Bulky Phosphine Ligands Research Articles

Use of Tunable Ligands Allows for Intermolecular Pd‐Catalyzed C—O Bond Formation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Efficient Pd-Catalyzed Amination of Heteroaryl Halides

The Pd-catalyzed amination of a variety of heteroaryl halides has been accomplished by utilizing bulky electron-rich biaryl phosphine ligands. In particular, we report the first couplings of amines with chloro- and bromoindoles bearing a free NH, as well as the first Pd-catalyzed aminations of a 5-halopyrimidine. [reaction: see text]

Use of Tunable Ligands Allows for Intermolecular Pd-Catalyzed C−O Bond Formation

Bulky biaryl phosphine ligands facilitate Pd-catalyzed C-O coupling reactions of aryl halides with primary and secondary alcohols by promoting reductive elimination at the expense of beta-hydride elimination. The key to their success is the ability to match the size of the ligand to that of the combination of substrates. The efficient coupling of a number of unactivated aryl chlorides and bromides with cyclic and acyclic secondary alcohols was achieved. This included the coupling of allylic alcohols for the first time in a Pd-catalyzed coupling process.

Dimerization of Terminal Alkynes Catalyzed by a Nickel Complex Having a Bulky Phosphine Ligand.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Monoligated Palladium Species as Catalysts in Cross‐Coupling Reactions

AbstractFor Abstract see ChemInform Abstract in Full Text.

Difluoro Complexes of Platinum(II) and -(IV) with Monodentate Phosphine Ligands: An Exceptional Stability of d6 Octahedral Organometallic Fluorides

Complexes (R3P)2PtF2 were prepared by reaction of the corresponding diiodo precursors with AgF in dichloromethane. The intermediate formation of trans- and cis-(R3P)2Pt(I)F was also observed. All fluoro complexes demonstrate a strong preference for the cis-configuration (R = Ph or Et) unless a bulky phosphine ligand is used (R = i-Pr), in which case the trans complex was observed. The Pt(IV) difluoro compounds (R3P)2Ar2PtF2 were obtained by reacting the Pt(II) diaryl precursors with XeF2. The fluoro ligands are located in the trans-position relative to the aryl groups in the overall octahedral environment. The representative Pt(II) and Pt(IV) difluoro complexes were characterized by X-ray crystallography. All fluoro compounds react rapidly with chlorotrimethylsilane to give the corresponding chloro complexes. The Pt(IV) difluorides are remarkably stable in the C-C reductive elimination reaction, relative to their dichloro analogs which reductively eliminate diaryl within several hours at 45 degrees C in N-methylpyrrolidone. It was found that phosphine dissociation from the octahedral Pt(IV) complex is essential for the reductive elimination reaction to take place, the difluoro complex being kinetically stable even at 60 degrees C.

(Z)-Selective cross-dimerization of arylacetylenes with silylacetylenes catalyzed by vinylideneruthenium complexes

The vinylideneruthenium(II) complexes bearing bulky and basic tertiary phosphine ligands, RuCl2(=C=CHPh)L2 (L = PPri3, PCy3), serve as good catalyst precursors for (Z)-selective cross-dimerization between arylacetylenes and silylacetylenes in the presence of N-methylpyrrolidine.

Monoligated Palladium Species as Catalysts in Cross‐Coupling Reactions

Palladium-mediated cross-coupling reactions are attractive organometallic transformations for the generation of C--C, C--N, C--O, and C--S bonds. Despite being widely employed in small-scale syntheses, cross-coupling reactions have not found important industrial applications because until recently, only reactive aryl bromides and iodides could be used as substrates. These substrates are generally more expensive and less widely available than their chloride counterparts. Over the past few years, new catalytic systems with the ability to activate unreactive and sterically hindered aryl chlorides have been developed. The new catalysts are based on palladium complexes that contain electron-rich and bulky phosphine or carbene ligands. The enhanced reactivity observed with these new systems has been attributed to the formation of unsaturated and reactive [PdL] species which can readily undergo oxidative addition reactions with ArX to yield [Pd(Ar)X(L)].

Synthesis of 5,5′‐Diarylated 2,2′‐Bithiophenes via Palladium‐Catalyzed Arylation Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Unsaturated Pd(0), Pd(I), and Pd(II) Complexes of a New Methoxy-Substituted Benzyl Phosphine. Aryl−X (X = Cl, I) Oxidative Addition, C−O Cleavage, and Suzuki−Miyaura Coupling of Aryl Chlorides

The 14e- Pd(0)L2 complex 2 was prepared by reduction of [Pd(2-methylallyl)Cl]2 in the presence of the new, electron-rich, bulky methoxy benzyl phosphine (dmobp) ligand 1. Structural characterization of this complex indicates that the methoxy groups are not coordinated to the metal center. Complex 2 undergoes oxidative addition of iodo- and chlorobenzene at room temperature to yield the monophosphine complexes LPd(Ph)X (4, X = I; 5, X = Cl) in which the methoxy group is coordinated to the Pd(II) center in the solid state, as indicated by the X-ray structure of 4. In solution there is no evidence for methoxy coordination, indicating the availability of a Pd(II) 14e- complex. The Me−O bond in 4 is longer than the corresponding bond in 2, indicating that coordination of the methoxy group weakens the C−O bond. Reaction of complex 4 or 5 with the free ligand 1 results in nucleophilic attack and C−O cleavage, leading to the dimeric phenoxy-bridged complex 7, which was structurally characterized. Partial reductio...

Synthesis of 5,5′-diarylated 2,2′-bithiophenes via palladium-catalyzed arylation reactions

2,2′-Bithiophene and 3,3′-dicyano-2,2′-bithiophenes are diarylated directly with aryl bromides at the 5- and 5′-positions accompanied by C–H bond cleavage in the presence of Pd(OAc) 2 and a bulky phosphine ligand using Cs 2CO 3 as base. In the reaction using (2,2′-bithiophen-5-yl)diphenylmethanol as the substrate, monoarylation at the 5-position via C–C bond cleavage occurs selectively to give 5-aryl-2,2′-bithiophenes and the subsequent arylation with a different aryl bromide affords the corresponding unsymmetrically 5,5′-diarylated products.

Palladium‐Catalyzed Suzuki Coupling Reactions Using Cobalt‐Containing Bulky Phosphine Ligands.

Abstract Three bulky mono-dentate alkyne-bridged dicobalt-phosphine complexes [(μ-PPh2CH2PPh2)Co2(CO)4](μ,η-PhCCPPh2) 4a , [(μ-PPh2CH2PPh2)Co2(CO)4](μ,η-Me3CCCPPh2) 5a and [(μ-PPh2CH2PPh2)Co2(CO)4](μ,η-Me3SiCCPPh2) 6a were prepared from the reactions of the bis(diphenylphosphino)methylene (dppm) bridged dicobalt complex Co2(CO)6(μ-Ph2PCH2PPh2) with PhCCPPh2 1 , Me3CCCPPh2 2 , and Me3SiCCPPh2 3 , respectively. These three metal-containing compounds 4a , 5a and 6a were employed as ligands, replacing conventional organic phosphines, in the Suzuki cross-coupling reactions and have been proved to be effective, authentic mono-dentate phosphine ligands.

Dimerization of terminal alkynes catalyzed by a nickel complex having a bulky phosphine ligand

Ni(cod)(2)/P(t)Bu(3) system catalyzed the dimerization of terminal alkynes to give (E)-head-to-head dimerization products, in which the stannylacetylene dimer could be applied to a one-pot synthesis of a conjugated enyne, when combined with Migita-Stille coupling.

Palladium‐Catalyzed Direct Arylation of Thiazoles with Aryl Bromides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Palladium-catalyzed direct arylation of thiazoles with aryl bromides

Thiazole, 2-phenyl or -alkyl substituted one and benzothiazole are efficiently arylated with aryl bromides at the 2- and/or 5-position(s) in the presence of Pd(OAc) 2 and a bulky phosphine ligand using Cs 2CO 3 as base. 2-Phenyl-5-thiazolecarboxanilide undergoes successive diarylation at the 4- and 5-positions accompanied by decarbamoylation.

New bulky phosphinopyridine ligands. P∼N∼C Tridentates in palladium complexes

The sterically bulky pyridinyl phosphine (P∼N) ligands have been prepared from the phosphinylation of 2,4-di-tert-butyl-6-methylpyridine. Due to the steric hindrance, substitution reaction of these P∼N ligands with (COD)PdMeCl yields the chloro-bridged dipalladium species [(P∼N)2Pd2Me2Cl2], in which the P∼N ligand acts as a monodentate. Treatment of these dimeric palladium compounds with AgBF4 in the presence of acetonitrile gives the corresponding C–H activation metal complex [(P∼N∼C)Pd(CH3CN)]BF4. Both spectral and X-ray single-crystal characterization of these palladium complexes are presented.

Synthesis and structural characterization of novel palladium complexes chelated by bulky cobalt-containing phosphine ligands: unusual palladium–cobalt bond formation

The reaction of a bulky phosphine, [Co2(CO)5{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}] 1 with P(OMe)3 gave a phosphite substituted tetracobalt-complex, [Co2(CO)4{P(OMe)3}{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}] 5. Further reaction of 5 with (COD)PdCl2 yielded a 5 -coordinated palladium complex, [Co2(CO)4{P(OMe)3}}{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)3(μ-CO){μ-P-(μ-PPh2CCPPh2)}]PdCl27. Similar results were obtained for the reaction of 1 with (COD)PdCl2, which yielded [Co2(CO)5{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)3(μ-CO){μ-P-(μ-PPh2CCPPh2)}]PdCl26. Likewise, reaction of another bulky phosphine [(μ-Ph2PCH2PPh2)Co2(CO)4(μ-PPh2CCP(O)Ph2)] 3 with (COD)PdCl2 yielded [{μ-P,P-PPh2CH2PPh2}Co2(CO)3(μ-CO){μ-PPh2CCP(O)Ph2}]PdCl28. The X-ray structural studies of 6, 7 and 8 reveal that unusual palladium–cobalt bonds were formed. A Suzuki type reaction employing complexes 6, 7 and 8, as catalysts in the reaction of 2-bromothiophene with boronic acid did not show encouraging signs.

Reactions of RuCp and RuCp* Allyl Carbene Complexes: Products Derived from Activation of Phenyl, Cyclohexyl, and Methyl C−H Bonds in PPh3, PCy3, and Cp* Ligands

Ruthenium allyl carbene complexes of the type [RuCp(C(R)-(η3-CHC(R)CHPR‘3))]PF6 (R, R‘ = aryl, alkyl substituents) are characterized by two reaction modes. (i) They behave as masked coordinatively unsaturated complexes and react readily with the donor ligands PR3 and P(OR)3 to give η3-butadienyl complexes. This is not a simple nucleophilic addition at the metal center but involves changes in both the bonding mode and the stereochemistry of the allyl carbene C4-chain. The incoming nucleophile induces C−H bond activation effecting formally a 1,4 hydrogen shift. (ii) They are capable of activating C−H bonds of aryl and alkyl groups in the bulky tertiary phosphine ligands PPh3 and PCy3 to give novel η4-butadiene complexes. In these, one R of PR3 is σ-bonded to the metal center. A divergent rearrangement results if the allyl carbene complex derives from parent acetylene (instead of a terminal alkyne). In this case the C4-unit features a η3-allyl moiety and the metal center is η2-coordinated to an arene ring of...

Synthesis of Novel Platinum Dichalcogenido-Complexes by Taking Advantage of Bulky Phosphine Ligands

The first stable disulfido and diselenido complexes of platinum-bearing bulky phosphine ligands were synthesized by the reaction of the corresponding zerovalent platinum complexes with elemental sulfur and selenium, respectively. The molecular structures of these complexes were determined by spectral data, elemental analysis, and X-Ray crystallographic analysis.

Chiral Crystallization of a Linear Two-coordinated Palladium(0) Complex Bearing Propeller-shaped Bulky Phosphine Ligands

Abstract A linear bis(phosphine) palladium(0) complex with the bulky aryl substituent, tris(2,2″,6,6″-tetramethyl-m-terphenyl-5′-yl (Tmtp), was found to crystallize as a spontaneously resolved homochiral clathrate with toluene molecules.