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A half-sandwich, coordinatively unsaturated N-heterocyclic carbene complex of iron with a metallacycle was found to cleave the Si-H bonds of hydrosilanes to give 16-electron iron-silyl complexes. The reactions of silyl complexes with H2 led to the formation of dihydride complexes, in which hydride ligands weakly interact with the silicon atom. The molecular structures of these new complexes have been determined by means of X-ray crystallography. [ABSTRACT FROM AUTHOR]

A half-sandwich, coordinatively unsaturated N-heterocyclic carbene complex of iron with a metallacycle was found to cleave the Si-H bonds of hydrosilanes to give 16-electron iron-silyl complexes. The reactions of silyl complexes with H2 led to the formation of dihydride complexes, in which hydride ligands weakly interact with the silicon atom. The molecular structures of these new complexes have been determined by means of X-ray crystallography. [ABSTRACT FROM AUTHOR]

The all-ferric [Fe4S4]4+ cluster [Fe4S4{N(SiMe3)2}4] 1 and its one-electron reduced form [1]- serve as convenient precursors for the synthesis of 3:1-site differentiated [Fe4S4] clusters and high-potential iron-sulfur protein (HiPIP) model clusters. The reaction of 1 with four equivalents (equiv) of the bulky thiol HSDmp (Dmp = 2,6-(mesityl)2C6H3, mesityl = 2,4,6-Me3C6H2) followed by treatment with tetrahydrofuran (THF) resulted in the isolation of [Fe4S4(SDmp)3(THF)3] 2. Cluster 2 contains an octahedral iron atom with three THF ligands, and its Fe(S)3(O)3 coordination environment is relevant to that in the active site of substrate-bound aconitase. An analogous reaction of [1]- with four equiv of HSDmp gave [Fe4S4(SDmp)4]- 3, which models the oxidized form of HiPIP. The THF ligands in 2 can be replaced by tetramethyl-imidazole (Me4Im) to give [Fe4S4(SDmp)3(Me4Im)] 4 modeling the [Fe4S4(Cys)3(His)] cluster in hydrogenases, and its one-electron reduced form [4]- was synthesized from the reaction of 3 with Me4Im. The reversible redox couple between 3 and [3]- was observed at E1/2 = -820 mV vs. Ag/Ag+, and the corresponding reversible couple for 4 and [4]- is positively shifted by +440 mV. The cyclic voltammogram of 3 also exhibited a reversible oxidation couple, which indicates generation of the all-ferric [Fe4S4]4+ cluster, [Fe4S4(SDmp)4]. [ABSTRACT FROM AUTHOR]

The all-ferric [Fe4S4]4+ cluster [Fe4S4{N(SiMe3)2}4] 1 and its one-electron reduced form [1]- serve as convenient precursors for the synthesis of 3:1-site differentiated [Fe4S4] clusters and high-potential iron-sulfur protein (HiPIP) model clusters. The reaction of 1 with four equivalents (equiv) of the bulky thiol HSDmp (Dmp = 2,6-(mesityl)2C6H3, mesityl = 2,4,6-Me3C6H2) followed by treatment with tetrahydrofuran (THF) resulted in the isolation of [Fe4S4(SDmp)3(THF)3] 2. Cluster 2 contains an octahedral iron atom with three THF ligands, and its Fe(S)3(O)3 coordination environment is relevant to that in the active site of substrate-bound aconitase. An analogous reaction of [1]- with four equiv of HSDmp gave [Fe4S4(SDmp)4]- 3, which models the oxidized form of HiPIP. The THF ligands in 2 can be replaced by tetramethyl-imidazole (Me4Im) to give [Fe4S4(SDmp)3(Me4Im)] 4 modeling the [Fe4S4(Cys)3(His)] cluster in hydrogenases, and its one-electron reduced form [4]- was synthesized from the reaction of 3 with Me4Im. The reversible redox couple between 3 and [3]- was observed at E1/2 = -820 mV vs. Ag/Ag+, and the corresponding reversible couple for 4 and [4]- is positively shifted by +440 mV. The cyclic voltammogram of 3 also exhibited a reversible oxidation couple, which indicates generation of the all-ferric [Fe4S4]4+ cluster, [Fe4S4(SDmp)4]. [ABSTRACT FROM AUTHOR]

A [NiFe] hydrogenase model compound having a distorted trigonal-pyramidal nickel center, (CO)3 Fe(μStBu)3Ni(SDmp), 1 (Dmp= C6H3-2;6-(mesityl)2), was synthesized from the reaction of the tetranuclear Fe-Ni-Ni-Fe complex [(CO)3Fe(μ-StBu)3Ni)2 (p-Br)2. 2 with NaSDmp at -40°C. The nickel site of complex 1 was found to add CO or CNtBU at -40°C to give (CO)3Fe(StBu)(μStBu)2Ni(CO) (SDmp), 3. or (CO)3 Fe(StBu) (μStBu)2Ni(CNtBu) (SDmp), 4, respectively. One of the CO bands of 3. appearing at 2055cm-1 in the infrared spectrum, was assigned as the Ni-CO band, and this frequency is comparable to those observed for the CO-inhibited forms of [NiFe] hydrogenase. Like the CO-inhibited forms of [NiFe] hydrogenase, the coordination of CO at the nickel site of 1 is reversible. while the CNtBu adduct 4 is more robust. [ABSTRACT FROM AUTHOR]

Abstract: Coordinatively unsaturated rhodium and iridium complexes having a bulky thiolate, [Cp∗M(PMe3)(SDmp)](BArF 4) (1a: M=Rh; 1b: M=Ir; Dmp=2,6-(mesityl)2C6H3, ArF =3,5-(CF3)2C6H3), catalyzed the hydrogenation of benzaldehyde, N-benzylideneaniline, and cyclohexanone, under 1atm of H2 at low temperatures. In these catalytic reactions, the M–H/S–H complexes [Cp∗M(PMe3)(H)(HSDmp)](BArF 4) (2a: M=Rh; 2b: M=Ir) generated via H2 heterolysis by 1a or 1b were suggested to transfer both M–H hydride and S–H proton to substrates. The catalytic reactions were terminated by the dissociation of H-SDmp from the metal centers of 2a and 2b that occurs at ambient temperature under H2 atmosphere. [Copyright &y& Elsevier]

The reaction of trithiomolybdate [PPh4]2[MoOS3] (1) with 2 equiv of trimethyichiorosilane generated trithio-chloro molybdate [PPh4][MoClS3] (2) in high yield; by way of a siloxy complex [PPh4][Mo(OSiMe3)S3] (3). This intriguing reaction provided us with a convenient entry into a series of mononuclear molybdenum trisulfido complexes, [PPh4][MoS3X] (4, X = Cp*; 6a, X = StBu; 6b, X = SPh; 6c, X = SMes (Mes = mesityl); 6d, X = STip (Tip = 2,4,6-trilsopropylphenyl); 6e, X = SDmp (Dmp = 2,6-dimesitylphenyl); 7, X = NPh2 8a, X = OtBu; 8b, X = OPh; 8c, X = OC(Ch2)tBu; 8d, X = OC(Ch2)Ph), which were obtained by the reactions of 2 with the corresponding potassium salts. In a similar manner, a citrate complex [PPh4][MoS3(Me3cit)] (9, Me3cit = OC(Ch2CO2Me)2(CO2Me)) was synthesized, which may model the molybdenum site of the nitrogenase FeMo-cofactor. The molecular structures of 2, 6c, 7, 8a, 8b, 8c, and 9 were determined by X-ray crystallography. [ABSTRACT FROM AUTHOR]

A series of [TmMeM(μ-Cl)]2 and TmRMCI (TmR = tris(mercaptoimidazolyl)borate; R = Me, tBu, Ph, 2,6-iPr2C6H3 (Ar); M = Mn, Fe, Co, Ni) complexes have been prepared by treatment of NaTmMe or LiTmR with an excess amount of metal(II) chlorides, MCl2. Treatment of TmRMCl (R = tBu, Ph, Ar) with NaI led to a halide exchange to afford TmRMl. The molecular structures of [TmMeM(μ-Cl)]2 (M = Mn, Ni), [TmMeNi(μ-Br)]2, TmtBuMCI (M = Fe, Co), TmPhMCl (M = Mn, Fe, Co, Ni), TmArMCl (M = Mn, Fe, Co, Ni), TmPhMl (M = Mn, Co), and TmArMl (M = Fe, Co, Ni) have been determined by X-ray crystallography. The TmR ligands occupy the tripodal coordination site of the metal ions, giving a square pyramidal or trigonal bipyramidal coordination geometry for [TmMeM(μ-Cl)]2 and a tetrahedral geometry for the TmRMCl complexes, where the S-M-S bite angles are larger than the reported N-M-N angles of the corresponding hydrotris(pyrazolyl)borate (TpR) complexes. Treatment of TmPh2Fe with excess FeCl2 affords TmPhFeCl, indicating that TmR2M as well as TmRMCl is formed at the initial stage of the reaction between MCl2 and the TmR anion. [ABSTRACT FROM AUTHOR]

The [MoCu] carbon monoxide dehydrogenase (CODH) is a Cu-containing molybdo-flavoprotein, the active site of which contains a pterin-dithiolene cofactor bound to a sulfido-bridged dinuclear Mo-Cu complex. In this paper, the synthesis and characterization of dinuclear Mo-Cu complexes relevant to the active site of [MoCu]-CODH are described. Reaction of [MoO2S2]2- with CuCN affords the dinuclear complex [O2MoS2Cu(CN)]2- (1), in which the CN- ligand can be replaced with various aryl thiolates to give rise to a series of dinuclear complexes [O2MoS2Cu(SAr)]2- (Ar = Ph (2), o-Tol (3), and p-Tol (4)). An alternative synthesis of complex 2 is the reaction of [MoO2S2]2- with [Cu(SPh)3]2-. Similarly, [O2MoS2Cu(PPh3)] (5), [O2MoS2Cu(dppe)]- (dppe = 1,2-bis-(diphenylphosphino)ethane) (6), and [O2MoS2Cu(triphos)]- (triphos = 1,1,1-tris[(diphenylphosphino)methyl]ethane) (7) were prepared from the reactions of [MoO2S2]2- with the Cu(I) phosphine complexes. Treatment of 1, 2, 4, or 5 with dithiols (1,2-(SH)2C6H4, 1,2-(SH)2C6H2-3,6-Cl2, and 1,2-(SH)2C2H4), in acetonitrile, leads to the replacement of a molybdenum-bound oxo ligand to yield [(dithiolate)Mo(O)S2CuL]2- (L - CN, SAr; dithiolate - 1,2-S2C6H4, 1,2-S2C6H2-3,6-Cl2, or 1,2-S2C2H4) (8–13) or [(1,2-S2C6H4)Mo(O)S2Cu(PPh3)]- (14) complexes. [ABSTRACT FROM AUTHOR]

A cyclometalated N-heterocyclic carbene ligand in a half-sandwich iron complex was found to couple with alkynes, leading to a unique type of ring opening of the carbene ligand and the formation of ferrocenyl-diimine complexes. An intermediary iron complex obtained from the reaction with phenylacetylene reveals that the ring opening follows the formation of a fused heterocycle consisting of an imidazole ring and two alkynes. [ABSTRACT FROM AUTHOR]

An oxygen-encapsulated iron sulfido cluster, [(DmpS)Fe4S3O][(DmpS)Fe4S3](μ-SDmp)20(μ- OCPh3) (2; Dmp = 2,6-(mesityl)2C6H3), has been synthesized fay the reaction of the preformed dinuclear iron thiolate/alkoxide [(Ph3CO)Fe]2(μ-SDmp)2 ( l ) with l/8,S8 and 1/4H2O in toluene. In the [Fe8S6O] core, the oxygen atom bridges unsymmetrically two incomplete Fe4S3 cubes, and two coordinatively unsaturated iron atoms are weakly bound to mesityl rings. Relevance of the cluster structure of 2 to the nitrogenase FeMo cofactor and its substrate binding mode is discussed. [ABSTRACT FROM AUTHOR]

A C-H bond of Cp*2Co was found to be cleaved by a [Fe8S7] cluster model of the nitrogenase P-cluster. This is the first example of C-H bond activation mediated by a biologically relevant Fe/S cluster. The reaction mechanism probably consists of electron transfer from Cp*2Co to the [Fe8S7] cluster and subsequent proton abstraction by the reduced form of the cluster. [ABSTRACT FROM AUTHOR]

The FeMo-cofactor of nitrogenase, a metal-sulfur cluster that contains eight transition metals, promotes the conversion of dinitrogen into ammonia when stored in the protein. Although various metal-sulfur clusters have been synthesized over the past decades, their use in the activation of N2 has remained challenging, and even the FeMo-cofactor extracted from nitrogenase is not able to reduce N2. Herein, we report the activation of N2 by a metal-sulfur cluster that contains molybdenum and titanium. An N2 moiety bridging two [Mo3S4Ti] cubes is converted into NH3 and N2H4 upon treatment with Brønsted acids in the presence of a reducing agent. Nitrogenase—whose cofactor consists of a metal-sulfur cluster—catalyzes the production of NH3 from N2, but designing metal-sulfur complexes capable of promoting this conversion remains challenging. Here, the authors report on the activation of N2 by a metal-sulfur cluster containing [Mo3S4Ti] cubes, demonstrating NH3 and N2H4 production. [ABSTRACT FROM AUTHOR]

The crystallization of 3‐[4′‐(diethylboryl)phenyl]pyridine (1), which formed a mixture of oligomers in solution with the cyclic trimer as a major component, in acetone at 0 °C afforded a cyclic tetramer that co‐crystallized with solvent molecules. Similarly, solutions of compound 1 in toluene at 10 °C and in benzene at 8 °C furnished the cyclic tetramer with the incorporation of toluene and benzene molecules, respectively, thus suggesting that the cyclic tetramer was the minor component. 13C CP/MAS NMR spectroscopy of precipitates of compound 1 suggested that precipitation from acetone and toluene each afforded mixtures of the cyclic trimer and the cyclic tetramer, whereas precipitation from benzene exclusively furnished the cyclic tetramer. Therefore, it appeared that crystallization readily shifted the equilibrium towards the cyclic tetramer in benzene. The thermodynamic parameters for the equilibrium between these two oligomers in [D6]benzene, as determined from a van′t Hoff plot, were ΔH°=−8.8 kcal mol−1 and ΔS°=−23.7 cal mol−1 K−1, which were coincident with previously reported calculations and observations. Four Your Eyes Only: Precipitates of compound 1 from acetone and toluene solutions contained both the cyclic trimer (13) and the cyclic tetramer (14), whereas precipitation from benzene only furnished the cyclic tetramer. Therefore, it appeared that crystallization readily shifted the equilibrium towards the cyclic tetramer in benzene solution. [ABSTRACT FROM AUTHOR]

Review: 63 refs. [ABSTRACT FROM AUTHOR]

The article reports on the reversible heterolysis of H2 arbitrated by an M-S(Thiolate) bond(M=Ir,Rh). It discusses that heterolytic segmentation of dihydrogen is a fundamental pace in the purpose of hydrogenases, which catalyze hydrogen development and consumption under mild conditions. It implies that various conversion metal complexes have been shown to promote heterolysis of H2.

The article reports on the synthesis of nickel complexes. Hydrogenase is essential to hydrogen metabolism by catalyzing the reversible interconversion of proton and molecular hydrogen. The enzyme has been found in many microorganisms of biotechnological interest, which can be grouped into two classes based on the type of metal-containing active sites, namely, [Fe]-only and [NiFe] hydrogenases. Two forms of the active sites are known. The intriguing dinuclear structure of [NiFe] hydrogenases has been a challenging target for inorganic/organometallic chemists, and several thiolate-bridged dinuclear Ni-Fe complexes have been prepared.

The reaction of iron(II) bis-amide Fe{N(SiMe3)2}2 with elemental sulfur afforded a direct entry to new [Fe2S2] and [Fe4S4] clusters with terminal amide groups, Fe4S2 {N(SiMe3)2}4 (1) and Fe2S2{N(SiMe3)2}2(tmtu)2 (2), whose structures have been determined by X-ray crystallography. Tetrameric cubane cluster 1 exhibits one reversible and one quasireversible processes in the cyclic voltammetry, whereas dimeric rhombus complex 2 reveals one irreversible reduction process. [ABSTRACT FROM AUTHOR]

A cubic metal‐sulfur cluster containing three Mo ions and a Pd ion, [CpSiEt33Mo3S4Pd]Cl (Mo3Pd, CpSiEt3=C5Me4SiEt3), was synthesized by the incorporation of the Pd ion into a Mo3S4 cluster [CpSiEt33Mo3S4] (Mo3). Mo3Pd was characterized by 1H NMR, UV‐vis, X‐ray crystallography, and cyclic voltammetry measurements. The electrochemical measurements demonstrated reversible one‐ and two‐electron reduction processes for Mo3Pd, which suggested potential catalytic activity for two‐electron substrate reductions such as hydrogen evolution reaction. Controlled potential electrolysis in the presence of Mo3Pd and trifluoroethanol in THF solvent displayed H2 formation with a constant current over 60 min. The amount of generated H2 by Mo3Pd was two times higher than Mo3, indicating the catalytic activity facilitated by the Pd center. The mechanism of the catalytic cycle was determined by density functional theory. [ABSTRACT FROM AUTHOR]

[Display omitted] • Activation and reduction of small molecules by metal-sulfur clusters. • Applications of metal-sulfur clusters in the transformation of small organic substrates. • Cuboidal [M 4 S 4 ] clusters have been major metal-sulfur species applied to reaction chemistry. The high affinity of sulfur (S) for transition metal ions (M), as well as the flexible M−S bonding and bridging modes, enable the formation of a wide range of multi-metallic compounds called metal-sulfur (M−S) clusters. Even though M−S clusters tolerate various nuclearities in principle, the number of metals in molecular entities, particularly those applicable in catalytic reactions, are typically 4 or lower, while the highest number of 8 has been found in the biological N 2 -reducing catalyst. Other than the N 2 reduction, M−S clusters in nature have been found in the conversion of small molecules such as CO 2 , CO, and H 2. With the detailed structures of these native M−S clusters elucidated by recent biochemical studies, we can take steps toward the development of artificial catalysts superior to enzymes and/or those for biologically inaccessible reactions, while another direction is to deeply understand the enzymatic reactions and their relationship between the M−S structures. Here we review the progress in the reaction studies on synthetic M−S clusters, focusing on their utility in the activation and transformation of small molecules. The main part of this review has been divided into three sections: i) transformations of N 2 and related small molecules, ii) reduction of CO 2 , and iii) transformations of organic small molecules. Remarkable recent progress includes the development of catalytic N 2 -silylation toward N(SiMe 3) 3 and CO 2 reduction toward C 1 –C 4 hydrocarbons. Tandem reduction and N -methylation of nitroarenes have also been accomplished in the last decade. Through the review process, the development of catalytic reactions by M−S clusters was found to be still challenging. Collaborative works among chemists who can synthesize M−S clusters, those who are skilled in developing homogeneous catalytic reactions, those having spectroscopic techniques, and theoretical chemists may provide new insights into this field. [ABSTRACT FROM AUTHOR]

5‐Diethylboryl‐2,3′‐bipyridine (1), which is inaccessible by conventional batch methods, was synthesized by using a flow microreactor. Compound 1 was obtained as an equilibrium mixture of a cyclic trimer and a cyclic tetramer in solution, the latter of which was crystallized in benzene by vapor diffusion of hexane at 7 °C. The dynamic nature of this system was confirmed by solvent‐ and concentration‐dependent experiments. Notably, the dynamics was verified by using flow NMR spectroscopy, which revealed that the time required to reach equilibrium was influenced by the solvent ratio (<18 s, 24–28 s, and 34–42 s in 2 : 1, 1 : 1, and 1 : 2 mixtures of [D6]acetone and C6D6, respectively). Compound 1 and 3‐[4′‐(diethylboryl)phenyl]pyridine (2) exhibited different self‐assembly behavior in solution and crystals. Density functional theory calculations suggested that this difference was largely due to enhanced planarity between two consecutive aromatic rings. [ABSTRACT FROM AUTHOR]

Nitrogenase catalyzes substrate reduction at its cofactor center ([(Cit)MoFe7S9C]n-; designated M-cluster). Here, we report the formation of an artificial, nitrogenasemimicking enzyme upon insertion of a synthetic model complex ([Fe6S9(SEt)2]4-; designated Fe6 RHH) into the catalytic component of nitrogenase (designated NifDKapo). Two Fe6 RHH clusters were inserted into NifDKapo, rendering the conformation of the resultant protein (designated NifDKFe) similar to the one upon insertion of native M-clusters. NifDKFe can work together with the reductase component of nitrogenase to reduce C2H2 in an ATP-dependent reaction. It can also act as an enzyme on its own in the presence of EuIIDTPA, displaying a strong activity in C2H2 reduction while demonstrating an ability to reduce CN- to C1-C3 hydrocarbons in an ATP-independent manner. The successful outcome of this work provides the proof of concept and underlying principles for continued search of novel enzymatic activities based on this approach. [ABSTRACT FROM AUTHOR]

Abstract: We aimed to develop a phase selection methodology for a weak basic active pharmaceutical ingredient (API) that would require less than 10mg of the API and monitor the real-time kinetic solubility of the API in two bio-relevant media. Three sets of kinetic solubility measurements were conducted for free form I and the disulfate salt of an API (compound A) in order to determine the better API phase for further development of the compound. Tests consisted of solid API dissolution in both simulated gastric fluid (SGF) and fasted-state intestinal fluid (FaSSIF), and precipitation kinetics by injection of liquid state API into FaSSIF. All dissolution tests were conducted above the saturated concentrations in order to determine the compounds’ thermodynamic and kinetic solubility to trace the API’s phase transitions during dissolution. The pharmacokinetic profiles of compound A following oral administration of two API phases were evaluated in dogs. Results of the three sets of kinetic solubility measurements showed different kinetic solubility profiles for the two API phases under gastrointestinal conditions, indicating that the disulfate salt is preferred over free form I due to its superior kinetic solubility profile. This conclusion is consistent with the bioavailability results obtained in dogs. [Copyright &y& Elsevier]

The method of preparing monophosphaferrocenes originally reported by Roberts and Wells, which requires two equivalents of [(mesitylene)FeCp]PF6 (A), was reinvestigated. By the use of inexpensive aluminum chloride as a phenyllithium scavenger, a 50 % reduction of required A could be attained. Diverse monophosphaferrocene derivatives having aliphatic C‐substituents, including four new compounds, were prepared in good yields from the corresponding P‐phenylphospholes, A (1 equiv.), and aluminum chloride (1/3 equiv.) under the modified conditions. These modified conditions showed comparable to better yields of monophosphaferrocenes and the far better atom‐economy compared to the original conditions. [ABSTRACT FROM AUTHOR]

Two transition‐metal atoms bridged by hydrides may represent a useful structural motif for N2 activation by molecular complexes and the enzyme active site. In this study, dinuclear MoIV‐FeII complexes with bridging hydrides, CpRMo(PMe3)(H)(μ‐H)3FeCp* (2 a; CpR=Cp*=C5Me5, 2 b; CpR=C5Me4H), were synthesized via deprotonation of CpRMo(PMe3)H5 (1 a; CpR=Cp*, 1 b; CpR=C5Me4H) by Cp*FeN(SiMe3)2, and they were characterized by spectroscopy and crystallography. These Mo−Fe complexes reveal the shortest Mo−Fe distances ever reported (2.4005(3) Å for 2 a and 2.3952(3) Å for 2 b), and the Mo−Fe interactions were analyzed by computational studies. Removal of the terminal Mo−H hydride in 2 a–2 b by [Ph3C]+ in THF led to the formation of cationic THF adducts [CpRMo(PMe3)(THF)(μ‐H)3FeCp*]+ (3 a; CpR=Cp*, 3 b; CpR=C5Me4H). Further reaction of 3 a with LiPPh2 gave rise to a phosphido‐bridged complex Cp*Mo(PMe3)(μ‐H)(μ‐PPh2)FeCp* (4). A series of Mo−Fe complexes were subjected to catalytic silylation of N2 in the presence of Na and Me3SiCl, furnishing up to 129±20 equiv of N(SiMe3)3 per molecule of 2 b. Mechanism of the catalytic cycle was analyzed by DFT calculations. [ABSTRACT FROM AUTHOR]

The Mo nitrogenase catalyzes the ambient reduction of N2 to NH3 at its M-cluster site. A complex metallocofactor with a core composition of [MoFe7S9C], the M-cluster, can be extracted from the protein scaffold and used to facilitate the catalytic reduction of CN−, CO, and CO2 into hydrocarbons in the isolated state. Herein, we report the synthesis, structure, and reactivity of an asymmetric M-cluster analogue with a core composition of [MoFe5S9]. This analogue, referred to as the Mo-cluster, is the first synthetic example of an M-cluster mimic with Fe and Mo positioned at opposite ends of the cluster. Moreover, the ability of the Mo-cluster to reduce C1 substrates to hydrocarbons suggests the feasibility of developing nitrogenase-based biomimetic approaches to recycle C1 waste into fuel products. [ABSTRACT FROM AUTHOR]

Reactions of manganese(II) dichlorides bearing a N -heterocyclic carbene ligand (L), [MnCl( μ -Cl)(L)] 2 ( 1a , L = 1,3-diisopropyl-4,5-dimethylimidazole-2-ylidene (I i Pr); 1b , L = 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-ylidene (IMes); 1c , L = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene (IPr)) with MeLi afford the dinuclear dimethylmanganese(II) complexes, [MnMe( μ -Me)(L)] 2 ( 2a , L = I i Pr; 2b , L = IMes; 2c , L = IPr). Complexes 2a - c achieve nucleophilic substitution of Si(OEt) 4 to selectively form MeSi(OEt) 3 . Related arylmanganese(II) complexes analogously react with Si(OEt) 4 to afford ArSi(OEt) 3 and Ar 2 Si(OEt) 2 (Ar = Ph, 2,6-Me 2 (C 6 H 3 )). Kinetic studies support an associative mechanism for the observed transformation of Si(OEt) 4 , in which both the manganese species and Si(OEt) 4 are involved in the rate-limiting step. [ABSTRACT FROM AUTHOR]

A facile method for the synthesis of 3-(dimethylboryl)pyridine (1a) is described. Compound 1a assembles into a rigid cyclic tetramer stabilized via intermolecular boron-nitrogen coordination bonds both in the crystalline state and in solution. The outstanding structural feature of la, as compared with previously reported 3-(diethylboryl)pyridine (2a) (which adopts a cone conformation), is that the tetramer of la adopts a 1 ,2-alternate conformation. To investigate the effect of substituents at the boron atom on the stabilities of the oligomers, scrambling experiments of the component molecules using 1, 2, and 3-(di- n-butylboryl)pyridines 3 were carried out. Although heating at 80-90 °C for 20 h was required to attain the equilibrium of the scrambling reactions when the component molecules of the tetramers were 2 or 3, the scrambling in 1 proceeded under relatively mild conditions (60 °C, 3 h). This difference in reaction conditions required for 1, as compared to conditions required for 2 or 3, could not be explained solely by the stabilities based on bond lengths or THC.1g It appears that whereas only an SNI-type pathway may be involved in the scrambling of 2 or 3, both SN1- and SN2-type mechanisms operate simultaneously during scrambling reactions of 1 or an intermediate mechanism between SN1 and SN2 operates, which was supported by kinetic studies and calculations using model compounds. [ABSTRACT FROM AUTHOR]