Beyond Common Metal-Metal Bonds, κ3 -Bis(donor)ferrocenyl→Transition-Metal Interactions

Influence of the Steric/Electronic Properties of N-Aryl Substituents in Cycloplatinated Guanidinate(1-) Complexes on the Formation of Discrete Pt → Ag Complexes and One-Dimensional Coordination Polymer

The reactions of cycloplatinated guanidinate(1-) complexes 1-6 with AgTFA (TFA = OC(O)CF₃) in 1:1 and 1:2 Pt^II/Ag^I molar ratios afforded complexes containing three types of Pt₂Ag₂ skeletons (7-10, 11, and 13), one 1D CP containing Pt₂Ag₃ skeleton (16), and a Pt₂Ag₄ complex (17) in 91-95% (method 1), 73-82% (method 2) (7-10), and 54-79% (11, 13, 16, and 17) yields. The reactions of 11 with 2,6-XylNC (2,6-Xyl = 2,6-Me₂C₆H₃) and 4-DMAP (4-dimethylaminopyridine) gave a neutral complex 18 and an ionic complex 19, respectively. Molecular structures of 12 complexes were unambiguously determined by single-crystal X-ray diffraction. Ten complexes contain unprecedented PtAg skeletons and are shown to contain multiple number of dative Pt → Ag bonds supported by the TFA ligand, platinated carbon of the TAG ligand, or both these ligands in conjunction with the Ag-Ag contacts stabilized by argentophilic interaction. Further, the new complexes were characterized by analytical, IR, and multinuclear NMR (¹⁹F, ¹H, ¹³C{¹H}, and ¹⁹⁵Pt) spectroscopies, powder X-ray diffraction, and TGA/DTA. In solution, 9 and 19 exist in more than one form as identified by multinuclear NMR, and this behavior is ascribed to the restricted (N₂)C-N(H)Ar single-bond rotation of the TAG ligand. The photophysical properties of 9 and 11 are reported.

Synthesis and coordination of hybrid phosphinoferrocenes with extended donor pendants

Combining a phosphinoferrocene fragment with extended multidonor moieties affords novel, flexible multidonor pro-ligands. This contribution describes the synthesis of two structurally similar functional phosphines, Ph₂PfcNHC(O)CH₂PPh₂ (1) and Ph₂PfcNHCH₂CH₂PPh₂ (2, fc = ferrocene-1,1'-diyl), and their coordination behaviour towards Pd(II). The former amidophosphine reacts with [PdCl₂(MeCN)₂] to produce the chelate complex [PdCl₂(1-κ²P,P')] as a mixture of cis and trans isomers, which convert into bis-chelate [PdCl₂(Ph₂PfcNC(O)CH₂PPh₂-κ³P,P',N)] upon reacting with a strong base (KOt-Bu). In contrast, the more flexible and more basic phosphinoamine 2 directly forms the cationic bis-chelate complex [PdCl(2-κ³P,P',N)]Cl via spontaneous self-ionisation. Subsequent halogen abstraction with Ag[SbF₆] results either in counter ion exchange to give [PdCl(2-κ³P,P',N)][SbF₆] or in the formation of a structurally unique complex [PdCl(2-κ⁴Fe,P,P',N)][SbF₆]₂ with an Fe → Pd dative interaction, depending on the amount of silver(I) salt used (1 or 2 equiv.).

Investigation of the Coordination Chemistry of a Bisamidinate Ferrocene Ligand with Cu, Ag, and Au

The coordination chemistry of a ferrocene ligand with one bulky amidinate function attached to each ring toward two different coinage metal precursors was investigated. In dependence of the metal and the co-ligands, "ansa" type structures and non-bridged structures were obtained. Six different compounds are reported. In the "ansa" type structures, short Fe-M (M = Cu, Ag) distances were observed in the molecular structures in the solid state. However, theoretical calculations (DFT) did not reveal a stabilizing metal-metal interaction. Instead, dispersion interactions within the ligand and between the ligand and metal seem to represent the main stabilization forces.

Diphosphanylmetallocenes of Main-Group Elements

Several 1,1'-diphosphanyl-substituted metallocenes of magnesium (magnesocenes) were synthesized, structurally characterized, and their reactivity and coordination chemistry were investigated. Transmetalation of these magnesocenes gives access to group 14 metallocenes (tetrelocenes), as well as to group 15 stibonocenes. These s- and p-block metallocenes represent a novel class of bis(phosphanyl) ligands, exhibiting Lewis-amphiphilic character. Their coordination chemistry towards different transition-metal and main-group fragments was investigated and different complexes are presented.

Triple the fun: tris(ferrocenyl)arene-based gold(i) complexes for redox-switchable catalysis

The modular syntheses of C₃-symmetric tris(ferrocenyl)arene-based tris-phosphanes and their homotrinuclear gold(i) complexes are reported. Choosing the arene core allows fine-tuning of the exact oxidation potentials and thus tailoring of the electrochemical response. The tris[chloridogold(i)] complexes were investigated in the catalytic ring-closing isomerisation of N-(2-propyn-1-yl)benzamide, showing cooperative behaviour vs. a mononuclear chloridogold(i) complex. Adding one, two, or three equivalents of 1,1′-diacetylferrocenium[tetrakis(perfluoro-tert-butoxy)aluminate] as an oxidant during the catalytic reaction (in situ) resulted in a distinct, stepwise influence on the resulting catalytic rates. Isolation of the oxidised species is possible, and using them as (pre-)catalysts (ex situ oxidation) confirmed the activity trend. Proving the intactness of the P–Au–Cl motif during oxidation, the tri-oxidised benzene-based complex has been structurally characterised.

Trinuclear gold(i) complexes of C₃-symmetric tris(ferrocenyl)arene-based tris-phosphanes with four accessible oxidation states catalyse the ring-closing isomerisation of N-(2-propyn-1-yl)benzamide with different rates depending on their redox state.

(Electrochemical) Properties and Computational Investigations of Ferrocenyl-substituted Fe3(μ3-PFc)2(CO)9 and Co4(μ4-PFc)2(CO)9 Clusters and Their Reduced Species

The formation of ferrocenyl-functionalized iron and cobalt carbonyl clusters is reported, based on a reaction of FcPCl₂ (3) (Fc = Fe(η⁵-C₅H₅)(η⁵-C₅H₄)) with Fe₂(CO)₉ and Co₂(CO)₈, respectively. Therein, nido-Fe₃(CO)₉(μ₃-PFc)₂ (4) and nido-Co₄(CO)₁₀(μ₃-PFc)₂ (5) clusters were obtained as the first diferrocenyl-substituted carbonyl clusters with a symmetrical cluster core. Cluster 4 shows two reversible one-electron processes within the anodic region, based on Fc/Fc⁺ redox events, as well as two processes in the cathodic region. In situ IR and electron paramagnetic resonance (EPR) measurements of all electronic states confirmed an Fc-based oxidation and a core-based reduction. On the basis of the results of a single-crystal X-ray analysis of structures of 4 and 5, computational studies of the highest occupied molecular orbital-lowest unoccupied molecular orbital energies, the spin density, quantum theory of atom-in-molecule delocalization indices, and the atomic charges were performed to explain the experimental results. The latter revealed a reorganization of the cluster core upon reduction and the existence of weak P···P interactions in 4 and 5. Ferrocenyl-related redox processes, occurring reversibly in case of 4, were absent for 5, due to a different distribution of the HOMO energies. EPR measurements furthermore confirmed the core-based radical anion and the formation of a decomposition product at potentials lower than [M]^2- (M = Fe, Co).

Synthesis and study of Fe → Pd interactions in unsymmetric Pd(ii) complexes with phosphinoferrocene guanidine ligands

Readily available phosphinoferrocene guanidines coordinate Pd(ii) as P,N-chelating or κ3P,N,Fe-bound ligands. As the latter, they give rise to the first donor-asymmetric complexes featuring Fe-Pd dative bonds, which were studied using direct (spectroscopic and electrochemical) methods and theoretical (DFT) approaches.

Cooperative activation of X-H (X = H, C, O, N) bonds by a Pt(0)/Ag(i) metal-only Lewis pair

Metal-only Lewis pairs made of Pt(0)/Ag(i) combinations have been previously reported, but their cooperative reactivity remains unexplored. Here we demonstrate that these systems are capable of synergistically activating a wide variety of X-H (X = H, C, O, N) bonds, including those in dihydrogen, alkynes, water and ammonia.