Synthesis, Characterization, and Reactivity of Cationic Molecular Hydrogen Complexes of Manganese(I)

Abstract

Hydride complexes MnH(CO)3P2 (1), MnH(CO)2P3 (2), and MnH(CO)P4 (3) (P = P(OEt)3 (a), PPh(OEt)2 (b), PPh2OEt (c), PPh(OiPr)2 (d) were prepared by allowing the MnH(CO)5 species to react with an excess of phosphine upon UV irradiation or under reflux conditions. Their formulation and geometry in solution were established by IR and 1H, 13C, and 31P NMR spectroscopy. Protonation reactions with HBF4·Et2O of the monocarbonyls MnH(CO)P4 (3) afford isolable dihydrogen derivatives [Mn(η2-H2)(CO)P4]BPh4 (5), which were characterized by variable-temperature 1H and 31P NMR spectra, T 1 measurements, and J HD values. Thermally unstable (above 0 °C) [Mn(η2-H2)(CO)2P3]+ (4) cations were also prepared by protonation of the dicarbonyl hydrides MnH(CO)2P3 (2) and fully characterized in solution. Evolution of H2 from 4 and 5 results in the formation of the unsaturated complexes [Mn(CO)2P3]BPh4 (6) and [Mn(CO)P4]BPh4 (7), which are probably stabilized by an agostic interaction between the metal center and a C−H proton of the phosphite. Treatment of the unsaturated complexes 6 and 7 and of the triflate compounds [Mn(η1-OSO2CF3)(CO)3P2] (8) with Li+RC⋮C- gave the new acetylide derivatives [Mn(C⋮CR)(CO)P4] (9), [Mn(C⋮CR)(CO)2P3] (10), and [Mn(C⋮CR)(CO)3P2] (11) (R = Ph, p-tolyl). The new series of cationic manganese compounds [Mn(CO)2(p-tolylCN)P3]BPh4 (12), [Mn(CO)(p-tolylCN)P4]BPh4 (13), [Mn(CO)2(p-tolylNC)P3]BPh4 (14), [Mn(CO)(p-tolylNC)P4]BPh4 (15), [Mn(CO)3P3]BPh4 (16), and [Mn(CO)2P4]BPh4 (17) were also obtained by reacting the unsaturated compounds 6 and 7 with the appropriate ligands.

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

“…The importance of choosing an appropriate WCA precursor is exemplified by the protonation of the closely related manganese hydride species Mn(PR 3 ) 2 (CO) 3 H (where PR 3 =P(OEt) 3 , PPh(OEt) 2 , or PPh 2 (OEt)) with H[BF 4 ] or triflic acid. These reactions resulted in anion or water coordination rather than permitting the characterization of the corresponding dihydrogen complexes (Scheme ) …”

Brønsted–Lowry Acid Strength of Metal Hydride and Dihydrogen Complexes

“…The series of cationic manganese carbonyl hydrides (entries 15 and 17) is less extensive than that of rhenium discussed above. [Mn­(H 2 )­(CO)­(P­(OEt) 3 ) 4 ] + in CD 2 Cl 2 is deprotonated by NEt 3 , providing an upper limit of the p K a of 13 (p K a LAC predicted to be 7). The hydride complex [MnH­(CO)­(PAr′ 2 CH 2 PAr′ 2 )­( cyclo -PPhCH 2 NBnCH 2 PPhCH 2 NHBnCH 2 -)]­BAr′ 4 , Ar′ = 3,5-(CF 3 ) 2 C 6 H 3 , has a protonated amine in the ligand.…”

Synthesis and Characterization of Di‐ and Tricarbonylhydridomanganese(I) Complexes

“…Determination of the minimum spin‐lattice relaxation time [ T 1(min) ] for the hydrido nuclei of compounds 1 – 3 , at 400 MHz by the standard inversion‐recovery method, gave values in the range expected for this type of complex (Table 1) 4a and significantly lower than those for the analogous rhenium(I) derivatives 3f.…”

“…Longitudinal relaxation times of the hydrido resonance were measured in CD 2 Cl 2 solutions at 400 MHz by the inversion‐recovery method at different temperatures. The T 1(min) values obtained for the compounds (Table 3) are similar to those reported for other hydridocarbonylmanganese compounds bearing these types of phosphorus ligands 4a. The T 1(min) values observed for compounds 2a – d are lower than those of compounds 1a – d , which is probably due to the nature of the R groups attached to the bidentate L ligand.…”