An Experimental and Theoretical Evaluation of the Reactions of Silver Hyponitrite with
Phosphorus Halides. In Search of the Elusive Phosphorus-Containing Hyponitrites
posted on 2005-02-24, 00:00authored byHyun Joo, M. A. Salam Biswas, William E. Hill, Michael L. McKee
In the reaction of F2PBr, F2P(O)Br, (C6F5)2PBr, (CH3)2P(S)Br, and (CH3)2P(O)Cl with silver hyponitrite
(AgONNOAg), nitrous oxide (N2O) and μ-oxo phosphorus species were obtained in all cases rather than
the plausible hyponitrite alternative. Theoretical calculations of the geometries and expected decomposition
pathways of the phosphorus-containing hypothetical hyponitrites were carried out at the B3LYP/6-311+G(2df)//B3LYP/6-31+G(d) level. The cis-hyponitrite, XONNOX (XPF2, OPF2), is predicted to concertedly
decompose to N2 plus phosphorus-containing radicals (OPF2, O2PF2) or to N2O plus the μ-oxo phosphorus
species, XOX, (XPF2, OPF2) with the former pathway having a smaller activation barrier (4.6 kcal/mol, XPF2; 10.5 kcal/mol, XOPF2). On the other hand, trans-hyponitrite can only decompose to N2 plus
the phosphorus-containing radicals, because there is a very high barrier for rearrangement to cis-hyponitrite.
These results are in disagreement with experiment, because only the μ-oxo phosphorus species are observed.
Reconciliation between experiment and theory is made for XOPF2 when a silver cation is included in the
calculations. In THF (as a model for neat F2P(O)Br), the silver cation is predicted to reverse the order of the
two transition states through stronger interactions with the oxygen atoms in the transition state of the N2O-producing pathway. Thus, Ag(I) is predicted to be not only catalytic for XOPF2 but also product-specific
toward the μ-oxo products.