Reactions of phosphonates with organohaloboranes: New route to molecular borophosphonates

Phosphonates RPO(OR')(2) (R = Me, R' = Et (1); R = CH2Ph, R' = Et (2); R = CH=CH2, R' = Et (3); R = CH2-CH=CH2, R' = Me (4); R = CH2N3, R' = Et (5)) r eact with CyBCl2 (6; Cy = C6H11) in a 1:1 molar ratio in toluene at -30 deg reesC to form the primary adducts CyBCl2.O=PR(OR')(2) (7-11). These product s 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 3BCy](4)-Cy, which may be attributed to tetramers [RPO3BCy](4) (22'-26'), a re detected. Compounds 22'-26' presumably possess a central cubic M4O12P4 f ramework that is analogous to those found in alumino- and gallophosphate ma terials. NMR monitoring shows that [CyBCl(mu (2)-O)(2)PR(OR')](2) (12-16) a re formed as intermediates in these reactions. These unstable dimers 12-16 possess a cyclic core analogous to the single-four-ring (4R) secondary buil ding units (SBUs) found in zeolites and phosphate molecular sieves. Hydroly sis of 1216 and 22-26 with methanol at 30 degreesC gave respectively RPO(OH )(OR') (17-21) and RPO(OH)(2)P(CH2Ph)(OEt)](2) (27-31). NMR monitoring reve als that the cyclic dimer [Me2B(mu (2)-O)(2)P(CH2Ph)(OEt)](2) (35a) is the primary adduct in the reaction of PhCH2PO(OEt)(2) (2) with MezBBr (34). Hea ting or prolonged storage at room temperature leads to a mixture of 35a, cy clic borophosphonate Me2BC(mu (2)-O)(2)P(CH2Ph)(OEt) (35b), and the mixed a nhydride of benzylphosphonic acid and dimethylborinic acid (35c).