Syntheses and Reactivities of New PC_sp3P Pincer Complexes of Nickel

Abstract

Heating Ni(II) halides with 1 equiv of Bu t 2 P(CH 2 ) 5 PBu t 2 gives the PC sp3 P pincer complexes [{(Bu t 2 P-(CH 2 ) 2 ) 2 CH}NiX] (X ) Cl, 1a; Br, 1b; I, 1c). These compounds react with MeMgCl or n-BuLi to give, respectively, the methyl species {(Bu t 2 P(CH 2 ) 2 ) 2 CH}NiMe, 2, or the hydride species {(Bu t 2 P(CH 2 ) 2 ) 2 -CH}NiH, 3, while reaction with NaBPh 4 in a mixture of benzene/acetonitrile gives the cationic species [{(Bu t 2 P(CH 2 ) 2 ) 2 CH}Ni (NtCCH 3 )][BPh 4 ], 4. Complexes 1-3 are inert toward olefins, but react with PhSiH 3 to give (PhSiH) n . The cationic complex 4 is also inert toward most olefins, but its reaction with excess acrylonitrile results in displacement of coordinated acetonitrile to give [{(Bu t 2 P(CH 2 ) 2 ) 2 CH}Ni-(NtCCHdCH 2 )][BPh 4 ], 5. Complexes 1-5 have been characterized by NMR spectroscopy and, in the case of 1, 4, and 5, by X-ray crystallography.

Nickel(II) and Palladium(II) Bis-Aminophosphine Pincer Complexes

“…A similar zwitterionic by-product was observed by Zargarian and co-workers in their efforts to isolate Ni-pincer complexes incorporating tBu 2 P(CH 2 ) 5 PtBu 2 . 35 In this case, further protonation gave the salt [(tBu 2 PH(CH 2 ) 2 ) 2 CH 2 ]- [NiCl 4 ].…”

Ammonia Activation by a Nickel NCN‐Pincer Complex featuring a Non‐Innocent N‐Heterocyclic Carbene: Ammine and Amido Complexes in Equilibrium

“…The crystal structure confirmed the distorted tetrahedral geometry of the N2CH carbon on the NCN pincer complex, with the sum of the bond angles formed by the heavier elements at C1 measuring 332.5º (Figure 1). With 1.848(5) Å, the C1-Ni1 bond is short when compared to similar bonds in nickel(II) pincer complexes featuring dialkylmethyl 16 or diarylmethyl 11 central platforms (av. Ni-C 1.98(2) and 1.986(3) Å, respectively).…”

Catalytic Reactivities of Indenyl–nickel, Indenyl–palladium, and PCsp3P–nickel Complexes

“…Oligomerization of PhSiH 3 and its addition to styrene. Our preliminary investigations of the reactivities of our PC sp3 P-Ni compounds showed that complexes ((tBu) 2 P(CH 2 ) 2 CH(CH 2 ) 2 P(t-Bu) 2 )NiX (X = Cl, Br, I, Me, H) [27] can catalyze the oligomerization of PhSiH 3 . For example, the reaction of excess PhSiH 3 (50-100 equivalents) with these complexes (ca.…”

“…Dry, oxygen-free solvents were employed throughout. The Ni and Pd organometallic complexes used in our studies as pre-catalysts have been prepared according to published procedures given in [15] (Ni complexes bearing amine-and olefin-functionalized Ind ligands), [20] (Ni-Ind complexes bearing SiMe 3 substituents), [21] (Pd-Ind complexes), and [27] (PC sp3 P-Ni complexes). PhSiH 3 was prepared from PhSiCl 3 and LiAlH 4 according to a published procedure [31].…”

“…The catalyzed addition of amines to double bonds is thus of great importance since it constitutes an atom-efficient route to amines (i.e., no by-products such as salts or water are formed). Since a number of sterically hindered group 10 metals bearing tridentate PCP, PPP or PNP ligands have proven to be active catalysts for this reaction [24,29], we decided to evaluate the catalytic potential of the cationic derivative [PC sp3 P-Ni(acrylonitrile)] + [27] for the hydroamination of acrylonitrile. We chose aniline as the amine substrate because the weak nucleophilicity of this amine should prevent its possible competition with the olefin for coordination to the metal centre, which is an important step in the proposed mechanism for the hydroamination reaction [30].…”