Cobalt complexes phosphonates

If a chiral cobalt complex, instead of Co(salen)2, is used, enantioselectivity during the ring-opening process is induced (at —20°C the optimal ee was 76%) <2002CC28>. The application of stabilized Horner-Wadsworth-Emmons phosphonates represents a viable alternative to ylides in the cyclopropanation reaction <2002JOC3142>. 

Table 46 Structures Cobalt Phosphate, Phosphonate, Phosphite, ADP and ATP Complexes... 

Table 45 Preparations Cobalt Phosphate, Phosphate Ester, Phosphonate and Phosphite Complexes...

Recent work has shown that simple nonlabile mono-aqua metal complexes function as general base catalysts in the hydrolysis of neutral phosphate and phosphonate esters in aqueous solution. If general base catalysis operates the reaction of [Co(NH3)50H] with 4-nitrophenyldiethyl phosphate, then (1 = PNPDEP) will give free diethylphosphonic acid in solution, while direct nucleophilic displacement will give the (diethylphosphate)cobalt(III) cation (2). 

Nucleosides. Nucleotides, and Derivatives.- 2, 3 ,5 -Trl-0 -acetyl-adenosine and -guanosine, 4- -ethyl-thymidlne, N -methyl-2 -deoxyadenoslne, 5-raethoxymethyl-2 -deoxy-urldlne and its 0-D-threo-isomer, 5-fluoroarablnosylcytoslne, the 2 -deoxynucleo-side (17), cls-thymldine 3 ,5 -cyclic methyl phosphonate and the corresponding 3, 5 -cycllc N,N-dlmethylphosphoramldate,a cobalt(II) complex with 2 -deoxyinosine 5 -monophosphate,... 

Crystal structure analysis of one of these complexes (R = Me) reveals that the three cobalt atoms are arranged linearly [436]. The two terminal ones are equivalent with each being coordinated to a cyclopentadienyl ring and the phosphorus atoms of three phosphonate groups. The middle cobalt atom is located at the center of synunetry of the metal cluster and is surrounded octahedrally by six oxygen atoms. 

A water-soluble hydroformylation catalyst was developed by Xi and co-workers [65]. Third generation PAMAM dendritic ligands, with hydrophilic amine or sulfonic acid end groups, were phosphonated and the rhodium complexes thus formed were found to catalyse efficiently the hydroformylation of 1-octene and styrene, under very mild conditions. Water-soluble dendritic cobalt phthalocyanines that exhibited catalytic activities and oxidised thiols in the presence of oxygen, have been synthesised by Kimura and co-workers [66]. The catalytic activity of the phthalocyanines was influenced by a egation of the catalytic sites that results fi om strong intermolecular cohesive forces. It was proposed that steric isolation, enforced by the addition of a bulky dendritic coaf around the active phthalocyanine unit, could improve the catalytic activity. Acid terminated polyamide dendrimers were coupled to a phthalocyanine core to produce the desired water-soluble cobalt phthalocyanines, which were tested subsequently for catalytic activity and stability. The results obtained showed that the aggregation of phthalocyanines was reduced the catalytic activity was improved and the stability of the catalyst was improved by addition of the dendritic substituents. 

The cobalt(II) porphyrin complex (CoTPP) has been found to be an efficient catalyst for the Wittig type olefination of acyl phosphonates (96) with ethyl diazoacetate (EDA) in the presence of triphenylphosphine (Seheme 32). ° In a one pot reaction under mild conditions, highly functionalized vinyl phosphonates (97) could be obtained in high yields (72-92%) and high E/Z selectivities (95/5-100/0), in relatively short reaction times. 

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