Problem 1

In 1956 Huisgen and Ugi obtained the compound

\ce{PhX}

(A), unambiguously confirmed 27 years later by single-crystal X-ray diffraction. In 2001 quantum chemistry predicted the

\ce{FeX2}

molecule (B) with

\ce{Fe^{2+}}

and

2\ce{X-}

binding energy close to the isoelectronic molecule

\ce{FeY2}

(C, discovered in 1951, light-orange, mp

173\ ^{\circ}\mathrm{C}

, bp

249\ ^{\circ}\mathrm{C}

, stable to

450\ ^{\circ}\mathrm{C}

). A derivative of A was later prepared from 4-methoxyaniline with

\ce{NaQ}

. Oxidation with CAN at

-40\ ^{\circ}\mathrm{C}

in the presence of zinc nitrate gave the mixed salt

\ce{Zn(X)(NO3)}

(D). At

-20\ ^{\circ}\mathrm{C}

D decomposes releasing a gas and another salt

\ce{Zn(Q)(NO3)}

(E), containing the same elements as D, including 38.59 % zinc. The isomer F of B (obtained in 1999) is isoelectronic to iron compound G (a light-yellow liquid immiscible with cold water, used to prepare high-purity iron powder). In 2017 stable salt H was obtained: it contains

\ce{X-}

anions, chloride, ammonium and hydronium (

\ce{H3O+}

) cations, with 4.31 % H, 81.42 % N and 6.06 % Cl. (1) Write the molecular formulas of

\ce{HX}

, D, E, and identify A–C. (2) Write equations for the synthesis of

\ce{PhX}

by Huisgen and Ugi. (3) Identify F and G. (4) Calculate the formula of H.

Step 2 of 5: Aromatic analogies

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\ce{C} = \ce{Fe(C5H5)2}\ \text{(ferrocene)};\quad \ce{B} = \ce{Fe(N5)2};\quad \ce{A} = \ce{PhN5}\ \text{(phenylpentazole)};\quad \ce{HX} = \ce{HN5}

Analysis

The 1951 discovery of stable $\ce{FeY2}$ is ferrocene (Y = cyclopentadienyl $\ce{C5H5-}$ ). Its isoelectronic all-nitrogen analogue is bis(pentazolyl)iron $\ce{Fe(N5)2}$ , and A is phenylpentazole $\ce{PhN5}$ .