Accessing the Cp^ArNi(I) Synthon: Reactions with N-Heterocyclic Carbenes, TEMPO, Sulfur, and Selenium

Abstract

A reactive "Cp Ar Ni I " surrogate (Cp Ar = C 5 (C 6 H 4 -4-Et) 5 ) is accessible via the reduction of the dimer [Cp Ar Ni(μ-Br)] 2 with two equivalents of KC 8 . A trapping reaction with TEMPO afforded the new nickel(II) complex [Cp Ar Ni(η 2 -TEMPO)] (3), while the addition of N-heterocyclic carbenes gave the new nickel(I) radicals [Cp Ar Ni(IPr)] (4a, IPr = 1,3bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and [Cp Ar Ni(IiPr 2 Me 2 )] (4b, IiPr 2 Me 2 = 1,3-diisopropyl-4,5-dimethylimidazol-2ylidene). EPR spectra supported by DFT calculations on 4a and 4b indicate that the spin density mainly resides at the nickel center. The reaction of the "Cp Ar Ni(I) source" with yellow sulfur gave the Ni 2 S 6 complex [(Cp Ar Ni) 2 (μ-S 6 )] (5); the "subselenide" [(Cp Ar Ni) 2 (μ-Se 2 )] ( 6) was formed in the analogous reaction with grey selenium. All new complexes were characterized by NMR, EPR, and UV−vis spectroscopy; their molecular structures were determined by X-ray crystallography.

Functionalization of Pentaphosphorus Cations by Complexation

“…These reactions presumably involve a disproportionation of the metal(II) precursors to metal(I) and metal(III) compounds, which is induced by phosphorus ligand coordination, explaining the lower than expected yield. However, 2‐R [GaCl 4 ] and 3‐R [GaCl 4 ] can be formed in good to high yield (55–85 %) by reacting [P 5 R 2 ][GaCl 4 ] salts directly with the cobalt(I) and nickel(I) compounds, that is, [Cp Ar Co(cod)] (1 equiv, cod=1,5‐cyclooctadiene) and the transient “Cp Ar Ni I ” (2 equiv, generated from [Cp Ar Ni(μ‐Br)] 2 and KC 8 ; Scheme ) …”

“…[28i] Reactions of [P 5 R 2 ][GaCl 4 ](R= iPr and Cy) with [Cp Ar M-(m-Br)] 2 (M = Co,1 equiv;M = Ni, 2equiv) [25] [30] and the transient "Cp Ar Ni I "( 2equiv, generated from [Cp Ar Ni(m-Br)] 2 and KC 8 ;Scheme 2). [31] Single crystals of 2-R[GaCl 4 ]( R= iPr and Cy;d ark red blocks) and 3-iPr[GaCl 4 ]( pink-violet blocks) were obtained from THF/n-hexane at À35 8 8Ca nd analyzed by X-ray crystallography ( Figure 3). Thep entaphosphorus ligand is h 4 -coordinated to the metal, resulting in an envelope conformation of the P 5 fragment in 2-R[GaCl 4 ].…”

Functionalization of Pentaphosphorus Cations by Complexation

“…to those of 2-R[GaCl 4 ] 31. For 2-R[GaCl 4 ], the data are similar to those of related a-diimine complexes (IV inFigure 1) 31. Thes pectral parameters were determined by an iterative fitting procedure in each case (see the Supporting Information for details).…”

“…to those of 2-R[GaCl 4 ] 31. P{ 1 H} NMR spectra of 2-R[GaCl 4 ]i nC6 D 6 show three multiplets of an AMM'XX' spin system in agreement with ap ersistent, symmetrical P 5 R 2 ligand.…”

“…Thefluxional behavior of the Ni complexes is another notable aspect, which was observed by variable temperature (VT) 31 Thefluxional behavior of the Ni complexes is another notable aspect, which was observed by variable temperature (VT) 31 …”