Reactions of Phosphonates with Organohaloboranes: New Route to Molecular Borophosphonates

Phosphonates RPO(OR‘) 2 (R = Me, R‘ = Et ( 1 ); R = CH 2 Ph, R‘ = Et ( 2 ); R = CH CH 2, R‘ = Et ( 3 ); R = CH 2 −CH CH 2, R‘ = Me ( 4 ); R = CH 2 N 3, R‘ = Et ( 5 )) react with CyBCl 2 ( 6; Cy = C 6 H 11 ) in a 1:1 molar ratio in toluene at −30 °C to form the primary adducts CyBCl 2 · O PR(OR‘) 2 ( 7 − 11 ). These products undergo a thermally induced bis-chlorodealkylation with the formation of mixtures of oligomers [−O−PR(O−)−O−BCy(O−)] n ( 22 − 26 ) having isovalent P−O−B groupings. Under electron impact mass spectral conditions, the ions [RPO 3 BCy] 4 −Cy, which may be attributed to tetramers [RPO 3 BCy] 4 ( 22 ‘− 26 ‘), are detected. Compounds 22 ‘− 26 ‘ presumably possess a central cubic M 4 O 12 P 4 framework that is analogous to those found in alumino- and gallophosphate materials. NMR monitoring shows that [CyBCl( μ 2 -O) 2 PR(OR‘)] 2 ( 12 − 16 ) are formed as intermediates in these reactions. These unstable dimers 12 − 16 possess a cyclic core analogous to the single-four-ring (4R) secondary building units (SBUs) found in zeolites and phosphate molecular sieves. Hydrolysis of 12 − 16 and 22 − 26 with methanol at 30 °C gave respectively RPO(OH)(OR‘) ( 17 − 21 ) and RPO(OH) 2 ( 27 − 31 ). NMR monitoring reveals that the cyclic dimer [Me 2 B( μ 2 -O) 2 P(CH 2 Ph)(OEt)] 2 ( 35a ) is the primary adduct in the reaction of PhCH 2 PO(OEt) 2 ( 2 ) with Me 2 BBr ( 34 ). Heating or prolonged storage at room temperature leads to a mixture of 35a, cyclic borophosphonate Me 2 BC( μ 2 -O) 2 P(CH 2 Ph)(OEt) ( 35b ), and the mixed anhydride of benzylphosphonic acid and dimethylborinic acid ( 35c ).