Forever young: the first seventy years of ferrocene

The discovery of ferrocene, [Fe(η5-C5H5)2], seventy years ago has significantly influenced chemical research and provided a key impetus for establishing and rapidly expanding organometallic chemistry, which has continued at a...

The protonation state governs the coordination of phosphinoferrocene guanidines

Compared to phosphines with guanidinium tags, studied as polar ligands for aqueous catalysis, their counterparts bearing guanidine substituents received only limited attention. This contribution focuses on the coordination of phosphinoferrocene guanidine Ph₂PfcNC(NHiPr)₂ (1iPr, fc = ferrocene-1,1'-diyl) as a hybrid, P,N-donor ligand to Group 10 metals. In its native state, 1iPr coordinated as a P,N-chelating ligand, affording [M(X)(Y)(1iPr-κ²P,N)] (M/X/Y = Pd/Cl/Cl, Pd/Br/4-C₆H₄CN, Pt/Cl/Cl; the corresponding Ni(II) complex was not isolated). While [PdCl₂(1iPr-κ²P,N)] converted into [PdCl(1iPr-κ³Fe,P,N)]⁺ species with Fe-Pd interaction, upon chloride removal, the analogous Pt(II) complex dimerised into [Pt₂(μ-Cl)₂(1iPr-κ²P,N)₂]²⁺. Deprotonation of [PdCl₂(1iPr-κ²P,N)] produced a unique, doubly chelating phosphinoguanidinate complex [PdCl{(1iPr-H)-κ³P,N,N'}], which was smoothly converted into [Pd(MeCN){(1iPr-H)-κ³P,N,N'}][SbF₆]. The latter, a convenient starting material for substitution reactions, was used to prepare either [Pd(L){(1iPr-H)-κ³P,N,N'}][SbF₆] (L = 4-(dimethylamino)pyridine and 2-phenylpyridine), by simple substitution, or the hydroxide and acetylacetonate (acac) complexes, [Pd₂(μ-OH)₂(1iPr-κ²P,N)₂][SbF₆]₂ and [Pd(acac)(1iPr-κ²P,N)][SbF₆], by substitution with concomitant proton transfer. In contrast, protonation of the guanidine moiety prevented its coordination, as shown in reactions of the salts (1iPrH)Cl and (1iPrH)[SbF₆]. Depending on the metal-to-ligand ratio, adding (1iPrH)[SbF₆] to [PdCl₂(MeCN)₂] produced [Pd₂Cl₂(μ-Cl)₂(1iPrH-κP)₂][SbF₆]₂ or [PdCl₂(1iPrH-κP)₂][SbF₆]₂. Analogous reactions involving (1iPrH)Cl were more complicated due to competing coordination of the chloride anion, leading to (in addition to other compounds) the zwitterionic complex [PdCl₃(1iPrH-κP)], which was alternatively obtained by selective protonation of [PdCl₂(1iPr-κ²P,N)] with HCl. Apparently, the protonation state of the guanidine moiety controls the coordination behaviour of phosphinoferrocene guanidines.

Synthesis and coordination of a hybrid phosphinoferrocene sulfonamide ligand

A hybrid, phosphinoferrocene sulfonamide ligand was synthesised and studied as a ligand in Pd(ii) complexes, which were structurally characterised. Selected compounds were studied by cyclic voltammetry.

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.

Synthesis and characterisation of Pd(ii) and Au(i) complexes with mesoionic carbene ligands bearing phosphinoferrocene substituents and isomeric carbene moieites

While numerous functional ligands combining phosphine and imidazole-2-ylidene (or imidazolin-2-ylidene) donor moieties have already been reported, the chemistry of the corresponding functional mesoionic carbenes (MIC) derived from 1,2,3-triazoles remains nearly untapped. This contribution describes the synthesis of two isomeric series of triazolium salts bearing 1'-(diphenylphosphino)ferrocenyl substituents by [3 + 2] cycloaddition of a P-protected phosphinoferrocene alkyne with azides, or alternatively of a P-protected phosphinoferrocene azide with terminal alkynes, and by subsequent methylation. These salts were used to synthesize structurally unique Pd(ii) complexes featuring a P,C-chelating triazolylidene carbene ligands and Au(i)-MIC complexes with free phosphine groups. The latter were further utilised to prepare Pd(ii)Au(i) heterometallic complexes containing bridging ferrocene phosphino-carbenes as structurally flexible, donor-unsymmetric metalloligands. In addition, the reactivity of the newly prepared, P-protected phosphinoferrocene alkyne Ph₂PfcC[triple bond, length as m-dash]CH·BH₃ (fc = ferrocene-1,1'-diyl) was investigated, and representatives from all reported compound classes were structurally characterised.

Novel dual ROS-sensitive and CD44 receptor targeting nanomicelles based on oligomeric hyaluronic acid for the efficient therapy of atherosclerosis

Although the clinical usage of drugs administration was raising, the application of nanoparticles encapsulating the hydrophobic drugs with plummy efficiency was very scarce for atherosclerosis (AS) treatment. In this work, a novel dual ROS-sensitive and CD44 receptors targeting amphiphilic carrier material, oligomeric hyaluronic acid-2'-[propane-2,2-diyllbls (thio)] diacetic acl-hydroxymethylferrocene (oHA-TKL-Fc), named HASF, was synthesized and characterized by ¹H-NMR spectra. Then, we combined curcumin (Cur) with HASF into nano-micelles (HASF@Cur micelles) by self-assembling method. The resulting HASF@Cur micelles had the average size of 150.8 nm and zeta potential of -35.04 mV to maintain the will-defined spheroidal structure and stability. Importantly, the HASF@Cur micelles had ultrahigh entrapment efficiency (about 51.41 %). Moreover, in vitro release study, Cur release from HASF@Cur micelles was effective in the reactive oxygen species (ROS) condition, and the release rate was interrelated with the concentration of hydrogen peroxide (H₂O₂). Further, fluorescence imaging showed that the HASF@Cur micelles could more selective access to Raw 264.7 cells than free Cur via oHA-receptor mediated endocytosis. The MTT assay attested the safety of amphiphilic carrier material HASF. Additionally, the results of in vivo Oil red O lipid staining studies showed that the lesion area of the aorta was reduced to 47.3±3.4 % with HASF@Cur micelles, compared with the lesion area of Cur group (63.2±2.7 %), HASF@Cur micelles had the more remarkable effect in reducing lesion area (*P < 0.05). Consequently, the novel dual ROS-sensitive and CD44 receptors targeting drug delivery system would become a promising strategy for atherosclerosis.