Rhodium(I) and iridium(I) complexes of pyrazolyl-N-heterocyclic carbene ligands

Several Rh(I) and Ir(I) complexes containing an N-heterocyclic carbene-pyrazolyl chelate ligand have been synthesised. Determination of the single-crystal X-ray structure of the Ir(I) complex showed a novel binding mode with the iridium centre coordinated to two ligands via two carbene donors in preference to one ligand forming the entropically favoured chelate. The hydrogenation activity of several of these complexes was investigated along with that of previously synthesised Rh(I) and Ir(I) complexes containing an analogous phosphine-pyrazolyl chelate.     

Rhodium(I) carbonyl complexes based on naphthophosphacyclophanes

Naphthphosphacyclophanes based on symmetrical dihydroxynaphthalenes linked by diethylamidophospite groups were used to synthesize rhodium(I) complexes containing carb-onyl and acetylacetonato fragments. The physicochemical and spectral characteristics of the synthesized coordination systems were studied.

     

Rhodium(I) bisaldimine complexes in transfer hydrogenation

The reactions of hydrogen transfer from 2-propanol on acetophenone in the presence of the system [Rh(cod)Cl]₂–L] (L is bisaldimine ligands based on (R,R)-1,2-cyclohexanediimine and pyridine-, quinoline-, and thiophenecarboxaldehyde) were studied. Rhodium(I) complexes with optically active ligand showed a high catalytic activity (up to 345 h^–1) and moderate enantioselectivity [up to 55% ee of (R)-1-phenyethanol]. The structure of rhodium complex with N,N'-(1R,2R)-cyclohexane-1,2-diyl-bis[1-(pyridine-2-yl)methanimine] was determined on the basis of the data of ¹H and ¹³C NMR spectroscopy and quantum chemical calculations.     

Rhodium(I) carbonyl complexes with sulphur and nitrogen donor ligands

Summary Rhodium(I) carbonyl complexes, namely [Rh(CO)₂ClL] where L = thiourea (Tu), 1,3-diphenyl-2-thiourea (DTu), dithizone (Dtz), indole (Id), 3-chloropyridine (Clpy), 3-hydroxypyridine (HOpy), 3-methylpyridine (Mepy), 2,5-dimethylpyridine (Me₂py) or 2,5-dichloropyridine (Cl₂py)] were prepared. [Rh(CO)₂Cl(Clpy)₂] has also been isolated. In the (Tu) complex, (C-S) occurs at ca. 710cm^-1, indicating the presence of a metal-sulphur bond. The carbonyl stretching frequencies in [Rh (CO)₂ClL] and [Rh(CO)₂CIL₂] occur at ca. 2100–1990 and 1830–1800 cm^-1, respectively. PPh₃ reacts with the complexes to form trans-[Rh(CO)Cl(PPh₃)₂]. The complexes were characterized by elemental analyses, conductivity measurements and by their i.r. spectra.     

Rhodium(I) carbonyl complexes with heterocyclic and nonheterocyclic nitrogen-donor ligands

Summary Complexes of the [Rh(N-N)(CO)₂][RhCl₂(CO)₂], [Rh(N-N)(CO)₂]BF₄ and Rh(N-N)(CO)₂Cl types where (N-N) = 2,9-dimethyl-1,10-phenanthroline (Me₂Phen), 4,7-diphenyl-1,10-phenanthroline (Ph₂Phen), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (Me₂2Ph₂Phen) or 2,2-biquinoline (biq), have been prepared and investigated. Benzidine (benz) ando-tolidine (tol) also form complexes of the first type. The complexes of the first two types behave as 11 electrolytes. While Ph₂Phen forms the four coordinate monocarbonyl Rh(Ph₂Phen)(CO)Cl complex, benzo(f)-quinoline (Q) yields the Rh(CO)₂ (Q)Cl compound. Triphenyl-phosphine and triphenylarsine react with the above complexes to form the well knowntrans-Rh(CO)ClL₂ where L = PPh₃ or AsPh₃. The i.r. and u.v.-visible spectra of the compounds are discussed.     

Rhodium(I) and rhodium(III) arene complexes with N-carbazolyltriphenylphosphinegold(I) and other polycyclic arene ligands

The new heteronuclear arene complexes [(COD)Rh(μ-cbz)AuPPh₃]ClO₄, [{(COD)Rh}₂(μ-cbz)AuPPh₃](ClO₄)₂, [(C₅Me₅)Rh(μ-cbz)AuPPh₃](ClO₄)₂ and [{C₅Me₅) Rh}₂(μ-cbz)AuPPh₃](ClO₄)₄ (COD = 1,5-cyclooctadiene, cbz = carbazolyl), and the mononuclear arene complexes [(COD)Rh(arene)]ClO₄ (arene = tetralin, biphenyl, fluorene, indene, 9,10-dihydroanthracene or carbazole) have been prepared by reaction of the acetone solvated complexes [(COD)Rh(Me₂CO)_x]ClO₄ or [(C₅Me₅)Rh(Me₂CO)₃](ClO₄)₂ with (cbz)AuPPh₃ or the appropriate polycyclic arene ligand.     

Rhodium(I) carbonyl complexes of triphenylphosphine chalcogenides and their catalytic activity

Rhodium(I) carbonyl complexes [Rh(CO)₂ClL] where L = Ph₃PO, Ph₃PS and Ph₃PSe, were synthesized and characterized by elemental analysis, i.r. and by ¹H-, ¹³C- and ³¹P-n.m.r. spectroscopy. The vBD;(CO) band frequencies in the complexes follow the order: Ph₃PO > Ph₃PS > Ph₃PSe, in keeping with the hard/soft nature of the interactions. The complexes undergo oxidative additions with electrophiles such as MeI, PhCH₂Cl and I₂ to give, e.g. [Rh(CO)(COMe)ClIL] which react with PPh₃ to give trans-[Rh(CO)Cl(PPh₃)₂]. The catalytic activity of the [Rh(CO)₂ClL] complexes in carbonylation of MeOH is higher than that of the well-known [Rh(CO)₂I₂]⁻ species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rhodium(I) complexes bound to silica via bidentate phosphine ligands

Triethoxysilyl substituted diphosphines of the novel type (EtO)₃Si(CH₂)_nP(Ph)CH₂CH₂PPh₂ (n=1, 3) have been prepared and used to immobilize rhodium(I) complexes to silica. The complexes were found to be effective catalysts for hydrogenation of 1,3-cyclooctadiene under mild conditions.

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- (EtO)₃Si(CH₂)_nP(Ph)CH₂CH₂PPh₂ (n=1,3) SiO₂. 1,3- .

     

Rhodium(I) and platinum(II) complexes of aminomethylphosphines as hydrogenation and hydroformylation catalysts

Hydrogenation of α-acetamidocinnamic acid with chiral aminomethylphosphine complexes of rhodium(I), [Rh(cyclo-octa-1, 5-diene) {(R₂PCH₂)₂NR¹}]-PF₆ (R = Ph or Cy, R¹ = D(+)-CHMePh, L-CHMeCO₂Et, (R)(+)-bornyl) shows no asymmetric induction. The hydroformylation of styrene using the catalyst mixture [PtCl₂(P–P)]/SnCl₂ shows asymmetric induction with up to 31% enantiomeric excess of 2-phenyl-propanol being observed.     

Pseudotetrahedral Rhodium(I) Complexes

A combination of four‐electron donors, such as alkynes, with strongly donating and strong‐field scorpionate ligands is appropriate to create pseudotetrahedral rhodium(I) environments, as found in [Rh(PhBP₃)(HC?CPh)], which promotes H?C bond activation and C?C coupling reactions under very smooth conditions.     

Rhodium(I) phosphine complexes containing bidentate unsaturated thio ligands: I. Synthesis and characterisation

The rhodium(I) complexes (Ph₃P)₂Rh(LL′), in which LL′ is an unsaturated chelate coordinating via L = S and L′ = N, O, P or S, have been prepared from RhCl(PPh₃)₃ by two routes.Direct substitution of one Ph₃P and Cl^? by the chelate anion gives (Ph₃P)₂Rh[Ph₂PC(S)S] (L = S, L′ = P). Oxidative addition of an NH bond followed by reductive elimination of HCl results in (Ph₃P)₂Rh[Me₂NC(S)NC(S)NMe₂] (L = S, L′ = S), (Ph₃P)₂Rh[PhNC(S)NMe₂] (L = S, L′ = N), (Ph₃P)₂Rh[Ph₂PC(S)NPh) (L = S, L′ = P) and (Ph₃P)₂Rh[Ph₂P(O)C(S)NPh] (L = S, L′ = O).Reaction of the complexes (Ph₃P)₂Rh(LL′) with CO gives (CO)(Ph₃P)Rh(LL′) with CO trans to the chelate donor atom with the lowest trans-influence. Pt(PPh₃)₄ reacts with Me₂NC(S)N(H)C(S)NMe₂ and HN(Ph)C(S)PPh₂, respectively, to give H(Ph₃P)Pt[Me₂NC(S)NC(S)NMe₂] (L = S, L′ = S) and H(Ph₃P)Pt[Ph₂PC(S)NPh] (L = S, L′ = P).The coordinating atoms and their configurations have been assigned by IR ³¹P NMR and ¹H NMR. Some trend in IR and ³¹P NMR paramaters are discussed.     

Rhodium(I) catalyzed four-component reaction of Fischer alkenyl carbene complexes and 1,1-diphenylallene

Alkyl substituted chromium Fischer carbene complexes react with 1,1-diphenylallene in the presence of rhodium(I) catalysts (10 mol%) to yield highly substituted dienyl indenone derivatives. In this process a catalytic chromium(0)-rhodium(I) exchange occurs, four new C-C bonds are created, and four-components (two allenes, the carbene ligand and one CO ligand) are joined in a chemo- and regioselective manner.     

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.     

Rhodium(I) carbonyl complexes of quinoline carboxaldehyde ligands and their catalytic carbonylation reaction

The dimeric rhodium precursor [Rh(CO)₂Cl]₂ reacts with quinoline (a) and its three isomeric carboxaldehyde ligands [quinoline-2-carboxaldehyde (b), quinoline-3-carboxaldehyde (c), and quinoline-4-carboxaldehyde (d)] in 1:2 mole ratio to afford complexes of the type cis-[Rh(CO)₂Cl(L)] (1a-1d), where L = a-d. The complexes 1a-1d have been characterised by elemental analyses, mass spectrometry, IR and NMR (¹H, ¹³C) spectroscopy together with a single crystal X-ray structure determination of 1c. The X-ray crystal structure of 1c reveals square planar geometry with a weak intermolecular pseudo dimeric structure (Rh?Rh = 3.573 Å). 1a-1d undergo oxidative addition (OA) with different electrophiles such as CH₃I, C₂H₅I and I₂ to give Rh(III) complexes of the type [Rh(CO)(COR)Cl(L)I] {R = -CH₃ (2a-2d), R = -C₂H₅ (3a-3d)} and [Rh(CO)Cl(L)I₂] (4a-4d) respectively. 1b exhibits facile reactivity with different electrophiles at room temperature (25 °C), while 1a, 1c and 1d show very slow reactivity under similar condition, however, significant reactivity was observed at a temperature ∼40 °C. The complexes 1a-1d show higher catalytic activity for carbonylation of methanol to acetic acid and methyl acetate [Turn Over Frequency (TOF) = 1551-1735 h⁻¹] compared to that of the well known Monsanto’s species [Rh(CO)₂I₂]⁻ (TOF = 1000 h⁻¹) under the reaction conditions: temperature 130 ± 2 °C, pressure 33 ± 2 bar, 450 rpm and time 1 h. The organometallic residue of 1a-1d was also isolated after the catalytic reaction and found to be active for further run without significant loss of activity.     

Rhodium(I) Tristyrylphosphine Cyclooctadiene Complexes

Rhodium complexes with unsaturated phosphines as ligands were studied by NMR spectroscopy. Tris[(E,Z,Z)-styryl)phosphine is a stronger complex-forming agent compared with tris[(Z,Z,Z)-styryl)phosphine in view of the easier accessibility of its lone electron pair. The composition of the complexes and their NMR parameters suggest a square-planar structure with cis phosphine ligands.