Highly efficient syntheses of [methyl-11C]thymidine and its analogue 4'-[methyl-11C]thiothymidine as nucleoside PET probes for cancer cell proliferation by Pd(0)-mediated rapid C-[11C]methylation

Pd(0)-mediated rapid couplings of CH(3)I (and then [(11)C]CH(3)I) with excess 5-tributylstannyl-2'-deoxyuridine and -4'-thio-2'-deoxyuridine were investigated for the syntheses of [methyl-(11)C]thymidine and its stable analogue, 4'-[methyl-(11)C]thiothymidine as PET probes for cancer diagnosis. The previously reported conditions were attempted using Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3) (1?:?4 in molar ratio) at 130 °C for 5 min in DMF, giving desired products only in 32 and 30% yields. Therefore, we adapted the current reaction conditions developed in our laboratory for heteroaromatic compounds. The reaction using CH(3)I/stannane/Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3)/CuCl/K(2)CO(3) (1?:?25?:?1?:?32?:?2?:?5) at 80 °C gave thymidine in 85% yield. Whereas, CH(3)I/stannane/Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3)/CuBr/CsF (1?:?25?:?1?:?32?:?2?:?5) including another CuBr/CsF system promoted the reaction at a milder temperature (60 °C), giving thymidine in 100% yield. Chemo-response of thiothymidine-precursor was different from thymidine system. Thus, the above optimized conditions including CuBr/CsF system gave 4'-thiothymidine only in 40% yield. The reaction using 5-fold amount of CuBr/CsF at 80 °C gave much higher yield (83%), but unexpectedly, the reaction was accompanied by a considerable amount of undesired destannylated product. Such destannylation was greatly suppressed by changing to a CuCl/K(2)CO(3) system using CH(3)I/stannane/Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3)/CuCl/K(2)CO(3) (1?:?25?:?1?:?32?:?2?:?5) at 80 °C, giving the 4'-thiothymidine in 98% yield. The each optimized conditions were successfully applied to the syntheses of the corresponding PET probes in 87 and 93% HPLC analytical yields. [(11)C]Compounds were isolated by preparative HPLC after the reaction conducted under slightly improved conditions, exhibiting sufficient radioactivity of 3.7-3.8 GBq and specific radioactivity of 89-200 GBq μmol(-1) with radiochemical purity of ≥99.5% for animal and human PET studies.     

Pd0‐Mediated Rapid Coupling between Methyl Iodide and Heteroarylstannanes: An Efficient and General Method for the Incorporation of a Positron‐Emitting 11C Radionuclide into Heteroaromatic Frameworks

The Pd⁰‐mediated rapid trapping of methyl iodide with an excess amount of a heteroaryl‐substituted tributylstannane has been investigated with the aim of incorporating a short‐lived ¹¹C‐labelled methyl group into the heteroaromatic carbon frameworks of important organic compounds, such as drugs with various heteroaromatic structures, in order to execute a positron emission tomography (PET) study of vital systems. The reaction was first performed by using our previously developed CH₃I/stannane/[Pd₂(dba)₃]/P(o‐CH₃C₆H₄)₃/CuCl/K₂CO₃ (1:40:0.5:2:2:2) system in DMF at 60 °C for 5 min (conditions A), however, the reaction gave low yields for various heteroaromatic compounds. Increasing the amount of phosphine ligand (conditions B) led to a significant improvement in the yield, but the conditions were still not suitable for a range of basic heteroaromatic structures. Use of the CuBr/CsF system (conditions C) also provided a result similar to that obtained under conditions B with an increased amount of the phosphine. Thus, pyridine and related heteroaromatic compounds remained less reactive substrates. The problem was overcome by replacing the DMF solvent with N‐methyl‐2‐pyrolidinone (NMP). The reaction in NMP at 60–100 °C for 5 min using a CH₃I/stannane/[Pd₂(dba)₃]/P(o‐CH₃C₆H₄)₃/CuBr/CsF (1:40:0.5:16:2:5) combination (conditions D) gave the methylated products in yields of more than 80 % (based on the reaction of CH₃I) for all of the heteroaromatic compounds listed in this study. Thus, the combined use of NMP and an increased amount of phosphine is important for promoting the reaction efficiently. The use of this general approach to rapid methylation has been well demonstrated by the synthesis of the PET tracers 2‐ and 3‐[¹¹C]methylpyridines by using [Pd₂(dba)₃]/P(o‐CH₃C₆H₄)₃/CuBr/CsF (1:16:2:5) in NMP at 60 °C for 5 min, which gives the desired products in HPLC analytical yields of 88 and 91 %, respectively.     

N,N-Dialkyl-2-iodoanilines: a versatile source for the synthesis of Pd(ii) complexes. Synthesis of novel OCP- and CCN-pincer palladium complexes

The reactivity of a series of N,N-dimethyl-2-iodoanilines bearing different chelating "arms" at the 3-position with Pd(2)(dba)(3) has been explored. 3-[(Diphenylphosphino)methyl]-2-iodo-N,N-dimethylaniline reacted with Pd(2)(dba)(3) and PPh(3) under aerobic conditions to give the OCP-pincer complex , which was formed by sequential C(sp(3))-H activation/oxidation at the alpha-position of the aniline N atom. On the other hand, under similar reaction conditions, 3-[2-(dimethylamino)ethyl]-2-iodo-N,N-dimethylaniline afforded the CCN-pincer complex , after a second C-H activation process at the formyl group of the initially formed OCN-pincer complex. In contrast, 2-iodo-3-(1H-1,2,4-triazol-1-ylmethyl)-N,N-dimethylaniline and 2-iodo-3-(pyrazol-1-ylmethyl)-N,N-dimethylaniline reacted with Pd(2)(dba)(3) and PPh(3), respectively, to give the 6-membered azapalladacycles and , in which the aniline nitrogen is merely a spectator substituent. Finally, treatment of iodide complex with Tl(TfO) afforded the CN-bidentate cationic complex. Solid-state structures of palladium complexes, and CH(2)Cl(2).3CH(3)OH.5H(2)O were determined by X-ray analysis.     

Unusual palladium-catalyzed silaboration of allenes using organic iodides as initiators: mechanism and application

A highly regio- and stereoselective method for the synthesis of various 2-silylallylboronates 7 from allenes 1 and 2-(dimethylphenylsilanyl)-4,4,5,5-tetramethyl[1,3,2]dioxaborolane (5) catalyzed by palladium complexes and initiated by organic iodides is described. Treatment of monosubstituted aryl and alkylallenes RCH=C=CH(2) (1a-m) and 1,1-dimethylallene (1n) with borylsilane 5 in the presence of Pd(dba)(2) (5 mol %) and organic iodide 3a (10 mol %) afforded the corresponding silaboration products 7a-n in moderate to excellent yields. This catalytic silaboration is totally regioselective with the silyl group of 5adding to the central carbon and the boryl group to the unsubstituted terminal carbon of allene. Furthermore, the reactions show very high E stereoselectivity with the Z/E ratios lying in the range from 1/99 to 7/93. In the absence of an organic iodide, silaboration of 1 with 5 still proceeds, but gives products having completely different regiochemistry as that of 7. The silaboration chemistry can be applied to the synthesis of homoallylic alcohols. Treatment of allenes (1) with borylsilane 5 and aldehydes 14 in the presence of Pd(dba)(2) (5 mol %) and 3a (10 mol %) at 80 degrees C in ethyl acetate for 5 h afforded homoallylic alcohols 15a-p in one pot in good to excellent yields, with exceedingly high syn selectivity (>93%). Mechanistic pathways involving an unusual palladium-catalyzed three-component assembling reaction of dimethylphenylsilyl iodide, allene 1, and borylsilane 5 were proposed to account for these catalytic reactions.     

A highly effective catalyst system for the Pd-catalyzed amination of vinyl bromides and chlorides

[reaction: see text] A highly efficient synthesis of enamines and imines by Pd-catalyzed amination of vinyl bromides or chlorides with amines is described using the Pd2(dba)3/P(i-BuNCH2CH2)3N catalyst system.     

Controlled Pd(0)/t-Bu(3)P-Catalyzed Suzuki Cross-Coupling Polymerization of AB-Type Monomers with PhPd(t-Bu(3)P)I or Pd(2)(dba)(3)/t-Bu(3)P/ArI as the Initiator

Controlled Pd(0)/t-Bu(3)P-catalyzed Suzuki cross-coupling polymerizations of AB-type monomers via the chain-growth mechanism with an ArPd(t-Bu(3)P)I complex as the initiator are described. ArPd(t-Bu(3)P)I complexes, either prepurified or generated in situ from Pd(2)(dba)(3)/t-Bu(3)P/ArI (dba = dibenzylideneacetone) without separation/purification, were found to be efficient initiators in general for the controlled Suzuki cross-coupling polymerization, with narrow polydispersity indexes (PDIs) of 1.13-1.35 being observed. The Pd(2)(dba)(3)/t-Bu(3)P/p-BrC(6)H(4)I combination was identified as a highly robust initiator system, with PDIs of ≤1.20 in general and as low as 1.13 being obtained. Higher number-average molecular weights (M(n)) were achieved without a significant increase in the PDI (from 1.14 for a polymer with a M(n) = 9500 to 1.20 for a polymer with M(n) = 31?400) by using a smaller amount of the Pd(2)(dba)(3)/t-Bu(3)P/p-BrC(6)H(4)I initiator in the polymerization.     

Scope and limitations of Pd2(dba)3/P(i-BuNCH2CH2)3N-catalyzed Buchwald-Hartwig amination reactions of aryl chlorides

Proazaphosphatrane ligands in combination with Pd(2)(dba)(3) generate highly active catalysts for Buchwald-Hartwig amination of aryl chlorides. In particular, commercially available P(i-BuNCH(2)CH(2))(3)N is a highly general and efficient ligand, allowing the coupling of an electronically diverse set of aryl chlorides, including chloropyridines, with a wide variety of amines using 1 mol % of Pd at 100 degrees C. Either a 1:1 or 2:1 ratio of ligand to Pd was found to be effective. This catalyst system performs exceptionally well for sterically hindered substrates, even with only 0.25 mol % of Pd. It is shown that NaOH can also be used as the base (instead of NaO-t-Bu) allowing functionalized substrates to participate in these reactions.     

Direct observation of reductive elimination of methyl iodide from a rhodium(III) pincer complex: the importance of sterics

A rare case of directly observed alkyl halide reductive elimination from rhodium is reported. Treatment of the naphthyl-based PCP-type Rh(III) methyl complexes 2a,b [(C10H5(CH2PR2)2)Rh(CH3)(I)] (R = iPr 2a, R = tBu 2b) with CO resulted in facile reductive elimination of methyl iodide in the case of 2b, yielding the Rh(I) carbonyl complex [(C10H5(CH2PR2)2)Rh(CO)] 3b (R = tBu), while the less bulky 2a formed CO adducts and did not undergo reductive elimination, contrary to expectations based on electron density considerations. Moreover, 3b oxidatively added methyl iodide, while 3a did not. CD3I/CH3I exchange studies in the absence of CO indicate that reversible formation of (ligated) methyl iodide takes place in both systems. Subsequently, when CO is present, it displaces methyl iodide in the bulkier tBu system, whereas with the iPr system formation of the Rh(III) CO adducts is favored. Iodide dissociation followed by its attack on the rhodium-methyl group is unlikely.     

Neutral molecular Pd6 hexagons using kappa3-P2O-terdentate ligands

The one-step synthesis of three new P2O-terdentate carboxylic acid ditertiary phosphines 2-{(Ph2PCH2)2N}-3-(X)C6H3CO2H (X = OCH3, L1; X = OH, L2) and 2-{(Ph2PCH2)2N}-5-(OH)C6H3CO2H (L3) by a phosphorus-based Mannich condensation reaction using Ph2PCH2OH and the appropriate amine in CH3OH is reported. Compounds L1-L3 function as typical kappa2-P2-didentate ligands upon complexation to Pd(CH3)Cl(cod) (cod = cycloocta-1,5-diene), affording the neutral, mononuclear complexes Pd(CH3)Cl(L1-L3) (1-3). Metathesis of 1 with NaX (X = Br, I) gave the corresponding (methyl)bromopalladium(II) (4) and (methyl)iodopalladium(II) (5) complexes, respectively. When chloroform or chloroform/methanol solutions of 1-3 (or 5) were allowed to stand, at ambient temperatures, yellow crystalline solids were isolated in very high yields (71-88%) and were analyzed for the novel hexameric palladium(II) compounds 6-9. All new compounds reported have been fully characterized by a combination of spectroscopic (multinuclear NMR, Fourier transform IR, electrospray mass spectrometry, matrix-assisted laser desorption ionization time-of-flight mass spectrometry) and analytical methods. The self-assembly reactions are remarkably clean as monitored by 31P{1H} and 1H NMR spectroscopy. Single-crystal X-ray structures have been determined for L1, 4, 7.17CDCl3.2Et2O, 8.6CHCl3.8CH3OH, and 9.17CDCl3. In hexamers 7-9, all six square-planar palladium(II) metal centers comprise a kappa2-P2-chelating diphosphine, a kappa1-O-monodentate carboxylate, and either a chloride or iodide ligand, leading to 48-membered metallomacrocycles (with outside diameters of ca. 2.5 nm). Whereas only intramolecular O-H...N hydrogen bonding between the hydroxy group and tertiary amine has been observed in 7, strong intermolecular O-H...O hydrogen bonding of the type CO...HO(CH3)...HO, involving a methanol solvate, has been found in 8, leading to an unprecedented three-dimensional network motif.     

Palladium-catalyzed cross-coupling of sterically demanding boronic acids with α-bromocarbonyl compounds

A catalyst system generated in situ from Pd(dba)(2) and tri(o-tolyl)phosphine mediates the coupling of arylboronic acids with alkyl α-bromoacetates under formation of arylacetic acid esters at unprecedented low loadings. The new protocol, which involves potassium fluoride as the base and catalytic amounts of benzyltriethylammonium bromide as a phase transfer catalyst, is uniquely effective for the synthesis of sterically demanding arylacetic acid derivatives.     

Catalytic C-phenylation of methyl acrylate with tetraphenylantimony(v) halides and carboxylates

Catalytic C-phenylation of methyl acrylate to methyl cinnamate with the Ph₄SbX complexes (X = F, Cl, Br, OH, OAc, O₂CEt) in the presence of the palladium compounds PdCl₂, Pd(OAc)₂, Pd₂(dba)₃, Pd(Ph₃P)₂Cl₂, and Pd(dppf)Cl₂ (dba is dibenzylideneacetone and dppf is bis(diphenylphosphinoferrocene)) was studied in organic solvents (MeCN, THF, DMF, MeOH, and AcOH). The highest yield of methyl cinnamate (73% based on the starting organometallic compound) was obtained for the Ph₄SbCl—PdCl₂ (1 : 0.04) system in acetonitrile.     

Palladium-catalyzed alpha-arylation of esters with chloroarenes

Palladium-catalyzed alpha-arylations of esters with chloroarenes are reported. The reactions of chloroarenes with the sodium enolates of tert-butyl propionate and methyl isobutyrate occur in high yields with 0.2-1 mol % of {[P(t-Bu)3]PdBr}2 or the combination of Pd(dba)2 and P(t-Bu)3 as catalyst. The reactions of chloroarenes with the Reformatsky reagent of tert-butyl acetate were most challenging but occurred in high yields for chlorobenzene and electron-poor chloroarenes catalyzed by 1 mol % of Pd(dba)2 and pentaphenylferrocenyl di-tert-butylphosphine (Q-phos).     

Formation of cyclic ethers via the palladium-catalyzed cycloaddition of activated olefins with allylic carbonates having a hydroxy group at the terminus of the carbon chain

The reaction of the activated olefins 1 with the allylic carbonate 2, having a hydroxy group at the terminus of the carbon chain, in the presence of catalytic amounts of Pd(2)dba(3).CHCl(3) and dppe in THF at room temperature gave the corresponding cycloaddition products, tetrahydrofuran derivatives 5, in good to very high yields. The diastereoselectivities (trans/cis ratios) of the products were in the range of ca. 60-70/40-30. The reaction of 1 with the hydroxy allylic carbonate 3 in the presence of catalytic amounts of Pd(2)dba(3).CHCl(3) and (o-tolyl)(3)P in THF at 50 degrees C afforded the corresponding cycloaddition products, tetrahydropyran derivatives 6, in good to high yields. The trans/cis ratios of the products were in the range of ca. 0-40/99-80. The reaction of 1a with the hydroxy allylic carbonate 4 needed higher reaction temperatures (approximately 100 degrees C) to give the cycloaddition product, the oxepane 7a, in 31% yield with low diastereoselectivity. Next, catalytic asymmetric syntheses of tetrahydrofuran and -pyran derivatives were carried out. With the Trost ligand 15, good to high ees were accomplished in the cycloaddition, although the diastereoselectivities were of low level. With the Hayashi ligand 16, good to high ees were also achieved in the cycloaddition. The absolute stereochemistries of the major enantiomers of 5l, 5m, and 6d were determined unambiguously by X-ray crystallographic analysis: trans-(2R,4R)-5l, cis-(2S,4R)-5l, 4R-5m, trans-(2S,4S)-6d, and cis-(2R,4S)-6d were major enantiomers. Based upon the absolute stereochemistries of the major enantiomers, the mechanism of catalytic asymmetric induction in the cycloaddition reaction is discussed.     

Ni(II), Pd(II) and Pt(II) complexes of PNP and PSP tridentate amino-phosphine ligands

The ligands D((CH(2))(2)NHPiPr(2))(2) (D = NH 1, S 2) react with (dme)NiCl(2) or (PhCN)(2)MCl(2) (M = Pd, Pt) to give complexes of the form [D((CH(2))(2)NHPiPr(2))(2)MX]X (X = Cl, I; M = Ni, Pd, Pt) which were converted to corresponding iodide derivatives by reaction with Me(3)SiI. Reaction of 1 or 2 with (COD)PdMeCl affords facile routes to [κ(3)P,N,P-NH((CH(2))(2)NHPiPr(2))(2)PdMe]Cl (8a) and [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)PdMe]Cl (9a) in high yields. An alternative synthetic approach involves oxidative addition of MeI to a M(0) precursor yielding [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)NiMe]I (10), [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MMe]I (M = Pd 8b Pt 11) and [κ(3)P,S,P-S(CH(2)CH(2)NHPiPr(2))(2)MMe]I (M = Pd 9b, Pt 12). Alternatively, use of NEt(3)HCl in place of MeI produces the species [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MH]X (X = Cl, M = Ni 13a, Pd 14a, Pt 16a). The analogs containing 2; [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)MH]X (M = Pd, X = PF(6)15: M = Pt, X = Br, 17a, PF(6)17b) were also prepared in yields ranging from 74-93%. In addition, aryl halide oxidative addition was also employed to prepare [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MC(6)H(4)F]Cl (M = Ni 18, Pd 19) and [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)Pd(C(6)H(4)F)]Cl (20). Crystal structures of 3a, 4a, 5a, 6a, 8a, 9a, 14b and 16b are reported.     

Suzuki-Miyaura coupling reaction using pentafluorophenylboronic acid

[reaction: see text] We have found new conditions for the Suzuki-Miyaura coupling reaction applicable to pentafluorophenylboronic acid (C(6)F(5)B(OH)(2)) (1), which is an inactive substrate under normal conditions. The reactions of 1 with phenyl iodide or bromide under Pd(PPh(3))(4)/CsF/Ag(2)O or Pd(2)(dba)(3)/P(t-Bu)(3)/CsF/Ag(2)O catalytic system conditions gave 2,3,4,5,6-pentafluoro-1,1'-biphenyl (3a) in more than 90% yields. Combination of CsF and Ag(2)O was essential for promoting these reactions.     

Synthesis of an unprecedented bicapped adamantoid [Cu6(mu2-I)(mu3-I)4(mu4-I)(m-tolyl3P)4(CH3CN)2] cluster

The reaction of copper(I) iodide with tri-m-tolylphosphine (m-tolyl(3)P) in acetonitrile yielded the cluster [Cu(6)(mu2-I)(mu3-I)4(mu4-I)(m-tolyl(3)P)4(CH(3)CN)2] (1), with a bicapped adamantoid geometry. In this compound, four Cu atoms are coordinated to four terminally bonded m-tolyl(3)P ligands, two Cu atoms are bonded to two CH(3)CN ligands, and iodide ligands have mu2-I, mu3-I, and mu4-I bonding modes. This compound has four CuI(3)P and two CuI(3)N cores, and geometry around each Cu center is distorted tetrahedral.The polarizable iodide ligand and the position of the methyl group in the phenyl ring attached to the P atom appear to have played the pivotal role in the formation of monomeric bicapped adamantoid geometry, which is unique in copper chemistry.     

蛋氨酸合成酶辅酶模型的合成及其催化反应的初步研究

生物体内的蛋氨酸合成酶(methioninesynthase)以N^5-甲基四氢叶酸作为辅酶,通过两步SN2反应,将甲基转移到高半胱氨酸的巯基上生成蛋氨酸。该酶起到中间甲基载体的功能。为了进一步研究甲基转移的机理,报道了作为活化的5-甲基四氢叶酸模型:碘化2-氨基-4-羟基-5,5,6-三甲基吡啶并[3,2-d]嘧啶的合成以及与模拟蛋氨酸合成酶[Co(I)(dmgH)~2Py]的反应。     

Palladium-catalyzed cross-coupling reactions of 2-indolyldimethylsilanols with substituted aryl halides

[reaction: see text] A mild and general cross-coupling reaction of 2-indolylsilanols has been developed. The experimental variables that lead to successful coupling are (1) the use of sodium tert-butoxide as the activator, (2) the use of copper(I) iodide in stoichiometric quantities, and (3) the use of Pd2(dba)3.CHCl3 as the catalyst. Under these conditions N-(Boc)-2-indolyldimethylsilanol reacts with a variety of aromatic iodides to afford the coupling products in good yield (70-84%).     

Self-assembly of D-penicillaminato M6M'8 (M = Ni(II), Pd(II), Pt(II); M' = Cu(I), Ag(I)) clusters and their organization into extended La(III)M6M'8 supramolecular structures

A series of chiral M(6)M'(8) cluster compounds having twelve free carboxylate groups, [M(6)M'(8)(D-pen-N,S)(12)X](5-) (M/M'/X = Pd(II)/Ag(I)/Cl(-) ([1](5-)), Pd(II)/Ag(I)/Br(-) ([2](5-)), Pd(II)/Ag(I)/I(-) ([3](5-)), Ni(II)/Ag(I)/Cl(-) ([4](5-)), Pt(II)/Ag(I)/Cl(-) ([5](5-)), Pd(II)/Cu(I)/Cl(-) ([6](5-)); D-H(2)pen = D-penicillamine), in which six cis-[M(D-pen-N,S)(2)](2-) square-planar units are bound to a [M'(8)X](7+) cubic core through sulfur-bridges, was synthesized by the reactions of cis-[M(D-pen-N,S)(2)](2-) with M' in water in the presence of halide ions. These M(6)M'(8) clusters readily reacted with La(3+) in aqueous buffer to form La(III)(2)M(6)M'(8) heterotrimetallic compounds, La(2)[1](CH(3)COO), La(2)[2](CH(3)COO), La(2)[3](CH(3)COO), La(2)[4](CH(3)COO), La(2)[5](CH(3)COO) and La(2)[6]Cl, in which the M(6)M'(8) cluster units are linked by La(3+) ions through carboxylate groups in a 1?:?2 ratio. While the La(III)(2)M(6)Ag(I)(8) compounds derived from [1](5-), [2](5-), [3](5-), [4](5-) and [5](5-) have a 1D helix supramolecular structure with a right-handedness, the La(III)(2)Pd(II)(6)Cu(I)(8) compound derived from [6](5-) has a 2D sheet-like structure with a triangular grid of the Pd(II)(6)Cu(I)(8) cluster units. When aqueous HCl was added to the reaction solution of [6](5-) and La(3+), another La(III)(2)Pd(II)(6)Cu(I)(8) heterotrimetallic compound, La(2)[6]Cl·HCl, in which the Pd(II)(6)Cu(I)(8) cluster units are linked by La(3+) ions to form a 2D structure with a rectangular grid, was produced. The solid-state structures of these La(III)(2)M(6)M'(8) compounds, determined by single-crystal X-ray crystallography, along with the spectroscopic properties of the M(6)M'(8) cluster compounds in solution, are described.     

Mixed-metal metallocryptands. Short metal-metal separations strengthened by a dipolar interaction

The deep-red, air-stable mixed-metal metallocryptands, [AuPdTl(P2phen)3](PF6)2, 1.(PF6)2, and [AuPtTl(P2phen)3](PF6)2, 2.(PF6)2, are easily prepared in good yield (60-70%) by reacting 3 equiv of P2phen with 1 equiv of Au(THT)Cl, excess thallous acetate, and the appropriate amount of either Pd2(dba)3 for 1 or Pt(dba)2 for 2 in acetonitrile where P2phen is 2,9-bis(diphenylphosphino)-1,10-phenanthroline, THT is tetrahydrothiophene, and dba is dibenzylidineacetone. Compared to the more symmetrical bimetallic metallocryptands, these trimetallic species show shorter than expected Au(I)-Tl(I), Pt(0)-Tl(I), and Pd(0)-Tl(I) separations. The enhanced bonding interaction is attributed to the incorporation of the dissimilar capping metals introducing dipole moments that strengthen the dispersion forces responsible for maintaining the metallophilic interactions.