Mono- and dinuclear Ni(I) products formed upon bromide abstraction from the Ni(I) ring-expanded NHC complex [Ni(6-Mes)(PPh3)Br]

Bromide abstraction from the three-coordinate Ni(I) ring-expanded N-heterocyclic carbene complex [Ni(6-Mes)(PPh3)Br] (1; 6-Mes = 1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) with TlPF6 in THF yields the T-shaped cationic solvent complex, [Ni(6-Mes)(PPh3)(THF)][PF6] (2), whereas treatment with NaBAr4F in Et2O affords the dimeric Ni(I) product, [{Ni(6-Mes)(PPh3)}(2)(mu-Br)][BAr4F] (3). Both 2 and 3 act as latent sources of the cation [Ni(6-Mes)(PPh3)](+), which can be trapped by CO to give [Ni(6-Mes)(PPh3)(CO)](+) (5). Addition of [(Et3Si)(2)(mu-H)][B(C6F5)(4)] to 1 followed by work up in toluene results in the elimination of phosphine as well as halide to afford a co-crystallised mixture of [Ni(6-Mes)(eta(2)-C6H5Me)][B (C6F5)(4)] (4), and [6MesH center dot center dot center dot C6H5Me][B(C6F5)(4)]. Treatment of 1 with sodium salts of more strongly coordinating anions leads to substitution products. Thus, NaBH4 yields the neutral, diamagnetic dimer [{Ni(6-Mes)} (2)(BH4)(2)] (6), whereas NaBH3(CN) gives the paramagnetic monomeric cyanotrihydroborate complex [Ni(6-Mes)(PPh3)(NCBH3)] (7). Treatment of 1 with (NaOBu)-Bu-t/NHPh2 affords the three-coordinate Ni(I) amido species, [Ni(6-Mes)(PPh3)(NPh2)] (8). The electronic structures of 2, 5, 7 and 8 have been analysed in comparison to that of previously reported 1 using a combination of EPR spectroscopy and density functional theory.