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 (d_Ni–Ni = 3.397(1) Å) in contrast to the two-electron oxidation product, Ni₂(CO)₄(μ-PPh₂)₂ (1) (d_Ni–Ni = 2.510(2) Å). 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 (d_Ni–Ni = 2.4930(9) Å).