Synthesis and characterization of yttrium complexes bearing a bulky arylamido ancillary ligand

Reaction of anhydrous YCl₃ with 1 equiv. of arylamido lithium 2,6-ⁱPr₂C₆H₃NSiⁱPr₃Li in THF gave an anionic mono-arylamido-ligated yttrium dichloride complex {[2,6-ⁱPr₂C₆H₃NSiⁱPr₃]YCl₂(THF)}₂[LiCl(THF)₂] (1). Alkylation of 1 with 4 equiv. of LiCH₂SiMe₃ afforded an anionic arylamido-ligated yttrium tris(alkyl) complex [2,6-ⁱPr₂C₆H₃NSiⁱPr₃]Y(CH₂SiMe₃)₃Li(THF)₂ (2). Both complexes were characterized by NMR, elementary analysis, and X-ray structural determination.     

Synthesis, reactivity, and structures of dialuminum complexes containing linked ketiminate ligands

Linked bis(ketimine) (1) can be prepared with the reaction of excess 2,4-pentanedione and 4,4′-methylene-bis(2,6-diisopropylaniline) in methanol in the presence of catalytic amount of formic acid. The dialuminum alkyl complexes containing the linked bis(ketiminate) dianionic ligands, [OC(Me)CHC(Me)N(2,6-ⁱPr₂C₆H₂-4)AlR₂]₂CH₂ (2, R = Me; 3, R = Et), were prepared by a reaction of 2 equiv AlR₃ with [OC(Me)CHC(Me)NH(2,6-ⁱPr₂C₆H₂-4)]₂CH₂ in methylene chloride. Reactions of 2 with 2 and 4 equiv of I₂ gave corresponding aluminum iodo complexes 4 and 5, respectively. Treatment of 5 with 2 equiv of AgBF₄, however, gave a diboron complex, [OC(Me)CHC(Me)N(2,6-ⁱPr₂C₆H₂-4)BF₂]₂CH₂ (6), in 18% isolated yield. All new complexes have been characterized by ¹H and ¹³C NMR spectroscopy and complexes 2, 3, and 6 are also confirmed by X-ray diffraction.     

Dinuclear metal phosphonates and -phosphates

The reaction of Cu(II) or Cd(II) salts with 2,4,6-iPr₃C₆H₂PO₃H₂, 2,4,6-iPr₃C₆H₂CH₂PO₃H₂ or 2,6-iPr₂C₆H₃OPO₃H₂ in the presence of strong chelating nitrogen ligands such as 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2-pyridylpyrazole (pypz) or 3,5-dimethyl pyrazole (dmpz) as the ancillary ligands afforded dinuclear copper or cadmium complexes [Cu₂(2,4,6-iPr₃C₆H₂PO₃H)₄(bpy)₂] (4), [Cu₂(2,6-iPr₂C₆H₃OPO₃H)₂(bpy)₂(OAc)₂(CH₃OH)₂]·(CH₃OH) (5), [Cd₂(2,6-iPr₂C₆H₃OPO₃H)₄ (bpy)₂(CH₃OH)₂]·2(CH₃OH) (6), [Cd₂(2,6-iPr₂C₆H₃OPO₃H)₄(phen)₂] (7), [Cu₂(2,6-iPr₂C₆H₃OPO₃H)₂(PyPz)₂(CH₃OH)₂] (8) and [Cu₂(2,4,6-iPr₃C₆H₂CH₂PO₃H)₂(DMPz)₂Cl₂]·(CH₃OH) (9) The molecular structures of 4-7 are grossly similar. The common structural features in these complexes are that the two metal centers are bridged by two bidentate [RPO₂(OH)]⁻ ligands generating a central eight-membered ring. Each of the metal centers also contains a chelating nitrogen ligand and a monodentate phosphonate or a phosphate ligand. In 5 and 6 other terminal ancillary ligands are also present. In compound 8, each of the two copper centers contains a monodentate [RPO₂(OH)]⁻ ligand along with a molecule of methanol. The two coppers are bridged by two monoanionic pyridylpyrazole ligands. The molecular structure of 9 is similar to that of 4-7. However, in 9 each of the two copper centers contain only terminal monodentate ligands in the form of two chlorides and a pyrazole. Magnetic studies on all of these copper complexes reveal an anti-ferromagnetic behavior at low temperatures. In addition, these complexes were found to be artificial nucleases and can convert supercoiled pBR322 DNA form I into nick form II in 1 min in the presence of an external oxidant through a hydrolytic and/or an oxidative pathway.     

Uncovering alternate reaction pathways to access uranium(IV) mixed-ligand aryloxide-chloride and alkoxide-chloride metallocene complexes: Synthesis and molecular structures of (C5Me5)2U(O-2,6-Pr2C6H3)(Cl) and (C5Me5)2U(O-Bu)(Cl)

Reaction of the trivalent uranium complex (C₅Me₅)₂U(O-2,6-ⁱPr₂C₆H₃)(THF) (1) with copper(I) chloride affords the corresponding tetravalent mixed-ligand aryloxide-chloride complex (C₅Me₅)₂U(O-2,6-ⁱPr₂C₆H₃)(Cl) (2). The oxidative functionalization protocol cannot be extended to the synthesis of (C₅Me₅)₂U(O-^tBu)(Cl) (3) since the corresponding trivalent precursor is not stable. Salt metathesis between (C₅Me₅)₂UCl₂ and KO^tBu is the method of choice for the preparation of the tetravalent alkoxide-chloride derivative (C₅Me₅)₂U(O-^tBu)(Cl) (3). The X-ray crystal structures of (C₅Me₅)₂U(O-2,6-ⁱPr₂C₆H₃)(Cl) (2) and (C₅Me₅)₂U(O-^tBu)(Cl) (3) are reported and represent the first structurally characterized uranium(IV) metallocene aryloxide-chloride and alkoxide-chloride complexes, respectively. Both complexes adopt a pseudo-tetrahedral geometry, with a chloride and aryloxide/alkoxide ligand occupying the plane bisecting the metallocene unit.     

Two new bulky amido ligands useful for the preparation of metal complexes and examples of their reactivity

The search for new ligands with interesting properties is a quest that can occupy much of a synthetic chemist’s time. We have recently discovered two new ligands based on an adamantyl-substituted, 2,6-ⁱPr₂-substituted phenyl (Dipp) system. In an attempt to prepare the extremely bulky amine [(ad)(2,6-ⁱPr₂C₆H₃)NH] (ad = adamantyl) we found instead that the adamantyl group attacks the aromatic ring in the 4-position to form a new primary amine, (4-ad-2,6-ⁱPr₂C₆H₂)NH₂ (1) (ad-Dipp-NH₂), characterized by normal techniques. Compound 1 could be converted into a Li salt by a 1:1 reaction with ⁿBuLi, or converted into a more bulky silylamine, [(ad-Dipp)NH(SiMe₃)] (3), by treatment with Me₃SiCl. We have characterized the lithium salt by X-ray crystallography as the dimeric complex, [(ad-Dipp)NHLi(Et₂O)]₂ (2). The lithium amide can be used as a reagent towards metal halides, and we have discovered that its reaction with SnCl₂ yields a compound with a tetrameric, [Sn-N]₄ cubane-like cage structure. We have also demonstrated the ligand behavior of 3 by its reaction with Bu₂Mg in THF to form a monomeric Mg-amide with two THF solvent molecules attached. These new ligands can provide advantages over conventional ligands in terms of improved solubility and ease of crystallization.     

Novel rhodium complexes containing a bulky iminophosphine ligand and their use as catalysts for the hydroboration of vinylarenes

Addition of o-Ph₂PC₆H₄CHN-2,6-ⁱPr₂C₆H₃ (1) to [RhCl(coe)₂]₂ (coe = cis-cycloctene) gave several new iminophosphino rhodium(I) complexes including [Rh(κ²-o-Ph₂PC₆H₄CHN-2,6-ⁱPr₂C₆H₃)(μ-Cl)]₂ (2). Addition of 1 to Rh(acac)(coe)₂ (acac = acetylacetonato) gave [Rh(acac)(κ²-o-Ph₂PC₆H₄CHN-2,6-ⁱPr₂C₆H₃)] (3) in yields of up to 75%. Complex 3 has been examined for its ability to catalyze the hydroboration of a series of vinyl arenes. Reactions using catecholborane and pinacolborane seem to proceed largely through a dehydrogenative borylation mechanism to give a number of boronated products.     

Synthesis, structures, photoluminescent and electroluminescent properties of boron complexes with anilido-imine ligands

Syntheses of three new N-arylanilido-arylimine bidentate Schiff base type ligand precursors, ortho-C₆H₄[NH(2,6-ⁱPr₂C₆H₃)](CHNAr¹) [Ar¹ = p-FC₆H₄ (2a); C₆H₅ (2b); p-OMeC₆H₄ (2c)], and their four-coordinated boron complexes, ortho-C₆H₄[N(2,6-ⁱPr₂C₆H₃)](CHNAr¹)BF₂ [Ar¹ = p-FC₆H₄ (3a); C₆H₅ (3b); p-OMeC₆H₄ (3c)] are described. The boron complexes 3a-3c were synthesized from the reaction of BF₃(OEt₂) with the lithium salt of their corresponding ligand. All complexes were characterized by ¹H and ¹³C NMR spectroscopy and molecular structures of complexes 3a and 3c were determined by X-ray crystallography. The photophysical properties of complexes 3a-3c were briefly examined. All three complexes display bright green fluorescence in solution and in the solid state. Electroluminescent devices with complex 3c as the emitter were fabricated. These devices were found to give green emission with maximum current efficiency of 2.92 cd/A and maximum luminance of 670 cd/m².     

Diffusion NMR studies on neutral and cationic square planar palladium(II) complexes

Diffusion NMR investigations were carried out in CD₂Cl₂ for a series of neutral (1-7) and cationic (8-10) square planar palladium complexes. Diffusion data were elaborated through a modified Stokes-Einstein equation that takes into account the size and shape of molecules. The hydrodynamic volume at infinite dilution of all complexes was found to be similar to the crystallographic volume and always much larger than the van der Waals volume. The self-aggregation tendency of [Pd(N,C⁻)(N,N)][PF₆] ionic complexes [(N,C⁻) = (C₆H₄-(Ph)C(O)-CN-Et); 8, (N,N) = 2,2′-bipirydine; 9, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(Me)-C(Me)N(2,6-(iPr)₂-C₆H₃); 10, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(R′)-C(R′)N(2,6-(iPr)₂-C₆H₃), R′₂ = naphthalene-1,8-diyl] was investigated by performing ¹H and ¹⁹F diffusion experiments as a function of the concentration. Clear evidence for the formation of ion triples containing two cationic units was obtained for 8, most likely due to the establishment of a weak Pd?O interaction. The tendency to form ion triples was much reduced in 9 and 10, having an increased steric hindrance in the apical positions. While 9 showed the usual tendency to afford a mixture of free ions and ion pairs, solvated ions were the predominant species in the case of 10 even at high concentration values (approaching 100 mM).     

Synthesis and characterization of β-diketiminate germanium(II) and tin(II) bromides

The equimolar reaction of a β-diketiminate lithium salt LLi(OEt₂) [L = HC(CMeNAr)₂; Ar = 2,6-iPr₂C₆H₃] with either GeBr₂ or SnBr₂ in diethyl ether affords the synthetically useful monomeric β-diketiminate-element halides LGeBr (1) and LSnBr (2), respectively. Both are soluble in hydrocarbon solvents, stable in inert atmosphere, and have been characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction analysis.     

Efficient guanylation of aromatic and heterocyclic amines catalyzed by cyclopentadienyl-free rare earth metal amides

Diamido-supported rare earth metal amides with the general formula {(CH₂SiMe₂)[(2,6-ⁱPr₂C₆H₃)N]₂}LnN(SiMe₃)₂(THF) [(Ln = Yb(1), Y(2), Dy(3), Sm (4), Nd (5)] were found to be highly efficient catalysts for the guanylation of both aromatic and heterocyclic amines under mild conditions. It is found that these catalysts are compatible with a wide range of substituents such as ⁱPr, Me, and MeO having electron-donating property and substituents such as Cl, Br, and O₂N having electron-withdrawing property on the aromatic rings of the aromatic or the heterocyclic amines. The methodology has also the advantages of easy preparation of the catalysts, quick conversion of the substrates to products, mild reaction conditions, and low catalyst loading.     

Diphosphine substitution in pentakis(arylisocyanide)cobalt(I) complexes; 31P NMR,cyclic voltammetric and ESI mass spectrometry studies

Five new complexes of the type [Co(CNC₆H₃iPr₂-2,6)₄PPh₂-R′-PPh₂]X, X = BF₄, ClO₄; R′ =–(CH₂)₂– (1), –(CH₂)₃– (2), –CHCH-trans (3), –CC– (4) and –C₆H₄-p (5); and two new bimetallic complexes, [{Co(CNC₆H₃iPr₂-2,6)₄}₂(μ-PPh₂(CH₂)₃PPh₂)](ClO₄)₂ (6) and [{Co(CNC₆H₃iPr₂-2,6)₄}₂(μ-PPh₂C₆H₄PPh₂-p)](ClO₄)₂ (7), have been synthesized and characterized by various spectroscopic methods.Known monometallic and bimetallic complexes bearing the ligand CNC₆H₃Et₂-2,6 instead of CNC₆H₃iPr₂-2,6 have been included in the ³¹P NMR, cyclic voltammetric and mass spectrometry studies.Comparison of the CNC₆H₃iPr₂-2,6 with the CNC₆H₃Et₂-2,6 complexes shows that the increased steric bulkiness of the former makes it more suitable for synthesis of the monometallic complexes, whilst the CNC₆H₃Et₂-2,6 is more apt to give bimetallic complexes.Thus, the two arylisocyanides are complementary with respect to synthesis of the monometallic and bimetallic complexes.The ³¹P NMR indicates that the diphosphines in monometallic complexes behave as non-fluxional, monodentate ligands at ambient temperature, with ³¹P–³¹P coupling shown for the PPh₂CH₂PPh₂, PPh₂(CH₂)₂PPh₂ and PPh₂CCPPh₂ ligands. Cyclic voltammetry fails to show electronic communication in the bimetallic complexes, and mass spectrometry indicates significantly greater stability for fragments containing potentially chelating diphosphines as compared to diphosphines that cannot chelate.     

Neutral and cationic Fe(II) β-diketiminate complexes

The three-coordinate, 12-valence electron complexes [(^MeBDK)FeR] (^MeBDK = [HC(C(Me)NAr)₂]⁻, Ar = 2,6-iPr₂C₆H₃, R = CH₂Ph, CH₂SiMe₃) are reported as well as their reactivity towards Lewis bases. With perfluoroaryl borane and -borate type activators, the monoalkyls react to give alkyl-free paramagnetic cationic iron species counterbalanced by perfluorinated arylborate anions. The paramagnetic nature of the cations permits the observation of weak and dynamic interactions with these anions via ¹⁹F NMR spectroscopy.     

Facile synthesis and characterization of μ-chloro, azido, thiocyanato bridged cyclometallated Pd(II) containing Schiff-base ligands

μ-Chloro bridged dinuclear cyclometallated Pd(II) complexes [Pd{(4-R)C₆H₃CHNC₆H₃-2,6-i-Pr₂}(μ-Cl)]₂ (R = H, OMe) were prepared by reaction of Na₂PdCl₄ with benzylideneanilines. Unexpectedly, Na₂PdCl₄ reacted with Schiff-bases bearing a furyl or a thienyl ring to give N-coordinated non-cyclometallated Pd(II) species [Pd(C₄H₃XCHNC₆H₃-2,6-i-Pr₂)₂Cl₂] (X = O, S). Treating [Pd{(4-R)C₆H₃CHNC₆H₃-2,6-i-Pr₂}(μ-Cl)]₂ (R = H, OMe) with an excess of NaN₃ or NH₄SCN generated μ-N₃ bridged or μ-SCN bridged cyclometallated Pd(II) complexes [Pd{(4-R)C₆H₃CHNC₆H₃-2,6-i-Pr₂}(μ-Y)]₂ (R = H, OMe; Y = N₃, NCS). The complexes were characterized by FTIR, NMR spectroscopy, elemental analysis and X-ray crystallography.     

Synthesis and structural investigations of Ni(II)- and Pd(II)-coordinated α-diimines with chlorinated backbones

Novel square planar Pd(II) α-diimines [PdX₂{ArNC(Cl)}₂], where Ar = C₆H₅, (2,6-Me₂C₆H₃), (2,6-ⁱPr₂C₆H₃) and X = Cl or Br, and the octahedral Ni(II) complex [NiBr₂{(C₆H₅)NC(Cl)}₂(THF)₂] have been prepared and characterised by spectroscopic methods. For two of the Pd(II) complexes and the Ni(II) complex the crystal structures were determined by X-ray crystallography. A further insight into the geometry and electronic structure of [PdBr₂{(2,6-Me₂C₆H₃)NC(Cl)}₂] was gained using density functional theoretical calculations (DFT). This compound resembles structurally and electronically typical olefin polymerisation pre-catalysts supported by α-diimines incorporating methyl- and 1,8-naphtalenyl substituents at the ligand backbone. The chlorine-substituted backbone of the free ligand [2,6-Me₂C₆H₃NC(Cl)]₂ can be employed in further alkylation reactions to generate new multifunctional ligand prototypes with potential uses as ansa-metallocene/diimines building blocks for catalytic applications of heterobimetallic complexes.     

Reactivity study of arene(azido)ruthenium N∩O-base complexes with activated alkynes

Substitution reaction of chloro η⁶-arene ruthenium N∩O-base complexes [(η⁶-arene)Ru(N∩O)Cl] [N∩O = pyrazine-2-carboxylic acid (pca-H), 8-hydroxyquinoline (hq-H); arene = p-ⁱPrC₆H₄Me, N∩O = hq (1); arene = C₆Me₆, N∩O = hq (2)] with NaN₃ yield the neutral arene ruthenium azido complexes of the general formula [(η⁶-arene)Ru(N∩O)N₃] [N∩O = pca, arene = p-ⁱPrC₆H₄Me (3), arene = C₆Me₆ (4); N∩O = hq, arene = p-ⁱPrC₆H₄Me (5), arene = C₆Me₆ (6)]. These complexes undergo [3 + 2] dipolar cycloaddition reaction with activated alkynes dimethyl and diethyl acetylenedicarboxylates to yield the arene triazole complexes [(η⁶-arene)Ru(N∩O){N₃C₂(CO₂R)₂}] [N∩O = pca, R = Me, arene = p-ⁱPrC₆H₄Me (7), C₆Me₆ (8); R = Et, arene = p-ⁱPrC₆H₄Me (9), C₆Me₆ (10); N∩O = hq, R = Me, arene = p-ⁱPrC₆H₄Me (11) C₆Me₆ (12); R = Et, arene = p-ⁱPrC₆H₄Me (13), C₆Me₆ (14)]. On the bases of proton NMR study, in the above triazole complexes N(2) isomers are assigned with dimethylacetylenedicarboxylate whereas N(1) isomers with diethylacetylenedicarboxylate. All complexes have been characterized by IR and NMR spectroscopy as well as by elemental analysis. The molecular structures of the azido complexes [(η⁶-p-ⁱPrC₆H₄Me)Ru(pca)N₃] (3), [(η⁶-p-ⁱPrC₆H₄Me)Ru(hq)N₃] (5) and [(η⁶-C₆Me₆)Ru(hq)N₃] (6) have been established by single crystal X-ray diffraction studies.     

The synthesis of technetium(V) complexes containing sterically bulky thiolate ligands. The molecular structure of tetrabutylammonium oxotetrakis(2,4,6-trimethylbenzenethiolato)technetate(V)

The reactions between [TcOCl₄]⁻ and the sterically bulky thiols ArSH (Ar = 2,4,6-Me₃C₆H₂, 2,4,6- Prⁱ₃C₆H₂ and 2,6-Ph₂C₆H₃) in methanol afford complexes of formula [TcO(SAr)₄]⁻ which may be isolated as salts with bulky organic cations. The molecular structure of [Buⁿ₄N][TcO(2,4,6-Me₃C₆H₂S)₄] was determined by X-ray diffraction methods. The Tc(V) centre was found to adopt the expected square pyramidal geometry in which an oxo group occupies the apical site and the four thiolate sulphurs the basal sites. The TcO distance is 1.659(11) Å and the average TcS distance 2.38(2) Å. The average cis STcS, trans STcS and OTcS angles are respectively 82.7(6)°, 138.4(3)° and 110.8(4)°.     

Nickel promoted C-H, C-C and C-O bond activation in solution

Reaction of NiI₂ with the PCP-ligand {1-Et-2,6-(CH₂PⁱPr₂)₂-C₆H₃} (1) results in selective activation of the strong sp²-sp³ aryl-ethyl bond to afford the aryl-nickel complex [Ni{2,6-(CH₂PⁱPr₂)₂-C₆H₃}I] (2), whereas reaction of NiI₂ with {1,3,5-(CH₃)₃-2,6-(CH₂PⁱPr₂)₂-C₆H} (4) leads to the formation of the benzylic complex [Ni{1-CH₂-2,6-(CH₂PⁱPr₂)₂-3,5-(CH₃)₂-C₆H}I] (5) by selective C-H bond activation. Thermolysis of 5 results in formation of [Ni{2,6-(CH₂PⁱPr₂)₂-3,5-(CH₃)₂-C₆H}I] (6) by activation of the sp²-sp³ C-C bond. The identity of the new 16-electron complexes 2 and 6 was confirmed by reaction of NiI₂ with {1,3-(CH₂PⁱPr₂)₂-C₆H₄} (3) and {1,3-(CH₃)₂-4,6-(CH₂PⁱPr₂)₂-C₆H₂} (7), respectively, lacking the aryl-alkyl groups between the “phosphines arms” (alkyl=ethyl, methyl). Complexes 2 and 5 have been fully characterized by X-ray analysis. Nickel-based activation of an unstrained C-O single bond was observed as well. Reaction of the aryl-methoxy bisphosphine {1-OMe-2,6-(CH₂PⁱPr₂)₂-C₆H₃} (8) with NiI₂ results in the formation of the phenoxy complex [Ni{1-O-2,6-(CH₂PⁱPr₂)₂-C₆H₃}I] (9) by selective sp³-sp³ C-O bond activation.     

Synthesis, crystal structures and spectroscopic properties of copper(I) complexes containing β-dialdiminato supporting ligands

Two mononuclear neutral copper(I) complexes, Cu(L¹)PPh₃ (1), Cu(L²)(PPh₃)₂ (2) ([L¹]⁻ = [{N(C₆H₃ⁱPr₂-2,6)C(H)}₂CPh]⁻; [L²]⁻ = [{N(C₆H₅)C(H)}₂CPh]⁻) have been synthesized and structurally characterized by X-ray crystallography. In complex 1, the copper(I) atom is in a distorted three-coordinate trigonal planar environment, whereas in complex 2 with the less sterically hindered β-dialdiminato ligand, the copper(I) atom is the centre of a four-coordinate distorted tetrahedron. At room temperature complexes 1 and 2 in a film of PMMA exhibit green emission at 543 and 549 nm with lifetimes of 5.28 and 5.32 ns, respectively.     

m-Terphenylphosphines: Synthesis, structures and coordination properties

A series of m-terphenylphosphines TerphPCl₂, TerphPH₂ and TerphPMe₂ (Terph = 2,6-Mes₂C₆H₃-, 2,6-(4-t-BuC₆H₄)₂C₆H₃-, 2,6-(3,5-Me₂C₆H₃)₂C₆H₃-, 2,6-(2,6-Et₂C₆H₃)₂C₆H₃-, and 2,6-(2,6-i-Pr₂C₆H₃)₂C₆H₃-; Mes = 2,4,6-Me₃C₆H₂-) was prepared and fully characterized. The structural investigation by X-ray crystallography and density functional theory revealed significant distortions in the environment of the ipso carbon and phosphorus centers. These can be traced back to steric interactions and repulsions of the chlorine and methyl substituents on phosphorus with one of the flanking arenes of the m-terphenyl substituents. The primary phosphine 2,6-Mes₂C₆H₃PH₂, 6, and the dimethylphosphine 2,6-(3,5-Me₂C₆H₃)₂C₆H₃PMe₂, 9, readily form complexes with the Cl₂Ru(p-cymene) complex fragment, whereas the larger phosphine 2,6-Mes₂C₆H₃PMe₂, 8, does not. Heating of the complexes TerphPR₂Ru(Cl₂)(p-cymene) 11 and 12 and the mixture of 8 and {(p-cymene)RuCl₂}₂ lead to expulsion of the p-cymene ligand and intramolecular η⁶ coordination of one of the flanking arene rings to the ruthenium center to afford the complexes Cl₂RuP(H₂)C₆H₃-2-η⁶-Mes-6-Mes, 13, Cl₂RuP(Me₂)C₆H₃-2-η⁶-Mes-6-Mes, 14, and Cl₂RuP(H₂)C₆H₃-2-η⁶-(3,5-Me₂C₆H₃)-6-(3,5-Me₂C₆H₃), 15. All complexes were characterized by NMR spectroscopy and complexes 14 and 15 also by X-ray crystallography.     

Bis(acetylacetonato)ruthenium(II) complexes containing bulky tertiary phosphines. Formation and redox behaviour of Ru(acac)2 (PR3) (R = Pr, Cy) complexes with ethene, carbon monoxide, and bridging dinitrogen

Reaction of cis-[Ru(acac)₂(η²-C₈H₁₄)₂] (1) (acac = acetylacetonato) with two equivalents of PⁱPr₃ in THF at −25 °C gives trans-[Ru(acac)₂(PⁱPr₃)₂], trans-3, which rapidly isomerizes to cis-3 at room temperature. The poorly soluble complex [Ru(acac)₂(PCy₃)₂] (4), which is isolated similarly from cis-[Ru(acac)₂(η²-C₂H₄)₂] (2) and PCy₃, appears to exist in the cis-configuration in solution according to NMR data, although an X-ray diffraction study of a single crystal shows the presence of trans-4. In benzene or toluene 2 reacts with PⁱPr₃ or PCy₃ to give exclusively cis-[Ru(acac)₂(η²-C₂H₄)(L)] [L = PⁱPr₃ (5), PCy₃ (6)], whereas in THF species believed to be either square pyramidal [Ru(acac)₂L], with apical L, or the corresponding THF adducts, can be detected by ³¹P NMR spectroscopy. Complexes 3-6 react with CO (1 bar) giving trans-[Ru(acac)₂(CO)(L)] [L = PⁱPr₃ (trans-8), PCy₃ (trans-9)], which are converted irreversibly into the cis-isomers in refluxing benzene. Complex 5 scavenges traces of dinitrogen from industrial grade dihydrogen giving a bridging dinitrogen complex, cis-[{Ru(acac)₂(PⁱPr₃)} ₂(μ-N₂)] (10). The structures of cis-3, trans-4, 5, 6 and 10 · C₆H₁₄ have been determined by single-crystal X-ray diffraction. Complexes trans- and cis-3, 5, 6, cis-8, and trans- and cis-9 each show fully reversible one-electron oxidation by cyclic voltammetry in CH₂Cl₂ at −50 °C with E_1/2(Ru^3+/2+) values spanning −0.14 to +0.92 V (versus Ag/AgCl), whereas for the vinylidene complexes [Ru(acac)₂ (CCHR)(PⁱPr₃)] [R = SiMe₃ (11), Ph (12)] the process is irreversible at potentials of +0.75 and +0.62 V, respectively. The trend in potentials reflects the order of expected π-acceptor ability of the ligands: PⁱPr₃, PCy₃ <C ₂H₄ < CCHR < CO. The UV-Vis spectrum of the thermally unstable, electrogenerated Ru^III-ethene cation 6⁺ has been observed at −50 °C. Cyclic voltammetry of the μ-dinitrogen complex 10 shows two, fully reversible processes in CH₂Cl₂ at −50 °C at +0.30 and +0.90 V (versus Ag/AgCl) corresponding to the formation of 10⁺ (Ru^II,III) and 10²⁺ (Ru^III,III). The former, generated electrochemically at −50 °C, shows a band in the near IR at ca. 8900 cm⁻¹ (w_1/2 ca. 3700 cm⁻¹) consistent with the presence of a valence delocalized system. The comproportionation constant for the equilibrium 10 + 10²⁺ ? 2 10⁺ at 223 K is estimated as 10^13.6.