Chromium(0)-rhodium(I) metal exchange: Synthesis and X-ray structure of new Fischer (NHC)carbene complexes of rhodium(I)

An easy approach to Fischer (NHC)carbene complexes of rhodium(I) 3 from methoxy- and aminocarbene complexes of chromium 1 and (NHC)(cod)RhCl (2) is described. The process involves the transfer of the carbene unit and a CO ligand from chromium to rhodium. The X-ray analysis is provided for 3d and the preliminary results on their thermal stability and reactivity toward alkynes and allenes are also reported.     

Mono and dinuclear iridium, rhodium and ruthenium complexes containing chelating carboxylato pyrazine ligands: Synthesis, molecular structure and electrochemistry

The mononuclear complexes [(η⁵-C₅Me₅)IrCl(L¹)] (1), [(η⁵-C₅Me₅)RhCl(L¹)] (2), [(η⁶-p-PrⁱC₆H₄Me)RuCl(L¹)] (3) and [(η⁶-C₆Me₆)RuCl(L¹)] (4) have been synthesised from pyrazine-2-carboxylic acid (HL¹) and the corresponding complexes [{(η⁵-C₅Me₅)IrCl₂}₂], [{(η⁵-C₅Me₅)RhCl₂}₂], [{(η⁶-p-PrⁱC₆H₄Me)RuCl₂}₂], and [{(η⁶-C₆Me₆)RuCl₂}₂], respectively. The related dinuclear complexes [{(η⁵-C₅Me₅)IrCl}₂(μ-L²)] (5), [{(η⁵-C₅Me₅)RhCl}₂(μ-L²)] (6), [{(η⁶-p-PrⁱC₆H₄Me)RuCl}₂(μ-L²)] (7) and [{(η⁶-C₆Me₆)RuCl}₂(μ-L²)] (8) have been obtained in a similar manner from pyrazine-2,5-dicarboxylic acid (H₂L²). Compounds isomeric to the latter series, [{(η⁵-C₅Me₅)IrCl}₂(μ-L³)] (9), [{(η⁵-C₅Me₅)RhCl}₂(μ-L³)] (10), [{(p-PrⁱC₆H₄Me)RuCl}₂(μ-L³)] (11) and [{(η⁶-C₆Me₆)RuCl}₂(μ-L³)] (12), have been prepared by using pyrazine-2,3-dicarboxylic acid (H₂L³) instead of H₂L². The molecular structures of 2 and 3, determined by X-ray diffraction analysis, show the pyrazine-2-carboxylato moiety to act as an N,O-chelating ligand, while the structure analyses of 5-7, confirm that the pyrazine-2,5-dicarboxylato unit bridges two metal centres. The electrochemical behaviour of selected representatives has been studied by voltammetric techniques.     

A Symmetrically Bridging Triarylsilyl Ligand in a Dinuclear Rhodium Complex: Synthesis and Structure of [LRh(H)(µ-Cl)(µ-SiAr2)(µ-SiAr3)Rh(H)L] (Ar=Ph,p-FC6H4; L=PiPr3)

Simply warming solutions of the dinuclear complexes 1 provides novel complexes 2 [Eq. (a); Ar = Ph, p-FC₆H₄; L = PiPr₃], which contain a bridging triarylsilyl ligand and show unusual thermal stability. Compounds with this type of symmetric structure are of interest as models of the transition state for the migration of tertiary silyl groups in a bimetallic framework.     

Square planar diphosphinoazine rhodium(I) amido carbonyl complexes with an unsymmetrical PNP′ pincer-type coordination

A series of novel diphosphinoazine rhodium amido carbonyl complexes [{R₂PCHC(Bu^t)–NNC(Bu^t)CH₂PR₂}Rh(CO)] (R = Ph, Prⁱ, c-C₆H₁₁, Bu^t) was prepared by deprotonation of cationic diphosphinoazine rhodium amino carbonyl complexes. The complexes were characterized by NMR as were also their precursors. The crystal structures of two cationic and one neutral deprotonated complex were determined by X-ray diffraction showing the complexes to be essentially planar with mutual trans arrangement of phosphine groups and nitrogens trans to carbonyl ligands. Measurement of valence vibration frequencies of carbonyl groups in the complexes allowed to estimate the electron density on the rhodium centre. The ene-hydrazone ligand backbone (nitrogen covalently bonded) is more electron donating than the azine backbone (nitrogen bonded by electron pair donation) as expected. In the neutral series of complexes electron donation increases with phosphine substitution in the order Ph < Prⁱ = c-C₆H₁₁ < Bu^t with the corresponding decrease of carbonyl valence vibration frequency. The tert-butyl cationic complex undergoes in a low yield an unusual diphosphinoazine bond cleavage with simultaneous oxidation of the metal resulting in a binuclear bis(iminophosphine)dirhodium complex [{(Bu^t)₂PCH₂C(Bu^t)NH}Rh(Cl)₂(μ-Cl)]₂ the structure of which was also determined by X-ray diffraction.     

Synthesis and reactivity of substituted cyclopentadienyl rhodium(I) and (III) complexes

New cyclopentadienyl derivatives of rhodium COD complexes [Cp*=C₅H₄COOCH₂CHCH₂ (1); C₅H₄CH₂CH₂CHCH₂ (2); C₅H(i-C₃H₇)₄ (3)] and carbonyl complex [Cp*=C₅H(i-C₃H₇)₄ (4)] were synthesized from [RhCl(COD)]₂ and [RhCl(CO)₂]₂. 1, 2 and 3 oxidized by iodine gave iodine bridged dimers 5, 6 and 7, respectively. Triphenyl phosphine, carbon monoxide and carbon disulfide molecules broke down the iodine bridged structure easily and produced monomer products Cp*RhI₂L [Cp*=C₅H₄COOCH₂CHCH₂, L=CS₂ (8); L=PPh₃ (9). Cp*=C₅H(i-C₃H₇)₄, L=CO (10)]. All of these new compounds were characterized by elemental analysis, ¹H NMR, IR, UV-Vis and mass spectroscopy. The crystal structure of 1 was solved in the triclinic space group with one molecule in the unit cell, the dimensions of which are a=7.082(9) Å, b=8.392(3) Å, c=13.889(5) Å, α=101.19(3)°, β=99.06(6)°, γ=105.11(5)°, and V=763(1) ų. The crystal structure of 3 was solved in the orthorhombic space group Pn21a with four molecules in the unit cell, the dimensions of which are a=9.748(3) Å, b=16.054(5) Å, and V=2319(1) ų. Least squares refinement leads to values for the conventional R₁ of 0.0251 for 1 and 0.0558 for 3, respectively. Compared to that in 1, a shorter metal-ligand bond length in 3 was observed and this is attributed to the rich electron density on Rh(I) metal center piled up by the C₅H(i-C₃H₇)₄ ligand.     

Synthesis and structure of a chiral dinuclear palladium(0) complex with a 30-membered hexaolefinic macrocyclic ligand

Selective and efficient preparation of a new chiral dipalladium(0) complex with an olefinic macrocyclic ligand named (E,E,E,E,E,E)-1,6,11,16,21,26-hexakis[(4-methylphenyl)sulfonyl]-1,6,11,16,21,26-hexaazacyclotriaconta-3,8,13,18,23,28-hexaenedipalladium(0) (5) is reported. Dinuclear palladium(0) complex 5 has been fully characterized by means of NMR spectroscopy and X-ray diffraction analysis.     

Carbonyl rhodium(I) complexes containing (H)PNX (X = O or N) ligands deriving from natural aminoacid–amides. Synthesis, X-ray structure and spectroscopic characterization

The polyfunctional (H)PNX (X = O or N) ligands 1 and 2 react with [Rh(CO)₂Cl]₂ to give the corresponding chloro carbonyl complexes {Rh[κ²-(H)PN](CO)Cl} (1a and 2a), where the neutral ligands coordinate in a κ²-PN bidentate fashion, the square planar coordination being completed by the CO trans to N and the chloride trans to P. In chloroform solution 1a maintains its original structure, while 2a partially transforms into the cationic species {Rh[κ³-(H)PNO](CO)}Cl. The chloroform solutions of 1a and 2a react with AgPF₆ to give the purely cationic species {Rh[κ³-(H)PNO](CO)}PF₆ ([1a]⁺ and [2a]⁺), while addition of Et₃N originates the neutral species {Rh[κ³-PNN′](CO)} (1b and 2b). All the complexes have been characterized by microanalysis, IR, ¹H NMR as well as ³¹P{¹H} NMR spectroscopy. The X-ray structures of ligand 1 and complex 1b are also reported.     

The Staudinger reaction of platinum(II)- and palladium(II)-coordinated 2-(azidomethyl)phenyl isocyanide. X-ray structure of trans-[PtCl{(H)}(PPh3)2][BF4] · CDCl3 · H2O

2-(Azidomethyl)phenyl isocyanide, 2-(CH₂N₃)C₆H₄NC (AziNC), coordinates to some cationic Pt(II) and Pd(II) species to afford isocyanide complexes of the type trans-[MCl(AziNC)(PPh₃)₂][BF₄] (M=Pt, l; Pd, 2). AziNC is coordinated also in some neutral Pt(II) and Pd(II) species such as [MCl₂(AziNC)₂] (M=Pt, 3; Pd, 4) derived from the reactions of 2 equiv. of AziNC with [PtCl₂(COD)] and [PdCl₂(MeCN)₂], respectively. Complexes 1 and 2 react with 1 equiv. of PPh₃ affording the heterocyclic carbene complexes trans-[MCl{(H)}(PPh₃)₂][BF₄] (M=Pt, 5; Pd, 6). Complexes 3 and 4 react with 1 equiv. of PPh₃ displacing the isocyanide with the formation of the complexes cis-[MCl₂(AziNC)(PPh₃)] (M=Pt, 7; Pd, 8). These latter ones react with 2 equiv. of PPh₃ affording as the final products the cationic carbene species trans-[MCl{(H)}(PPh₃)₂][Cl] (M=Pt, 9; Pd, 10). Complex 5 was also characterized by single crystal X-ray diffraction. The carbene complex is square-planar and the angle formed between the platinum square plane and the heterocyclic carbene ligand is 87.9(2)°. The C(1)-N(1) and C(1)-N(2) bond distances in the latter of 1.32(2) and 1.30(2) Å, respectively, are short for a single bond and indicate extensive π-bonding between the nitrogen atoms and the carbene carbon.     

Structural and spectroscopic trends in mononuclear arylchalcogenolato-palladium(II) and -platinum(II) complexes: Crystal structures of [M(TeAr)2(dppe)] {M = palladium, platinum; Ar = phenyl, 2-thienyl; dppe = 1,2-bis(diphenylphosphino)ethane}

A series of mononuclear [M(EAr)₂(dppe)] [M = Pd, Pt; E = Se, Te; Ar = phenyl, 2-thienyl; dppe = 1,2-bis(diphenylphosphino)ethane] complexes has been prepared in good yields by the reactions of [MCl₂(dppe)] and corresponding ArE⁻ with a special emphasis on the aryltellurolato palladium and -platinum complexes for which the existing structural information is virtually non-existent. The complexes have crystallized in five isomorphic groups: (1) [Pd(SePh)₂(dppe)] and [Pt(SePh)₂(dppe)], (2) [Pd(TePh)₂(dppe)] and [Pt(TePh)₂(dppe)], (3) [Pd(SeTh)₂(dppe)], (4) [Pt(SeTh)₂(dppe)] and [Pd(TeTh)₂(dppe)], and (5) [Pt(TePh)₂(dppe)]. In addition, solvated [Pd(TePh)₂(dppe)] · CH₃OH and [Pd(TeTh)₂(dppe)] · 1/2CH₂Cl₂ could be isolated and structurally characterized. The metal atom in each complex exhibits an approximate square-planar coordination. The Pd-Se, Pt-Se, Pd-Te, and Pt-Te bonds span a range of 2.4350(7)-2.4828(7) Å, 2.442(1)-2.511(1) Å, 2.5871(7)-2.6704(8) Å, and 2.6053(6)-2.6594(9) Å, respectively, and the respective Pd-P and Pt-P bond distances are 2.265(2)-2.295(2) Å and 2.247(2)-2.270(2) Å. The orientation of the arylchalcogenolato ligands with respect to the M(E₂)(P₂) plane has been found to depend on the E-M-E bond angle. The NMR spectroscopic information indicates the formation of only cis-[M(EAr)₂(dppe)] complexes in solution. The trends in the ³¹P, ⁷⁷Se, ¹²⁵Te, and ¹⁹⁵Pt chemical shifts expectedly depend on the nature of metal, chalcogen, and aryl group. Each trend can be considered independently of other factors. The ⁷⁷Se or ¹²⁵Te resonances appear as second-order multiplets in case of palladium and platinum complexes, respectively. Spectral simulation has yielded all relevant coupling constants.     

Mono and dinuclear rhodium, iridium and ruthenium complexes containing chelating 2,2′-bipyrimidine ligands: Synthesis, molecular structure, electrochemistry and catalytic properties

The mononuclear cations [(η⁵-C₅Me₅)RhCl(bpym)]⁺ (1), [(η⁵-C₅Me₅)IrCl(bpym)]⁺ (2), [(η⁶-p-PrⁱC₆H₄Me)RuCl(bpym)]⁺ (3) and [(η⁶-C₆Me₆)RuCl(bpym)]⁺ (4) as well as the dinuclear dications [{(η⁵-C₅Me₅)RhCl}₂(bpym)]²⁺ (5), [{(η⁵-C₅Me₅)IrCl}₂(bpym)]²⁺ (6), [{(η⁶-p-PrⁱC₆H₄Me)RuCl}₂(bpym)]²⁺ (7) and [{(η⁶-C₆Me₆)RuCl}₂(bpym)]²⁺ (8) have been synthesised from 2,2′-bipyrimidine (bpym) and the corresponding chloro complexes [(η⁵-C₅Me₅)RhCl₂]₂, [(η⁵-C₅Me₅)IrCl₂]₂, [(η⁶-PrⁱC₆H₄Me)RuCl₂]₂ and [(η⁶-C₆Me₆)RuCl₂]₂, respectively. The X-ray crystal structure analyses of [3][PF₆], [5][PF₆]₂, [6][CF₃SO₃]₂ and [7][PF₆]₂ reveal a typical piano-stool geometry around the metal centres; in the dinuclear complexes the chloro ligands attached to the two metal centres are found to be, with respect to each other, cis oriented for 5 and 6 but trans for 7. The electrochemical behaviour of 1-8 has been studied by voltammetric methods. In addition, the catalytic potential of 1-8 for transfer hydrogenation reactions in aqueous solution has been evaluated: All complexes catalyse the reaction of acetophenone with formic acid to give phenylethanol and carbon dioxide. For both the mononuclear and dinuclear series the best results were obtained (50 °C, pH 4) with rhodium complexes, giving turnover frequencies of 10.5 h⁻¹ for 1 and 19 h⁻¹ for 5.     

Two‐Coordinate Fe0 and Co0 Complexes Supported by Cyclic (alkyl)(amino)carbenes

The CAAC [CAAC=cyclic (alkyl)(amino)carbene] family of carbene ligands have shown promise in stabilizing unusually low‐coordination number transition‐metal complexes in low formal oxidation states. Here we extend this narrative by demonstrating their utility in affording access to the first examples of two‐coordinate formal Fe⁰ and Co⁰ [(CAAC)₂M] complexes, prepared by reduction of their corresponding two‐coordinate cationic Fe^I and Co^I precursors. The stability of these species arises from the strong σ‐donating and π‐accepting properties of the supporting CAAC ligands, in addition to steric protection.     

Cationic half-sandwich complexes (Rh, Ir, Ru) containing 2-substituted-1,8-naphthyridine chelating ligands: Syntheses, X-ray structure analyses and spectroscopic studies

Reactions of the dinuclear complexes [(η⁶-arene)Ru(μ-Cl)Cl]₂ (arene = C₆H₆, p-ⁱPrC₆H₄Me) and [(η⁵-C₅Me₅)M(μ-Cl)Cl]₂ (M = Rh, Ir) with 2-substituted-1,8-naphthyridine ligands, 2-(2-pyridyl)-1,8-naphthyridine (pyNp), 2-(2-thiazolyl)-1,8-naphthyridine (tzNp) and 2-(2-furyl)-1,8-naphthyridine (fuNp), lead to the formation of the mononuclear cationic complexes [(η⁶-C₆H₆)Ru(L)Cl]⁺ {L = pyNp (1); tzNp (2); fuNp (3)}, [(η⁶-p-ⁱPrC₆H₄Me)Ru(L)Cl]⁺ {L = pyNp (4); tzNp (5); fuNp (6)}, [(η⁵-C₅Me₅)Rh(L)Cl]⁺ {L = pyNp (7); tzNp (8); fuNp (9)} and [(η⁵-C₅Me₅)Ir(L)Cl]⁺ {L = pyNp (10); tzNp (11); fuNp (12)}. All these complexes are isolated as chloro or hexafluorophosphate salts and characterized by IR, NMR, mass spectrometry and UV/Vis spectroscopy. The molecular structures of [1]Cl, [2]PF₆, [4]PF₆, [5]PF₆ and [10]PF₆ have been established by single crystal X-ray structure analysis.     

Cationic rhodium(I)–diolefin complexes containing an optically active C2-symmetric bis(sulfoximine) ligand: Synthesis and catalytic activity

A series of cationic rhodium(I) complexes [Rh(diene)(N^N)][BF₄] (diene = 1,5-cyclooctadiene (cod), norbornadiene (nbd), tetrafluorobenzobarralene (tfb)), containing the optically pure bis(sulfoximine) ligand 1,2-bis(S-methyl-S-phenylsulfonimidoyl)benzene, have been synthesized and fully characterized. The structure of the R,R enantiomer of the ligand, and that of its cyclooctadiene–Rh(I) complex, were confirmed by means of single-crystal X-ray diffraction techniques. Studies on the catalytic activity of these complexes in acetophenone hydrosilylation and dimethyl itaconate hydrogenation are also reported.     

Heterobi‐ and ‐trinuclear Complexes with an Amino(ethynyl)carbene as Bridging Ligand

The sequential reaction of the amino(trimethylsilyl)carbene complex [(CO)₅W=C(NH₂)C≡CSiMe₃] ( 1 ) with nBuLi and [I‐Fe(CO)₂Cp] affords the C(carbene)‐N bridged heterobinuclear complex [(CO)₅W=C{NHFe(CO)₂Cp}C≡CSiMe₃] ( 2 ). Desilylation of 1 is achieved by treatment with KF in THF/MeOH. From the reaction of the resulting complex [(CO)₅W=C(NH₂)C≡CH] ( 3 ) with nBuLi and [I‐Fe(CO)₂Cp] two binuclear WFe compounds in a ratio of approximately 1:1 are obtained: the C(carbene)‐C≡C bridged complex 4 and the C(carbene)‐N bridged complex 5 . Repetition of the deprotonation/metallation sequence yields the trinuclear WFe₂ complex 6 . One Fe(CO)₂Cp fragment in 6 is bonded to the amino group and the other one to the terminal carbon atom of the ethynyl substituent. The analogous reaction of 3 with nBuLi and [Br‐Ni(PMe₂Ph)₂Mes] gives a ca. 1:1 mixture of two heterobinuclear complexes ( 7 and 8 ). Complex 7 is bridged by the C(carbene)‐C≡C and complex 8 by the C(carbene)‐N fragment. Subsequent reaction of 7 with BuLi and [Br‐Ni(PMe₂Ph)₂Mes] finally affords the trinuclear WNi₂ complex 9 related to 6 . The solid‐state structure of 2 is established by an X‐ray diffraction analysis. The spectroscopic data of the bi‐ and trinuclear complexes indicate electronic communication between the metal centers through the bridging group.     

Effects on Coordination of Thioether Sites. 4. Structural Analysis of η3-Tripodal Ligand Manganese(I) Complexes

Crystal structures of a series of manganese(I) complexes containing tripodal ligands were determined. For [η³-{CH₃C(CH₂PPh₂)₂(CH₂SPh)-P,P′,S}Mn(CO)₃]PF₆ ( 1 ): a = 10.856(3) Å, b = 19.698(3) Å, c = 17.596(5) Å, β = 96.17(2)°, monoclinic, Z = 4, P2₁/c, R(F_o) = 0.068, R_w(F_o) = 0.055 for 3617 reflections with I_o > 2σ(I_o). For [η³-{CH₃C(CH₂PPh₂)(CH₂SPh)₂-P,P′,S}Mn(CO)₃]PF₆ ( 2 ): a = 9.890(2) Å, b = 20.403(4) Å, c = 10.269(3) Å, β = 117.44(2)°, monoclinic, Z = 2, P2_l, R(F_o) = 0.050, R_w(F_o) = 0.037 for 1760 reflections with I_o > 2σ(I_o). For [η³-{CH₃C(CH₂PPh₂)₂(CH₂S)-P,P′,S}Mn(CO)₃] ( 4 ): a = 8.191(7) Å, b = 10.495(3) Å, c = 19.858(6) Å, α = 99.61(2)°, β = 96.17(2)°, γ = 92.70(4)°, triclinic, Z = 2, P-I, R(F_o) = 0.048, R_w(F_o) = 0.039 for 2973 reflections with I_o > 2σ(I_o). There is no significant difference in the bond lengths of Mn-S bonds among three species in their crystal structures [2.325(2) Å in 1; 2.358(4) in 2; 2.380(2) in 4], but the better donating ability of thiolate in complex 4 appears on the lower frequencies of its carbonyl stretching absorptions.     

Bis‐NHC Chelate Complexes of Nickel(0) and Platinum(0)

For a long time d¹⁰‐ML₂ fragments have been known for their potential to activate unreactive bonds by oxidative addition. In the development of more active species, two approaches have proven successful: the use of strong σ‐donating ligands leading to electron‐rich metal centers and the employment of chelating ligands resulting in a bent coordination geometry. Combining these two strategies, we synthesized bis‐NHC chelate complexes of nickel(0) and platinum(0). Bis(1,5‐cyclooctadiene)nickel(0) and ‐platinum(0) react with bisimidazolium salts, deprotonated in situ at room temperature, to yield tetrahedral or trigonal‐planar bis‐NHC chelate olefin complexes. The synthesis and characterization of these complexes as well as a first example of C? C bond activation with these systems are reported. Due to the enforced cis arrangement of two NHCs, these compounds should open interesting perspectives for bond‐activation chemistry and catalysis.     

Hydroformylation of oct-1-ene catalyzed by dinuclear gem-dithiolato-bridged rhodium(I) complexes and phosphorus donor ligands

The dinuclear gem-dithiolato bridged compounds [Rh₂(μ-S₂Cptn)(cod)₂] (1) (CptnS₂²⁻ = 1,1-cyclopentanedithiolato), [Rh₂(μ-S₂Chxn)(cod)₂] (2) (ChxnS₂²⁻ = 1,1-cyclohexanedithiolato), [Rh₂(μ-S₂CBn₂)(cod)₂] (3) (Bn₂CS₂²⁻ = 1,3-diphenyl-2,2-dithiolatopropane) and [Rh₂(μ-S₂CⁱPr₂)(cod)₂] (4) (ⁱPr₂CS₂²⁻ = 2,4-dimethyl-2,2-dithiolatopentane) dissolved in toluene in the presence of monodentate phosphine or phosphite P-donor ligands under carbon monoxide/hydrogen (1:1) atmosphere are efficient catalysts for the hydroformylation of oct-1-ene under mild conditions (6.8 atm of CO/H₂ and 80 °C). The influence of the gem-dithiolato ligand, the P-donor co-catalyst and the P/Rh ratio on the catalytic activity and selectivity has been explored. Aldehyde selectivities higher than 95% and turnover frequencies up to 245 h⁻¹ have been obtained using P(OMe)₃ as modifying ligand. Similar activity figures have been obtained using P(OPh)₃ although the selectivities are lower. Regioselectivities toward linear aldehyde are in the range 75–85%. The performance of the catalytic systems [Rh₂(μ-S₂CR₂)(CO)₂(PPh₃)₂]/PPh₃ has been found to be comparable to the systems [Rh₂(μ-S₂CR₂)(cod)₂] at the same P/Rh ratio. The system [Rh₂(μ-S₂CBn₂)(cod)₂] (3)/P(OPh)₃ has been tested in the hydroformylation-isomerization of trans-oct-2-ene. Under optimized conditions up to 54% nonanal was obtained. Spectroscopic studies under pressure (HPNMR and HPIR) evidenced the formation of hydrido mononuclear species under catalytic conditions that are most probably responsible for the observed catalytic activity.     

Experimental (solid + liquid) phase equilibria of (alkan-1-ol + benzonitrile), (amine + benzonitrile) binary mixtures,and (decan-1-ol + decylamine + benzonitrile) ternary mixtures

(Solid + liquid) phase diagrams, SLE have been determined for (octan-1-ol, or nonan-1-ol, or decan-1-ol, or undecan-1-ol + benzonitrile) and for (hexylamine, or octylamine, or decylamine, or 1,3-diaminopropane + benzonitrile) using a cryometric dynamic method at atmospheric pressure. Simple eutectic systems with complete immiscibility in the solid phase and complete miscibility on the liquid phase have been observed. The solubility decreases with an increase of the number of carbon atoms in the alkan-1-ol, or amine chain. The temperature of the eutectic points increases and shifts to lower alkan-1-ol, or amine mole fractions as the alkyl chain length of the alkan-1-ol, or amine increases. The higher intermolecular interaction was observed for the (alkan-1-ol + benzonitrile) systems.     

First X‐Ray Structure Analyses of Rhodium(III) η1‐Allyl Complexes and a Mechanism for Allylic Isomerization Reactions

Metal‐to‐metal allyl transfer : Using the first structurally characterized rhodium η¹‐allyl complexes it is shown that the σ‐bound allyl substituent can be transferred from the Rh^III complex to a Rh^I complex in a fast equilibrium. This process may account for the decrease in regioselectivity observed in allylic alkylation reactions in which complex 1 is used as a catalyst.

     

Quinobis(imidazolylidene): Synthesis and Study of an Electron‐Configurable Bis(N‐Heterocyclic Carbene) and Its Bimetallic Complexes

Reaction of bromanil with N,N′‐dimesitylformamidine followed by deprotonation with NaN(SiMe₃)₂ afforded 1,1′,3,3′‐tetramesitylquinobis(imidazolylidene) ( 1 ), a bis(N‐heterocyclic carbene) (NHC) with two NHC moieties connected by a redox active p‐quinone residue, in 72 % yield of isolated compound. Bimetallic complexes of 1 were prepared by coupling to FcN₃ ( 2 ) or FcNCS ( 3 ; Fc=ferrocenyl) or coordination to [M(cod)Cl] ( 4 a or 4 b , where M=Rh or Ir, respectively; cod=1,5‐cyclooctadiene). Treatment of 4 a and 4 b with excess CO(g) afforded the corresponding [M(CO)₂Cl] complexes 5 a and 5 b , respectively. Analysis of 2 – 5 by NMR spectroscopy and X‐ray diffraction indicated that the electron‐deficient quinone did not significantly affect the inherent spectral properties or coordination chemistry of the flanking imidazolylidene units, as compared to analogous NHCs. Infrared spectroscopy and cyclic voltammetry revealed that decreasing the electron density at ML_n afforded an increase in the stretching energy and a decrease in the reduction potential of the quinone, indicative of metal–quinone electronic interaction. Differential pulse voltammetry and chronoamperometry of the metal‐centered oxidations in 2 – 4 revealed two single, one‐electron peaks. Thus, the metal atoms bound to 1 are oxidized at indistinguishable potentials and do not appear electronically coupled. However, the metal–quinone interaction was used to increase the electron density at coordinated metal atoms. Infrared spectroelectrochemistry revealed that the average ν_CO values for 5 a and 5 b decreased by 14 and 15 cm^?1, respectively, upon reduction of the quinone embedded within 1 . These shifts correspond to 10 and 12 cm^?1 decreases in the Tolman electronic parameter of this ditopic ligand.