Complexes with Hybrid Phosphorus-NHC Ligands: Pincer-Type Ir Hydrides, Dinuclear Ag and Ir and Tetranuclear Cu and Ag Complexes

Abstract

Three types of hybrid phosphorus-imidazolium salts, 1-methyl-3-(3-((diphenylphosphino)methyl)benzyl)-1H-imidazol-3-ium hexafluorophosphate (2·PF6), 1-methyl-3-(3-(di-tert-butylphosphinooxy)phenyl)imidazolium iodide (8a), and 3-(3-((diphenylphosphoryl)methyl)phenyl)-1-methyl-1H-imidazol-3-ium iodide (11) have been prepared and used as precursors to phosphine-NHC, phosphinite-NHC, and phosphoryl-NHC metal complexes, respectively. The structure of 11 has been determined by X-ray diffraction. The Ag(I) and Ir(I) complexes of the phosphine-NHC ligand, [Ag(μ-P-NHC,κC,κP)]2(PF6)2 (3) and [Ir(cod)(μ-P-NHC,κC,κP)]2(PF6)2 (4), were obtained and characterized by NMR, ESI-MS, elemental analysis, and X-ray diffraction. Both complexes are dinuclear and dicationic, with two P-NHC ligands bridging the two metal centers. The presence of the P donor led for 3 to an unprecedented structure compared to that of related Ag(I) complexes with trans spanning bis-NHC ligands. Complex 4 is the first example of a dinuclear iridium complex with a hybrid P-NHC ligand. The new hydrido, Ir(III) pincer-type complex [IrH(CNHCCCNHC)(MeCN)]PF6 (7) is suggested to have a square-pyramidal structure. The tetranuclear Ag(I) complex with the phosphinite-NHC ligand, [Ag2(μ3-I)(μ-PO-NHC,κP,κCNHC)]2 (9a) has a cubane-type structure, with alternating silver and iodine apexes and two PO-NHC ligands bridging opposite edges of the Ag4 tetrahedron. The Ir(III) pincer complexes [IrH(I)(PO-NHC,κP,κC,κCNHC)(Me)] (10a) and [IrH(I)(PO-NHC,κP,κC,κCNHC)(n-Bu)] (10b), with Me or n-Bu substituents on the nitrogen atom, respectively, have been prepared and characterized. Ag(I) and Cu(I) complexes with the phosphoryl-NHC ligand are reported and the centrosymmetric structure of the latter, [Cu(OP-NHC,κCNHC)2(μ-I){Cu(μ-I)}]2 (13), was established by X-ray diffraction and consists of a central Cu2(μ-I)2 rhombus connected by single iodide bridges to two Cu(OP-NHC,κCNHC)2 moieties. The Ir(III) hydride pincer complexes 10a,b were tested as catalyst precursors for the C-H bond activation of alkanes. Although their efficiency was significantly lower for transfer dehydrogenation from cyclooctane (coa) to t-butylethylene (tbe) than that of known PCP-Ir systems, these results represent the first attempts to study the catalytic properties of hybrid P-NHC iridium pincer complexes.

Mono- and dimeric complexes of an asymmetric heterotopic P,CNHC,pyr ligand

“…Repeated efforts to improve the yield were unsuccessful with only small amounts of crystalline material being acquired from any given synthesis. The 31 P{ 1 H} spectrum 15 of the complex recorded immediately after dissolution in normal aerated CD 3 OD showed the two peaks noted above in ratios that varied from 1:1 to 1:3 from batch to batch. The 1 H NMR spectrum was also complicated by the presence of duplicate signals for the isomeric mixture.…”

“…Attempts to isolate a pure compound from this mixture were unsuccessful and it was clear that the coordination 10 chemistry of S-N Me CP with Cu(I) was neither simple nor appropriate for the formation of desired stereogenic-at-metal complexes. The 1:1 complexation of Ag(I) with NCN' and PCP' mimicked that observed with Cu(I) in that numerous intractable species 15 were observed with the former while a single species was isolated for the latter. The formation of a single species for the PCP' ligand was partly assisted by the prior synthesis of a discrete, precomplex of the amidinium precursor, namely and one equivalent of Ag(OTf) was stirred overnight a white solid (2.OTf) was deposited which was subsequently recrystallised from THF/Et 2 O at 4 °C as large colourless blocks (scheme 2).…”

“…The formulation was confirmed by mass spectrometry where a peak at m/z = 1441.4806 for the complex trication plus one PF 6 -and one Cl + and subsequent addition of the gold starting complex or from complex 5 upon addition of base. The molecular structure, shown in figure 4, is a head-to-tail dimer 15 where the two gold ions are coordinated to one NHC and one phosphine donor from the two bridging S-N Me CP ligands respectively. The geometry at the metal is linear two coordinate as expected with a slightly acute average P-Au-C bond angle of 171.3° and a distance of 4.871 Å between the two gold atoms.…”

Room-temperature C–H activation of the phosphino-ketone Ph2PCH2C(O)Ph leading to an iridium(III) complex with a hybrid phosphino-enolate ligand

“…We recently reported the synthesis of Ir(I) pincer-type complexes involving phosphorus and NHC donors, [IrH(I)(PO-NHC,kP,kC,kC NHC ) Me ] (1a) and [IrH(I)(PO-NHC,kP,kC,kC NHC ) n-Bu ] (1b), with a Me or n-Bu group as N-substituent, respectively [4].…”

“…Thus, with related NHC,P hybrid ligands, dinuclear Ir(I) complexes were obtained, also from the corresponding imidazolium salt, in which two such ligands behave as bridges rather than chelates, as in, e.g., the dicationic complex [Ir(cod)(m-P-NHC,kP,kC NHC )] 2 [PF 6 ] 2 (2) (cod = 1,5-cyclooctadiene) [4].…”