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On the kinetics and chemistry of some reactions of phosphonitrilic derivatives Stewart, Charles John

Abstract

The kinetic parameters in acetonitrile of the nucleophilic substitution reaction: N₃P₃C1₆ + KCNS -> N₃P₃C1₅NCS + KC1 have been determined. The Arrhenius activation energy is 15.5 ± 5 Kcal moleˉ¹ and the common logarithm of the pre-exponential factor is 10.2 ± 3. The reaction is first order in each reagent and is probably bimolecular. Comparison with similar reactions indicates a lone pair electron donation from the nitrogen to the phosphorus atoms of the ring. The compound, N₄P₄(NMe₂)₈HCuCl₃ was prepared by the reaction of tetrameric phosphonitrilic dimethylamide with copper (II) chloride in butanone. The infra-red spectrum indicates that the copper atom is bound to one ring nitrogen atom, and the proton to the opposite nitrogen atom. The ring is found to be too small to allow chelation of the copper atom. The salt, N₆P₆(NMe₂)₁₂CuCl⁺CuCl₂ˉ was prepared by the dehydro-halogenation of N₆P₆(NMe²)₁₂HClCu₂Cl₃. The hydrochloride was prepared by the reaction of hexameric phosphonitrilic dimethylamide (H.P.D.) with ' copper (II) chloride in the reducing solvent butanone. The salt was also produced by the reaction of H.P.D. with an equimolar mixture of copper (I) chloride and copper (II) chloride in acetonitrile. Chemical and magnetic studies on the salt showed it to have one copper (II) atom per molecule. The x-ray crystal structure showed the copper (II) atom to be in a distorted square pyramidal environment, bonded to four ring nitrogen and one chlorine atom. The salt contains the first known example of the CuC1₂ˉ anion. This is linear with a Cu-C1 bond length of 2.11A. The anion is also one of the few examples of a finite species containing a two co-ordinate copper (I) atom. The infra-red spectrum of the salt was very similar to that of the parent H.P.D. The main difference was in the frequencies of the stretching modes of the phosphorus nitrogen ring bonds; which is consistent with copper chelation. Conductiometric and analytical studies showed that the salt does not retain the form form N₆P₆(NMe₂)₁₂CuCl⁺CuCl₂ˉ in acetonitrile solution; the limiting molecular conductance 377 ± 10 Ohmsˉ¹ being too large to be consistent with a 1:1 electrolyte.

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