Insertion reactions of SO2 into Pd-OR bonds: preparation of alkyl sulfito complexes of palladium(II)

Mononuclear palladium-hydroxo complexes of the type [Pd(N-N)(C6F5)(OH)][(N-N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me2bipy), or N,N,N',N'-tetramethylethylenediamine (tmeda) react with SO2(1 atm) at room temperature in alcohol (methanol, ethanol, propanol or isopropanol) to yield alkyl sulfito palladium complexes [Pd(N-N)(C6F5)(SO2OR)](R = Me, Et, Pr or iPr). Similar alkyl sulfito complexes [Pd(N-N)(C6F5)(SO2OR)](N-N = bis(3,5-dimethylpyrazol-1-yl)methane); R = Me or Et) are obtained when [Pd(N-N)(C6F5)Cl] is treated with KOH in the corresponding alcohol ROH and SO2 is bubbled through the solution. The reaction of [Pd(bipy)(C6F5)(OH)] with SO2 in tetrahydrofuran gives [Pd(N-N)(C6F5)(SO2OH)]. The X-ray diffraction study of [Pd(tmeda)(C6F5)(SO2OPr)] has established the sulfur coordination of the propyl sulfito ligand.     

Insertion reactions into Pd[bond]O and Pd[bond]N bonds: preparation of alkoxycarbonyl,carbonato, carbamato,thiocarbamate, and thioureide complexes of palladium(II)

Mononuclear palladium hydroxo complexes of the type [Pd(N[bond]N)(C(6)F(5))(OH)] [(N[bond]N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me(2)bipy), 1,10-phenanthroline (phen), or N,N,N',N'-tetramethylethylenediamine (tmeda)] have been prepared by reaction of [Pd(N[bond]N)(C(6)F(5))(acetone)]ClO(4) with KOH in methanol. These hydroxo complexes react, in methanol, with CO (1 atm, room temperature) to yield the corresponding methoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)Me)]. Similar alkoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)R)] (N[bond]N = bis(3,5-dimethylpyrazol-1-yl)methane); R = Me, Et, or (i)Pr) are obtained when [Pd(N[bond]N)(C(6)F(5))Cl] is treated with KOH in the corresponding alcohol ROH and CO is bubbled through the solution. The reactions of [Pd(N[bond]N)(C(6)F(5))(OH)] (N[bond]N = bipy or Me(2)bipy) with CO(2), in tetrahydrofuran, lead to the formation of the binuclear carbonate complexes [(N[bond]N)(C(6)F(5))Pd(mu-eta(2)-CO(3))Pd(C(6)F(5))(N[bond]N)]. Complexes [Pd(N[bond]N)(C(6)F(5))(OH)] react in alcohol with PhNCS to yield the corresponding N-phenyl-O-alkylthiocarbamate complexes [Pd(N[bond]N)(C(6)F(5))[SC(OR)NPh]]. Similarly, the reaction of [Pd(bipy)(C(6)F(5))(OH)] with PhNCO in methanol gives the N-phenyl-O-methylcarbamate complex [Pd(bipy)(C(6)F(5))[NPhC(O)OR]]. The reactions of [(N[bond]N)Pd(C(6)F(5))(OH)] with PhNCS in the presence of Et(2)NH yield the corresponding thioureidometal complexes [Pd(N[bond]N)(C(6)F(5))[NPhCSNR(2)]]. The crystal structures of [Pd(tmeda)(C(6)F(5))(CO(2)Me)], [Pd(2)(Me(2)bipy)(2)(C(6)F(5))(2)(mu-eta(2)-CO(3))].2CH(2)Cl(2), and [Pd(tmeda)(C(6)F(5))[SC(OMe)NPh]] have been determined.     

Highly air-stable anionic mononuclear and neutral binuclear palladium(II) complexes for C-C and C-N bond-forming reactions

The short-bite aminobis(phosphonite), PhN{P(-OC10H6(mu-S)C10H6O-)}2 (2), containing a mesocyclic thioether backbone is synthesized by either treating PhN(PCl2)2 with 2 equiv of thiobis(2,2'-naphthol) or reacting chlorophosphite (-OC10H6(mu-S)C10H6O-)PCl (1) with aniline in the presence of a base. Treatment of 2 with an equimolar amount of Pd(COD)Cl2 in the presence of H2O affords a P-N-P-bridged and P,S-metalated binuclear complex, [PhN(P(-OC10H6(mu-S)C10H6O-)-kappaP)2Pd2Cl2{P(-OC10H6(mu-S)C10H6O-)(O)-kappaP,kappaS}2] (3), whereas the same reaction with 2 equiv of Pd(COD)Cl2 in the presence of H2O and Et3N produces the mononuclear anionic complex [{(-OC10H6(mu-S)C10H6O-)P(O)-kappaP,kappaS}PdCl2](Et3NH) (5). By contrast, reaction of 2 with 2 equiv of Pd(COD)Cl2 and H2O in the absence of Et3N gives the hydrogen phosphonate coordinated complex [{(-OC10H6(mu-S)C10H6O-)P(OH)}PdCl2] (4) which converts to the anionic complex in solution or in the presence of a base. Compound 2 on treatment with Pt(COD)X2 (X = Cl or I) afforded P-coordinated four-membered chelate complexes [PhN(P(-OC10H6(mu-S)C10H6O-)-kappaP)2PtX2] (6 X = Cl, 7 X = I). The crystal structures of compounds 2, 3, 5, and 7 are reported. Compound 3 is the first example of a crystallographically characterized binuclear palladium complex containing a bidentate bridging ligand and its hydrolyzed fragments forming metallacycles containing a palladium-phosphorus sigma bond. All palladium complexes proved to be very good catalysts for the Suzuki-Miyaura and Mizoroki-Heck cross-coupling and amination reactions with excellent turnover numbers (TON up to 1.46 x 105 in the case of the Suzuki-Miyaura reaction).     

Tridentate, anionic tethered N-heterocyclic carbene of Pd(II) complexes

The synthesis of a series of azolium salts such as azolium iodides and chlorides having both N-anionic functional group and N-alkyl group have been developed. Reaction of azolium iodides or chlorides with Ag₂O gave the corresponding NHC-Ag complexes. It was found that the resulting NHC-Ag complexes derived from azolium iodides or chlorides differ in their physical properties. The azolium chlorides as well as azolium iodides were successfully converted into the NHC-Ag complexes, which subsequently reacted with PdCl₂(CH₃CN)₂ to give the anionic amidate/NHC-Pd complexes. Thus, a variety of the NHC-Pd complexes could be obtained from benzimidazolium and imidazolium salts.     

Insertion of molecular oxygen into a palladium(II) hydride bond

Insertion of molecular oxygen into a palladium(II) hydride bond to form an (eta1-hydroperoxo)palladium(II) complex is reported. The hydroperoxo palladium(II) product has been crystallographically characterized. A second-order rate law (first-order in palladium and first-order in oxygen) is observed for the reaction and a large kinetic isotope effect implicates Pd-H bond cleavage in the rate-determining step. The results of studies with radical inhibitors and light suggest that the reaction does not proceed by a radical chain mechanism.     

Insertion of CO2 into a palladium allyl bond and a Pd(II) catalysed carboxylation of allyl stannanes

The complex 2,6-bis[(di-t-butylphosphino)methyl]phenyl allyl palladium (PCP(tBu)Pd-allyl, 3) reacts with CO(2) in a very fast insertion reaction to give the corresponding butenoate complex. The reaction is thought to occur via a cyclic six-membered transition state (7), where the gamma-carbon of the allyl group is linked up with the CO(2)-carbon. A group of related PCP complexes were investigated as catalysts for the carboxylation of tributyl(allyl)stannane. A catalytic cycle is proposed for this reaction where the rate determining step is the transmetallation between tin and palladium. The carboxylation reaction is faster using less sterically crowded catalysts whereas the electron richness of the palladium complexes seems less important for reactivity. Thus, there was no apparent difference in reactivity between 2,6-bis[(di-phenylphosphino)methyl]phenyl palladium triflouroacetate (13) and resorcinolbis(diphenyl)phosphinite palladium triflouroacetate (10). Both of these complexes give high turnovers for the carboxylation of tributyl(allyl)stannane (80% in 16 h using a ca. 5% catalyst loading and 4 atm CO(2) pressure). On the other hand complex 3 was inactive in the catalytic carboxylation reaction.     

Insertion of unsaturated organic electrophiles into molybdenumbond-alkoxide and rheniumbond-alkoxide bonds of neutral,stable carbonyl complexes

Alkoxo complexes [Re(OR)(CO)(3)(N-N)] (R=Me, Et, tBu; N-N=2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'bipyridine (bipy'), 1,10-phenanthroline (phen)) and [M(OMe)(eta(3)-allyl)(CO)(2)(phen)] (M=Mo, W) have been synthesized in good yields and using mild conditions by the reaction of sodium alkoxides with [Re(OTf)(CO)(3)(N-N)] and [MCl(eta(3)-allyl)(CO)(2)(phen)] precursors. These have been characterized by IR and NMR spectroscopy as well as by X-ray diffraction for [W(OMe)(eta(3)-allyl)(CO)(2)(phen)] (10). The reactions of the molybdenum and rhenium alkoxo complexes with isocyanates, R'NCO, yield [L(n)M[N(R')C(O)OR]] complexes; the carbamate ligand, which results from an R'NCO insertion into the Mbond;OR bond, is monodentate through the nitrogen atom. The solid-state structures of Mo and Re examples have been determined by X-ray diffraction. The geometry around the carbamate nitrogen of these compounds is planar, and the distances indicate delocalization of the nitrogen lone pair involving mainly the carbonyl groups. Experiments carried out with the Re complexes showed that aryl isocyanates are more reactive than their alkyl counterparts, and that bulky R' groups led to slow rates of insertion. Insertion reactions were also observed with isothiocyanates, although here it is the Sbond;C bond that inserts into the Mbond;OR bond, and the resulting ligand is bound to the metal by sulfur. Competition experiments with the Re compounds indicate that isocyanates are more reactive than isothiocyanates towards the Rebond;OR bonds. Tetracyanoethylene inserts into the Rebond;OMe bond of [Re(OMe)(CO)(3)(bipy')], forming a complex with a 2-methoxytetracyanoethyl ligand; the structure of which was determined by X-ray diffraction. The formation of the xanthato complex [Re(SC(S)OtBu)(CO)(3)(bipy)] (20) by reaction of [Re(OTf)(CO)(3)(bipy)] with CS(2) and NaOtBu, but not by the reaction of CS(2) and [Re(OtBu)(CO)(3)(bipy)] (5 a), suggests that the insertion reactions do not take place by ionization of the alkoxo complexes to give the free alkoxide ion.     

Insertion of acetylene into osmium-hydrogen bonds incluster complexes

Complex H₂ Os₃ (CO)₁₀ reacts with acetylene or methyl-substituted acetylenes to give complexes of type HOs₃ (CH=CHR)(CO)₁₀ (R = H or Me) and Os₃ (R₁ C₂ R₂)(CO)₁₀ (R₁ and R₂ are H or Me) which convert to nonacarbonyl complexes with hydrogen transfer from ligand to metal.     

Synthesis of neutral (Pd(II), Pt(II)), cationic (Pd(II)), and water-induced anionic (Pd(II)) complexes containing new mesocyclic thioether-aminophosphonite ligands and their application in the Suzuki cross-coupling reaction

Mesocyclic thioether-aminophosphonite ligands, {-OC10H6(mu-S)C10H6O-}PNC4H8O (2a, 4-(dinaphtho[2,1-d:1',2'-g][1,3,6,2]dioxathiaphosphocin-4-yl)morpholine) and {-OC10H6(mu-S)C10H6O-}PNC4H8NCH3 (2b, 1-(dinaphtho[2,1-d:1',2'-g][1,3,6,2]dioxathiaphosphocin-4-yl)-4-methylpiperazine) are obtained by reacting {-OC10H6(mu-S)C10H6O-}PCl (1) with corresponding nucleophiles. The ligands 2a and 2b react with (PhCN)2PdCl2 or M(COD)Cl2 (M = Pd(II) or Pt(II)) to afford P-coordinated cis-complexes, [{(-OC10H6(mu-S)C10H6O-)PNC4H8X-kappaP}2MCl2] (3a, M = Pd(II), X = O; 3b, M = Pd(II), X = NMe; 4a, M = Pt(II), X = O; 4b, M = Pt(II), X = NMe). Compounds 2a and 2b, upon treatment with [Pd(eta3-C3H5)Cl]2 in the presence of AgOTf, produce the P,S-chelated cationic complexes, [{(-OC10H6(mu-S)C10H6O-)PNC4H8X-kappaP,kappaS}Pd(eta3-C3H5)](CF3SO3) (5a, X = O and 5b, X = NMe). Treatment of 2a and 2b with (PhCN)2PdCl2 in the presence of trace amount of H2O affords P,S-chelated anionic complexes, [{(-OC10H6(mu-S)C10H6O-)P(O)-kappaP,kappaS}PdCl2](H2NC4H8X) (6a, X = O and 6b, X = NMe), via P-N bond cleavage. The crystal structures of compounds 1, 2a, 2b, 4a, and 6a are reported. Compound 6a is a rare example of crystallographically characterized anionic transition metal complex containing a thioether-phosphonate ligand. Most of these palladium complexes proved to be very active catalysts for the Suzuki-Miyaura reaction with excellent turnover number ((TON), up to 9.2 x 10(4) using complex 6a as a catalyst).     

N-aminorhodamne complexes of palladium(II), palladium(IV) and platinum(II)

Summary TheN-aminorhodanine (L) complexes: PdLX, (X = Br or I), ML_1.5Cl₂ (M = Pd or Pt), PtL₂X₂ (X = Br, I or ClO₄), PdL₃(ClO₄)₂, PdL_1.5Cl₄ and PdL₃(ClO₄)₄ have been prepared and investigated. The ligand is bonded to the metal ion through the aminic nitrogen atom as monodentate or through this atom and the thiocarbonylic sulphur atom when it acts as chelating or bridging ligand. The carbonylic oxygen atom is never coordinated.     

Coordination insertion reactions of acrylonitrile into Pd-H and Pd-methyl bonds in a diimine-palladium(II) system

Acrylonitrile (AN) displaces the ethyl ether ligand of the cationic complex [Pd(N-N)Me(Et₂O)]⁺ (N-N = (2,6-(i-Pr)₂C₆H₃)-NCMeCMeN-(2,6-(i-Pr)₂C₆H₃)) to form the N-bonded AN complex [Pd(N-N)Me(AN)]⁺, which exists as two interconverting rotamers. On standing or heating, [Pd(N-N)Me(AN)]⁺ undergoes 2,1-insertion to give [Pd(N-N)(CH(CN)CH₂Me)(AN)]⁺, which undergoes β-hydrogen elimination to give the intermediate hydride, [Pd(N-N)H(AN)]⁺, which in turn inserts AN to give the cyanoethyl complex [Pd(N-N)(CH(CN)Me)]⁺. Dimerization of the [Pd(N-N)(CH(CN)CH₂CH₃)]⁺ moiety via bridging nitrile groups also occurs, giving the dicationic species . Although [Pd(N-N)Me(AN)]⁺ does behave as a typical Brookhart ethylene polymerization catalyst, it does not catalyze AN polymerization and in fact added AN suppresses ethylene polymerization.     

Neutral and anionic pentafluorophenyl complexes of palladium and platinum(II) and their reactivity towards amines

Summary The (n-Bu₄N)[M(C₆F₅)₃(CNR)] complexes (M=Pd or Pt; R=p-Tolyl, Me, Cy ort-Bu, prepared from (n-Bu₄N)[M(C₆F₅)₃(tht)] (tht = tetrahydrothiophene) and the appropriate isocyanide, RNC, prove to be unreactive towards benzylamine or MeOH. Thetrans-[Pd(C₆F₅)₂(CNR)₂] complexes react slowly with benzylamine to give the corresponding carbene complexestrans-[Pd(C₆F₅)₂{C(NHR)(NHBz)}₂], the rate of the reaction decreasing in the order:p-Tolyl > Me > Cy t-Bu (for R=t-Bu the carbene complex cannot be prepared). In the corresponding Pt complexes a marked decrease in reactivity is observed and only the most reactive isonitrile complex (R=p-Tolyl) gives the carbene complextrans-[Pt(C₆F₅)₂{C(NHTolyl-p)(NHBz)}_2}. Thecis-[M(C₆F₅)₂(CNTolyl)₂] complexes do not show any change in reactivity compared to the correspondingtrans-complexes, and givecis[M(C₆F₅)₂{C(NHTolyl-p)(NHBz)}₂].     

Formation of palladium hydride complexes upon the reduction of Pd(II) by hydrogen

Conclusions The reduction of palladium(II) acetate by hydrogen in the presence of 1,10-phenanthroline or 2,2-dipyridyl gives palladium hydride clusters containing a massive metal-like nucleus with interstitial hydrogen atoms. The ligands are found to be peripheral palladium atoms, while the acetate groups are found in the external sphere.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2381–2384, October, 1985.The authors express their gratitude to S. G. Ellert for measuring the magnetic susceptibility and to A. L. Chuvilin for the electron microscopic data.     

2-Methylimidazole palladium(II) complexes

Summary The preparation of two new tetracoordinated complexes of palladium(II) with 2-methylimidazole, 2-MeIm, and chloride as ligands is described.     

Cationic organocarbonyl palladium(II) complexes

The carbonylation under normal pressure, at 0°C, of organometallic perchlorato palladium(II) complexes in solution leads to the displacement of the perchlorato group and the formation of a series of cationic organocarbonyl palladium(II) compounds of the general formula [CO(C₆F₅)PdL₂]ClO₄, where L₂ are either two tertiary phosphine groups or a nitrogen chelate, such as 2,2′-bipyridine, 1,10-phenanthroline or N,N,N′,N′-tetramethylethylenediamine.     

Synthesis and characterization of some methyl complexes of palladium(II). Part 2(1)

Summary Dichloro complexes of Pd^II, [Pd(L–L)Cl₂], where L–L=1-(thiomethyl)-2-(diphenylarsino)ethane (S–As) or 1-(thiomethyl)-2-(diphenylphosphino)ethane (S–P) andtrans-[PdL₂Cl₂], where L=diphenyl(2-phenylethyl)-phosphine (PE), diphenyl(1-naphthyl)phosphine (PN) orN-methyl-2-thiophenealdimine (SN), have been prepared and characterized. The reactions of these complexes with MeLi were investigated. The dimethyl complexes [Pd(L–L)Me₂] (L–L=S–As, S–P) and [Pd(PE)Me₂] were isolated and characterized. Reaction of [Pd(L–L)Me₂] (L–L=S–As, S–P) with HCl affords the monomethyl derivatives [Pd(L–L)Me(Cl)]. In contrast to the Pt analogues, [Pd(L–L)Me₂] and [Pd(L–L)Me(Cl)] are relatively less stable than [Pt(L–L)Me₂] and [Pt(L–L)Me(Cl)].     

Preparation and structural characterization of ionic five-coordinate palladium(II) and platinum(II) complexes of the ligand tris[2-(diphenylphosphino)ethyl]phosphine. Insertion of SnCl(2) into M-Cl bonds (M = Pd,Pt) and hydroformylation activity of the Pt-SnCl(3) systems

The five-coordinate palladium(II) and platinum(II) complexes [M(PP(3))Cl]Cl [M = Pd (1), Pt (2)] (PP(3) = tris[2-(diphenylphosphino)ethyl]phosphine) were prepared by interaction of aqueous solutions of MCl(4)(2-) salts with PP(3) in CHCl(3). Complexes 1 and 2 undergo facile chloro substitution reactions with KCN in 1:1 and 1:2 ratios to afford complexes [M(PP(3))(CN)]Cl [M = Pt (3)] and [M(PP(3))(CN)](CN) [M = Pd (4), Pt (5)] possessing M-C bonds, both in solution and in the solid state. The reaction of 1 and 2 with SnCl(2) in CDCl(3) occurs with insertion of SnCl(2) into M-Cl bonds leading to the formation of [M(PP(3))(SnCl(3))](SnCl(3)) [M = Pd (6), M = Pt (7)]. The isolation as solids of complexes 6 and 7 by addition of SnCl(2) to the precursors requires the presence of PPh(3) which activates the cleavage of M-Cl bonds, favors the SnCl(2) insertion, and does not coordinate to M in any observable extent. Solutions of 6 in CDCl(3) undergo tin dichloride elimination in higher proportion than solutions of 7. The reaction of complexes 1 and 2 with SnPh(2)Cl(2) leads to [M(PP(3))Cl](2)[SnPh(2)Cl(4)] [M = Pd (8)]. Complexes 2, 5, 7, and 8 were shown by X-ray diffraction to contain distorted trigonal bipyramidal monocations [M(PP(3))X](+) [M = Pt, X = Cl(-) (2), X = CN(-) (5), X = SnCl(3)(-) (7); M = Pd, X = Cl(-) (8)], the central P atom of PP(3) being trans to X in axial position and the terminal P donors in the equatorial plane of the bipyramids. The "preformed" catalyst 7 showed a relatively high aldehyde selectivity compared to most of the platinum catalysts.     

Cationic (fluoromesityl)palladium(II) complexes

Halide abstraction from [Pd(μ-Cl)(Fmes)(NCMe)]₂ (Fmes = 2,4,6-tris(trifluoromethyl)phenyl or nonafluoromesityl) with TlBF₄ in CH₂Cl₂/MeCN gives [Pd(Fmes)(NCMe)₃]BF₄, which reacts with monodentate ligands to give the monosubstituted products trans-[Pd(Fmes)L(NCMe)₂]BF₄ (L = PPh₃, P(o-Tol)₃, 3,5-lut, 2,4-lut, 2,6-lut; lut = dimethylpyridine), the disubstituted products trans-[Pd(Fmes)(NCMe)(PPh₃)₂]BF₄, cis-[Pd(Fmes)(3,5-lut)₂(NCMe)]BF₄, or the trisubstituted products [Pd(Fmes)L₃]BF₄ (L = CN^tBu, PHPh₂, 3,5-lut, 2,4-lut). Similar reactions using bidentate chelating ligands give [Pd(Fmes)(L-L)(NCMe)]BF₄ (L-L = bipy, tmeda, dppe, OPPhPy₂-N,N′, (OH)(CH₃)CPy₂-N,N′). The complexes trans-[Pd(Fmes)L₂(NCMe)]BF₄ (L = PPh₃, tht) (tht = tetrahydrothiophene) and [Pd(Fmes)(L-L)(NCMe)]BF₄ (L-L = bipy, tmeda) were obtained by halide extraction with TlBF₄ in CH₂Cl₂/MeCN from the corresponding neutral halogeno complexes trans-[Pd(Fmes)ClL₂] or [Pd(Fmes)Cl(L-L)]. The aqua complex trans-[Pd(Fmes)(OH₂)(tht)₂]BF₄ was isolated from the corresponding acetonitrile complex. Overall, the experimental results on these substitution reactions involving bulky ligands suggest that thermodynamic and kinetic steric effects can prevail affording products or intermediates different from those expected on purely electronic considerations. Thus,water, whether added on purpose or adventitious in the solvent, frequently replaces in part other better donor ligands, suggesting that the smaller congestion with water compensates for the smaller M-OH₂ bond energy.     

Pnictogen-thiacrown complexes with Pt(II) and Pd(II)

Platinum(II) and palladium(II) complexes of the trithiacrown [9]aneS(3) containing a range of Group 15 donors are reviewed. These complexes have the general formula [M([9]aneS(3))(L(2))](n+) where L represents at least one Group 15 donor. Complexes involving pnictogens, with the exception of bismuth, are observed. The complexes generally have an elongated square pyramidal geometry with a long distance interaction to the third sulphur of the [9]aneS(3) which forms the apex of the square pyramid. This axial metal-sulphur distance is quite sensitive to the donor properties of L. Poorer donors such as Sb and As ligands show short axial distances whereas the better N donor ligands show longer distances. Pt(II) complexes of the formula [Pt([9]aneS(3))(EPh(3))(2)](2+) (E = P, As, Sb) show a considerable distortion towards a trigonal bipyramidal geometry due to intramolecular π-π interactions. Over seventy of these types of complexes have been crystallographically characterized and are discussed in this article. Other unique features of the complexes, including NMR spectroscopy, redox chemistry, and electronic spectroscopy, are also discussed.