Solvento Complexes Research Articles

Bis(N-Heterocyclic Carbene) Manganese(I) Complexes in Catalytic N-Formylation/N-Methylation of Amines Using Carbon Dioxide and Phenylsilane.

A series of six Mn(I) complexes with general formula [MnBr(bisNHC)(CO)3 ], having a bidentate bis(N-heterocyclic carbene) ligand (bisNHC), has been developed by varying the bridging group between the NHC donors, the nitrogen wingtip substituents and the heterocyclic ring. The synthesis of the complexes has been accomplished by in situ transmetalation of the bisNHC from the corresponding silver(I) complexes. Removal of the bromide anion affords the corresponding solvento complexes [Mn(bisNHC)(CO)3 (CH3 CN)](BF4 ). The influence of the bisNHC structure on its electron donor ability has been evaluated by FTIR and 13 C NMR spectroscopy, both in the neutral and cationic complexes. Finally, the isolated Mn(I)-bisNHC complexes have been employed as homogeneous catalysts in the reductive N-formylation and N-methylation of amines with CO2 as C1 source and phenylsilane as reducing agent, showing a high selectivity for the N-methylated product. Preliminary mechanistic investigations suggest that, in the adopted reaction conditions, the formylated product can be formed via different reaction pathways, either metal-catalyzed or not, while the methylation reaction requires the use of the Mn(I) catalyst.

Organometallic flow chemistry: solvento complexes.

Photolysis under optimised flow conditions of metal carbonyls [{Ln}M(CO)x] [{Ln}M(CO)x = Cr(CO)6, Mo(CO)6, W(CO)6, Mn(CO)3(η-C5H4Me), Re(CO)3(η-C5H5)] in tetrahydrofuran (THF) conveniently affords the synthetically versatile and labile solvento complexes [{Ln}M(CO)x-1(THF)], thereby obviating many of the caveats associated with photochemical syntheses using either 'batch' or falling film techniques. Conversions were optimised and yields assayed by a combination of in situ infrared spectroscopy and derivatisation as the corresponding triphenylphosphine complexes [{Ln}M(CO)x-1(PPh3)].

Noncovalent Interactions at Lanthanide Complexes.

Lanthanide complexes have attracted a widespread attention due to their structural diversity, as well as multifunctional and tunable properties. The development of lanthanide based functional materials has often relied on the design of the secondary coordination sphere of the corresponding lanthanide complexes. For instance, usually simple lanthanide salts (solvento complexes) do not catalyze effectively organic reactions or provide low yield of the expected product, whereas the presence of a suitable organic ligand with a noncovalent bond donor or acceptor centre (secondary coordination sphere) modifies the symmetry around the metal centre in lanthanide complexes which then successfully can act as catalysts in both homogenous and heterogenous catalysis. In this minireview, we discuss several relevant examples, based on X-ray crystal structure analyses, in which the hydrogen, halogen, chalcogen, pnictogen, tetrel and rare-earth bonds, as well as cation-π, anion-π, lone pair-π, π-π and pancake interactions, are used as a synthon in the decoration of the secondary coordination sphere of lanthanide complexes.

New route to strong, long-lived room-temperature phosphorescence using organic phosphor guest-friendly matrices [Al(DMSO)6]X3 (X=Cl−, Br−)

Developing highly desirable organic compounds with strong long-lived room-temperature phosphorescence (RTP) under ambient conditions has been a grand challenge. Present here is a new type of crystalline matrices based on ionic solvento complexes, [Al(DMSO)6]X3 (X− = Cl−, Br−) which can trap various trace amount of organic phosphors to prepare low-cost RTP materials. The phosphorescence of such phases in the air at RT can demonstrate both long lifetime (up to 229.7 ms) and high quantum efficiency (up to 15.8%) due to RTP-enhancing X− anions and phosphor-protecting matrices. Further, the guest-friendly feature of the matrices enables the development of a multiple-RTP doped phase via the simultaneous inclusion of two phosphors into one matrix, enabling unprecedented two-dimensional anti-counterfeiting. The work not only finds a new and facile route to develop low-cost RTP materials including multiple-RTP materials but also expands their application domains.

Solution and Solid-State Characterization of PbSe Precursors.

The addition of lead to diphenyl diselenide in ethylenediamine (en) or pyridine (py) allowed for the observation of the solvento complexes, (en)Pb(SePh)2 or (py)2Pb(SePh)2, respectively. Performing this reaction in dimethyl sulfoxide and subsequent crystallization was found to afford Pb(SePh)2. Inductively coupled plasma optical emission spectroscopy revealed a 1:2 lead to selenium ratio for all three complexes. Nuclear magnetic resonance spectroscopy confirms that Pb(SePh)2 is readily solubilized by ethylenediamine, and electrospray ionization mass spectrometry supports the presence of Pb(SePh)2 moieties in solution. Single-crystal X-ray diffraction analysis of the pyridine adduct, (py)2Pb(SePh)2, revealed a seesaw molecular geometry featuring equatorial phenylselenolate ligands. Crystals of Pb(SePh)2 grown from dimethyl sulfoxide revealed one-dimensional polymeric chains of Pb(SePh)2. We believe that the lead(II) phenylselenolate complexes form via an oxidative addition reaction.

An Aerobic Synthetic Approach toward Bis-Alkynyl Cobalt(III) Compounds.

Reported herein is an expanded investigation into a new method for the preparation of Co(III) cyclam bis-alkynyls (cyclam = 1,4,8,11-tetraazacyclotetradecane) under aerobic, weak base conditions. Treatment of trans-[Co(cyclam)(C2Ar)Cl]Cl-type complexes (Ar = C6F5 (1a), 4-C6H4NMe2 (1b)) with AgOTf in MeCN resulted in the doubly charged complexes [Co(cyclam)(C2Ar)(NCMe)](OTf)2 (Ar = C6F5 (2a), 4-C6H4NMe2 (2b)). These solvento complexes 2a,b undergo rapid alkynylation under aerobic conditions in the presence of an organic base and HC2Ar' to form the symmetrical or unsymmetrical bis-alkynyl complexes trans-[Co(cyclam)(C2Ar)(C2Ar')](OTf) (Ar/Ar' = C6F5 (3a), 4-C6H4NMe2 (3b); Ar = C6F5 and Ar' = 4-C6H4NMe2 (3c), C2Ph (3d)) in good yields. Molecular structures of the new compounds were established using single-crystal X-ray diffraction. Structural studies revealed a notable trans influence for the Co-Cα bond lengths in the unsymmetrical complex 3c with a bond length of 1.929(7) Å for the electron-withdrawing -C2C6F5 ligand and 1.944(7) Å for -C2-4-C6H4NMe2. The optical HOMO-LUMO gaps for the bis-alkynyl complexes follow the trend 3a (2.83 eV) > 3d (2.77 eV) > 3c (2.70 eV) > 3b (2.64 eV). Although [Co(cyclam)(C2R)2]+ type complexes typically have irreversible electrochemical reductions, reversibility of the Co(+3/+2) couple improves in Co(III) cyclam complexes bearing more electron withdrawing substituents. Voltammetric analysis also revealed a modest NMe2/NMe2 coupling across the Co-alkynyl backbone in 3b, while DFT calculations identified the HOMO in 3b as the superexchange pathway for such coupling.

Controlled cis Labilization of CO from Manganese(I) Mixed Carbonyl/Isocyanide Complexes: An Entry Point to Coordinatively Unsaturated Metallo-Lewis Acids

Presented herein is a general design strategy for the formation of coordinatively unsaturated Mn(I) fragments via the cis labilization of CO using metal carboxylates and subsequent deprotection by a range of abstraction agents. A consistent trend is observed in the ability of carboxylate ligands to facilitate CO dissociation as a function of the electron-releasing properties of the carboxylate R group. This is in agreement with previous theoretical work on cis-labilizing ligands. A variety of κ2-coordinated carboxylates function as site-protection ligands for the [Mn(CO)2(CNArDipp2)2]+ scaffold and can be liberated using a range of synthetic techniques. The coordinatively unsaturated species thus formed are shown to be strong metal-based Lewis acids and can engage in agostic-type interactions; in addition, they can be trapped as the corresponding solvento complexes by ethereal solvents.

Synthesis and catalytic alcohol oxidation and ketone transfer hydrogenation activity of donor-functionalized mesoionic triazolylidene ruthenium(ii) complexes

We report on the synthesis of a variety of C,E-bidentate triazolylidene ruthenium complexes that comprise different donor substituents E (E = C: phenyl anion; E = O: carboxylate, alkoxide; E = N: pyridine at heterocyclic carbon or nitrogen). Introduction of these donor functionalities is greatly facilitated by the synthetic versatility of triazoles, and their facile preparation routes. Five different complexes featuring a C,E-coordinated ruthenium center with chloride/cymene spectator ligands and three analogous solvento complexes with MeCN spectator ligands were prepared and evaluated as catalyst precursors for direct base- and oxidant-free alcohol dehydrogenation, and for transfer hydrogenation using basic iPrOH as a source of dihydrogen. In both catalytic reactions, the neutral/mono-cationic complexes with chloride/cymene spectator ligands performed better than the solvento ruthenium complexes. The donor functionality had a further profound impact on catalytic activity. For alcohol dehydrogenation, the C,C-bidentate phenyl-triazolylidene ligand induced highest conversions, while carboxylate or pyridine donor sites gave only moderate activity or none at all. In contrast, transfer hydrogenation is most efficient when a pyridyl donor group is linked to the triazolylidene via the heterocyclic carbon atom, providing turnover frequencies as high as 1400 h(-1) for cyclohexanone transfer hydrogenation. The role of the donor group is discussed in mechanistic terms.

Control of the Mutual Arrangement of Cyclometalated Ligands in Cationic Iridium(III) Complexes. Synthesis, Spectroscopy, and Electroluminescence of the Different Isomers

Synthetic control of the mutual arrangement of the cyclometalated ligands (C^N) in Ir(III) dimers, [Ir(C^N)(2)Cl](2), and cationic bis-cyclometalated Ir(III) complexes, [Ir(C^N)(2)(L^L)](+) (L^L = neutral ligand), is described for the first time. Using 1-benzyl-4-(2,4-difluorophenyl)-1H-1,2,3-triazole (HdfptrBz) as a cyclometalating ligand, two different Ir(III) dimers, [Ir(dfptrBz)(2)Cl](2), are synthesized depending on the reaction conditions. At 80 °C, the dimer with an unusual mutual cis-C,C and cis-N,N configuration of the C^N ligands is isolated. In contrast, at higher temperature (140 °C), the geometrical isomer with the common cis-C,C and trans-N,N arrangement of the C^N ligand is obtained. In both cases, an asymmetric bridge, formed by a chloro ligand and two adjacent nitrogens of the triazole ring of one of the cyclometalated ligands, is observed. The dimers are cleaved in coordinating solvents to give the solvento complexes [Ir(dfptrBz)(2)Cl(S)] (S = DMSO or acetonitrile), which maintain the C^N arrangement of the parent dimers. Controlling the C^N ligand arrangement in the dimers allows for the preparation of the first example of geometrical isomers of a cationic bis-cyclometalated Ir(III) complex. Thus, N,N-trans-[Ir(dfptrBz)(2)(dmbpy)](+) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine), with cis-C,C and trans-N,N arrangement of the C^N ligands, as well as N,N-cis-[Ir(dfptrBz)(2)(dmbpy)](+), with cis-C,C and cis-N,N C^N ligand orientation, are synthesized and characterized. Interestingly, both isomers show significantly different photophysical and electroluminescent properties, depending on the mutual arrangement of the C^N ligands. Furthermore, quantum chemical calculations give insight into the observed photophysical experimental data.

Insertion of nitrene and chalcogenolate groups into the Ir–C σ bond in a cyclometalated iridium(III) complex

Treatment of [Cp∗Ir(ppy)Cl] (Cp∗ = η 5-C 5Me 5, ppyH = 2-(2-pyridyl)phenyl) with Ag(OTf) (OTf − = triflate) in MeOH and MeCN gave the solvento complexes [Cp∗Ir(ppy)(solv)][OTf] (solv = MeOH ( 1) and MeCN ( 2)). Complex 1 is capable of catalyzing oxidation and azirdination of styrene with PhIO and PhINTs (Ts = tosyl), respectively. Treatment of 2 with a stoichiometric amount of PhINTs resulted in the insertion of the NTs group into the Ir–C(ppy) bond and formation of [Cp∗Ir(η 2-ppy-NTs)(MeCN)][OTf] ( 3). Treatment of 1 with R 2E 2 afforded [Cp∗Ir(ppy)(η 1-R 2E 2)][OTf] (E = S ( 4), Se ( 5), Te ( 6)). Reactions of 4 and 5 with Ag(OTf) resulted in cleavage of the E–E bond and insertion of an ER group into the Ir–C(ppy) bond. The crystal structures of complexes 2– 6 and [Cp∗Ir(η 2-ppy-S- p-tol)(H 2O)][OTf] 2 have been determined.

Dialkylamino cyclopentadienyl ruthenium(ii) complex-catalyzed α-alkylation of arylacetonitriles with primary alcohols

Aminocyclopentadienyl ruthenium complexes, [(eta(5)-C(5)H(4)NMe(2))Ru(PPh(3))(2)(CH(3)CN)](+)BF(4)(-) and [(eta(5)-C(5)H(4)NEt(2))Ru(PPh(3))(2)(CH(3)CN)](+)BF(4)(-), are moderately active catalysts for alpha-alkylation of arylacetonitriles with primary alcohols; on the other hand, the analogous unsubstituted cyclopentadienyl ruthenium complex [(eta(5)-C(5)H(5))Ru(PPh(3))(2)(CH(3)CN)](+)BF(4)(-) shows very low catalytic activity. On the basis of experimental results and theoretical calculations, rationalization for the much higher catalytic activity of the aminocyclopentadienyl complexes over that of the unsubstituted Cp complex is provided. In the catalytic systems with the former, it is possible to regenerate the active solvento complexes via protonation of the metal hydride intermediates and subsequent ligand substitution; this process is, however, very nonfacile in the catalytic system with the latter.

Fe–Cu octahedral carbide clusters, and the replacement of their labile halide ligands: Synthesis, solid state structure, substitution and electrochemical reactivity of [Fe 5C(CO) 14(CuBr)] 2−, [Fe 4C(CO) 12(CuCl) 2] 2−, [{Fe 4Cu 2C(CO) 12(μ-Cl)} 2] 2−, [Fe 5C(CO) 14(CuOC 4H 8)] − and [Fe 4C(CO) 12(CuNCMe) 2

The reactions between [Fe 6C(CO) 16] 2− and CuCl, in refluxing THF, yield [Fe 5C(CO) 14(CuCl)] 2− ( 1), [Fe 4C(CO) 12(CuCl) 2] 2− ( 2), or [{Fe 4Cu 2C(CO) 12(μ-Cl)} 2] 2− ( 3), depending on the Fe 6/CuCl ratio. The chloro ligands of these clusters can be displaced either spontaneously, or by metal-assisted substitution, to give the bromo derivative [Fe 5C(CO) 14(CuBr)] 2− ( 4) or the solvento complexes [Fe 5C(CO) 14(CuTHF)] − ( 5) and [Fe 4C(CO) 12(CuNCMe) 2] ( 6). The latter can be also obtained directly, by metal substitution from [Fe 6C(CO) 16] 2− and [Cu(NCMe) 4]BF 4, or by polyhedral expansion from [Fe 4C(CO) 12] 2−. All the clusters are octahedral, with the copper atoms in a pseudo-linear geometry, where one of the coordination positions is occupied by the interstitial carbide. The two copper atoms in the Fe 4Cu 2 clusters are always in cis geometry and, in the dimer [{Fe 4Cu 2C(CO) 12(μ-Cl)} 2] 2−, they are joined through chlorides. The role of the different metal centres in determining the redox activity of the heteronuclear Fe–Cu clusters 1, 2, 3, has been studied by electrochemical methods. In the bridged dimer 3, the two Fe 4Cu 2C cluster units resulted electronically not communicating.

Photochemical Ligand Substitution Reactions of fac-[Re(bpy)(CO)3Cl] and Derivatives

Excitation by high-energy light, such as that of 313 nm wavelength, induces a photochemical ligand substitution (PLS) reaction of fac-[Re(bpy)(CO)3Cl] (1a) to give the solvento complexes (OC-6-34)- and (OC-6-44)-[Re(bpy)(CO)2(MeCN)Cl] (2 and 3) in good yields. The disappearance quantum yield of 1a was 0.01+/-0.001 at 313 nm. The products were isolated, and X-ray crystallographic analysis was successfully performed for 2. Time-resolved IR measurements clearly indicated that the CO ligand dissociates with subpicosecond rates after excitation, leading to vibrationally hot photoproducts, which relax within 50-100 ps. Detailed studies of the reaction mechanism show that the PLS reaction of 1a does not proceed via the lowest vibrational level in the 3MLCT excited state. The PLS reaction gives 2 and (OC-6-24)-[Re(bpy)(CO)2(MeCN)Cl] (5) as primary products, and one of the products, 5, isomerizes to 3. This type of PLS reaction is more general, occurring in various fac-rhenium(I) diimine tricarbonyl complexes such as fac-[Re(X2bpy)(CO)3Cl] (X2bpy=4,4'-X2-bpy; X=MeO, NH2, CF3), fac-[Re(bpy)(CO)3(pyridine)]+, and fac-[Re(bpy)(CO)3(MeCN)]+. The stable photoproducts (OC-6-44)- and (OC-6-43)-[Re(bpy)(CO)2(MeCN)(pyridine)]+ and (OC-6-32)- and (OC-6-33)-[Re(bpy)(CO)2(MeCN)2]+ were isolated. The PLS reaction of rhenium tricarbonyl-diimine complexes is therefore applicable as a general synthetic method for novel dicarbonyls.

Chromium(iii) catalysed ethylene tetramerization promoted by bis(phosphino)amines with an N-functionalized pendant

Several N-functionalized bis(phosphino)amine ligands with ether, thioether and pyridyl tethers [(R'')2PN(R')P(R'')2=PNP] () have been synthesized. They react with CrCl3(THF)3 in CH2Cl2 to give dinuclear chloro bridged Cr2(micro-Cl)2Cl4(PNP)2 () which converts to the corresponding mononuclear solvento complexes fac-CrCl3(PNP)(NCR) (). The structures of the ligand with R'=-(CH2)3SCH3 and R''=Ph, and the complexes with R=CH3 () and C2H5 (), R'=-(CH2)3SCH3 and R''=Ph) have been established by single-crystal X-ray crystallography. All ligands are active towards ethylene tetramerization in the presence of Cr(III) and excess MAO at 80 degrees C in toluene. The ligand with thioether pendant Et2PN(CH2CH2CH2SCH3)PEt2 () shows the highest selectivity (55% weight in liquid product distribution) towards 1-octene. Complexes and are active towards ethylene polymerization under thermal conditions.

Comparative Studies with Zwitterionic Platinum(II) Bis(pyrazolyl)borate and 2,2‘-Bipyridylborate Complexes

A comparison between the mononuclear platinum complexes of three structurally different monoanionic borato ligands is presented: [Ph_2B(pyrazolyl)_2]- ([Ph_2B(pz)_2], 1), [4-Ph_3B(2,2‘-bipyridine)]- ([(4-BPh_3)bpy], 2), and [Ph_2B(CH_2PPh_2)_2]- ([Ph_2BP_2], 3). The new bipyridylborate ligand 2 is introduced in this study. The relative trans influence of these ligands has been assessed by comparison of the structural and spectroscopic (NMR) data of the platinum dimethyl complexes [[Ph_2B(pz)_2]Pt(Me)_2][NBu_4] (4), [[(4-BPh_3)bpy]Pt(Me)_2][NBu_4] (5), and [[Ph_2BP_2]Pt(Me)_2][ASN] (6). The neutral complexes [Ph_2B(pz)_2]Pt(Me)(NCCH_3) (7), [Ph_2B(pz)_2]Pt(Me)(CO) (8), [Ph_2B(pz)_2]Pt(Me)(P(C_6F_5)_3) (9), [(4-BPh_3)bpy]Pt(Me)(NCCH_3) (10), [(4-BPh_3)bpy]Pt(Me)(CO) (11), and [(bpy)Pt(Me)(CO)][BPh_4] (12) were prepared, and the carbonyl complexes 8, 11, and 12 provide information pertaining to the relative electron-releasing character of each ligand type. The CO stretching frequencies suggest that the charged borate moiety renders the borato ligands more electron-donating than their neutral analogues. Of the neutral platinum methyl solvento complexes supported by ligands 1, 2, and 3, only those of 1 display very different C−H activation propensities. Upon protonation or methide abstraction in benzene at room temperature, complex 4 rapidly activates two molecules of benzene to generate [[Ph_2B(pz)_2]Pt(Ph)_2][NBu_4] (13). Isotopic scrambling of deuterium into methane in C_6D_6 solvent suggests the intermediacy of a methane σ-adduct in this reaction. The double C−H activation reaction can be halted by addition of acetonitrile to trap the intermediate [Ph_2B(pz)_2]Pt(Ph)(NCCH_3) (14). Complex 3 also displays reactivity toward the benzylic C−H bonds of mesitylene at room temperature to form [Ph_2B(pz)_2]Pt(pzH)(CH_2C_6H_3(CH_3)_2) (15) in modest yield.

Cu(I) beta-diketiminates for alkene aziridination: reversible Cu-arene binding and catalytic nitrene transfer from PhI=NTs.

beta-Diketiminato Cu(I)-lutidine complexes [RMeNN]Cu(2,4-lutidine) (R = Me (4a), (i)Pr (4b)) were prepared in high yield from Tl[RMeNN] and [CuBr(2,4-lutidine)(2)](2). Both 4a and 4b reversibly dissociate lutidine base in toluene to give [RMeNN]Cu(toluene) solvento complexes. A related base-free dicopper species [[Me(2)NN]Cu](2) (6) bridged via eta(2)-binding of opposing N-aryl rings could be isolated by the addition of Tl[Me(2)NN] to CuBr. The lutidine precursors serve as precatalysts for the aziridination of alkenes with PhI=NTs. Styrene, beta-methylstyrene, and cyclooctene gave the highest yields (59-96%) with a low olefin to PhI=NTs ratio (3:1) and 5 mol % catalyst loading.

Solvent Stabilization and Hydrogenation Catalysis of Trimethylphosphine-Substituted Carbonyl Rhenium Cations

A series of cationic complexes were designed as catalysts for imine hydrogenation processes, and it was anticipated that for this purpose naked 16e- cations or relatively labile solvent-coordinated ones possessing noncoordinating counterions would suffice. Solvento complexes [Re(CO)3(PMe3)2(S)][BArF] (4(PhCl) and 4(THF)) and [mer-Re(CO)2(PMe3)3(S)][BArF] (5(PhCl) and 5(THF)) (BArF = [B(3,5-(CF3)2C6H3)4]-; S = PhCl)) were obtained from their corresponding hydride complexes 1 and 2 after treatment with [Ph3C][BArF] in chlorobenzene. The five-coordinated cationic complex [Re(CO)(PMe3)4][BArF] (6) (BArF = [B(3,5-(CF3)2C6H3)4]-) was obtained by the reaction of ReH(CO)(PMe3)4 (3) with 1 equiv of [Ph3C][BArF] in chlorobenzene. Hydride abstraction also occurred except for 1 from 2 and 3 with B(C6F5)3, producing [Re(CO)2(PMe3)3(S)][BH(C6F5)3] and [Re(CO)(PMe3)4][BH(C6F5)] (S = PhCl, THF). Treatment of ReH(CO)3(PMe3)2 (1) and ReH(CO)2(PMe3)3(2) with 1 equiv of [isopropylisopropylideneiminium][BArF] in chlorobenzene...

Why Cationic Mono-Organo Bis-Phosphine Solvento Complexes of Platinum(II) Are Short-Lived Species? A Mechanistic and Synthetic Problem

Complexes of the type cis -[Pt(PR 3 ) 2 (R′)(S)] + (PR 3 =tertiary phosphine, R′=alkyl- or aryl groups; S=solvent), unlike their trans isomers, are short-lived species. These elusive compounds can be formed "in situ" easily by protonolysis of precursor dialkyls or mixed alkyl-aryl platinum complexes. The reason for their instability in solution is a facile conversion into the trans isomers with a mechanism which involves dissociative loss of the solvent molecule and interconversion of two geometrically distinct 3-coordinate T-shaped 14-electron intermediates. The application of QALE (quantitative analysis of ligand effects) to NMR and rate data provide a means of ascertaining the relative importance of electronic ad steric properties of the "spectator" phosphine ligands in governing the structural characteristics of the precursor dialkyls and the lability of the monoalkyl solvento species. The overall structure-reactivity correlation has been rationalized. The velocity of the geometrical isomerization depends dramatically upon the nature of the ancillary phosphine ligands. The following factors combine to stabilize the 3-coordinate T-shaped transition state and to accelerate the rate of conversion: ( i ) electron release by the phosphine ligands, ( ii ) steric repulsions and distortion of the original 4-coordinate square-planar configuration, ( iii ) interaction of the vacant coordination site of the metal with β-hydrogen atoms of the alkyl chain. The stabilization energy involved in the kinetic β-hydrogen effect for cis -[Pt(PR 3 ) 2 (Et)(MeOH)] + is around 24 kJ mol −1 at 298 K.

Preparation of heteroatom compounds by stepwise atom/group transfer in cis- and trans-[OS(VI)(tpy)(Cl)2(N)](+).

Rapid 2e-, N- transfer reactions occur between both cis- and trans-[OsVI(tpy)(Cl)2(N)]+ and Me2C6H3SH to give cis- and trans-[OsIV(tpy)(Cl)2(NS(H)C6H3Me2)]+ with retention of stereochemistry. These complexes undergo further reactions with PPh3 or p-MeOC6H4NH2 by net 2e-, NSC6H3Me22- group transfer reactions to give the solvento complexes, cis- and trans-[OsII(tpy)(Cl)2(NCCH3)], and the organic products, Ph3PNSC6H3Me2 and p-MeOC6H4N(H)NS(H)C6H3Me2, respectively. The sequential atom/group transfer reactions at the nitrido nitrogen atom provide a new stepwise synthetic route to PNS and NNS heteroatom compounds.

Formation of Novel 1:1 Adducts Accompanied by Regioselective Hydride Transfer from Transition-Metal Hydrido Complexes to NAD(P) Models

Important intermediates in regioslective hydride reduction of NAD(P) model compounds were detected by various spectroscopic methods. The metal hydrido complexes [Ru(tpy)(bpy)H]+ and [Re(bpy)(CO)3H] react with the NAD(P) models to give 1:1 adducts, which are cleaved to the 1,4-dihydro form of the models and the solvento complexes, quantitatively.