Gregorio Sánchez

Halide and pseudohalide effects in Pd-catalysed cross-coupling reactions

The presence of halide and pseudohalide anions dramatically affects the outcome of transition-metal catalysed reactions, both in terms of selectivity and activity. In this perspective, the roles and effects of these anionic ligands in topical and important Pd-catalysed cross-coupling reactions involving the formation of C–C bonds, e.g. Sonogashira, Stille and Suzuki–Miyaura cross-coupling, will be described. The use of imidate anions (derived from succinimide, maleimide and phthalimide) in several different classes of neutral and anionic Pd catalysts/precatalysts will be highlighted.

New cyclometalated palladium(II) complexes with iminophosphines: Crystal structures of [Pd(C^N)(o-Ph2PC6H4–CH=NR)][PF6] (C^N=azobenzene, R=Et; C^N=2-phenylpyridine, R=Me)

Abstract The synthesis of new cyclometalated compounds of palladium(II) with the mixed-donor bidentate ligands o-Ph2PC6H4–CH=NR is described. Two series of complexes [Pd(C^N)(o-Ph2PC6H4–CH=NR)][PF6] have been prepared using either azobenzene or 2-phenylpyridine as cyclometalated ligands [C^N=azobenzene (azb); R=Me (1a), Et (2a), nPr (3a), iPr (4a), tBu (5a), Ph (6a), NH–Me (7a); C^N=2-phenylpyridine (phpy); R=Me (1b), Et (2b), nPr (3b), iPr (4b), tBu (5b), Ph (6b), NH–Me (7b)]. The new complexes were characterized by partial elemental analyses and spectroscopic methods (IR, FAB, 1H and 31P NMR). The molecular structures of compounds 2a (monoclinic, P 21/n) and 1b (monoclinic, C 2/c) have been determined by a single-crystal diffraction study. In both cases this technique revealed the relative trans configuration between the phosphorus atom and the nitrogen atom of the ortho-metalated ligand.

Synthesis and characterisation of cyclometallated palladium(II) complexes with phosphine–carboxylate and phosphine–amide ligands

The coordination properties of hybrid phosphino-amide ligands o-Ph2PC6H4CONHR [R = iPr (a), Ph (b)] have been investigated. New cyclometallated palladium(II) complexes in which a and b act as P-monodentate ligands have been synthesised by reacting them with selected cyclometallated precursors containing bridging chloride or acetate groups. The crystal structures of the compounds [Pd(Bzq)(o-Ph2PC6H4CO–NHiPr)(Cl)] and [Pd(Phox)(o-Ph2PC6H4CO–NHiPr)(CH3COO)] (Bzq = 7,8-benzoquinolyl; Phox = 2-(2-oxazolinyl)phenyl) have been determined. Hemilability of coordinated ligand b is detected when it appears combined with certain cyclometallated backbones. A rigid P,O-chelating behaviour of the ligands, confirmed by the crystal structure determination of [Pd(Bzq)(o-Ph2PC6H4CO–NHiPr)][PF6], is observed in complexes obtained by adding stoichiometric KPF6 to [Pd(C^N)(μ-Cl)]2 compounds. The reactions of hydroxo-bridged precursors [Pd(C^N)(μ-OH)]2 with a and b afforded mononuclear derivatives in which a less common anionic P,N-binding mode is exhibited. The crystal structure of Pd(Phpy)(o-Ph2PC6H4CO–NiPr)] (Phpy = 2-phenylpyridine) is also reported. Furthermore, related compounds with phosphino-carboxylate ligands have been prepared by direct reaction between 2-(diphenylphosphinobenzoic) acid and [Pd(C^N)(μ-CH3COO)]2 precursors, and the X-ray structures of [Pd(C^N)(o-Ph2PC6H4COO)] (C^N = Bzq and Phpy) have been determined.

Reactivity towards some weak protic electrophiles of the di-μ-hydroxo complex [{Pd(μ-OH)(tmeda)}2][BPh4]2: crystal structure of [{Pd(tmeda)}2(μ-OH)(μ-HNC6H4Cl-p)][BPh4]2

Abstract The hydroxo complex [{Pd(μ-OH)(tmeda)} 2 ][BPh 4 ] 2 (tmeda= N , N , N ′, N ′-tetramethylethylenediamine) reacts with a wide variety of weak protic electrophiles H(LL) in a 1:2 molar ratio to give the mononuclear cationic palladium(II) derivatives with the general formula of [Pd(LL)(tmeda)][BPh 4 ] (LL=acetylacetonate (acac) ( 1 ); salicylaldehydate (sal) ( 2 ); salicylaldiminate ( o -RNCHC 6 H 4 O: R=CH(CH 3 ) 2 ( 3 ), C 6 H 5 ( 4 ), p -ClC 6 H 4 ( 5 ), p -BrC 6 H 4 ( 6 ), p -MeC 6 H 4 ( 7 )); 2-pyrrole–carbaldehydate (pcal) ( 8 ); 2-pyridine–methoxo(OCH 2 –py) ( 9 ); picolinate (pic) ( 10 ); 8-hydroxyquinolinate (oxin) ( 11 ) or the dinuclear complexes [{Pd(μ-pz)(tmeda)} 2 ][BPh 4 ] 2 ( 12 ) and [{Pd (tmeda)} 2 (μ-OH)(μ-HNC 6 H 4 R- p )][BPh 4 ] 2 (R=H ( 13 ), Cl ( 14 ) or Me ( 15 )) when reacting with pyrazole or anilines in the same molar ratio. In a related reaction, deprotonation of secondary amines by the hydroxo complex in the presence of carbon disulfide leads to the corresponding dithiocarbamate complexes [Pd(S 2 CNR 2 )(tmeda)][BPh 4 ] R=Me ( 16 ), Et ( 17 ) C 5 H 10 ( 18 ). The new compounds have been characterized by partial elemental analyses, conductance measurements and spectroscopic (IR, 1 H and 13 C NMR) methods. The crystal structure of compound 14 has been determined by X-ray diffraction analysis.

Solid state conformational and theoretical study of complexes containing the (CxN)Pd moiety (CxN = 2-(phenylazo)phenyl-C,N and its derivatives)

Palladium complexes having the 2-(phenylazo)phenyl-C,N ligand exhibit a planar chelating ring with NN and N–C distances longer and shorter respectively than those found in trans-azobenzene. The ligand is not planar upon complexation, the mean angle between the phenyl ring and the chelating one found in the Cambridge Structural Database being of 45.6°. We have quantified and characterised the kind of distortion from planar coordination around metallic centers. The method employed makes use of two improper torsion angles, tetrahedral distortion being most frequently found in phenylazophenyl palladium complexes. Crystal structures of three succinimidate complexes having the title moiety are reported. The succinimidate ligand adopts a nearly perpendicular conformation to the metal coordination plane. A theoretical study using either Molecular Mechanical, Semiempirical and Density Functional Theory ab initio levels helps to grasp the main geometrical features.

New palladium(II) complexes with bis(pyrazol-1-yl)alkanes

Abstract The replacement of chloride ligands in [Pd(NN)Cl2] (NN=bpzm: bis(pyrazol-1-yl)methane, bpzm*: bis(3,5-dimethylpyrazol-1-yl)methane) by a weak donor ligand such as acetonitrile has been achieved by treating the dichloro complexes with AgClO4 in this solvent. The reactivity of the new precursors [Pd(NN)(CH3CN)2][ClO4]2 towards a variety of neutral N- and P-donor ligands L (pyridine, triphenylphosphine, triethylphosphine) or L2 (1,2-bis(diphenylphosphino) ethane, ethylenediamine, N,N,N′,N′-tetramethylethylenediamine, 2,2′-bipyridine, o-phenylenediamine) has been studied. When chloride abstraction from [Pd(NN)Cl2] is carried out in Me2CO/H2O, the cationic hydroxo-bridged dimeric complexes [(NN)Pd(μ-OH)2Pd(NN)]2+ are isolated as their perchlorate salts. The hydroxo complexes react with the protic electrophiles H(LL) (acetylacetone, salicylaldehyde and 2-pyrrol carbaldehyde) in a 1:2 molar ratio to give the corresponding mononuclear complexes [Pd(NN)(LL)][ClO4]. The 13C and 1H NMR assignments have been made on the basis of NOE studies and 1H–1H COSY and 1H–13C HETCOR experiments. The structures of [Pd(bpzm)(tmeda)][ClO4]2 and [Pd(bpzm*)(sal)][ClO4] have been determined by single-crystal X-ray diffraction studies; in both complexes the bis(pirazolyl)alkanes act as chelating ligands with coordination around the palladium atom slightly distorted from the square-planar geometry.

Reactivity of the [Ni(C6F5)2(μ-OH)2]2− ion towards β-diketones, 8-hydroxiquinoline and heterocyclic thiones. Crystal structure of [NBu4][Ni(C6F5)2(C5H4NS-2)]

The di-μ-hydroxo-complex [NBu4]2[Ni(C6F5)2(μ-OH)2] reacts with protic electrophiles H(LL) in the 1/2 molar ratio to give (NBu4) [Ni(C6F5)2(LL)][(LL) = acetylacetonate (acac) (I), benzoylacetonate (bzac) (II), 8-hydroxyquinolinate (oxin) (III), pyridine-2-thiolate (pyt) (IV), pyrimidine-2-thiolate (pymt) (V), 2,6-dimethyl-5-oxo-1,2,4-triazine-3-thiolate (tazt) (VI), N-methylimidazole-2-thiolate (mimt) (VII), thiazolidine-2-thiolate (tzt) (VIII), benzoimidazole-2-thiolate (bimt) (IX) or benzothiazole-2-thiolate (btzt) (X)]. The new compounds have been characterized by analysis, conductivity measurements, and spectroscopic (IR, UV-VIS, 1H, and 19F) methods. The crystal structure of compound IV has been determined by X-ray diffraction. It crystallizes in the monoclinic space group P21/n with a 11.7076(4), b 22.183(1), c 14.0280(6) A, β 105.012(3)°. Final R = 0.075 and Rw = 0.067 based on 3815 reflections.

A novel route for the synthesis of dithiocarbamate and xantrate nickel(II) complexes starting from the di-μ-hydroxo-bis[bis(pentafluorophenyl)nickelate(II)] ion

In dichloromethane, [NBU4]2[{Ni(C6F5)2(μ-OH)}2] reacts with amines [EtNH2, PrNH2, Me2NH, Et2NH, pirrolidine (C4H8NH), piperidine (C5H10NH) and morpholine (C4H8ONH)] or alcohols (MeOH and EtOH) in the presence of carbon disulphide to give the corresponding dithiocarbamate or xanthate complexes [NBu4][(C6F5)2Ni(S2C-X)] [X = NHEt (1), NHPr (2), NMe2 (3), NEt2 (4), NC4H8 (5), NC5H10 (6), NC4H8O (7), OMe (8) or OEt (9)]. In the same solvent, the reaction of the hydroxo-nickel complex with carbon disulphide and [NBu4]OH leads to the formation of the dithiocarbonate complex [NBu4]2[(C6F5)2Ni(S2CO)] (10). The new complexes are air-stable, orange solids which have been studied by conductance measurements and spectroscopic (IR, V-UV, 1H- and 19F-NMR) methods.

Synthesis and reactivity of the di-μ-hydroxo-bis[bis(pentachlorophenyl)palladate(II)] ion

Abstract The binuclear hydroxo-pentachlorophenyl palladium complex Q 2 [{Pd(C 6 Cl 5 ) 2 (μ-OH)} 2 ] (I) (Q = NBu 4 has been obtained by reaction between Q 2 [{Pd(C 6 Cl 5 ) 2 (μ-Cl)} 2 ] and QOH in acetone. Reaction of the hydroxo-complex I with protic electrophiles HL gives complexes of the types Q 2 [{Pd(C 6 Cl 5 ) 2 (μ-L)} 2 ] [L = pyrazolate (pz) (II), 3-methylpyrazolate (mpz) (III), indazolate (indz) (IV), or methoxo (V)], Q 2 [{Pd(C 6 Cl 5 ) 2 } 2 (μ-OH)(μ-dmpz)] (VI) (dmpz = 3,5-dimethylpyrazolate), or [Pd(C 6 Cl 5 ) 2 L] [L = acetylacetonate (acac) (VII), benzoylacetonate (bzac) (VIII), or 8-hydoxyquinolinate (oxin) (IX)]. However, complex VI is best prepared by reaction of the above chloro-complex with QOH and Hdmpz. The neutral mononuclear complex cis -[Pd(C 6 Cl 5 ) 2 (PhCN) 2 ] (X) has been obtained by treating complex I with benzonitrile in the presence of tetrafluoroboric acid. The lability of complex X is manifested by its reactivity towards aniline and 1,5-cyclooctadiene (cod), with which it gives the corresponding complexes cis -[Pd(C 6 Cl 5 ) 2 (PhNH 2 ) 2 ] (XI) and [Pd(C 6 Cl 5 ) 2 (cod)] (XII). The reaction between complex X and the chloro-complex [PdCl 2 (PEt 3 ) 2 ] yields the asymmetric binuclear complex [(C 6 Cl 5 ) 2 Pd(μ-Cl) 2 Pd(PEt 3 ) 2 ] (XIII).

Synthesis and characterization of new cyclometallated Pd(II) complexes with bridging or terminal imidato ligands. Crystal structures of [{Pd(μ-succinimide)(phpy)}2] and [pd(azb)(succinimide)(PPh3)] (phpy = 2-phenylpyridine;azb = azobenzene)

Abstract Two series of new dinuclear cyclometallated palladium complexes [{Pd(μ-NCO)(C∧N)}2] containing asymmetric imidato –NCO– bridging units have been synthesized [C∧N=azobenzene (azb); –NCO–=succinimide (1a), phthalimide (2a) or maleimide (3a); C∧N=2-phenylpyridine (phpy); –NCO–=succinimide (1b), phthalimide (2b) or maleimide (3b)]. The reaction of both succinimidato precursors with tertiary phosphines to form the mononuclear N-bonded imidato derivatives of general formula [Pd(C∧N)(suc)(L)] [C∧N=azb; L=PPh3 (4a), PPh2Me (5a), PPhMe2 (6a), P(4-F–C6H4)3, (7a), P(4-MeO–C6H4)3 (8a); C∧N=phpy; L=PPh3 (4b), PPh2Me (5b), PPhMe2 (6b), P(4-F–C6H4)3 (7b), P(4-MeO–C6H4)3 (8b)] has been investigated. The new complexes were characterized by partial elemental analyses and spectroscopic methods (IR, FAB, 1H, 13C and 31P). The single-crystal structures of compounds 1b and 4a have been established.