From Ferrocenecarbonitriles to Ferrocenylimines: Synthesis, Structure, and Reaction Chemistry

From the reaction of [PtCl₂(NCMe)₂] with FcCN (<b>1</b>) (Fc = Fe­(η⁵-C₅H₄)­(η⁵-C₅H₅)) complex [PtCl₂(FcCN)­(NCMe)] (<b>2</b>) was obtained, which on subsequent treatment with <b>1</b> gave <i>trans</i>-[PtCl₂(NCFc)₂] (<i>trans</i>-<b>3</b>). The latter complex and the appropriate <i>cis</i> isomer (<i>cis</i>-<b>3</b>) were also accessible when [PtCl₂] or [PtCl₂(NCMe)₂] is reacted with a 2.6-fold excess of <b>1</b>. Appropriate treatment of [PtCl₂(NCMe)₂] with two equivalents of 1-acetyl-1′-cyanoferrocene (<b>4</b>) produced <i>trans</i>-[PtCl₂(Fe­(η⁵-C₅H₄CN)­(η⁵-C₅H₄C­(O)­Me))₂] (<i>trans</i>-<b>5</b>). Coordination polymer [PtCl₂(Fe­(η⁵-C₅H₄CN)₂)]_<i>n</i> (<b>7</b>) was obtained by combining [PtCl₂(NCPh)₂] with [Fe­(η⁵-C₅H₄CN)₂] (<b>6</b>). However, when <b>7</b> was reacted with PPh₃ for deaggregation, [PtCl₂(PPh₃)₂] was formed. Addition of FcCCLi (<b>8-Li</b>) to <i>trans</i>-<b>3</b> gave pentametallic <i>trans</i>-[Pt­(CCFc)₂­(NHC^<i>n</i>BuFc)₂] (<b>10</b>) via <i>trans</i>-[Pt­(CCFc)₂­(NCFc)₂] (<b>9</b>). When <i>trans</i>-<b>3</b> is reacted with two equivalents of ^<i>n</i>BuLi in the absence of FcCCH (<b>8</b>), <i>trans</i>-[PtCl₂(NHC^<i>n</i>BuFc)₂] (<b>11</b>) was obtained, which decomposed to FcC­(NH)^<i>n</i>Bu (<b>12</b>), giving FcC­(O)^<i>n</i>Bu (<b>13</b>). Electrochemical measurements of the nitrile platinum complexes show no redox separation for the oxidation of the Fc and Fe­(η⁵-C₅H₄)₂ moieties. Compared with the noncoordinated ferrocenecarbonitriles, a shift to higher potentials is observed. In contrast, for <b>10</b> four well-separated redox events (−185, <b>–</b>90, +460, +545 mV) were found, which could be assigned to the oxidation of the Fc units. UV–vis/NIR spectroscopy allowed to determine an IVCT absorption (ν_max = 6495 cm^–1, ε_max = 270 L·mol^–1·cm^–1, Δν_1/2 = 2270 cm^–1) for <b>10</b>^<b>+</b>, classifying this mixed-valent species as a weakly coupled class II system according to Robin and Day, while no IVCT transitions were observed for <b>10</b>^{<b><i>n</i>+</b>} (<i>n</i> = 2, 3). The structures of <i>trans</i>-<b>3</b>, <i>cis</i>-<b>3</b>, <b>10</b>, and FcC­(O)^<i>t</i>Bu (<b>15</b>) in the solid state were determined by single-crystal X-ray diffraction. Although the bond distances and angles of <i>trans-</i><b>3</b> and <i>cis</i>-<b>3</b> are similar, the <i>cis</i> isomer crystallizes as a dimer possessing Pt–Pt distances within the sum of the van der Waals radii