Carbonyl rhodium(I) complexes with α-diimines ligands

The reactions of [Rh(CO)₂Cl]₂ with α-diimines, RN=CR′-CR′=NR (R = c-Hex, C₆H₅, p-C₆H₄OH, p-C₆H₄CH₃, p-C₆H₄OCH₃, R′ = H; R = c-Hex, C₆H₅, p-C₆H₄OH, p-C₆H₄OCH₃; R′ = Me) in 2:1 Rh/R-dim ratio gave rise to ionic compounds [(CO)₂Rh.R-dim(R′,R′)][Rh(CO)₂Cl₂] which have been characterized by elemental analyses, electrical conductivity, ¹H-NMR and electronic and IR spectroscopy. Some of these complexes must involve some kind of metal-metal interaction. The complex [Rh(CO)₂Cl.c-Hex-dim(H,H)] has been obtained by reaction of [Rh(CO)₂Cl]₂ with the c-Hex-dim(H,H) ligand in 1:1 Rh/R-dim ratio. The reactions between [(CO)₂Rh.R-dim(H,H)][Rh(CO)₂Cl₂](R = c-Hex or p-C₆H₄OCH₃) with the dppe ligand have been studied. The known complex RhCl(CO)(PPh₃)₂ has been isolated from the reaction of [(CO)₂Rh.R-dim(H,H)]-[Rh(CO)₂Cl₂] (R = c-Hex or p-C₆H₄OCH₃) with PPh₃ ligand.     

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.     

ESR investigation of the substitution reactions in rhodium(I) complexes with spin-labeled ligands

A number of new spin-labelled Rh^I complexes containing both the 3,6-ditert-butyl-o-benzosemiquinone (3,6-SQ) fragment and n- and π-donor ligands have been prepared. The tetracoordinate derivatives of the composition L₂Rh-(3,6-SQ), where L  CO, P(OPh)₃, L  1/2 1,5-COD and the pentacoordinate complex (PPh₃)₂Rh(3,6-SQ)(CO) were isolated in individual state, the formation of other rhodium compounds was registered by ESR spectroscopy. The presence of an o-benzosemiquinolate ligand in the molecule with the unpaired electron located essentially on this fragment does not significantly influence on the reactivity of the metal ion in most cases; the n- and π-donor ligands exchange reactions studied by ESR confirm this fact. (PPh₃)₂Rh(3,6-SQ) has an abnormal distribution of spin density of the unpaired electron in the molecule, mostly located on the metal atom, this derivative bearing a close analogy to the rhodium(II) (d⁷) complexes.     

Spectroscopic studies of 4-substituted pyridinium 2-pyridylcarbonylmethylide-rhodium(I) complexes and x-ray molecular structure of (1,5-cyclooctadiene) (4-methylpyridinium 2-pyridylcarbonylmethylide)rhodium(I) perchlorate

(1,5-Cyclooctadiene) (4-substituted pyridinium 2-pyridylcarbonylmethylide)- rhodium(I) perchlorates, [Rh(COD)(C₅H₄NC(O)C?H₊C₅H₄X-4)]ClO₄ [COD = 1,5-cyclooctadiene; X = CH₃C(O), CH₃OC(O), C₆H₅, CH₃, and H], have been prepared. They are shown to have the geometry with coordination by the pyridyl nitrogen and carbonyl oxygen atoms of the ylide ligands and to exhibit intramolecular rearrangement of coordinated COD in chloroform, methanol, and dimethyl sulphoxide based on IR and ¹H NMR spectroscopies. Although the ylides have exhibited fluorescence bands due to an intramolecular charge-transfer transition and phosphorescence bands due to a carbonyl ³(n?π^*) transition, the complexes have given emission bands due to the metal-to-ylide ligand charge-transfer transition. A.single crystal X-ray crystal structure has been determined for [Rh(COD)(C₅H₄NC(O)C?H₊C₅H₄CH₃-4)]ClO₄. The crystals are monoclinic, space group P2₁/n with cell dimensions a = 14.887(3), b = 20.274(4), c = 6.966(1) Å, β = 96.13(1)°, and Z = 4. The structure has been refined by a block-diagonal least-squares method to final R = 0.060 for 2997 independent reflections with |F_o| > 3σ(F). The ylide carbon-pyridinium nitrogen bond distance is 1.420(10) Å. The bonded distances from rhodium to the midpoints of the double bonds of COD are 1.982(11) and 2.014(12) Å.     

The chemistry of hetero-allene and -allylic derivatives with rhodium : I. The reactions of rhodium(I)-hetero-allylic compounds with hetero-allenes; B. Carbon Disulfide

The rhodium(I) complexes Rh[X-C(Z)-Y] (PPh₃)₂, in which [X-C(Z)-Y] represents an uninegative unsaturated heteroallylic bidentate ligand, coordinating via two of the three hetero atoms (X, Y, Z  P, S or N), react at elevated temperature with an excess of the hetero-allene SCS to give the rhodium(I)-thiocarbonyl complexes Rh[X-C(Z)-Z](CS)(PPh₃). In the initial step a first CS₂ molecule is coordinated side-on by one of the CS double bands. Subsequent reactions can be blocked at this stage by addition of pyridine, resulting in RhCl(η²-CS₂)(PPh₃)(py)₂. The formation of the CS complexes occurs in two ways. Either by direct sulfur abstraction from the Rh^I(η²-CS₂) complex by PPh₃ or by a dimerisation of two CS₂ molecules and elimination of a CS moiety, resulting in a Rh^III-thiocarbonyl-trithiocarbonato complex, immediately followed by demolition of the trithiocarbonato-CS^?2₃ fragment, by PPh₃ to SPPh₃ and CS₂.Complexes containing a CS^?2₃ fragment, but no CS moiety, can also be identified by IR measurements. These products may be formed in a sidereaction upon elimination of CS.     

The synthesis of a cationic ylide complex of platinum(II) by the reaction of tetrakis(triphenylphosphine)platinum(O) with choloroiodomethane.

The reaction of Pt(PPh₃)₄ with CH₂Cl1 in benzene yields the cationic ylide complex $\text{cis}$-[Pt(PPh₃)₂(CH₂PPh₃)Cl]I in high yield. This complex has been converted to $\text{cis}$-[(PPh₃)₂(CH₂PPh₃)X]X (X  Br or I) by reaction with LiBr or NaI. Reaction of $\text{cis}$-[Pt(PPH₃)I]I with iodine yields $\text{cis}$-[Pt(PPh₃)₂(CH₂PPh₃)I]I₃. Nmr data are given in support of the suggested structures.     

The preparation and X-ray crystal and molecular structure of (α,1,2-η-6-methylbenzyl) bis(triphenylphosphine)rhodium(I)

Reaction of [RhCl(PPh₃)₃] with [o-MeC₆H₄CH₂MgBr] affords high yields of the non-fluxional complex, [Rh(CH₂C₆H₄Me)(PPh₃)₂] which has been shown crystallographically to contain a 1-3-η-benzyl group bound through the phenyl carbon atom that is not substituted with the methyl group. Crystals of this compound are triclinic, space group P$\text{1}$, with a = 10.561(6). b = 17.705(3), c = 10.934(4) Å, α = 80.69(3), β = 116.86(4), γ = 102.30(4)° and Z = 2. The structure was solved via the heavy-atom method and refined to R = 0.032 using 5379 diffractometer data with I > 1.56(I). Attempts to prepare π-bonded xylylene complexes from this compound by reaction with base have been unsuccessful, but protonation followed by recrystallisation from acetone gives [Rh{(CH₃)₂CO}₂(PPh₃)₂]BF₄.     

Mechanistic aspects of (CC) isomerization in vinylic rhodium(III) complexes

Observations concerning the (CC) isomerization of several vinylic Rh^III complexes suggest an intramolecular pathway; isomerization occurs at a rate which is affected by the backbonding ability of the metal and the π-acidity of the vinylic ligand in the complex.     

Binuclear schiff-base complexes of copper(II) linked by phthaloyl as a bridging group

Binuclear Schiff-base complexes were prepared by bridging an unsymmetrical tetradentate Schiff-base complex of copper(II) with m- or p-phthaloyl. The complexes were characterized by means of elemental analyses, molecular weights, UV, IR and ¹H NMR (for metal-free ligands) spectra. ESR and magnetic susceptibility measurements show that the copper(II)copper(II) interaction is negligibly small.     

3,3′-Dicarbomethoxy-2,2′-bipyridyl complexes of palladium(II), platinum(II) and rhodium(III)

3,3′-Dicarbomethoxy-2,2′-bipyridyl(DCMB)reacts with K₂MCl₄(M = Pd,Pt) to give M(DCMB)Cl₂ and with RhCl₃ to give the cis-[Rh(DCMB)₂Cl₂]⁺ ion. Attempts to prepare the tris (DCMB) complex with Rh(III) and analogous Co(III) complexes were unsuccessful.     

Conversion of dextrose into hydrogen using aqueous tris(2,2′-bipyridine)rhodium(III) complex as a photocatalyst and enhanced by efficient heterogeneo

Photoreduction of water is achieved with the system tris(2,2′-bipyridine)rhodium(III)/dextrose under UV illumination. A strong pH effect is exhibited     

A binuclear tantalum(III) complex with a bridging carboxylato ligand

Ta₂Cl₆(SMe₂)₃ reacts with one equivalent of C₄H₉CO₂Li to give a complex with a bridging carboxylate ligand, Ta₂Cl₅(O₂CC₄H₉)(SMe₂)(THF)₂. The product was isolated in two crystalline forms, 1 and 2, from a THF/hexane and benzene/hexane solvent mixture, respectively. The following are the unit cell parameters, for 1: monoclinic (P2₁/n), a = 10.537(5) Å, b = 22.015(4) Å, c = 11.663(4) Å, β = 107.80(3)°, V = 2576(3) ų, and Z = 4; for 2: monoclinic (P2₁/c), a = 15.584(4) Å, b = 15.647(4) Å, c = 11.275(3) Å, β = 106.04(5)°, V = 2642(3) ų and Z = 4. The complex is a dimer with a distorted octahedra-sharing-an-edge geometry. The TaTa distances in 1 and 2 were 2.766(1) Å and 2.779(1) Å, respectively, which is somewhat longer than in previously reported Nb(III) and Ta(III) dinuclear compounds. Diamagnetism of the complex is shown by NMR. Fenske—Hall calculations, which correctly predict an electronic transition at about 16,000 cm^?1, indicate a double TaTa bond. The observed elongation of the metalmetal bond is attributed mainly to steric crowding. The complex is the first proven low-valent Ta species with a coordinated carboxylate ion.     

Structure of a diruthenium(II,III) complex with benzamidato bridging ligands

The compound Ru₂Cl(C₆H₅CONH)₄ has now been obtained in crystalline form and the crystal and molecular structure determined by X-ray met     

Homogeneous catalysis: VI. Hydrosilylation using tris(pentanedionato)rhodium(III) or tetrakis(μ-acetato)dirhodium(II) as catalyst

The catalytic activity of tris(pentanedionato)rhodium(III), (or rhodium(III) acetylacetonate) (I) has been investigated for the hydrosilylation of a variety of organic substrates: alkenes, terminal or internal acetylenes, conjugated dienes, or α,β-unsaturated carbonyls or nitriles. With PhCHCH₂ or PhCH₂CHCH₂, ω-substitution was unexpectedly observed, as well as addition. Compound I is an active hydrosilylation catalyst in the absence of any added reducing agent, as is tetrakis(μ-acetato)dirhodium(II) (II) which does not, however, show any unusual catalytic activity due to the two metal atom cluster. Possible mechanisms are suggested.     

The nature of bridging and semi-bridging carbonyl groups

Calculations indicate the existence of “semi-bridging” bonding in Mn₂(CO)₁₀ but not in Re₂(CO)₁₀.     

Trans-1,2-dithiooxalate as bridging ligand—II: The X-ray crystal structure of μ-1,2-dithiooxalato-bis[bis(triphenylphosphine)silver(I)]

The X-ray structure of (Ph₃P)₂Ag(SOC₂SO)Ag(PPh₃)₂ shows this complex as the second authentic example containing a bridging trans-1,2-dithiooxalate ligand. The compound crystallizes in the monoclinic space group P2₁/c with a=13.159(2), b=11.895(2), c=20.939(5)Å, β= 101.35(2)° and Z = 2. The structure was solved by Patterson and Fourier methods for 5649 diffractometer data and refined to a final R value of 0.066 for 03545 observed reflections. The dimensions of the dithiooxalate bridge are compared with those of the corresponding trans-dithiooxalate in (Ph₄As)₄ (O₂C₂S₂)₂In(SOC₂SO)In(S₂C₂O₂)₂]. Differences between structures containing bridging trans-dithiooxalate or bridging cis-dithiooxalate, respectively, are discussed.     

Tridentate chelate π-bonded complexes of rhodium(I), iridium(I), and iridium(III) and chelate σ-bonded complexes of nickel(II), palladium(II), and platinum(II) formed by intramolecular hydrogen abstraction reactions

2,2′-Bis(o-diphenylphosphino)bibenzyl, o-Ph₂PC₆H₄CH₂CH₂C₆H₄PPh₂-o (bdpbz), is dehydrogenated by various rhodium complexes to give the planar rhodium(I) complex

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, from which the ligand, 2,2′-bis(o-diphenylphosphino)-trans-stilbene (bdpps) can be displaced by treatment with sodium cyanide. The stilbene forms stable chelate olefin complexes with planar rhodium(I) and iridium(I) and with octahedral iridium(III). On reaction with halide complexes of nickel(II), palladium(II) or platinum(II), the stilbene ligands

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(R = Ph or o-CH₃C₆H₄) lose a vinyl proton in the form of hydrogen chloride to give chelate, planar σ-vinyls of general formula =CHC₆H₄PR₂-o) (M = Ni, Pd, Pt; X = Cl, Br, I) of high thermal stability; analogous methyl derivatives =CHC₆H₄PR₂-o) are obtained from Pt(CH₃)₂(COD) (COD = 1,5-cyclooctadiene) and the stilbene ligands. The bibenzyl also forms chelate σ-benzyls HCH₂C₆H₄PPh₂-o) (M = Pd, Pt; X = Cl, Br, I). The ¹H NMR spectra of the o-tolyl methyl groups in the compounds =CHC₆H₄PR₂-o) (M = Ni, Pd, Pt; R = o-CH₃C₆H₄) vary with temperature, probably as a consequence of interconversion of enantiomers arising from restricted rotation about the M---P and M---C bonds. Possible mechanisms for the dehydrogenation reactions are briefly discussed.     

Synthesis of rhodium(II) pyrazolate complexes: Crystal structure of tetra-μ-3,5-dimethylpyrazolato dirhodium(II) bis-acetonitrile, (Rh-Rh)

The reaction of Rh₂(O₂CMe)₄ with the sodium salt of 3,5-dimethylpyrazole (3,5-Me₂pzH) in acetonitrile gives Rh₂(3,5-Me₂pz)₄ · 2MeCN. This yellow diamagnetic compound on heating gives Rh(3,5-Me₂pz)₄ which in turn forms adducts with different unidentate ligands, L, to give Rh₂(3,5-Me₂pz)₄ · 2L. The binuclear tetra bridged structure has been established for the acetonitrile complex by X-ray diffraction. The Rh-Rh distance is 2.353(3) Å and the Rh-N (acetonitrile) distance is 2.202(5) Å. Some unsubstituted pyrazolates have been made.     

Carbonyl-organocobalt(I) and -(II) complexes

Passage of CO through solutions of complexes (C₆F₅)₂CoL₂ gives carbonyl derivatives (C₆F₅)₂CoL₂(CO) (L₂ = 2 PEt₃, 2 P-n-Bu₃, 2 PPh₃, Ph₂PCH₂CH₃PPh₂). The properties of these compounds are described.The compounds are also produced by treating solutions of (C₆F₅)₂Co-(dioxane)₂ with CO, but a simultaneous reduction to (C₆F₅)Co(CO)₄ takes place. Treatment of the latter complex with monodentate ligands gives substitution products (C₆F₅)Co(CO)₃L (L = PEt₃, P-n-Bu₃, PPh₃) all of which are monomeric, whereas the addition of Ph₂PCH₂CH₂PPh₂ gives the dimer (C₆F₅)(CO)₂CoLLCo(CO)₂(C₆F₅). The properties of these compounds are discussed.     

Interaction of organic azides with methyl compounds of cobalt,rhodium, iridium,ruthenium and zirconium to give azido or 1,3-triazenido complexes. The crystal structures of tris-trimethylphosphineazido-dimethylcobalt(III) and bis(carbonyl)trimethylphosphineazidocobalt(I)

The interaction of azidotrimethylsilane with mer-CoMe₃(PMe₃)₃, fac-RhMe₃(PMe₃)₃, fac-IrMe₃(PMe₂Ph)₃, cis-RuMe₂(PMe₃)₄ and (η⁵-C₅H₅)₂ZrMe₂ gives tetramethylsilane and, respectively, the azido compounds MMe₂(N₃)(PMe₃)₃, M = Co, Rh, IrMe₂(N₃)(PMe₂Ph)₃, cis-Ru(N₃)₂(PMe₃)₄ and (η⁵-C₅H₅)₂ZrMe(N₃). The crystal structures of CoMe₂(N₃)(PMe₃)₃ and of the derived complex Co(N₃(CO)₂(PMe₃)₂ have been determined by X-ray diffraction.The dimethyl cobalt(III) compound has an octahedral structure with a mer arrangement of the three PMe₃ groups. The Co^III-N distance is rather long, at 2.071(4) Å. The cobalt(I) carbonyl compound has a trigonal bypyramidal structure with the two phosphines occupying the axial sites. The Co^I-N distance is 2.03(1) Å.The interaction of PhN₃ with (η⁵-C₅H₅)₂ZrR₂, R = Me, Ph, gives the 1,3-triazenido complexes (η⁵-C₅H₅)₂ZrR(RNNNPh) while mer-CoMe₃(PMe₃)₃ and p-MeC₆H₄N₃ react to give CoMe₂(MeNNNp-tol)(PMe₃)₂. In all three cases the triazenido group appears to be bidentate.