Rücktitelbild: The Mo?Mo Quintuple Bond as a Ligand to Stabilize Transition‐Metal Complexes (Angew. Chem. 31/2015)

Herein, we report the employment of the Mo Mo quintuple bonded amidinate complex to stabilize Group 10 metal fragments {(Et₃P)₂M} (M=Pd, Pt) and give rise to the isolation of the unprecedented δ complexes. X‐ray analysis unambiguously revealed short contacts between Pd or Pt and two Mo atoms and a slight elongation of the Mo Mo quintuple bond in these two compounds. Computational studies show donation of the Mo Mo quintuple‐bond δ electrons to an empty σ orbital on Pd or Pt, and back‐donation from a filled Pd or Pt d_π orbital into the Mo Mo δ* level (LUMO), consistent with the Dewar–Chatt–Duncanson model.     

The MoMo Quintuple Bond as a Ligand to Stabilize Transition‐Metal Complexes

Herein, we report the employment of the Mo? Mo quintuple bonded amidinate complex to stabilize Group 10 metal fragments {(Et₃P)₂M} (M=Pd, Pt) and give rise to the isolation of the unprecedented δ complexes. X‐ray analysis unambiguously revealed short contacts between Pd or Pt and two Mo atoms and a slight elongation of the Mo? Mo quintuple bond in these two compounds. Computational studies show donation of the Mo? Mo quintuple‐bond δ electrons to an empty σ orbital on Pd or Pt, and back‐donation from a filled Pd or Pt d_π orbital into the Mo? Mo δ* level (LUMO), consistent with the Dewar–Chatt–Duncanson model.     

Synthesis, structures, and properties of group 9- and group 10-group 6 heterodinuclear nitrosyl complexes

The reaction of the group 9 bis(hydrosulfido) complexes [Cp*M(SH)2(PMe3)] (M=Rh, Ir; Cp*=eta(5)-C 5Me5) with the group 6 nitrosyl complexes [Cp*M'Cl2(NO)] (M'=Mo, W) in the presence of NEt3 affords a series of bis(sulfido)-bridged early-late heterobimetallic (ELHB) complexes [Cp*M(PMe3)(mu-S)2M'(NO)Cp*] (2a, M=Rh, M'=Mo; 2b, M=Rh, M'=W; 3a, M=Ir, M'=Mo; 3b, M=Ir, M'=W). Similar reactions of the group 10 bis(hydrosulfido) complexes [M(SH)2(dppe)] (M=Pd, Pt; dppe=Ph 2P(CH2) 2PPh2), [Pt(SH)2(dppp)] (dppp=Ph2P(CH2) 3PPh2), and [M(SH)2(dpmb)] (dpmb=o-C6H4(CH2PPh2)2) give the group 10-group 6 ELHB complexes [(dppe)M(mu-S)2M'(NO)Cp*] (M=Pd, Pt; M'=Mo, W), [(dppp)Pt(mu-S)2M'(NO)Cp*] (6a, M'=Mo; 6b, M'=W), and [(dpmb)M(mu-S)2M'(NO)Cp*] (M=Pd, Pt; M'=Mo, W), respectively. Cyclic voltammetric measurements reveal that these ELHB complexes undergo reversible one-electron oxidation at the group 6 metal center, which is consistent with isolation of the single-electron oxidation products [Cp*M(PMe3)(mu-S)2M'(NO)Cp*][PF6] (M=Rh, Ir; M'=Mo, W). Upon treatment of 2b and 3b with ROTf (R=Me, Et; OTf=OSO 2CF 3), the O atom of the terminal nitrosyl ligand is readily alkylated to form the alkoxyimido complexes such as [Cp*Rh(PMe3)(mu-S)2W(NOMe)Cp*][OTf]. In contrast, methylation of the Rh-, Ir-, and Pt-Mo complexes 2a, 3a, and 6a results in S-methylation, giving the methanethiolato complexes [Cp*M(PMe3)(mu-SMe)(mu-S)Mo(NO)Cp*][BPh 4] (M=Rh, Ir) and [(dppp)Pt(mu-SMe)(mu-S)Mo(NO)Cp*][OTf], respectively. The Pt-W complex 6b undergoes either S- or O-methylation to form a mixture of [(dppp)Pt(mu-SMe)(mu-S)W(NO)Cp*][OTf] and [(dppp)Pt(mu-S) 2W(NOMe)Cp*][OTf]. These observations indicate that O-alkylation and one-electron oxidation of the dinuclear nitrosyl complexes are facilitated by a common effect, i.e., donation of electrons from the group 9 or 10 metal center, where the group 9 metals behave as the more effective electron donor.     

Metal "capture" by a heterotrimetalloligand, heterometallic d(10)-d(10) interactions, and unexpected iron-to-platinum silyl ligand migration: a combined experimental and theoretical study

The heterotrinuclear chain complex Hg[Fe{Si(OMe)(3)}(CO)(3)(dppm-P)](2) (dppm = Ph(2)PCH(2)PPh(2)) 1 which has a transoid arrangement of the phosphine donors was used as a versatile chelating metallodiphosphine ligand owing to the easy rotation of its metal core about the Fe-Hg sigma-bonds. Its reaction with the labile Pt(0) olefin complex [Pt(C(7)H(10))(3)] yielded [HgPt{Si(OMe)(3)}Fe(2)(CO)(6){Si(OMe)(3)}(mu-dppm)(2)] 5 which resulted, after coordination of the dangling phosphine donors to Pt, from an unprecedented intramolecular rearrangement involving a very rare example of silyl ligand migration between two different metal centers, and the first one in metal cluster chemistry. The major structural differences observed between the heterometallic complexes obtained from 1 and d(10) Cu(I), Pd(0), or Pt(0) precursors have been established by X-ray diffraction. The bonding situation in the silyl migrated Pt complex 5 was analyzed and compared to those in the isoelectronic, but structurally distinct complexes obtained from Cu(I) and Pd(0) precursors, [Hg{Fe[Si(OMe)(3)](CO)(3)(mu-dppm)}(2)Cu](+) (2) and [Hg{Fe[Si(OMe)(3)](CO)(3)(mu-dppm)}(2)Pd] (4), respectively, by means of extended Hückel interaction diagrams. DFT calculations then allowed the energy minima associated with the three structures to be compared for 2, 4, and 5. All three minima are in close competition for the Pd complex 4, but silyl migration is favored by approximately 10 kcal mol(-)(1) for 5, mainly due to the more electronegative character of Pt with respect to Pd.     

The Critical Role Played by the Catalytic Moiety in the Early‐Time Photodynamics of Hydrogen‐Generating Bimetallic Photocatalysts

The effect of the catalytic moiety on the early‐time photodynamics of Ru/M (M=Pt or Pd) bimetallic photocatalysts is studied by ultrafast transient absorption spectroscopy. In comparison to the Ru/Pd photocatalyst described earlier, the Ru/Pt analogue shows complex excited‐state dynamics with three distinct kinetic components ranging from sub‐ps to 10² ps, requiring a more sophisticated photophysical model than that developed earlier for the Ru/Pd complex. In the Pu/Pt photocatalyst, an additional lower‐lying excited state is proposed to quench the hot higher‐lying triplet metal‐to‐ligand charge‐transfer states. Furthermore, a strong excitation wavelength dependence on the population of excited states is observed for both the Ru/Pt and Ru/Pd complexes, indicating a non‐equilibrated distribution even on the 10² ps timescale. These insights shed light on the significant impact of the catalytic moiety on the fundamental early‐time photophysics of Ru‐based photocatalysts.     

Design and self-assembly of ditopic and tetratopic cavitand complexes

The self-assembly of open ditopic and tetratopic cavitand complexes has been investigated by using monofunctionalized cavitand ligands and suitable metal precursors. In the case of ditopic complexes, self-assembly protocols, leading exclusively to the formation of both thermodynamically stable cis-Pt square-planar complexes 8 and 9 and the kinetically inert fac-Re octahedral complex 14, have been elaborated. The use of cis-[Pt(CH3)CN)2Cl2] as metal precursor led to the formation of monotopic trans-10 and ditopic trans-11 cavitand complexes, while cis-[Pt(dmso)2Cl2] afforded both cis-13 and trans-11 isomers. The self-assembly of tetratopic cavitand complexes has been achieved by using mononuclear [Pd(CH3CN)4(BF4)2] and dinuclear [M2(tppb)(OTf)4] (19: M = Pt; 20: M = Pd) metal precursors. Only the tetratopic dinuclear complexes 21 and 22 were stable. The ligand configuration with two phosphorus and two cavitand ligands at the metal centers is the most appropriate to build tetratopic cavitand complexes with sufficient kinetic stability.     

Exceptionally small colloidal zeolites templated by Pd and Pt amines

Monomodal colloidal suspensions containing EDI-type zeolite nanocrystals with sizes below 20 nm were prepared via a palladium and platinum amine templating approach. The role of the metal complexes in zeolite crystallization is elucidated using spectroscopic and microscopic characterization techniques in a series of samples containing pure Pd, Pt, and Cu amine complexes as well as mixtures of two compounds. The crystallization process of colloidal zeolites in precursor suspensions containing both [Pd(NH3)4]2+ and [Pt(NH3)4]2+ proceeds faster than in [Cu(NH3)4]2+ systems. The Pd and Pt complexes lead to a faster and enhanced nucleation rate in the precursor aluminosilicate suspensions in comparison to the copper amine complex. The latter explains both the smaller particle size and the higher monodispersity in the samples templated by Pd and Pt as compared to pure Cu-containing samples. Precursor systems containing mixed metal templates were used to control further the particle size and degree of metal loadings in the colloidal molecular sieves.     

Electronic structure and ionization energies of palladium and platinum N-heterocyclic carbene complexes

Density functional methods have been used to calculate the geometries, electronic structure and ionization energies (IE) of N-heterocyclic carbene complexes of palladium and platinum, [M(CN2R2C2H2)2](M = Pd, Pt; R = H, Me, Bu t). Agreement with X-ray structures (R = Bu t) was good. Calculated IE agreed well with the photoelectron (PE) spectra (R = Bu t); metal bands were calculated to be within 0.25 eV of the experimental values, whereas the higher lying ligand bands deviated by up to 0.9 eV. Spin-orbit methods were needed to achieve this level of agreement for the Pt complex, but the calculations were found to underestimate the spin-orbit splitting somewhat. The principal metal-ligand bonding is between the carbene lone pair HOMO and a (d(z2)+ s) hybrid on the metal. The metal p(z) orbital contributes very little to the bonding. The metal d(xz,yz) orbitals mix primarily with the filled pi3 orbitals on the ligands and secondarily with the empty pi5 orbitals. Consequently they are little stabilized in comparison to the metal d(xy,x2- y2) orbitals, which are non-bonding in the complex. The first PE band for both the Pd and Pt complexes is from ionization of a (s - d(z2)) hybrid orbital. The IE is greater for Pt than for Pd on account of the post-lanthanide relativistic stabilization of the Pt 6s orbital.     

Pd, Pt, and Ru complexes of a pincer bis(amino)amide ligand

An improved synthesis of pincer ligand bis[(2-dimethylamino)phenyl]amine ((Me)N(2)NH) was reported. Reaction of the Li complex of (Me)N(2)N with suitable Pd, Pt, and Ru precursors gave the corresponding metal complexes. The structures of the Pd, Pt, and Ru complexes were determined. The Ru complex showed activity in catalytic transfer hydrogenation of aryl and alkyl ketones.     

On the prospects of polynuclear complexes with acetylenedithiolate bridging units

The generation of polynuclear complexes with one, two, or four acetylenedithiolate bridging units via the isolation of eta2-alkyne complexes of acetylenedithiolate K[Tp'M(CO)(L)(C2S2)] (Tp'=hydrotris(3,5-dimethylpyrazolyl)borate, M=W, L=CO (K-3a), M=Mo, L=CNC6H3Me2 (K-3b)) is reported. The strong electronic cooperation of Ru and W in the heterobimetallic complexes [(eta5-C5H5)(PPh3)Ru(3a)] (4a) and [(eta5-C5H5)(Me2C6H3NC)Ru(3a)] (4b) has been elucidated by correlation of the NMR, IR, UV-vis, and EPR-spectroscopic properties of the redox couples 4a/4a+ and 4b/4b+ with results from density functional calculations. Treatment of M(II) (M=Ni, Pd, Pt) with K-3a and K-3b afforded the homoleptic bis complexes [M(3a)2] (M=Ni (5a), Pd (5b), Pt (5c)), and [M(3b)2] (M=Pd (6a) and Pt (6b)), in which the metalla-acetylendithiolates exclusively serve as S,S'-chelate ligands. The vibrational and electronic spectra as well as the cyclic voltammetry behavior of all the complexes are compared. The structural analogy of 5a/5b/5c and 6a/6b with dithiolene complexes is only partly reflected in the electronic structures. The very intense visible absorptions involve essential d orbital contributions of the central metal, while the redox activity is primarily attributed to the alkyne complex moiety. Accordingly, stoichiometric reduction of 5a/5b/5c yields paramagnetic complex anions with electron-rich alkyne complex moieties being indistinguishable in the IR time scale. K-3a forms with Cu(I) the octanuclear cluster [Cu(3a)]4 (7) exhibiting a Cu4(S2C2)4W4 core. The nonchelating bridging mode of the metalla-acetylenedithiolate 3a- in 7 is recognized by a high-field shift of the alkyne carbon atoms in the 13C NMR spectrum. X-ray diffraction studies of K[Tp'(CO)(Me3CNC)Mo(eta2-C2S2)] (K-3c), 4b, 6a, 6b, and 7 are included. Comparison of the molecular structures of K-3c and 7 on the one hand with 4b and 6a/6b on the other reveals that the small bend-back angles in the latter are a direct consequence of the chelate ring formation.     

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.     

Influence of metal and ligand types on stacking interactions of phenyl rings with square-planar transition metal complexes

In order to find out whether metal type influences the stacking interactions of phenyl rings in square-planar complexes, geometrical parameters for Cu, Ni, Pd and Pt complexes, with and without chelate rings, were analyzed and compared. By searching the Cambridge Structural Database, 220 structures with Cu complexes, 211 with Ni complexes, 285 with Pd complexes, and 220 with Pt complexes were found. The results show that the chelate ring has a tendency to make the stacking interaction with the phenyl ring independent of metal type in the chelate ring. However, there are some differences among metals for complexes without a chelate ring. There are a number of structures containing Pd and Pt complexes, without chelate rings, that have short carbon-metal distances and parallel orientations of the phenyl ring with respect to the coordination plane. It was found that some of these complexes have a common fragment, CN, as a part of the ligands. This indicates that the CN supports stacking interactions of square planar complexes with the phenyl ring.      

Control of Metal Arrays Based on Heterometallics Masquerading in Heterochiral Aggregations of Chiral Clothespin‐Shaped Complexes

Heterometal arrays in molecular aggregations were obtained by the spontaneous and ultrasound‐induced gelation of organic liquids containing the chiral, clothespin‐shaped trans‐bis(salicylaldiminato) d₈ transition‐metal complexes 1 . Heterometallic mixtures of complexes 1 a (Pd) and 1 b (Pt) underwent strict heterochiral aggregation entirely due to the organic shell structure of the clothespin shape, with no effect of the metal cores. This phenomenon provides an unprecedented means of generating highly controlled heterometallic arrangements such as alternating sequences [(+)‐Pd(?)‐Pt(+)‐Pd(?)‐Pt ??? ] as well as a variety of single metal‐enriched arrays (e.g., [(+)‐Pt(?)‐Pd(+)‐Pd(?)‐Pd(+)‐Pd(?)‐Pd ??? ] and [(+)‐Pd(?)‐Pt(+)‐Pt(?)‐Pt(+)‐Pt(?)‐Pt ??? ]) upon the introduction of an optically active masquerading unit with a different metal core in the heterochiral single‐metal sequence. The present method can be applied to form various new aggregates with optically active Pd and Pt units, to allow 1) tuning of the gelation ultrasound sensitivity based on the different hearing abilities of the metal units; 2) aggregation‐induced chirality transfer between heterometallic species; and 3) aggregation‐induced chirality enhancement. A mechanistic rationale is proposed for these molecular aggregations based on the molecular structures of the units and the morphologies of the aggregates.     

Synthesis and characterization of Ni(II), Pd(II) and Pt(II) complexes of 2,4-diamino-5-(3, 4, 5-trimethoxybenzyl)pyrimidine complexes

The Ni(II), Pd(II) and Pt(II) complexes of 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine (trimethoprim) have been synthesized and characterized by elemental analysis, electronic and IR spectroscopy, and magnetic susceptibility measurements. The single-crystal X-ray structure of the Ni(II) complex is reported. Ni(II) is coordinated to the N(1) atoms of two trimethoprim molecules that act as monodentates. Octahedral coordination around the nickel atom is completed by coordination to two molecules of methanol and two acetate ions. Pd(II) and Pt(II) complexes are square planar and the metal ions coordinate one molecule of trimethoprim, two chloride ions and a molecule of water.     

New discrete metallocycles incorporating palladium(II) and platinum(II) corners and dipyridyldibenzotetraaza[14]annulene side units

The interaction of the extended, fully-conjugated macrocycle, dipyridyldibenzotetraaza[14]annulene (1), with the square planar palladium(II) and platinum(II) complexes [M(dppp)(triflate)(2)].2H(2)O (M = Pd, Pt) has been investigated in both solution and the solid state. In each case solid products showing a 1:1 ratio of metal complex: 1 were obtained. A 1:1 mixture of and [Pd(dppp)(2)(triflate)(2)].2H(2)O in dichloromethane yielded two major products as evidenced by the presence of two singlets in the (31)P {(1)H}-NMR spectrum of the reaction solution. Similarly, two singlets were evident in the corresponding spectrum obtained on dissolving the 1:1 product in nitrobenzene. The temperature and concentration dependence of the spectra clearly showed that the two species present in each case were in equilibrium. From the temperature dependence, the low field signal was assigned to the smaller of the two species. Broadly parallel behaviour was observed for the corresponding platinum-containing system. The MS-ESI spectrum of the platinum derivative showed the presence of a dinuclear species corresponding to [Pt(dppp)(1)](2)(2+) and an X-ray structure of this product confirmed that a corresponding dinuclear complex exists in the solid state. This product has a geometry in which two curved macrocyclic side units bridge two metal centres to yield an ellipse-shaped structure. Attempts to employ pulsed-field gradient spin-echo (PGSE) (31)P NMR confirmed that the lower-field resonance corresponded to the smaller of the two species in solution. STM (HOPG) imaging of the palladium- and platinum-containing products revealed arrays that appear to be composed of "zipper-like" rows of dimer units, with the dimensions of the latter comparing well with those found in the X-ray structure of [Pt(dppp)(1)](2)(2+).     

Chelating or bridging Pd(II) and Pt(II) metalloligands from the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine. New heterometallic Pd(II)/Pt(II) and Pt(II)/Au(I) complexes

The reaction of two equivalents of the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine Ph2PNHC=NNCHS (2) with [PdCl2(NCPh)2] in the presence of NEt3 gives the neutral, P,N-chelated complex cis-[Pd(Ph2PN=CNN=CHS)2] ([Pd(2-H)2], 3b), which is analogous to the Pt(II) analogue cis-[Pt (Ph2PN=CNN=CHS)2] ([Pt(2-H)2], 3a) reported previously. These complexes function as chelating metalloligands when further coordinated to a metal through each of the CH-N atoms. In the resulting complexes, each endo-cyclic N donor of the thiadiazole rings is bonded to a different metal centre. Thus, the heterodinuclear palladium/platinum complexes cis-[Pt(Ph2PN=CNN=CHS)2PdCl2]([Pt(2-H)2·PdCl2], 4a) and cis-[Pd(Ph2PN=CNN=CHS)2PtCl2]([Pd(2-H)2·PtCl2], 4b) were obtained by reaction with [PdCl2(NCPh)2] and [PtCl2(NCPh)2], respectively. In contrast, reaction of 3a with [AuCl(tht)] occurred instead at the P-bound N atom, and afforded the platinum/digold complex cis-[Pt{Ph2PN(AuCl)=CNN=CHS}2] ([Pt(2-H)2(AuCl)2], 5). For comparison, reaction of 4a with HBF4 yielded cis-[Pt(Ph2PNH=CNN=CHS)2PdCl2](BF4)2([H24a](BF4)2, 6), in which the chelated PdCl2 moiety is retained. Complexes 3b, 4a·CH2Cl2, 4b·0.5C7H8, 5·4CHCl3 and 6 have been structurally characterized by X-ray diffraction.     

Influence of Metallic Modification on Ethylbenzene Dealkylation over ZSM‐5 Zeolites

A series of metal‐modified HZSM‐5 catalysts were prepared by impregnation and were used for ethylbenzene dealkylation of the mixed C8 aromatics (ethylbenzene, m‐xylene and o‐xylene). The effects of different supported metals (Pt, Pd, Ni, Mo) on catalytic performance, including reaction conditions, were investigated. The physicochemical properties of catalysts were characterized by means of XRD, BET, TEM and NH₃‐TPD. Experimental results showed that metallic modification obviously increased the ethylbenzene conversion and reduced the coke deposition, greatly improving the catalyst stability. The distinction of ethylbenzene conversion depended on the interaction between hydrogenation reactivity and acidic cracking of bifunctional metal‐modified zeolites. Compared with Pt and Ni, Pd and Mo were easier to disperse into HZSM‐5 micropores during loading metals. The acidic density of different metal‐modified HZSM‐5 declined in the following order: HZSM‐5>Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. The activity of ethylene hydrogenation decreased with Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. In comparison, Pd/HZSM‐5 showed the best catalytic performance with both high activity and high selectivity, with less cracking loss of m‐xylene and o‐xylene. Moreover, the following reaction conditions were found to be preferable for ethylbenzene dealkylation over Pd/HZSM‐5: 340°C, 1.5 MPa H₂, WHSV 4 h^?1, H₂/C8 4 mol/mol.     

Synthesis and characterisation of triselenocarbonate [CSe3]2- complexes

[Pt(CSe3)(PR3)2] (PR3= PMe3, PMe2Ph, PPh3, P(p-tol)3, 1/2 dppp, 1/2 dppf) were all obtained by the reaction of the appropriate metal halide containing complex with carbon diselenide in liquid ammonia. Similar reaction with [Pt(Cl)2(dppe)] gave a mixture of triselenocarbonate and perselenocarbonate complexes. [{Pt(mu-CSe3)(PEt3)}4] was formed when the analogous procedure was carried out using [Pt(Cl)2(PEt3)2]. Further reaction of [Pt(CSe3)(PMe2Ph)2] with [M(CO)6] (M = Cr, W, Mo) yielded bimetallic species of the type [Pt(PMe2Ph)2(CSe3)M(CO)5] (M = Cr, W, Mo). The dimeric triselenocarbonate complexes [M{(CSe3)(eta5-C5Me5)}2] (M = Rh, Ir) and [{M(CSe3)(eta6-p-MeC6H4(i)Pr)}2] (M = Ru, Os) have been synthesised from the appropriate transition metal dimer starting material. The triselenocarbonate ligand is Se,Se' bidentate in the monomeric complexes. In the tetrameric structure the exocyclic selenium atoms link the four platinum centres together.     

Preparation of colloidal solutions of noble metals stabilized by polyoxometalates and supported catalysts based on these solutions

Conditions for the preparation of stable aqueous monometallic and bimetallic colloidal solutions (sols) of noble metals (Ru, Rh, Pd, Pt, Ir, Ag, and Au) in the presence of polyoxometalates containing W, Mo, V, and Nb were found. The stability of sols against coagulation at room temperature was studied. The metal/C samples prepared by metal adsorption from sols were studied by powder X-ray diffraction analysis and transmission electron microscopy. The following factors of importance for the preparation of a stable sol are discussed: (1) the formation of a sol of a metal polyhydroxo complex stabilized by a polyoxometalate (preliminary stage) and (2) the formation of polyoxometalate-metal clusters in the course of reduction of polyhydroxo complexes.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 921–929.Original Russian Text Copyright © 2004 by Maksimova, Chuvilin, Moroz, Likholobov, Matveev.     

Symmetrical and unsymmetrical pincer complexes with group 10 metals: synthesis via aryl C-H activation and some catalytic applications

Aryl-based pincer metal complexes with anionic terdentate ligands have been widely applied in organic synthesis, organometallic catalysis and other related areas. Synthetically, the most simple and convenient method for the construction of these complexes is the direct metal-induced C(aryl)-H bond activation, which can be fulfilled by choosing the appropriate functional donor groups in the two side arms of the aryl-based pincer preligands. In this perspective, we wish to summarize some results achieved by our group in this context. Successful examples include symmetrical chiral bis(imidazoline) NCN pincer complexes with Ni(II), Pd(II) and Pt(II), bis(phosphinite) and bis(phosphoramidite) PCP pincer Pd(II) complexes, unsymmetrical (pyrazolyl)phosphinite, (amino)phosphinite and (imino)phosphinite PCN pincer Pd(II) complexes, chiral (imidazolinyl)phosphinite and (imidazolinyl)phosphoramidite PCN pincer complexes with Ni(II) and Pd(II) as well as unsymmetrical (oxazolinyl)amine and (oxazolinyl)pyrazole NCN' pincer Pd(II) complexes. Among them, the P-donor containing complexes are efficiently synthesized by the "one-pot phosphorylation/metalation" method. The obtained symmetrical and unsymmetrical pincer complexes have been used as catalysts in Suzuki-Miyaura reaction (Pd), asymmetric Friedel-Crafts alkylation of indole with trans-β-nitrostyrene (Pt) as well as in asymmetric allylation of aldehyde and sulfonimine (Pd). In the Suzuki couplings conducted at 40-50 °C, some unsymmetrical Pd complexes exhibit much higher activity than the related symmetrical ones which can be attributed to their faster release of active Pd(0) species resulting from the hemilabile coordination of the ligands. Literature results on the synthesis of some related pincer complexes as well as their activities in the above catalytic reactions are also presented.