Tris(trichlorosilyl)tetrelide Anions and a Comparative Study of Their Donor Qualities

Trichlorosilylated tetrelides [(Cl₃Si)₃E]⁻ have been prepared by adding 1 equiv of a soluble Cl⁻ salt to (Cl₃Si)₄Si (E=Si) or 4 Si₂Cl₆/GeCl₄ (E=Ge). To assess their donor qualities, the anions [(Cl₃Si)₃E]⁻ (E=C, Si, Ge) have been treated with BCl₃, AlCl₃, and GaCl₃. Both BCl₃ and GaCl₃ give 1:1 adducts with the anionic centers. AlCl₃ leads to Cl⁻ abstraction from [(Cl₃Si)₃E]⁻ with formation of (Cl₃Si)₄E (E=Si or Ge). (Cl₃Si)₄Ge is cleanly converted to the perhydrogenated (H₃Si)₄Ge by use of Li[AlH₄]. Another case of Cl⁻ abstraction was observed for [(Cl₃Si)₃Ge ⋅ GaCl₃]⁻, which reacts with GaCl₃ to afford the neutral dimer [(Cl₃Si)₃Ge−GaCl₂]₂.     

Periodicity in Structure,Bonding, and Reactivity for p-Block Complexes of a Geometry Constraining Triamide Ligand

The use of pincer ligands to access non-VSEPR geometries at main-group centers is an emerging strategy for eliciting new stoichiometric and catalytic reactivity. As part of this effort, several different tridentate trianionic substituents have to date been employed at a range of different central elements, providing a patchwork dataset that precludes rigorous structure–function correlation. An analysis of periodic trends in structure (solid, solution, and computation), bonding, and reactivity based on systematic variation of the central element (P, As, Sb, or Bi) with retention of a single tridentate triamide substituent is reported herein. In this homologous series, the central element can adopt either a bent or planar geometry. The tendency to adopt planar geometries increases descending the group with the phosphorus triamide ( 1 ) and its arsenic congener ( 2 ) exhibiting bent conformations, and the antimony ( 3 ) and bismuth ( 4 ) analogues exhibiting a predominantly planar structure in solution. This trend has been rationalized using an energy decomposition analysis. A rare phase-dependent dynamic covalent dimerization was observed for 3 and the associated thermodynamic parameters were established quantitatively. Planar geometries were found to engender lower LUMO energies and smaller band gaps than bent ones, resulting in different reactivity patterns. These results provide a benchmark dataset to guide further research in this rapidly emerging area.     

Non-Oxido-Vanadium(IV) Metalloradical Complexes with Bidentate 1,2-Dithienylethene Ligands: Observation of Reversible Cyclization of the Ligand Scaffold in Solution

Derivatives of 1,2-dithienylethene (DTE) have superb photochromic properties due to an efficient reversible photocyclization reaction of their hexatriene structure and, thus, have application potential in materials for optoelectronics and (multi-responsive) molecular switches. Transition-metal complexes bearing switchable DTE motifs commonly incorporate their coordination site rather distant from the hexatriene system. In this work the redox active ligand 1,2-bis(2,5-dimethylthiophen-3-yl)ethane-1,2-dione is described, which reacts with [V(TMEDA)₂Cl₂] to give a rare non-oxido vanadium(IV) species 3(M,M/P,P) . This blue complex has two bidentate en-diolato ligands which chelate the V^IV center and give rise to two five-membered metallacycles with the adjacent hexatriene DTE backbone bearing axial chirality. Upon irradiation with UVA light or prolonged heating in solution, the blue compound 3(M,M/P,P) converts into the purple atropisomer 4(para,M/para,P) . Both complexes were isolated and structurally characterized by single-crystal X-ray diffraction analysis (using lab source and synchrotron radiation). The antiparallel configuration (M or P helicity) present in both 3(M,M/P,P) and 4(para,M/para,P) is a prerequisite for (reversible) 6π cyclization reactions. A CW EPR spectroscopic study reveals the metalloradical character for 3(M,M/P,P) and 4(para,M/para,P) and indicates dynamic reversible cyclization of the DTE backbone in complex 3(M,M/P,P) at ambient temperature in solution.     

The Addition of Platinum and Palladium Groups to the Disulfido Ligand in Cyclopentadienyl Molybdenum-Manganese Carbonyl Complexes

The reaction of the complexes CpMoMn(CO)₅(-S₂), 2a, Cp=C₅H₅ and Cp*MoMn(CO)₅(-S₂), 2b, Cp*=C₅Me₅with (PPh₃)₂Pt(PhC₂Ph) yielded the new bis-sulfido mixed metal complexes CpMoMn(CO)₅Pt(PPh₃)₂( ₃-S)₂, 3a and Cp*MoMn(CO)₅Pt(PPh₃)₂( ₃-S)₂, 3b by insertion of a platinum metal grouping into the S–S bond. A mono-phosphine complex, Cp*MoMn(CO)₆Pt(PPh₃)( ₃-S)₂, 4b was also isolated from the reaction of 2b with (PPh₃)₂Pt(PhC₂Ph). Compounds 3b and 4b were both characterized crystallographically. Both complexes consist of open MoMnPt clusters with a Mo–Mn single bond, Mo–Mn=2.7570(16) Å for 3b and Mo–Mn=2.7837(13) Å for 4b, and two triply bridging sulfido ligands. The trimetallic complexes CpMo(O)MnPd(PBu ^t ₃)(CO)₅( ₃-S), 5a and Cp*Mo(O)MnPd(PBu ^t ₃)(CO)₅( ₃-S), 5b containing an oxo ligand bonded to molybdenum were obtained from the reaction of 2a–b with Pd(PBu ^t ₃)₂. The molecular structure of the 5a was also established crystallographically.     

Coordination Complexes of Ph3Sb2+ and Ph3Bi2+: Beyond Pnictonium Cations

The syntheses of salts containing ligand‐stabilized Ph₃Sb²⁺ and Ph₃Bi²⁺ dications have been realized by in situ formation of Ph₃Pn(OTf)₂ (Pn=Sb or Bi) and subsequent reaction with OPPh₃, dmap and bipy. The solid‐state structures demonstrate diversity imposed by the steric demands and nature of the ligands. The synthetic method has the potential for broad application enabling widespread development of the coordination chemistry for Pn^V acceptors.     

Electronic and Steric Ligand Effects in the Radical Polymerization of Vinyl Acetate Mediated by β‐Ketoiminate Complexes of Cobalt(II)

Complexes Co[OC(Ph)CHC(Me)NAr]₂ [Ar=Ph, 1 ; o,o′‐C₆H₃Me₂ (Xyl), 2 ; p‐C₆H₄CF₃, 3 ] are tested in the polymerization of vinyl acetate (VAc) initiated by V‐70 (0.8 equiv) at 30 °C. Polymerization occurs without any notable induction time yielding PVAc with relatively low polydispersity, but with higher than expected M_n values, which indicates inefficient trapping processes. The apparent polymerization rate constant varies in the order 2 > 1 > 3 . Controlled polymer growth is also observed when the polymerization is conducted in the presence of a much higher V‐70/ 1 ratio, demonstrating that this system can also function as a transfer agent in a degenerative transfer process. Competition between chain growth and catalyzed chain transfer (CCT) is also observed, the latter prevailing at higher temperatures. Comparison of these results with previous reports on bis(β‐diketonato) complexes allows a separate assessment of ligand electronic and steric effects in the ability to control polymerization.     

基于柔性多元羧酸配体构筑的两例过渡金属配位聚合物的合成、结构及性质

以柔性配体5-(吡啶-2-甲氧基)-间苯二甲酸为主配体在水热条件下合成了2例过渡金属配位聚合物[Cu(L)·H₂O]_n (1), {[Co(L)·H₂O]₂·5H₂O}_n (2)(H₂L=5-(吡啶-2-甲氧基)-间苯二甲酸),并通过X射线单晶衍射、红外光谱、X射线粉末衍射、元素分析和热重分析方法对其进行表征。结构分析表明:配合物1为单斜晶系P2₁/n空间群的二维平面结构,并呈现2-节点(3,4)-连接的拓扑网络。2为三斜晶系,P1空间群的一维链状结构,在分子间氢键的作用下构筑出三维超分子网络结构。同时对配合物1和2进行了发光性质的研究。     

Dinuclear Palladium Complexes with Two Ligand‐Centered Radicals and a Single Bridging Ligand: Subtle Tuning of Magnetic Properties

The facile and tunable preparation of unique dinuclear [(L^?)Pd?X?Pd(L^?)] complexes (X=Cl or N₃), bearing a ligand radical on each Pd, is disclosed, as well as their magnetochemistry in solution and solid state is reported. Chloride abstraction from [PdCl( NNO^ISQ )] ( NNO^ISQ =iminosemiquinonato) with TlPF₆ results in an unusual monochlorido‐bridged dinuclear open‐shell diradical species, [{Pd( NNO ^ISQ)}₂(μ‐Cl)]⁺, with an unusually small Pd‐Cl‐Pd angle (ca. 93°, determined by X‐ray). This suggests an intramolecular d⁸–d⁸ interaction, which is supported by DFT calculations. SQUID measurements indicate moderate antiferromagnetic spin exchange between the two ligand radicals and an overall singlet ground state in the solid state. VT EPR spectroscopy shows a transient signal corresponding to a triplet state between 20 and 60 K. Complex 2 reacts with PPh₃ to generate [Pd(NNO^ISQ)(PPh₃)]⁺ and one equivalent of [PdCl( NNO^ISQ )]. Reacting an 1:1 mixture of [PdCl( NNO^ISQ )] and [Pd(N₃)( NNO^{I SQ})] furnishes the 1,1‐azido‐bridged dinuclear diradical [{Pd( NNO ^ISQ)}₂(κ¹‐N;μ‐N₃]⁺, with a Pd‐N‐Pd angle close to 127° (X‐ray). Magnetic and EPR measurements indicate two independent S=1/2 spin carriers and no magnetic interaction in the solid state. The two diradical species both show no spin exchange in solution, likely because of unhindered rotation around the Pd?X?Pd core. This work demonstrates that a single bridging atom can induce subtle and tunable changes in structural and magnetic properties of novel dinuclear Pd complexes featuring two ligand‐based radicals.     

Biomimetic Interaction between FeII and O2: Effect of the Second Coordination Sphere on O2 Binding to FeII Complexes: Evidence of Coordination at the Metal Centre by a Dissociative Mechanism in the Formation of μ‐Oxo Diferric Complexes

We report that the formation of μ‐oxo diferric compounds from O₂ and FeCl₂ complexes within the tris(2‐pyridylmethyl)amine series (N. K. Thallaj et al. Chem. Eur. J., 2008 , 14, 6742–6753) involves coordination of O₂ to the metal centre and that this reaction occurs following initial dissociation of the bound equatorial chloride anion. We also report evidence of the formation of a reduced form of dioxygen by an inner‐sphere mechanism, thus leading to modification of the ligand. The solid‐state structures of [FeCl₂L] complexes (L¹=mono(α‐pivalamidopyridylmethyl)bis(2‐pyridylmethyl)amine, L²=mono(α‐pivalesteropyridylmethyl)bis(2‐pyridylmethyl)amine, L³=bis(α‐pivalamidopyridylmethyl)mono(2‐pyridylmethyl)amine are described, and spectroscopic data support the structural retention in solution. In [FeCl₂L³], the two amide hydrogen atoms stabilise the equatorial chloride anion in such a way that its exchange by a weak ligand is impossible: [FeCl₂L³] is perfectly oxygen‐stable. In [FeCl₂L²], the equatorial chloride anion is completely free to move and coordination of O₂ can take place. The reaction product with [FeCl₂L²] is a μ‐oxo diferric complex in which the ester function has been transformed into a phenol group. This conversion can be seen as a hydrolysis reaction in basic medium, hence supporting the initial formation of a reduced form of dioxygen in the medium. Complex [FeCl₂L¹] exhibits a very weak reactivity with O₂, in line with a semistabilised equatorial chloride counteranion.     

An alternative way of characterising the bonding in compounds featuring main-group elements and with the potential for multiple bonding: on the dissociation of binary main-group hydrides

Herein the bonding in compounds featuring main-group elements and with the potential for multiple bonding is studied theoretically by examination of their fragmentation into two fragments that still exhibit the same structure as they had in the molecule prior to dissociation. The fragments were calculated both in their electronic ground state and in an excited electronic state, in which the number of unpaired electrons is equal to the maximal number of bonds in the compounds before dissociation. The energies of the fragmentation processes (DeltaE(frag)) can be more directly linked to the bond strengths than the dissociation energies (DeltaE(diss)), because of the absence of any secondary effects like relaxation of the electronic state or of the geometry of the fragments. These relaxation energies of the fragments (DeltaE(frag)) are also studied herein. The energies derived in this work allow for an accurate comparison of the bonding properties in main-group-element hydrides. The trends of the fragmentation and relaxation energies are discussed in detail. It will be shown that the relaxation energies allow for a classification of the bonds ("classical" sigma and pi bonds or donor-acceptor interactions), while the fragmentation energies are good quantitative measures for the total bond strength. Similar calculations are on the way to explore the bonding in systems in which the hydrogen atoms are replaced by organic groups or halogen atoms.     

Influence of Coordination Geometry on the Ring Opening of Benzoxazine: Oxidovanadium(V), Dioxidomolybdenum(VI) and Dioxidotungsten(VI) Complexes of Benzoxazine Based Ligands and their Bio Inspired Catalytic Applications

Mono benzoxazine appended N-capped amino bis(disubstitutedphenol) ligands [ II ( a–c )] upon reaction with V^VO(OEt)₃ in a 1 : 1 molar ratio in EtOH/MeOH give [{V^VO}en(3,5-dtbb)₃] ( 1 ), [{V^VO}en(3-tb,5-mb)₃] ( 2 ) and [{V^VO}en(3,5-dmb)₃] ( 3 ). During the reaction, the benzoxazine ring opens with the loss of methylene group and the newly formed ligands, N,N-bis(2-hydroxy-3,5-disubstitutedbenzyl)-N’-2-hydroxy-3,5-disubstituted benzyledene-1,2-diaminoethane [ III ( a–c )], behave as tribasic pentadentate in these complexes. Under similar conditions, when [M^VIO₂(acac)₂] (M=Mo or W; Hacac=acetylacetone) reacts with II ( a–c ), these ligands retain their identity and form cis-[M^VIO₂] complexes, [{Mo^VIO₂}{en(3,5-dtbb)₂(6,8-dtbbenzox)}] ( 4 ), [{Mo^VIO₂}{en(3-tb,5-mb)₂(6-tb,8-mbbenzox)}] ( 5 ) and [{Mo^VIO₂}{en(3,5-dmb)₂(6,8-dmbenzox)}] ( 6 ), [{W^VIO₂}{en(3,5-dtbb)₂(6,8-dtbbenzox)}] ( 7 ), and [{W^VIO₂}{en(3-tb,5-mb)₂(6-tb,8-mbbenzox)}] ( 8 ). However, the benzoxazine ring ruptures in case of ligand IIc under these conditions and form [{W^VIO₂}{en(3,5-dmb)₃}] ( 10 ), similar to complexes 1–3 . Complex [{W^VIO₂}{en(3,5-dmb)₂(6,8-dmbenzox)}] ( 9 ), having structure similar to 4–8 , could only be obtained when the reaction was carried out in toluene. Not only 9 , even complexes 4–8 can be isolated in toluene. Rupturing of both benzoxazine rings has also been experienced when ligands 1,2-bis(6,8-disubstitutedbenzo[e][1,3]oxazin-3(4H)-yl)ethane [ I ( a–c )] react with [M^VIO₂(acac)₂] (M=Mo or W) in MeOH and give salan type complexes [(M^VIO₂)en(3,5-dtbb)₂] [M=Mo ( 11 ), M=W ( 14 )], [(M^VIO₂)en(3-tb,5-mb)₄] [M=Mo ( 12 ), M=W ( 15 )] and [(M^VIO₂)en(3,5-dmb)₄] [M=Mo ( 13 ), M=W ( 16 )]. Complexes 1–9 have been used as catalyst for the multicomponent Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) and oxidative bromination of phenol derivatives.     

Platinum Complexes of a Borane‐Appended Analogue of 1,1′‐Bis(diphenylphosphino)ferrocene: Flexible Borane Coordination Modes and in situ Vinylborane Formation

A bis(phosphine)borane ambiphilic ligand, [Fe(η⁵‐C₅H₄PPh₂)(η⁵‐C₅H₄PtBu{C₆H₄(BPh₂)‐ortho})] (FcPPB), in which the borane occupies a terminal position, was prepared. Reaction of FcPPB with tris(norbornene)platinum(0) provided [Pt(FcPPB)] ( 1 ) in which the arylborane is η³BCC‐coordinated. Subsequent reaction with CO and CNXyl (Xyl=2,6‐dimethylphenyl) afforded [PtL(FcPPB)] {L=CO ( 2 ) and CNXyl ( 3 )} featuring η²BC‐ and η¹B‐arylborane coordination modes, respectively. Reaction of 1 or 2 with H₂ yielded [PtH(μ‐H)(FcPPB)] in which the borane is bound to a hydride ligand on platinum. Addition of PhC₂H to [Pt(FcPPB)] afforded [Pt(C₂Ph)(μ‐H)(FcPPB)] ( 5 ), which rapidly converted to [Pt(FcPPB′)] ( 6 ; FcPPB′=[Fe(η⁵‐C₅H₄PPh₂)(η⁵‐C₅H₄PtBu{C₆H₄(BPh‐CPh=CHPh‐Z)‐ortho}]) in which the newly formed vinylborane is η³BCC‐coordinated. Unlike arylborane complex 1 , vinylborane complex 6 does not react with CO, CNXyl, H₂ or HC₂Ph at room temperature.