Synthesis and structural characterization of 1′-(diphenylphosphino)ferrocene-1-carboxamide, its corresponding hydrazide, some heterocycles derived from the hydrazide and palladium(II) complexes with these functional phosphinoferrocene ligands

Synthesis and Structural Characterisation of an N-Phosphanyl Ferrocene Carboxamide and its Ruthenium, Rhodium and Palladium Complexes

[((Diphenylphosphanyl)amino)carbonyl]ferrocene (1) has been synthesized and coordinated to light platinum metals, ruthenium, rhodium and palladium, in diverse coordination modes. Specifically, compound 1 was used to prepare the following phosphane complexes, [(η⁶ -mes)RuCl₂ (1-κP)], [(η⁵ -C₅ Me₅ )RhCl₂ (1-κP)], trans-[PdCl₂ (1-κP)₂ ], and [(L^NC )PdCl(1-κP)] (mes=mesitylene, L^NC =[2-(dimethylamino-κN)methyl]phenyl-κC¹ ). They were subsequently converted into cationic O,P-chelate complexes by halide abstraction with AgClO₄ and into neutral O,P-chelate complexes by deprotonation with potassium tert-butoxide. All coordination compounds and phosphane chalcogenides 1E (P-bound chalcogen atom E=O, S and Se), which were also synthesised, were structurally characterised using spectroscopic methods (IR, multinuclear NMR and ESI MS) and single-crystal X-ray diffraction analysis. The electrochemical behaviour of the prepared compounds was studied by cyclic voltammetry, and the (L^NC )Pd-1 complexes were further studied by Mössbauer spectroscopy.

Versatile coordination and C-H activation of a multi-donor phosphinoferrocene carboxamide ligand in Pd(ii) complexes

A multi-donor phosphinoferrocene carboxamide, FcCONHCH₂CH₂PPh₂ (1, Fc = ferrocenyl), was prepared, converted into the corresponding phosphine oxide 1O and phosphine selenide 1Se and, mainly, studied as a ligand in Pd(ii) complexes. In its native form, amide 1 preferentially coordinated soft Pd(ii) as a simple phosphine, giving rise to mixtures of cis and trans-[PdX₂(1-κP)₂] (2; X = Cl (a), Br (b), and I (c)), wherein the isomer ratios depended on the auxiliary halide ligand or, alternatively, to the complex [(L^NC)PdCl(1-κP)] (6, L^NC = 2-[(dimethylamino)methyl-κN]phenyl-κC¹). This coordination mode was nevertheless easily changed when creating a vacant coordination site at the palladium. Thus, treatment of 2a with NH₄[PF₆] in the presence of free 1 produced [PdCl(1-κP)₃][PF₆] (3), while complete halogen removal with a Ag(i) salt led to cationic complexes cis-[Pd(1-κ²O,P)₂]X₂ (4, X = CF₃SO₃ (a), ClO₄ (b), BF₄ (c)) or [(L^NC)Pd(1-κ²O,P)]X (7a and 7b), containing seven-membered O,P-chelate rings. In contrast, amide nitrogen deprotonation with KOt-Bu followed by spontaneous intramolecular halogen substitution resulted in the transformation of 6 into the chelate complex [(L^NC)Pd{(1- H)-κ²N,P}] (8) featuring a five-membered N,P-chelate ring, and in the conversion of 2a and 2b into the product of C-H bond activation [Pd{Fe(η⁵-C₅H₃CONCH₂CH₂PPh₂-κ³C,N,P)(η⁵-C₅H₅)}(1-κP)] (5), with doubly chelating deprotonated 1. Importantly, complexes 2-4-5 and 6-7-8 were mutually interconverted in triads (by protonation/deprotonation and by halide addition/abstraction), which highlights the flexible coordination and chemical stability of ligand 1. The crystal structures of 1O·½H₂O, trans-2a·MeCN, trans-2b·3C₂H₄Cl₂, trans-2c·2.5C₂H₄Cl₂, 4a·CH₂Cl₂, 5·3CHCl₃·Et₂O, and 8 were determined by single-crystal X-ray diffraction analysis, and the representative compounds were studied by cyclic voltammetry.

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.

Synthesis, structure and dynamics of NHC-based palladium macrocycles

A series of macrocyclic CNC pincer pro-ligands based on bis(imidazolium)lutidine salts with octa-, deca- and dodecamethylene spacers have been prepared and their coordination chemistry investigated. Using a Ag2O based transmetallation strategy, cationic palladium(II) chloride complexes [PdCl{CNC-(CH2)n}][BAr(F)4] (n = 8, 10, 12; Ar(F) = 3,5-C6H3(CF3)2) were prepared and fully characterised in solution, by NMR spectroscopy and ESI-MS, and in the solid-state, by X-ray crystallography. The smaller macrocyclic complexes (n = 8 and 10) exhibit dynamic behaviour in solution, involving ring flipping of the alkyl spacer across the Pd-Cl bond, which was interrogated by variable temperature NMR spectroscopy. In the solid-state, distorted coordination geometries are observed with the spacer skewed to one side of the Pd-Cl bond. In contrast, a static C2 symmetric structure is observed for the dodecamethylene based macrocycle. For comparison, palladium(II) fluoride analogues [PdF{CNC-(CH2)n}][BAr(F)4] (n = 8, 10, 12) were also prepared and their solution and solid-state structures contrasted with those of the chlorides. Notably, these complexes exhibit very low frequency (19)F chemical shifts (ca. -400 ppm) and the presence of C-H···F interactions ((2h)J(FC) coupling observed by (13)C NMR spectroscopy). The dynamic behaviour of the fluoride complexes is largely consistent with the smaller ancillary ligand; [PdF{CNC-(CH2)8}][BAr(F)4] exceptionally shows C(2v) time averaged symmetry in solution at room temperature (CD2Cl2, 500 MHz) as a consequence of dual fluxional processes of the pincer backbone and alkyl spacer.

Electrochemical evidence of intramolecular electronic communication in Zr and Hf phthalocyanines bearing ferrocene-containing β-diketonato axial ligands: structure of [PcHf(FcCOCHCOC6H5)2]

The series of zirconium(IV) and hafnium(IV) phthalocyanine complexes [PcM(FcCOCHCOR)2] (Pc = phthalocyaninato; M = Zr; R = CF3 (1), CH3 (2), C6H5 (3), Fc ((C5H5)Fe(C5H4), 4), as well as M = Hf ; R = CF3 (5), CH3 (6), C6H5 (7), and Fc (8)) were synthesized. A single-crystal X-ray diffraction analysis of the structure of [PcHf(FcCOCHCOC6H5)2], 7 (Z = 2, space group P1), showed the two axial β-diketonato ligands were orientated in such a way that the ferrocenyl groups were positioned diagonally opposite each other. From the structural determination of 7 it was clear that these complexes have a distorted D4h symmetry at the coordination site of the metal centers, which explains a splitting of the UV-vis Q band into Qx and Qy components with 3 ≤ Δλ(max,Q) ≤ 10 nm. Cyclic and square wave voltammetric studies in CH2Cl2/[N((n)Bu)4][B(C6F5)4] allowed observation of at least three phthalocyaninato macrocycle-based redox couples as well as all (i.e., two or four) well-resolved ferrocenyl couples in 1-8. For M = Zr and R = Fc, formal reduction potentials of the four ferrocenyl groups were found to be E°' = 296, 386, 538, and 687 mV versus free ferrocene. Spectroelectrochemical evidence, UV-vis Q-band maximum wavelengths, and HOMO-LUMO energy gaps as expressed by ΔE°'I-III = ΔE°'wave I - ΔE°'wave III were mutually consistent, indicating that the first phthalocyaninato ring-based oxidation occurs before ferrocenyl oxidations take place. The potential for each redox process was found to be dependent on the sum of β-diketonato R-group group electronegativities, ΣχR. Mathematical relationships for the dependency of E°' on ΣχR for all four observed ring-based redox processes as well as for the ferrocenyl-based redox processes were determined. This allowed prediction of potentials for redox processes that fall outside the workable potential window of the solvent. No significant differences were found between the corresponding redox potentials of zirconium and hafnium analogues bearing the same axial ligands.

An Alternative Preparation of 1-(N,N-Dimethylaminomethyl)-1'-(diphenylphosphanyl)ferrocene: Synthesis and Structural Characterization of Au(I) and Pd(II) Complexes with this Hybrid Ligand

1-(N,N-Dimethylaminomethyl)-1′-(diphenylphosphanyl)ferrocene (1) was synthesized in good yield by lithiation of 1-bromo-1′-(diphenylphosphanyl)ferrocene and subsequent reaction with Eschenmoser's salt (dimethylmethylideneammonium iodide). Making use of an easily accessible, nontoxic starting material, this procedure represents a convenient alternative to the original synthetic protocol based on stepwise lithiation/functionalization of 1,1′-bis(tributylstannyl)ferrocene and reductive amination [M. E. Wright, Organometallics1990, 9, 853–856]. Compound 1 has typical hybrid-donor properties. When reacted with [AuCl(tht)] (tht=tetrahydrothiophene), it afforded the expected Au^I phosphane complex [AuCl(1-κP)] (2). An attempted removal of the chloride ligand from 2 with AgClO₄ produced an ill-defined material formulated as Au(1)ClO₄. The uncoordinated amine substituent reacted with traces of hydrogen chloride formed by slow decomposition typically occurring in solution. In this manner, complexes [AuCl(Ph₂PfcCH₂NHMe₂)]Cl (3, fc=ferrocene-1,1′-diyl) and [AuCl(Ph₂PfcCH₂NHMe₂)]ClO₄ (4) were isolated from crystallizations experiments with 2 and Au(1)ClO₄, respectively. On a larger scale, complex 3 was prepared easily from 2 and hydrogen chloride. The course of reactions between [PdCl₂(cod)] (cod=cycloocta-1,5-diene) and 1 were found to depend on the ligand-to-metal ratio. Whereas the reaction with two equivalents of 1 afforded bis(phosphane) complex trans-[PdCl₂(1-κP)₂] (5), that of a Pd:P ratio 1:1 produced ligand-bridged dimer [(μ-1)PdCl₂]₂ (6). With hydrogen chloride, complex 6 reacted to afford zwitterionic complex [PdCl₃(1H-κP)] (7), which was also formed when ligand 1 and [PdCl₂(cod)] were allowed to react slowly by liquid-phase diffusion of their chloroform solutions. The compounds were characterized by spectroscopic methods (multinuclear NMR and ESI–MS), and the molecular structures of complex 2–4, 6⋅2CHCl₃ and 7⋅1.5CHCl₃ were determined by single-crystal X-ray diffraction analysis.