M. Teresa Pinillos

Hydroformylation of 1-hexene under mild conditions catalyzed by various μ-pyrazolato dirhodium(I) complexes

Abstract The selective hydroformylation reaction of 1-hexene into the corresponding aldehydes has been achieved under very mild conditions of pressure and temperature by various catalyst precursors of the type [Rh2(μ-pyrazolato) 2(CO)2L2] where L = P(OR)3 or PPh3. The electronic effects of the ligands, which play an essential role in the reaction rates, are discussed.

Rhodium and iridium complexes containing the anion of 1-phenyl-3-methyl-4-benzoyl- pyrazolone-5, a sophisticated analogue of β-diketones

Abstract Several (diolefin)M(A) complexes (M = Rh, Ir) were prepared, where AH is 1-phenyl-3-methyl- 4-benzoylpyrazolone-5, a very stable asymmetric analogue of acetylacetone. In these complexes the diolefin could be replaced by one mole of (Ph2PCH2CH2)2, two of CO or of PPh3, or three of CNBut, while 1,10-phenanthroline displaced the chelating ligand to yield [(cyclooctadiene)Rh(phen)]+ (A)−. Some compounds X−Y (X−Y = iodine or MeI) added oxidatively yielding the corresponding trivalent species. Using 31P NMR spectra the presence of the expected steric isomers was detected in (Ph3P)(CO)Rh(A) and in (Ph3P) (CO)Rh(A)(X)(Y).

Synthesis and hydroformylation reaction of dinuclear rhodium(I) complexes with mixed bridging ligands. X-Ray structure of [Rh2(µ-pz)(µ-SBut)(CO)2{P(OMe)3}2]

The preparation and properties of dinuclear complexes containing one azolate (az) and one t-butylthio group as bridging ligands are described. Bubbling of carbon monoxide through dichloromethane solutions of [Rh2(µ-az)(µ-SBut)(η4-cod)2](cod = cyclo-octa-1,5-diene), followed by addition of phosphorus donor ligands (L) affords the complexes [Rh2(µ-az)(µ-SBut)(CO)2L2]. The crystal and molecular structure of cis-[Rh2(µ-pz)(µ-SBut)(CO)2{P(OMe)3}2](pz = pyrazolate) was determined from a single crystal by X-ray diffraction. Crystals are monoclinic, space group P21, with a= 10.789(2), b= 12.226 0(3), c= 10.431 4(2)A, β= 110.515(1)°, and Z= 2. The final agreement factors were R= 0.036 and R′= 0.044. In the dinuclear complex each rhodium atom is in a distorted square arrangement. The dihedral angle of 63.1(2)° between the two co-ordination planes leads to a bent geometry with a rhodium–rhodium distance of 3.477 0(9)A. The [Rh2(µ-az)(µ-SBut)(CO)2L2] complexes are good precursors for the hydroformylation reaction of olefins under mild conditions.

Benzamidinatorhodium complexes. X-Ray structures of [Rh{CPh(NPh)2}(cod)] and [Rh2{µ-CPh(NPh)2}2(tfbb)2]

Complexes [{MCl(diolefin)}2](M = Rh or Ir) react with N,N′-diphenylbenzamidinate to yield binuclear [Rh2{µ-CPh(NPh)2}2(diolefin)2][diolefin = norbornadiene (nbd) or tetrafluorobarrelene (tfbb)] or mononuclear [M{CPh(NPh)2}(cod)](cod = cycle-octa-1,5-diene) complexes. The rhodium complexes react with carbon monoxide to give [Rh2{µ-CPh(NPh)2}2(CO)4]. The latter complex undergoes a two-centre oxidative addition with iodine yielding the rhodium(II) complex [Rh2{µ-CPh(NPh)2}2I2(CO)4]. An A-frame compound of formula [Rh2{µ-CPh(NPh)2}(µ-dppm)2(CO)] ClO4(dppm = Ph2PCH2PPh2) has been isolated. Some related mononuclear complexes containing a unidentate benzamidine ligand have also been prepared. The crystal structures of the complexes [Rh{CPh(NPh)2}(cod)](1) and [Rh2{µ-CPh(NPh)2}2(tfbb)2](4) have been determined by X-ray diffraction methods. Complex (1) crystallizes in the monoclinic space group P21/n, with a= 10.315(2), b= 19.507(3), c= 11.429(3)A, β= 103.62(1)°, and Z= 4. Crystals of compound (4) are monoclinic, space group P21/c, with Z= 4 and a unit cell of dimensions a= 21.692(2), b= 12.512(2), c= 19.969(2)A, and β= 107.90(1)°. Both structures were solved by Patterson and Fourier methods and refined by full-matrix least squares to R 0.040 and 0.047, respectively. The structure of (1) is mononuclear with the N,N′-diphenylbenzamidinate acting as a chelating ligand, through the nitrogen atoms. In contrast, complex (4) is binuclear with the benzamidinate ligand bridging two rhodium atoms [ Rh ⋯ Rh 2.982(3)A].

1,2,4-Triazolate (tz) complexes of rhodium(I), iridium(I), and palladium(II). Crystal structure of [Rh3(µ3-tz)(µ-Cl)Cl(η4-tfbb)(CO)4]·0.5CH2Cl2(tfbb = tetrafluorobenzobarrelene), a trinuclear complex with extended metal–metal interactions

New binuclear complexes of formula [M2(µ-tz)2(L2)2][tz = triazolate; M = Rh or Ir, L2= diolefin, (CO)2, or (CO)(PPh3); M = Pd, L2=η3-C3H5 or η3-C4H7] have been prepared. These binuclear complexes, having unco-ordinated N atoms from the triazolate ligands, react with [M2(µ-Cl)2(L2)2](M = Rh, Ir, or Pd) to give tetranuclear compounds of formula [Rh2M2(µ3-tz)2Cl2(L2)4]. The latter complexes can also be prepared by reacting triazole and [Rh(acac)(CO)2] with [M2(µ-Cl)2(L2)2]. The heteronuclear rhodium–gold complex [Rh2Au2(µ3-tz)2Cl2(cod)2](cod = cyclo-octa- 1,5-diene) has been synthesized. Trinuclear complexes of formula [Rh2M(µ3-tz)(µ-X)ClL2(CO)4](X = Cl or OH) have been isolated by several routes starting from the above mentioned tetra-, bi-, or mononuclear complexes. In general, these trinuclear complexes show metallic lustre and marked dichroism, suggesting metal–metal interactions which were confirmed by the X-ray determination of [Rh3(µ3-tz)(µ-Cl)Cl(tfbb)(CO)4](tfbb = tetrafluorobenzobarrelene). This complex shows a stacking arrangement of centred rhodium units with an intermetallic separation of 3.425(4)A.

Benzotriazole and benzotriazolate complexes of rhodium(I)

Abstract The preparation and properties of mono- and di-nuclear rhodium(I) complexes of general formulae RhClL 2 (btzH), [Rh(μ-btz)L 2 ] 2 , Rh 2 (μ-btz)(μ-N 3 )(L 2 ) 2 and Rh 2 (μ-btz)(μ-SCN)(COD) 2 [L 2 = diolefin, (CO) 2 or (CO)(PPh 3 )], and of the related tetranuclear derivatives are reported. The latter compounds have benzotriazolate ligands simultaneously bonded to three rhodium atoms.

Tetrazolate rhodium(I) complexes. Crystal structures of the trinuclear complexes [Rh3(µ3-ttz)(µ-Cl)Cl(cod)2(CO)2](ttz = tetrazolate, cod = cyclo-octa-1,5-diene) and [Rh3(µ3-ttz)(µ-Cl)Cl(CO)6], an unusual example of metal–metal interactions

Homo- and hetero-bridged binuclear complexes of general formulae [Rh2(µ-ttz)2(L2)2][ttz = tetrazolate, L2= diolefin or (CO)2] and [Rh2(µ-ttz)(µ-X)L2L′2][X = Cl, L2= L′2= diolefin; X = N3, L2= L′2= diolefin, L2= cyclo-octa-1,5-diene (cod), L′2=(CO)2] have been prepared. The heterobridged complexes, having unco-ordinated N atoms from the tetrazolate group, react with [Rh2(µ-Cl)2(L″2)2](2 : 1 molar ratio)[L″2= cod or (CO)2] to give trinuclear compounds of general formula [Rh3(µ3-ttz)(µ-X)ClL2L′2L″2](X = Cl or N3). The latter complexes can also be obtained by reaction of [Rh2(µ-ttz)2(L2)2] with [Rh2(µ-Cl)2(L′2)2](1 : 2 molar ratio). X-Ray crystallographic studies of the complexes [Rh3(µ3-ttz)(µ-Cl)Cl(cod)2(CO)2](12) and [Rh3(µ3-ttz)(µ-Cl)Cl(CO)6](13) show them to contain trinuclear units, with bridging Cl atoms and tetrazolate groups. In complex (13) the units pack in the crystal with infinite chains, through Rh ⋯ Rh interactions of 3.457(2), 3.229(2), and 3.399(2)A. In compound (12) the complex consists only of two units, related by a symmetry centre with a Rh ⋯ Rh distance equal to 3.519(2)A.

Trinuclear pyrazolate complexes. Crystal structure of [(OC)2Rh(µ-pz)2Pd(µ-pz)2Rh(CO)2]

The preparation and properties of trinuclear complexes containing pyrazolate and chloride as bridging ligands are reported. Representative formulae are [L2M(µ-Cl)(µ-pz)Pd(µ-Cl)(µ-pz)ML2][M = Rh, L2= diolefin or (CO)2; M = Ir, L2= diolefin; M = Pd, L2=η3-C3H5 or η3-C4H7]. These complexes react with the pyrazolate anion to give trinuclear homobridged compounds of formula [L2M(µ-pz)2Pd(µ-pz)2ML2]. The crystal structure of the carbonyl derivative [(OC)2Rh(µ-pz)2Pd(µ-pz)2Rh(CO)2] has been determined by single-crystal X-ray methods. Crystal are monoclinic, space group P21/c with cell constants a= 8.9281(5), b= 11.7961(6), c= 10.391 6(5)A, β= 94.727(4)°, and Z= 2. The intermetallic distance palladium–rhodium is equal to 3.578 9(6)A.

The influence of various azolate bridging ligands on the catalytic activity of dinuclear rhodium(I) precursors in the hydroformylation reaction

Abstract The selective catalytic activity of various [Rh 2 (μ-Az) 2 (CO) 2 L 2 ] complexes in the low pressure hydroformylation reaction has been examined. With Az = triazolate or benzotriazolate, the activity decreases in the sequence PPh 3 > P(OMe) 3 > P(OPh) 3 , and the dinuclear structure is presumably retained during the catalytic cycle. However, with Az = tetrazolate the inverse order of activity (P(OPh 3 ) 3 > P(OMe) 3 > PPh 3 ) is observed; this is probably due to cleavage of the bridging ligand during the reaction. Under the same conditions the mixed complex [(COD)Rh(μ-pyrazolate) 2 Pt(dppe)] + is completely inactive.

Preparation and X-ray structure of a rhodium(III)–rhodium(I) pyrazolate complex with a mercury atom asymmetrically bridging the metal atoms

Reaction of [Rh2(µ-pz)2(CO)2(PPh3)2](1)(pz = pyrazolate) with HgCl2 gives [(Ph3P)(CO)ClRh(µ-HgCl)(µ-pz)2Rh(CO)(PPh3)](2); the X-ray stucture of (2) shows the presence of two rhodium atoms in different oxidation states asymmetrically bridged by a mercury atom, so that a unique RhIII–Hgâ†�RhI fragment is present.