Solvent effects on the structural and formyl substrate reactivity properties of a nitrogen/sulfur-ligated zinc hydroxide complex

The solution structural and formyl substrate reactivity properties of a nitrogen/sulfur-ligated zinc hydroxide complex, [(bmnpaZn)(2)(A-OH)(2)](ClO4)(2) ( 1, bmnpa = N, N-bis-2-(methylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl) amine), in acetonitrile and methanol are reported. In CH3CN, 1 has a binuclear cation [(bmnpaZn)(2)(mu-OH)(2)](2+) that is stabilized by secondary hydrogen bonding and CH/pi interactions involving the bmnpa chelate ligand. In CH3OH, 1 undergoes reaction with solvent to yield a zinc methoxide species, as determined by H-1 NMR and electrospray mass spectral analysis. Treatment of 1 with methyl formate in CH3CN results in stoichiometric hydrolysis of the formyl ester to produce [(bmnpa)Zn(O2CH)]ClO4 ( 2) and methanol. The formate complex was identified via independent synthesis and characterization (X-ray crystallography, H-1 and C-13 NMR, FTIR, LRFAB-MS, conductance, and elemental analysis). In the solid state, 2(n) has a formate- bridged coordination polymer-type structure. However, in CH3CN, 2 behaves as 1: 1 electrolyte, indicating cleavage of the polymer structure into mononuclear [( bmnpa) Zn(O2CH)] ClO4 species. Treatment of 1 with a stoichiometric amount of formanilide in CH3CN for 48 h at 45 C results in decomposition of the zinc hydroxide complex to yield the free bmnpa ligand and an inorganic solid, presumably a zinc hydroxide or oxide species. Treatment of 1 with a stoichiometric amount of ethyl formate in CD3OD results in rapid, quantitative transesterification of the formyl carboxylate ester. A control reaction indicates that this transesterification reaction does not occur on the same time scale in the absence of the catalyst. Treatment of 1 with an excess of ethyl formate in CD3OD results in catalytic formyl carboxylate ester transesterification, with approximately 1000 turnovers in 60 min at 22(1) degrees C. Treatment of a CD3OD solution of 1 (0.5 equiv) with formanilide ( 1 equiv) results in the formation of aniline, d(3)-methyl formate, and the zinc formate complex 2. While aniline is produced stoichiometrically, the yield of d(3)-methyl formate varied from 30 to 50%, and the yield of 2 varied from 50 to 70% in repetitive experiments. Formation of both d(3)-methyl formate and 2 indicates that both methanolysis and hydrolysis reactions take place.