THE PHOSPHA-WITTIG REACTION - A NEW METHOD FOR BUILDING PHOSPHORUS CARBON DOUBLE AND SINGLE BONDS FROM CARBONYL-COMPOUNDS

The so-called “phospha-Wittig” reagents [(EtO)2P(O)PHR]M(CO)5 (M = Mo, W) are obtained via the reaction of primary phosphine complexes (RPH2)M(CO)5 with lithium diisopropylamide and diethyl chlorophosphate. The corresponding anions [(EtO)2P(O)—P-R]M(CO)5 react with carbonyl compounds under mild conditions to give the phosphaalkene complexes [R1R2C=PR]M(CO)5. A study of this reaction with R = Ph, R1 = i-Pr, and R2 = H has shown that the kinetic product is the (Z)-phosphaalkene complex, whereas the thermodynamic product is the E isomer. The stereochemistry of these complexes was established by X-ray crystal structure analysis. With α-diketones, only one carbonyl bond is converted into a P=C double bond, probably for steric reasons. Most of the phosphaalkene complexes thus obtained easily react with methanol or 2,3-dimethylbutadiene. The phosphane-Mo(CO)5 complexes synthesized via such a scheme are easily transformed into the corresponding P-sulfides by simple heating with sulfur in toluene. Thus, the “phospha-Wittig” reaction can also be viewed as a new tool for building organophosphorus species with P—C single bonds. © 1990, American Chemical Society. All rights reserved.