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Formation energies, chemical bonding, electronic structure, and optical properties of metal-organic frameworks of alkaline earth metals, A-IRMOF-1 (where A = Be, Mg, Ca, Sr, or Ba), have been systemically investigated with DFT methods. The unit cell volumes and atomic positions were fully optimized with the Perdew-Burke-Ernzerhof functional. By fitting the E-V data into the Murnaghan, Birch and Universal equation of states (UEOS), the bulk modulus and its pressure derivative were estimated and provided almost identical results. The data indicate that the A-IRMOF-1 series are soft materials. The estimated bandgap values are all ca. 3.5 eV, indicating a nonmetallic behavior which is essentially metal independent within this A-IRMOF-1 series. The calculated formation energies for the A-IRMOF-1 series are -61.69 (Be), -62.53 (Mg), -66.56 (Ca), -65.34 (Sr), and -64.12 (Ba) kJ mol(-1) and are substantially more negative than that of Zn-based IRMOF-1 (MOF-5) at -46.02 kJ mol(-1). From the thermodynamic point of view, the A-IRMOF-1 compounds are therefore even more stable than the well-known MOF-5. The linear optical properties of the A-IRMOF-1 series were systematically investigated. The detailed analysis of chemical bonding in the A-IRMOF-1 series reveals the nature of the A-O, O-C, H-C, and C-C bonds, i.e., A-O is a mainly ionic interaction with a metal dependent degree of covalency. The O-C, H-C, and C-C bonding interactions are as anticipated mainly covalent in character. Furthermore it is found that the geometry and electronic structures of the presently considered MOFs are not very sensitive to the k-point mesh involved in the calculations. Importantly, this suggests that sampling with Γ-point only will give reliable structural properties for MOFs. Thus, computational simulations should be readily extended to even more complicated MOF systems.

The asymmetric unit of the title structure, C14H30N2O42+·2PF6−, contains the anion and half of the cation, the latter being completed by a crystallographic twofold axis. The cation has a cage structure with the ammonium H atoms pointing into the cage. These H atoms are shielded from intermolecular interactions and form only intramolecular contacts. There are short intermolecular C—H...F interactions in the structure, but no conventional intermolecular hydrogen bonds.

The performance of recently reported highly cis-diastereoselective Rh(I) cyclopropanation catalysts has been significantly improved by a systematic study of different reaction parameters (catalyst activation, solvent, temperature, stoichiometry). The catalyst efficiency and diastereoselectivity were enhanced by changing the activating agent from AgOTf to NaBArf. With this new system, the Rh(I) catalyst was shown to be a highly efficient and cis-diastereoselective cyclopropanation catalyst in reactions between α-diazoacetates and a range of different alkenes and substituted derivatives. Particularly noteworthy is the remarkable reactivity and cis-diastereoselectivity displayed in the reactions between ethyl diazoacetate and cyclopentene, 2,5-dihydrofuran, and benzofuran, with yields up to 99% and cis-selectivities greater than 99%.

Cyclic voltammetry of 1, Cp * Ru(P)(H) 3 (P=PPh 3 ), in MeCN at a gold electrode (20 o C, 1 V/s) is irreversible but produces in high yield 2, Cp * RuP(MeCN) 2 + , which does show a reversible cyclic voltammogram. The reaction consumes 1 faraday/mol of Ru, and thus all hydride ligands are converted to H 2

The energetics of the deprotonation and metal-hydrogen bond homolysis reactions of TpM(CO) 3 H and Tp'M(CO) 3 H (Tp=hydridotris(pyrazolyl)borate; Tp'=hydridotris(3,5-dimethylpyrazolyl)borate; M=Cr, Mo, W) and their cation radicals have been investigated, and the results are compared with available data for the analogous CpM(CO) 3 H complexes. Proton-transfer equilibrium measurements have established that for a given metal, acetonitrile pK a values of the metal hydrides decrease in the order CpM(CO) 3 H>TpM(CO) 3 H>Tp'M(CO) 3 H. This trend is the opposite of that expected on the basis of the relative electron-richness of the metal centers, as measured by infrared ν CO frequencies and oxidation potential data for the corresponding metal anions

Comparison of [Cat] [CpCr(CO) 2 PEt 3 ] (Cat=Et 4 N + and Ph 3 PNPPh 3 + (PPN + )) by NMR, visible/UV, and infrared spectroscopy in CH 3 CN and in THF shows that ion pairing for the PPN complex occurs in THF, and that such pairing involves a detectable amount of charge transfer from anion to cation. This cause a rise in the CO stretching frequencies, which can be compared to the values in the fully-oxidized species CpCr(CO) 2 (PEt 3 ) .

The dimethylrhodium compound Cp[sup *]Rh(PPh[sub 3])(CH[sub 3])[sub 2] (1; Cp[sup *] = [eta][sup 5]-C[sub 5]Me[sub 5]) undergoes an overall 2-electron oxidation at 0.04 V vs the ferrocene/ferrocenium (Fc) couple in 9:1 acetonitrile/dichloromethane, 0.1 M Bu[sub 4]N[sup +]PF[sub 6][sup [minus]]. The oxidation results in the intramolecular reductive elimination of ethane and yields Cp[sup *]Rh(PPh[sub 3])(NCMe)[sub 2][sup 2+] (2) as the Rh-containing product. A mechanistic and kinetic investigation of the reaction by derivative cyclic voltammetry (DCV) showed the reductive elimination to be a first-order reaction with respect to 1[sup [sm bullet]+]. Very small solvent effects (acetonitrile, acetone, THF, dichloromethane) on the reaction rate indicated the nonintervention of 19-electron species in the reductive elimination. The DCV analysis provided kinetic parameters k(20[degrees]C) = 96 [plus minus] 3 s[sup [minus]1], [Delta]H[sup [double dagger]] = 53.1 [plus minus] 0.8 kJ/mol, and [Delta]S[sup [double dagger]] = [minus]25.9 [plus minus] 3.3 J/(K[center dot]mol) in acetonitrile. The data are interpreted in terms of a direct, concerted elimination of ethane from the 17-electron cation radical 1[sup [sm bullet]+]. It is estimated that the rate of reductive elimination has been increased by a factor of at least 3 [times] 10[sup 9] due to the oxidation of 1 to 1[sup [sm bullet]+].more » In dichloromethane, the intramolecular elimination of ethane was initiated by an overall 1-electron process. The major product in this case was Cp[sup *]Rh(PPh[sub 3])(CH[sub 3])X[sup +] (X most likely is coordinated dichloromethane or the counterion PF[sub 6][sup [minus]]) as a result of a secondary intermolecular methyl-transfer process. The methyl transfer was mimicked by a quantitative ([sup 1]H NMR) reaction between 1 and 2 which yielded Cp[sup *]Rh(PPh[sub 3])(NCMe)CH[sub 3][sup +] (3). 18 refs., 4 figs., 1 tab.« less

The development in the field MOF materials is moving from the discovery of new structures toward applications of the most promising materials. In most cases, specialized applications require incorporation of functional chemical groups. This work is a systematic investigation of the effect that simple substituents attached to the aromatic linker have on the stability and property to the parent MOF. A family of isoreticular MOFs, based on the UiO-66 structure was obtained from the three different linker ligands H2N−H2BDC, O2N−H2BDC, and Br−H2BDC. The physicochemical and chemical investigation of these materials demonstrate that this class of MOFs retains high thermal and chemical stabilities, even with functional groups present at the linker units. The results demonstrate the possibility of incorporating active functional groups into the UiO-66 structure almost without losing its exceptionally high thermal and chemical stability. It has been established that the functional groups, at least in the amino func...

The tungsten(IV) dication CpW(CO){sub 2}(NCMe){sub 2}Me{sup 2+}, obtained from the 2-electron oxidation of CpW-(CO){sub 3}Me, serves as the precursor to a number of tungsten(IV) complexes via a series of CO insertion and substitution reactions. In acetonitrile, the dication undergoes smooth CO insertion ({Delta}H* = 89.5 {sup +}{sub -} 2.5 kJ/mol, {Delta}S* = -43.9 {sup +}{sub -} 8.4J/(K{lg_bullet}mol), k(20{degrees}C) = 3.3 x 10{sup -6} 8{sup -1}) and substitution to give the {eta}{sup 2}-acetyl complex CpW(NCMe){sub 3}({eta}{sup 2}-COMe){sup 2+}. The oxidation of CpW(CO){sub 3}Et provides CpW(CO)(NCMe){sub 2}({eta}{sup 2}-COEt){sup 2+} via the intermediacy of CpW(CO){sub 2}(NCMe){sub 2}Et{sup 2+}. CpW(CO)(NCMe){sub 2}({eta}-COEt){sup 2+} in turn undergoes CO substitution to yield CpW(CO){sub 3}(NCMe)Me{sup 2+}. Analogous CO insertion reactions were not observed for the compounds CpW(CO){sub 3}(NCMe)Me{sup 2+} and CpW(CO){sub 3}(NCMe)Et{sup 2+}. 21 refs., 3 figs., 3 tabs.

The oxidation chemistry of CpMo(CO) 2 (PPh 3 )H ( 1 ) has been investigated by electrochemical and other methods. The molybdenum hydride 1 undergoes oxidation at +0.26 V vs. the ferrocene/ferricinium couple in acetonitrile solution, forming cis -CpMo(CO) 2 (PPh 3 )(NCMe) + ( cis - 2 ). Hydride abstraction from 1 by the substituted trityl reagent ( p -MeOC 6 H 4 )Ph 2 C + BF 4 − generates trans - 2 . The stereochemical outcome of this reaction implies a non-electron-transfer pathway for the hydride abstraction. The thermal isomerization of trans - 2 to the more stable cis - 2 in acetonitrile- d 3 proceeds without concomitant ligand exchange with the solvent. The kinetics of the isomerization have been investigated, and give the activation parameters Δ H # = 24.2±0.4 kcal/mol and Δ S # = −3.4±1.4 cal/K mol. The near-zero entropy of activation is in accord with an intramolecular non-dissociative isomerization process. In contrast, treatment of trans - 2 with a catalytic amount of cobaltocene results in fast partial isomerization to cis - 2 accompanied by ligand exchange with the solvent. This behavior is compared with the non-dissociative nature of the previously reported electrocatalytic isomerization of cis -CpW(CO) 2 (PMe 3 )(NCMe) + , and suggests that the intermediate 19-electron radicals are more loosely bound for molybdenum than for tungsten.

A detailed kinetic study of the protonation and subsequent benzene elimination reactions of a (diimine)Pt(II) diphenyl complex (denoted as (N-N)PtPh(2)) has been undertaken in dichloromethane solution with and without acetonitrile as a cosolvent. Spectroscopic monitoring of the reactions by UV-vis stopped-flow and NMR techniques over the temperature range -80 to +27 degrees C allowed the assessment of the effects of acid concentration, coordinating solvent (MeCN) concentration, temperature, and pressure. Protonation of (N-N)PtPh(2) with HBF(4) x Et(2)O in CH(2)Cl(2)/MeCN occurs with a kinetic preference for protonation at the metal, rather than at a phenyl ligand, and rapidly produces (N-N)PtPh(2)H(NCMe)(+) (DeltaH(double dagger) = 29 +/- 1 kJ mol(-1), DeltaS(double dagger) = -47 +/- 4 J K(-1) mol(-1)). At higher temperatures, (N-N)PtPh(2)H(NCMe)(+) eliminates benzene to furnish (N-N)PtPh(NCMe)(+). This reaction proceeds by rate-limiting MeCN dissociation (DeltaH(double dagger) = 88 +/- 2 kJ mol(-1), DeltaS(double dagger) = +62 +/- 6 J K(-1) mol(-1), DeltaV(double dagger) = +16 +/- 2 cm(3) mol(-1)). Protonation of (N-N)PtPh(2) in dichloromethane in the absence of MeCN cleanly produces the Pt(II) pi-benzene complex (N-N)PtPh(eta(2)-C(6)H(6))(+) at low temperatures. Addition of MeCN to a solution of the pi-benzene complex causes an associative substitution of benzene by acetonitrile, the kinetics of which were monitored by (1)H NMR (DeltaH(double dagger) = 39 +/- 2 kJ mol(-1), DeltaS(double dagger) = -126 +/- 11 J K(-1) mol(-1)). When the stronger triflic acid is employed in dichloromethane/acetonitrile, a second protonation-induced reaction also occurs. Thus, (N-N)PtPh(NCMe)(+) produces (N-N)Pt(NCMe)(2)(2+) and benzene with no detectable intermediates (DeltaH(double dagger) = 69 +/- 1 kJ mol(-1), DeltaS(double dagger) = -43 +/- 3 J K(-1) mol(-1)). The mechanisms for all steps are discussed in view of the accumulated data. Interestingly, the data allow a reinterpretation of a previous report on proton exchange between the phenyl and benzene ligands in (N-N)PtPh(eta(2)-C(6)H(6))(+). It appears that the exchange occurs by a direct sigma-bond metathesis pathway, rather than by the oxidative cleavage/reductive coupling sequence that was proposed.

A structurally characterized Rh(I) iminocarbene complex (N,C)Rh(CO)Cl is activated with AgOTf to act as a highly cis-selective catalyst for the cyclopropanation of substituted styrenes and other alkenes with ethyl diazoacetate (11 examples, 10−99% yield, up to >99% cis-selectivity).

Treatment of CpRu(PPh 3 ) 2 H ( 1 ) with 1 equivalent of the substituted trityl reagent Tol 3 C + PF 6 − (Tol = p -Mec 6 H 4 )in 9/1 dichloromethane- d 2 /acetonitrile- d 3 at − 80° C led to attachment of the trityl cation to the Cp ring and generation of the ring-substituted dihydride complex trans -[η 5 -C 5 H 4 (Tol 3 C)]Ru(PPh 3 ) 2 + ( 5 ). At ambient temperature the reaction yielded a mixture of 5 , CpRu(PPh 3 ) 2 H 2 + ( 2 ), and CpRu(PPh 3 ) 2 (NCCD 3 ) + ( 3 - d 3 ). Oxidation of 1 with 1 equivalent of Cp 2 Fe + PF 6 − yielded a 1:1 mixture of 2 and 3 - d 3 . The mechanism of the generation of the products is discussed in the light of the experimental evidence that suggests that 5 is formed by electrophilic attack by the trityl cation at the Cp ring of 1 via initial electron transfer.

A structurally characterized Rh(I) iminocarbene complex (N,C)Rh(CO)Cl is activated with AgOTf to act as a highly cis-selective catalyst for the cyclopropanation of substituted styrenes and other alkenes with ethyl diazoacetate (11 examples, 10−99% yield, up to >99% cis-selectivity).

The oxidation chemistry of the organometallic hydride complexes ({eta}{sup 5}C{sub 5}H{sub 5})M(CO){sub 3}H (M = Cr, 1; Mo, 2; W, 3), ({eta}{sup 5}-C{sub 5}Me{sub 5})Mo(CO){sub 3}H (4), and ({eta}{sup 5}-C{sub 5}H{sub 5})W(CO){sub 2}(PMe{sub 3})H (5) has been investigated in acetonitrile solution by electrochemical and other methods. The thermodynamic acidities of the cation radicals of 1-5 have been estimated by the use of a thermochemical cycle based on the oxidation potentials of 1-5 and their conjugate bases (anions) as well as the solution pK{sub a} values of 1-5. The metal hydride cation radical pK{sub a} estimates fall in the range {minus}10 to +5, which makes these complexes the most acidic hydrides for which pK{sub a} values have been determined. Coulometric measurements show that 1-5 undergo overall two-electron oxidations. Chemical oxidation of 5 gives a 1:1 mixture of dihydride ({eta}{sup 5}-C{sub 5}H{sub 5})W(CO){sub 2}(PMe{sub 3})H{sub 2}{sup +} (13) and ({eta}{sup 5}-C{sub 5}H{sub 5})W(CO){sub 2}(PMe{sub 3})(NCMe){sup +} (10), the latter as a mixture of cis and trans isomers in the thermodynamic 95:5 ratio.

The lithium (1) and thallium (2) salts of five new tert-butyl-tris(3-hydrocarbylpyrazol-1-yl)borate ligands [t-BuTp(R)]- (R = H, a; Me, b; i-Pr, c; t-Bu, d; Ph, e) have been synthesized and characterized. Because of steric congestion at B, the reaction between t-BuBH3Li x 0.5 Et2O and excess 2,5-dimethylpyrazole Hpz(Me2) afforded the bis-pz(Me2) derivative, Tl[t-BuBH(3,5-Me2pz)2] (3) after metathesis with TlNO3. The compounds were characterized by elemental analysis and NMR spectroscopy. The Li salts 1a and 1c exhibit fluxional behavior on the NMR time scale in solution at room temperature. The solid-state 7Li and 11B NMR spectra of 1c suggest that this salt exists as a mixture of axial and equatorial isomers. The partial hydrolysis of 1d afforded the dimeric Li complex {Li[t-BuB(pz(t-Bu))2(mu-OH)]}2 (4). The crystal structure of 4 shows two Li cations encapsulated by the heteroscorpionate [t-BuB(OH)(3-t-Bupz)2]- ligands. A salt elimination reaction between FeCl2(THF)1.5 and 2 equiv of Li[t-BuTp(R)] (R = H, Me) followed by an in situ one-electron oxidation produced good yields of the homoleptic, paramagnetic low-spin iron(III) complexes [Fe(t-BuTp)2]PF6 (5) and [Fe(t-BuTp(Me))2]PF6 (6) that were characterized by elemental analyses, magnetic susceptibility measurements in solution and the solid phase, 1H NMR, high-resolution mass spectrometry, Mössbauer spectroscopy, and single-crystal X-ray diffraction. The crystals are composed of discrete molecular units with the central Fe(III) ion in an almost perfectly octahedral coordination to six nitrogen atoms. Compound 5 has the shortest Fe-N bond lengths ever reported for [Fe(RTp(R)')2]+-type compounds.

A detailed kinetic study of the protonation and subsequent reductive elimination reaction of a (diimine)platinum(II) dimethyl complex was undertaken in dichloromethane over the temperature range of -90 to +10 degrees C by stopped-flow techniques. Time-resolved UV-vis monitoring of the reaction allowed the assessment of the effects of acid concentration, coordinating solvent (MeCN) concentration, temperature, and pressure. The second-order rate constant for the protonation step was determined to be 15200 +/- 400 M(-1) s(-1) at -78 degrees C, and the corresponding activation parameters are DeltaH = 15.2 +/- 0.6 kJ mol(-1) and DeltaS = -85 +/- 3 J mol(-1) K(-1), which are in agreement with the addition of a proton that results in the formation of the platinum(IV) hydrido complex. The kinetics of the second, methane-releasing reaction step do not show an acid dependence, and the MeCN concentration also does not significantly affect the reaction rate. The activation parameters for the second reaction step were found to be DeltaH = 75 +/- 1 kJ mol(-1), DeltaS = +38 +/- 5 J mol(-1) K(-1), and DeltaV = +18 +/- 1 cm(3) mol(-1), strongly suggesting a dissociative character of the rate-determining step for the reductive elimination reaction. The spectroscopic and kinetic observations were correlated with NMR data and assisted the elucidation of the underlying reaction mechanism.

Protonation of (N-N)PtPh(2) (1; N-N = diimine ArN=CMe-CMe=NAr with Ar = 2,6-Me(2)C(6)H(3) (a), 2,4,6-Me(3)C(6)H(2) (b), 4-Br-2,6-Me(2)C(6)H(2) (c), 3,5-Me(2)C(6)H(3) (d), and 4-CF(3)C(6)H(4) (e)) in the presence of MeCN at ambient temperature generates (N-N)Pt(Ph)(NCMe)(+) (2). At -78 degrees C, protonation of 1a yielded (N-N)PtPh(2)(H)(NCMe)(+) (3a), which produced benzene and 2a at ca. -40 degrees C. Protonation of 1a-e in CD(2)Cl(2)/Et(2)O-d(10) furnished (N-N)Pt(C(6)H(5))(eta(2)-C(6)H(6))(+) (4a-e). The pi-benzene complexes 4a-c, sterically protected at Pt, eliminate benzene at ca. 0 degree C. The sterically less protected 4d-e lose benzene already at -30 degrees C. SST and 2D EXSY NMR demonstrate that phenyl and pi-benzene ligand protons undergo exchange with concomitant symmetrization of the diimine ligand, most likely via oxidative insertion of Pt into a C-H bond of coordinated benzene. The kinetics of the exchange processes for 4a-c were probed by quantitative EXSY spectroscopy, resulting in DeltaH() of 70-72 kJ mol(-1) and DeltaS of 37-48 J K(-1) mol(-1). A large, strongly temperature-dependent H/D kinetic isotope effect (9.7 at -34 degrees C; 6.9 at -19 degrees C) was measured for the dynamic behavior of 4a versus 4a-d(10), consistent with the proposed pi-benzene C-H bond cleavage. The fact that the pi-benzene complex 4a is thermally more robust in the absence of MeCN than is the Pt(IV) hydridodiphenyl complex 3a in the presence of MeCN agrees with the notion that arene elimination from Pt(IV) hydridoaryl complexes occurs via Pt(II) pi-arene intermediates that eliminate the hydrocarbon associatively, in this case, promoted by MeCN. Compounds 1a, 1b, 1d, 2a, and 2b have been crystallographically characterized.

A general one-pot synthetic route for mixed methyl−aryl Pt(II) diimine complexes is described. Performing the alkylation in neat Me_2S instead of ether or THF greatly reduces the amount of comproportionation products otherwise formed, diminishes separation problems, and improves yields. Treatment of the intermediate methyl−aryl complexes (Me_2S)_2Pt(Me)(Ar) with diimines (N−N) furnishes the methyl−aryl Pt(II) diimine complexes (N−N)Pt(Me)(Ar) in 76−84% yields. The Pt methyl−phenyl complex [p-Tol-N ═ VC(Me)C(Me) ═ N-p-Tol]Pt(Me)(Ph) has been characterized by X-ray diffraction.

A metal-organic framework (MOF) based on Pt, Y, and 2,2'-bipyridine-5,5'-dicarboxylate (BPDC), stable up to 400 degrees C, has been synthesized and characterized. In this MOF, the Pt centers are coordinated to Cl and the N atoms of the BPDC unit, giving a local environment similar to that found in a series of Pt-organic complexes with catalytic activity toward C-H bond cleavage of alkanes. This new material is a heterogeneous counterpart to the corresponding metal-organic complex. The structure, determined by single-crystal XRD data, is the repetition of three covalently bonded layers. These layers form a block, which is stacking as an (a)(b)(c) sequence along the crystallographic b-axis. Each layer contains the Pt-organic unit, while Y atoms represent the connection between adjacent layers. No covalent connection is present between layer (a) of a block and layer (c) of an adjacent block. EXAFS (BM29 at the ESRF) analysis supports the XRD data. As this MOF crystallizes under hydrothermal conditions, water acts both as solvent and as a direct ligand of Y. Accessibility to the metal centers is demonstrated by reversible water desorption/readsorption, as determined by TPA/TPD, FTIR, UV-vis, EXAFS, and XANES. Importantly, the results show that the as-synthesized material will not suffer a permanent loss in porosity upon solvent removal. In addition to water, methanol, ethanol, and acetonitrile can also access the internal void of the dehydrated phase.

Rapid equilibria between M(a-hydrocarbon) and M(H)(hydrocarbyl) species is a distinct feature of C-H activation reactions at transition-metal complexes of great structural diversity. In this contribution, we summarize recent work that has been done in order to better understand intimate details about important steps in C-H activation reactions at cationic Pt diimine complexes. An experimental design involving competitive trapping of the rapidly interconverting intermediates is utilized. The results provide new information about the processes by which hydrocarbons enter the coordination sphere of Pt, and about the kinetically preferred site of protonation of (diimine)Pt(CH 3 ) 2 complexes.

A series of novel half-sandwich M(I) and M(III) complexes (M = Co, Rh) bearing the N-heterocyclic carbene ligand 1,3-dimesitylimidazol-2-ylidene (IMes) have been prepared and characterized. Thus, (eta5-C(5)R(5))M(IMes)(C(2)H(4))(M = Co, Rh; R = H, Me) were obtained from the corresponding bis(ethene) complexes (eta5-C(5)R(5))M(C(2)H(4))(2), except for CpRh(IMes)(C(2)H(4)) which was prepared via the novel 16-electron Rh(I) compound Rh(IMes)(C(2)H(4))(2)Cl. The carbonyl compounds (eta5-C(5)R(5))Co(IMes)(CO)(R = H, Me) were synthesized by thermal CO substitution of (eta5-C(5)R(5))Co(CO)(2). A diamagnetic, apparently 16-electron Co(III) compound [CpCo(IMes)I](+)[I(3)(-)] was obtained from CpCo(IMes)(CO) and I(2). Finally, Co(III) and Rh(III) complexes CpCo(IMes)Me(2) and Cp*Rh(IMes)Me(2) were prepared by methylation of [CpCo(IMes)I](+)[I(3)(-)], and ligand exchange at Cp*Rh(Me(2)SO)Me(2), respectively. The molecular structures of CpCo(IMes)(CO), CpRh(IMes)(C(2)H(4)), Cp*Rh(IMes)(C(2)H(4)), and Cp*Rh(IMes)Me(2) were determined by single crystal X-ray diffraction. Steric and electronic factors imposed by the strongly donating and sterically demanding IMes ligand are discussed on the basis of X-ray crystallographic, NMR, and IR spectroscopic analyses. Very poor correlations are found between values for (1)J(Rh-C(carbene)) and dRh-C(carbene) data for Rh(i) N,N-heterocyclic carbene complexes including literature data and this work.

Protonolysis of (diimine)PtMe2 (1) complexes in CD2Cl2 containing CD3CN at -78 degrees C yields (diimine)PtMe2(H)(NCCD3)+ (4), (diimine)PtMe(NCCD3)+ (5), and methane. The relative yields of 5 and methane decrease with increasing concentrations of CD3CN. This is consistent with protonation of 1 occurring directly at the metal, rather than at a methyl group. The principle of microscopic reversibility then implies that the deprotonation in "Shilov-type C-H activation" occurs from a Pt(IV) hydridomethyl intermediate, rather than from a Pt sigma-methane complex.

The trimethylrhodium(III) complex CnRhMe(3) (1, Cn = 1,4,7-trimethyl-1,4,7-triazacyclononane) undergoes a nearly reversible one-electron oxidation at E degrees = -0.15 V vs Cp(2)Fe/Cp(2)Fe(+) (cyclic voltammetry, 1.0 V/s) in acetonitrile/0.1 M Bu(4)NPF(6). Preparative electrolysis as well as homogeneous oxidations with substituted ferricinium salts gives a mixture of CnRhMe(2)(NCMe)(+) (2) and CnRhMe(NCMe)(2)(2+) (3), the 2:3 ratio being independent of the nature of the oxidant. In addition, the reactions yielded ethane, mostly by intramolecular elimination. An investigation of the kinetics of the reaction of 1(*)(+) by derivative cyclic voltammetry revealed a unimolecular reaction (DeltaH() = 57.0 +/- 0.9 kJ/mol, DeltaS() = -35.4 +/- 3.0 J/(K.mol), k(20 degrees C) = 5.9 s(-)(1)) with negligible solvent effects (MeCN vs CH(2)Cl(2)). It is proposed that 1(*)(+) eliminates ethane to generate the formally 15-electron CnRhMe(*)(+) in the rate-determining step. The final Rh-containing products are likely formed from this species and 1(*)(+).

The compounds Cp*Fe(dppe)X ([Fe]X) and the corresponding cation radicals [Fe*]X*+ are available for the series X = F, Cl, Br, I, H, CH3. This has allowed for a detailed investigation of the dependence of the nature of Fe-X bonding on the identity of X and the oxidation state (charge) of the complex. Cyclic voltammetry demonstrates that the electrode potentials for the [Fe]X0/+ couples decrease in the order I > Br > Cl > H > F > CH3. An "inverse halide order" is seen, in which the most electronegative X leads to the most easily oxidized complex. This suggests that F is the best donor among the halides. The halide trend is also reflected in NMR spectroscopic data. Mossbauer spectroscopy data also suggest that the F ligand is a strong donor (relative to H and CH3) in [Fe*]X*+. DFT calculations on CpFe(dpe)X ([Fe]X) model complexes nicely reproduce the trend in the electrode potentials for the [Fe*]X0/+ couples. Analysis of the theoretical data within the halogen series indicates that the energy of the [Fe]X HOMO does not correlate with the extent of its Fe(d(pi))-X(p(pi)) antibonding character, which varies in the order I > Br > Cl > F, but rather depends on the destabilizing electrostatic effect caused by X. This effect varies in the order F > Cl > Br > I. A thermochemical cycle that incorporates the [Fe*]X0/+ and [Fe*]0/+ electrode potentials was used to investigate the effect of the oxidation state of the complex on the homolytic bond dissociation energy (BDEhom), defined for the processes Fe-X --> Fe* + X* and Fe-X*+ --> Fe*+ + X*. For all X, it was found that a one-electron oxidation leads to a weakening of the Fe-X bond. This trend was reproduced by the DFT calculations. On the other hand, IR nu(Fe-X) spectroscopy data showed an increase in the stretching frequencies for X = H and Cl upon oxidation. X-ray crystallographic data showed a shortening of the Fe-Cl bond upon oxidation. The trends in IR and Fe-Cl bond distances were reproduced in the DFT calculations. The combined data therefore suggest that oxidation leads to weaker, but shorter, Fe-X bonds. A second thermochemical cycle was applied to investigate the effect of the one-electron oxidation on the heterolytic bond dissociation energies (BDEhet), defined for the processes Fe-X --> Fe+ + X- and Fe-X*+ --> Fe2+ + X-. In this case, the oxidation led to bond strengthening in all cases. The computed BDE values have been analyzed within Ziegler's transition state methodology and decomposed into two components, one electrostatic and one covalent, describing the interaction between the unrelaxed fragments. In all the computed BDEhom and BDEhet values of the [Fe]X models the electrostatic component is important. This helps to understand their respective variations upon oxidation.

The asymmetric unit of the title coordination polymer, [Y(2)(C(8)H(5)NO(4))(3)(C(3)H(7)NO)(4)](n), contains one Y(3+) ion, three half-mol-ecules of the 2-amino-benzene-1,4-dicarboxyl-ate (abz) dianion and two O-bonded N,N-dimethyl-formamide (DMF) mol-ecules. Each abz half-mol-ecule is completed by crystallographic inversion symmetry and its -NH(2) group is disordered in each case [relative occupancies within the asymmetric unit = 0.462 (18):0.538 (18), 0.93 (2):0.07 (2) and 0.828 (16):0.172 (16)]. The combination of disorder and crystal symmetry means that each of the four C-H atoms of the benzene ring of each of the dianions bears a statistical fraction of an -NH(2) group. The coordination geometry of the yttrium ion is a fairly regular YO(8) square anti-prism arising from its coordination by two DMF mol-ecules, four monodentate abz dianions and one O,O-bidentate abz dianion. The polymeric building unit is a dimeric paddle-wheel with two metal ions linked by four bridging abz dianions. Further bridging linkages connect the dimers into a three-dimensional framework containing voids in which highly disordered DMF mol-ecules are presumed to reside.

Detailed, quantitative knowledge about the energetics of metal-ligand bonding in organotransition-metal complexes is crucial to the understanding of stoichiometric and catalytic reactions and may eventually help in the design of new and improved processes [1]. While numerous methods are available to estimate the energetics of homolytic as well as heterolytic metal-ligand cleavage reactions, many of these can only be applied under equilibrium conditions. Thus, if the reactions involve transient species, the techniques may not be applicable.

The chemical bonding, electronic structure, and optical properties of the experimentally available metal-organic framework IRMOF-14 and its metal-substituted analogues M-IRMOF-14 (M = Zn, Cd, Be, Mg, Ca, Sr, Ba), which contain a pyrene-2,7-dicarboxylate linker group, have been systematically investigated using DFT calculations. The unit cell volume and atomic positions were optimized with the Perdew-Burke-Ernzerhof (PBE) functional and showed good agreement between experimental and theoretical equilibrium structural parameters for Zn-IRMOF-14. The calculated bulk moduli indicate that the whole M-IRMOF-14 series are soft materials. The estimated band gap from DOS calculations for the M-IRMOF-14 series is ca. 2.5 eV, essentially independent of the metal ion and indicative of nonmetallic character. The band gap value is distinctly different from those calculated previously for the M-IRMOF-1 (benzene-1,4-dicarboxylate linker; ca. 3.5 eV) and M-IRMOF-10 (biphenyl-4,4'-dicarboxylate linker; ca. 3.0 eV) series and this confirms that the identity of the linker is a key parameter to control band gaps in an isoreticular series of main-group MOFs. In view of potential uses of MOFs in organic semiconducting devices such as field-effect transistors, solar cells, and organic light-emitting devices, the linear optical properties of these materials were also investigated. Comparisons are made with the M-IRMOF-1 and M-IRMOF-10 series.

Intermediate band (IB) materials are attractive for multiple photon harvesting in solar cells thus increasing their efficiency beyond the Shockley–Quassier limit. However, it has so far been demonstrated that this can only be achieved in a few inorganic solids by appropriate doping. Here we demonstrate that it may be possible to achieve intermediate band materials with the isoreticular metal–organic framework IRMOF-993 and metal-substituted analogues. The equilibrium crystal structures, electronic structures, formation enthalpies, chemical bonding, and optical properties of M-IRMOF-993 (M = Zn, Cd, Be, Mg, Ca, Sr, Ba) were systematically investigated using density functional theory methods. The unit cell volume and atomic positions were optimized with the Perdew–Burke–Ernzerhof (PBE) functional; there was good agreement between the current theoretical equilibrium structural parameters and previously reported structural data for Zn-IRMOF-993. The calculated bulk moduli indicate that Zn-IRMOF-993 and its analogues are soft materials. The estimated fundamental bandgap values from the electronic structure studies for the whole series are ca. 3.5–3.6 eV, indicating a semiconducting character. The bandgap values estimated from the bottom of the IB to the top of VB are ca. 1.5–1.6 eV, and those from the top of IB to the bottom of CB are ca. 2.0 eV, suggesting that these materials may be suitable for enhancing the efficiency of solar cells. As MOFs are considered as potential materials for photocatalysts, active components in hybrid solar cells, electroluminescence cells, organic semiconducting devices such as field-effect transistors, and organic light-emitting devices, the optical properties and chemical bonding of M-IRMOF-993 were also systematically investigated.

Reduction of the metal - metal-bonded complex FvW[sub 2](CO)[sub 6] generated the dianion FvW[sub 2](CO)[sub 6][sup 2[minus]]. An X-ray crystallographic analysis of [Et[sub 4]N[sup +]][sub 2]FvW[sub 2](CO)[sub 6][sup 2[minus]] (monoclinic space group P2[sub 1]/c, a = 7.687(2) [angstrom], b = 13.752(4) [angstrom], c = 16.297(5) [angstrom], [beta] = 94.80(2)[degree], V = 1716.8(8) A[sup 3], Z = 4) showed the dianion to contain a planar Fv ring system bonded to the two metal centers in an anti fashion. The dianion reacted with a number of electrophiles to yield the neutral species FvW[sub 2](CO)[sub 6]E[sub 2] E = H, Me, Et, [sigma]-C[sub 3]H[sub 6], CH[sub 2]Ph. The pK[sub a] values for the two consecutive deprotonations of FvW[sub 2](CO)[sub 6]H[sub 2] were determined as 14.0 and 16.6 by equilibrium measurements in acetonitrile. Thermolysis and photolysis of FvW[sub 2](CO)[sub 6]H[sub 2] yielded FvW[sub 2]-(CO)[sub 6] and H[sub 2]. Unlike Cp[sub 2]W[sub 2](CO)[sub 6], FvW[sub 2](CO)[sub 6] underwent protonation at the W-W bond by HBF[sub 4][center dot]Et[sub 2]O in acetonitrile. Reactions of FvW[sub 2](CO)[sub 6] and FvMo[sub 2](CO)[sub 6] with PMe[sub 3] and Me[sub 2]-PCH[sub 2]PMe[sub 2] (dmpm) resulted in generation of the dinuclear zwitterions FvM[sub 2](CO)[sub 5](PMe[sub 3])[sub 2] and FvM[sub 2](CO)[sub 5](dmpm), respectively.more » 62 refs., 5 figs., 7 tabs.« less

Four new Rh(I) complexes bearing chelating imine-functionalized N-heterocyclic carbene ligands have been synthesized and characterized. The catalytic activity of these new Rh(I) complexes has been tested in the cyclopropanation reaction between ethyl diazoacetate and styrene. One of the new complexes, having ethyl groups on the ligand N-aryl ring, exhibited a reactivity and a cis-diastereoselectivity that were comparable to our previously reported Rh(I) cyclopropanation catalyst of this type, and a higher yield and cis-diastereoselectivity were obtained at lower catalyst loadings and higher temperatures. The other new Rh(I) complexes were found to be inferior to the previously reported Rh(I) cyclopropanation catalyst. The catalytic study gave important information about the effect that changing the steric requirements of the substituents at the ligand system has on the efficiency and cis-diastereoselectivity of the complexes as cyclopropanation catalysts.

The electrocatalytic ligand substitutions of Cp’Mn(CO)2(NCMe) and Cp’Mn(CO)2(pyr) with phosphines and phosphites have been investigated by derivative cyclic voltammetry (DCV) at sweep rates that are sufficiently fast to preclude high catalytic turnovers on the experimental time scale. Digital simulations have established that a single working curve may be used to analyze the DCV data, provided that the substrate is more readily oxidized than the product by 250 mV or more. Rate constants and activation parameters were obtained for the reactions between Cp’Mn(CO)2(NCMe)+ and PPh3 and P(OMe)3, and between Cp’Mn(CO)2(pyr)+ and PEt3 and PBu3. Excellent agreement is observed between the kinetic data obtained with this technique and previously reported values that were obtained under conditions that allowed for high catalytic turnover numbers.

When Cp*Rh(C(2)H(4))(2)H(+) (2) is exposed to C(2)H(4) in the gas phase, inside the cell of an FT-ICR mass spectrometer, the most notable feature is the lack of any bimolecular reactivity. Collisional activation of 2 leads to ethylene loss and formation of Cp*Rh(C(2)H(4)-mu-H)(+) (3). In contrast to the reactivity of 2 in solution, ethylene dimerisation is negligible in the gas phase. Coordinatively unsaturated 3, rather than 2, is the major species in which reactivity is observed to occur. Compound 3 reacts with ethylene in three parallel processes: (a) Slow addition of ethylene to give 2; (b) rapid, intermolecular hydrogen atom exchange (monitored in separate reactions with free C(2)D(4) to give 3-d(1-5)); (c) ligand substitution of ethylene in 3. DFT calculations reproduce these observations, showing low barriers for hydrogen scrambling, high barrier to ligand loss in 2, and even higher barriers to elimination of either H(2) or ethane. Mechanistic models for the elimination and scrambling processes are discussed.

Post-synthetic modification is a viable route for the introduction of surface sites with new chemical properties in metal–organic framework compounds. Herein we demonstrate that it is possible to perform covalent post-synthetic modifications of the UiO-66–NH2 MOF with four different acid anhydrides. FT-IR is employed to monitor the reactions and the extent of reaction depends on the bulkiness of the anhydrides. For the smallest one, acetic anhydride, 100% conversion to UiO-66–NHCOCH3 was observed.

Derivative cyclic voltammetry (DCV) can offer significant advantages in the investigation of electrode reactions when compared with conventional cyclic voltammetry (CV). Redox potentials can be accurately determined for incorporation in thermochemical cycles that allow for the determination of thermodynamic quantities that are of interest to organometallic chemists. Applications towards the determination of solution bond dissociation energies and Bronsted acidities for metal hydrides and metal hydride cation radicals are presented. However, perhaps the greatest advantages of DCV arise from the absence of double-layer charging currents in the derivative voltammograms. This effect makes the technique especially suitable for kinetic and mechanistic studies of the reactions of electrode-generated reactive intermediates. The use of DCV for this purpose is highlighted with case studies from our laboratories. This includes the substitution of one- and two-electron donors in 17-electron cation radicals by two-electron donor nucleophiles. Kinetic parameters show that both types of processes appear to involve 19-electron intermediates or transition states. Also included are some rather unusual reactions that proceed via initial reversible cation radical dimerization.

Publisher Summary This chapter presents the results from an investigation of the mechanism of the oxidatively induced decomposition of (η 5 -C 5 Me 5 )Ru(CO)(PPh 3 )CH 3 . It is anticipated that introduction of the sterically demanding pentamethylcyclopentadienyl ligand would effectively inhibit any possible second-order decomposition pathways for 1 •+ . The results are rationalized in terms of metal-methyl bond homolysis in 1 •+ via the prior formation of a cationic 19-electron intermediate or transition state. The resulting methyl radical generates methane by hydrogen atom abstraction, or it is attached to the pentamethylcyclopentadienyl ligand, giving rise to hexamethylcyclopentadiene after decomplexation from the metal center.

The heterobimetallic metal-organic framework {[(BPDC)PtCl(2)](3)(Gd(H(2)O)(3))(2)}.5H(2)O (BPDC = 2,2'-bipyridine-5,5'-dicarboxylate) has been designed and synthesized by hydrothermal methods. The new coordination polymer contains subunits of (BPDC)PtCl(2) (1) where both N atoms of the BPDC ligand are attached to a square-planar Pt(II) center. The two remaining cis coordination sites at Pt(II) are occupied by chloride ions. The final structure (2) of the polymeric network is obtained when Gd(III) ions link together the (BPDC)PtCl(2) units, which are organized in sheets, into larger blocks. These blocks are stacked along the crystallographic [010] direction and are held together by a hydrogen bonding scheme that involves carboxylate oxygen atoms and water molecules in the coordination sphere of Gd. The coordination polymer 2 can be obtained in a single-step reaction or in a two-step synthesis where the corresponding Pt complex (1) was first synthesized followed by reacting 1 with Gd(NO(3))(3).6H(2)O. In situ high temperature powder X-ray diffraction shows that the crystalline coordination polymer transforms into an anhydrous modification at 100 degrees C. This modification is stable to 350 degrees C, at which temperature the structure starts to decompose. The coordination sphere around platinum in the polymer closely resembles organometallic Pt complexes that have been previously found to catalytically or stoichiometrically activate and functionalize hydrocarbon C-H bonds in homogeneous systems.