Synthesis, structural characterization, and ligand replacement reactions of gem-dithiolato-bridged rhodium and iridium complexes

The reaction of gem-dithiol compounds R 2C(SH) 2 (R = Bn (benzyl), (i) Pr; R 2 = -(CH 2) 4-) with dinuclear rhodium or iridium complexes containing basic ligands such as [M(mu-OH)(cod)] 2 and [M(mu-OMe)(cod)] 2, or the mononuclear [M(acac)(cod)] (M = Rh, Ir, cod = 1,5-cyclooctadiene) in the presence of a external base, afforded the dinuclear complexes [M 2(mu-S 2CR 2)(cod) 2] ( 1- 4). The monodeprotonation of 1,1-dimercaptocyclopentane gave the mononuclear complex [Rh(HS 2Cptn)(cod)] ( 5) that is a precursor for the dinuclear compound [Rh 2(mu-S 2Cptn)(cod) 2] ( 6). Carbonylation of the diolefin compounds gave the complexes [Rh 2(mu-S 2CR 2)(CO) 4] ( 7- 9), which reacted with P-donor ligands to stereoselectively produce the trans isomer of the disubstituted complexes [Rh 2(mu-S 2CR 2)(CO) 2(PR' 3) 2] (R' = Ph, Cy (cyclohexyl)) ( 10- 13) and [Rh 2(mu-S 2CBn 2)(CO) 2{P(OR') 3} 2] (R' = Me, Ph) ( 14- 15). The substitution process in [Rh 2(mu-S 2CBn 2)(CO) 4] ( 7) by P(OMe) 3 has been studied by spectroscopic means and the full series of substituted complexes [Rh 2(mu-S 2CBn 2)(CO) 4- n {P(OR) 3} n ] ( n = 1, 4) has been identified in solution. The cis complex [Rh 2(mu-S 2CBn 2)(CO) 2(mu-dppb)] ( 16) was obtained by reaction of 7 with the diphosphine dppb (1,4-bis(diphenylphosphino)butane). The molecular structures of the diolefinic dinuclear complexes [Rh 2(mu-S 2CR 2)(cod) 2] (R = Bn ( 1), (i) Pr ( 2); R 2 = -(CH 2) 4- ( 6)) and that of the cis complex 16 have been studied by X-ray diffraction.     

Cationic carbonyl complexes of rhodium(I) and rhodium(III): syntheses,vibrational spectra,NMR studies,and molecular structures of tetrakis(carbonyl)rhodium(I) heptachlorodialuminate and -gallate, [Rh(CO)4][Al2Cl7] and [Rh(CO)4][Ga2Cl7

Dimeric rhodium(I) bis(carbonyl) chloride, [Rh(CO)(2)(mu-Cl)](2), is found to be a useful and convenient starting material for the syntheses of new cationic carbonyl complexes of both rhodium(I) and rhodium(III). Its reaction with the Lewis acids AlCl(3) or GaCl(3) produces in a CO atmosphere at room temperature the salts [Rh(CO)(4)][M(2)Cl(7)] (M = Al, Ga), which are characterized by Raman spectroscopy and single-crystal X-ray diffraction. Crystal data for [Rh(CO)(4)][Al(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.705(3), b = 9.800(2), c = 10.268(2) A; alpha = 76.52(2), beta = 76.05(2), gamma = 66.15(2) degrees; V = 856.7(5) A(3); Z = 2; T = 293 K; R(1) [I > 2sigma(I)] = 0.0524, wR(2) = 0.1586. Crystal data for [Rh(CO)(4)][Ga(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.649(1), b = 9.624(1), c = 10.133(1) A; alpha = 77.38(1), beta = 76.13(1), gamma = 65.61(1) degrees; V = 824.4(2) A(3); Z = 2; T = 143 K; R(1) [I > 2sigma(I)] = 0.0358, wR(2) = 0.0792. Structural parameters for the square planar cation [Rh(CO)(4)](+) are compared to those of isoelectronic [Pd(CO)(4)](2+) and of [Pt(CO)(4)](2+). Dissolution of [Rh(CO)(2)Cl](2) in HSO(3)F in a CO atmosphere allows formation of [Rh(CO)(4)](+)((solv)). Oxidation of [Rh(CO)(2)Cl](2) by S(2)O(6)F(2) in HSO(3)F results in the formation of ClOSO(2)F and two seemingly oligomeric Rh(III) carbonyl fluorosulfato intermediates, which are easily reduced by CO addition to [Rh(CO)(4)](+)((solv)). Controlled oxidation of this solution with S(2)O(6)F(2) produces fac-Rh(CO)(3)(SO(3)F)(3) in about 95% yield. This Rh(III) complex can be reduced by CO at 25 degrees C in anhydrous HF to give [Rh(CO)(4)](+)((solv)); addition of SbF(5) at -40 degrees C to the resulting solution allows isolation of [Rh(CO)(4)][Sb(2)F(11)], which is found to have a highly symmetrical (D(4)(h)()) [Sb(2)F(11)](-) anion. Oxidation of [Rh(CO)(2)Cl](2) in anhydrous HF by F(2), followed in a second step by carbonylation in the presence of SbF(5), is found to be a simple, straightforward route to pure [Rh(CO)(5)Cl][Sb(2)F(11)](2), which has previously been structurally characterized by us. All new complexes are characterized by vibrational and NMR spectroscopy. Assignment of the vibrational spectra and interpretation of the structural data are supported by DFT calculations.     

A mechanistic investigation into the elimination of phosphonium salts from rhodium-TRIPHOS complexes under methanol carbonylation conditions

Phosphine modified rhodium complexes are currently the topic of considerable research as methanol carbonylation catalysts, but often suffer from poor stability. This paper reports on an investigation into how coordination mode affects the elimination of phosphonium salts from rhodium complexes, namely [trans-RhCl(CO)(PPh(3))(2)] , [RhCl(CO)(dppe)] , [RhCl(CO)(dppb)](2), [Rh(TRIPHOS)(CO)(2)]Cl . These complexes are all potential pre-catalysts for methanol carbonylation. The reaction of these complexes with methyl iodide at 140 degrees C under both N(2) and CO atmospheres has been studied and has revealed clear differences in the stability of the corresponding Rh(iii) complexes. In contrast to both monomeric and dimeric that react cleanly with CH(3)I to give stable Rh(iii) acetyl complexes, forms a novel bidentate complex after the elimination of the one arm of the ligand as a quaternised phosphonium salt. The structure of this complex has been determined spectroscopically and using X-ray crystallography. The mechanism of formation of this novel complex has been investigated using (13)CH(3)I and strong evidence that supports a dissociative mechanism as the means of phosphine loss from the rhodium centre is provided.     

Probing the stereo‐electronic properties of cationic rhodium complexes bearing chiral diphosphine ligands by 103Rh NMR

¹⁰³Rh NMR represents a powerful tool to assess the global electronic and steric contribution of diphosphine ligands on [Rh(COD)(diphosphine)]⁺ complexes. In the case of DIOP, BINAP and MeDUPHOS, this approach proved to be more informative than classical CO‐stretching frequency measurements. After validation, this method has been extended to a set of seven diphosphines. ¹⁰³Rh NMR measurements on [Rh(COD)(diphosphine)]PF₆ lead to the following order of donor properties: dppe > MeBPE > MeDUPHOS > dppb > DIOP > BINAP > Tol‐BINAP. This trend has been validated by DFT in the case of DIOP, BINAP and MeDUPHOS. In conjunction, ³¹P NMR chemical shift has been shown to reflect the ring constraints of the Rh‐diphosphine scaffold. This contribution is a step towards a mechanistic investigation of the catalytic hydrogenation of unsaturated substrates by ¹⁰³Rh NMR and DFT. Copyright © 2010 John Wiley & Sons, Ltd.     

Syntheses and Structures of Homo‐ and Heterobimetallic Complexes Containing a (Cyclopentadienone)rhodium(I) Fragment

The reaction of [RhCl(η⁴‐Ph₂R₂C₄CO)]₂ (R=Ph, 2‐naphthyl) with the dimeric complexes [RuCl₂(p‐cymene)]₂ p‐cymene=1‐methyl‐4‐(1‐methylethyl)benzene, [RuCl₂(1,3,5‐Et₃C₆H₃)]₂, [MCl₂(Cp*)]₂ (M=Rh, Ir; Cp*=1,2,3,4,5‐pentamethylcyclopenta‐2,4‐dien‐1‐yl), [RuCl₂(CO)₃]₂, [RuCl₂(dcypb)(CO)]₂ (dcypb=butane‐1,4‐diylbis[dicyclohexylphosphine]), [(dppb)ClRu(μ‐Cl)₂(μ‐OH₂)RuCl(dppb)] (dppb=butane‐1,4‐diylbis[diphenylphosphine]), and [(dcypb)(N₂)Ru(μ‐Cl)₃RuCl(dcypb)] was investigated. In all cases, mixed, chloro‐bridged complexes were formed in quantitative yield (see 5 – 8, 9 – 16, 18, 19, 21 , and 22 ). The six new complexes 5, 8, 9, 13, 15 , and 22 were characterized by single‐crystal X‐ray analysis (Figs. 1–3).     

Crescent-shaped rhodium(I) complexes with bis(o-carboxymethylphenyl)triazenide

Reaction of [[Rh(mu-Cl)(CO)2]2] with the triazene ArNNNHAr (Ar = o-CO2MeC6H4) produced the mononuclear complex [RhCl(ArNNNHAr)(CO)2] (1). Complex 1 reacted with KOH in methanol to give the dinuclear compound [[Rh(mu-ArNNNAr)(CO)2]2] (2), which showed a "mu-(1kappaN1,2kappaN3)-ArNNNAr" coordination mode for both bridging ligands. The dinuclear complex [[Rh(mu-ArNNNAr)(CO)2]2] (2) easily undergoes redistribution reactions in which the eight-membered "Rh2(NNN)2" core is broken. Thus, reaction of 2 with the anionic complex (NHEt3)[RhCl2(CO)2] gave the single-bridged complex (NHEt3)[Rh2(mu-ArNNNAr)Cl2(CO)4] (4), while the trinuclear complexes [Rh3(mu-ArNNNAr)(mu-Cl)(mu-CO)Cl(CO)4] (5) and [Rh3(mu-ArNNNAr)2(mu-Cl)(mu-CO)(CO)3] (6) were isolated by addition of the neutral compound [[Rh(mu-Cl)(CO)2]2] to 2, depending on the molar ratio employed. The formation of 5 and 6 involved the loss of carbonyl groups and the coordination of the oxygen atoms of the CO2Me groups. The structures of 4, 5, and 6 have been determined by X-ray diffraction methods, which show the ability of bis(o-carboxymethylphenyl)triazenide to act as bi-, tri-, and tetra-dentate ligand-spanning dinuclear moieties in trinuclear complexes.     

Steric and electronic effects on the reactivity of rh and ir complexes containing P-S,P-P,and P-O ligands. Implications for the effects of chelate ligands in catalysis

Kinetic studies of the reactions of [M(CO)(L-L)I] [M = Rh, Ir; L-L = Ph(2)PCH(2)P(S)Ph(2) (dppms), Ph(2)PCH(2)CH(2)PPh(2) (dppe), and Ph(2)PCH(2)P(O)Ph(2) (dppmo)] with methyl iodide have been undertaken. All the chelate ligands promote oxidative addition of methyl iodide to the square planar M(I) centers, by factors of between 30 and 50 compared to the respective [M(CO)(2)I(2)](-) complexes, due to their good donor properties. Migratory CO insertion in [Rh(CO)(L-L)I(2)Me] leads to acetyl complexes [Rh(L-L)I(2)(COMe)] for which X-ray crystal structures were obtained for L-L = dppms (3a) and dppe (3b). Against the expectations of simple bonding arguments, methyl migration is faster by a factor of ca. 1500 for [Rh(CO)(dppms)I(2)Me] (2a) than for [Rh(CO)(dppe)I(2)Me] (2b). For M = Ir, alkyl iodide oxidative addition gives stable alkyl complexes [Ir(CO)(L-L)I(2)R]. Migratory insertion (induced at high temperature by CO pressure) was faster for [Ir(CO)(dppms)I(2)Me] (5a) than for its dppe analogue (5b). Reaction of methyl triflate with [Ir(CO)(dppms)I] (4a) yielded the dimer [[Ir(CO)(dppms)(mu-I)Me](2)](2+) (7), which was characterized crystallographically along with 5a and [Ir(CO)(dppms)I(2)Et] (6). Analysis of the X-ray crystal structures showed that the dppms ligand adopts a conformation which creates a sterically crowded pocket around the alkyl ligands of 5a, 6, and 7. It is proposed that this steric strain can be relieved by migratory insertion, to give a five-coordinate acetyl product in which the sterically crowded quadrants flank a vacant coordination site, exemplified by the crystal structure of 3a. Conformational analysis indicates similarity between M(dppms) and M(2)(mu-dppm) chelate structures, which have less flexibility than M(dppe) systems and therefore generate greater steric strain with the "axial" ligands in octahedral complexes. Ab initio calculations suggest an additional electronic contribution to the migratory insertion barrier, whereby a sulfur atom trans to CO stabilizes the transition state compared to systems with phosphorus trans to CO. The results represent a rare example of the quantification of ligand effects on individual steps from catalytic cycles, and are discussed in the context of catalytic methanol carbonylation. Implications for other catalytic reactions utilizing chelating diphosphines (e.g., CO/alkene copolymerization and alkene hydroformylation) are considered.     

The synthesis, characterisation and reactivity of 2-phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C(5)R'(4)(CH(2))(2)PR(2)] (R = Et, R' = H or Me, R = Ph, R' = Me), have been prepared from the reaction of spirohydrocarbons C(5)R'(4)(C(2)H(4)) with LiPR(2). C(5)Et(4)HSiMe(2)CH(2)PMe(2), was prepared from reaction of Li[C(5)Et(4)] with Me(2)SiCl(2) followed by Me(2)PCH(2)Li. The lithium salts were reacted with [RhCl(CO)(2)](2), [IrCl(CO)(3)] or [Co(2)(CO)(8)] to give [M(C(5)R'(4)(CH(2))(2)PR(2))(CO)] (M = Rh, R = Et, R' = H or Me, R = Ph, R' = Me; M = Ir or Co, R = Et, R' = Me), which have been fully characterised, in many cases crystallographically as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values of nu(CO) for these complexes are usually lower than those for the analogous complexes without the bridge between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (Cp' = C(5)Me(4)), the most electron rich of the complexes. [Rh(C(5)Et(4)SiMe(2)CH(2)PMe(2))(CO)] may be a dimer. [Co(2)(CO)(8)] reacts with C(5)H(5)(CH(2))(2)PEt(2) or C(5)Et(4)HSiMe(2)CH(2)PMe(2) (L) to give binuclear complexes of the form [Co(2)(CO)(6)L(2)] with almost linear PCoCoP skeletons. [Rh(Cp'(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are active for methanol carbonylation at 150 degrees C and 27 bar CO, with the rate using [Rh(Cp'(CH(2))(2)PPh(2))(CO)] (0.81 mol dm(-3) h(-1)) being higher than that for [RhI(2)(CO)(2)](-) (0.64 mol dm(-3) h(-1)). The most electron rich complex, [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (0.38 mol dm(-3) h(-1)) gave a comparable rate to [Cp*Rh(PEt(3))(CO)] (0.30 mol dm(-3) h(-1)), which was unstable towards oxidation of the phosphine. [Rh(Cp'(CH(2))(2)PEt(2))I(2)], which is inactive for methanol carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cp'(CH(2))(2)PEt(2))(CO)]. Neither of [M(Cp'(CH(2))(2)PEt(2))(CO)] (M = Co or Ir) was active for methanol carbonylation under these conditions, nor under many other conditions investigated, except that [Ir(Cp'(CH(2))(2)PEt(2))(CO)] showed some activity at higher temperature (190 degrees C), probably as a result of degradation to [IrI(2)(CO)(2)](-). [M(Cp'(CH(2))(2)PEt(2))(CO)] react with MeI to give [M(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] (M = Co or Rh) or [Ir(Cp'(CH(2))(2)PEt(2))Me(CO)]I. The rates of oxidative addition of MeI to [Rh(C(5)H(4)(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are 62 and 1770 times faster than to [Cp*Rh(CO)(2)]. Methyl migration is slower, however. High pressure NMR studies show that [Co(Cp'(CH(2))(2)PEt(2))(CO)] and [Cp*Rh(PEt(3))(CO)] are unstable towards phosphine oxidation and/or quaternisation under methanol carbonylation conditions, but that [Rh(Cp'(CH(2))(2)PEt(2))(CO)] does not exhibit phosphine degradation, eventually producing inactive [Rh(Cp'(CH(2))(2)PEt(2))I(2)] at least under conditions of poor gas mixing. The observation of [Rh(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] under methanol carbonylation conditions suggests that the rhodium centre has become so electron rich that reductive elimination of ethanoyl iodide has become rate determining for methanol carbonylation. In addition to the high electron density at rhodium.     

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.     

Oxidative addition of different electrophiles with rhodium(I) carbonyl complexes of unsymmetrical phosphine–phosphine monoselenide ligands

Dimeric chlorobridge complex [Rh(CO)₂Cl]₂ reacts with two equivalents of a series of unsymmetrical phosphine–phosphine monoselenide ligands, Ph₂P(CH₂)_nP(Se)Ph₂ {n = 1( a ), 2( b ), 3( c ), 4( d )}to form chelate complex [Rh(CO)Cl(P∩Se)] ( 1a ) {P∩Se = η²‐(P,Se) coordinated} and non‐chelate complexes [Rh(CO)₂Cl(P～Se)] ( 1b–d ) {P～Se = η¹‐(P) coordinated}. The complexes 1 undergo oxidative addition reactions with different electrophiles such as CH₃I, C₂H₅I, C₆H₅CH₂Cl and I₂ to produce Rh(III) complexes of the type [Rh(COR)ClX(P∩Se)] {where R = ? C₂H₅ ( 2a ), X = I; R = ? CH₂C₆H₅ ( 3a ), X = Cl}, [Rh(CO)ClI₂(P∩Se)] ( 4a ), [Rh(CO)(COCH₃)ClI(P～Se)] ( 5b–d ), [Rh(CO)(COH₅)ClI‐(P～Se)] ( 6b–d ), [Rh(CO)(COCH₂C₆H₅)Cl₂(P～Se)] ( 7b–d ) and [Rh(CO)ClI₂(P～Se)] ( 8b–d ). The kinetic study of the oxidative addition (OA) reactions of the complexes 1 with CH₃I and C₂H₅I reveals a single stage kinetics. The rate of OA of the complexes varies with the length of the ligand backbone and follows the order 1a > 1b > 1c > 1d . The CH₃I reacts with the different complexes at a rate 10–100 times faster than the C₂H₅I. The catalytic activity of complexes 1b–d for carbonylation of methanol is evaluated and a higher turnover number (TON) is obtained compared with that of the well‐known commercial species [Rh(CO)₂I₂]^?. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and structures of homo- and heterobimetallic rhodium(I) and/or iridium(I) complexes of binucleating bis(1-pyrazolyl)methane ligands

The synthesis of a series of Rh(I) and Ir(I) homobimetallic complexes using three different linking scaffolds is described. The cyclooctadiene (COD) complexes [M(2)(COD)(2)(L(scaffold))][BAr(F)(4)](2) (2-7) where M = Rh(I) or Ir(I), and L(scaffold) = bis(1-pyrazolyl)methane ligands, p-C(6)H(4)[CH(pz)(2)](2) (1a), m-C(6)H(4)[CH(pz)(2)](2) (1b) and the anthracene-bridged 1,8-C(14)H(8)[CH(pz)(2)](2) (1c) were synthesized. The COD co-ligands of 2-7 were replaced with the carbonyl co-ligands to form the analogous homobimetallic complexes, [M(2)(CO)(4)(L(scaffold))][BAr(F)(4)](2) (8-13). The solid-state structures of the dicationic homobimetallic complexes 2, 3, 5, 6, 9, and 10, as well as cationic monometallic complexes 15 and 22 of ligands 1b and 1c respectively, were characterized using X-ray crystallography. The solid-state XRD structures of the resulting dirhodium and diiridium complexes with the para- and meta-phenylene and anthracene scaffolds show that there are distinct differences between structures of complexes 2-10 due to the variation in the scaffold structures, in particular the relative positions of the two metal centres. Heterobimetallic RhIr complexes of the m-C(6)H(4)[CH(pz)(2)](2) ligand were also synthesized using a stepwise approach, and the observed exchange of the metal centres in the heterobimetallic complexes was found to be dependent on the nature of the coligand.     

Synthesis and X-ray structures of water-soluble tris(hydroxymethyl)phosphine complexes of rhodium(I)

The water-soluble Rh(I)-THP complexes: RhCl(1,5-cod)(THP) (), [Rh(1,5-cod)(THP)(2)]Cl (), RhCl(THP)(4) (), and trans-RhCl(CO)(THP)(2) () have been synthesized and characterized, where THP = P(CH(2)OH)(3); - are the first potentially useful entries into Rh(I)-THP chemistry, while and are the first structurally characterized Rh(I)-THP complexes.     

Iodination of triazenide-bridged rhodium and iridium complexes: oxidative addition vs. one-electron oxidation

The triazenide-bridged tetracarbonyls [(OC)(2)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)M(CO)(2)] (M = Rh or Ir) undergo oxidative addition of iodine across the dimetal centre, giving the [RhM](4+) complexes [I(OC)(2)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)M(CO)(2)I], structurally characterised for M = Ir. The anionic tricarbonyl iodide [I(OC)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)Rh(CO)(2)](-) forms [I(2)(OC)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)Rh(CO)I](-) by initial one-electron transfer whereas the analogous tricarbonyl phosphine complexes [(OC)(Ph(3)P)Rh(mu-p-MeC(6)H(4)NNNC(6)H(4)Me-p)(2)M(CO)(2)] (M = Rh or Ir) undergo bridge cleavage, giving mononuclear [Rh(p-MeC(6)H(4)NNNC(6)H(4)Me-p)I(2)(CO)(PPh(3))] and dimeric [I(OC){RNNN(R)C(O)}M(mu-I)(2)M{C(O)N(R)NNR}(CO)I] (M = Rh or Ir, R = C(6)H(4)Me-p) in which CO has been inserted into a metal-nitrogen bond.     

Anionic platinum complexes with 2-pyridylphosphines as ligands for rhodium: synthesis of zwitterionic Pt-Rh organometallic compounds

Bimetallic zwitterionic platinum(II)-rhodium(I) complexes of the type [(C(6)F(5))(3)Pt(micro-PPy(n)Ph(3)(-)(n)Rh(CO)(2))] and [(C(6)F(5))(3)Pt(micro-PPy(n)Ph(3)(-)(n)())Rh(diene))] (n = 2, 3; Py = 2-pyridyl) have been prepared. The P end of the bridging ligands (micro-PPy(n)Ph(3)(-)(n)) is always coordinated to the Pt center, while the N-donor ends chelate the Rh atom, giving metallacycles comparable to pyrazolylborate-Rh complexes. These metallacycles can adopt two conformations, either with the Pt complex in pseudoaxial position approaching the Rh center or with the Pt complex in a remote position. The preferred conformation depends on the steric hindrance at the rhodium center. In less sterically demanding Rh-carbonyl complexes the Pt moiety gets close to the Rh moiety as this brings closer the opposite charges of the zwitterion. For diene complexes mixtures of conformers are obtained. The X-ray structures of [(C(6)F(5))(3)Pt(micro-PPhPy(2))Rh(COD)] (COD = 1,5-cyclooctadiene) and [(C(6)F(5))(3)Pt(micro-PPhPy(2))Rh(CO)(2)] are reported.     

Reactions of a gold(I) thiolate complex [Au(Tab)(2)](2)(PF(6))(2) (Tab = 4-(trimethylammonio)benzenethiolate) with diphosphine ligands

Reactions of a gold(i) thiolate complex [Au(Tab)(2)](2)(PF(6))(2) (Tab = 4-(trimethylammonio)benzenethiolate) with equimolar 1,2-bis(diphenylphosphine)ethane (dppe), 1,3-bis-(diphenylphosphine)propane (dppp) or 1,4-bis-(diphenylphosphine)butane (dppb) in MeOH-DMF-CH(2)Cl(2) gave rise to three polymeric complexes [Au(2)(Tab)(2)(dppe)](2)(PF(6))(4)·2MeOH (1·2MeOH), [Au(2)(Tab)(2)(dppp)]Cl(2)·0.5MeOH·4H(2)O (2·0.5MeOH·4H(2)O), and [Au(4)(μ-Tab)(2)(Tab)(2)(dppb)](PF(6))(4)·4DMF (3·4DMF), respectively. Analogous reaction of 1 with dppb in DMF/C(2)H(4)Cl(2) produced one tetranuclear complex [Au(2)(μ-Tab)(Tab)(2)](2)Cl(4)·2DMF·4H(2)O (4·2DMF·4H(2)O). Complexes 1-4 were characterized by elemental analysis, IR spectra, UV-vis spectra, (1)H and (31)P{(1)H} NMR and single crystal X-ray analysis. Compounds 1 and 2 consist of [Au(Tab)](2) dimeric fragments that are bridged by dppe or dppp ligands to form a 1D linear chain extending along the a axis. For 3, each [Au(4)(Tab)(2)(μ-Tab)(2)] fragment is linked by a pair of dppb ligands to afford another 1D chain extending along the c axis. For 4, the four [Au(Tab)](+) fragments are linked by two Au-Au bonds and two doubly bridging Tab ligands to form a {[Au(Tab)](4)(μ-Tab)(2)} chair-like cyclohexane structure. Hydrogen-bonding interactions in 2 and 4 lead to the formation of interesting 2D hydrogen-bonded networks. The luminescent properties of 1-4 in solid state were also investigated.     

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.     

Isomerism in rhodium(I) N,S-donor heteroscorpionates: ring substituent and ancillary ligand effects

The heteroscorpionate ligands [HB(taz)(2)(pz(R))](-) (pz(R) = pz, pz(Me2), pz(Ph)) and [HB(taz)(pz)(2)](-), synthesised from the appropriate potassium hydrotris(pyrazolyl)borate salt and 4-ethyl-3-methyl-5-thioxo-1,2,4-triazole (Htaz), react with [{Rh(cod)(μ-Cl)}(2)] to give [Rh(cod)Tx] {Tx = HB(taz)(2)(pz), HB(taz)(2)(pz(Me2)), HB(taz)(2)(pz(Ph)), HB(taz)(pz)(2)}; the heteroscorpionate rhodaboratrane [Rh{B(taz)(2)(pz(Me2))}{HB(taz)(2)(pz(Me2))}] is the only isolable product from the reaction of [{Rh(nbd)(μ-Cl)}(2)] with K[HB(taz)(2)(pz(Me2))]. Carbonylation of the cod complexes gave a mixture of [Rh(CO)(2)Tx] and [(RhTx)(2)(μ-CO)(3)] which reacts with PR(3) to give [Rh(CO)(PR(3))Tx] (R = Cy, NMe(2), Ph, OPh). In the solid state the complexes are square planar with the particular structure dependent on the steric and/or electronic properties of the scorpionate and ancillary ligands. The complex [Rh(cod){HB(taz)(pz)(2)}] has the heteroscorpionate κ(2)[N(2)]-coordinated to rhodium with the B-H bond directed away from the rhodium square plane while [Rh(cod){HB(taz)(2)(pz(Me2))}] is κ(2)[SN]-coordinated, with the B-H bond directed towards the metal. The complexes [Rh(CO)(PPh(3)){HB(taz)(2)(pz)}] and [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Me2))}] are also κ(2)[SN]-coordinated but with the pyrazolyl ring cis to PPh(3); in the former the B-H bond is directed towards rhodium while in the latter the ring is pseudo-parallel to the rhodium square plane, as also found for [Rh(CO)(2){HB(taz)(2)(pz(Me2))}]. The analogues [Rh(CO)(PR(3)){HB(taz)(2)(pz(Me2))}] (R = Cy, NMe(2)) have the phosphines trans to the pyrazolyl ring. Uniquely, [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Ph))}] is κ(2)[S(2)]-coordinated. A qualitative mechanism is given for the rapid ring-exchange, and hence isomerisation, observed in solution.     

Bis(alkoxycarbonyl) complexes of platinum: preparation,reactivity and their role in carbonylation reactions

bis(alkoxycarbonyl) complexes of platinum of the type [Pt(COOR)₂L] [L = 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), l,4-bis(diphenylphosphino)butane (dppb), 1,1'-bis(diphenylphosphino)ferrocene (dppf) or 1,2-bis-(diphenylphosphino)benzene (dpb); R = CH₃, C₆H₅ or C₂H₅] were obtained by reaction of [PtCl₂L] with carbon monoxide and alkoxides. Palladium and nickel complexes gave only carbonyl complexes of the type [M(CO)L] or [M(CO)₂L]. The new complexes were characterized by chemical and spectroscopic means. The X-ray structure of [Pt(COOCH₃)₂(dppf] · CH₃OH is also reported. The reactivity of some alkoxycarbonyl complexes was also investigated.     

Synthesis and characterization of half-sandwich N-heterocyclic carbene complexes of cobalt and rhodium

A series of novel half-sandwich M(I) and M(III) complexes (M = Co, Rh) bearing the N-heterocyclic carbene ligand 1,3-dimesitylimidazol-2-ylidene (IMes) have been prepared and characterized. Thus, (eta5-C(5)R(5))M(IMes)(C(2)H(4))(M = Co, Rh; R = H, Me) were obtained from the corresponding bis(ethene) complexes (eta5-C(5)R(5))M(C(2)H(4))(2), except for CpRh(IMes)(C(2)H(4)) which was prepared via the novel 16-electron Rh(I) compound Rh(IMes)(C(2)H(4))(2)Cl. The carbonyl compounds (eta5-C(5)R(5))Co(IMes)(CO)(R = H, Me) were synthesized by thermal CO substitution of (eta5-C(5)R(5))Co(CO)(2). A diamagnetic, apparently 16-electron Co(III) compound [CpCo(IMes)I](+)[I(3)(-)] was obtained from CpCo(IMes)(CO) and I(2). Finally, Co(III) and Rh(III) complexes CpCo(IMes)Me(2) and Cp*Rh(IMes)Me(2) were prepared by methylation of [CpCo(IMes)I](+)[I(3)(-)], and ligand exchange at Cp*Rh(Me(2)SO)Me(2), respectively. The molecular structures of CpCo(IMes)(CO), CpRh(IMes)(C(2)H(4)), Cp*Rh(IMes)(C(2)H(4)), and Cp*Rh(IMes)Me(2) were determined by single crystal X-ray diffraction. Steric and electronic factors imposed by the strongly donating and sterically demanding IMes ligand are discussed on the basis of X-ray crystallographic, NMR, and IR spectroscopic analyses. Very poor correlations are found between values for (1)J(Rh-C(carbene)) and dRh-C(carbene) data for Rh(i) N,N-heterocyclic carbene complexes including literature data and this work.     

High-pressure investigations under CO/H2 of rhodium complexes containing hemispherical diphosphites

The two rhodium complexes [Rh(acac)(L(R))] (L(R)=(S,S)-5,11,17,23-tetra-tert-butyl-25,27-di(OR)-26,28-bis(1,1'-binaphthyl-2,2'-dioxyphosphanyloxy)calix[4]arene; 6: R=benzyl, 7: R=fluorenyl), each based on a hemispherical chelator forming a pocket about the metal centre upon chelation, are active in the hydroformylation of 1-octene and styrene. As expected for this family of diphosphanes, both complexes resulted in remarkably high selectivity towards the linear aldehyde in the hydroformylation of 1-octene (l/b≈15 for both complexes). Linear aldehyde selectivity was also observed when using styrene, but surprisingly only 6 displayed a marked preference for the linear product (l/b=12.4 (6) vs. 1.9 (7)). A detailed study of the structure of the complexes under CO or CO/H(2) in toluene was performed by high-pressure NMR (HP NMR) and FT-IR (HP-IR) spectroscopies. The spectroscopic data revealed that treatment of 6 with CO gave [Rh(acac)(CO)(η(1)-L(benzyl))] (8), in which the diphosphite behaves as a unidentate ligand. Subsequent addition of H(2) to the solution resulted in a well-defined chelate complex with the formula [RhH(CO)(2)(L(benzyl))] (9). Unlike 6, treatment of complex 7 with CO only led to ligand dissociation and concomitant formation of [Rh(acac)(CO)(2)], but upon addition of H(2) a chelate complex analogous to 9 was formed quantitatively. In both [RhH(CO)(2)(L(R))] complexes the diphosphite adopts the bis-equatorial coordination mode, a structural feature known to favour the formation of linear aldehydes. As revealed by variable-temperature NMR spectroscopy, these complexes show the typical fluxionality of trigonal bipyramidal [RhH(CO)(2)(diphosphane)] complexes. The lower linear selectivity of 7 versus 6 in the hydroformylation of styrene was assigned to steric effects, due to the pocket in which the catalysis takes place being less adapted to accommodate CO or larger olefins and, therefore, possibly leading to facile ligand decoordination. This interpretation was corroborated by an X-ray structure determination carried out for 7.