Synthesis, Characterization, and Reactivity of Nickel Hydride Complexes Containing 2,6-C₆H₃(CH₂PR₂)₂(R =tBu,cHex, andiPr) Pincer Ligands

Abstract

The syntheses and full characterization of nickel hydrides containing the PCP "pincer"-type ligand, where PCP = 2,6-C(6)H(3)(CH(2)PR(2))(2) (R = tBu, cHex, and iPr), are reported. These Ni-H complexes are prepared by the conversion of ((R)PCP)NiCl precursors into the corresponding nickel hydrides by use of appropriate hydride donors. Surprisingly, although the ((R)PCP)NiCl precursors are quite similar chemically, the conversions to the hydrides were not straightforward and required different hydride reagents to provide analytically pure products. While NaBH(4) was effective in the preparation of pure ((tBu)PCP)NiH, Super-Hydride solution (LiEt(3)BH in THF) was required to prepare either ((cHex)PCP)NiH or ((iPr)PCP)NiH. Attempts to prepare a Ni-H from ((Ph)PCP)NiCl with a variety of hydride reagents yielded only the free ligand as an identifiable product. Two of the derivatives, tBu and cHex, have also been subjected to single crystal X-ray analysis. The solid-state structures each showed a classic, near-square planar arrangement for Ni in which the PCP ligand occupied three meridional ligand points with the Ni-H trans to the Ni-C bond. The resulting Ni-H bond lengths were 1.42(3) and 1.55(2) A for the tBu and cHex derivatives, respectively.

Synthesis and Reactivity of Nickel and Palladium Fluoride Complexes with PCP Pincer Ligands. NMR-Based Assessment of Electron-Donating Properties of Fluoride and Other Monoanionic Ligands

“…17 In our hands, the reaction of [( iPr PCP)Ni-Br] with LiBHEt 3 (Super-Hydride) was clean and essentially complete, but the purification of the hydride from the boron byproducts was problematic, leading to erratic isolated yields. Alternatively, this compound can be prepared by reacting [( iPr PCP)Ni-OMe] with triethoxysilane.…”

“…15 Several pincer derivatives of nickel have also been prepared by direct metalation, 16 including the chloro derivative [( iPr PCP)Ni-Cl]. 17 This method can be regarded as being more practical than those based on oxidative addition methods, because it does not require the previous synthesis of organometallic precursors. Hence, we developed a new synthesis of [( iPr PCP)Ni-Br] involving direct reaction of ( iPr PCP)H and NiBr 2 (dme), using triethylamine to neutralize the resulting HBr.…”

Nickel Hydrides Supported by a Non-Innocent Diphosphine Arene Pincer: Mechanistic Studies of Nickel−Arene H-Migration and Partial Arene Hydrogenation

“…Treatment of Ni(0) diphosphine 1 with one equivalent of HCl/Et 2 O (Scheme 1) generates a new species that displays a triplet at −29.0 ppm ( J PH = 79 Hz) in the 1 H NMR spectrum and a doublet in the 31 P NMR spectrum, consistent with formation of a nickel hydride complex with two equivalent phosphines 5,8,11,21–24. Two singlets are observed in the 1 H NMR spectrum corresponding to the central ring, supporting a C s -symmetric structure ( 2 ).…”

Acid–Base Interaction between Transition‐Metal Hydrides: Dihydrogen Bonding and Dihydrogen Evolution

“…[1] The simultaneous presence of both types of bonds was also observed. [6] To further investigate this unconventional acid-base interaction, we report herein on the reaction of the stable electron-rich nickel(II) pincer hydride [( tBu PCP)Ni(H)] (1) ( tBu PCP = 2,6-C 6 H 3 (CH 2 PtBu 2 ) 2 ) [7] with the acidic tungsten(II) complex [CpW(H)(CO) 3 ] (2). [5] However, DHB interactions where transition metal hydride complexes serve as both proton acceptor and proton donor in a hydrogen bond have not been described to date, although dihydrogen evolution was observed when "hydridic" and "acidic" hydride complexes such as [OsH 2 (PMePh 2 ) 4 ]/[CpM(H)(CO) 3 ] system (Cp = h 5 -C 5 H 5 À , M = Mo, W) were allowed to react.…”