 

Casey and coworkers [22] found a trend between calculated bite angle and the linearity of the product of 1-alkene hydroformylation. In hindsight we can extend the list with a number of ligands that were tested long before these studies and it is seen that they fit quite nicely in the series [24, 59). DIOP [60] (17) had been reported as early as 1973 by ConsigUo to give l/b=12 and dppf [61] in 1981 by Unmh with l/f =5, clearly higher than PPhs systems. We have not included Xantphos, which will be discussed later 

Beller and coworkers used NAPHOS, a BISBI analog backbone, substituted with 3,5-bistrifluoromethylphenyl groups as the ligand in rhodium-catalyzed hydroformylation of internal alkenes and obtained high selectivities to the linear product [63]. 

---

Keto esters are obtained by the carbonylation of alkadienes via insertion of the aikene into an acylpalladium intermediate. The five-membered ring keto ester 22 is formed from l,5-hexadiene[24]. Carbonylation of 1,5-COD in alcohols affords the mono- and diesters 23 and 24[25], On the other hand, bicy-clo[3.3.1]-2-nonen-9-one (25) is formed in 40% yield in THF[26], 1,5-Diphenyl-3-oxopentane (26) and 1,5-diphenylpent-l-en-3-one (27) are obtained by the carbonylation of styrene. A cationic Pd-diphosphine complex is used as the catalyst[27]. 

A diphosphine of the following stmcture [124788-09-6] has been offered by American Cyanamid. 

Some phosphoms—hydrogen compounds are pyrophoric, eg, diphosphine [13445-50-6] 2 4 common impurity in phosphine. Such contaminated phosphine usually ignites spontaneously on contact with air. 

All phosphoms oxides are obtained by direct oxidation of phosphoms, but only phosphoms(V) oxide is produced commercially. This is in part because of the stabiUty of phosphoms pentoxide and the tendency for the intermediate oxidation states to undergo disproportionation to mixtures. Besides the oxides mentioned above, other lower oxides of phosphoms can be formed but which are poorly understood. These are commonly termed lower oxides of phosphoms (LOOPs) and are mixtures of usually water-insoluble, yeUow-to-orange, and poorly characteri2ed polymers (58). LOOPs are often formed as a disproportionation by-product in a number of reactions, eg, in combustion of phosphoms with an inadequate air supply, in hydrolysis of a phosphoms trihahde with less than a stoichiometric amount of water, and in various reactions of phosphoms haUdes or phosphonic acid. LOOPs appear to have a backbone of phosphoms atoms having —OH, =0, and —H pendent groups and is often represented by an approximate formula, (P OH). LOOPs may either hydroly2e slowly, be pyrophoric, or pyroly2e rapidly and yield diphosphine-contaminated phosphine. LOOP can also decompose explosively in the presence of moisture and air near 150° C. 

Commercially, phosphinic acid and its salts are manufactured by treatment of white phosphoms with a boiling slurry of lime. The desired product, calcium phosphinite [7789-79-9], remains ia solution andiasoluble calcium phosphite [21056-98-4] is precipitated. Hydrogen and phosphine are also formed, the latter containing sufficient diphosphine to make it spontaneously flammable. The details of this compHcated reaction, however, are imperfectly understood. Under some conditions, equal amounts of phosphoms appear as phosphine and phosphite, and the volume of the hydrogen Hberated is nearly proportional to the hypophosphite that forms. 

Phosphine generated by the above procedures is usually contaminated to varying degrees with diphosphine, which renders it spontaneously flammable. Pure phosphine can be produced by hydrolysis of phosphonium iodide [12125-09-6] PH I, which can be made by the action of water on a mixture of phosphoms and diphosphoms tetraiodide [13455-00-0] (71). 

The alkah metal phosphides of formula M P and the alkaline-earth phosphides of formula M2P2 contain the P anion. Calcium diphosphide [81103-86-8] CaP2, contains P reaction with water Hberates diphosphine and maintains the P—P linkage. 

Monsanto s commercial route to the Parkinson s drug, L-DOPA (3,4-dihydroxyphenylalanine), utilizes an Erlenmeyer azlactone prepared from vanillin. The pioneering research in catalytic asymmetric hydrogenation by William Knowles as exemplified by his reduction of 24 to 25 in 95% ee with the DiPAMP diphosphine ligand was recognized with a Nobel Prize in Chemistry in 2001. ... 

Reaction of the diphosphine ligand R2P(CH2)2PR2 (R = benzothiazolyl) (L) with [RhCl(PPh3)3] gives the exclusively P-coordinated product [RhCl(PPh3)(L)] (88JOM(338)C31, 92JCS(D)241), which is perhaps a common feature of the P-substituted derivatives of oxazole and thiazole. 

The results obtained in the biphasic hydroformylation of 1-octene are presented in Table 5.2-1. In order to evaluate the properties of the ionic diphosphine ligand... 

BMIM][PFg] with a guanidinium-modified diphosphine ligand with xanthene backbone. 

The most effective catalysts for enantioselective amino acid synthesis are coordination complexes of rhodium(I) with 1,5-cyclooctadiene (COD) and a chiral diphosphine such as (JR,jR)-l,2-bis(o-anisylphenylphosphino)ethane, the so-called DiPAMP ligand. The complex owes its chirality to the presence of the trisubstituted phosphorus atoms (Section 9.12). 

The disclosure, in 1982, that cationic, enantiopure BINAP-Rh(i) complexes can induce highly enantioselective isomerizations of allylic amines in THF or acetone, at or below room temperature, to afford optically active enamines in >95 % yield and >95 % ee, thus constituted a major breakthrough.67-68 This important discovery emerged from an impressive collaborative effort between chemists representing Osaka University, the Takasago Corporation, the Institute for Molecular Science at Okazaki, Japan, and Nagoya University. BINAP, 2,2 -bis(diphenylphosphino)-l,l -binaphthyl (Scheme 7), is a fully arylated, chiral diphosphine which was introduced in... 

Both cis- and (rans-structures are possible RuH2(PMe3)4 is cis (Ru-H 1.507, 1.659 A, Ru-P 2.276-2.306 A) [90] while spectra show that RuH2(PF3)4 and others have this configuration. RuH2[PPh(OEt)2]4 is definitely trans (X-ray) with Ru-H 1.6 A, Ru-P 2.272 A. Many diphosphines form dihydrides. Ru(dmpe)2H2 has been a useful starting material for the synthesis of thiolate complexes [91] such as fra s-Ru(SPh)2(dmpe)2. 

Complexes of diphosphines and diarsines can be prepared by various routes the following are typical... 

Several m-platinum(II) dihydrides lose H2 reversibly in solution, forming dinuclear platinum(I) hydrides [(diphosphine)PtH]2 [62],... 

Reaction of the diphosphines Ph2P(CH2) PPh2 (n = 1-3) with MCl2(PhCN)2 affords 1 1 m-complexes (Figure 3.46) [102]. (Note the use of the labile PhCN adducts if the MCl salts are used, Magnus type compounds M(P-P)2+MCl4- are formed.) Similar complexes are formed with other halides for the thiocyanates see section 3.8.6. The structures of the palladium complexes have been determined (Table 3.10) with square coordination only achieved for n = 3 with the formation of a six-membered metal-chelate ring. 

With bulky diphosphines Bu2P(CH2) PBu2 (n = 8-12), similar reactions of the diphosphines with MCl2(PhCN)2 give separable mixtures of monomer, dimer and trimer. With small phosphines (n = 5-7) dimers predominate (Figure 3.48). 

Figure 3.47 The dimeric diphosphine-bridged complex [Pd Ph2P(CH2)6PPh2 Cl2]2.

Figure 3.48 The diphosphine complexes [Pd Bu2P(CH2) PBu2 Cl2]2 and [Pt PBu2P(CH2) 2-...

Figure 3.49 The rranj-cotriplexes of a phenanthrene-derived diphosphine ligand (M = Pd, Pi).

Rigid diphosphines have been used to enforce n-ans-geometries thus with the phenanthrene-derived diphosphine (Figure 3.49, R = Et) the complexes PdLCb and PtLCl2 have closely similar geometries (Pd-P 2.307 A, Pd-Cl 2.306 A, P-Pd-P 177.4° Pt-P 2.293 A, Pt-Cl 2.304 A, P-Pt-P 177.1°)... 

Elimination reactions have been particularly studied in the case of dialkyls. They depend on the alkyl groups being cis trans-complexes have to isomerize before they can eliminate, and a complex with a trans-spanning diphosphine ligand is stable to 100°C (Figure 3.56). 

---