14221-00-2

Four new alkylnickel(II)-phosphine complexes, NiR2(PR'3)2 (R=CH3, C2H5; PR'3=triethylphosphine (PEt3), tributylphosphine (PBu3), 1,2-bis(diphenylphosphino)ethane(dpe)) and Ni(CH3)(acac)(PEtPh2) (PEtPh2=ethyldiphenylphosphine), have been prepared by reacti

Bis(acetylacetonato)nickel(II), Ni(acac)2, quenched triplet state aromatic ketones with high efficiently but only certain aromatic ketones with high triplet energy levels successfully sensitized the photoreduction of Ni(acac)2 to give the acetylacetone radical and Ni(I) complexes.A short-lived Ni(I) species was detected by ESR and UV spectroscopy, and the acetylacetonyl radical was trapped by 2-nitroso-2-methylpropane or phenyl-tert-butylnitrone as a stable nitroxide and by H atom donors as acetylacetone.The transient Ni(I) complexes decayed by either first order or second-order kinetics, depending on the concentrations, to give Ni(0) complexes or ferromagnetic colloidical nickel.The photoreduction of Ni(acac)2 occurs only if the acetylacetone radical was trapped.Various evidence suggested that the quenching mechanism was not likely to occur by energy transfer and was best interpreted to involve a partial charge transfer within an excited-state complex.The acetylacetonyl radical in the complex undergoes hydrogen abstractions from solvent in competition with reverse electron transfer.The quantum effeiciency of the photoreduction is attributed to the extent of charge-transfer contribution and the hydrogen atom donating ability of solvents.It is also confirmed that the ketyl radical derived from triplet state ketones is not responsible for the reduction of Ni(acac)2.

The activation and reduction of nickel(II) salts under conditions relevant to Ni-catalyzed borylation reactions is reported. Methanolic solutions of NiCl2·6H2O reacted with >2 equiv of (iPr)2NEt were converted to polymeric Ni(OMe)2, which was characterized by IR spectroscopy, magnetic susceptibility measurements, and verified by independent synthesis from NaOMe. When diboron reagents such as bis(neopentylglycolato) diboron (B2(npg)2) were exposed to methanolic solutions of Ni(II) salts and (iPr)2NEt, nickel metal was deposited along with the evolution of hydrogen gas. A direct relationship between yield of nickel metal and equivalents of B2(npg)2 relative to [Ni] was also observed, reaching >99% yield at 8 equiv. Ni(0) coordination complexes were also isolated when a phosphine, phosphite, and/or diene ligand was present, all starting from NiCl2·6H2O, including the following: Ni[P(OPh)3]4 (74% yield), Ni[P(OiPr)3]4 (54% yield), Ni(PPh3)4 (75% yield), (dppp)2Ni + Ni(1,5-cod)2 (dppp = 1,3-bis(diphenylphosphine)propane) (91% yield), Ni(1,5-cod)2 (1,5-cod = 1,5-cyclooctadiene) (69% yield), and (dppf)Ni(1,5-cod) (dppf = 1,1′-bis(diphenylphosphino)ferrocene) (84% yield). The high yields observed indicated the efficient reduction of Ni(II) to Ni(0) and a likely route for precatalyst entry into the Ni-borylation catalytic cycle. These in situ reduction conditions were also successfully applied to a previously developed Ni-catalyzed alpha-arylation reaction where the requisite Ni(1,5-cod)2 precatalyst was substituted for NiCl2·6H2O and catalytic diboron. Comparable yields to the original report were observed under these conditions, further demonstrating that Ni(0) active species can be efficiently accessed with diboron reagents under protic conditions from Ni(II) salt hydrates.

Tetrahedral nickel(0) complexes [NiL4], [Ni(dppe)2] and [Ni(CO)2(SbPh3)2] (L=AsPh3, SbPh3, P(OPh)3, dppe=1,2-bis(diphenylphosphino)ethane) were prepared by reduction of NiCl2·6H2O with NaBH4 under N2 or CO atmosphere in the presence of the ligand. The complex [Ni(SbPh3)4] was also obtained by electrolysis at -1.3 V (Ag/Ag+), under a platinum gauze, of the system NiCl2·6H2O/SbPh3 (molar ratio=1:4). These complexes, both in the solid state and in solution, show an orange emission at room temperature, when excited with UV radiation. A qualitative molecular orbital diagram for the [NiL4] complexes is proposed. Electronic absorption spectra of the complexes show bands near 400 nm assigned as MLCT π*2e←d2t2. A 1A1←3T1 transition is suggested for the emission observed in these systems. Lifetimes in microsecond range were estimated from time-resolved emission spectra. Spectroscopic properties of the free ligands have also been investigated.

The reactions of Ni(cod)2 (cod = 1,5-cyclooctadiene), Ni(cdt) (cdt = trans,trans,trans-1,5,9-cyclododecatriene), and Ni(C2H4)3 with N,N,N',N'-tetramethylethylenediamine (tmeda) and tetrafluoroethene in ether yield almost quantitatively yellow needles of (

Spectrophotometric measurements by IR and vis/UV on solutions containing olefins, phosphorus ligands, and nickel(0) show that competition for coordination is strongly affected by both olefin structure and the steric and electronic properties of the phosph

Oxidative addition reactions of 2- and 3-chloropyridines and of 2-chloropyrazine to tetrakis(triphenylphosphine)nickel(0) occurred in toluene at ambient temperature to afford dinuclear nickel(II) complexes containing carbon-bonded heterocycles as a ligand.They are quite stable and the bridging chloride was readily substituted by other halides and pseudohalides preserving the dinuclear structure. 8-Chloroquinoline yielded a mononuclear complex as an exception.These novel organonickel(II) complexes were characterized by analytical and molecular weight data together with IR, 1H NMR, and 13C NMR spectra.Di-μ-chloro-bis(2-pyridyl)bis(triphenylphosphine)dinickel(II) was found to be an excellent catalyst for selective cross coupling of 2-chloropyridine with methylmagnesium bromide.

Liquid poly(methylphenylsiloxanes) react at 0 deg C with Ti, V, Cr, Mo, and W atoms to give high yields of bis(η6-arene)metal complexes .The coloured complexes are very thermally stable but all are sensitive to air or moisture.Condensation of Fe, Co, or Ni atoms into the poly(methylphenylsiloxanes) at 0 deg C gives only metal slurries, although at low temperatures we observe the formation of an unstable arene-iron complex.Liquid poly(phenyl ethers) give stable bis(η6-arene)metal complexes with V or Cr atoms at 30 deg C.Polystyrene in solution in diethylene glycol dibutyl ether at -50 deg C, reacts with Cr atoms to yield a complex in which 55percent of the available phenyl groups are co-ordinated to the metal.