Electrochemical, EPR and computational results on [Fe2Cp2(CO)2]-based complexes with a bridging hydrocarbyl ligand

The dimetallacyclopentenone complexes [Fe₂Cp₂(CO)(μ−CO){μ−η¹:η³−C_αHC_β(R)C(O)}] (R = CH₂OH, 1a; R = CMe₂OH, 1b; R = Ph, 1c) were prepared by photolytic reaction of [Fe₂Cp₂(CO)₄] with alkyne according to the literature procedure. The X-ray and the electrochemical characterization of 1c are presented. The μ-allenyl compound [Fe₂Cp₂(CO)₂(μ−CO){μ−η¹:η²_α,β−C_αHC_βCMe₂][BF₄] ([2][BF₄]), obtained by reaction of 1b with HBF₄, underwent monoelectron reduction to give a radical species which was detected by EPR at room temperature. The EPR signal has been assigned to [Fe₂Cp₂(CO)₂(μ−CO){μ−η¹:η²_α,β-C_αHC_βCMe₂}], [2]^•. The molecular structures of [2]⁺ and [2]^• were optimized by DFT calculations. The unpaired electron in [2]^• is localized mainly at the metal centers and, coherently, [2]^• does not undergo carbon-carbon dimerization, by contrast with what previously observed for the μ-vinyl radical complex [Fe₂Cp₂(CO)₂(μ−CO){μ−η¹:η²-CHCH(Ph)}]^•, [3]^•. Electron spin density distributions similar to the one of [2]^• were found for the μ-allenyl radical complexes [Fe₂Cp₂(CO)₂(μ-CO){μ-η¹:η²_α,β-C_αHC_βC(R¹)(R²)}]^• (R¹ = R² = H, [4]^•; R¹ = H, R² = Ph, [5]^•; R¹ = R² = Ph, [6]^•).     

A 2-iridathiophene from reaction between IrCl(CS)(PPh3)2 and Hg(CHCHPh)2

The thiocarbonyl analogue of Vaska’s compound is produced in high yield by first treating IrCl(CO)(PPh₃)₂ with CS₂ and methyl triflate to give [Ir(κ²-C[S]SMe)Cl(CO)(PPh₃)₂]CF₃SO₃ (1), secondly, reacting 1 with NaBH₄ to give IrHCl(C[S]SMe)(CO)(PPh₃)₂ (2), and finally heating 2 to induce elimination of both MeSH and CO to produce IrCl(CS)(PPh₃)₂ (3). When IrCl(CS)(PPh₃)₂ is treated with Hg(CHCHPh)₂ the novel 2-iridathiophene, Ir[SC₃H(Ph-3)(CHCHPh-5)]HCl(PPh₃)₂ (4) is produced. The X-ray crystal structure of the iodo-derivative of 4, Ir[SC₃H(Ph-3)(CHCHPh-5)]HI(PPh₃)₂ (5) confirms the unusual 2-metallathiophene structure. Treatment of IrCl(CS)(PPh₃)₂ with Hg(CHCPh₂)₂ produces both a coordinatively unsaturated 1-iridaindene, Ir[C₈H₅(Ph-3)]Cl(PPh₃)₂ (6) and a chelated dithiocarboxylate complex, Ir(κ²-S₂CCHCPh₂)Cl(CHCPh₂)(PPh₃)₂ (7). X-ray crystal structure determinations for 6 and 7 are reported.     

Synthesis and structures of bimetallic silicon-containing imido alkylidene complexes of tungsten (R′O)2(ArN)WCH-SiR2-CHW(NAr)(OR′)2 (R = Me, Ph) and (R′O)2(ArN)WCH-SiMe2SiMe2-CHW(NAr)(OR′)2

Bimetallic alkylidene complexes of tungsten (R′O)₂(ArN)WCH-SiR₂-CHW(NAr)(OR′)₂ (R = Me (1), Ph (2)) and (R′O)₂(ArN)WCH-SiMe₂SiMe₂-CHW(NAr)(OR′)₂ (3) (Ar = ; R′ = CMe₂CF₃) have been prepared by the reactions of divinyl silicon reagents R₂Si(CHCH₂)₂ with known alkylidene compounds R′′-CHMo(NAr)(OR′)₂. (R′′ = Bu^t, PhMe₂C) Complexes 1-3 were structurally characterized. Ring opening metathesis polymerization (ROMP) of cyclooctene using compounds 1-3 as initiators led to the formation of high molecular weight polyoctenamers with predominant trans-units content in the case of 1 and 3 and predominant cis-units content in the case of 2.     

Synthesis and characterisation of the amidine complexes trans-[PtCl(NH3){HNC(NH2)R}2]Cl (R = Me, Ph, CH2Ph) derived from addition of NH3 to the coordinated nitriles in trans-[PtCl2(NCR)2]

The di-nitrile complexes trans-[PtCl₂(NCR)₂] (R = Me, Ph, CH₂Ph) react with an excess of gaseous NH₃ in CH₂Cl₂ at −10 °C to form, in high yield, the corresponding di-amidine complexes trans-[PtCl(NH₃){HNC(NH₂)R}₂]Cl in which also one chlorine ligand has been displaced by NH₃. The ¹H NMR spectra in DMSO showed the formation of different species which were characterized through NOESY, TOCSY and ¹H/¹³C heteronuclear correlations as trans-[Pt(NH₃){HNC(NH₂)R}₂(DMSO)]Cl₂ and trans-[PtCl{HNC(NH₂)R}₂(DMSO)]Cl.     

Silicon version of enamines: Amino-substituted disilenes by the reactions of the disilyne RSiSiR (R = SiPr[CH(SiMe3)2]2) with amines

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with secondary or primary amines produced amino-substituted disilenes R(R₂′N)SiSiHR 2a-d (R = SiⁱPr[CH(SiMe₃)₂]₂, R₂′NEt₂N (2a), (CH₂CH₂)₂N (2b), ^tBu(H)N (2c), and Ph₂N (2d)). Spectroscopic and X-ray crystallographic analyses of 2 showed that 2a-c have a nearly coplanar arrangement of the SiSi double bond and the amino group, giving π-conjugation between the SiSi double bond and the lone pair on the nitrogen atom, whereas 2d has a nearly perpendicular arrangement precluding such conjugation. Theoretical calculations indicate that π-conjugation between the π-orbital of the SiSi double bond and the lone pair on the nitrogen atom is markedly influenced by the torsional angle between the SiSi double-bond plane and the amino-group plane.     

On the reactivity of [IrCl(N2)(PPh3)2] with alkynylsilanes - A new route to vinylidene iridium(I) complexes

The iridium dinitrogen complex [IrCl(N₂)(PPh₃)₂] (1) was found to react with alkynylsilanes to form the vinylidene iridium(I) complexes trans- (R/R′ = Ph/Me, 2; Me/Me, 3; Bn/Me, 4; SiMe₃/Me, 5; SiEt₃/Et, 6; ⁱPr/Me, 7) and with Me₃SiCCC(O)R to yield the iridium η²-alkyne complexes trans-[IrCl{η²-Me₃SiCCC(O)R}(PPh₃)₂] (R = OEt, 9; Me, 11). Complex 9 was found to isomerize upon heating or upon UV irradiation yielding the vinylidene complex trans-[IrCl{CC(SiMe₃)CO₂Et}(PPh₃)₂] (10). The reaction of 1 with Me₃SiCCCCSiMe₃ yielded the complex trans-[IrCl{CC(SiMe₃)CCSiMe₃}(PPh₃)₂] (8), whereas with MeO₂CCCCO₂Me the iridacyclopentadiene complex [Ir{C₄(CO₂Me)₄}Cl(PPh₃)₂] (13) was formed. The complexes were characterized by means of ¹H, ¹³C and ³¹P NMR spectroscopy as well as by IR spectroscopy and microanalysis.     

The synthesis and single-crystal X-ray structures of palladium(II) and platinum(II) complexes of the difluorovinyl and 1-chloro-2-fluorovinyl-substituted phosphines, PPh2(Z-CFCFH) and PPh2(E-CClCFH)

The coordination chemistry of the fluorovinyl substituted phosphines PPh₂(Z-CFCFH) and PPh₂(E-CClCFH) with K₂MX₄ (M = Pd, Pt; X = Cl, Br, and I) salts has been investigated resulting in the first reported palladium(II) and platinum(II) complexes of phosphines containing partially fluorinated vinyl groups. The complexes have been characterised by a combination of multinuclear [¹H, ¹³C{¹H}, ¹⁹F, ³¹P{¹H}] NMR spectroscopy, and IR/Raman spectroscopy. The single-crystal X-ray structures of trans-[PdX₂{PPh₂(CFCFH)}₂], X = Cl (1), Br (2), I (3), trans-[PdCl₂{PPh₂(CClCFH)}₂] (4), cis-[PtX₂{PPh₂(CFCFH)}₂], X = Cl (5), Br (6), trans-[PtI₂{PPh₂(CFCFH)}₂] (7), and both cis- and trans-[PtCl₂{PPh₂(CClCFH)}₂] (8), have been determined. Results obtained from spectroscopic and crystallographic data suggest that replacement of a β-fluorine by hydrogen, whilst reducing the steric demand of the ligand, has little effect on the electronic character of the ligand. The presence of a proton in the vinyl group results in short proton-halide secondary interactions in the solid state (d(H?X) = 2.72(3) for 1, and 2.92(5) Å for 2) forming an infinite chain ribbon motif.     

Oxime-substituted NCN-pincer palladium and platinum halide polymers through non-covalent hydrogen bonding (NCN = [C6H2(CH2NMe2)2-2,6])

The oxime-substituted NCN-pincer molecules HONCH-1-C₆H₃(CH₂NMe₂)₂-3,5 (2a) and HONCH-4-C₆H₂(CH₂NMe₂)₂-2,6-Br-1 (2b) were accessible by treatment of the benzaldehydes H(O)C-4-C₆H₃(CH₂NMe₂)₂-3,5 (1a) and H(O)C-4-C₆H₂(CH₂NMe₂)₂-2,6-Br-1 (1b) with an excess of hydroxylamine. In the solid state both compounds are forming polymers with intermolecular O-H?N connectivities between the Me₂NCH₂ substituents and the oxime entity of further molecules of 2a and 2b, respectively. Characteristic for 2a and 2b is a helically arrangement involving a crystallographic 2₁ screw axis of the HONCH-1-C₆H₃(CH₂NMe₂)₂-3,5 and HONCH-4-C₆H₂(CH₂NMe₂)₂-2,6-Br-1 building blocks.The reaction of 2b with equimolar amounts of [Pd₂(dba)₃ · CHCl₃] (3) (dba = dibenzylidene acetone) or [Pt(tol)₂(SEt₂)]₂ (4) (tol = 4-tolyl) gave by an oxidative addition of the C-Br unit to M coordination polymers with a [(HONCH-4-C₆H₂(CH₂NMe₂)₂-2,6)MBr] repeating unit (5: M = Pd, 6: M = Pt). Complexes 5 and 6 are in the solid state linear hydrogen-bridged polymers with O-H?Br contacts between the oxime entities and the metal-bonded bromide.     

Understanding the role of an easy-to-prepare aldimine-alkyne carboamination catalyst, [Ti(NMe2)3(NHMe2)][B(C6F5)4]

A series of reactivity studies of the carboamination pre-catalyst [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄] as well as the preparation of other catalysts are reported in this work. Treatment of [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄] with the aldimines Ar′NCHtol (Ar′ = 2,6-Me₂C₆H₃, tol = 4-MeC₆H₄), and depending on the reaction conditions, results in isolation of [Me₂NCHR′][B(C₆F₅)₄] (1) or (Me₂N)₂CHtol, as well as the asymmetric titanium dimer [(Me₂N)₂(HNMe₂)Ti(μ₂-N[2,6-Me₂C₆H₃])₂Ti(NHMe₂)(NMe₂)][B(C₆F₅)₄] (2). Protonation of CpTi(NMe₂)₃ and Cp^∗Ti(NMe₂)₃ results in isolation of the salts, [CpTi(NMe₂)₂(NHMe₂)][B(C₆F₅)₄] (3) and [Cp^∗Ti(NMe₂)₂(NHMe₂)][B(C₆F₅)₄] (4), respectively. Treatment of compounds 3 or 4 with H₂N[2,6-ⁱPr₂C₆H₃] results in formation of the imido salts [CpTi(N[2,6-ⁱPr₂C₆H₃])(NHMe₂)₂][B(C₆F₅)₄] (5) (58% yield) or [Cp^∗Ti(N[2,6-ⁱPr₂C₆H₃])(NHMe₂)₂][B(C₆F₅)₄] (6). When Ti(NMe₂)₄ is treated with [Et₃Si][B(C₆F₅)₄], the salt [Ti(NMe₂)₃(N[SiEt₃]Me₂)][B(C₆F₅)₄] (7) is obtained, and treatment of the latter with [2,6-ⁱPr₂C₆H₃]NCHtol produces the imine adduct [Ti(NMe₂)₃(κ¹-[2,6-ⁱPr₂C₆H₃]NCHtol)][B(C₆F₅)₄] (8). The carboamination catalytic activity of complexes 2-7 was investigated and compared to [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄]. Likewise, a proposed mechanism to the active carboamination catalyst stemming from [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄] is described.     

Self-assembly directed by C-H activation: Synthesis and characterization of [(CpIr)2(R-NC-Ph-CNR)]2(4,4-bipyridine)2·(OTf)4 (R = Ph, Me)

Self-assembly of a novel class of bis-imine-cyclometalated macrocycles [(Cp^∗Ir)₂(Ph-NC-Ph-CN-Ph)]₂(4,4′-bipyridine)₂·(OTf)₄ (3a) and [(Cp^∗Ir)₂(Me-NC-Ph-CN-Me)]₂(4,4′-bipyridine)₂·(OTf)₄ (3b) was directed by double-site C-H activations of aromatic bis-imine substrates. Two synthetic routes were established, using either (i) binuclear cyclometalated complexes (Cp^∗Ir)₂L1Cl₂ (1a) and (Cp^∗Ir)₂L2Cl₂ (1b) or (ii)4,4′-bipyridine(bpy)-bridged complex (Cp^∗IrCl₂)₂(bpy) (2) as starting materials. All the products were characterized by IR, ¹H NMR and EA. Isomers were found in macrocyclic complexes, which were thermodynamically stable from reversible transformation in days. Highly robust structure of the cyclometalated macrocycles was indicated by the existence of stable isomer pairs. One isomer of 3b was determined by single-crystal X-ray diffraction. It was a rare case for half-sandwich metallosupramolecular macrocycles that weak interactions between macrocycles and OTf ions were fully captured in detail, and were demonstrated to be essential for the maintenance of tunnel structures of macrocycles in crystal packing.