Dinickel mixed-valent

A mixed-valent dinickel monohydride 49 was found to react with bases ( BuOK, LiN(SiMe3)j) to produce dinickel(I) compounds 50 and 51, both of which feature a Ni(I)-Ni(I) bond (Scheme 10.21) [22]. Complex 50 features a triangular Ni P core with Ni(I)-Ni(I) bond length of 2.515(1) A (Entry 21, Table 10.2) while 51 features a fused Ni PC and NiPC bicyclic core, with a significantly shorter Ni(I)-Ni(I) bond (2.408(2) A) (Entry 22, Table 10.2) in comparison with that in 50. These reactions involve sequences of deprotonation, C-H/C-P bond activation, and C-H bond formation, although the mechanism is still ambiguous. 

Related dinickel(II) p-N bridging compounds with NHC ligands were reported by Hillhouse et al. in 2009 (Scheme 10.31) [40]. [Ni(I)(p-Cl)(l Pr)]2 underwent one-electron oxidation by MesNj to afford a dinickel(II) bridging imide [ Ni(ll)(l Pr)(Cl) 2(p-NMes)] 66, in which one of the chlorides can be abstracted by NaBAr, to produce the dinickel(ll) ion pair compound 67. The Ni(ll)-Ni(ll) bond lengths in 66 and 67 are 2.5767(15) and 2.2911(8) A, respectively (Entries 5 and 6, Table 10.3). Complex 66 can also undergo one-electron reduction of the [(Ni(ll)Cl 2(p-NMes)] core, to afford a mixed-valent Ni(I)-Ni(II) compound 68, which upon treating with a one-electron oxidant gives 67 as the product. It is noteworthy that 67 and 68 bear similar core structures, but the Ni-Ni bond... 

Scheme 10.31 Formation and interconversion of dinickel(ll) compounds 66 and 67, via a mixed-valent Ni(l)-Ni(ll) compound 68.

In this section, advancements on mixed-valent dinickel compounds which were made in... 

Scheme 10.37 Synthesis of a mixed-valent dinickel compound 82 with bridging COj and CO.

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