Syntheses, crystal structures and properties of [PPh4]2[SbFe3H(CO)12] and [PPh4]2[AsFe3H(CO)12]
Abstract
Reaction of Sb2O3 or As2O3 with methanolic solutions of Fe(CO)5–OH– have resulted in the formation of the a nionic species [SbFe3H(CO)12]2– or [AsFe3H(CO)12]2–, which maybe precipitated as their PPh4+ salts. The anions have also been obtained as the NEt4+, NMe4+ or N (PPh3)2+ salts. The PPh4+ salts of the anions are not isomorphous, with [PPh4]2[SbFe3H(CO)12] crystallizing in the monoclinic space group P21/c, with a= 11.165(5), b= 49.223(9), c= 10.903(5)Å, β= 108.13(2)° and Z= 4, while [PPh4]2-[AsFe3H(CO)12] is triclinic, space group P, with a= 12.088(5), b= 13.257(5), c= 19.389(8)Å, α= 80.43(3), β= 83.55(3), γ= 70.83(3)° and Z= 2. Each anion consists of a central antimony or arsenic atom surrounded by three Fe(CO)4 groups in a trigonal-pyramidal arrangement, together with a hydrogen atom, although this was not crystallographically located and is inferred on the basis of charge considerations and, more importantly, 1H NMR data. The Sb–Fe and As–Fe bond distances average 2.596(1) and 2.459(2)Å, respectively. The 1H NMR spectra exhibit slightly broad singlets at δ–1.39 for [SbFe3H(CO)12]2– and δ 1.34 for [AsFe3H(CO)12]2–, both with W½, of ca. 6 Hz, which are indicative of hydrogen attached to antimony and arsenic. Attempts to synthesize the corresponding bismuth species were unsuccessful, which may be attributed to the poor Lewis basicity of the lone pair on bismuth and to the lack of stability displayed by a Bi–H bond. The reaction in this case generally results in the formation of [BiFe4(CO)16]3– and bismuth metal, likely involving the disproportionation of an anionic BiIII–Fem(CO)n intermediate such as [BiFe3(CO)12]3–, the deprotonated bismuth analogue of [SbFe3H(CO)12]2– and [AsFe3H(CO)12]2–.