1,2-Addition of Formic or Oxalic Acid to ^–N{CH₂CH₂(PiPr₂)}₂‑Supported Mn(I) Dicarbonyl Complexes and the Manganese-Mediated Decomposition of Formic Acid

(PN^HP)­Mn­(CO)₂ (I) carboxylate complexes (PN^HP = HN­{CH₂CH₂(PiPr₂)}₂) were prepared via 1,2-addition of either formic or oxalic acid to (PNP)­Mn­(CO)₂ (PNP = the deprotonated, amide form of the ligand ^–N­{CH₂CH₂(PiPr₂)}₂). The structural and spectral properties of these complexes were compared. The manganese formate complex was found to be dimeric in the solid state and monomeric in solution. Half an equivalent of oxalic acid was employed to form the bridging oxalate dimanganese complex. The catalytic competencies of the carboxylate complexes were assessed, and the formate complex was found to decompose formic acid catalytically. Both dehydrogenation and dehydration pathways were active as assessed by the presence of H₂, CO₂, and H₂O. The addition of LiBF₄ exhibited a strong inhibitory effect on the catalysis

Reversible 1,2-Addition of Water To Form a Nucleophilic Mn(I) Hydroxide Complex: A Thermodynamic and Reactivity Study

(^iPrPN^HP)­Mn­(CO)₂(OH) (<b>2</b>; ^iPrPN^HP = HN­{CH₂CH₂(PⁱPr₂)}₂) was formed from the reversible 1,2-addition of water to (^iPrPNP)­Mn­(CO)₂ (<b>1</b>; ^iPrPNP = the deprotonated, amide form of the ligand, ^–N­{CH₂­CH₂(PⁱPr₂)}₂). This reversible reaction was probed via variable-temperature NMR experiments, and the energetics of the 1,2-addition/elimination was found to be slightly exothermic (−0.8 kcal/mol). The corresponding manganese hydroxide was found to react with aldehydes, yielding the corresponding manganese carboxylate complexes (^iPrPN^HP)­Mn­(CO)₂(CO₂R), where R = H, methyl, phenyl. While no reaction between <b>1</b> and neat benzaldehyde was observed, in the presence of water, conversion to the corresponding manganese-bound benzoate with formation of H₂ was observed. The catalytic oxidation of benzaldehyde by water without additives was unsuccessful due to strong product inhibition, with the manganese benzoate formed under a variety of reaction conditions. Upon addition of base, a catalytic cycle for the conversion of aldehyde to carboxylate and hydrogen can be devised

A Tertiary Carbon–Iron Bond as an Fe^ICl Synthon and the Reductive Alkylation of Diphosphine-Supported Iron(II) Chloride Complexes to Low-Valent Iron

Ligand-induced reduction of ferrous alkyl complexes via homolytic cleavage of the alkyl fragment was explored with simple chelating diphosphines. The reactivities of the sodium salts of diphenylmethane, phenyl­(trimethylsilyl)­methane, or diphenyl­(trimethylsilyl)­methane were explored in their reactivity with (py)₄FeCl₂. A series of monoalkylated salts of the type (py)₂FeRCl were prepared and characterized from the addition of 1 equiv of the corresponding alkyl sodium species. These complexes are isostructural and have similar magnetic properties. The double alkylation of (py)₄FeCl₂ resulted in the formation of tetrahedral high-spin iron complexes with the sodium salts of diphenylmethane and phenyl­(trimethylsilyl)­methane that readily decomposed. A bis­(cyclohexadienyl) sandwich complex was formed with the addition of 2 equiv of the tertiary alkyl species sodium diphenyl­(trimethylsilyl)­methane. The addition of chelating phosphines to (py)₂FeRCl resulted in the overall transfer of Fe­(I) chloride concurrent with loss of pyridine and alkyl radical. (dmpe)₂FeCl was synthesized via addition of 1 equiv of sodium diphenyl­(trimethylsilyl)­methane, whereas the addition of 2 equiv of the sodium compound to (dmpe)₂FeCl₂ gave the reduced Fe(0) nitrogen complex (dmpe)₂Fe­(N₂). These results demonstrate that iron–alkyl homolysis can be used to afford clean, low-valent iron complexes without the use of alkali metals