Synthesis of [Ir3Rh(CO)12] and Fluxional Behaviour of Some of Its Substituted Derivatives

The redox condensation of [Ir(CO)₄]^–, [Ir(cod)(THF)₂]⁺, and [Rh(cod)(THF)₂]⁺ (cod = cycloocta-1,5-diene) followed by saturation with CO (1 atm) in THF afforded the first synthetic route to pure [Ir₃Rh(CO)₁₂] ( 1 ). Substitution of CO by monodentate ligands gave [Ir₃Rh(CO)₈(μ₂-CO)₃L] (L = Br^–, 2 ; I^–, 3 ; bicyclo[2.2.1]hept-2-ene, 4 ; PPh₃, 5 ). Clusters 2 – 5 have C_s symmetry with the ligand L bound to the basal Rh-atom in axial position. They are fluxional in solution at the NMR time scale due to two CO scrambling processes: the merry-go-round of basal CO's and changes of basal face. An additional process takes place in 5 above room temperature: the intramolecular migration of PPh₃ from the Rh- to a basal Ir-atom. Substitution of CO by polydentate ligands gave [Ir₃Rh(CO)_7–x(μ₂-CO)₃(η⁴-L)x] (L = bicyclo[2.2.1]hepta-2,5-diene (= norbornadiene; nbd), x = 1, 6 ; L = nbd, x = 2, 13 ; L = cod, x = 1, 7 ; L = cod x = 2, 15 ), [Ir₃Rh(CO)₇(μ₂-CO)₃(η²-diars)] (diars = 1,2-phenylenebis-(dimethylarsine); 8 ), [Ir₃Rh(CO)₇(μ₂-CO)₃(η⁴-L)] (L = methylenebis(diphenylphosphine), bonded to 2 basal Ir-atom ( 9a ) or one Ir- and one Rh-atom ( 9b )), [Ir₃Rh(CO)₆(μ₂-CO)₃(η⁴-nbd)PPh₃] ( 12 ), and [Ir₃Rh(CO)₆(μ₂-CO)₃(μ₃-L)] (L = 1,3,5-trithiane, 10 ; L = CH(PPh₂)₃, 11 ). Complexes 6 – 8 , 9a , 10 , and 11 have C_s symmetry, the others C₁ symmetry. They are fluxional in solution due to CO scrambling processes involving 1, 3, or 4 metal centres as deduced from 2D-EXSY spectra. Comparison of the activation energies of these processes with those of the isostructural Ir₄ and Ir₂Rh₂ compounds showed that substitution of Ir by Rh in the basal face of an Ir₄ compound slows the processes involving 3 or 4 metal centres (merry-go-round and change of basal face), but increases the rate of carbonyl rotation about an Ir-atom.     

Addition of C2(CO2Me)2 to trans-MeIr(CO)(PPh3)2. Formation and isomerization of MeIr(CO)(PPh3)2[C2(CO2Me)2], and crystal structure of the thermodynamic isomer

The reaction of C₂(CO₂Me)₂ with trans-MeIr(CO)(PPh₃)₂ leads to a kinetic isomer which has been characterized by ¹H and ³¹P NMR and infrared spectra and to a thermodynamic isomer which has been characterized by ¹H and ³¹P NMR, infrared, microanalysis and X-ray crystallography. The isomerization occurs readily in solution at room temperature; somewhat more slowly at −20°C. The thermodynamically stable isomer of MeIr(CO)(PPh₃)₂[C₂(CO₂Me)₂] crystallizes in the centrosymmetric monoclinic space group P2₁/c with a 14.847(2), b 16.648(2), c 15.656(3) Å, β 90.595(14)°, V 3869.7(11) ų and Z = 4. Single-crystal X-ray diffraction data were collected with a Syntex P2₁ automated diffractometer (Mo-K_α radiation, 2θ 5–40°) and the structure was solved and refined to R_F 8.6% for all 3631 independent data (R_F 4.0% for those 2318 data with |F_o| > 6σ(|F_o|)). The Ir^I center has a trigonal-bipyramidal environment with the methyl ligand and one PPh₃ ligand occupying axial sites (Ir-Me 2.193(14), Ir-P(1) 2.425(4) Å). The C₂(CO₂Me)₂ ligand is π-bonded to the iridium atom and lies with its triple bond parallel to the equatorial coordination plane; the equatorial ligands are completed by the second PPh₃ ligand (Ir-P(2) 2.402(3) Å) and a CO ligand (Ir-CO 1.812(15) Å).     

Structural spectroscopic and conformational studies of H2Ru2Rh2(CO)11(PPh3)

The structure of H₂Ru₂Rh₂(CO)₁₁(PPh₃) has been studied by X-ray crystallography and by NMR spectroscopy. The arrangement of the carbonyl and the hydride ligands is similar to that in H₂Ru₂Rh₂(CO)₁₂. The phosphine is equatorially coordinated to the same basal rhodium as the other edge-bridging hydride ligand. A position cis to the phosphine is sterically favourable for the bridging hydride.     

Diminished electron density in the Vaska‐type rhodium(I) complex trans‐[Rh(NCBH3)(CO)(PPh3)2]

Vaska‐type complexes, i.e. trans‐[RhX(CO)(PPh₃)₂] (X is a halogen or pseudohalogen), undergo a range of reactions and exhibit considerable catalytic activity. The electron density on the Rh^I atom in these complexes plays an important role in their reactivity. Many cyanotrihydridoborate (BH₃CN⁻) complexes of Group 6–8 transition metals have been synthesized and structurally characterized, an exception being the rhodium(I) complex. Carbonyl(cyanotrihydridoborato‐κN)bis(triphenylphosphine‐κP)rhodium(I), [Rh(NCBH₃)(CO)(C₁₈H₁₅P)₂], was prepared by the metathesis reaction of sodium cyanotrihydridoborate with trans‐[RhCl(CO)(PPh₃)₂], and was characterized by single‐crystal X‐ray diffraction analysis and IR, ¹H, ¹³C and ¹¹B NMR spectroscopy. The X‐ray diffraction data indicate that the cyanotrihydridoborate ligand coordinates to the Rh^I atom through the N atom in a trans position with respect to the carbonyl ligand; this was also confirmed by the IR and NMR data. The carbonyl stretching frequency ν(CO) and the carbonyl carbon ¹J_C–Rh and ¹J_C–P coupling constants of the C_ipso atoms of the triphenylphosphine groups reflect the diminished electron density on the central Rh^I atom compared to the parent trans‐[RhCl(CO)(PPh₃)₂] complex.     

Synthesis,Reactivity, and Fluxional Behaviour of [Ir2Rh2(CO)12], and Crystal Structure of [Ir2Rh2(CO)8(norbornadiene)2]

The synthesis of [Ir₂Rh₂(CO)₁₂] ( 1 ) by the literature method gives a mixture 1 /[IrRh₃(CO)₁₂] which cannot be separated using chromatography. The reaction of [Ir(CO)₄]^? with 1 mol-equiv. of [Rh(CO)₂(THF)₂]⁺ in THF gives pure 1 in 61% yield. Crystals of 1 are highly disordered, unlike those of its derivative [Ir₂Rh₂(CO)₅(μ₂-CO)₃(norbornadiene)₂] which were analysed using X-ray diffraction. The ground-state geometry of 1 in solution has three edge-bridging CO's on the basal IrRh₂ face of the metal tetrahedron. Time averaging of CO's takes place above 230 K. The CO site exchange of lowest activation energy is due to one synchronous change of basal face, as shown by 2D- and VT-¹³C-NMR. Substitution of CO by X^? in 1 takes place at a Rh-atom giving [Ir₂Rh₂(CO)₈(μ₂-CO)₃X]^? (X = Br, I). Substitution by bidentate ligands gives [Ir₂Rh₂(CO)₇(μ₂-CO)₃(η⁴-L)] (L = norbornadiene, cycloocta-1,5-diene) where the ligand L is chelating a Rh-atom of the basal IrRh₂ face. Carbonyl substitution by tridentate ligands gives [Ir₂Rh₂(CO)₆(μ₂-CO)₃(μ₃-L)] (L = 1,3,5-trithiane, tripod) with L capping the triangular basal face of the metal tetrahedron. Carbonyl scrambling is also observed in these substituted derivatives of 1 and is mainly due to the rotation of three terminal CO's about a local C₃ axis on the apical Ir-atom.     

Synthesis,stereodynamics, and reactivity of isonitrile derivatives of dodecacarbonyltetrairidium

The reaction of Ir₄₍CO)₁₂ with t-BuNC or MeNC in the presence of trimethylamine oxide in refluxing tetrahydrofuran provides the substituted iridium clusters Ir₄(CO)_12-x(RNC)_x] (χ  14; R  t-Bu, Me). The infrared and ¹³C NMR spectra of these molecules indicate that most of them adopt structures related to Ir₄(CO)₁₂, i.e., they have only terminal carbonyl ligands. The variable temperature ¹³C NMR spectra for Ir₄(CO)₁₁(t-BuNC) establish a carbonyl scrambling process which is the formal inverse of the C_3v→ T_d scrambling mechanism proposed for Rh₄(CO)₁₂. The kinetics of substitution of Ir₄(CO)₁₂ by t-BuNC have been studied. Each substitution step occurs by a ligand-dependent, overall second-order reaction at a rate much greater than for substitution by PPh₃. The observed differences between t-BuNC and PPh₃, can be rationalized on the basis of steric differences between the two ligands.     

Regioselectivity in the rhodium catalysed 1,4-hydrosilylation of isoprene. Aspects on reaction conditions and ligands

The regioselectivity in the Rh catalysed 1,4-hydrosilylation of isoprene was investigated. Variation of solvents and temperature did not significantly affect the isomer distribution between tail-product (I) and head-product (II). The choice of ligands had the greater influence, where Rh^I-based catalysts with the strong electron withdrawing ligand CO favoured production of isomer II, while Rh^I catalysts with strong electron donating ligands (for example triarylphosphines) gave isomer I as the main product. In contrast to the square planar carbonyl complex RhCl(CO)(PPh₃)₂, the square planar thiocarbonyl complex RhCl(CS)(PPh₃)₂, gave I as the major isomer.     

Synthesis and molecular structure of [Rh3(μ-PPh2)3(CO)6(PPh2-H)], an unusual six-membered inorganic ring complex

Reaction of [{Rh(μ-Cl)(CO)₂}₂] with PPh₂H in CO-saturated ethanol yields [Rh₃(μ-PPh₂)₃ (CO)₆ (PPh₂H)], a red trinuclear cluster of rhodium containing a near-planar six-membered Rh₃P₃ ring; this compound reversibly undergoes elimination of CO and PPh₂H to afford [Rh₃(μ-PPh₂)₃(CO)₅].     

Intramolecular rearrangement of the bridging σ,π-acetylide ligand in the Os3H(CO)9(L)(μ-η2-CCPh) (L = CO,PMe2Ph) clusters and crystal structure of Os3H(CO)9(PMe2Ph)(μ-η2-CCPh)

Clusters Os₃H(Cl)(CO)₉(L) (L= CO, PMe₂Ph) react with lithium phenyl-acetylide to yield Os₃H(CO)₉(L)(μ-η²-CCPh),which has a bridging acetylide ligand. The Os₃H(CO)₁₀(μ-η²-CCPh) complex (II) is fluxional owing to rapid π → σ, σ → π interchange of acetylide ligand between the bridged osmium atoms, whereas the phosphine-substituted derivative, Os₃H(CO)₉(PM₂Ph)(μ-η²-CCPh) (III), is stereochemically rigid and exists at room temperature in two isomeric forms. These isomers have been isolated as solids and have been characterized by ¹H and ³¹P{¹H} NMR spectroscopy. According to the spectroscopic data, in the major (IIIa) and minor (IIIb) isomers the phosphine ligand is coordinated to the metal atom which is σ- or π-bonded to the bridging acetylide group, respectively. The isomerization of IIIb into IIIa occurs only at 80°C. The structure of IIIa has been confirmed by an X-ray diffraction study.     

Formation of the Salt‐like Complexes [Co{S2CC(PPh3)2}3][Co(CO)4]3 and [(CO)4Mn{S2CC(PPh3)2}][Mn(CO)5] from the Reaction of the Related Carbonyl Compounds with S2CC(PPh3)2

The betain‐like compound S₂CC(PPh₃)₂ ( 1 ), which is obtained from CS₂ and the double ylide C(PPh₃)₂, reacts with [Co₂(CO)₈] and [Mn₂(CO)₁₀] in THF to afford the salt‐like complexes [Co{S₂CC(PPh₃)₂}₃][Co(CO)₄]₃ ( 2 ) and [(CO)₄Mn{S₂CC(PPh₃)₂}][Mn(CO)₅] ( 3 ), respectively, in good yields. At both d⁶ cations 1 acts as a chelating ligand. Disproportionation reactions from formal Co⁰ into Co^III and Co^?I and from Mn⁰ into Mn^I and Mn^?I occurred with the removal of four or one carbonyl groups, respectively. The crystal structures of 2· 5.5THF and 3· 2THF are reported, which show a shortening of the C–C bond in the ligand upon complex formation. The compounds are further characterized by ³¹P NMR and IR spectroscopy.     

The crystal and molecular structure of the tetraphenylphosphonium salt of the anion bromotri-μ-carbonyloctacarbonyl-tetrahedro-tetrairidate(-1)

Crystal of [Ir₄Br(CO)₁₁] (PPh₄) are orthorhombic, space group P2₁2₁2₁, with a 13.276(3), b 18.347(4), c 16.041(4) Å. The structure has been elucidated by the analysis of 2876 observed intensities recorded on an automatic diffractometer, and refined by the least-squares method to R  0.043. The anion contains a tetrahedral cluster of iridium atoms (mean IrIr 2.710 Å). The carbonyl arrangement differs from that of the parent Ir₄(CO)₁₂, and is similar to that known for Co₄(CO)₁₂ and Rh₄(CO)₁₂, with one terminal CO group in the basal M₃(CO)₉ moiety replaced by the bromide ligand; two of the bridging CO groups become markedly assymetric.     

Solution Equilibria in Trialkyl-Phosphite Derivatives of [Ir4(CO)12]. Crystal Structure of [Ir4(CO)11{P(OCH2)3CEt}]

The monosubstituted [Ir₄(CO)₁₁L] clusters (L = P(OPh)₃, 1 ; L = P(OMe)₃, 2 ; L = P(OCH₂)₃CEt, 3 ) were obtained in good yields by the reaction of [Ir₄(CO)₁₁ I ]^? with the corresponding phosphite. In the solid state, cluster 3 has a C_s geometry with all terminal ligands as shown by an X-ray analysis. Three isomers are present in solution: one with terminal ligands ( A ) and two with three edge-bridging CO's and with L in axial ( B ) or radial ( C ) position (see Scheme). The thermodynamic and kinetic parameters of isomerisations B ? A and A ? C were determined by simulation of the variable-temperature ³¹P-NMR spectra. The three isomers correspond to three minima on the kinetic pathway of CO scrambling, whose relative energies vary independently within a small range (1–9 kJ mol^?1 at 298 K). At low temperature, isomer C is always the least stable and is not observed for 1 which bears the most bulky phosphite ligand. The isomerisations are due to two intramolecular merry-go-rounds of CO groups about two unequivalent faces of the unbridged species A .     

Intramolecular Dynamics of Tetranuclear Carbonyliridium Cluster Compounds. Part II. Disubstituted complexes with one chelating ligand. Crystal structure of [Ir4(CO)7(μ-CO)3(1,5-cyclooctadiene)]

The two complexes [Ir₄(CO)₁₀(diarsine)] (1) and [Ir₄(CO)₁₀(1,5-cyclooctadiene)] (2) bear a bidentate ligand chelating one metal atom of the basal face of the Ir₄ tetrahedron. However, they differ in fluxional behaviour as observed by 2D-exchange and variable-temperature ¹³C-NMR. The CO-site exchange with lowest activation energy proceeds via an unbridged intermediate in 2 , whereas that in 1 occurs via a concerted edge-bridging of CO's to an alternative face of the metal core. This difference is apparently related to different ground-state geometries: the basal CO's are symmetrically bridging in 2 , whereas two CO's are semi-bridging in 1 . The molecular structure of 2 was determined by single crystal X-ray diffractometry. The crystals are orthorhombic, space group Pbca, a = 11.651(4), b = 13.118(3), c = 28.64(1)Å. The idealized molecular symmetry is C_s. The diolefin chelates a basal Ir-atom replacing an axial and a radial CO group on the tetrahedral metal-atom framework.     

The Reaction of the Betain‐like Compound O2C2(PPh3)2 with [(cod)PtI2] – Crystal Structure of the Salt (HC{PPh3}2)[(η3‐C8H11)PtI2]

The reaction of the betain‐like compound O₂C₂(PPh₃)₂ ( 1 ) with [(cod)PtX₂] in THF solution gives the salt‐like compounds (HC{PPh₃}₂)[(η³‐C₈H₁₁)PtX₂] ( 3 , X = I; 4 , X = Cl) in about quantitative yields. The new η³‐bonded C₈H₁₁ ligand is the result of a proton transfer from the coordinated cod ligand to 1 with subsequent release of CO₂. The X‐ray analysis of 3 shows the presence of two isomers in a 60:40 ratio, which differ in the bonding of the C₈H₁₁ ligand. 3 crystallizes in the triclinic space group with the unit cell dimensions a = 1091.7(1), b = 1141.5(1), c = 1649.4(2) pm; α = 80.34(1)°, β = 83.62(1)°, γ = 89.03(1)°, V = 2013.7(4)·10⁶ pm³, Z = 2.     

Synthesis,structure and NMR spectroscopy of some rhodium(III) cyclometallated Schiff's base complexes derived from 2-benzylidene-3-methylpyridines. Crystal structure of [RhHI{2-(3-nitrobenzylidene)-3-methylpyridine}; (PPh3)2]

The Schiff's base derived from 2-amino, 3-methylpyridine and an aryl aldehyde reacts with either RhCI(PPh₃)₃ or [Rh(μ-C1)(cyclooctene)₂]₂ in the presence of four equivalents of L (L = PPh₃, P(4-C1C₆H₄)₃, P(cyclohexyl)₃, AsPh₃, SbPh₃) to give a Rh^III cyclometallated complex (2), in which the imine CH bond has oxidatively added to the metal. The complexes 2 react with reagents such as Br^-, CN^-, CH₃I, CNR (R = cyclohexyl, t-butyl), P(OCH₃)₃, CO, to give substitution products (3), in which the Cl has been replaced. The complexes 2 and 3, as well as some few Ir^III analogs (4), have been isolated and characterized using ¹H, ³¹P, and (occasionally) ¹³C NMR spectroscopy. The crystal structure of the complex RhHI{2-(3-nitrobenzylidene)-3-methylpyridine} (PPh₃)₂ (3b) has been determined by X-ray diffraction. The complex shows a distorted octahedral structure with the following bond distances (Å) and angles (°): Rh-I, 2.771(2); Rh-N(1), 2.15(1); Rh-C(7′), 1.98(2); Rh-P(1), 2.326(5); Rh-P(2) 2.332(5); P-Rh-P, 159.7(2), N(1)-Rh-C(7′), 78.5(6). In the light of the NMR and X-ray data, it is suggested that the C(R)N moiety exerts a large trans influence.     

Synthesis and structural characterization of the first transition metal cluster containing a PPh2AuPPh3 ligand,Ir4(CO)8(μ-CO)3(PPh2AuPPh3), and its conversion into Ir4(CO)9(μ-CO)(μ-PPh2)(μ-AuPPh3)

Deprotonation of Ir₄(CO)₁₁PPh₂H (1) in the presence of [AuPPh₃][PF₆] yields the novel species Ir₄(CO)₁₁(PPh₂AuPPh₃) (2), which possesses a tetrahedral framework bearing a terminally bound PPh₂AuPPh₃ ligand. When heated in toluene, 2 is converted into the phosphido species Ir₄(CO)₁₀(μ-PPh₂)(μ-AuPPh₃).     

Synthesis and structures of new heteronuclear cluster complexes [PPh4][Fe4Rh3Se2(CO)16] and [PPh4]2[Fe3Rh4Te2(CO)15]

The reaction of the K₂[Fe₃Q(CO)₉] clusters (Q = Se or Te) with Rh₂(CO)₄Cl₂ under mild conditions is accompanied by complicated fragmentation of cores of the starting clusters to form large heteronuclear cluster anions. The [PPh₄][Fe₄Rh₃Se₂(CO)₁₆] and [PPh₄]₂[Fe₃Rh₄Te₂(CO)₁₅] compounds were isolated by treatment of the reaction products with tetraphenylphosphonium bromide. The structures of the products were established by X-ray diffraction. In both compounds, the core of the heteronuclear cluster consists of two octahedra fused via a common Rh₃ face. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 775–778, May, 2006.     

Reactivity study of a hydroxyl coordinated osmium vinyl complex OsCl2(PPh3)2[CH=C(PPh3)CHPh(OH)]

We studied the reactivity of an osmium vinyl complex containing a coordinated hydroxyl group OsCl2(PPh3)2[CH=C(PPh3)CHPh(OH)] (1) toward bidentate ligand 1,4-bis(diphenylphosphino)butane (DPPB),acid ligand (CO),base (Cs2CO3) and heat.Two osmium vinyl complexes OsCl2(dppb)[CH=C(PPh3)CHPh(OH)](2) and OsCl2(CO)2(PPh3)[CH=C(PPh 3)CHPh(OH)] (3),as well as two relatively rare phosphonium-containing osmafuran complexes Os(2-OCOO)(PPh3)2[CHC(PPh3)CPhO](4) and OsCl2 (PPh3)2[CHC(PPh3)CPhO](5),were obtained in high yields from these reactions.All products were characterized by NMR spectroscopy,elemental analysis,and their structures were further confirmed by single crystal X-ray diffraction.     

Synthesis and Crystal Structures of the Molybdenum(II) Complexes with the N,N‐dimethylthiocarbamoyl Containing Ligand: Crystal Structures of β [Mo(CO)2{η2‐S2P(OEt)2}(η2‐SCNMe2)(PPh3)] and [Mo(CO)2(η3‐Tp)(η2‐SCNMe2)(PPh3)]

Reactions of the thiocarbamoyl‐molybdenum complex [Mo(CO)₂(η²‐SCNMe₂)(PPh₃)₂Cl] 1 , and ammonium diethyldithiophosphate, NH₄S₂P(OEt)₂, and potassium tris(pyrazoyl‐1‐yl)borate, KTp, in dichloromethane at room temperature yielded the seven coordinated diethyldithiophosphate thiocarbamoyl‐molybdenum complexe [Mo(CO)₂{η²‐S₂P(OEt)₂}(η²‐SCNMe₂)(PPh₃)] β‐3 , and tris(pyrazoyl‐1‐yl)borate thiocabamoyl‐molybdenum complex [Mo(CO)₂(η³‐Tp)(η²‐SCNMe₂)(PPh₃)] 4 , respectively. The geometry around the metal atom of compounds β‐3 and 4 are capped octahedrons. The α‐ and β‐isomers are defined to the dithio‐ligand and one of the carbonyl ligands in the trans position in former and two carbonyl ligands in the trans position in later. The thiocabamoyl and diethyldithiophosphate or tris(pyrazoyl‐1‐yl)borate ligands coordinate to the molybdenum metal center through the carbon and sulfur and two sulfur atoms, or three nitrogen atoms, respectively. Complexes β‐3 and 4 are characterized by X‐ray diffraction analyses.     

New tetrahedral cluster compounds of iridium. Synthesis of the anions [Ir4(CO)11X]− (X = Cl,Br, I,CN, SCN) and x-ray structure of [PPh4] [Ir4(CO)11Br]

[Ir₄(CO)₁₁X]^? anions are obtained by reaction of halide and pseudo-halide ions with Ir₄(CO)₁₂. X-ray determination of the structure of [Ir₄(CO)₁₁Br]^? shows that the carbonyl arrangement differs from that of the parent Ir₄(CO)₁₂, and is similar to that known for Co₄(CO)₁₂; one terminal CO group in the basal M₃(CO)₉ moiety is replaced by the bromide ligand, and two of the bridging CO groups become markedly asymmetric.