An Experimental and Theoretical Evaluation of the Reactions of Silver Hyponitrite with Phosphorus Halides.In Search of the Elusive Phosphorus-Containing Hyponitrites

摘要

In the reaction of F_2PBr,F_2P(O)Br,(C_6F_5)_2PBr,(CH_3)_2P(S)Br,and (CH_3)_2P(O)C1 with silver hyponitrite (AgON=NOAg),nitrous oxide (N_2O) and mu-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,XON=NOX (X=PF_2,OPF_2),is predicted to concertedly decompose to N_2 plus phosphorus-containing radicals (OPF_2,O_2PF_2) or to N_2O plus the mu-oxo phosphorus species,X-O-X,(X=PF_2,OPF_2) with the former pathway having a smaller activation barrier (4.6 kcal/ mol,X=PF_2;10.5 kcal/mol,X=OPF_2).On the other hand,trans-hyponitrite can only decompose to N_2 plus the phosphorus-containing radicals,because there is a very high barrier for rearrangement to cid-hyponitrite.These results are in disagreement with experiment,because only the mu-oxo phosphorus species are observed.Reconciliation between experiment and theory is made for X=OPF_2 when a silver cation is included in the calculations.In THF (as a model for neat F_2P(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 N_2O-producing pathway.Thus,Ag(I) is predicted to be not only catalytic for X=OPF_2 but also product-specific toward the mu-oxo products.