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Ganguly, Rakesh/0000-0002-9523-6918; Dege, Necmi/0000-0003-0660-4721; Pathak, Devendra Deo/0000-0002-2097-4975 WOS: 000465289800002 Five new pincer type Ni(II)-Schiff base complexes of the general formula [NiL1(PPh3)] 1, [NiL2(PPh3)] 2, [NiL3(PPh3)] 3, [NiL4(PPh3)] 4 and [NiL4(4-MePy)] 5 [where H2L1 = 2-(2,3-dihydroxybenzylideneamino) phenol, H2L2 = N-(2,3-dihydroxybenzylidene) benzohydrazide, H2L3 = 2-(2,3-dihydroxybenzylidene) hydrazinecarbothioamide, H2L4 = 5-(diethylamino)-2-(2-hydroxybenzylideneamino) phenol, 4-MePy = 4-Methylpyridine] were synthesized by the reaction of the Ni(OAc)(2).4H(2)O with the corresponding Schiff base ligand in methanol as coloured crystalline solids in high yields. All the five complexes were fully characterized by FT-IR, UV-Vis, H-1 NMR, C-13{H-1} NMR, P-31{H-1} NMR, mass spectrometry and single crystal X-ray diffraction studies. The crystal structures of all five new complexes confirmed the tridentate nature of the pincer type Schiff base ligands (ONO and ONS) and distorted square planar geometry around the metal centre in all cases. The monodentate ligand (triphenylphosphine/4-Methylpyridine) occupied the fourth site at nickel. The catalytic potential of the complexes has been demonstrated in the synthesis of a series of 2- substituted benzimidazoles at room temperature using low catalyst loading (0.5 mol %), and without the use of any additives. All organic products were isolated in high yields (85-96%) and fully characterized by H-1 and C-13{H-1} NMR studies. (C) 2019 Elsevier B.V. All rights reserved. IIT (ISM) fellowship We are thankful to the CRF IIT (ISM), SAIF Panjab University, Chandigarh and IISER Bhopal for providing help in the analysis of the samples. Bhumika Agrahari and Samaresh Layek acknowledges the receipt of IIT (ISM) fellowship.

The Sonogashira reaction of 9-bromoanthracene and ethynyltrimethylsilane furnishes not only the anticipated 9-(trimethylsilylethynyl)anthracene and 2-(trimethylsilyl)aceanthrylene but also (E)-4-(9-anthracenyl)-1,3-bis(trimethylsilyl)-but-3-en-1-yne, all in moderate yields. A mechanistic rationale is proposed that invokes the intermediacy of bromo(anthracenyl)bis(triphenylphosphine)palladium(II) that can undergo coupling either directly, or after coordination and migratory insertion of the free alkyne.

The reactions of 3,4-bis(dimethylsilyl)thiophene (1) and 2,3,4,5-tetrakis(dimethylsilyl)thiophene (17) with alkynes and alkenes have been reported. The reactions of 1 with alkynes such as diphenylacetylene, 3-hexyne, phenyltrimethylsilylacetylene, and trimethylsilylacetylene, in the presence of a catalytic amount of tetrakis(triphenylphosphine)platinum(0) at 80 °C gave the [1,4]disilino[2,3-c]thiophene derivatives. With alkenes under the same conditions, 1 afforded the five-membered ring products, in addition to hydrosilylation products. Treatment of 2,3,4,5-tetrakis(dimethylsilyl)thiophene (17) with diphenylacetylene and styrene gave the respective dehydrogenative double silylation products, arising from 2 equivalents of the alkyne and alkene, and compound 17.

A novel method for synthesis of diamagnetic Ru(II) carborane clusters based on reduction of corresponding Ru(III) species by amines was developed. The interaction of paramagnetic 17-electron complex (1) with aliphatic amines in dichloromethane solution at 40 °C proceeds with the abstraction of chlorine atom from the ruthenium center and results in formation of corresponding 16-electron species. The latter can be stabilized by 2-electron ligands such as triphenylphosphine or acetonitrile through the formation of novel stable complexes of ruthenium (II): (2: L = PPh3; 4: L = CH3CN). A bis(ortho-phenylene)cycloboronated complex (6) may be obtained in a similar way from corresponding precursor. The related reaction conducted with diamagnetic closo-carborane cluster of ruthenium (IV) 3,3-Ph2P(CH2)4PPh2-3-H-3-Cl-closo-3,1,2-RuC2B9H11] (7) gives 3-CH3CN-3,3-Ph2P(CH2)4PPh2-closo-3,1,2-RuC2B9H11] (8). The obtained complexes were characterized by means of NMR and IR spectroscopy and mass spectrometry. A single-crystal X-ray diffraction study confirmed closo-structure of the obtained complexes and the presence of acetonitrile molecule as a ligand. The performed electrochemical investigation of the obtained ruthenacarboranes testified its ability to undergo reversible oxidation to Ru(III) species. The comparison of the properties of the obtained complex 2 with its analogue with shorter alkyl fragment in diphosphine moiety shows that the slight difference in the structure leads to the decrease of stability.

Deprotonation of [exo-5,6,10-{RuCl(PPh3)2}-5,6,10-(μ-H)3-nido-7,8-C2B9H9] (1a) and its C,C-diphenyl analogue (1b) affords the anions [3,3-(PPh3)2-3-Cl-closo-3,1,2-RuC2B9H11]− (2a) and [1,2-Ph2-3,3-(PPh3)2-3-Cl-closo-3,1,2-RuC2B9H9]− (2b), respectively. Dehalogenation of 2b in the presence of one equivalent of tBuNC yields [1,2-Ph2-3,3-(tBuNC)2-3-PPh3-pseudocloso-3,1,2-RuC2B9H9] (3), and if 2b is dehalogenated in the presence of CO a very similar compound, [1,2-Ph2-3,3-(CO)2-3-PPh3-pseudocloso-3,1,2-RuC2B9H9] (4), is formed. Treatment of 2b with Ag+ in the absence of a donor ligand affords, amongst a number of products, the compound [{1,2-Ph2-pseudocloso-3,1,2-RuC2B9H9}{1′,8′-Ph2-closo-2′,1′,8′-RuC2B9H9}] (5) in which two different {RuPh2C2B9H9} units both achieve electronic and coordinative saturation at their Ru centres by η6-coordination of a Ph ring on the other cluster in a symbiotic manner. Compounds 1b, 3, 4 and 5 were fully characterised, including by crystallographic studies.

A series of new osmacarborane complexes were synthesized by treatment of the 11-vertex carborane [closo-СВ10Н11]–[Me4N]+ (1) with tris(triphenylphosphine)osmiumdichloride OsCl2(PPh3)3 (2). We managed to control the process of the carborane framework transformation {closo-CB10} → {hypercloso-OsCB10} → {hypercloso-OsCB9} → {hypercloso-OsCB8}, and each stage of this polyhedral carborane contraction was experimentally confirmed. The isolated clusters are electron-deficient hypercloso-osmacarboranes with 2n skeletal electrons. The structures of two “anti-Wade” complexes (10- and 11-vertex osmacarboranes) were confirmed by X-ray diffraction.

Reaction of [PPN][HFe(CO)4] (PPN = bis(triphenylphosphine)iminium) with PCl3 in a 1:1 ratio produced small amounts of [PPN][P{Fe(CO)4}2Cl2] ([PPN][Ia]). Reaction of [Et4N][HFe(CO)4] with AsCl3 in a 1:0.75 ratio in THF at −78 °C produced [Et4N][As{Fe(CO)4}2Cl2] ([PPN][Ib]) as the majority product. The compound [PPN][(CO)4FePCl2O] ([PPN][II]) was obtained from the reaction of Fe2(CO)9 with PCl3 in THF. In contrast, [Et4N][HFe(CO)4] reacted with PCl3 at −78 °C in a 2:1 ratio to yield [Et4N][Fe2(CO)6{(μ4-PFe(CO)4)2(μ-CO)}{μ-PCl2}] ([Et4N][III]) as the majority product. The compounds were characterized spectroscopically and by single-crystal X-ray diffraction analyses.

Rhodium-catalyzed hydroformylation of styrene, α-methylstyrene, dimethyl itaconate, and ( R )-limonene was performed in gamma-valerolactone (GVL) as a proposed biomass-based environmentally benign solvent for hydroformylation referring to toluene as a generally used conventional solvent. Both achiral (triphenylphosphine, 1,3-bis(diphenylphoshino)propane) and enantiopure bidentate phosphine ligands (( S , S )-BDPP, ( R )-BINAP, ( R )-QUINAP, ( R , R )-DIOP, ( R c ),( S p )-JOSIPHOS, ( S )-SEGPHOS, ( S )-(DM)-SEGPHOS) were investigated in in situ generated Rh-diphosphine catalyst systems. In general, the catalysts' activity in GVL was lower than in toluene; however, remarkable chemo- (>99%) and regioselectivities (>95%) were achieved in GVL under identical conditions. The BDPP-modified Rh-catalyst was recycled for three consecutive cycles; however a decrease in its activity was detected.

Pincer complexes can act as efficient catalysts for many industrially important organic transformations under environmentally benign and mild conditions. The NNN pincer ligands have been prepared from the reactions between pyridine-2,6-dicarbonyldichloride and benzylamine or its derivatives in the presence of 4-dimethylaminopyridine (DMAP). Pd(II) complexes containing NNN pincer ligand and acetonitrile/triphenylphosphine have been synthesized and characterized by analytical, spectroscopic (FT-IR, UV-Visible, 1H, 13C & 31P NMR and Mass) and single crystal X-ray diffraction techniques. Single crystal X-ray analysis reveals a distorted square planar geometry around Pd in all the complexes. These pincer complexes have been used as catalysts in Suzuki-Miyaura cross-coupling reaction. The effect of ancillary ligands (CH3CN and PPh3) in the complexes has been investigated towards the coupling reaction. The conversions have been determined from GC analyses. Scope of the system has been extended with various substituted halides.

Asymmetrical NHC complexes of cymantrene and methylcymantrene have been synthesised through the photochemical substitution of carbonyl ligands in the presence of the imidazol-2-ylidene salts. The carbene substituents have been varied between compact ( L1 ) and bulky ( L2 and L3 ) substituents to produce an array of differently sized carbene ligands. The solid state crystal structures of three of the complexes confirmed the bonding pattern of the ligand towards available metal centres and an in-depth DFT study provided insight into electronic and steric aspects. Application of the Extended Transition State coupled with Natural Orbitals for Chemical Valence (ETS-NOCV) energy decomposition technique indicated various NOCV channels for each Mn–L bond (L = 3-ethyl-1-methylimidazolylidene carbene, triphenylphosphine or acetonitrile), describing the density and energy changes of specific (σ and π) attributes of each bond. N-heterocyclic carbenes of cymantrene derivatives and their triphenylphosphine-substituted analogue are equivalent σ-donors, with 53% and 56%, respectively, of the total binding energy originating from σ-donation. However, NHC complexes show considerably less π character in the metal-carbene bond. Hydrogen interactions in the NHC complexes were also identified in the ETS-NOCV calculations and provided quantification of the hydrogen interactions witnessed in the solid state structures. Calculated Wiberg bond indices, bond dissociation enthalpies, percentage buried volumes and percentage sigma and pi-bonding characteristics quantified the bonding and electronic aspects of the ligand-metal interactions within the complex.

In this report we have presented synthesis of a new air stable bidentate selenium ligand (L1) by the reaction of 1,8-bis(2-(chloromethyl)phenoxy)octane with sodium salt of diphenyl diselenide. The reaction of bidentate selenium ligand (L1) with Pd(CH3CN)2Cl2 in acetonitrile under reflux conditions resulted nineteen membered ring macrocyclic palladium(II) complex. The structure of ligand precursors, ligand, and macrocyclic palladium(II) complex were authenticated by using 1H, 13C{1H} NMR spectroscopy and elemental analysis. The repeated attempts to obtain single crystals of macrocyclic palladium(II) complex were unsuccessful probably due to long flexible aliphatic chain in the molecule. The air and moisture stable, thermally robust macrocyclic palladium(II) complex was employed as catalyst to catalyze the regioselective arylation reaction of imidazole derivatives. The reaction works efficiently without any need of inert atmosphere. The current protocol works under mild reaction conditions with exclusive C-5 regioselectivity. Excellent yields (~73–95%) were obtained by using only 1.5 mol% of C1, with wide range of derivatives and large functional group tolerance. Homogeneous nature of catalysis process was confirmed with the help of mercury and triphenylphosphine poisoning tests. Further, the catalyst can be reused with significant loss (22%) in the efficiency.

Photolysis of the monohalocymantrenes [(C5H4X)Mn(CO)3] (X= F, Cl, Br, I) in the presence of triphenylphosphine yields the corresponding dicarbonyl complexes [(C5H4X)Mn(CO)2(PPh3)]. Stepwise metalation and electrophilic quench with (PhSO2)2NF, C2Cl6, C2HBr5 or I2, respectively leads to [(C5H2F3)Mn(CO)2(PPh3)], [(C5X5)Mn(CO)2(PPh3)] (X= Cl, Br) and [(C5HI4)Mn(CO)2(PPh3)]. Further fluorination or iodination leads only to decomposition. However, lithiation of [(C5H2F3)Mn(CO)2(PPh3)] is possible and electrophilic quench with C2Cl6 leads finally to [(C5F3Cl2)Mn(CO)2(PPh3)]. The crystal structures of the tetra- and pentasubstituted compounds are reported.

A new synthetic methodology based on transmetallation was developed for the preparation of SCS indenediide pincer complexes. Upon reaction of the 1,3-bis(thiophosphinoyle)indene 1 with [Zr(NMe2)4], Csp3-H activation proceeds readily to give the new complex 2. Thermolysis at 100 °C for 5 h then affords the SCS pincer complex 3. Complex 2 can be stored under inert atmosphere for several weeks without decomposition. It is much more stable than 3 and was thus used as precursor to study transmetallation. Zr to Pd/Pt Transmetallation occurs rapidly and cleanly at room temperature. Accordingly, the pincer complexes 4, 5, 7 and 8 with triphenylphosphine or chloride as co-ligand were obtained in good to excellent yields under mild conditions.

The reactions of 2,3-bis(diisopropylsilyl)thiophene (1) with diphenylacetylene, phenylacetylene, trimethylsilylacetylene, and mesitylacetylene have been reported. The reactions of 1 with diphenylacetylene and phenylacetylene in the presence of a catalytic amount of tetrakis(triphenylphosphine)platinum(0) at 80 °C gave [1,4]disilino[2,3-b]thiophene derivatives. With trimethylsilylacetylene, 1 afforded two types of products arising from sp-hybridized C–H bond activation of the acetylene, together with [1,3]disilolo[4,5-b]thiophene derivatives. A similar treatment of 1 with mesitylacetylene produced two regioisomers of products arising from the C–H bond activation of mesitylacetylene. Theoretical calculations for the intramolecular reactions of 10a and 10b are also discussed.

New dinuclear cyclometallated palladium complexes of general formula [{Pd(μ-NCO)(CˆN)} 2 ] (CˆN = 2-benzoylpyridine (bzpy) I ; NCO = saccharinate (sacc) a , Phthalimidate (phthal) b or 4,5-dichlorophthalimidate (DiClphthal) c have been synthesized by a simple acid-base reaction involving the di-μ-hydroxo-precursor [{Pd(μ-OH)(bzpy)} 2 ] recently reported. Analogous to Ic , complex IIc with CˆN = 2-phenylpyridine (phpy) II has also been prepared, meaning the first examples reported to date of complexes including 4,5-dichlorophthalimidate as ligand coordinating a metal centre. The reaction of bridged imidato precursors against triphenylphosphine to form the mononuclear N-bonded imidato derivatives of general formula [Pd(CˆN)(N-imidate)(PPh 3 )] IaP , IbP , IcP and IIcP has been achieved under mild conditions. The new complexes were characterized by partial elemental analyses and spectroscopic methods. Structural characterization by X-ray diffraction of Ib and IIcP , the first crystal structure of a complex containing 4,5-diClphthal that has been deposited to date on the Cambridge Structural Database, have confirmed the proposed formulae.

Stable mono- and dicarboxylate phosphabetaines with α-location of the phosphonium center relative to the carboxylate group on the basis of methyldiphenylphosphine, triphenylphosphine, 3-(diphenylphosphino)propionic acid, various bisdiphenylphosphines and glyoxylic acid have been synthesized.

The reaction of a dinuclear palladium complex [Pd2(CH3CN)6][BF4]2 with cycloheptatriene (CHT) in the presence of triphenylphosphine afforded an anti dinuclear addition product, anti-[Pd2(μ-C7H8)(PPh3)4][BF4]2. Deprotonation of the CHT ligand in the dinuclear CHT complex gave a mixed-valence cycloheptatrienyl (Tr) complex, anti-[Pd2(μ-C7H7)(PPh3)4][BF4]2. A platinum congener of the dinuclear Tr complex was also synthesized by the double addition of Pt0(PPh3)2 moieties to [C7H7][BF4].

The conjugation of the gold(I) complex having planar phenyl isocyanide or bulky triphenylphosphine with 6-ethynyl-1-octyluracil afforded the corresponding gold(I) complexes U6AuCNPh and U6AuPPh3, respectively, as bioorganometallic conjugates. The crystal structure of U6AuCNPh revealed the formation of a head-to-tail dimer through the Au(I)–Au(I) and π–π interactions between the uracil and benzene moieties of phenyl isocyanide. Furthermore, each head-to-tail dimer was connected not only through the intermolecular hydrogen bonds of N–H···O pattern between the uracil moieties but the weak hydrogen bonds of C–H···O pattern between the uracil and benzene moieties of phenyl isocyanide. In contrast, the Au(I)–Au(I) interaction was not observed in a crystal structure of U6AuPPh3 probably due to the steric hindrance of the bulky triphenylphosphine ligand although a dimeric structure through the intermolecular hydrogen bonds of N–H···O pattern between the uracil moieties was formed.

Os3(CO)12 reacts with phenazine in refluxing xylene to yield the monohydride cluster Os3(CO)9(μ3,η2-C12H7N2)(μ-H) (1) in 18% yield and the dihydride cluster Os3(CO)9(μ3,η2-C12H6N2)(μ-H)2 (2) in 21% yield. Compound 1 reacts reversibly with CO to give the decacarbonyl compound Os3(CO)10(μ,η2-C12H7N2)(μ-H) (3) and with PPh3 to afford the addition product Os3(CO)9(μ,η2-C12H7N2)(PPh3)(μ-H) (4). Compounds 1, 2, and 4 have been structurally characterized. 1 contains a C-metalated phenazine ligand that is coordinated to the cluster by a dative nitrogen bond and a benzylidene-type bond, the latter which bridges the same cluster edge as the bridging hydride. The activated phenazine ligand in 2 derives from a double C–H bond metalation sequence, affording a face-capping heterocyclic ligand that binds adjacent osmium centers through two σ–Os–C bonds and the third osmium atom via an aryl π bond in an η2 fashion. Compound 4 exhibits a closed trimetallic Os3(CO)9 core that contains edge-bridging phenazine (C,N coordination) and hydride moieties, and a triphenylphosphine ligand that is coordinated at the non-phenazine-ligated osmium center. These compounds represent rare examples of polynuclear osmium clusters containing C-metalated phenazine ligands. The potential energy surfaces that afford clusters 1 and 2 from Os3(CO)12 and phenazine have been modeled by DFT calculations, and these data indicate that both product clusters originate from the unsaturated cluster Os3(CO)11.

We here report the synthesis of new cyclopentadienyl ruthenium(II) complexes of general formula [(η5-C5H5)Ru(PP)(L)]+ (PP = two triphenylphosphine, 1,2-diphenylphosphinoethane), isolated as PF 6 − salts, with L being galactose and fructose carbohydrate derivative ligands, N-coordinated to the metal centre by nitrile, tetrazole and 1,3,4-oxadiazole moieties. The ten new organometallic compounds were fully characterized by FT-IR, 1H, 13C, and 31P NMR spectroscopies, and by elemental analysis. The cytotoxicity of the ruthenium(II) compounds was tested on HeLa cancer cells (cervical carcinoma), unveiling IC50 values in the low micromolar range.

The metathesis reaction of IrCl(CO)(PPh3)2 (4) and Vaska-type derivatives IrCl(CO)(PR3)2 (PR3 = MePh2, 5; Me2Ph, 6; Me3, 7) with 1–2 equivalents of the potassium butadienesulfinate salts K(SO2CHCRCHCH2) (R = H, 2; Me, 3) led to the formation of mixtures of chiral diastereomers “a” and “b” of general formula Ir(1–2,5-η-CH2CHCRCHSO2)(CO)(L)2 (R = H, L = PPh3, 8a,b; PMePh2, 9a,b; PMe2Ph, 10a,b; PMe3, 11a,b; R = Me, L = PPh3, 12a,b; PMePh2, 13a,b; PMe2Ph, 14a,b; PMe3, 15a,b) In isomer “a” both phosphine ligands L are located at the open mouth of the butadienesulfonyl ligand, and between the non-coordinated double bond of the same non-planar ligand, respectively; while the CO is opposite to the SO2 group. In isomer “b”, one phosphine remains in the open mouth of the butadienesulfonyl ligand, and the CO and the second phosphine have exchanged positions, being now the CO near to the SO2 group, and the phosphine opposite to the SO2 group. The most abundant isomer is assignable to a for 9a-11a and 12a-15a, while the opposite is observed in 8a and 12a with the bulkier triphenylphosphine. Electronic and predominant steric factors have been implicated as being most responsible for leading to a preference for one isomeric form over the other. A comparative study of these derivatives was carried out through the analysis of the IR, mass spectrometry, and 1H, 13C{1H} and 31P{1H} NMR, as well as through crystalline structures of 9a′, 11a, 12b′, 13a′, 14a and 15a, as well as precursors 5–7. The presence of the butadienesulfonyl ligand in all isomers 8a,b-15a,b induces a total asymmetry that is reflected through the 1H and 13C{1H} NMR, in addition to the preferred coordination mode (1–2,5-η-) of this ligand. Monitoring reactions through 1H and 31P{1H} NMR of 8a,b in CDCl3 and 9a,b in C6D6 and CDCl3 showed the influence of the temperature and solvent in the equilibrium of isomers in the reaction mixture.

The iminophosphorane ligands (Ph3P NC6H4SR) [R = CH3 (1) and C6H5 (2)] were easily synthesized from triphenylphosphine and 2-(methylthio)aniline or 2-(phenylthio)aniline respectively by the Horner and Oediger variation of the Kirsanov reaction. The reactivity of both ligands was explored with [Na2PdCl4] to afford the corresponding non-symmetric iminophosphorane pincer derivatives [PdCl{C6H4(Ph2P NC6H4SR-κ3-C,N,S)}] [R = CH3 (3) and C6H5 (4)]. A careful monitoring of the reaction by 31P{1H} NMR experiments revealed the N,S chelated species [PdCl2{C6H4(Ph2P NC6H4SR-κ2-N,S)}] [R = CH3 (5) and C6H5 (6)] to be stable intermediates through the formation of the pincer compounds. Thus, carrying out the reaction for the attaining of (4) at room temperature allowed the isolation and full characterization of the chelated complex [PdCl2{C6H4(Ph2P NC6H4SPh-κ-N,S)}] (6). All above mentioned species were unequivocally characterized by single crystal X-ray diffraction experiments. In addition, the newly synthesized pincer complexes [PdCl{C6H4(Ph2P NC6H4SR-κ3-C,N,S)}] [R = CH3 (3) and C6H5 (4)] were tested as catalyst, proven to be efficient in the Suzuki–Miyaura C–C cross coupling reactions of a series of para-substituted bromobenzenes.

The H-shaped molecule, 5,5′-bis{[bis(5′- tert -butyldimethylsilyl)-2,2′-(bithiophen-5-yl)]methylsilyl}-2,2′-bithiophene ( 3 ) was prepared by the reaction of 5′-( tert -butyldimethylsilyl)-5-lithio-2,2′-bithiophene with 2-bromo-5-(dichloromethylsilyl)thiophene, followed by treatment of the resulting product (5-bromothiophen-2-yl)bis[5′-( tert -butyldimethylsilyl)-2,2′-bithiophen-5-yl](methyl)silane ( 1 ) with compound ( 2 ), obtained by the reaction of the lithiated derivative of 1 with 2-isopropyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, in the presence of dichlorobis(triphenylphosphine)palladium, as light yellow solids. Compound 3 showed absorption maximum ( λ max ) at 336 nm with a molar absorption coefficient ( e ) of 113,000 M −1 cm −1 in dioxane. The fluorescence spectrum of 3 excited at 336 nm in dioxane displayed the emission maxima at 377 and 387 nm, with the fluorescence quantum yield of 48%. We also carried out theoretical treatment of compound 3 to elucidate the geometrical and electronic structure, using the Gaussian 03 program package, with the 6-31G and 6-31G(d) basis sets.

The dirhenium complexes Re2(CO)6(μ-thpymS)2 (1) and eq-Re2(CO)9{κ1-(S)-SN2C4H8} (2) are obtained from the reaction of tetrahydropyrimidine-2-thiol (thpymSH) with Re2(CO)8(NCMe)2 or Re2(CO)10. Complex 1 proves to be an excellent precursor to a range of monometallic and cluster complexes acting as a source of “Re(CO)3(thpymS)”. Thus, reactions with triphenylphosphine (PPh3) and bis(diphenylphosphino)methane (dppm) afford mononuclear fac-Re(CO)3(PPh3)(κ2-thpymS) (3) and fac-Re(CO)3(κ1-dppm)(κ2-thpymS) (4), respectively. A crystal structure of 3 reveals that the pyrimidine-2-thiolate binds in a chelating fashion. Reactions with M3(CO)12 (M = Ru, Os) at moderate temperatures afford mixed-metal clusters. With Ru3(CO)12 in boiling thf isomeric tetranuclear butterfly clusters ReRu3(CO)13(μ3-thpymS) (5–6) result which differ in the position of the capping pyrimidine-2-thiolate ligand on the cluster surface. Thus in the kinetic isomer 5, the pyrimidine-2-thiolate caps the ReRu2 face while in the thermodynamic isomer 6 it caps the Ru3 face. A similar reaction with Os3(CO)10(NCMe)2 in boiling benzene affords predominantly the ReOs2-capped tetranuclear cluster ReOs3(CO)13(μ3-thpymS) (7), together with small amounts of (μ-H)Os3(CO)9(μ3-thpymS) (8) resulting from loss of rhenium. Cluster 7 is stable in refluxing toluene but slowly converts to isomeric 9 in xylene at 140 °C but only in low yields. The crystal structures of isomeric 5–6 have been solved and show only small variations in the cluster core geometry. Density functional calculations show that clusters 6 and 9 are slightly more stable than 5 (ΔG 2.0 kcal mol−1) and 7 (ΔG 1.5 kcal mol−1), respectively, and a mechanism is proposed for these conversions in which the pyrimidine-2-thiolate becomes bidentate after release of the pyrimidine group.

Upon reaction with Pd(PPh3)2Cl2 benzaldehyde thiosemicarbazone undergoes a geometrical change around the imine bond and affords a mixed-ligand complex 1, incorporating an NS-coordinated thiosemicarbazone, a triphenylphosphine and a chloride. Similar reactions with benzophenone thiosemicarbazone and acetophenone thiosemicarbazone proceed without any geometrical change to afford complexes 2 and 3 respectively, containing a CNS-coordinated thiosemicarbazone and a triphenylphosphine. Crystal structures of complexes 1, 2 and 3 have been determined. All the complexes display intense absorptions in the visible region. Catalytic activity of complexes 1, 2 and 3 toward Suzuki type C–C coupling reactions has been examined, and all three are found to efficiently activate all types of C–X bonds (X = I, Br, Cl and even F) and bring about the C–C bond formation with high yield. These complexes are also found to catalyze C–N coupling reactions between aryl halides and primary or secondary amines. While all three complexes are found to be efficient catalysts for both C–C and C–N coupling reactions, complex 2 is found to be a better catalyst than the other two complexes.

Reaction of μ -azido bridged Schiff base palladacycles [Pd{(4-R)C 6 H 3 CH N–C 6 H 3 –2,6- i -Pr 2 }( μ -N 3 )] 2 (R = H; OMe) with 1-methylimidazole generated different conformational mononuclear palladacycles. Complexes [Pd{(4-R)C 6 H 3 CH N–C 6 H 3 –2,6- i -Pr 2 }( μ -N 3 )] 2 (R = H; OMe) reacted with bidentate 1,2-bis(4-pyridyl)-ethene to give mononuclear palladacycles. Also the reaction of [Pd{C 6 H 4 CH N–C 6 H 3 –2,6- i -Pr 2 }( μ -N 3 )] 2 with 4,4′-bipyridine (bpy) produced mononuclear palladacycles. However, the reaction of [Pd{(4-MeO)C 6 H 3 CH N–C 6 H 3 –2,6- i -Pr 2 }( μ -N 3 )] 2 with 4,4′-bipyridine formed a 4,4′-bipyridine bridged binuclear palladacycle [Pd{(4-OMe)C 6 H 3 CH N–C 6 H 3 –2,6- i -Pr 2 }(N 3 )] 2 ( μ -bpy). In contrast, μ -thiocyanato bridged Schiff base palladacycles were relatively unreactive toward aromatic N -heterocycles. Only the reaction of [Pd{C 6 H 4 CH NC 6 H 3 -2,6- i -Pr 2 }( μ -SCN)] 2 with imidazole generated a thiocyanato coordinated mononuclear Schiff base palladacycle [Pd(C 6 H 4 CH NC 6 H 3 -2,6- i -Pr 2 )(imidazole)(SCN)]. Moreover, reactions of μ -azido and μ -thiocyanato bridged Schiff base palladacycles with triphenylphosphine and 1,4-bis(diphenylphosphino) butane routinely formed mono- and bi-nuclear terminal azido or isothiocyanato coordinated palladacycles [Pd{(4-R)C 6 H 3 CH N–C 6 H 3 –2,6- i -Pr 2 }(PPh 3 )(N 3 )], [Pd{(4-R)C 6 H 3 CH N–C 6 H 3 –2,6- i -Pr 2 }(PPh 3 )(NCS)], [Pd{(4-R)C 6 H 3 –CH N–C 6 H 3 –2,6- i -Pr 2 }(N 3 )] 2 ( μ -dppb) and [Pd{(4-R)C 6 H 3 CH N–C 6 H 3 –2,6- i -Pr 2 }(NCS)] 2 ( μ -dppb) (R = H; OMe).