A Straightforward Access to Stable, 16 Valence-electron Phosphine-Stabilized Fe0 Olefin Complexes and their Reactivity

The use of the dialkene divinyltetramethyldisiloxane (dvtms) allows easy access to the reactive 16 valence-electron complexes [Fe⁰(L-L)(dvtms)], (L-L) = dppe (1,2-bis(diphenylphosphino)ethane), (1), dppp (1,2-bis(diisopropylphosphino)propane), (2), pyNMeP(ⁱPr)₂ (N-(diisopropylphosphino)-N-methylpyridin-2-amine), (4), dipe (1,2-bis(diisopropylphosphino)ethane), (5), and [Fe⁰(L)₂(dvtms)], L = PMe₃, (3), by a mild reductive route using AlEt₂(OEt) as reducing agent. In contrast, by the same methodology, the 18 valence-electron complexes [Fe⁰(L-L)₂(ethylene)], (L-L) = dppm (1,2-bis(diphenylphosphino)methane), 6, (L-L) = dppa (1,2-bis(diphenylphosphino)amine) 7 or (L-L)=dppe, 8, were obtained, which do not contain dvtms. In addition, a combined DFT and solid-state paramagnetic NMR methodology is introduced for the structure determination of 5. A comparative study of the reactivity of 1,2,4-6 and 8 with 3-hexyne highlights emerging mechanistic implications for C-C coupling reactions using these complexes as catalysts.

Changes in molecular film metallicity with minor modifications of the constitutive quinonoid zwitterions

The electronic properties of molecular films formed by quinonoid zwitterions deposited on gold are highly dependent on the nature of the N-substituent.

Mono- and polynuclear Ag(i) complexes of N-functionalized bis(diphenylphosphino)amine DPPA-type ligands: synthesis, solid-state structures and reactivity

DPPA-type ligands (Ph₂P)₂N(p-Z)C₆H₄ (Z = H, SMe, OMe) led to Ag(i) complexes of various nuclearities and an unexpected influence of the para-substituent Z is observed, including for CH₂Cl₂ activation.

Non-symmetrical, potentially redox non-innocent imino NHC pyridine ‘pincers’ via a zinc ion template-assisted synthesis

A Zn^II-promoted modular synthesis allows access to new non-symmetrical, redox-active imino NHC pyridine pincer ligands. Radical anionic and dianionic redox states of the ligand are involved in its Fe^II complexes obtained from FeBr₂/KC₈.

Functional Short-Bite Ligands: Synthesis, Coordination Chemistry, and Applications of N-Functionalized Bis(diaryl/dialkylphosphino)amine-type Ligands

The aim of this review is to highlight how the diversity generated by N-substitution in the well-known short-bite ligand bis(diphenylphosphino)amine (DPPA) allows a fine-tuning of the ligand properties and offers a considerable scope for tailoring the properties and applications of their corresponding metal complexes. The various N-substituents include nitrogen-, oxygen-, phosphorus-, sulfur-, halogen-, and silicon-based functionalities and directly N-bound metals. Multiple DPPA-type ligands linked through an organic spacer and N-functionalized DRPA-type ligands, in which the PPh2 substituents are replaced by PR2 (R = alkyl, benzyl) groups, are also discussed. Owing to the considerable diversity of N-functionalized DPPA-type ligands available, the applications of their mono- and polynuclear metal complexes are very diverse and range from homogeneous catalysis with well-defined or in situ generated (pre)catalysts to heterogeneous catalysis and materials science. In particular, sustained interest for DPPA-type ligands has been motivated, at least in part, by their ability to promote selective ethylene tri- or tetramerization in combination with chromium. Ligands and metal complexes where the N-substituent is a pure hydrocarbon group (as opposed to N-functionalization) are outside the scope of this review. However, when possible, a comparison between the catalytic performances of N-functionalized systems with those of their N-substituted analogs will be provided.

Coinage metal complexes with bridging hybrid phosphine-NHC ligands: synthesis of di- and tetra-nuclear complexes

A series of P-NHC-type hybrid ligands containing both PR2 and N-heterocyclic carbene (NHC) donors on meta-bis-substituted phenylene backbones, L(Cy), L(tBu) and L(Ph) (R = Cy, tBu, Ph, respectively), was accessed through a modular synthesis from a common precursor, and their coordination chemistry with coinage metals was explored and compared. Metallation of L(Ph)·n(HBr) (n = 1, 2) with Ag2O gave the pseudo-cubane [Ag4Br4(L(Ph))2], isostructural to [Ag4Br4(L(R))2] (R = Cy, tBu) (T. Simler, P. Braunstein and A. A. Danopoulos, Angew. Chem., Int. Ed., 2015, 54, 13691), whereas metallation of ·HBF4 (R = Ph, tBu) led to the dinuclear complexes [Ag2(L(R))2](BF4)2 which, in the solid state, feature heteroleptic Ag centres and a 'head-to-tail' (HT) arrangement of the bridging ligands. In solution, interconversion with the homoleptic 'head-to-head' (HH) isomers is facilitated by ligand fluxionality. 'Head-to-tail' [Cu2Br2(L(R))2] (R = Cy, tBu) dinuclear complexes were obtained from L(R)·HBr and [Cu5(Mes)5], Mes = 2,4,6-trimethylphenyl, which also feature bridging ligands and heteroleptic Cu centres. Although the various ligands L(R)l ed to structurally analogous complexes for R = Cy, tBu and Ph, the rates of dynamic processes occurring in solution are dependent on R, with faster rates for R = Ph. Transmetallation of both NHC and P donor groups from [Ag4Br4(L(tBu))2] to AuI by reaction with [AuCl(THT)] (THT = tetrahydrothiophene) led to L(tBu) transfer and to the dinuclear complex [Au2Cl2L(tBu)] with one L(tBu) ligand bridging the two Au centres. Except for the silver pseudo-cubanes, all other complexes do not exhibit metallophilic interactions.

Zwitterionic Cobalt Complexes with Bis(diphenylphosphino)(N-thioether)amine Assembling Ligands: Structural, EPR, Magnetic, and Computational Studies

The coordination of two heterofunctional P,P,S ligands of the N-functionalized DPPA-type bearing an alkylthioether or arylthioether N-substituent, (Ph2P)2N(CH2)3SMe (1) and (Ph2P)2N(p-C6H4)SMe (2), respectively, toward cobalt dichloride was investigated to examine the influence of the linker between the PNP nitrogen and the S atoms. The complexes [CoCl2(1)]2 (3) and [CoCl2(2)]2 (4) have been isolated, and 3 was shown by X-ray diffraction to be a unique dinuclear, zwitterion containing one CoCl moiety bis-chelated by two ligands 1 and one CoCl3 fragment coordinated by the S atom of a thioether function. The FT-IR, UV-vis, and EPR spectroscopic features of 3 were analyzed as the superposition of those of constitutive fragments identified by a retrosynthetic-type analysis. A similar approach provided insight into the nature of 4 for which no X-ray diffraction data could be obtained. A comparison between the spectroscopic features of 4 and of its constitutive fragments, [CoCl(2)2]PF6 (7) and [H2']2[CoCl4] (8) (2' = NH2(p-C6H4)SMe), and between those of 4 and 3 suggested that 4 could either have a zwitterionic structure, similar to that of 3, or contain a tetrahedral dicationic bis-chelated Co center associated with a CoCl4 dianion. Magnetic and EPR studies and theoretical calculations were performed. Doublet spin states were found for the pentacoordinated complexes [CoCl(1)2]PF6 (5) and 7 and anisotropic quadruplet spin states for the tetrahedral complexes [CoCl3(H1')] (6) (1' = NH2(CH2)3SMe) and 8. A very similar behavior was observed for 3 and 4, consisting in the juxtaposition of noninteracting doublet and quadruplet spin states. Antiferromagnetic interactions explain the formation of dimers for 6 and of layers for 8. The EPR signatures of 3 and 4 correspond to the superposition of low-spin nuclei in 5 and 7 and high-spin nuclei in 6 and 8, respectively. From DFT calculations, the solid-state structure of 4 appears best described as zwitterionic, with a low-spin state for the Co1 atom.

Homo- and Heterodinuclear Ir and Rh Imine-functionalized Protic NHC Complexes: Synthetic, Structural Studies, and Tautomerization/Metallotropism Insights

The influence of the potentially chelating imino group of imine-functionalized Ir and Rh imidazole complexes on the formation of functionalized protic N-heterocyclic carbene (pNHC) complexes by tautomerization/metallotropism sequences was investigated. Chloride abstraction in [Ir(cod)Cl{C3 H3N2 (DippN=CMe)-κN3}] (1 a) (cod=1,5-cyclooctadiene, Dipp=2,6-diisopropylphenyl) with TlPF6 gave [Ir(cod){C3 H3N2 (DippN=CMe)-κ(2) (C2,Nimine )}](+) [PF6 ](-) (3 a(+) [PF6 ](-)). Plausible mechanisms for the tautomerization of complex 1 a to 3 a(+) [PF6 ](-) involving C2-H bond activation either in 1 a or in [Ir(cod){C3 H3 N2 (DippN=CMe)-κN3}2](+) [PF6 ](-) (6 a(+) [PF6 ](-)) were postulated. Addition of PR3 to complex 3 a(+) [PF6 ](-) afforded the eighteen-valence-electron complexes [Ir(cod)(PR3){C3 H3N2 (DippN=CMe)-κ(2) (C2,Nimine )}](+) [PF6 ](-) (7 a(+) [PF6 ](-) (R=Ph) and 7 b(+) [PF6 ](-) (R=Me)). In contrast to Ir, chloride abstraction from [Rh(cod)Cl{C3H3N2 (DippN=CMe)-κN3}] (1 b) at room temperature afforded [Rh(cod){C3 H3N2 (DippN=CMe)-κN3}2](+) [PF6 ](-) (6 b(+) [PF6 ](-)) and [Rh(cod){C3 H3N2 (DippN=CMe)-κ(2) (C2,Nimine )}](+) [PF6 ](-) (3 b(+) [PF6 ](-) ) (minor); the reaction yielded exclusively the latter product in toluene at 110 °C. Double metallation of the azole ring (at both the C2 and the N3 atom) was also achieved: [Ir2 (cod)2 Cl{μ-C3H2N2 (DippN=CMe)-κ(2) (C2,Nimine ),κN3}] (10) and the heterodinuclear complex [IrRh(cod)2 Cl{μ-C3H2N2 (DippN=CMe)-κ(2) (C2,Nimine ),κN3}] (12) were fully characterized. The structures of complexes 1 b, 3 b(+) [PF6 ](-) , 6 a(+) [PF6 ](-) , 7 a(+) [PF6 ](-), [Ir(cod){C3HN2 (DippN=CMe)(DippN=CH)(Me)-κ(2) (N3,Nimine )}](+) [PF6 ](-) (9(+) [PF6 ](-)), 10⋅ Et2 O⋅toluene, [Ir2 (CO)4 Cl{μ-C3H2N2 (DippN=CMe)-κ(2) (C2,Nimine ),κN3}] (11), and 12⋅2 THF were determined by X-ray diffraction.

A Bis(Diphosphanyl N-Heterocyclic Carbene) Gold Complex: A Synthon for Luminescent Rigid AuAg2 Arrays and Au5 and Cu6 Double Arrays

A mononuclear bis(NHC)/Au(I) (NHC=N-heterocyclic carbene) cationic complex with a rigid bis(phosphane)-functionalized NHC ligand (PC(NHC)P) was used to construct linear Au3 and Ag2 Au arrays, a Au5 cluster with two intersecting crosslike Au3 arrays, and an unprecedented Cu6 complex with two parallel Cu3 arrays. The impact of metallophilic interactions on photoluminescence was studied experimentally.

Magnesium and aluminum complexes bearing bis(5,6,7-trihydro quinolyl)-fused benzodiazepines for ε-caprolactone polymerization

New bis(5,6,7-trihydroquinolyl)-fused benzodiazepine ligands were synthesized and used to form dinuclear magnesium and aluminum complexes which showed efficient catalytic activity toward the ROP of ε-CL.

Influence of steric hindrance on the molecular packing and the anchoring of quinonoid zwitterions on gold surfaces

The N-substituent on quinonoid zwitterions influences the molecules packing and impacts their anchoring on gold surfaces.

Colour tuning by the stepwise synthesis of mononuclear and homo- and hetero-dinuclear platinum(ii) complexes using a zwitterionic quinonoid ligand

The colour of a mononuclear Pt(ii) complex bearing a [O,N,N,O] quinonoid ligand is judiciously tuned by stepwise deprotonation and successive homo- and hetero-metalation.

Direct synthesis of doubly deprotonated, dearomatised lutidine PNP Cr and Zr pincer complexes based on isolated K and Li ligand transfer reagents

Double deprotonation of a hybrid bis(phosphino)picoline ligand yields lithium or potassium pincer salts with dearomatised lutidine backbones that afford unusual chromium and zirconium complexes by transmetallation.

Cobalt PNCNHC ‘pincers’: ligand dearomatisation, formation of dinuclear and N2 complexes and promotion of C–H activation

Ligand dearomatisation in Co^II phosphino-picoline NHC-type pincers and dicobalt complexes result from side-arm metalation or C–H activation at the NHC backbone; in the latter case, an ‘anionic dicarbene’ originates from a dearomatised Co^I–N₂ complex.

Transition metal (Rh and Fe) complexes and main-group (Se and B) adducts with N,N′-diphosphanyl NHC ligands: a study of stereoelectronic properties

The reactions ofN,N′-bis(di-tert-butylphosphanyl)-imidazole-2-ylidene (PCNHCP) with [Rh(μ-Cl)(COD)]₂, [Rh(μ-Cl)(CO)₂]₂, [Fe₄Cl₈(THF)₆], elemental Se and [(C₆F₅)BO]₃, have been investigated to evaluate the stereoelectronic properties of this hybrid ligand.