Synthesis of Two Isomeric Ferrocene Phosphanylcarboxylic Acids and their Pd II Complexes with and without Auxiliary ortho ‐Metalated C,E‐Ligands (E = N and S)

Control over Anion Coordination on Pd(II), Cu(I), and Ag(I) with Regioisomeric Phosphine-Carboxylate Ligands

The coordination of anionic donors is involved at various stages of catalytic cycles in transition-metal catalysis, but control over the spatial positioning of anions around a metal center is a challenge in coordination chemistry. Here we show that regioisomeric phosphine-carboxylate ligands provide spatial anion control on palladium(II) centers by favoring either κ2, cis-κ1, or trans-κ1 coordination of the carboxylate donor. Additionally, the palladium(II) carboxylates, which contain a methyl donor, upon protonation, deliver metal-alkyl complexes that feature a coordinated carboxylic acid. Such complexes can be considered as models for the minima that follow the concerted metalation-deprotonation transition state for C-H activation. The predictability of the coordination modes is further demonstrated on silver(I) and copper(I) centers, for which less common structures of mononuclear and dinuclear complexes can be obtained by using spatial anion control. Our results demonstrate the potential for spatial control over carboxylate anions in coordination chemistry.

Hybrid Phosphine/Amino-Acid Ligands Built on Phenyl and Ferrocenyl Platforms: Application in the Suzuki Coupling of o-Dibromobenzene with Fluorophenylboronic Acid

We describe the synthesis and characterization of two classes of hybrid phosphino ligands functionalized with amino ester or amino acid groups. These compounds are built either on a rigid planar phenyl platform or on a functionalized - conformationally controlled - rotational ferrocene backbone. Modifications at the -PR2 phosphino groups (R=aryl and alkyl, with various steric bulk, Ph, Mes, i-Pr, Cy) and at the amino acid/amino ester functions are reported, showing a valuable high modularity. The coordination chemistry of these compounds regarding palladium and gold was investigated, in particular with respect to the coordination mode of the phosphino groups and the preferred interaction with metals for the amino ester and amino acid functions. For all the hybrid ligands, based either on ferrocenyl or phenyl platforms, the (P,N)-chelating effect dominates in solution for coordination to Pd(II), while linear P-Au(I) complexes without interaction with the amino groups are assumed. The investigation of the catalytic activity of these new ligands in the demanding palladium-catalyzed Suzuki-Miyaura coupling of o-dibromoarenes with fluorophenylboronic acid underlined the importance of the amino ester dicyclohexylphosphinoferrocene for avoiding the deleterious homocoupling and arene oligomerization side-reactions that were otherwise observed with the other phosphine ligands.

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.

Cyclopalladation of a ferrocene acylphosphine and the reactivity of the C-H activated products

Acylphosphines are an attractive subclass of phosphine ligands with specific reactivity and ligating properties. This study describes the synthesis of a ferrocene-based acylphosphine, FcC(O)PPh₂ (1, Fc = ferrocenyl), the corresponding phosphine chalcogenides FcC(O)P(E)Ph₂ (E = O, S and Se), and palladium(ii) complexes resulting from the orthometallation of 1, viz. [Pd(μ-X)(1- H)]₂ (2-X, where X = Cl, Br and I), which in turn serve as a convenient entry point to a range of monopalladium complexes. Thus, the cleavage of 2-X with phosphines, 4-(dimethylamino)pyridine and in situ-generated 1,3-dimesitylimidazolin-2-ylidene (L) provided complexes [PdX(L)(1- H)] (3-5), which are typically obtained as single isomers by crystallisation but undergo spontaneous isomerisation in solution leading to equilibrium mixtures of cis and trans isomers. Upon treatment with sodium acetylacetonate (Na(acac)), 2-Cl was transformed into [Pd(acac)(1- H)] (6), which reacted with (diphenylphosphino)acetic acid under proton transfer to give [Pd(Ph₂PCH₂CO₂-κ²O,P)(1- H)] (7), while the reaction with allylating agents produced the π-allyl complex [Pd(η³-C₃H₅)(1- H)] (9). Compound [PdCl(PMe₃)(1- H)] was further used to prepare a series of diorganopalladium complexes [Pd(R)(PMe₃)(1- H)] (8; R = Me, 4-C₆H₄Me, 4-C₆H₄CF₃, CH[double bond, length as m-dash]CHC₆H₄Me-4 and C[triple bond, length as m-dash]CC₆H₄Me-4). All compounds were structurally characterised using spectroscopic methods and, in most cases, also by X-ray diffraction analysis. The structural data indicated the rigidity of the Pd(1- H)⁺ fragment and revealed variations in the Pd-donor distances dictated by an interplay between the trans influence and steric demands of the ligands surrounding Pd(ii). Moreover, some compounds were studied by DFT to rationalise their isomerisation equilibria and electrochemical properties, which were examined by cyclic voltammetry.

Ferro-self-assembly: magnetic and electrochemical adaptation of a multiresponsive zwitterionic metalloamphiphile showing a shape-hysteresis effect

Metallosurfactants are molecular compounds which combine the unique features of amphiphiles, like their capability of self-organization, with the peculiar properties of metal complexes like magnetism and a rich redox chemistry. Considering the high relevance of surfactants in industry and science, amphiphiles that change their properties on applying an external trigger are highly desirable. A special feature of the surfactant reported here, 1-(Z)-heptenyl-1′-dimethylammonium-methyl-(3-sulfopropyl)ferrocene (6), is that the redox-active ferrocene constituent is in a gemini-position. Oxidation to 6⁺ induces a drastic change of the surfactant's properties accompanied by the emergence of paramagnetism. The effects of an external magnetic field on vesicles formed by 6⁺ and the associated dynamics were monitored in situ using a custom-made optical birefringence and dual dynamic light scattering setup. This allowed us to observe the optical anisotropy as well as the anisotropy of the diffusion coefficient and revealed the field-induced formation of oriented string-of-pearls-like aggregates and their delayed disappearance after the field is switched off.

The self-organization properties of a stimuli responsive amphiphile can be altered by subjecting the paramagnetic oxidized form to a magnetic field of 0.8 T and monitored in real time by coupling optical birefringence with dynamic light scattering.

Rhodium(I)-NHC Complexes Bearing Bidentate Bis-Heteroatomic Acidato Ligands as gem-Selective Catalysts for Alkyne Dimerization

A series of Rh(κ² -BHetA)(η² -coe)(IPr) complexes bearing 1,3-bis-hetereoatomic acidato ligands (BHetA) including carboxylato (O,O), thioacetato (O,S), amidato (O,N), thioamidato (N,S), and amidinato (N,N), have been prepared by reaction of the dinuclear precursor [Rh(μ-Cl)(IPr)(η² -coe)]₂ with the corresponding anionic BHetA species. The Rh^I -NHC-BHetA compounds catalyze the dimerization of aryl alkynes, showing excellent selectivity for the head-to-tail enynes. Among them, the acetanilidato-based catalyst has shown an outstanding catalytic performance reaching unprecedented TOF levels of 2500 h^-1 with complete selectivity for the gem-isomer. Investigation of the reaction mechanism supports a non-oxidative pathway in which the BHetA ligand behaves as proton shuttle through intermediate κ¹ -HBHetA species. However, in the presence of pyridine as additive, the identification of the common Rh^III H(C≡CPh)₂ (IPr)(py)₂ intermediate gives support for an alternative oxidative route.

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.

Generation of a zinc and rhodium containing metallomacrocycle by rearrangement of a six-coordinate precursor complex

Two pentadentate N3,P2 ligands coordinate zinc(ii) by their N3 pocket. Four free phosphine donors allow the coordination of four AuCl moieties leading to a pentanuclear ZnAu4 complex. In contrast, the attempt to use the phosphines for chelating coordination of two Rh(CO)Cl units results in a well-organized rearrangement that ends up with the formation of a metallomacrocycle in high yields.

Synthesis and characterisation of palladium(ii) complexes with hybrid phosphinoferrocene ligands bearing additional O-donor substituents

Coordination of phosphinoferrocene ligands with O-donor substituents to Pd(ii) is affected by the nature of the oxygen functions and may results in hemilabile species.

Comparing the reactivity of isomeric phosphinoferrocene nitrile and isocyanide in Pd(ii) complexes: synthesis of simple coordination compounds vs. preparation of P-chelated insertion products and Fischer-type carbenes

Isomeric phosphinoferrocene ligands, viz. 1'-(diphenylphosphino)-1-cyanoferrocene (1) and 1'-(diphenylphosphino)-1-isocyanoferrocene (2), show markedly different coordination behaviours. For instance, the reactions of 1 with [PdCl2(MeCN)2] and [(LNC)Pd(μ-Cl)]2 (LNC = [2-(dimethylamino-κN)methyl]phenyl-κC1) produced the "phosphine" complexes [PdCl2(1-κP)2] (7) and [(LNC)PdCl(1-κP)] (8), and the latter was converted into the coordination polymer [(LNC)Pd(μ(P,N)-1)][SbF6] (9). Conversely, the reaction of 2 with [(LNC)Pd(μ-Cl)]2 involved coordination of the phosphine moiety and simultaneous insertion of the isocyanide group into the Pd-C bond, giving rise to the P,η1-imidoyl complex [PdCl(Ph2PfcN[double bond, length as m-dash]CC6H4CH2NMe2-κ3C,N,P)] (10; fc = ferrocene-1,1'-diyl). Compound 10 was further transformed into the Fischer carbene [PdCl(Ph2PfcN(Me)CC6H4CH2NMe2-κ3P,C,N)][BF4] (11) by methylation with [Me3O][BF4]. The reactions of 2 with Pd-Me and Pd(η3-allyl) precursors also led to imidoyl complexes [Pd(μ-Cl)(Ph2PfcN[double bond, length as m-dash]CR-κ2C,P)]2 (R = Me: 12, R = allyl: 15), which were cleaved with PPh3 into the corresponding monopalladium complexes [PdCl(PPh3)(Ph2PfcN[double bond, length as m-dash]CR-κ2C,P)] (R = Me: 13, R = allyl: 16). The treatment of 12 and 15 with thallium(i) acetylacetonate (acac) produced [Pd(acac-O,O')(Ph2PfcN[double bond, length as m-dash]CR-κ2C,P)] (R = Me: 17, R = allyl: 18). Through proton transfer, these complexes reacted with Ph2PCH2CO2H, ultimately producing bis-chelate complexes [Pd(Ph2PCH2CO2-κ2O,P)(Ph2PfcN[double bond, length as m-dash]CR)] (R = Me: 19, R = prop-1-enyl (sic!): 20). In addition, compound 13 was converted into the P-chelated carbene [PdCl(PPh3)(Ph2PfcN(Me)CMe-κ2C,P)][BF4] (14). Compounds 10, 11, 13 and 14 were studied by cyclic voltammetry and by DFT computations.

Crystal structure of {[1'-(di-phenyl-phosphino)ferrocen-yl]meth-yl}di-methyl-ammonium chloride monohydrate

Individual ions and the solvating water mol-ecule constituting the structure of the title compound, [Fe(C8H13N)(C17H14P)]Cl·H2O, assemble into dimeric units located around crystallographic inversion centers via N-H⋯Cl and O-H⋯Cl hydrogen bonds. These discrete fragments are further inter-connected into chains by C-H⋯O inter-actions. The disubstituted ferrocene core in the {[1'-(di-phenyl-phosphino)ferrocen-yl]meth-yl}di-methyl-ammonium cation has an approximate synclinal eclipsed conformation and is tilted by 3.40 (11)°.