2,2′-biimidazole, 2,2′-bibenzimidazole and imidazoles as ligands in cationic rhodium(I) complexes

Summary Cationic rhodium(I) complexes of the type [Rh(diolefin)(L-L)]ClO₄ and [Rh(diolefin)L₂]ClO₄, (diolefin = 1,5-cyclooctadiene, 2,5-norbornadiene and tetrafluorobenzobarrelene; L-L = 2,2-biimidazole, 2,2-bibenzimidazole; L = pyrazole or imidazoles) are described. [Rh(CO)₂(L-L)]-C1O₄ complexes, which can be obtained by reaction of cyclooctadiene derivatives with CO, react with P-donor ligands in equimolar ratios to yield [Rh(CO)(P-donor)(L-L)]ClO₄ monocarbonyl derivatives. The catalytic activity of some of these complexes is considered.     

Rhodium(I) indazole and indazolate complexes

The preparation of cationic indazole (HIdz) rhodium(I) complexes of the types [(diolefin)Rh(HIdz)₂]ClO₄ and [(CO)₂Rh(HIdz)₂]ClO₄ is described. Neutral binuclear rhodium(I) complexes of the type [Y₂Rh(μ-Idz)]₂ (Y₂  COD, TFB, NBD, (CO)₂ or (CO)(PPh₃)) are obtained by treating the corresponding complexes [Y₂RhCl]₂ with indazole and organic or inorganic bases. The cationic mononuclear derivatives react with the solvated species [Y₂Rh(acetone)_x]ClO₄ in the presence of triethylamine to give neutral binuclear complexes of the types [(CO)₂Rh(μ-Idz)₂Rh(diolefin)], [(Ph₃P)(CO)Rh(μ-Idz)₂Rh(diolefin)] and [(diolefin)Rh(μ-Idz)Rh(diolefin′)] (diolefin  COD, TFB or NBD; diolefin′  COD or TFB). Alternative methods for the synthesis of the binuclear complexes are also described.     

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.     

Dicarboxylate rhodium complexes with diolefins and carbon monoxide

Dinuclear rhodium complexes of the type [Rh₂(C₂O₄)(diolefin)₂] (diolefin)₂  1,5-cyclooctadiene, 2,5-norbornadiene and tetrafluorobenzobarrelene) with bridging oxalate ligands have been obtained by reaction of [Rh(acac)(diolefin)] with oxalic acid (2: 1 mol ratio). The use of a 1 : 1 molar ratio affords [Rh(HC₂O₄)(COD)], that reacts with [Ir(acac)(COD)] yielding the heterodinuclear [(COD)Rh(C₂O₄)Ir(COD)] complex. Treatment of [Rh₂(C₂O₄)(diolefin)₂] complexes with phenanthroline type ligands leads to ionic complexes of formula [Rh(diolefin) (phen)][Rh(C₂O₄)(diolefin)]. Bubbling of carbon monoxide through solutions of the diolefin complexes leads to the formation of carbonylrhodium species of formula [Rh₂(C₂O₄)(CO)₂L₂] (L = CO, PPh₃t-BuNC) or [Rh(CO)₂(phen)] - [Rh(C₂O₄)(CO)₂]. Other related malonate complexes are also described.     

Solvent-free synthesis of bisferrocenylimines and their rhodium(I) complexes

The solvent-free reaction of ferrocenecarboxaldehyde and diaminoalkanes under solvent-free conditions gave bisferrocenylimines (L) in excellent yields. Cationic rhodium(I) complexes with the formulation [Rh(COD)(L)]ClO₄ were prepared by the reaction of [Rh(COD)Cl]₂ with the bisferrocenylimines in the presence of silver perchlorate. The compounds were characterised by NMR, IR, MS and elemental analysis. The X-ray crystal structures of two rhodium(I) complexes are also reported.     

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.     

Cationic complexes of rhodium(I) with phenanthroline type ligands

Summary Complexes [Rh(COD)(L-L)]ClO₄ are prepared by reaction of [Rh(COD)₂]ClO₄ with the appropriate ligand L-L (4,7-Ph₂Phen, 2,9-Me₂-4,7-Ph₂Phen, 2,9-Me₂Phen or 5,6-Me₂Phen). Treatment of these complexes with carbon monoxide gives [Rh(CO)₂(L-L)]ClO₄. When the carbonylation reaction is performed in the presence of P(4-RC₆H₄)₃, pentacoordinate complexes [Rh(CO)(L-L){P(4-RC₆-H₄)}_{3 2}]ClO₄ (R=Me, H, F or Cl) are formed. The use of [Rh(COD)(L-L)]ClO₄ as homogeneous hydroformylation catalyst precursors was studied (50 atm, 80°C). Under these conditions no hydrogenation of the olefin or of the aldehydes is observed, but isomerisation reactions are significant.     

[RhCl(CO)(PPh3)]2. A precursor for the synthesis of cationic rhodium complexes with nitrogen donor ligands

Summary The use of [RhCl(CO)(PPh₃)]₂ as a precursor for the synthesis of complexes of the types [Rh(CO)L₂(PPh₃)]A (A = [ClO₄]^– or [BPh₄]^–; L = pyridine type ligand) and [Rh(CO)(L-L)(PPh₃)]A (A = [ClO₄]^– or [BPh₄]^–; L-L = bidentate nitrogen donor) and the preparation of several complexes of the types [Rh(CO)L(PPh₃){P(p-RC₆H₄)₃}]BPh₄ and [Rh(CO)(phen)(PPh₃){P(p-RC₆H₄)₃}]A (A = [ClO₄]^– or [BPh₄]^–; R = H or Me) is described.Author to whom all correspondence should be directed.     

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.     

Carbonyl complexes of rhodium(I) and rhodium(III) with 2,2′-biquinoline

Novel carbonyl complexes of rhodium(I) and rhodium(III) containing the bidenate nitrogen donor ligand 2,2′-biquinoline (biq) have been prepared; they are of the types RhX(CO)₂ biq and RhX(CO)biq (X = Cl, Br, I). Cationic carbonyl and substituted carbonyl complexes of the types [Rh(CO)₂biq]ClO₄ and [Rh(CO)biqL₂]ClO₄, where L is tertiary phosphine or arsine have also been isolated. In spite of considerable steric crowding around the nitrogen atoms, 2,2′-biquinoline behaves much like 2,2′-bipyridine in forming carbonyl complexes of rhodium.     

Rhodium(I) carbonyl complexes of ether‐phosphine ligands and their reactivity

The reactions of dimeric complex [Rh(CO)₂Cl]₂ with hemilabile ether‐phosphine ligands Ph₂P(CH₂) _nOR [n = 1, R = CH₃ (a); n = 2, R = C₂H₅ (b)] yield cis‐[Rh(CO)₂Cl(P ～ O)] (1) [P ～ O = η ¹‐(P) coordinated]. Halide abstraction reactions of 1 with AgClO₄ produce cis‐[Rh(CO)₂(P ∩ O)]ClO₄ (2) [P ∩ O = η ²‐(P,O)chelated]. Oxidative addition reactions of 1 with CH₃I and I₂ give rhodium(III) complexes [Rh(CO)(COCH₃)ClI(P ∩ O)] (3) and [Rh(CO)ClI₂(P ∩ O)] (4) respectively. The complexes have been characterized by elemental analyses, IR, ¹H, ¹³C and ³¹P NMR spectroscopy. The catalytic activity of 1 for carbonylation of methanol is higher than that of the well‐known [Rh(CO)₂I₂]^? species. Copyright © 2002 John Wiley & Sons, Ltd.     

Formation of Trinuclear Rhodium‐Hydride Complexes [{Rh(PP*)H}3‐ (μ2‐H)3(μ3‐H)][anion]2—During Asymmetric Hydrogenation?

Recently described and fully characterized trinuclear rhodium‐hydride complexes [{Rh(PP*)H}₃(μ₂‐H)₃(μ₃‐H)][anion]₂ have been investigated with respect to their formation and role under the conditions of asymmetric hydrogenation. Catalyst–substrate complexes with mac (methyl (Z)‐ N‐acetylaminocinnamate) ([Rh(tBu‐BisP*)(mac)]BF₄, [Rh(Tangphos)(mac)]BF₄, [Rh(Me‐BPE)(mac)]BF₄, [Rh(DCPE)(mac)]BF₄, [Rh(DCPB)(mac)]BF₄), as well as rhodium‐hydride species, both mono‐([Rh(Tangphos)‐ H₂(MeOH)₂]BF₄, [Rh(Me‐BPE)H₂(MeOH)₂]BF₄), and dinuclear ([{Rh(DCPE)H}₂(μ₂‐H)₃]BF₄, [{Rh(DCPB)H}₂(μ₂‐H)₃]BF₄), are described. A plausible reaction sequence for the formation of the trinuclear rhodium‐hydride complexes is discussed. Evidence is provided that the presence of multinuclear rhodium‐hydride complexes should be taken into account when discussing the mechanism of rhodium‐promoted asymmetric hydrogenation.     

Formation of 18e− and 16e− Acyl(η3‐cyclooctenyl)rhodium(III) Complexes in the Reaction of Cationic (Cycloocta‐1,5‐diene)rhodium(I) Compounds with 2‐(Diphenylphosphino)benzaldehyde

The reaction of cationic diolefinic rhodium(I) complexes with 2‐(diphenylphosphino)benzaldehyde (pCHO) was studied. [Rh(cod)₂]ClO₄ (cod=cycloocta‐1,5‐diene) reacted with pCHO to undergo the oxidative addition of one pCHO with (1,2,3‐η)cyclooct‐2‐en‐1‐yl (η³‐C₈H₁₃) formation, and the coordination of a second pCHO molecule as (phosphino‐κP)aldehyde‐κO(σ‐coordination) chelate to give the 18e⁻ acyl(allyl)rhodium(III) species [Rh(η³‐C₈H₁₃)(pCO)(pCHO)]ClO₄ (see 1 ). Complex 1 reacted with [Rh(cod)(PR₃)₂]ClO₄ (R=aryl) derivatives 3 – 6 to give stable pentacoordinated 16e⁻ acyl[(1,2,3‐η)‐cyclooct‐2‐en‐1‐yl]rhodium(III) species [Rh(η³‐C₈H₁₃)(pCO)(PR₃)]ClO₄ 7 – 10 . The (1,2,3‐η)‐cyclooct‐2‐en‐1‐yl complexes contain cis‐positioned P‐atoms and were fully characterized by NMR, and the molecular structure of 1 was determined by X‐ray crystal diffraction. The rhodium(III) complex 1 catalyzed the hydroformylation of hex‐1‐ene and produced 98% of aldehydes (n/iso=2.6).     

Synthesis and catalytic activity of some cationic rhodium(I) complexes with substituted quinolines

Summary The synthesis and properties of cationic complexes of the type [Rh(NBD)L₂]ClO₄, [Rh(NBD)L(PPh₃)]ClO₄ and [Rh(CO)L(PPh₃)₂]ClO₄ (L = substituted quinolines) are described. The diolefin complexes catalyse hydrogen transfer from isopropanol to some unsaturated substrates.     

Rhodium(I) diolefin complexes with polycyclic π-arene ligands. Synthesis of bimetallic complexes with diphenylmethane as bridging ligand

Summary The preparation and properties of cationic arenerhodium(I) complexes of general formula [Rh(diolefin)(⁶arene)]ClO₄ (diolefin=1,5-cyclooctadiene, tetrafluorobenzobarrelene or trimethyltetrafluorobenzobarrelene; arene = biphenyl or diphenylmethane) are described. These complexes react with the solvated intermediate complex [Rh(diolefin)(Me₂CO)_x]ClO₄ to give homobimetallic [(diolefin)Rh(Ph₂CH₂)Rh(diolefin)](ClO₄)₂ derivatives. New heterobimetallic complexes of the type [(diolefin)Rh(Ph₂CH₂)Cr(CO)₃]ClO₄ have been synthesized by reaction of Cr(CO)₃(⁶-Ph₂CH₂) with the solvated complex [Rh(diolefin)(Me₂CO)_x]ClO₄ or, alternatively by treatment of [Rh(diolefin)(⁶-arene)]ClO₄ with the complex Cr(CO)₃(⁶Me₃B₃N₃Me₃) in chloroform solution.     

Catalytic polymerization of phenylacetylene by cationic rhodium and iridium complexes of ferrocene-based ligands

Some new Rh(I) and Ir(I) complexes of the types [(COD)M(LL)]ClO₄ and [(COD)MCl]₂ [COD = cyclooctadiene; M = Rh, Ir; LL = 1,1′-bis(diphenylphosphino)ferrocene (DPPF), 1-diphenylphosphino-2-(N,N-dimethylamino)methylferrocene (FcNP), 1,6-diferrocenyl-2,5-diazahexane (FcNN)] were prepared, and their catalytic activities toward polymerization of phenyl acetylene were examined. The rhodium complexes proved to be very effective catalysts to yield highly stereoregular polyphenylacetylene (cis-transoidal-PPA) in high yields under mild conditions. The number-average molecular weight (M _n) of the PPA obtained is in the range of 19,000–33,000 and the weight-average molecular weight (M _ω) is in the range of 47,000–95,000. Comparative studies revealed that of various catalysts employed, the cationic mononuclear [Rh(FcNN)(COD)]ClO₄ complex exhibited the best results to give exclusively the cis-transoidal-PPA (cis content ∼100%) with the highest molecular weight (M _n = 33,340) in the highest chemical yield (94%). Other reaction parameters such as the softness of the ligand, the solvent, the relative amount of catalyst, and the reaction temperature were also investigated to find that all these factors played crucial roles. The iridium systems worked better for the trimerization rather than polymerization to yield 1,3,5-triphenybenzene as major product. © 1996 John Wiley & Sons, Inc.     

Reactions of cationic rhodium(I) carbonyl compounds with nucleophiles to form alkoxo,carboalkoxy and carboxylato complexes. Part II

Summary The rhodium(I) carbonyl compounds [Rh(CO)L₂2] [BF₄]. 1/2CH₂Cl_nn2 (L = PPh₂ or AsPh₃) react with the nucleophiles OMe⁻, RCOO⁻ (R = Me, Et) under nitrogen to form [Rh(OR)(CO)L₂] (1)–(2) and [Rh(OOCR)(CO)L₂] (7)–(₁₀), respectively. Addition of [Rh(CO)₂(PPh₃)₂]-[BF ₄] to OMe⁻ under nitrogen produces [Rh(COOMe)-(CO) (PPh₃)₂]-MeOH (3), whilst reactions of [Rh(CO)-(PPh₃)₂] [BF₄]·1/2CH₂Cl₂ and [Rh(CO)₂(PPh₃)₂] [BF₄] with OR_- (R = Me, Et or n-Pr) in the presence of CO produce [Rh(COOR)(CO)₂(PPh₃)₂] (4)–(6). The products have been characterised by i.r., ¹H, ³¹P, ¹³Cn.m.r. spectroscopy and elemental analysis.     

Rhodium-Catalyzed Addition of Organoboronic Acids to Aldehydes

Highly inert to ionic additions to aldehydes , aryl- and 1-alkenylboronic acids succumb to a catalytic variant mediated by a [Rh(acac)(CO)₂]–diphosphane complex in aqueous phase at 80–95°C to yield secondary alcohols [Eq. (a)]. A key step in the catalytic cycle is the transmetalation between the boron reagent and the rhodium complex. L_n=diphosphane (e.g. 1,1′-bis(diphenylphosphanyl)ferrocene); R=aryl, 1-alkenyl; R′=alkyl, aryl; acac=acetylacetonate.     

Rhodium(I) complexes with pyridazine, 4,6-dimethyl-pyrimidine, 4,6-bis(3,5-dimethylpyrazol-1-yl)pyrimidine, 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine and 3-(3,5-dimethylpyrazol-1-yl)-6-chloropyridazine

The synthesis and properties of rhodium(I) complexes of formulae [“RhCl(diolefin)”₂(L)] (or [Rh(Cl(diolefin)(L)]), and [Rh(diolefin)(L)]_n(ClO₄)_n are reported. These complexes react with carbon monoxide to yield the related carbonyl derivatives. Ligands used were pyridazine, 4,6-dimethyl-pyrimidine, 4,6-bis(3,5-dimethylpyrazol-1-yl)pyrimidine, 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine and 3-(3,5-dimethyl-pyrazol-1-yl)-6-chloropyridazine. Related iridium(I) and gold(I) compounds are also reported.     

Double Stereoselection in the Hydrogenation over Cationic Rh(I) Complexes with Two Different Chiral Ligands

The catalytic activity and stereoselectivity in the hydrogenation of itaconic and -(acetylamino)cinnamic acids were studied in the presence of the complex [Rh(COD)(L¹)₂]⁺ TfO^- (where COD is cyclooctadiene and L¹ is (1S,2S,5R)-(+)-neomenthyldiphenylphosphine] which was generated in situ. The optical yield of the hydrogenation of itaconic acid increases both on addition of chiral (4S,5S)-(+)-2,2-dimethyl-4,5-bis(dimethylaminomethyl)-1,3-dioxolane (L²) as an auxiliary ligand to the complex [Rh(COD)(L¹)₂]⁺ TfO^- and on addition of achiral and chiral tertiary phosphines to the complex [Rh(L²)₂]⁺ TfO^-. The result of joint action of two ligands can be regarded as "matched effect." Transformations of the complexes in a hydrogen atmosphere were examined by ¹H and ^{3 1}P NMR spectroscopy. It was found that at least three complexes: diamine complex [Rh(L²)₂]⁺ TfO^-, solvate complex [Rh(L¹)₂(solv)₂]⁺ TfO^-, and diamine-bis-phosphine complex [Rh(L¹)₂L²]⁺ TfO^- may be catalytic precursors.