The Coordination Chemistry of “[BP₃]NiX” Platforms:  Targeting Low-Valent Nickel Sources as Promising Candidates to L₃NiE and L₃Ni⋮E Linkages

Abstract

A series of divalent, monovalent, and zerovalent nickel complexes supported by the electron-releasing, monoanionic tris(phosphino)borate ligands [PhBP3] and [PhBPiPr 3] ([PhBP3] = [PhB(CH2PPh2)3]-, [PhBPiPr 3] = [PhB(CH2PiPr2)3]-) have been synthesized to explore fundamental aspects of their coordination chemistry. The pseudotetrahedral, divalent halide complexes [PhBP3]NiCl (1), [PhBP3]NiI (2), and [PhBPiPr 3]NiCl (3) were prepared by the metalation of [PhBP3]Tl or [PhBPiPr 3]Tl with (Ph3P)2NiCl2, NiI2, and (DME)NiCl2 (DME = 1,2-dimethoxyethane), respectively. Complex 1 is a versatile precursor to a series of complexes accessible via substitution reactions including [PhBP3]Ni(N3) (4), [PhBP3]Ni(OSiPh3) (5), [PhBP3]Ni(O-p- t Bu-Ph) (6), and [PhBP3]Ni(S-p- t Bu-Ph) (7). Complexes 2−5 and 7 have been characterized by X-ray diffraction (XRD) and are pseudotetrahedral monomers in the solid state. Complex 1 reacts readily with oxygen to form the four-electron-oxidation product, {[PhB(CH2P(O)Ph2)2(CH2PPh2)]NiCl} (8A or 8B), which features a solid-state structure that is dependent on its method of crystallization. Chemical reduction of 1 using Na/Hg or other potential 1-electron reductants generates a product that arises from partial ligand degradation, [PhBP3]Ni(η2-CH2PPh2) (9). The more sterically hindered chloride 3 reacts with Li(dbabh) (Hdbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene) to provide the three-coordinate complex [κ2-PhBPiPr 3]Ni(dbabh) (11), also characterized by XRD. Chemical reduction of complex 1 in the presence of L-type donors produces the tetrahedral Ni(I) complexes [PhBP3]Ni(PPh3) (12) and [PhBP3]Ni(CN t Bu) (13). Reduction of 3 following the addition of PMe3 or tert-butyl isocyanide affords the Ni(I) complexes [PhBPiPr 3]Ni(PMe3) (14) and [PhBPiPr 3]Ni(CN t Bu) (15), respectively. The reactivity of these [PhBP3]NiIL and [PhBPiPr 3]NiIL complexes with respect to oxidative group transfer reactions from organic azides and diazoalkanes is discussed. The zerovalent nitrosyl complex [PhBP3]Ni(NO) (16) is prepared by the reaction of 1 with excess NO or by treating 12 with stoichiometric NO. The anionic Ni(0) complexes [[κ2-PhBP3]Ni(CO)2][ n Bu4N] (17) and [[κ2-PhBPiPr 3]Ni(CO)2][ASN] (18) (ASN = 5-azoniaspiro[4.4]nonane) have been prepared by reacting [PhBP3]Tl or [PhBPiPr 3]Tl with (Ph3P)2Ni(CO)2 in the presence of R4NBr. The photolysis of 17 appears to generate a new species consistent with a zerovalent monocarbonyl complex which we tentatively assign as {[PhBP3]Ni(CO)}{ n Bu4N}, although complete characterization of this complex has been difficult. Finally, theoretical DFT calculations are presented for the hypothetical low spin complexes [PhBP3]Ni(N t Bu), [PhBPiPr 3]Ni(N t Bu), [PhBPiPr 3]Ni(NMe), and [PhBPiPr 3]Ni(N) to consider what role electronic structure factors might play with respect to the relative stability of these species.

Coordination chemistry of the main group elements with phosphine, arsine and stibine ligands

“…The complex is unstable in air and has limited thermal stability, but is an effective ligand transfer reagent for the synthesis of some d-block metal-PNP complexes. Peters and co-workers have prepared several Tl(I) complexes with phosphinoborates [247][248][249][250][251][252]. The diphosphinoborates include [Tl{Ph 2 B(CH 2 PPh 2 ) 2 }] (chain polymer with thallium coordinated 6 to one Ph ring and one -PPh 2 from each of two [Ph 2 B(CH 2 PPh 2 ) 2 ] − ligands) and [Tl{3-MeC 6 H 4 ) 2 B(CH 2 P t Bu 2 ) 2 }] in which the ligand chelates via the two phosphine groups and forms an interaction best described as 2 with the arene ring of another ligand.…”

Beyond Triphos – New hinges for a classical chelating ligand

“…A detailed analysis of bonding motifs via spectroscopic and/or computational studies will not be explicitly explained for every complex, despite this being the focus of many of the primary reports [13][14][15]. On the other hand, interesting spin-states and/or geometries will be mentioned as these characteristics often lead to, or influence, the observed reactivity.…”

“…Ph )], which has two short Sn-P bonds (2.6746 (14) and 2.690(2) Å) and one long bond (3.036(2) Å) which sits beyond the standard covalent bonding distance for tin and phosphorus. The first iridium complexes featuring ligand 1 were reported in 1999, and initial investigations were focused on the activation of silanes [16b].…”

“…Iron [17], cobalt [25] and nickel [14] complexes featuring ligands 1-4 have been studied extensively, and display many common coordination motifs. In general (κ 3 -PhBP 3 R )M=E and (κ 3 -PhBP 3 R )M E (M = Fe, Co, Ni; E = π-basic ligands such as O 2-, NR 2-and N 3-) structures were targeted, as prior to this, ligands coordinated with formally double or triple bonds to late first row transition metals were rarely observed [25].…”

“…Initially, pseudo-tetrahedral halide complexes of general formula (PhBP 3 R )M-X (R = Ph, i Pr, CH 2 Cy, mter; M = Fe, Co, Ni; X = Cl, Br, I) were synthesized as a convenient way to access the "M(PhBP 3 R )" fragment (25-38, Scheme 4) [13,14,[17][18][19]28]. In general these complexes were obtained in high yields (>83%) except for [CoCl(κ 3 -PhBP 3…”