Synthesis and chemistry of bis(triisopropylphosphine) nickel(i) and nickel(0) precursors

Abstract

High yield syntheses of ((i)Pr(3)P)(2)NiX (3a-c), (where X = Cl, Br, I) were established by comproportionation of ((i)Pr(3)P)(2)NiX(2) (1a-c) with ((i)Pr(3)P)(2)Ni(η(2)-C(2)H(4)) (2). Reaction of 1a with either NaH or LiHBEt(3) provided ((i)Pr(3)P)(2)NiHCl (4), along with 3a as a side-product. Reduction of ((i)Pr(3)P)(2)NiCl (3a-c) with Mg in presence of nitrogen saturated THF solutions provided the dinitrogen complex [((i)Pr(3)P)(2)Ni](2)(μ-η(1):η(1)-N(2)) (5). In aromatic solvents such as benzene and toluene a thermal equilibrium exists between 5 and the previously reported monophosphine solvent adducts ((i)Pr(3)P)Ni(η(6)-arene) (6a,b). Reaction of 5 with carbon dioxide provided ((i)Pr(3)P)(2)Ni(η(2)-CO(2)) (7). Thermolysis of 9 at 60 °C provided a mixture of products that included the reduction product ((i)Pr(3)P)(2)Ni(CO)(2) (8) along with (i)Pr(3)P=O, as identified by NMR spectroscopy. Complex 8 was also prepared in high yield from the reaction of 5 with CO. Reaction of 5 with CS(2) gave the dimeric carbon disulfide complex [((i)Pr(3)P)Ni(μ-η(1):η(2)-CS(2))](2) (9). Diphenylphosphine reacts with 5 to form the dinuclear Ni(I) complex [((i)Pr(3)P)Ni(μ(2)-PPh(2))](2) (10). Complex 5 reacts with PhSH to form ((i)Pr(3)P)(2)Ni(SPh)(H) (11), which slowly loses H(2) and (i)Pr(3)P to form the dimeric Ni(I) complex [((i)Pr(3)P)Ni(μ(2)-SPh)](2) (12) at room temperature. Complex 12 was also accessed by salt metathesis from the reaction of ((i)Pr(3)P)(2)NiCl (3a) with PhSLi, which demonstrates the utility of 3a as a Ni(I) precursor. With the exception of 6a,b, all compounds were structurally characterized by single-crystal X-ray crystallography.

Mechanistic insight into carbon–fluorine cleavage with a ( Pr3P)2Ni source: Characterization of ( Pr3P)2NiC6F5 as a significant Ni(I) byproduct in the activation of C6F6

“…The 31 P{ 1 H} NMR of the products in pentane showed a doublet for 2 at d 28.1 (d, 2 J PF = 40 Hz), but no observable resonance for 3, as anticipated given the proximity of the phosphine to the metal-centered radical. The 1 H NMR spectrum has sharp peaks for 2 at the typical expected diamagnetic values of d 1.18 and 1.70 for the isopropyl group, whereas broad peaks were observed for 3 at d 4.8 and 11.1 in a 6:1 ratio, and comparable to the 1 H NMR spectra for the isopropyl substituents of other paramagnetic ( i Pr 3 P) 2 NiX species (where X = Cl, Br and I) [16]. The 19 F{ 1 H} NMR spectra revealed three resonances for 2 at d À109.1, À160.7, and À163.6 corresponding to two ortho-fluorines, para-fluorine, and two meta-fluorines, respectively.…”

“…The relative NMR yields of 2 and 3 are 49% and 22%, which is suggestive of a third Ni species being made in the reaction in equal amounts to 3, to account for all the Ni, but all attempts to identify this product have failed. Although ( i Pr 3 P) 2 NiF might be expected as a concomitant product with 3, no species with sufficient intensity peaks was observed in the solution spectra, and no precipitate was observed; it is notable that although ( i Pr 3 P) 2 NiX species (where X = Cl, Br, and I) all give similar paramagnetically shifted 1 H NMR spectra, previous attempts to prepare ( i Pr 3 P) 2 NiF as well as trans-( i Pr 3 P) 2 NiF 2 failed [16].…”

“…(14); Ni(1)-P(2), 2.2521 (14); Ni(1)-C(1), 1.888 (5); F(2)-C(2), 1.360 (6); F(3)-C(3), 1.354 (5); F(4)-C(4), 1.352 (5); F(5)-C(5), 1.345 (6); F(6)-C(6), 1.371 (5). Selected bond angles (°): P(1)-Ni(1)-P(2), 165.57 (5); C(1)-Ni(1)-F(1), 177.73 (16). (b) ORTEP of the solid-state molecular structure of 3 as determined by X-ray crystallography.…”

“…Hexafluorobenzene, pentafluorobenzene, and all isomers of tetrafluorobenzene and trifluorobenzene were purchased from Aldrich and used as received. Compound 1 and [( i Pr 3 P) 2 Ni] 2 N 2 were prepared as described in the literature [14,16].…”

When Weaker Can Be Tougher: The Role of Oxidation State (I) in P- vs N-Ligand-Derived Ni-Catalyzed Trifluoromethylthiolation of Aryl Halides

“…29 The formation of [(dppf)Ni II X 2 ] as an intermediate was also unambiguously confirmed through its isolation (in addition to Ni I ) and characterization (via 1 H NMR and X-ray crystallography) from the reaction of Ni 0 and PhI in benzene. 30 Our computational data indicate that the ligand exchange step from [(dppf)Ni II (X)(Ph)] to [(dppf)Ni II X 2 ] and [(dppf)Ni II (Ph) 2 ] is favorable, being exergonic for all halides (Δ G = −7.5, −5.9, and −3.3 kcal/mol for X = Cl, Br, I, respectively; see Figure 5).…”