Addition of palladium and platinum tri-tert-butylphosphine groups to Re-Sn and Re-Ge bonds

The reaction of Re2(CO)8[mu-eta2-C(H)=C(H)Bu(n)](mu-H) with Ph3SnH at 68 degrees C yielded the new compound Re2(CO)8(mu-SnPh2)2 (10) which contains two SnPh2 ligands bridging two Re(CO)(4) groups, joined by an unusually long Re-Re bond. Fenske-Hall molecular orbital calculations indicate that the bonding in the Re2Sn2 cluster is dominated by strong Re-Sn interactions and that the Re-Re interactions are weak. The 119Sn M?ssbauer spectrum of 10 exhibits a doublet with an isomer shift (IS) of 1.674(12) mm s(-1) and a quadrupole splitting (QS) of 2.080(12) mm s(-1) at 90 K,characteristic of Sn(IV) in a SnA2B2 environment. The IS is temperature dependent, -1.99(14) x 10(-4) mm s(-1) K(-1); the QS is temperature independent. The temperature-dependent properties are consistent with the known Gol'danskii-Kariagin effect. The germanium compound Re2(CO)8(mu-GePh2)2 (11) was obtained from the reaction of Re2(CO)8[mu-eta2-C(H)=C(H)Bu(n)](mu-H) with Ph3GeH. Compound 11 has a structure similar to that of 10. The reaction of 10 with Pd(PBu(t)3)2 at 25 degrees C yielded the bis-Pd(PBu(t)3) adduct, Re2(CO)8(mu-SnPh2)2[Pd(PBu(t)3)]2 (12); it has two Pd(PBu(t)3) groups bridging two of the four Re-Sn bonds in 10. Fenske-Hall molecular orbital calculations show that the Pd(PBu(t)3) groups form three-center two-electron bonds with the neighboring rhenium and tin atoms. The mono- and bis-Pt(PBu(t)3) adducts, Re2(CO)8(mu-SnPh2(2)[Pt(PBu(t)3)] (13) and Re2(CO)8(mu-SnPh2)2[Pt(PBu(t)3)]2 (14), were formed when 10 was treated with Pt(PBu(t)3)2. A mono adduct of 11, Re2(CO)8(mu-GePh2)2[Pt(PBu(t)3)] (15), was obtained similarly from the reaction of 11 with Pt(PBu(t)3)2.     

Metallochain cluster complexes and metallomacrocyclic triangles based on coordination bonds between palladium or platinum and diphosphinoacetylene ligands

To explore the potential of the coordination chemistry of Pd and Pt halides with phosphinoacetylene ligands for the generation of novel, highly metallated organometallic coordination polymers, investigations on model compounds [MX2(PPh2 C identical to CPh)2] that exhibit trans-configured Pd centers and cis-configured Pt centers have been performed. The molecular structure of the trans-Pd complexes 2 (M = Pd, X = Br) and 5 (M = Pd, X = I) appeared suitable for the generation of linear materials, whereas the cis-Pt complex 6 (M = Pt, X = I) suggested the prospective formation of ring systems. The presence of acetylene moieties allowed for further increase of metal concentration by cluster formation with [Co2(CO)8]. Two novel bimetal cluster complexes 7 and 8 were obtained from 5 and 6, respectively, and these exhibit a bridging iodine ligand as an interesting structural motif leading to heterocyclic systems with M-I-Co-C-P skeletons (M = Pd or Pt). A similar approach with [Fe2(CO)9] led to the formation of several products, including an unusual Pd-Fe cluster-containing compound 10. The extension of the coordination strategy to rigid bis(phosphinoacetylene) ligands gave rise to strained ring systems. Surprisingly, for the cis-configured PtCl2 center, a rarely observed triangular structure 12 was obtained exclusively. The corresponding PtI2 analog, 13a rearranged over time to form a "ring-fused" system 13b with an extended BINAP-like ligand.     

High asymmetric induction with beta-turn-derived palladium phosphine complexes

[reaction: see text] Work toward the development of a bisphosphine ligand system for the palladium-catalyzed addition to cyclic allyl acetates is reported. A parallel approach using phosphine-containing amino acids in conjunction with natural amino acids was used to develop a selective ligand system. The ligand system was examined while attached to the polymer support as well as in solution. Selectivites with the difficult substrate 3-acetoxycyclopentene of up to 95% ee are reported.     

Retention of palladium and phosphine ligands using nanoporous polydicyclopentadiene thimbles

Thimbles composed of polydicyclopentadiene retained Pd and phosphines used in Buchwald-Hartwig and Sonogashira coupling reactions but allowed the products to permeate. The products were isolated in high yields on the exteriors of the thimbles with no detectable contamination from phosphine and with Pd loadings as low as < 5.5 ppm.     

Hydrogenation catalysts containing phosphine complexes of palladium bound to silica

Catalysts have been obtained containing surface phosphine palladium complexes on SiO₂. A comparison has been made between the catalytic properties of the complexes obtained and those of the catalysts containing supported palladium; it has been shown that the catalysts containing supported palladium complexes possess several features characteristic of homogeneous catalytic systems.

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CO-oligomerization of butadiene and cyclic ketones catalyzed by palladium phosphine complexes

Palladium(0) phosphine complexes in the presence of water catalyze the co-oligomerization of butadiene and cyclic ketones to yield α-octadienyl derivatives. It is assumed that the hydrido hydroxo complex [PdH(L)₃]OH, formed through the oxidative addition of water to PdL_n(L = tertiary phosphine), is the catalytically active species. The co-oligomerization of butadiene and cyclopentanone has been studied in detail. The ligand size appears to affect the conversion of butadiene to products.     

Preparation and properties of sandwiched trinuclear palladium(II) complexes with tridentate phosphine and phosphine sulfide ligands

The central phosphino group of tripodal tetradentate tris[2-(diphenylphosphino)ethyl]phosphine (pp₃) was selectively oxidized by the reaction with diethyl disulfide to give tridentate phosphine ligand pOp₃. The terminal phosphino groups were reacted with sulfur to give pOp₃ trisulfide (pOp₃S₃). Three palladium(II) ions were sandwiched in the two pOp₃ and pOp₃S₃ ligands to form the trinuclear complexes with three trans(P) and trans(S) PdX₂ (X = Cl, Br, I) moieties, respectively. The tripodal triphosphine, 1,1,1-tris(diphenylphosphinomethyl)ethane (i-p₃), and its mono- and tri-sulfide, which have shorter carbon chains compared with pOp₃, form the mononuclear dichloro palladium(II) complexes with cis(P) and cis(S) geometries. Difference in the catalytic activity for the C–C coupling reaction was discussed in connection with the coordinated groups and geometries of the complexes.     

Stepwise delivery of two methoxy groups of arylaldehyde acetals across the phenyl ring. Vacant site-controlled palladium catalysis

A new catalytic cyclization of o-alkynylbenzaldehyde acetals 1 to the functionalized indenes 2 was found to be strictly controlled by the number of triphenylphosphine ligands on the Pd catalyst. Only complexes with three available coordination sites on Pd catalyze this reaction. Mechanistic study suggests that pi-coordination of Pd to the benzene ring is a key step controlled by the number of vacant coordination sites.     

Preparation of high-performance nanosized palladium hydrogenation catalysts using white phosphorus and phosphine

The nature and properties of nanosized palladium hydrogenation catalysts modified with elemental phosphorus and phosphine (PH₃) were studied.     

C-S bond formation catalyzed by N-heterocylic carbene palladium phosphine complexes

N-Heterocyclic carbenes (NHCs) are known to be useful ligands for palladium-complex catalysis. It was found that [(NHC)Pd(PPh₃)Cl₂] is an effective pre-catalyst in Pd-catalyzed C-S cross coupling reactions to produce the functionalized sulfides in excellent yields. The turn over frequency (TOF) for the coupling of p-CH₃C₆H₄Br with p-CH₃C₆H₄SH reaches to 6.25 (mol of product) (mole of catalyst)⁻¹ h⁻¹.     

New polydentate amino-substituted phosphine oxides

Conclusions We have synthesized new diamino-substituted bis(phosphine oxides) in which the coordination centers are separated by fragments with different rigidities.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2114–2117, September, 1978.     

Latent cationic palladium(II) phosphine carboxylate complexes for norbornene polymerization

The catalytic efficacy of trans‐[(R₃P)₂Pd(O₂CR′)(LB)][B(C₆F₅)₄] ( 1 ) (LB = Lewis base) and [(R₃P)₂Pd(κ²‐O,O‐O₂CR′)][B(C₆F₅)₄] ( 2 ) for mass polymerization of 5‐n‐butyl‐2‐norbornene (Butyl‐NB) was investigated. The nature of PR₃ and LB in 1 and 2 are the most critical components influencing catalytic activity/latency for the mass polymerization of Butyl‐NB. Further, it was shown that 1 is in general more latent than 2 in mass polymerization of Butyl‐NB. 5‐n‐Decyl‐2‐norbornene (Decyl‐NB) was subjected to solution polymerization in toluene at 63(±3) °C in the presence of several of the aforementioned palladium complexes as catalysts and the polymers obtained were characterized by gel permeation chromatography. Cationic trans‐[(R₃P)₂PdMe(MeCN)][B(C₆F₅)₄] [R = Cy ( 3a ), and ⁱPr ( 3b )] and trans‐[(R₃P)₂PdH (MeCN)][B(C₆F₅)₄] [R = Cy ( 4a ), and ⁱPr ( 4b )], possible products from thermolysis of trans‐[(R₃P)₂Pd(O₂CMe)(MeCN)][B(C₆F₅)₄] [R = Cy ( 1a ) and ⁱPr ( 1g )], as well as trans‐[(R₃P)₂Pd(η³‐C₃H₅)][B(C₆F₅)₄] [R = Cy ( 5a ), and ⁱPr ( 5b )], were also examined as catalysts for solution polymerization of Decyl‐NB. A maximum activity of 5360 kg/(molPd h) of 2a was achieved at a Decyl‐NB/Pd: 26,700 ratio which is slightly better than that achieved with 5a [activity: 5030 kg/(molPd h)] but far less compared with 4a [activity: 6110 kg/(molPd h)]. Polydispersity values indicate a single highly homogeneous character of the active catalyst species. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 103–110, 2009     

Preparation of a palladium dimer with a cobalt-containing bulky phosphine ligand: Its application in palladium catalyzed Suzuki reactions

A palladium dimer with a cobalt-containing phosphine ligand, {(μ-PPh₂CH₂PPh₂)Co₂(CO)₄(μ,η-(tBu)₂PCCC₆H₄-κC¹)Pd(μ-Cl)}₂ (3), was prepared from the reaction of its monomer precursor, (μ-PPh₂CH₂PPh₂)Co₂(CO)₄(μ,η-(tBu)₂PCCC₆H₄-κC¹)Pd(μ-OAc) (2), with LiCl. The crystal structure of 3, determined by X-ray diffraction methods, revealed a doubly chloride-bridged palladium dimeric conformation. Suzuki coupling reactions of bromobenzene with phenylboronic acid were carried out catalytically using these two novel palladium complexes 2 and 3 as catalyst precursors. Factors such as the molar ratio of substrate/catalyst, reaction temperature, base and solvent that might affect the catalytic efficiencies were investigated. As a general rule, the performance is much better by employing 3 than 2 as the catalyst precursor.     

Catalytic properties of palladium complexes with silica-anchored phosphine ligands in vinyl exchange reaction

Catalytic properties of Pd complexes with phosphine ligands anchored to silica have been studied. The valence state of Pd and the acidity of the alcohol were found to influence the rate of vinyl exhange. A possible reaction mechanism is proposed.

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Novel chiral ferrocenyl-imino phosphine ligands and their use in palladium catalyzed allylic alkylations

New chiral P,N-ferrocenyl imino-phosphine ligands have been synthesized and the absolute configuration of the stereocenters in each molecule has been determined by a single-crystal X-ray analysis of a common intermediate. Pd^II-allyl complexes of the new ligands have been isolated and tested as catalyst precursors in the asymmetric allylic alkylation of 1,3-diphenylprop-2-en-1-yl acetate with dimethyl malonate in different solvents. Quantitative yields and enantiomeric excesses as high as 80% have been obtained.