Phosphito Complexes

A proposed mechanism (Scheme 5-44) begins with deprotonation of dimethyl phosphite to give an Al-phosphito complex (32) which can react with the aldehyde via either a chelate or open transition state, the latter possibly involving cooperative action of two aluminum centers, consistent with the observation of co-catalysis. Following P-C bond formation, several possible rearrangements could regenerate the achve catalyst and form the product... 

The ligand by itself acted as the reducing agent of Ni11 in several reactions, usually performed in ethanolic solution. In the case of trialkyl phosphito complexes, trialkylamine has been added to the reactants to neutralize the acidity which arises from the reduction reaction.68,69... 

Table (3 Some Structural Data for Selected Phosphito Complexes...

The rate law for aquation of the newly characterized phosphito-complex [Cr(0H2)6(03PHa)] + is... 

This procedure is similar to that used for the synthesis of bis(dimethyl phosphito-P)[ethylenebis(diphenylphosphine)]platinum(Il).8 To a solution of bis(dimethyl hydrogen phosphite-i>)bis(dimethyl phosphito- )platinum(II) (0.976 g, 1.5 mmole) in benzene (50 mL) is added o-phenylenebis(dimethylarsine) 9 (0.441 g, 1.5 mmole). The solution is heated at reflux with stirring for 1 hour and then allowed to cool to room temperature. The colorless compound precipitates and is collected by suction filtration on a medium-porosity fritted glass. The complex is washed with benzene (two 5-mL portions) and then... 

The Henbest reagent (a phosphito-iridium complex of uncertain structure ) is highly efficient for reducing either 5a- or 5 -3-oxosteroids to give the corresponding axial alcohols. Oxo-functions at the C-2,6,7,11,12,17, and 20 positions are completely unreactive, although reduction of pregnane-3,20-diones is complicated by equilibration at C-17 (17a 17 ). ... 

The reaction products are altered when the transformations outlined in Scheme 2 are carried out starting from phosphito derivatives [L = P(OMe)3 or PPh(OMe)2j. Phosphonato complexes are isolated either as the sole products (M = Nb, R = Me M = Ta, R = Ph) or together with the expected metallophosphines in variable yields (M = Nb, R = Ph). A complete transformation from metallophosphine to the corresponding phosphonato complex occurs over 24 h. 

Phosphines metallated at remote atoms other than carbon have also been applied in synthesis, including the bis(phosphinophenyl)amide salt (44), used to prepare various uranium complexes, N-metallated 2-phosphi-noindoles, used to prepare new chiral hybrid phosphino-phosphito... 

Most recently studied are the phosphito (RO>2PO-, phosphonito R(RO)PO- and phosphinito R2PO-complexes. These compounds can involve both M-P and M-O-P linkages. 

Phosphite ion coordinated to dinuclear 06ISDIEN dicobalt-p-hydroxo-p-peroxo complex is oxidized to phosphate via apparent 0-atom insertion into the P-H bond, which resembles a hydioxylation reaction The proposed mechanism (Figure 51) of phosphite to phosphate oxidation within the p.-phosphito- x-pCFOXo complex involves the intermediate in Figure 52. 

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