Abstract
The five-coordinate, sixteen-electron manganese(I) complex [N(PPh <sub>3</sub> ) <sub>2</sub> ][Mn(CO) <sub>3</sub> (S,S-C <sub>6</sub> H <sub>4</sub> )] 1 was prepared from reaction of [N(PPh <sub>3</sub> ) <sub>2</sub> ][Mn(CO) <sub>3</sub> (NH,S-C <sub>6</sub> H <sub>4</sub> )] and 1,2-benzenedithiol via the hexacoordinate intermediate fac-[Mn(CO) <sub>3</sub> (S-C <sub>6</sub> H <sub>4</sub> SH)(NH <sub>2</sub> ,S-C <sub>6</sub> H <sub>4</sub> )] <sup>-</sup> . Alternatively, oxidative addition of 1,2-benzenedithiol to [Mn(CO) <sub>5</sub> ] <sup>-</sup> , followed by a Lewis acid-base reaction, with evolution of H <sub>2</sub> gas (identified by gas chromatography), led to formation of the coordinatively-unsaturated complex 1. In contrast, reaction of bis(2-pyridyl) disulfide and [N(PPh <sub>3</sub> ) <sub>2</sub> ][Mn(CO) <sub>5</sub> ] afforded hexacoordinate fac-[N(PPh <sub>3</sub> ) <sub>2</sub> ][Mn(CO) <sub>3</sub> (S-C <sub>5</sub> H <sub>4</sub> -N)(S-C <sub>5</sub> H <sub>4</sub> N)] 2, with one anionic [S-C <sub>5</sub> H <sub>4</sub> N] <sup>-</sup> ligand bound to Mn <sup>I</sup> in a monodentate (S-bonded) manner and the other [S-C <sub>5</sub> H <sub>4</sub> -N] <sup>-</sup> ligand bound in a bidentate manner (S,N-bonded). Complexes 1 and 2 have been characterized in solution by infrared spectroscopy and in the solid state by X-ray crystallography. The strong π-donating ability of the bidentate [S,S-C <sub>6</sub> H <sub>4</sub> ] <sup>2-</sup> ligand stabilizes the unsaturated complex 1 which has short Mn <sup>I</sup> -S bond lengths of 2.230(1) Å (average) as a result. The existence of one π and two σ bonds between the [Mn(CO) <sub>3</sub> ] <sup>+</sup> and [S,S-C <sub>6</sub> H <sub>4</sub> ] <sup>2-</sup> fragments, based on qualitative frontier molecular orbital analysis, also indicates that the lone-pair electrons are delocalized around the sulfur-manganese-sulfur system stabilizing the five-coordinate complex 1. The IR carbonyl stretching frequencies and the Mn <sup>I</sup> -S bond distances of complexes 1 and [N(PPh <sub>3</sub> ) <sub>2</sub> ][Mn(CO) <sub>3</sub> (NH,S-C <sub>6</sub> H <sub>4</sub> )] suggest that the relative π-donating ability of the bidentate ligands is [NH,S-C <sub>6</sub> H <sub>4</sub> ] <sup>2-</sup> > [S,S-C <sub>6</sub> H <sub>4</sub> ] <sup>2-</sup> . The Mulliken atomic charges derived from Hartree-Fock calculations roughly quantify the charge distribution in the complex [Mn(CO) <sub>3</sub> (NH,S-C <sub>6</sub> H <sub>4</sub> )] <sup>-</sup> (δ(N) = -1.14; δ(S) = -0.43; δ(Mn) = 1.14), and supports the premise that the reactions of [Mn(CO) <sub>3</sub> (NH,S-C <sub>6</sub> H <sub>4</sub> )] <sup>-</sup> with electrophiles (1,2-benzenedithiol, thiophene-2-thiol, 1,2-ethanedithiol) occur at the more electron-rich amide site, yielding charge-controlled, collision complexes.