Two new bimetallic phosphido carbonyl complexes of nickel(0): [Ni2(CO)2(PPh3)2(μ-CO)(μ-PPh2)]− and [Ni2(CO)4(μ-PPh2)2]2−

Abstract

Toluene solutions of Ni(CO)2(PPh3)2 react with excess potassium metal to give the [Ni2(CO)4(μ-PPh2)2]2− ion (2) which contains two tetrahedral Ni centers fused along a common edge. Each Ni achieves an 18 electron configuration without the formation of a Ni–Ni bond (dNi–Ni = 3.397(1) A) in contrast to the two-electron oxidation product, Ni2(CO)4(μ-PPh2)2 (1) (dNi–Ni = 2.510(2) A). The anion 2 shows a reversible oxidation at −1.5 V and a quasi-reversible oxidation at −1.1 V vs. FeCp2/FeCp2+. The negative ion electrospray mass spectrum of 2 shows the one-electron oxidation product of 2, [Ni2(CO)4(μ-PPh2)2]−, along with three decarbonylation products [Ni2(CO)3(μ-PPh2)2]−, [Ni2(CO)2(μ-PPh2)2]−, and [Ni2(CO)(μ-PPh2)2]− where [Ni2(CO)3(μ-PPh2)2]− is the base peak. Ethylenediamine solutions of Sn94− react with Ni(CO)2(PPh3)2 in the presence of 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) to reproducibly give [Ni2(CO)2(PPh3)2(μ-CO)(μ-PPh2)]− (3), as one of three products. The anion 3 also has an edge-shared bitetrahedral geometry but, unlike 2, possesses a Ni–Ni bond (dNi–Ni = 2.4930(9) A).