Synthesis and catalytic activity of some cationic complexes of rhodium(I) with norbornadiene and group Vb ligands

Summary The syntheses of [Rh(NBD)L₂ ]ClO₄ complexes (L=nitrogen donor ligand), obtained from [Rh(NBD)₂]ClO₄, and their reactions with triphenylphosphine and carbon monoxide are described.The catalytic activity of some of these and related complexes is considered.     

Preparation and catalytic activity of cationic rhodium(I) and iridium(I) complexes with phosphine sulphide ligands

The preparation and properties of cationic rhodium and iridium complexes of types [M(diolefin)L₂](ClO₄) and [M(diolefin)L(PPh₃)](ClO₄) [M = Rh, diolefin = 1,5-cyclooctadiene (COD) or 2,5-norbornadiene; M = Ir, diolefin = COD; L = phosphine sulphide] are described. The complexes have been characterized by IR, ¹H NMR and ³¹P NMR spectroscopy. The use of [M(diolefin)L₂](ClO₄) as catalyst precursors in homogeneous hydrogenation of olefins has been studied.     

Monocarbonyl cationic rhodium(I) complexes

Summary The preparations and characterisation of cationic complexes of the type [Rh(CO)(MeCN)(PR₃)₂]ClO₄, [Rh(CO)L(PR₃)₂]ClO₄ (L=py or 2-MeOpy), [Rh(CO)(L-L)(PR₃)₂]ClO₄ (L-L = bipy or phen) and [Rh(CO)(PR₃)₃]ClO₄ with PR₃ = P(p-YC₆H₄)₃ (Y=Cl, F, Me or MeO) are described.     

Preparation and properties of some cationic norbornadiene rhodium(I) complexes with triarylphosphines

Summary The synthesis of [Rh(NBD){P(p-RC₆H₄)₃}₂]A complexes (A=ClO ₄ ^– or BPh ₄ ^– ; R=Cl, F, Me or MeO) is described. Treatment of these complexes with molecular hydrogen leads to the isolation of [RhH₂{P(p-RC₆H₄)₃}₂(OCMe₂)₂]ClO₄ or Rh{P(p-RC₆H₄)₃}₂PhBPh₃. These latter complexes contain tetraphenylborate coordinated to the metalvia arene interaction. [Rh(CO)₃{P(p-RC₆H₄)₃}₂]ClO₄ complexes have been isolated by carbonylations. The use of these complexes as homogeneous hydroformylation catalysts is also briefly investigated.     

Synthesis and catalytic properties of cationic palladium(II) and rhodium(I) complexes bearing diphosphinidinecyclobutene ligands

Cationic palladium(II) and rhodium(I) complexes bearing 1,2-diaryl-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene ligands (DPCB–Y) were prepared and their structures and catalytic activity were examined (aryl = phenyl (DPCB), 4-methoxyphenyl (DPCB–OMe), 4-(trifluoromethyl)phenyl (DPCB–CF₃)). The palladium complexes [Pd(MeCN)₂(DPCB–Y)]X₂ (X = OTf, BF₄, BAr₄ (Ar = 3,5-bis(trifluoromethyl)phenyl)) were prepared by the reactions of DPCB–Y with [Pd(MeCN)₄]X₂, which were generated from Pd(OAc)₂ and HX in MeCN. On the other hand, the rhodium complexes [Rh(MeCN)₂(DPCB–Y)]OTf were prepared by the treatment of [Rh(μ-Cl)(cyclooctene)₂]₂ with DPCB–Y in CH₂Cl₂, followed by treatment with AgOTf in the presence of MeCN. The cationic complexes catalyzed conjugate addition of benzyl carbamate to α,β-unsaturated ketones.     

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.     

Some cationic carbonyl complexes of rhodium(I)

A number of cationic rhodium(I) complexes of the type [Rh(CO)₂(NN)]ClO₄, [Rh(CO)₂L₃]ClO₄ and [Rh(CO)(NN)L₂]ClO₄, where (NN) is 2,2^′-bipyridine or 1,10-phenanthroline and L is a tertiary phosphine or arsine, have been isolated and their structures assigned. The configuration of the complexes ion [Rh(CO)₂L₃]⁺ appears to depend critically on the size of the ligand L.     

Synthesis,stability and reactivity of cationic carbonyl complexes of rhodium(I)

Summary Trans-[RhCl(CO)L₂] (L = PPh₃, AsPh₃ or PCy₃) react with AgBF₄ in CH₂Cl₂ to give the novel species [Rh-(CO)L₂]⁺ [BF₄]^–.nCH₂Cl₂ (n = 1/2 or 1 1/2) (1–3), which we believe to be stabilised by weak solvent interaction. The corresponding stibine compound cannot be isolated by the same process, instead [Rh(CO)₂(SbPh₃)₃]⁺ [BF₄]^– (7) is formed when the reaction is carried out in the presence of CO. When reactions designed to prepare [Rh(CO)L₂]⁺ [BF₄]^– are performed in the presence of CO, or [Rh(CO)L₂]⁺ [BF₄]^– complexes are reacted with CO, [Rh(CO)₂L₂]⁺ [BF₄]^– (L = PPh₃, AsPh₃ or PCy₃) (4–6) are formed. If Me₂CO is used as solvent in the preparation of [Rh(CO)L₂]⁺ [BF₄]^– (L = PPh₃ or AsPh₃), then the products are the four-coordinate [Rh(CO)L₂-(Me₂CO)]⁺ [BF₄]^– (8,9) species. The complexes have been characterised by i.r., ³¹P and ¹H n.m.r. spectroscopy and elemental analyses.     

Synthesis,characterization and catalytic applications of rhodium(I) organometallics with substituted tertiary phosphines

Organometallics of the type [Rh(COD)(L)Cl] (where, L = carboxyl/formyl/pyridyl tertiary phosphines) have been synthesized by treating the precursor [Rh(COD)Cl]₂ with substituted tertiary phosphines. [Rh(COD)(Ph₂P-2-C₆H₄COO)] and [Rh(COD)(Ph₂P-CH₂COO)] were synthesized by halide abstraction from the precursor [Rh(COD)Cl]₂ in the presence of AgPF₆ in tetrahydrofuran by involving 2-carboxy phenyl/carboxy methyl group of tertiary phosphines in coordination as bidentate ligands. Similarly, the cationic compounds of the type [Rh(COD)L₂]PF₆ were also synthesized by treating [Rh(COD)Cl]₂ in the presence of AgPF₆. All these compounds were characterized by elemental analysis, conductance measurements, IR, ¹H, ¹³C, ³¹P NMR, mass, and electronic spectral studies. [Rh(COD)(Ph₂-P-2-C₆H₄COOH)Cl] and [Rh(COD)(Ph₂-P-2-C₆H₄COO)] were studied on the catalytic reduction reactions of 2-nitroanisole, 3-nitro anisole, 4-nitroanisole, 2-nitrobenzoicacid, 3-nitrobenzoicacid, 4-nitrobenzoicacid under mild conditions and [Rh(COD)(Ph₂-P-2-C₆H₄COO)] was found to be more efficient than [Rh(COD)(Ph₂-P-2-C₆H₄COOH)Cl]. This article is dedicated to Dr. D. R. M Walton, who successfully completed his tenure as Editor-in-Chief, Transition Metal Chemistry.     

Synthesis and catalytic properties of rhodium(I) complexes with anionic chelate nitrogen-oxygen ligands

Summary Dicarbonyl complexes of rhodium(I) [Rh(CO)₂(LL)], where LL = salicylaldoximate, 8-oxyquinolinate, glycinate, leucinate, aminophenolate or pyridine carboxylate and [Rh(COD)(LL)], where COD = 1,5-cyclooctadiene, were prepared and characterized by elemental analysis, and i.r. and n.m.r. spectra. Their activity to catalytic hydroformylation of styrene has been evaluated at atmospheric pressure of COH₂(11).     

Synthesis and catalytic properties of N -functionalised carbene complexes of rhodium(I)

Reaction of [RhCl(COD)]₂, with 1,3-dialkylimidazolinylidene (1) or 1,3-dialkylbenzimidazolinylidene (2) resulted in the formation of rhodium(I) 1,3-dialkylimidazolin-2-ylidene (3a-c) and 1,3-dialkylbenzimidazolin-2-ylidene (4a,b) complexes. Triethylsilane reacts with acetophenone derivatives in the presence of catalytic amounts of RhCl(COD)(1,3-dialkylimidazolin-2-ylidene) or RhCl(COD)(1,3-dialkylbenzimidazolin-2-ylidene) to give the corresponding silylethers in good yield (57–98%).     

Synthesis,formation constants and reactions of cationic rhodium(I) complexes of nitriles

Reactions of Rh(ClO₄)(CO)(PPh₃)₂ with nitriles produce new cationic rhodium(I) complexes, [RhL(CO)(PPh₃)₂]ClO₄ [L = CH₃CN (1), CH₃CH₂CH₂CN (2) or C₆H₅CN (3)], whose spectral data suggest that the nitriles are coordinated through the nitrogen atom. Formation constants for the reaction Rh(ClO₄)(CO)(PPh₃)₂ + L ⇋ [RhL(CO)(PPh₃)₂]ClO₄, have been measured to be 1.01 × 10⁵ M⁻¹ (CH₃CN), 1.07 × 10⁵ M⁻¹ (CH₃CH₂CH₂CN) and 2.59 × 10⁴ M⁻¹ (C₆H₅CN) at 25°C in monochlorobenzene. The differences in the formation constants for the different nitriles seem to be predominantly due to differences in ΔH (not to differences in ΔS). The nitriles in 1–3 are readily replaced with nitrogen base ligands (unsaturated nitriles and pyridine) and PPh₃.     

Asymmetric hydrogenation using ferrocenylphosphine rhodium(I) cationic complexes

High optical yields are obtained in the hydrogenation of α-acetamidocinnamic acid using [(COD)Rh((+)PPFA)]ClO₄ and related complexes as catalysts. (+)PPFA is (S)-α-[(R)-2-diphenylphosphinoferrocenyl] ethyldimethylamine.     

Preparation and catalytic activity of cationic rhodium tetrafluorobenzobarrelene complexes with nitrogen and phosphorus donor ligands

The preparation and properties of twenty five new cationic rhodium(I) complexes with tetrafluorobenzobarrelene and mono- or bidentate nitrogen or phosphorus donor ligands are described. The complexes with tertiary phosphines show high selectivities in the hydrogenation of 1-hexyne and several diolefins towards monoolefins. The dependence of the reduction rate upon the basicity of the phosphine has been studied.     

Carbonyl cationic rhodium(I) and iridium(I) complexes with sulphur donor and triphenylphosphine ligands

Summary The reaction of previously reported Rh^I and Ir^I cationic complexes towards carbon monoxide and triphenylphosphine has been studied. Carbonyl rhodium(I) mixed complexes of the formulae [Rh(CO)L₂(PPh₃)]ClO₄, (L=tetrahydrothiophene(tht), trimethylene sulfide(tms), SMe₂, or SEt₂), [(CO)(PPh₃)Rh{-(L-L)}₂Rh(PPh₃)(CO)](ClO₄)₂ (L-L= 2,2,7,7-tetramethyl-3,6-dithiaoctane (tmdto), (MeS)₂(CH₂)₃ (dth), or 1,4-dithiacyclohexane (dt), [Rh(CO)L(PPh₃)₂]ClO₄ (L= tht, tms, SMe₂, or SEt₂), and carbonyl iridium(I) complexes of the formulae [Ir(CO)₂(COD)(PPh₃)]ClO₄, [Ir(CO)(COD)(PPh₃)₂]ClO₄, [(CO)(COD)(PPh₃) Ir{-(L-L)} Ir(PPh₃)(COD)(CO)](ClO₄)₂ (L-L = tmdto or dt), [(CO)₂ (PPh₃)Ir(-tmdto)Ir(PPh₃)(CO)₂](ClO₄)₂, [(CO)₂(PPh₃) Ir(-dt)₂Ir(PPh₃)(CO)₂](ClO₄)₂, were prepared by different synthetic methods.     

Synthesis and catalytic activity of some π-allylic bis(trifluorophosphine)(triphenylphosphine)cobalt(I) complexes

The syntheses of Co(π-all)(PF₃)₂(PPh₃) complexes (π-all = π-allyl, anti-1-Me-π-allyl, syn-1-Me-π-allyl, 1,1-dimethyl-π-allyl, anti-1,2-diMe-π-allyl, syn,syn-1,3-diMe-π-allyl, 2Et-π-allyl, π-cyclooctenyl, h³-π-cycloheptadienyl) are described. ¹H and ¹⁹F NMR data are presented and discussed in relation to the structures of the complexes. The compound Co(π-C₅H₉)(PF₃)(PPh₃)₂ is also reported. Several of the π-allylic complexes are found to be active catalysts for the isomerisation of 1-octene to 2-octene under a hydrogen atmosphere.     

Synthesis and reactivity of formamidinato rhodium(I) complexes

The syntheses of [Rh(diol)(formamidine)]₂ complexes (diol  cycloocta-1,5-diene (1); diol  norbornadiene (2); formamidine  N,N′-di-p-tolylformamidine) are reported. These complexes are dimeric and contain the bridging formamidino ligand. They react with CO, dppe and PPh₃ with displacement of the diene ligand to yield the known [Rh(CO)₂(formamidine)]₂, [Rh(dppe)₂]⁺ and [Rh(PPh₃)₂(formamidine)], respectively; the last complex, in which the formamidine acts as a chelating ligand, was isolated only as the O₂ adduct. With HCl or HBF₄ aqueous 1 and 2 do not form hydrides but instead the formamidino cation [p-tolyl-NHCHNHtolyl-p]⁺ and the complexes [Rh(diol)X]₂ (X  Cl, F); a possible scheme for the reaction with HCl is proposed. The [Rh(C₈H₁₂)(formamidine)]₂ complex reacts with heterocumulenes as CS₂, SO₂, PhNCS and PhNCO with diene displacement; the only product isolated was [Rh(CS₂)₂(formamidine], to which a polymeric structure is assigned.     

Synthesis,reactions and catalytic activity of some mixed trifluorophosphine(triphenylphosphine)hydrido complexes of cobalt(I)

The complexes CoH(PF₃)_4?n (PPh₃)_n (n = 1–3) have been prepared by low from the reaction between CoH(PF₃)(PPh₃)₃ and butadiene. The hydrido complexes are active catalysts for the isomerisation of 1-octene to 2-octene under hydrogen or nitrogen.