Synthesis and Structures of Iron(II) Alkyl and Thiolate Compounds Containing Sterically Hindered N-Functionalized Alkyl Ligands

Iron(II) dialkyl compounds [FeR<sub>2</sub>] (R = C(SiMe<sub>3</sub>)<sub>2</sub>C<sub>5</sub>H<sub>4</sub>N-2 (<b>1</b>), C(Ph)(SiMe<sub>3</sub>)C<sub>5</sub>H<sub>4</sub>N-2 (<b>2</b>), CH(SiMe<sub>3</sub>)C<sub>9</sub>H<sub>6</sub>N-8 (<b>4</b>)) and [{Fe(CHSi<i><sup>t</sup></i><sup></sup>BuMe<sub>2</sub>C<sub>5</sub>H<sub>4</sub>N-2)<sub>2</sub>}<sub>2</sub>] (<b>3</b>) have been prepared from the reaction of FeCl<sub>2</sub> with the appropriate N-functionalized alkyllithium reagent in a 1:2 molar ratio. The monoalkylated iron(II) complex [Fe{CPhSiMe<sub>3</sub>C<sub>5</sub>H<sub>4</sub>N-2}(Cl)(TMEDA)] (<b>5</b>) has been prepared by treating FeCl<sub>2</sub> with a stoichiometric amount of the organolithium reagent. X-ray analysis revealed that the alkyl ligands are bonded to the metal centers in a chelating manner in the mononuclear compounds <b>1</b> and <b>5</b>, whereas in <b>3</b> one of the alkyl ligands forms an interligand bridge betwen the two iron centers. Compounds <b>1</b>, <b>2</b>,<b> 4</b>, and <b>5</b> have magnetic moments in the range 4.24−4.96 μ<sub>B</sub> that are characteristic of a high-spin d<sup>6</sup> electronic configuration with four unpaired electrons. The magnetic moment of the binuclear compound <b>3</b> is 2.92 μ<sub>B</sub> per iron atom, apparently a consequence of antiferromagnetic coupling between the two metal centers. Subsequent reaction of <b>1</b> with Ar<sup>Me</sup>OH (Ar<sup>Me</sup> = 2,6-<i><sup>t</sup></i><sup></sup>Bu<sub>2</sub>-4-MeC<sub>6</sub>H<sub>2</sub>) and ArSH (Ar = 2,4,6-<i><sup>t</sup></i><sup></sup>Bu<sub>3</sub>C<sub>6</sub>H<sub>2</sub>) gave the neutral monomeric iron(II) bis(aryloxide) [Fe(OAr<sup>Me</sup>)<sub>2</sub>{CH(SiMe<sub>3</sub>)<sub>2</sub>C<sub>5</sub>H<sub>4</sub>N-2}] (<b>6</b>) and dithiolate [Fe(SAr)<sub>2</sub>{CH(SiMe<sub>3</sub>)<sub>2</sub>C<sub>5</sub>H<sub>4</sub>N-2}] (<b>7</b>), respectively. Both of the latter compounds have a rare coordination number of 3 at the iron(II) center. The magnetic moment of 5.11 μ<sub>B</sub> for <b>7</b> indicates a high-spin configuration with four unpaired electrons on the iron(II) center. Electrochemical studies on the compoounds are also reported.