M. Angeles Ubeda

Tandem β-Boration/Arylation of α,β-Unsaturated Carbonyl Compounds by Using a Single Palladium Complex To Catalyse Both Steps

Diphenyl(3-methyl-2-indolyl)phosphine (C(9)H(8)NPPh(2), 1) gives stable dimeric palladium(II) complexes that contain the phosphine in P,N-bridging coordination mode. On treating 1 with [Pd(O(2)CCH(3))(2)], the new complexes [Pd(mu-C(9)H(7)NPPh(2))(NCCH(3))](2) (2) or [Pd(mu-C(9)H(7)NPPh(2))(mu-O(2)CCH(3))](2) (3) were isolated, depending on the solvent used, acetonitrile or toluene, respectively. Further reaction of 3 with the ammonium salt of 1 led to the substitution of one carboxylate ligand to afford [Pd(mu-C(9)H(7)NPPh(2))(3)(mu-O(2)CCH(3))] (4), in which the bimetallic unit is bonded by three C(9)H(7)NPPh(2)(-) moieties and one carboxylate group. Using this methodology, [Pd(2)(mu-C(6)H(4)PPh(2))(2)(mu-C(9)H(7)NPPh(2))(mu-O(2)CCX(3))] (X=H (7); X=F (8)) were synthesised from the ortho-metalated compounds [Pd(C(6)H(4)PPh(2))(mu-O(2)CCX(3))](2) (X=H (5); X=F (6)). Complexes 3, 4, 7, and 8 have been found to be active in the catalytic beta-boration of alpha,beta-unsaturated esters and ketones under mild reaction conditions. Hindrance of the carbonyl moiety has an influence on the reaction rate, but quantitative conversion was achieved in many cases. More remarkably, when aryl bromides were added to the reaction media, complex 7 induced a highly successful consecutive beta-boration/cross-coupling reaction with dimethyl acrylamide as the substrate (99% conversion, 89% isolated yield).

Orthometalation reactions in trifluoroacetate dirhodium(II) compounds. Molecular structure of Rh2(O2CCF3)2[(C6H4)PPh2]2·(PPh3)2·2(C7H8)

Abstract Rh 2 (O 2 CCF 3 ) 3 [(C 6 H 4 )PPh 2 ]·(HO 2 CCF 3 ) 2 reacts with PPh 3 yielding the doubly metalated compound Rh 2 (O 2 CCH 3 ) 2− [(C 6 H 4 )PPh 2 ] 2 ·(HO 2 CCF 3 ) 2 . The reaction proceeds via a reactive intermediate with an equatorial phosphine, Rh 2 (η 2 -O 2 CCF 3 )(μ-O 2 CCF 3 ) 2 [(C 6 H 4 )PPh 2 ](PPh 3 )·(HO 2 CCF 3 ), which can also be generated in moderate yield under photochemical conditions. The structure of the PPh 3 bis-adduct Rh 2 (O 2 CCF 3 ) 2 [(C 6 H 4 )PPh 2 ] 2 ·(PPh 3 ) 2 ·2(C 7 H 8 ) has been determined by X-ray diffraction. M r =1663.27, orthorhombic, space group Fdd 2, a =41.748(9), b =21.620(5), c =17.375(5) A, V =15683(6) A 3 , Z =8, D x =1.41 g cm −3 . Mo Kα radiation (graphite crystal monochromator, λ=0.71073 A), μ(Mo Kα)=5.57 cm −1 , F (000)=6800, T =293 K. Final conventional R factor=0.035 for 2789 ‘observed’ reflections and 422 variables. The molecule shows crystallographic two-fold axis symmetry through the RhRh bond. One toluene solvent molecule slightly disordered is present in the asymmetric unit.

Reactions of rhodium trifluoroacetate with triphenylphosphine and pyridine. Molecular structure of Rh2(O2CCF3)4(py)4

Abstract Rh 2 (O 2 CCF 3 ) 4 reacts with two mol of triphenylphosphine forming the adduct Rh 2 (O 2 CCF 3 ) 4 (PPh 3 ) 2 . This compound in solution, even at room temperature, undergoes slow stepwise orthometalation of the phosphine ligands forming the doubly metalated compound Rh 2 (O 2 CCF 3 ) 2 [(C 6 H 4 )P(C 6 H 5 ) 2 ] 2 . This reaction has been monitored by 31 P NMR spectroscopy detecting in solution three reaction intermediates. Rh 2 (O 2 CCF 3 ) 4 reacts with excess of pyridine to form the compound Rh 2 (O 2 CCF 3 ) 4 (py) 4 that can be structurally classified as a class III adduct. It contains two bridging and two monodentate equatorial carboxylates and two equatorial and two axial pyridine ligands. The structure of this compound has been determined by X-ray diffraction. M r =974.3, monoclinic, space group P 2 1 / n , a =10.504(1), b =18.108(1), c =35.377(1) A, β=96.416(8)°, V =6686.6(8) A 3 , Z =8, D x =1.94 Mg/m 3 . Mo Kα radiation (graphite crystal monochromator, λ=0.71073 A), μ(Mo Kα)=10.89 cm −1 , F(000)=3824, T =293 K. Final conventional R factor=0.12 for 2258 ‘observed’ reflections and 312 variables. The structure was solved by Patterson interpretation using the program SHELXS86 and the Fourier synthesis.

Dinuclear palladium(II) compounds with bridging cyclometalated phosphines. Synthesis, crystal structure and electrochemical study

The structural characterization of bis-cyclometalated palladium(II) compounds of formula Pd2[(micro-(C6X4)PPh2]2(micro-O2CR)2 [X = H, R = CH3 (3), CF3 (4), C(CH3)3 (5) and C6F5 (6); X = F, R = CH3 (7) and CF3 (8)], has confirmed its paddle wheel structure with two palladium atoms bridged by two acetates and two metalated phosphines in a head-to-tail arrangement. The Pd...Pd distances are in the range 2.6779(16)-2.7229(8) A. Under cyclic voltammetric conditions, compounds 3-6, in CH2Cl2 solution, were found to undergo a reversible oxidation peak in the range of potential values 0.84-1.25 V. A second partially-reversible oxidation is observed at more positive potentials (1.37-1.55 V). For compounds 3-5 in the presence of chlorides, the first oxidation becomes a two-electron process presumably leading to a neutral [Pd(III)-Pd(III)] species with a metal-metal bond.

Photochemical ligand rearrangement in dirhodium(II) compounds. Structure of Rh2(O2CCH3)2(η2-O2CCH3)[(C6H4)PPh2] (η2-PCCl)(PCClP-ClC6H4)Ph2

Abstract The photochemical reaction of the adducts Rh2(O2CCH3)3[(C6H4)P(o-ClC6H4)Ph]· (P(p-XC6H4)3) (X=H, Me, Cl), yield the compounds Rh2(O2CCH3)2(η2-O2CCH3)[(p-XC6H3)P (p-XC6H4)2](η2-PCCl), (PCCl=P(o-ClC6H4)Ph2) in a ligand rearrangement reaction that involves activation of CH and RhC bonds. The factors that favour this process are studied by carrying out photochemical reactions with different phosphines. The structures of Rh2(O2CCH3)2(η2-O2CCH3) [(C6H4)PPh2](η2-PCCl) has been determined by X-ray diffraction. Mr=1321.1, orthorhombic, space group Pbcn, a=20.339(8), b=20.07(6), c=23.07(3) A , V=9413(3) A 3 , Z=8, D x =1.86 g cm −3 . Mo Kα radiation (graphite crystal monochromator, λ=0.071073 A ), μ(Mo Kα) = 13.83 cm−1, F(000)=5280, T=293 K. Final conventional R factor=0.062 for 4889 ‘observed’ reflections and 500 variables. The compound contains three bridging ligands, two acetates and one metalated triphenylphosphine, and two chelating ligands, one acetate and one PCCl that acts as a P,Cl ligand, taking one equatorial (P) and one axial (Cl) coordination site. The axial RhCl bond distance is 2.573(4) A.

Exchange reactions of acetate ligands and electrophilic rhodium–carbon bond activation in orthometallated rhodium(II) compounds with trifluoroacetic acid. Crystal structure of [Rh2(O2CCF3)3{(C6H4)PPh2]·2CF3CO2H

Stepwise exchange reactions of acetate groups by trifluoroacetate groups have been observed for [Rh2(O2CMe)3{(C6H4)PPh2}]·2MeCO2H 1, in CDCl3–CF3CO2H at room temperature. The first reaction involves a fast exchange of the two axial molecules of acetic acid as well as the acetate group trans to the metallated phosphine. In a second step the exchange of one acetate group cis to the metallated phosphine occurs. The exchange of the second cis acetate group yielding [Rh2(O2CCF3)3{(C6H4)PPh2}]·2CF3CO2H 3, has been studied by 1H NMR spectroscopy. This exchange follows a rate equation which is dependent on the concentration of trifluoroacetic acid used, kobs=(k1+k2[CF3CO2H]½[Rh2]. The partially deuteriated compound [Rh2(O2CCF3)3{(C6D4)P(C6D5)2}]·2CF3CO2H 3D in the presence of trifluoroacetic acid undergoes D–H exchange at the ortho positions of the phenyl rings of the phosphine. This exchange has been studied at 318 K. The observed D–H exchange is explained by an electrophilic attack at the rhodium–carbon bond by the trifluoroacetic acid, which produces protonation of the ortho aromatic carbon atom, and subsequent demetallation followed by a reverse metallation reaction. An X-ray crystal structure determination of compound 3 has been carried out: space group P21/n(monoclinic), a= 12.369(2), b= 21.711 (6), c= 13.367(2), β= 90.11 (2)°, Z= 4 and R= 0.044. It contains three trifluoroacetate groups bridging a Rh24+ unit which has a Rh–Rh bond distance of 2.438(1)A; the fourth bridging ligand is a triphenylphosphine metallated at one of the ortho positions. Two molecules of trifluoroacetic acid occupy the axial positions.

Orthometallation reaction at a binuclear pyrazolyl(pz) bridged rhodium compound: synthesis and crystal structure determination of Rh2(µ-pz)2[µ-P(C6F4)Ph2]Br(CO)(pcBr), pcBr = P(o-BrC6F4)Ph2

The complex [Rh(µ-pz)(CO)(pcBr)]2[pz = pyrazoly, pcBr = P(o-BrC6F4)Ph2] undergoes orthometallation in refluxing toluene to give a new binuclear compound containing a rhodium–rhodium bond, Rh2 Rh2(µ-pz)2(µ-pc)Br(CO)(pcBr)[pc = P(C6F4)Ph2], which has been structurally characterized by X-ray crystallography; the complex has two pyrazolyl groups and one orthometallated phosphine bridging the two in equivalent rhodium atoms, and one phosphine ligand chelating one of the rhodium atoms via P and the bromine atom from the o-bromotetrafluorophenyl group.

Photo-assisted formation of a chelating diphos ligand from PPh3 and a cyclometallated [P(C6H4)(C6H5)2]− ligand. Crystal structure of Pd{η2-o-[P(C6H5)2]2(C6H4)}Br2

Abstract The cyclometallated palladium compound, Pd[η2-(C6H4)P(C6H5)2]Br[P(C6H5)3] (1), in the solid state by action of light, evolves to give Pd{η2-o-[P(C6H5)2]2(C6H4)}Br2 (2). This compound contains the diphosphine, o-[P(C6H5)2]2(C6H4), as chelated ligand that is formed by a couple reaction of the metallated ligand η2-[(C6H4)P(C6H5)2]− and the coordinated arylphosphine. A study by NMR spectroscopy confirms that the o-phenylene bridge in the diphosphine ligand in 2 comes from the metallated phosphine ligand in 1.

Cyclometallation reactions in complexes of the type Rh(oq)(CO)(P(o-BrC6F4)Ph2) ☆: III. Synthesis of the compounds cis-Rh(oq)Br(P(o-C6F4)Ph2)L. The Molecular structure of cis-Rh(oq)Br(P(o-C6F4)Ph2)(PPh3) (oq = 8-oxyquinolinate)

Abstract The reaction of Rh(oq)(CO)(PCBr) (PCBr = P(o-BrC6F4)Ph2; oq = 8-oxyquinolinte)_ in refluxing toluene in the presence of Et4NBr (1/4 molar ratio) gives Rh(oq)Br(PC) (H2O), PC = P (o-C6F4)Ph2, in practically quantitative yield. The water molecule is readily displaced by various P-donor ligands to give complexes of general formula Rh(oq)Br(PC) PR3 (PR3 = PPh3, P(p-MeC6H4)3, P(p-MeOC6H4)3, P(p-FC6H4)3, P(PMe)3 and P(OPh3). The molecular structure of the compound Rh(oq)Br(PC) (PPh3) has been determined by X-ray methods. Crystals of the title compound are monoclinic, space group P21/n with unit cell dimensions a 11.273(4), b 20.087(8), c 17.471(7) A and β 102.15(8)°. The final R for 2304 diffractometer data refined by least-squared is 0.0468. The compound has a distorted octahedral coordination with the phosphorus atoms in a cis disposition. The RhP bond lengths are significantly different. The P atom of the metallated phosphine, which is trans to N, has a RhP distance of 2.308(4) A, while the PPh3, which is trans to C, has a RhP distance of 2.422(4) A. The most distorted angles around the rhodium atom are P(1)Rh-P(2) 104.7(1)° and P(1)RhC(1) 69.2(3)°.

NOVEL UNSYMMETRICAL ORTHO-METALATED DIRHODIUM(II) CATALYSTS : TRANS INFLUENCE OF THE AXIAL LIGAND

Inductive effects of an X axial group which are transmitted through the RhRh bond influence the reactivity of ortho-metalated dirhodium complexes 3 in the cyclization of 1-diazo-5-penten-2-one (4).