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The Indox ligands, [{( S )-( i Pr)Indox} n ]H ( 1 ) [ n =2 ( a ), 3 ( b )] and [{(H)Indox} n =3 ]H ( 2 ), in which an indenyl group and an oxazoline ring are connected by an ethylene or propylene spacer, have been prepared. Reaction of [Ir(coe) 2 Cl] 2 or [RhCl(C 2 H 4 ) 2 ] 2 with the potassium salt of 1 afforded η 5 -[{( S )-( i Pr)Indox} n ]Ir(coe) 2 ( 3 ) or η 5 -[{( S )-( i Pr)Indox} n ]Rh(C 2 H 4 ) 2 ( 6 ) as a 1:1 mixture of two diastereomers. The oxazoline ring in 3 and 6 did not coordinate to the metal center. When the complexes 3 or 6 reacted with iodine in diethyl ether, oxidative addition proceeded and the oxazoline ring coordinated to the metal center to give diiodoiridium(III) or rhodium(III) complexes, η 5 :η 1 -[{( S )-( i Pr)Indox} n ]M(I) 2 [M=Ir ( 4 ), Rh ( 7 )]. The corresponding diiodoiridium(III) complex bearing the Indox ligand 2 , η 5 :η 1 -[{(H)Indox} n =2 ]Ir(I) 2 ( 5 ), was also prepared by a similar method. Reaction of 4 or 7 with PPh 3 in THF afforded diiodo-phosphine complexes, η 5 -[{( S )-( i Pr)Indox} n ]M(PPh 3 )(I) 2 [M=Ir ( 8 ), Rh ( 9 )] as a 1:1 mixture of two diastereomers in which the oxazoline ring dissociated from the metal center. The related reaction of 8 or 9 with more than 2 equiv. of AgOTf afforded the cationic complexes, [η 5 :η 1 -[{( S )-( i Pr)Indox} n ]M(PPh 3 )(OTf)]OTf [M=Ir ( 10 ), Rh ( 11 )], having a stereogenic center at the metal center as a mixture of only two diastereomers. From 1 H and 31 P NMR analyses, each diastereomer of 8 or 9 afforded only a single isomer of 10 or 11 . The corresponding iridium(III) complex bearing the Indox ligand 2 , [η 5 :η 1 -[{(H)Indox} n =3 ]Ir(PPh 3 )(OTf)]OTf ( 12 ) was also prepared. The coordinated triflate ligand of 12 was slowly replaced by water in CDCl 3 to afford the dicationic aquo complex, ( S * pl , R * Ir )-[η 5 :η 1 -[{(H)Indox} n =3 ]Ir(PPh 3 )(H 2 O)](OTf) 2 ( 13 ). The monocationic complex, [η 5 :η 1 -[{( S )-( i Pr)Indox} n =2 ]Ir(PPh 3 )(I)]OTf ( 14a ), having metal-centered chirality, was observed as a mixture of only two diastereomers in the reaction of 10a (a mixture of two diastereomers) with 1 equiv. of AgOTf. These observations indicated that the ligand exchange reaction of 8 or 9 with AgOTf contained the following three steps: (i) abstraction of one of the two prochiral iododes by AgOTf, (ii) recoordination of the oxazoline ring, and (iii) exchange of the remaining iodide for the triflate by AgOTf. The stereochemistry around the metal center was determined at the second step. All complexes have been characterized by usual spectroscopic methods as well as elemental analyses, and 4 and 13 have been characterized by X-ray analyses.

Reaction of the rhodium(I) carbonyl complexes [η5:η1-{3-(R)Ind-P}n=2]Rh(CO) (1; R = H (a), Et (b), Cy (c), (1‘S,2‘S,5‘R)-neomenthyl (NM) (d), (1‘R,2‘R,5‘R)-neoisomenthyl (NIM) (e)) with the Meerwein reagent (Me3OBF4) afforded the cationic rhodium(III) complexes [[η5:η1-{3-(R)Ind-P}n=2]RhMe(CO)]BF4, having metal-centered chirality, in good to excellent yields. When a bulkier substituent (R) was used, the corresponding cationic complex was obtained with higher diastereoselectivity. In the case of using an optically active substituent such as NM or NIM, complete stereodiscrimination around the rhodium center by the Meerwein reagent occurred to give the cationic complexes with 100% de.

Highly diastereoselective intramolecular C–H bond activation at a prochiral sp3 carbon was achieved with a cationic iridium complex having an optically active heterochelate PN*(R) [PN*(R)=o-Ph2PC6H4CH2OCH2 ligand.

Reaction of tridentate ligands, 2,5-bis(N-aryliminomethyl)pyrroles (1a–e), with 1 equiv of AlMe3 in toluene afforded aluminum dimethyl complexes, AlMe2[2,5-bis(N-aryliminomethyl)pyrrolyl] (2a–e) with the release of one equiv of methane. In solution the aluminum complexes 2a–e showed Cs-symmetry as characterized by their 1H NMR spectra, while in solid the geometry around the Al atom as crystallographically determined for 2a and 2b was found to a tetrahedral by an amido nitrogen atom of the pyrrolyl anion, a nitrogen atom of one of two imino groups and two methyl groups. The aluminum complex 2e upon activated by one equiv of B(C6F5)3 became a catalyst for ethylene polymerization (Activity = 80 g-PE/mol-cat·h).

A half-metallocene benzylidene complex of tantalum, Ta(CHPh)Cp*(η 4 -supine-2,3-dimethyl-1,3-butadiene) (1), was prepared by treating TaCl 2 Cp*(η 4 -supine-2,3-dimethyl-1,3-butadiene) (2) with Mg(CH 2 Ph) 2 in toluene. The structure of 1 was determined by X-ray analysis, indicating the syn rotamer of the Ta=CHPh moiety; the Ph group points upward toward the Cp* ligand. The coordinatively unsaturated 16-electron complex 1 reacted with some unsaturated organic molecules (ethylene, cyclopentene, and tert-butyl cyanide), an alcohol, and an amine. The cycloaddition of ethylene and cyclopentene gave rise to metallacyclobutanes. The addition of tert-butyl cyanide to 1 afforded an imido tantalum complex, Ta(NC-( t Bu)=CHPh)Cp*(η 4 -supine-2,3-dimethyl-1,3-butadiene) (6), which was derived from the metathesis reaction of a nascent 2-aza-1-tantalacyclobut-2-ene intermediate. Protonolysis of 1 by addition of methanol and p-methoxyaniline gave a methoxy benzyl complex, Ta-(CH2Ph)(OCH3)Cp*(η 4 -supine-2,3-dimethyl-1,3-butadiene) (7), and an amido benzyl complex, Ta(CH2Ph)(NHC6H40CH3)Cp*(η 4 -supine-2,3-dimethyl-1,3-butadiene) (8), respectively. Upon heating at 60 °C, complex 8 was converted to an imido butenyl complex, Ta(CH 2 Ph)(NC 6 H 4 -OCH 3 )(η 1 -2,3-dimethyl-2-butene)Cp* (9). Structures of the amido complex 8 and the imido complexes 6 and 9 were determined by X-ray analysis.

We report unique ring-methyl deprotonation of an η4-cyclobutadiene complex [PdCl2(η4-C4 tBu2Me2)]2 (1). Reaction of 1 with 2 equiv. of triphenylphosphine in the presence of triethylamine afforded an exo-methylene-η3-cyclobutenyl palladium complex [Pd(μ-Cl)(η3-C4(CH2)(tBu)2Me)(PPh3)]2 (3) in quantitative yield. The reaction of complex 1 with 2 equiv. of DPPE gave a cationic complex [Pd(η3-C4(CH2)(tBu)2Me)(DPPE)][Cl] (4a) with the release of HCl. Upon treated with triethylamine and AgOTf, a cationic complex [Pd(η3-C4(CH2)(tBu)2Me)(DPPE)][OTf] (4b) was isolated as yellow microcrystalline solids. The cationic exo-methylene-η3-cyclobutenyl structure of 4 was revealed by spectral data together with a crystallographic study for complex 4a.

Tantalum-alkyne complexes with the general formula TaCl3(R1C⋮CR2)(dme) (1a, R1 = R2 = Et; 1b, R1 = R2 = n-C5H11; 1c, R1 = Ph, R2 = Me; 1d, R1 = R2 = Ph; DME = 1,2-dimethoxyethane) were synthesized by treatment of the corresponding alkynes with a low-valent tantalum derived by reduction of tantalum pentachloride with zinc powder in a mixed solvent of toluene and DME. The DME ligand can be replaced by 2 equiv of pyridine to afford the corresponding dipyridine complexes TaCl3(R1C⋮CR2)(py)2 (2a, R1 = R2 = Et; 2b, R1 = R2 = n-C5H11; 2c, R1 = Ph, R2 = Me; 2d, R1 = R2 = Ph). Additionally, the reaction of 1a with the bidentate nitrogen ligands bipyridine and N,N,N‘,N‘-tetramethyethylenediamine (= TMEDA) gave TaCl3(EtC⋮CEt)(bipy) (3) and TaCl3(EtC⋮CEt)(tmeda) (4), respectively. The η2- and 4e-coordination mode of an alkyne with a large contribution of a metalacyclopropene canonical structure was revealed by spectroscopic methods (NMR and IR) and crystallographic analyses of 1a, 1c, 2a, and 4. The reactivies of the...

We found the first ring methyl activation of an η4-cyclobutadiene complex. Base-promoted ring methyl activation of the cyclobutadiene-palladium(II) complex [PdCl2(η4-C4Me2(tBu)2)]2 (2) in the presence of triethylamine afforded the dinuclear exo-methylene-η3-cyclobutenyl complex [PdCl(η3-C4(CH2)Me(tBu)2)]2 (3) in 81% yield. In the case of pyridine as base, a mixture of 3 and [C5H5NH][PdCl3(η4-C4Me2(tBu)2)] (4) was obtained. The complex 4 was alternatively derived from the reaction of 2 with 2 equiv of C5H5N·HCl. The ring methyl activation of 2 in the presence of 2,2‘-bipyridine and triethylamine followed by treatment with AgBF4 led to the formation of the cationic complex [Pd(η3-C4(CH2)Me(tBu)2)(bipy)]]BF4 (6) in 83% yield. The mononuclear exo-methylene-η3-cyclobutenyl structure of 6 was confirmed by spectral data and a crystallographic study.

We prepared some half-metallocene complexes of tantalum bearing ortho-substituted aryl derivatives of 1-aza-1,3-butadiene ligand. The coordination mode of the 1-aza-1,3-diene (abbr. AD) ligand highly depended on the substituent(s) on the aryl group of the AD ligand and also on the metal center. The number of methyl substituents on the aryl group of the AD ligand differentiated two coordination modes: one methyl substituent, TaCl2Cp*(η4-supine-o-Tol-AD) (1) (Cp* = pentamethylcyclopentadienyl; o-Tol-AD = 1-(2-methylphenyl)-4-phenyl-1-aza-1,3-butadiene), favored an η4-supine-coordination mode, while two methyl substituents, TaCl2Cp*(η2-C, N-Xyl-AD) (5) (Xy1-AD = 2,6-dimethylphenyl-4-phenyl-1-aza-1,3-butadiene), adopted an η2-C, N-imine coordination fashion. Furthermore, the preferential coordination mode of the AD ligand was delicately affected by the substituent(s) on the tantalum center. Dialkylation of 1 led to the formation of TaR2Cp*(o-Tol-AD) (6: R = Me; 8: R = CH2Ph) in the dimethyl complex 6. The equ...

Magnetic interactions between divalent chromium (Cr(II)) ions in tetra Cr(II) complex were estimated by using a magnetic effective density functional (MEDF) method. Those results were discussed in comparison with a di-Cr(II) complex to elucidate the types of magnetic interactions. Charge and spin densities and natural orbitals by MEDF were also examined in terms of the ligand effects. aligned tetrametal systems magnetic interaction effective exchange integrals Magnetic Effective Density Functional MEDF

Linearly aligned tetranuclear Pt(II)-Cr(II)-Cr(II)-Pt(II) complexes were prepared using a tridentate pyphos ligand (pyphos = 6-diphenylphosphino-2-pyridonate). The bonding between Cr(II) and Pt(II) was discussed on the basis of magnetic measurements. A dichromium complex, [Cr2(pyphos)4] (1), was prepared by the reaction of [Cr2(OAc)4] with the sodium salt of pyphos ligand. The complex 1 has four phosphorus atoms capable of holding transition metals at both of the axial positions of the Cr2 moiety. Three tetranuclear Pt(II)-Cr(II)-Cr(II)-Pt(II) complexes, i.e., [Cr2Pt2Me4(pyphos)4] (2), [Cr2Pt2Cl4(pyphos)4] (3), and [Cr2Pt2Cl2Me2(pyphos)4] (4), have been prepared by the addition of the respective platinum species, PtIIMe2, PtIICl2, and PtIIMeCl, to the axial positions of the Cr2 moiety of 1. Magnetic measurements of 1-4 together with a crystallographic study for the complexes 1 and 2 revealed that the quadruply-bonded Cr-Cr distance was delicately altered by the nature of the Pt atoms, i.e., the kind of su...

We report a practical one-pot synthesis of dialkylammonium salts of anionic dinuclear ruthenium complexes having chelating diphosphine ligands, BINAPs and DPB, with formula of [NEt2H2][{RuCl(diphosphine)}2(μ-Cl)3] [2a: diphosphine=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl; 6a: 2,2′-bis(di(p-tolyl)phosphino)-1,1′-binaphthyl; 8a: 1,2-bis(diphenylphosphino)benzene]. Treatment of cationic ruthenium complexes, [RuCl(η6-p-cymene)(diphosphine)]Cl (4) with a slight excess of NEt2H2Cl (5a) afforded 2a, 6a, and 8a in quantitative yields. Similar reactions with various dialkylammonium salts 5b–f gave the corresponding salts, [NR2H2][{RuCl(diphosphine)}2(μ-Cl)3]. A one-pot mixture of BINAP or its derivative, [RuCl2(η6-arene)]2, and NR2H2Cl produced salts of the anionic dinuclear complexes which can be applied as catalysts for the asymmetric hydrogenation of ketonic substrates such as acetol and methyl acetoacetate with high activity and high enantioselectivity. The anionic face-sharing bioctahedral structure of these complexes was confirmed by the X-ray analysis of 8a, which has two hydrogen bonds between two NH of the diethylammonium cation and two terminal chloro-ligands.

Organotin compounds [Tp*SnCl3-nBun] (2: n = 1; 3: n = 2) having a Tp* ligand (Tp* = tris(3,5-dimethylpyrazol-1-yl)hydroborate) are useful reagents for introducing a Tp* ligand on Group 4 and 5 metals and chromium. The test reactions of these organotin compounds along with [Tp*SnCl3] (1) with ZrCl4, affording a known complex [Tp*ZrCl3] (4), were examined. The reaction rates were in the order 3 > 2 1. This tendency was understood by the average Sn-N(Tp* ligand) bond distance being longer in the order 3 > 2 > 1 as revealed by the crystallographic studies and the orbital interactions between the Tp* ligand and the SnCl3-nBun fragments estimated by the ab initio calculations for 1—3. On the basis of the above findings, we applied the compound 3 to prepare Tp* complexes of Group 4—6 metals. Reactions of TiCl4 with an equimolar amount of 3 afforded [Tp*TiCl3] (7) in good yields after a simple rinse to remove the resulting tin compound, SnBu2Cl2. [Tp*HfCl3] (8) was prepared in moderate yield by reaction of [HfCl4...

By using femtosecond and picosecond transient absorption measurement techniques, we have investigated the dynamic behavior of the S 2 state of all-trans - α , ω -diphenylpolyenes, from diphenylhexatriene ( N =3) to diphenylhexadecaoctaene ( N =8), in solution. The S 2 state lifetimes, which were determined from the decay of the S n ←S 2 absorption band around 700 nm, were similar for N =3–7. The observed small energy gap dependence of the S 2 →S 1 internal conversion rate can be an indication of the large difference in the molecular geometry of the S 1 and S 2 states.

We report the synthesis of half-metallocene 1,4-diaza-1,3-butadiene (dad) complexes of niobium and tantalum and the flexible coordination modes of the dad ligand. Treatment of MCl4(η5-C5R5) (1a, M = Ta, R = CH3; 1b, M = Ta, R = H; 2a, M = Nb, R = CH3; 2b, M = Nb, R = H) with 1 equiv of a dilithium salt of 1,4-bis(p-methoxyphenyl)-1,4-diaza-1,3-butadiene (p-MeOC6H4-dad) in THF yielded the corresponding half-sandwich 1,4-diaza-1,3-butadiene complexes MCl2(η5-C5R5)(η4-supine-p-MeOC6H4-dad) (3a, M = Ta, R = CH3; 3b, M = Ta, R = H; 4a, M = Nb, R = CH3; 4b, M = Nb, R = H). Similar reaction of 1a with the dianions of 1,4-bis(p-tolyl)-1,4-diaza-1,3-butadiene (p-Tol-dad), 1,4-bis(o-tolyl)-1,4-diaza-1,3-butadiene (o-Tol-dad), and 1,4-dicyclohexyl-1,4-diaza-1,3-butadiene (Cy-dad) afforded tantalum complexes TaCl2Cp*(η4-supine-p-Tol-dad) (5) (Cp* = pentamethylcyclopentadienyl), TaCl2Cp*(η4-supine-o-Tol-dad) (6), and TaCl2Cp*(η4-supine-Cy-dad) (7), respectively. When a dinuclear Ta(III) complex [TaCl2Cp*]2 (8) was tre...

Preparations and reactivity of iridium complexes bearing several different kinds of ligands such as peraryldiphosphines, PN hybrid ligands, and an optically active chelated diamine and their application to catalysis are described. The catalyst system, iridium (I) /BINAP {2, 2'-bis (diphenylphosphino) -1, 1'- binaphthyl} /benzylamine, serves as an efficient asymmetric hydrogenation catalyst of imines in methanol. As the catalyst precursor and the related complex, complexes [IrCl (diphosphine)] 22 (diphosphine= peraryldiphosphine such as BINAP, BPBP {2, 2'-bis (diphenylphosphino) -1, V.-biphenyl}), which have been known as neutral complexes so far and used as catalyst precursors in many catalytic reactions, could be isolated and fully characterized including X-ray analysis of the BINAP complex. These complexes activated easily E-H (E= heteroatom) bonds and gave the corresponding hydride complexes, [{Ir(H) (diphosphine)} 2 (μ-Cl) (μ-ER) 2] Cl, (ER = OMe, OH, OC (= O) Me, OC (= O) Ph, and SPh). The structure of [{Ir (H) (binap)} 2 (μ-Cl) (μ-OMe) 2] Cl (4a) was determined by X-ray analysis. The complex 4a was found to catalyze hydrogenation of alkyne to trans-olefin selectively and the possible reaction pathways are shown on the basis of the isolated complexes related to the reaction intermediates. By employing the PN ligand which shows flexible coordination ability, we have succeeded in direct observation of the reversible intramolecular C (sp3) -H bond activation and estimated thermodynamic and kinetic parameters regarding the fundamental C-H activation reaction. We could isolate both complexes before and after the C-H activation and characterize them completely including the X-ray structures. By applying the concept of the isolobal analogy, we have shown that the rhodium and the iridium complexes bearing an optically active chelated diamine ligand become efficient asymmetric catalysts for asymmetric transfer hydrogenation of ketone.

The cation of the title compound, [Ir2ClH2(C6H5S)2(C48H40P2)2]Cl·2C2H4Cl2, exists as a bridged bifacial octahedral dinuclear iridium structure with C 2 symmetry (Cl lies on the rotation axis). The coordination environment of the Ir atom can be described as highly distorted octahedral with two P atoms, two bridging phenyl thiolato S atoms, a bridging chloride ligand, and a terminal hydride ligand.

A hypervalent compound 1,5-bis(trifluoromethylsulfonyloxy)-1λ4,5λ4-dithiabicyclo[3.3.0]octane (1) oxidatively reacted with Pd2(dba)3 (dba = dibenzylidene acetone) in acetonitrile to give a dication...

A new tantalum−imine complex TaCl3(dme)(PhCHNCH2Ph) (1) (DME = 1,2-dimethoxyethane) was synthesized by treatment of N-(benzylidene)benzylamine with low-valent tantalum derived from TaCl5 and zinc in DME and toluene. The molecular structure of complex 1 was determined by X-ray crystallographic analysis, and its reactivity toward unsaturated compounds examined.

The synthesis and the crystallographic characterization of two dialkylchromium complexes possessing a Tp* ligand, i.e. Tp*CrMe2(DMAP) (4) and Tp*Cr(CH2Ph)2(DMAP) (5) (Tp*=hydrotris(3,5-dimethylpyrazolyl)borate; DMAP=4-dimethylaminopyridine), are described. Treatment of Tp*CrCl2(DMAP) (3) with two equivalents of MeLi gave 4, while the complex 5 was prepared by the reaction of 3 with two equivalents of PhCH2MgCl. These complexes were found to be thermally robust and quite stable to air and moisture. Distorted octahedral geometry around each chromium center of 4 and 5 has been determined by X-ray analysis, the chromium center being surrounded with three nitrogen atoms of the Tp* ligand at facial positions, one nitrogen atom of the DMAP ligand, and two carbon atoms. The two benzyl ligands of 5 were found to coordinate to the chromium center in η1-fashion.

The diphenylphosphino-2-pyridone ligand (pyphosH) and its anion ligand, pyridonate (pyphos), coordinated to the ruthenium(II) center through two modes: bidentate P-N chelation and monodentate P coordination. Reaction of Mo2(pyphos)4 (2) with [RuCl2(η6-p-cymene)]2 (3) afforded an unexpected trinuclear complex (pyphosH)RuCl(μ-Cl)Mo2Cl(pyphos)3 (5) accompanied by a monomeric complex (η6-pcymene)RuCl2(pyphosH) (4). In complex 5, three pyphos ligands coordinated to a quadruply-bonded Mo2 core in three different modes: O-N chelation with free phosphine moiety, O-N chelation with a phosphorus atom bound to a ruthenium atom, P-N chelation with an oxygen atom bridged to the ruthenium atom; thereby the pseudo octahedral ruthenium center was surrounded by a phosphorus atom and a nitrogen atom of a pyphosH ligand (P-N chelation), two trans-arranged chloro atoms, the oxygen atom and the phosphorus atom of the two pyphos ligands. Reaction of RuClx(CO)y with pyphosH gave a mononuclear complex RuCl2(CO)(pyphosH)2 (6), which has two pyphosH ligands bound to the ruthenium atom through P-N chelation and monodentate P coordination and involves two hydrogen bondings, NH⋯Cl and OH⋯Cl. In addition, treatment of Ru2(OAc)4 (7) with the sodium salt of the pyphos ligand afforded a heterotetrametallic complex [Ru(pyphos)3](μ-Na)2[Ru(pyphos)3] (8) in which each pseudo octahedral ruthenium(II) center has three pyphos ligands through P-N chelation and two sodium ions were coordinated by four oxygen atoms in distorted tetrahedral geometry.

Reaction of 1,8-diphenyl-1,3,5,7-octatetraene with [Ru(μ-Cl)Cp*]4 (1) (Cp* = η5-pentamethylcyclopentadienyl) gave [μ-(s-cis-1,2,3,4-η:s-cis-5,6,7,8-η-PhCHCHCHCHCHCHCHCHPh)(RuClCp*)2] (2), whose crystal structure revealed that 2 has a planar tetraene backbone coordinated by two Cp*RuCl moieties in s-cis-η4-fashion; while the reaction with Ru(acac)3/Zn system resulted in the formation of [μ-(s-trans-1,2,3,4-η:s-trans-5,6,7,8-η-PhCHCHCHCHCHCHCHCHPh){Ru(acac)2}2] (3), where both of the two Ru(acac)2 moieties prefer s-trans coordination and thus the plane of the octatetraene backbone of 3 is deformed into an S-shape. Electrochemical studies for complexes 2 and 3 revealed that they have a coupling between the two ruthenium centers and are conjugatively interacted dπ−pπ organometallic systems.

The multiple metal–metal bonds between divalent molybdenum (Mo(II)) ions in dimers and tetramers were investigated theoretically. The orbital energy gaps, occupation numbers of natural orbitals (NO) and effective bond orders for the naked Mo(II)2 dimer (1) were calculated by ab initio UHF MO and density functional (DFT) methods. The effective exchange integrals (Jab) of 1 were calculated by approximately spin-projected UHF and DFT methods, and the complete active space (CAS) CI by the use of UHF NO. The calculated Jab values were discussed in relation to the temperature-dependent paramagnetism observed for the edge-sharing and face-sharing bioctahedral molybdenum complexes. The CAS CI calculations showed that the Heisenberg model is not appropriate for 1 under the condition that the Mo–Mo distance is shorter than 2.5 A. The UHF and DFT MO calculations were also performed for the linear naked Mo(II)4 tetramer (2) to elucidate possible electronic structures of the d–d conjugated systems. The continuous chan...

Addition of an excess hexamethylphosphoric triamide (abbr. HMPA) to a neutral complex SmI( ν 8 −C 8 H 8 (thf) ( 1 ) (C 8 H 8 = 1,3,5,7-cyclooctatetraene), which was prepared by a direct reaction of metallic samarium with C 8 H 8 in the presence of iodine in THF, afforded a cationic samarium complex [Sm( η 8 −C 8 H 8 )(hmpa) 3 ]I ( 2 ). Complex 2 can also be prepared by a simple one-pot reaction of stoichiometric amounts of metallic samarium, cyclooctatetraene, and iodine in the presence of an excess HMPA at 50°C. With a catalytic amount of iodine, ionic complexes of general formula Ln (η 8 − C 8 H 8 )( hmpa ) n ][ Ln (η 8 − C 8 H 8 ) 2 ] [ Ln = La and n = 4 ( 6 ); Ln = Sm and n = 3 ( 7 ) ] were obtained by treating metallic lanthanum or samarium, respectively with cyclooctatetraene in the presence of HMPA. The structure of the diamagnetic complex 6 as well as the paramagnetic complexes 2 and 7 was determined by 1 H NMR spectroscopy. Crystal structures of 2 and 7 were revealed by X-ray analyses, indicating that these complexes comprised of a cationic [Sm( η 8 −C 8 H 8 )(hmpa) 3 ] + and an anionic part; for 2 and 7 being I − and [Sm( η 8 −C 8 H 8 ) 2 ] − , respectively.

We demonstrate that half-metallocene diene complexes of tantalum Ta(η5-C5R5)(η4-1, 3-butadiene)2 [R=Me (6); R=H (7)] were catalyst precursors of the polymerization of MMA. Catalytic activity of these complexes sensitively depends on the choice of precatalyst's architecture as well as the polymerization condition whether an aluminum compounds, AlMe(OAr)2(Ar=2, 6-di(tBu)-4-Me-C6H2) (14), as a cocatalyst exists or not. When we used 6 as a catalyst precursor for the polymerization of MMA in the presence of 10 equiv. of 14, a syndiotactic polymer was obtained in quantitative yield within 40min. at 0°C.

A C−C single-bond-forming reaction from ketones with accompanying C−O bond cleavage mediated by a RMgBr or RLi−vanadium(II)−O2 system has been accomplished. Different from conventional reductive coupling reactions of ketones such as the McMurry coupling, the present method forms a C−C single (instead of a double) bond and yields a product that contains components derived from the ketone and the alkylating reagent in a one-pot reaction. Collaboration of both a low-valent vanadium(II) species and a higher-valent vanadium species produced from vanadium(II) and a catalytic amount of O2 effects the abstraction of the oxygen atom from a C−O bond.

The complete active space (CAS) configuration interaction (CI) and CASSCF calculations for naked Cr(II)-Cr(II) (1) and Mo(II)-Mo(II) (2) dimers were carried out in order to examine the reliability of the previous MO-theoretical results obtained by the ab initio UHF and DFT methods. From the CASCI and CASSCF calculations, it was concluded that the formal bond orders (one τ, two π, and one Δ bonds) are reduced to the effective ones due to the strong correlation and also that the valence-bond (VB) like model such as the Heisenberg model works well in 1. The effective exchange integrals (Jab) calculated for the system were compatible with the experimental results available. On the other hand, the σ and π bonds in 2 were strong, showing that the MO picture is reliable. The Δ bond of 2 was calculated to be rather weak, although it is stronger than that of 1. The CASCI and CASSCF results support the previous UHF and DFT results for 1 and 2.

As a continuation of previous UHF calculations, the complete active space (CAS) configuration interaction (CI) calculations by use of their natural orbitals (UNO) were carried out for the linear tetranuclear systems, i.e., M1Cr(II)Cr(II)M1 (M1 = Ni(II) or Ni(0)), to elucidate the nature of the d-d conjugated bonds. The energy levels for the ground and excited high-spin states of these species were also calculated by' UNO CASCI to estimate the effective exchange integrals in the Heisenberg model.

Allylation of carbonyl compounds with allyl halides mediated by a vanadium(II) complex in a mixed solvent system of THF and HMPA has been accomplished. The addition of HMPA stabilized a vanadium−carbon bond of an allyl vanadium species and prevented dimerization of allyl halides or pinacol coupling of carbonyl compounds. Other alkylations such as a benzylation of carbonyl compounds or a Reformatsky-type reaction could also be mediated by a low-valent vanadium(II) species and benzyl bromide or bromo acetate in a THF−HMPA solvent system. By isolation of the vanadium−HMPA complex, [V2Cl3(hmpa)6][ZnCl3(hmpa)] (HMPA = hexamethylphosphoric triamide), and clarification of its structure, it became clear that the coordination of bulky HMPA to vanadium centers played an important role in the carbon−carbon bond-forming reactions.

Direct geminal diallylation of a carbonyl compound with allyl bromide has been achieved in the presence of a low-valent vanadium complex and zinc. The diallylation has been found to proceed stepwise and the two allyl groups were introduced successively. By applying this method, one-pot synthesis of asymmetric quaternary carbons has been accomplished. As the first alkylating reagent a combination of allyl bromide and zinc, a Grignard reagent, or an alkyllithium can be used. The second one should be the combination of a low-valent vanadium(II) complex and allyl bromide, benzyl bromide, or propargyl bromide. Strong oxophilicity of the low-valent vanadium facilitated the deoxygenative allylation.

Mononuclear 16-electron arene−ruthenium(II)−thiolate complexes of the general formula (η6-arene)Ru(SAr)2 (2, Ar = 2,6-C6H3Me2 = Xyl; 3, Ar = 2,4,6-C6H2(CHMe2)3; arene = C6H6 (a), arene = p-MeC6H4(CHMe2) = p-cymene (b), arene = C6Me6 (c)) have been prepared by treatment of [(η6-arene)RuCl2]2 (1) with the corresponding sodium arenethiolate in methanol. Reaction of 2b with disodium of 1,2-benzenedithiolate (=S2C6H4) led to a mixture of monomer and dimer complexes (η6-p-cymene)Ru(S2C6H4) (4b) and [(η6-p-cymene)Ru(S2C6H4)]2 (5b) in solution. A complex (η6-C6Me6)Ru(S2C6H4) (4c) was predominantly monomeric, revealed by a crystal structure analysis of 4c. All these monomeric complexes show intense blue color of the LMCT band due to the donation from the filled S(pπ) orbital to the empty Ru(dπ*) orbital, which stabilizes coordinatively unsaturated ruthenium(II). The structures of these complexes are characterized by NMR and mass spectra and elemental analysis in addition to the X-ray crystal structure determinatio...

Coordinatively unsaturated 16-electron ruthenium-selenolate complexes (η6-arene)Ru(Se-2,4,6-C6H2Me3)2 [arene =p=CH3C6H4(CHMe2) (5b), C6Me6 (5c)] have been prepared by treating [((η6-arene)RuCl2]2 (1) with sodium salt of 2,4,6-trimethylphenyl-selenolate in methanol. The complexes 5 are compared with the thiolate complexes such as (η6-arene)Ru(SAr)2 [SAr = 2,6-dimethylbenzenethiolate (2), SAr = 2,4,6-tri(isopropyl)benzenethiolate (3), (SAr)2 = 1,2-benzenedithiolate (4); arene = C6H6 (a), p-CH3C6H4(CHMe2) (b), C6Me6 (c)], which have been recently prepared by us. However, the tellurolate analog has not been obtained in similar manner. These selenolate complexes are dark green, being ascribed to the LMCT band [pπ(Se)→ dπ*(Ru)]. The absorption bands of S are red-shifted compared to the thiolate complexes. In contrast to the bulky substituted chalcogenolate ligand system, the reaction of 1 with PhENa followed by the addition of KPF6 resulted in the formation of the cationic binuclear chalcogenolate complexes [(η6-arene)Ru(μ-E-Ph)3Ru(η6-arene)](PF6) [E=Se (7), E = Te (8); arene = p-CH3C6H4(CHMe2) (b) C6Me6 (c)]. Reactions of the 16-electron thiolate and selenolate complexes with σ-donor molecules such as DMSO, hydrazine and ammonia along with some electrophiles were investigated. DMSO can coordinate with the thiolate complex 2a to give a DMSO adduct of 9, which was characterized spectroscopically and crystallographically. The strength of complexation of hydrazine and ammonia to the thiolate and selenolate complexes 2, 3, 4c and 5 depends on the effective electron deficiency of the ruthenium supported by η6-arene ligand and two chalcogenolate ligands. Two new hydrazine complexes (η6-C6H6)Ru(η1-NH2)(S-2,6-C6H3Me2)2 (10a) and [(η6-C6Me6)Ru(S2C6H4)]2(μ-NH2NH2) (16) were crystallographically characterized. The observed two different coordination modes, mononuclear η1-hydrazine and binuclear μ-hydrazine, were the results of the combined steric effect of the arene and the thiolate coligands as well as the NH …S hydrogen bonding.

The ligand exchange reaction of a diene ligand bound to magnesium was investigated. Reaction of the magnesium-butadiene compound [Mg(C 4 H 6 )(thf) 2 ] n ( 2 ) with 1,4-diphenyl-1,3-butadiene afforded Mg(s- cis -1,4-diphenyl-1,3-butadiene)(thf) 3 ( 1 ) together with butadiene. Similarly, treatment of 2 with 1,6-diphenyl-1,3,5-hexatriene, anthracene, and 1,3,5,7-cycIooctatetraene afforded the corresponding magnesium adducts Mg(1,6-diphenyl-1,3,5-hexatriene)(thf) 3 ( 3 ) Mg(anthracene)(thf) 3 ( 4 ), and Mg(cot)(thf) 2,5 ( 5 ), respectively, in addition to the liberated butadiene. Reaction of 2 with diphenylacetylene in THF also induced the ligand exchange reaction, resulting in the formation of a diphenylacetylene adduct [Mg(PhC 2 Ph)(thf)] 4 ( 6 ) of magnesium.

Nucleophilic addition of methanol to nonactivated alkynes is catalyzed by platinum phosphine complexes derived from PtCl2(ligand) [ligand = 2PPh3, 2PPh2Me, diphos, dppt (1,5-bis(diphenylphosphino)pentane)] and a silver salt [AgPF6 or AgOTf (silver trifluoromethanesulfonate)] producing ketones in high yields. The catalytic activity is influenced by the phosphine ligand as well as by the anion and the ratio of the dichloroplatinum complex to the silver salt.

Allylation of carbonyl compounds with allyl bromide mediated by a vanadium(II) complex in a mixed solvent of THF and HMPA (HMPA = hexamethylphosphoric triamide) has been accomplished. Coordination of HMPA to a vanadium metal is essential for the stabilization of the allyl vanadium species.

The effective exchange integrals (Jab) and bond orders of naked Cr(II)-Cr(?) and Mo(?)-Mo(?) dimers were calculated by ab initio UHF MO and density functional (DFT) methods. Reduction of formal quadruple bond orders for these species by strong electron correlation effects are examined by these computational procedures. The calculated Jab values are compared with the experimental results for binuclear Cr(II) complexes with different interatomic distances.

The model clusters for the tetranucler transition metal complexes synthesized by Mashima et al. were investigated theoretically. The ab-initio UHF calculations were performed for the Ni-Cr(?)-Cr(II)-Ni and Pd-Mo(?)-Mo(?)-Pd systems to study the nature of the intermetallic bonds. The bond orders and the effective exchange integrals were calculated changing the intermetallic bond distances. It is shown that the tetranuclear dσ-bonds are formed in the cases: Ni(I) and Pd(I).

Two dinuclear complexes of palladium(I) and platinum(II) have been prepared by using a tridentate ligand containing three kinds of coordination sites, i.e. oxygen, nitrogen, and phosphorus atoms. Treatment of palladium(II) acetate with a mixture of 6-(diphenylphosphino)-2-pyridone (abbreviated as PyphosH) and sodium methoxide in diglyme produced a dimeric palladium(I) complex containing a metal−metal bond, Pd2(pyphos)2(pyphosH)2 (1), in 43% yield. The dinuclear complex 1 has a Pd−Pd single bond [2.623(1) A] surrounded by two pyphos ligands and two pyphosH ligands, where the pyphos ligand connected to pyphosH through an intramolecular hydrogen bond [1: monoclinic, space group C2/c with a = 19.794(7) A, b = 14.753(7) A, c = 25.626(5) A, β = 107.65(2)°, V = 7131(4) A3, Z = 4, and R = 0.058 for 4760 reflections with I > 3σ(I) and 451 parameters]. In the case of platinum, a dinuclear platinum(II) complex, Pt2(pyphos)4 (3), was prepared in 84% yield by treatment of PtCl2(pyphosH)2 (2) with 2 equiv of sodium me...

Some alkyl allyl carbonates and an allylammonium chloride bearing (1-(butyloxy)ethyl)oxy group at the 2-position of the allyl group were synthesized and successfully transformed to oxodimethylenemethane−palladium and −platinum complexes in one step by mixing with a transition metal(0) and triphenylphosphine. On the basis of the confirmation of vinyl ether formation by 1H NMR, the generation of oxodimethylenemethane complexes was rationalized to occur through abstraction of the β-hydrogen on the acetal carbon by an alkoxide ion which was generated from the allyl carbonate upon oxidative addition of the transition metal. The palladium-catalyzed cycloaddition of the acetonylidene group to strained olefins also proceeded successfully by using these alkyl allyl carbonates.

The molecular structures of C33H56P2S4, (1), and C 31 H 56 P 2 , (2), are reported. The structure analysis of (1) is the first of a CS2 adduct of an optically active diphosphine. The optically active compound (1) is not a simple CS2 adduct but contains two zwitterionic structures, i.e. 1,2-cyclopentylenedimethylenebis[(dicyclohexyl)phosphoniocarbodithioate], C 5 H 8 [CH 2 P + (C 6 H 11 ) 2 (CS 2 ) - ] 2 .

Direct geminal diallylation of propiophenone with allyl bromide has been achieved in the presence of vanadium(II) species. By applying this method, direct construction of asymmetric quaternary carbons from propiophenone has been accomplished. Strong oxophilicity of the low-valent vanadium facilitated the deoxygenative reaction. The present reaction is characteristic of vanadium complexes.

Reaction of ±-7-phenyldinaphtho[2,1- b ;1′,2′- d ]phosphole ( 1 ) with one-half equivalent of an optically active palladium complex, Pd[( S )-C 6 H 4 CH(CH 3 )N(CH 3 ) 2 ](μ-Cl) 2 (( S )- 3a ), proceeded stereoselectively to give one of the diastereomers, Pd( S )-C 6 H 4 CH(CH 3 )N(CH 3 ) 2 ( P )-PPh(C 20 H 12 )Cl (( S )( P ) 4a ), accompanying racemization of 1 . The X-ray crystallographic analysis of ( S ( P )- 4a determined the absolute configuration of the coordinated phosphole unequivocally to be P . The fluxional behavior of 4a and the related complex is also discussed.

As the first example of a crystallographically confirmed transition metal complex with a bidentate hybrid ligand spanning trans positions, the square-planar palladium(II) complex containing the trans chelating pyridyl-phosphine bidentate hybrid ligand, bound through a pyridine and a phosphine, trans-PdCl2{o-Ph2PC6H4CH2O(CH2)3-2-C5H4N}, is prepared and the crystal structure was determined.

The reaction of Na2[PdCl4] or [PdCl2(PhCN)2] with an equimolar amount of new bidentate hybrid ligands having a P and a N donor atom capable of trans chelation, o-Ph2PC6H4CH2O(CH2)nC5H4N-2 (n= 1–3), gave mainly the 1 : 1 complex [PdCl2{o-Ph2PC6H4CH2O(CH2)nC5H4N-2}]. Depending on the length of the backbone connecting the phosphino and the pyridyl groups, cis- or trans-co-ordinated complexes were mainly formed; when n= 1 the cis complex 1 was formed, but the ligands with longer bridges gave the trans complexes 2 and 3 respectively as the main products. From the reaction of the palladium(II) complex with o-Ph2PC6H4CH2O(CH2)nC5H4N-2 (n= 2 or 3) the trinuclear complexes [Pd3Cl6{o-Ph2PC6H4CH2O-(CH2)nC5H4N-2}2]4(n= 2) and 5(n= 3) were also obtained as minor products and the cis-chelated complexes analogous to 1 could not be isolated. The reaction of Na2[PdCl4] with 2 equivalents of o- Ph2PC6H4CH2O(CH2)3C5H4N-2 gave quantitatively the 1 : 2 complex trans-[PdCl2{o-Ph2PC6H4CH2O-(CH2)3C5H4N-2}2]7 in which the ligand is bound only through the P atom. This complex is in equilibrium with the trans 1 : 1 complex 3 in solution, dissociating one molecule of the ligand (Keq= 5.6 × 10–3 mol dm–3, 35 °C). On heating in CH2Cl2-tetrahydrofuran or diethyl ether, 3 partially isomerised to the dinuclear complex [Pd2Cl4{µ-o-Ph2PC6H4CH2O(CH2)3C5H4N-2}2]6, in which the hybrid ligands act as bridges. The crystal structures of 1, 3 and 6 were determined; 3 is the first example of a transition-metal complex with a trans-spanning chelate phosphine-pyridine hybrid ligand. The reaction of the ligand o-Ph2PC6H4CH2-O(CH2)3C5H4N-2 with K2[PtCl4], in contrast to the palladium complexes, always gave the 1 : 2 complex trans-[PtCl2{o-Ph2PC6H4CH2O(CH2)3C5H4N-2}2]8 in good yield regardless of the ligand: Pt ratio. It did not dissociate in solution and the trans-chelated complex analogous to 3 could not be isolated even from the reaction of K2[PtCl4] with an equimolar amount of the ligand o-Ph2PC6H4CH2O(CH2)3C5H4N-2.

We have shown concrete evidence for migration of an alkyl group in carbonyl insertion and deinsertion steps between the methyl carbonyl rhodium complex [{η5:η1-(Ind-P)n=3}Rh(CO)Me]BF4 (3) and the acetyl rhodium complex {η5:η1-(Ind-P)n=3}RhI(COMe) (1) by crystallography as well as by 1H NMR spectroscopy.