Carboxylated Diphosphines

Phosphines with carboxylic groups were some of the earliest water-soluble phosphines investigated [26]. The group of Podlahova prepared a diphosphine, the phosphine analog of ethylenediaminetetraacetic acid, which is obtained as a monohydrate of the tetrasodium salt (18) [26]. Jegorov and Podlahova recently published a short review on the catalytic uses of these carboxyalkylphosphines [27]. 

---

The dinuclear iridium(l) diphosphine complexes 42 can also activate carboxylic acids easily. For example, the reaction of [IrCl(binap)]2 (42b) with an excess of acetic acid or benzoic acid in toluene at room temperature gave the corresponding (hydri-... 

In a related report, ruthenium-catalyzed enantioselective hydrogenation of 3-keto esters was utilized to prepare the crucial alcohol intermediate 36 (Scheme 14.16). The required (3-keto ester 49 was readily prepared from commercial thiophene carboxylic acid 40. Hydrogenation of 49 then led to the desired (S)-alcohol 50 in quantitative yield and 90% enantiomeric excess, catalyzed by a chiral diphosphine-ruthenium complex generated in situ. Catalyst-substrate ratios used were as low as 1/20,000, rendering this approach amenable to industrial application. Alcohol 50 was then converted to known intermediate 36 in three steps and 60% overall yield. 

Formation of carboxylic acids from ethylene, isobutylene, and 1-octene was observed by in situ 13C solid-state MAS NMR over H-ZSM-5 zeolite at 23-100°C.298 A systematic study with various Pd complexes revealed that styrene is transformed into 2-phenylpropionic acid as the major product when monophosphine ligands were applied, whereas 3-phenylpropionic acid was obtained in the presence of diphosphines 299... 

The stereoselective hydrogenation of a-monosubstituted (3-keto carboxylates and phosphonates through dynamic kinetic resolution has been applied to the synthesis of a wide variety of useful bioactive compounds as well as some chiral diphosphines (Figure 1.16) [lc,20,162b,c,179,243,246,250,252], The stereogenic center determined by the BINAP-Ru... 

The above data which are presented in Tables I-IV show that the diphosphine complexes are effective catalysts for the aldehyde decarbonylation. Although these reactions tolerate various functional groups such as carboxylic acids, ethers, ketones, olefins, and aryl chlorides,... 

In the synthesis of specially substituted methylene diphosphines, made from secondary phosphines and carbonyl derivatives (7), a carbenium ion adjacent to trivalent phosphorus as the transition state has been discussed. The transfer of this reaction principle to primary phosphines and suitable carbonyl compound revealed a further pathway to derivatives of dicoordinated phosphorus (8). Aromatic phosphines react with carboxylic acid amide acetals under elimination of alcohol giving dialkylamino-alkylidene phosphines (Scheme 5). A modification of the synthesis... 

The diphosphine of choice for obtaining good regioselectivity is the bis(diphe-nylphosphino)butane (Scheme 4). It enables addition of a variety of carboxylic acids to phenylacetylene and hexyne. The reaction temperature, which enables complete conversion can be reduced from 80 to 0 °C when the acidity of the carboxylic acid increases in the pK, range from 5 to 1.5. The milder temperature conditions always lead to higher regioselectivity of the addition. The preparation of functionalized (Z)-cnol esters can be conducted in apolar solvents such as toluene or pentane dienyl esters are selectively produced from conjugated enynes [9]. 

For both reactivity and regioselectivity, however, a compromise must be found between the bulkiness of the reagents (alkyne and carboxylic acid) and the steric hindrance of the diphosphine ligand, all of which are present in the coordination sphere of the ruthenium center during the catalytic process. Thus, with the more bulky trimethylsilylacetylene, the less hindered bis(diphenylphosphino)ethane ligand provides an efficient ruthenium catalyst (Ru(methallyl)2(dppe)) for producing silylated enol esters. Better reactivity is also observed with Ru(methal-lyl)2(dppe) as catalyst precursor when propargylic ethers are used as acetylenic substrates (Scheme 5) [10]. 

In contrast, some rr- allyl ruthenium complexes containing a chelating diphosphine ligand were the first metal complexes which favoured the anti-Markovnikov addition of carboxylic acids to terminal alkynes to form (Z)-enol and (E)-enol esters with high regioselectivity and stereoselectivity [17-19] according to Eq. (1). 

Ru(02CCP3)2(ROH)2(PP), incorporating various chiral phosphines (PP (diphosphines)), have also been characterized. The two carboxylates act as monodentate ligands, and two solvent molecules remain in the coordination sphere of the metal, in cis positions. ... 

---