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A Convenient Synthesis of Phosphonic Anhydrides − Trimers [RPO 2 ] 3 (R = tert ‐Butyl, 2‐Methylphenyl, 2,4,6‐Trimethylphenyl): Their Structures and Reaction Products
Author(s) -
Diemert Klaus,
Kuchen Wilhelm,
Poll Wolfgang,
Sandt Frank
Publication year - 1998
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199803)1998:3<361::aid-ejic361>3.0.co;2-t
Subject(s) - chemistry , monoclinic crystal system , steric effects , crystal structure , yield (engineering) , molecule , stereochemistry , hydrogen bond , hydrolysis , acid anhydride , nuclear magnetic resonance spectroscopy , medicinal chemistry , crystallography , organic chemistry , materials science , epoxy , metallurgy
By reaction of RP(O)Cl 2 with RP(O)(OSiMe 3 ) 2 , phosphonic anhydrides (RPO 2 ) 3 (R = t Bu, 2‐methylphenyl, 2,4,6‐trimethylphenyl) 1a−c are conveniently obtained. In contrast to 1b and 1c , compound 1a is remarkably stable against protolysis. Intermediates of hydrolysis of 1a , namely tris( tert ‐butyl)triphosphonic acid ( 2 ) and bis( tert ‐butyl)diphosphonic acid ( 3 ), can also be isolated in good yield. The structures of 1−3 were determined mainly by NMR spectroscopy ( 1 H, 13 C, 31 P). Assuming an energetic preference for the chair conformations in solution, and considering the steric requirements of the bulky substituents R, configurations Ia (point group C s , two R in equatorial positions) for 1a and b , and IIa (point group C 3v , all R equatorial) for 1c are suggested. − Reaction of 1a with N ‐benzyloxycarbonylglycine ( 4 ) in methanol affords strong evidence that in the first step of peptide synthesis with (RPO 2 ) 3 , a mixed anhydride of triphosphonic acid and the N ‐protected amino acid is formed. − The crystal structure of 1a (monoclinic, space group P 2 1 / n ) widely corresponds to the suggested configuration Ia, but reveals an envelope conformation for the six‐membered ring with a P 3 O 2 plane in the crystal. In the crystal structure of the octahydrate of the disodium salt of 2 (monoclinic, space group P 2 1 / c ), it can be seen that the polar end groups of the anions [ t Bu 3 P 3 O 7 ] 2− together with the water molecules and the Na + cations, form hydrogen‐bonded double‐layers, strictly separated from each other by the non‐polar tert ‐butyl groups of the anions.