Transition Metal Polypnictides from Zintl Ions

Abstract

The chemistry of the soluble E7 3- ions (E = P, As, Sb) with various transition metal complexes has been investigated. Alloys of K3E7 react with (arene)M(CO)3 (M = Cr, Mo, W) complexes in the presence of three equivalents of 2,2,2-crypt in ethylenediamine to give [K(2,2,2-crypt)]3[E7M(CO)3] complexes. Nine [E7M(CO)3] 3- compounds (E = P, As, Sb; M = Cr, Mo, W) have been prepared. The compounds have norbomadiene-like E7 fragments, with a formal negative charge associated with the unique two-coordinate pnictogen furthest from the transition metal. The bonding is described as E7 π-type interactions with the metal center. 31p NMR studies show that these compounds undergo an intramolecular wagging process in solution. The [E7M(C0)3] 3- ions are modestly basic and highly nucleophilic. The complexes react with weak acids, tetraalkylammonium salts and (arene)M'(CO)3 complexes to form the [K(2,2,2-crypt)]2[HE7M(CO)3], [K(2,2,2- crypt)]2[RE7M(CO)3] and [K(2,2,2-crypt)]3[(L2)(CO)3M'E7M(CO)3] compounds, respectively. Each of the structures contains a norbornadiene-like E7 fragment bound η4 to the M(CO)3 fragment and η1 to the appended moiety [H+, R+, M(CO)3(en)] that is attached to the pnictogen atom furthest from the M(CO)3 center. The [K(2,2,2-crypt)]3 [η4-E7M(CO)3] complexes also react with carbon monoxide at the M(CO)3 center and reversible binds CO to form [K(2,2,2-crypt)]3[η4-E7M(CO)4] complexes. These complexes are more easily protonated and undergo faster alkylations of the E7 cages than the parent [K(2,2,2-crypt)]3[η4-E7M(CO)3] compounds. Each of these structures contains an E7 fragment bound η2 to the M(C0)4 center. Products were characterized by various physical and spectroscopic techniques including UV-vis, IR, 1H, 13C, and 31P NMR spectroscopies, mass spectrometry, elemental analyses, and single crystal X-ray diffraction studies.