Indenyl-Nickel Complexes Bearing a Pendant, Hemilabile Olefin Ligand: Preparation, Characterization, and Catalytic Activities

Reactions of cyclonickelated complexes with hydroxylamines and TEMPO˙: isolation of new TEMPOH adducts of Ni(II) and their reactivities with nucleophiles and oxidants

This contribution describes a study on the reactivities of the complexes [{κP,κC-(i-Pr)2PO-Ar}Ni(μ-Br)]2, 1a-d (Ar: C6H4, a; 3-Cl-C6H3, b; 3-OMe-C6H3, c; 4-OMe-napthalenyl, d), with hydroxylamines in the presence of TEMPO˙ (TEMPO˙ = (2,2,6,6-tetramethylpiperidinyl-1-yl)oxyl). The results of this study showed that treating 1a-d with a mixture of Et2NOH and TEMPO˙ did not afford the desired oxidation-induced functionalization of the Ni-aryl moiety in 1a-d, giving instead the corresponding κO-TEMPOH adducts [{κP,κC-(i-Pr)2PO-Ar}Ni(Br)(κO-TEMPOH)], 3a-d (TEMPOH = N-hydroxy-2,2,6,6-tetramethylpiperidine). The TEMPOH moiety in these zwitterionic compounds 3 can be displaced by a large excess of acetonitrile (MeCN), 10 equiv. of morpholine, or 1-2 equivalents of imidazole. Although these reactions have given the authenticated products [{κP,κC-(i-Pr)2PO-C6H4}Ni(Br)(NCMe)], 4a, [{κP,κC-(i-Pr)2PO-C6H4}Ni(Br)(morpholine)], 5a, and [{κP,κC-(i-Pr)2PO-C6H4}Ni(imidazole)2]Br, 6a, a few other products were also detected by NMR, indicating that the observed reactivities are far more complex than simple substitution of the TEMPOH moiety. Similarly, treating 3a with AgOC(O)CF3 results in the isolation of [{κP,κC-(i-Pr)2PO-C6H4}Ni{OC(O)CF3}(κO-TEMPOH)], 7a, arising from the substitution of the bromo ligand, whereas spectroscopic evidence suggests further reactivity, possibly including displacement of TEMPOH and oxidative decomposition.

First examples of neutral and cationic indenyl nickel(II) complexes bearing arsine or stibine ligands: highly active catalysts for the oligomerisation of styrene

New indenyl nickel(ii) complexes bearing arsine or stibine ligands synthesised by a new methodology exhibit very high catalytic activities for the oligomerisation of styrene.

(Salicylaldiminato)Ni(ii)-catalysts for hydrosilylation of olefins

Olefin hydrosilylation was attained at room temperature at 0.5 mol% Ni loading by using a series of (salicylaldiminato)methylnickel complexes as catalyst precursors.

General and practical one-pot synthesis of dihydrobenzosiloles from styrenes

A one-pot synthesis of dihydrobenzosiloles from styrenes has been developed. The reaction involves the nickel-catalyzed hydrosilylation of styrene with diphenylsilane, followed by the iridium-catalyzed dehydrogenative cyclization. This method is efficient for both electron-rich and -deficient styrenes and exhibits good functional group tolerance, as well as excellent regioselectivity. The forming dihydrobenzosiloles can be efficiently converted into valuable benzosiloles or 2-hydroxyphenethyl alcohols.

Diphenyl(dipyrazolyl)methane Complexes of Ni: Synthesis, Structural Characterization, and Chromotropism of NiBr2 Derivatives

The reaction of NiBr2 with the bidentate ligand diphenyl(dipyrazolyl)methane (dpdpm) gives the pentacoordinated complexes [(dpdpm)Ni(mu-Br)Br]2 (1), [(dpdpm)NiBr2(H2O)] (2a), and [(dpdpm)NiBr(H2O)2]Br (2b), or the octahedral complexes [(dpdpm)NiBr(H2O)2(CH3CN)]Br (3), [(dpdpm)2NiBr2] (4), and [(dpdpm)2NiBr(H2O)]Br (5). All of these complexes are paramagnetic, both in the solid state and in solution, and have been characterized by spectroscopic (IR, NMR, and UV-vis-NIR) and X-ray diffraction studies. The unoccupied coordination site in the pentacoordinated compounds allows long-range interactions, in the solid state, between the Ni center and a Ph substituent of the dpdpm ligand. These weak interactions are replaced by Ni-solvent interactions, both in the solid state and in solution, facilitating the interconversion of these compounds under various reaction conditions and leading to interesting solvato-, vapo-, and thermochromic properties. UV-vis-NIR spectroscopy has been used to study these phenomena. Absorption spectra for the room-temperature methanol or acetonitrile solutions of the pentacoordinate or octahedral compounds show three main bands in the region of 350-1000 nm that represent spin-allowed (d-d) transitions from the ground state 3A2g to the excited states 3T2g, 3T1g(3F), and 3T1g(3P). A weak shoulder was also detected on the middle peak in most spectra (700-800 nm), representing the spin-forbidden 3A2g-->1Eg transition. On the other hand, the spectra of high-temperature CH2Cl2 or acetone solutions of all complexes show four main bands at ca. 490, 650-660, 860, and 1000 nm, in addition to a shoulder on the first or second band.

New palladium(II)-(eta(3/5)- or eta1-indenyl) and dipalladium(I)-(mu,eta3-indenyl) complexes

Reaction of the dimeric species [(eta3-Ind)Pd(mu-Cl)]2 (1) (Ind = indenyl) with NEt3 gives the complex (eta(3-5)-Ind)Pd(NEt3)Cl (3), whereas the analogous reactions with BnNH2 (Bn = PhCH2) or pyridine (py) afford the complexes trans-L2Pd(eta1-Ind)Cl (L = BnNH2 (4), py (5)). Similarly, the one-pot reaction of 1 with a mixture of BnNH2 and the phosphine ligands PR3 gives the mixed-ligand, amino and phosphine species (PR3)(BnNH2)Pd(eta1-Ind)Cl (R = Cy (6a), Ph (6b)); the latter complexes can also be prepared by addition of BnNH2 to (eta(3-5)-Ind)Pd(PR3)Cl (R = Cy (2a), Ph (2b)). Complexes 6 undergo a gradual decomposition in solution to generate the dinuclear Pd(I) compounds (mu,eta3-Ind)(mu-Cl)Pd2(PR3)2 (R = Cy (7a), Ph (7b)) and the Pd(II) compounds (BnNH2)(PR3)PdCl2 (R = Cy (8a), Ph (8b)), along with 1,1'-biindene. The formation of 7 is proposed to proceed by a comproportionation reaction between in situ-generated Pd(II) and Pd0 intermediates. Interestingly, the reverse of this reaction, disproportionation, also occurs spontaneously to give 2. All new compounds have been characterized by NMR spectroscopy and, in the case of 3, 4, 5, 6a, 7a, 7b, and 8a, by X-ray crystallography.

The First Cyclopentadienylalkylphosphane Nickel Chelates: Synthesis, Structures, and Reactions

The first cyclopentadienylalkylphosphane nickel chelate complexes are reported. The anionic ligand obtained by reaction of spiro[2.4]hepta-4,6-diene with lithium di-tert-butylphosphide was treated with NiCl2 to yield [eta(5):kappa(1)-(di-tert-butylphosphanylethyl)cyclopentadienyl]chloronickel(II). From this complex, some acetonitrile-stabilized cationic complexes were obtained by reaction with the respective silver salts in acetonitrile. Methyl- and alkynylnickel chelates were prepared by reaction of the chloronickel complex with methyllithium and by copper-mediated coupling with terminal alkynes, respectively. Some of the complexes prepared were investigated by X-ray crystallography or cyclic voltammetry. The alkynylnickel chelates undergo cycloaddition reactions with ethoxycarbonylisothiocyanate or tetracyanoethylene, and the cyclobutenes obtained undergo ring opening to the corresponding dienes. The study includes an NMR spectroscopic investigation of the two conformers of one of these dienes.

Oligomerization and regioselective hydrosilylation of styrenes catalyzed by cationic allyl nickel complexes bearing allylphosphine ligands

The complexes [Ni(eta(3)-CH(2)CHCH(2))Br(kappa(1)P-PR(2)CH(2)CH=CH(2))] (R = Ph 1, (i)Pr2 ) and [Ni(eta(3)-CH(2)C(R')CH(2))(kappa(1)P-PR(2)CH(2)CH=CH(2))(2)][BAr'(4)] (R' = H, R = Ph 4a, R = (i)Pr 4b; R' = CH(3), R = Ph 5a, R = (i)Pr 5b; Ar' = 3,5-C(6)H(3)(CF(3))(2)) have been prepared and characterized. The X-ray crystal structures of 1, 2 and 5b have been determined. 4a-b and 5a-b are catalyst precursors for the oligomerization of RC(6)H(4)CH=CH(2) to oligostyrene (R = H) or oligo(4-methylstyrene) (R = CH(3)) respectively, without the need of a co-catalyst such as methylalumoxane. The catalytic activities range from moderate to high. The oligomerization reactions are carried out in the temperature interval 25-40 degrees C in 1,2-dichloroethane, using an olefin/catalyst ratio equal to 200, yielding oligostyrenes with a high isotactic fraction content P(m), with M(n) in the range 700-1900 Dalton, and polydispersities between 1.22 and 1.64. The cationic complexes 4a-b and 5a-b are also effective catalyst precursors for the hydrosilylation reactions of styrene or 4-methylstyrene with PhSiH(3) in 1,2-dichloroethane at 40 degrees C using an olefin/catalyst ratio equal to 100, leading selectively to RC(6)H(4)CH(SiH(2)Ph)CH(3) (R = H, CH(3)) in 50-79% yield.

New pincer-type diphosphinito (POCOP) complexes of NiII and NiIII

This communication reports the synthesis and characterization of the new, pincer-type, square-planar, 16-electron compounds {2,6-(OPPr(i)(2))(2)C(6)H(3)}Ni(II)Br, 1, and {(Pr(i)(2)POCH(2))(2)CH}Ni(II)Br, 2, and the square-pyramidal, 17-electron complex {(Pr(i)(2)POCH(2))(2)CH}Ni(III)Br(2), 3.