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Ligated metal(III) complexes, Al(III), In(III), Cr(III), and Co(III), containing tetraphenylporphyrin (TPP) and cyclohexylsalen (Cy-salen) ligands were investigated for the polymerization of rac-lactide (rac-LA). A combination of metal complexes, co-catalyst, and co-initiator was shown to be highly efficient for the ring-opening polymerization of rac-LA at room temperature. Influences of metal centers, ligands, and co-catalysts were investigated. Higher Lewis acidity of metal centers and ligands enhanced catalytic activity. Ionic co-catalysts showed increased polymerization rates. Polymerization of rac-LA catalyzed by tetraphenylporphyrin aluminum chloride ((TPP)AlCl) and bis(triphenylphosphine)iminium chloride (PPN+Cl−) in cyclohexene oxide (CHO) as a solvent produced isotactic-enriched polylactide. The order of reactivities based on the metals supported by the TPP ligand is Cr(III) > Al(III) > In(III) > Co(III) while the reactivities of the catalysts supported by Cy-salen ligands are in the order In(III) > Cr(III) > Al(III) > Co(III).

The interligand charge dynamics of the lowest singlet metal-to-ligand charge-transfer states (1MLCT S1 states) of a series of quadruply bonded trans-Mo2(NN)2(O2C–X)2 paddlewheel compounds are investigated, where NN is a π-accepting phenylpropiolamidinate ligand and O2C–X (X = Me, tBu, TiPB, or CF3) is an auxiliary carboxylate ligand. The compounds show strong light absorption in the visible region due to MLCT transitions from the Mo2 center to the NN ligands. The transferred electron density was followed by femtosecond time-resolved infrared (fs-TRIR) spectroscopy with vibrational reporters such as the ethynyl groups on the NN ligands. The observed fs-TRIR spectra show that these compounds have asymmetric 1MLCT S1 excited states where the transferred electron mainly resides on a single NN ligand. The presence of interligand electron transfer (ILET) is suggested to explain the shape of the ν(C≡C) bands and the influence of auxiliary ligands and solvents on the interligand electronic coupling. The ILET in t...

The compounds TMPMgnBu(L), where L = THF, 2-MeTHF, pyridine (py) and dimethylaminopyridine (DMAP) and TMP = 1,5,9-trimesityldipyrromethene, have been synthesized and allowed to initiate polymerization with rac-lactide (rac-LA) and e-caprolactone (e – CL). Both the rate of rac-LA polymerization and the tacticity were found to be solvent dependent, with CH2Cl2 being faster than THF and yielding heterotactic polylactic acid with Pr ∼70% and 95%, respectively. For e-CL, rates of polymerization were in the inverse order with THF being faster than CH2Cl2. In CH2Cl2, the reactions showed a dependence on the coordinating ligand with rates, 2-MeTHF > THF > py > DMAP in the polymerization of rac-LA and e-CL. The molecular structure of TMPMgnBu(2-MeTHF) was shown to contain a trigonally distorted tetrahedron of TMPMg(nBu) with a weak axial Mg---2-MeTHF bond.

Four photophysically interesting dimolybdenum paddlewheel compounds are synthesized and characterized: I and II contain amide ligand (N,3-diphenyl-2-propynamide), and III and IV contain thioamide ligand (N,3-diphenyl-2-propynethioamide). I and III are trans-Mo2L2(O2C-TiPB)2-type compounds, and II and IV are Mo2L4-type compounds, where O2C-TiPB is 2,4,6-triisopropylbenzoate. I–IV display strong light absorption due to metal to ligand charge transfer (MLCT) transitions from molybdenum to the amide/thioamide ligands. Charge transfer dynamics in the MLCT excited states of I–IV have been examined using femtosecond transient absorption (fs-TA) spectroscopy and femtosecond time-resolved infrared (fs-TRIR) spectroscopy. The asymmetric amide/thioamide ligands show two forms of regioarrangements in the paddlewheel compounds. Analyses of the ν(C≡C) bands in the fs-TRIR spectra of I and II show similar electron density distribution over ligands in their 1MLCT S1 states where only two amide ligands are involved and th...

Tetraphenylporphyrin aluminum(III) salts, TPPAlX, where X = Me, OEt, OiPr, OCHMeCH2Cl, and Cl, and bis(triphenylphosphine)imminium chloride, PPN+Cl− (1 : 1) react with rac-lactide, rac-LA, in neat propylene oxide, PO, to yield chains of enriched isotactic polylactide, PLA, with end groups of PO–Cl and with time these yield cyclic polymers (PO)n(PLA) where n = 2 or 3 and even higher. There is no reaction between TPPAlOR (R = Et or iPr), PPN+Cl−, and rac-LA in neat THF at 25 °C even though TPPAlOR (R = Et or iPr) and PPN+Cl− in neat PO yields polypropylene oxide with a terminal OR group, H(PO)nOR. Taken together, Al(III) acts as a Lewis acid in the ring-opening of PO, in which PPN+Cl− is present and the incipient ClCH2CHMeO− initiates the ROP of LA to yield anion chains of [(PLA)-OCHMeCH2Cl]−, and then the ring-opening of PO yields cycles, (PO)n(PLA), with the liberation of Cl−. The polymer was isolated by the addition of MeOH/HCl and end group analysis by mass spectrometry.

From the reaction between Zn[N(SiMe3)2]2 and TMP-H (1 equiv.) in toluene at room temperature TMPZn[N(SiMe3)2] was prepared and subsequently reacted with PriOH (1 equiv.) and HOCMe2C(O)OEt (1 equiv.) to give [TMPZn(μ-OPri)]2 and TMPZn[OCMe2C(O)OEt], respectively. The three compounds were each crystallized and characterized by single crystal X-ray diffraction. The compound TMPZn[N(SiMe3)2] was a three coordinated N3Zn compound with an anagostic N(SiMe3)2 ligand where one SiMe3 was annexed to the Zn2+ ion. The compound [TMPZn(μ-OPri)]2 has a molecular C2 axis and is dimeric in toluene-d8 solution having a N2ZnO2 core for each Zn2+ ion. In TMPZn[OCMe2C(O)OEt] compound the Zn2 + ion is four-coordinated. This too is present in solution (IR) and also present in toluene-d8 and THF where there is evidence of fluxionality with Tc ∼15 °C and −85 °C, respectively. The compound [TMPZn(μ-OPri)]2 polymerizes both e-caprolactone (e-CL) and rac-lactide (rac-LA) to give polycaprolactone (PCL) and polylactic acid (PLA), respectively. The rate of the reactions are e-CL > LA and are influenced by the nature of solvent, THF > CD2Cl2/CH2Cl2. The nature of PLA derived from rac-LA is heterotactic: Pr = 0.96 in THF and Pr = 0.75 in CD2Cl2/CH2Cl2. In the copolymerization of rac-LA: e-CL by both [TMPZn(μ-OPri)]2 and TMPZn[OCMe2C(O)OEt] only PLA is produced, PCL is not formed.

Two dimolybdenum compounds featuring amidinate ligands with a C≡C bond, Mo2(NN)4 (I), where NN = N,N′-diphenylphenylpropiolamidinate, and trans-Mo2(NN)2(TiPB)2 (II), where TiPB = 2,4,6-triisopropylbenzoate, have been prepared and structurally characterized by single-crystal X-ray crystallography. Together with Mo2(DAniF)4 (III), where DAniF = N,N′-bis(p-anisyl)formamidinate, all three compounds have been studied with steady-state UV–vis, IR, and time-resolved spectroscopy methods. I and II display intense metal to ligand charge transfer (MLCT). Singlet state (S1) lifetimes of I–III are determined to be 0.7, 19.1, and 2.0 ps, respectively. All three compounds have long-lived triplet state (T1) lifetimes around 100 μs. In femtosecond time-resolved infrared (fs-TRIR) experiments, one ν(C≡C) band is observed at the S1 state for I but two for II, which indicate different patterns of charge distribution. The electron would have to be localized on one NN ligand in I and partially delocalized over two NN ligands ...

BDI ∗ Mg n Bu(THF) and rac -LA to produce heterotactic PLA have been shown to increase from P r = 0.5–0.65 from DCM to neat THF. The increase in concentration of THF from M THF = 0 in toluene to neat THF is shown to occur by THF dissociation as deduced by 1 H NMR studies. In related systems where X = n Bu and O t Bu and with ligands L = THF, py and DMAP similar processes occur by which external exchange of L occurs with added free ligand. For X = n Bu and L = THF, the activation parameters for the dissociation process are ΔH ╪ = 7.0 ± 0.5 kcal mol −1 and ΔS ╪ = −11.6 ± 0.4 cal mol −1 and for X = O t Bu and L = THF are ΔH ╪ = 11.1 ± 1.0 kcal mol −1 and ΔS ╪ = −3.3 ± 3.9 cal mol −1 . The BDI ∗ (R = t Bu) is notably larger than BDI(R = Me) and this limits the use of THF to coordinate during catalysis. The three coordinate complex BDI ∗ Mg n Bu has been structurally characterized by single crystal X-ray crystallography: where Mg–N = 2.010(4) and 2.026(4) A and Mg–C = 2.117(5) A, with N–Mg–N = 94.2(2)° and N–Mg–C = 130.0(2)° and 135.8(2)°. The related complexes BDI ∗ Mg n Bu(L), where L = py and DMAP have similar structural features.

From the reactions between M2(T(i)PB)4 and two equivalents of the acids LH, the compounds trans-M2(T(i)PB)2L2 were isolated where M = Mo, compound I, and M = W, II, T(i)PB = 2,4,6-triisopropylbenzoate, and LH = 4-[2-(4-Pyridinyl)ethenyl]benzoic acid. In related reactions when tris(pentafluorophenyl)boron, A, was added, the Lewis acid-Lewis base complexes Mo2(T(i)PB)2(LA)2, IB, and W2(T(i)PB)2(LA)2, IIB, were isolated. Compounds I and IB are red and purple, respectively, while II and IIB are green. The new compounds have been characterized by (1)H NMR, UV-visible-NIR absorption spectroscopy, and electrochemical studies, which are tied together with density functional theory, DFT, and time-dependent DFT calculations. Chemical reduction of IB and IIB yields anions where the single electron occupies a ligand-based orbital as indicated by EPR spectroscopy. The LUMO and LUMO+1 are ligand-based, and are close in energy, and upon reduction, no IVCT is observed.

From the reactions between Mo2(TiPB)4, where TiPB is 2,4,6-triisopropylbenzoate, and 2 equiv of the acids 4-formylbenzoic acid, HBzald; 4-(3-oxo-3-phenylpropanoyl)benzoic acid, HAvo; and 4-(2,2-difluoro-6-phenyl-2H-1λ3,3,2λ4-dioxaborinin-4-yl)benzoic acid, HAvoBF2, the compounds Mo2(TiPB)2(Bzald)2, I; Mo2(TiPB)2(Avo)2, II; and Mo2(TiPB)2(AvoBF2)2, III, have been isolated. Compounds I and II are red, and compound III is blue. The new compounds have been characterized by 1H NMR, MALDI-TOF MS, steady-state absorption and emission spectroscopies, and femtosecond and nanosecond time-resolved transient absorption and infrared spectroscopies. Electronic structure calculations employing density functional theory and time-dependent density functional theory have been carried out to aid in the interpretation of these data. These compounds have strong metal-to-ligand charge transfer, MLCT, and transitions in the visible region of their spectra, and these comprise the S1 states having lifetimes ∼5–15 ps. The triplet ...

Photoinduced metal-to-ligand charge transfer transitions afford numerous applications in terms of photon energy harvesting. The majority of metal complexes studied to date involve diamagnetic systems of d(6), d(8), and d(10) transition metals. These typically have very short-lived, ∼100 fs, singlet metal to ligand charge transfer ((1)MLCT) states that undergo intersystem crossing to triplet metal to ligand charge transfer ((3)MLCT) states that are longer lived and are responsible for much of the photophysical studies. In contrast, the metal-metal quadruply bonded complexes of molybdenum and tungsten supported by carboxylate, O2CR, and related amidinate ligands (RN)2C(R') have relatively long-lived (1)MLCT states arising from M2δ to Lπ* transitions. These have lifetimes in the range 1-20 ps prior to intersystem crossing to T1 states that may be (3)MLCT or (3)MMδδ* with lifetimes of 1-100 ns and 1-100 μs, respectively. The M2 quadruply bonded complexes take the form M2L4 or M2L4-nL'n where n = 1-3. Thus, in their photoexcited MLCT states, these compounds pose the question of how the charge resides on the ligands. This Account reviews the current knowledge of how charge is positioned with time in S1 and T1 states with the aid of active IR reported groups located on the ligands, for example, C≡X multiple bonds (X = C, N, or O). Several examples of localized and delocalized charge distributions are noted along with kinetic barriers to the interconversion of MLCT and δδ* states. On the 50th anniversary of the recognition of the MM quadruple bond, these complexes are revealing some remarkable features in the study of the photophysical properties of metal-ligand charge transfer states.

From the reaction between BiCl3 (1 equiv.) and LiN(SiMe3)2 (4 equiv.) and LH2 (2 equiv.), where L = a tetraphenylporphyrin, TPP, an octaethylporphyrin, OEP and phsalen in THF the title compounds have been obtained LiBiTPP2, LiBiOEP2, and LiBi(phsalen)2 and LiBi(phsalen)2·THF. Crystals grown from CH2Cl2-hexanes are colored; (green), (red-purple) and and (red-orange). The molecular structures of compound , and were determined by single-crystal X-ray crystallography and are shown to have short LiBi bonds of distance 2.8 Å involving the LiL(-)BiL(+). Compound shows a slipped structure involving Li to two oxygens and a LiBi distance of 3.1 Å. Compounds and undergo a rapid reversible exchange in toluene-d8 at 90 °C. The MALDI-MS yields weak molecular ions due to LiBiL2(+/-) with more intense ions due to BiL(+) and LiL(-) in the positive and negative modes. The short Li(+) to Bi(3+) distances are comparable to those seen in LiBi compounds, such a LiBiR2, and are comparable to those seen by Pyykkö (P. Pyykkö, J. Phys. Chem. A, 2015, 119, 2326; P. Pyykkö and M. Atsumi, Chem. - Eur. J., 2009, 15, 186; P. Pyykkö and M. Atsumi, Chem. - Eur. J., 2009, 15, 12770) for Li-Bi bonds. These can be seen to be involving Bi6s6p hybrid lone-pairs to Li(+) atoms. The lithium bis(bistrimethylsilyl)amide (2 equiv.) and phsalenH2 in THF gave a compound having Li2L·2THF, . Crystallographically compound contains two Li(+) atoms, one coordinated to five atoms LiO2N2·THF. and the other being coordinated to three atoms, LiO2·THF. By (7)Li and (1)H NMR both lithium atoms share an equivalent environment.

The application of fs time resolved infrared, TRIR spectroscopy to complexes of the form M 2 L 4 , M 2 L 3 L 1 and M 2 L 2 L 2 1 where M = Mo or W and L or L 1 = a carboxylate or amidinate has allowed the nature of 1 MLCT S 1 states to be probed with respect to the location of charge on the ligands. The 3 MLCT states, which are formed by intersystem crossing, have similarly been probed in a few instances where M = W but for M = Mo the T 1 states are typically 3 MoMoδδ*. Examples of localized, valence trapped and delocalized ligand excited states have been found with the latter being favored by strong ligand–ligand coupling via the M 2 δ orbital.

From the reactions between M2(TiPB)4 compounds and meta and para-vinylbenzoic acids (2 equiv.) in toluene at room temperature the compounds trans-M2(TiPB)2L2, where L = m-vinylbenzoate 1A (M = Mo) and 1B (M = W) and TiPB = 2,4,6-triisopropylbenzoate, and where L = p-vinylbenzoate 2A (M = Mo) and 2B (M = W) have been isolated. Compounds 1A and 2A have been shown to undergo Heck carbon–carbon coupling reactions with phenyliodide to produce trans-Mo2(TiPB)2(O2CC6H4-m-CHCH–C6H5)2, 3A and trans-Mo2(TiPB)2(O2CC6H4-p-CHCH–C6H5)2, 4A. The molybdenum compounds 1A and 2A have been structurally characterized by single crystal X-ray crystallography. All the new compounds have been characterized by 1H NMR, IR, UV-visible absorption and emission spectroscopy, high resolution MALDI-TOF MS, fs- and ns-transient absorption spectroscopy and fs-time-resolved IR spectroscopy. Electronic structure calculations employing density functional theory, DFT, and time-dependent DFT have been employed to aid in the interpretation of spectral data. All compounds show intense absorptions in the visible region corresponding to M2δ to Lπ* charge transfer transitions. The lifetimes of the 1MLCT state fall in the range of 1–10 ps and for the molybdenum complexes the T1 states are 3δδ* with lifetimes ∼50 μs while for the tungsten complexes the T1 are 3MLCT with lifetimes in the range of 3–10 ns.

A series of compounds of the form Mo2(O2C-C6H4-X)4, 1-X, and trans-Mo2(TiPB)2(O2C-C6H4-X)2, 2-X, have been prepared where X = F, Cl, Br, and I and TiPB = 2,4,6-triisopropylbenzoate. The compounds 1-X (X = F, Cl) and 2-X (X = F, Cl, Br, and I) have been structurally characterized by single crystal X-ray crystallography, some of which are shown to form extended chains in the solid state due to the formation of halide–halide intermolecular interactions. Both families of compounds have been examined by electronic absorption and emission spectroscopy and the lifetimes of the singlet and triplet lifetimes have been determined. S1 lifetimes are ∼5–8 ps and T1 lifetimes are ∼50–80 μs. The heavy atom halogen appears to have little effect on the S1 lifetimes.

The interligand charge dynamics of the lowest singlet metal-to-ligand charge-transfer states (

Four photophysically interesting dimolybdenum paddlewheel compounds are synthesized and characterized: I and II contain amide ligand (N,3-diphenyl-2-propynamide), and III and IV contain thioamide ligand (N,3-diphenyl-2-propynethioamide). I and III are trans-Mo

The versatile role of alkoxide ligands in the development of organotransition metal chemistry is illustrated in the chemistry of M 2 (OR) 6 compounds (M = Mo or W) with particular emphasis on the activation of carbon monoxide, alkynes, ethene and allene. The specific selection of R allows for the tuning of reactivity as a result of the influence of steric and electronic factors.

The preparation, single crystal and molecular structures of the compounds (BDI)Mg(OCMe2COOEt)(L) are described where BDI = 2-[(2,6-diisopropylphenyl)amino]-4-[(2,6-diisopropylphenyl)imino]pent-2-ene and L = pyridine (py) and 4-dimethylaminopyridine (DMAP). In the solid-state the molecules have five coordinate Mg(2+) ions that may be considered as derived from a trigonal bipyramid where the chelating BDI and OCMe2COOEt ligands span equatorial-axial sites. IR spectroscopic data obtained in CH2Cl2 indicate that the chelating nature of the OCMe2COOEt ligand is maintained in solution and variable temperature NMR studies reveal that the ligands py or DMAP undergo a rapid reversible dissociation in toluene-d8 and especially in THF-d8. This leads to a facile exchange involving coordinated and free L upon the addition of L and evidence is presented to support the view that this occurs exclusively by a dissociative interchange mechanism. Zinc forms a related complex (BDI)Zn(OCMe2COOEt) lacking additional coordination of L but maintaining the chelating nature of the OCMe2COOEt ligand and undergoing reversible coordination of L in the presence of added ligands L. The magnesium and zinc complexes will initiate and sustain the living polymerization of lactide (L- or rac-LA) but not the ring-opening polymerization of ε-caprolactone.

From the reactions between Mo2(DAniF)3pivalate (DAniF = N,N'-di(p-anisyl)formamidinate) and the carboxylic acids LH, the title compounds Mo2(DAniF)3L have been prepared and characterized: compounds I (L = O2CC≡CPh), II (L = O2CC4H2SC≡CH), and III (L = O2CC6H4-p-CN). The new compounds have been characterized in their ground states by spectroscopy ((1)H NMR, ultraviolet-visible absorption, near-infrared absorption, and steady state emission), cyclic voltammetry, and density functional theory calculations. The compounds show strong metal Mo2 to ligand L δ-π* transitions in their visible spectra. The nature of the S1 (1)MLCT and T1 states has been probed by time-resolved (femtosecond and nanosecond) transient absorption and infrared spectroscopy. The observed shifts of the C≡C and C≡N vibrational modes are found to be consistent with the negative charge being localized on the single L in the S1 states, while the T1 states are (3)Mo2 δδ*. The present results are compared to earlier studies of the photoexcited states of trans-Mo2(2,4,6-triisopropylbenzoate)2L2 compounds that have been assigned as either localized or delocalized.

In today's world, a major scientific challenge is preserving the delicate balance between industrial growth and a pollutant free terrestrial environment. Thus, "greener" syntheses of commodity materials, capture and utilization of gaseous industrial by-products have become research areas of increasing significance. The pioneering work of Inoue showed a potential utilization of CO2, a major petrochemical by-product, and opened a new field of research. Inoue discovered the (porphyrin)Al(III)X catalyst systems, (X=Cl(-) or alkoxide) which copolymerize CO2 with epoxides to produce polycarbonates. This catalyst can also copolymerize epoxides and cyclic anhydrides to form polyesters. The current record describes our research aimed towards mechanistic understanding and further developments of (porphyrin)M(III)X catalyst systems. This detailed account shows the influence of the porphyrin ligands (tetraphenylporphyrin (TPP), octaethylporphyrin (OEP), tetrakis-pentafluorophenylporphyrin (TFPP)), metal centers (Al, Cr, and Co) and Lewis base co-catalysts on the individual reaction steps and equilibria involved in the copolymerization processes.

The complexes trans-M2(TiPB)2(O2CC6H4-4-NPh2)2 where M = Mo (I), and M = W (II) were prepared from the reaction between M2(TiPB)4 and the carboxylic acid Ph2N-4-C6H4CO2H (∼2 equiv.) in toluene (TiPB = 2,4,6-triisopropylbenzoate). The compounds were isolated as microcrystalline powders that are yellow, I or purple II, and are air-sensitive. Compound I was characterized by single-crystal X-ray crystallography and shown to have a centrosymmetric structure and a planar central C6H4-CO2M2O2C-C6H4 unit. Calculations indicate that the HOMO is principally M2δ with mixing of the filled π-orbitals of the N,N-diphenyl-4-aminobenzoate. Oxidation of I and II yield cationic species that have been characterized by EPR and UV–Vis–NIR spectroscopy. The radical cations show EPR spectra characteristic of M25+ centers having the MM configuration σ2π4δ1 and compound I+ shows a low energy NIR transition assignable to a ligand to metal charge transfer transition. The homoleptic compound Mo2(O2CC6H4-4-N-Ph2)4, III, was prepared from the reaction between Mo(CO)6 and Ph2N-4-C6H4CO2H in refluxing ortho-dichlorobenzene and is shown to exhibit similar spectroscopic features to those of I.

From the reaction between M2(T(i)PB)4 and 2 equiv of 5-ethynylthiophene-2-carboxylic acid (H-ThCCH) in toluene, the complexes trans-M2(T(i)PB)2(ThCCH)2, where M = Mo (I) or W (II) and T(i)PB = 2,4,6-triisopropyl benzoate, have been isolated and characterized by (1)H NMR, IR, MALDI-TOF MS, UV-vis, steady-state emission, transient absorption, and time-resolved infrared (TRIR) spectroscopies and single-crystal X-ray crystallography for I. The molecular structure of I confirms the trans-substitution pattern and the extended conjugation of the ethynylthienyl ligands via interaction with the Mo2δ orbital. The HOMO of both I and II is the M2δ orbital, and the intense color of the compounds (I is red and II is blue) is due to the M2δ-to-ThCCH (1)MLCT transition. The S1 states for I and II are (1)MLCT. The T1 state is (3)MLCT for II, but (3)MoMoδδ* for I. The TRIR spectra of the ν(C≡C) stretch in the MLCT states are consistent with the delocalization of the electron over both ThCCH ligands. Compound I is shown to be a synthon for the preparation of trans-Mo2(T(i)PB)2(ThCCPh)2 (III) and trans-Mo2(T(i)PB)2(ThCCAuPPh3)2 (IV). Both III and IV have been characterized spectroscopically and by single-crystal X-ray diffraction. The structure of III indicates the extended π-conjugation of the trans-ethynyl-thienyl units extends to the added phenyl rings.

A series of porphyrin metal(III) complexes of general formula LMX (L = tetraphenylporphyrin (TPP), octaethylporphyrin (OEP), tetrakispentafluorophenylporphyrin (TFPP), M = Al, Cr, Co, X = Cl, OH or OEt); has been investigated as catalyst systems for the copolymerization of propylene oxide (PO) and cyclic anhydrides to produce polypropylene carboxylates, with and without a Lewis base cocatalyst: bis(triphenylphosphine)iminium chloride (PPN + Cl − ). The highest rate of copolymerization was observed with 1.0 equiv. cocatalyst and the use of phthalic anhydride (PA) monomer allowed the formation of higher molecular weight polyesters. The terpolymerization of PO, cyclic anhydride and CO 2 produced poly(ester- b -carbonates). With PPN + Cl − cocatalyst, TPPCrCl catalyst system produced two polymer chains per metal. The polymerization processes were followed by 1 H NMR spectroscopy and polymer samples were characterized by GPC, Mass (ESI and MALDI TOF) and NMR ( 1 H, 13 C{ 1 H}) spectroscopy. The observed results are compared with earlier studies of salen and related complexes.

Linking organic conjugated systems with MM quadruple bonds (M = Mo or W) allows for the study of mixed valence metal and organic centered radicals in their ground and photo-excited states. A variety of spectroscopic studies have been employed to determine the nature of the charge distribution and the classification as Class II or III on the Robin and Day scheme.

A series of cobalt(III) complexes LCoX, where L = 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TFPP), and 2,3,7,8,12,13,17,18-octaethylporphyirn (OEP) and X = Cl or acetate, has been investigated for homopolymerization of propylene oxide (PO) and copolymerization of PO and CO2 to yield polypropylene oxide (PPO) and polypropylene carbonate (PPC) or propylene carbonate (PC), respectively. These reactions were carried out both with and without the presence of a cocatalyst, namely, 4-dimethylaminopyridine (DMAP) or PPN(+)Cl(-) (bis(triphenylphosphine)iminium chloride). The PO/CO2 copolymerization process is notably faster than PO homopolymerization. With ionic PPN(+)Cl(-) cocatalyst the TPPCoOAc catalyst system grows two chains per Co center and the presence of excess [Cl(-)] facilitates formation of PC by two different backbiting mechanisms during copolymerization. Formation of PPC is dependent on both [Cl(-)] and the CO2 pressure employed (1-50 bar). TPPCoCl and PO react to form TPPCo(II) and ClCH2CH(Me)OH, while with DMAP, TPPCoCl yields TPPCo(DMAP)2(+)Cl(-). The reactions and their polymers and other products have been monitored by various methods including react-IR, FT-IR, GPC, ESI, MALDI TOF, EXAFS, and NMR ((1)H, (13)C{(1)H}) spectroscopy. Notable differences are seen in these reactions with previous studies of (porphyrin)M(III) complexes (M = Al, Cr) and of the (salen)M(III) complexes where M = Cr, Co.

Chromium(III) tetraphenylporphyrin chloride, TPPCrCl, in the presence of bis(triphenylphosphine)iminium chloride, PPN+Cl–, is shown to react catalytically with styrene oxide, SO, under various conditions to lead to poly(styrene oxide), PSO, poly(styrene carbonate), PSC, styrene carbonate, SC, poly(styrene succinate), PSS, and β-hydroxyester. The stereochemical consequences of the ring-opening event in this coordination catalysis have been investigated by NMR spectroscopy, polarimetry, and chiral HPLC, employing both rac- and R-SO. The ring-opening event occurs by attack at both the methylene and methine carbons and nucleophilic attack at the methine occurs preferentially with inversion. These findings concerning coordinate catalysis are compared with the more common ring-opening reactions in organic chemistry and the recent report on the cobalt-catalyzed formation of PSC by Darensbourg and co-workers.

Over the counter oral relief aids or dietary supplements, namely calcium carbonate, calcium hydroxyapatite, magnesium oxide, zinc oxide, Tums® and Pepto-Bismol® have been investigated in the melt ring-opening polymerization of lactide and a direct comparison with that involving tin(II) octanoate has been made. Of these, Pepto-Bismol® is shown to be the most active and comparable to tin octanoate. The active ingredient in Pepto-Bismol® is bismuth subsalicylate and when this is employed as the initiator similar results are obtained in melt polymerizations which suggests it could be employed as an alternative to the commercially used tin(II) octanoate.

Two dimolybdenum compounds featuring amidinate ligands with a C≡C bond, Mo2(NN)4 (I), where NN = N,N'-diphenylphenylpropiolamidinate, and trans-Mo2(NN)2(T(i)PB)2 (II), where T(i)PB = 2,4,6-triisopropylbenzoate, have been prepared and structurally characterized by single-crystal X-ray crystallography. Together with Mo2(DAniF)4 (III), where DAniF = N,N'-bis(p-anisyl)formamidinate, all three compounds have been studied with steady-state UV-vis, IR, and time-resolved spectroscopy methods. I and II display intense metal to ligand charge transfer (MLCT). Singlet state (S1) lifetimes of I-III are determined to be 0.7, 19.1, and 2.0 ps, respectively. All three compounds have long-lived triplet state (T1) lifetimes around 100 μs. In femtosecond time-resolved infrared (fs-TRIR) experiments, one ν(C≡C) band is observed at the S1 state for I but two for II, which indicate different patterns of charge distribution. The electron would have to be localized on one NN ligand in I and partially delocalized over two NN ligands in II to account for the observations. The result is a standard showcase of excited-state mixed valence in coordination compounds.

The reactivities of chromium(III) complexes LCrX, where L = 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TFPP), and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) and X = Cl or OH, have been studied with respect to their ability to homopolymerize propylene oxide (PO) and copolymerize PO and CO(2) to yield polypropylene oxide (PPO) and polypropylene carbonate (PPC) or propylene carbonate (PC), respectively, with and without the presence of a cocatalyst, namely, 4-dimethylaminopyridine (DMAP) or PPN(+)Cl(-) (bis(triphenylphosphine)iminium chloride). The homopolymerization is notably faster (TOF ≈ 2000 h(-1) at room temperature) than copolymerization, which commonly leads to ether-rich polymers. Studies of kinetics reveal that for TPPCr(OH) with DMAP (1 equiv) the propagation reaction rate is first order in [Cr] with excess PO. With PPN(+)Cl(-) as a cocatalyst the reaction order in [Cr] and [Cl(-)] is complicated by the presence of two growing chains, and the presence of excess [Cl(-)] facilitates the formation of PC by two different backbiting mechanisms. The fixation of CO(2) is promoted by [Cl(-)] but is not greatly influenced by CO(2) pressure (1-50 bar). The reactions and polymers have been monitored by UV-visible spectroscopy, react-IR, GPC, ESI, and MALDI TOF, and NMR ((1)H, (13)C{(1)H}) spectroscopy. Notable differences are seen in these reactions when compared with earlier studies by Darensbourg et al. with salen chromium(III) systems and related aluminum(III) porphyrins.

The electronic structures of oxalate bridged oligomers of MM quadruply bonded complexes (M = Mo or W) have been calculated by density functional theory. The calculations predict the formation of a δ band width ~1.0 eV. With increasing number of oxalate bridges, the metal-to-ligand (oxalate) charge transfer band moves to lower energy. Two synthetic approaches have been investigated. (1) The direct reaction between oxalic acid and the homoleptic compound M2(T i PB)4, where T i PB = 2,4,6-triisopropylbenzoate and (2) the metathetic reaction between the herein reported salt Mo2(T i PB)2(CH3CN)4(BF4)2 and ( n Bu4N+)2(oxalate2−). Neither reaction yielded the desired oligomers though the latter resulted in the formation of the molecular triangle [Mo2(T i PB)2(O2CCO2)]3.

Metal–metal (MM) quadruply bonded units supported by four carboxylate ligands MM(O2CR)4, where MM = Mo2, MoW, or W2 react with dicarboxylic acids or monocarboxylic acids to generate compounds of the form [(RCO2)3MM]2 (O2C–X–CO2) (I), and trans-MM(O2CR)2 (O2C–X)2 (II), where X is a π-conjugated group, under appropriate conditions. (I) and (II) provide model compounds for extended-chain polymers/oligomers of formula [(RCO2)2MM(O2C–X–CO2)] (III). Oxidation of (I) and reduction of (II) lead to mixed valence (MV) metal- and organic-centered ions, respectively, which have been characterized by electron paramagnetic resonance and UV–Vis–near infrared spectroscopy. Photochemical excitation of compounds (I) and (II) leads to metal–ligand charge transfer states. Time-resolved infrared spectroscopy has been employed to determine the charge distribution and dynamics in the S1 and T1 states.

From the reactions between M(2)(T(i)PB)(4), where T(i)PB = 2,4,6-triisopropylbenzoate and two equivalents each of 2-furan carboxylic acid, FuCO(2)H, and 2-selenophene carboxylic acid, SpCO(2)H in toluene, the new compounds trans-M(2)(T(i)PB)(2)(O(2)CFu)(2) (1a M = Mo, 2a M = W) and trans-M(2)(T(i)PB)(2)(O(2)CSp)(2) (1b M = Mo, 2b M = W) were formed. These new compounds have been characterized by (1)H NMR, steady-state UV-Vis-NIR absorption and emission spectroscopy, cyclic and differential pulse voltammetry, and fs and ns transient absorption spectroscopy. The compound Mo(2)(T(i)PB)(2)(O(2)CSp)(2) (1b) has been characterized by single crystal X-ray crystallography. These data are compared with those previously reported for related 2-thiophene carboxylate derivatives: M(2)(T(i)PB)(2)(O(2)CTh)(2). The physico-chemical data correlate well with electronic structure calculations performed on model compounds. All compounds have detectible S(1) photoexcited states with lifetimes that vary from ∼5 ps to < 1 ps. The molybdenum compounds have T(1) states with microsecond lifetimes that are assigned as MMδδ* whereas the T(1) states for tungsten are (3)MLCT with lifetimes on the order of nanoseconds. In all cases, shorter lifetimes were seen in complexes containing heavier atoms.

The application of fs time resolved infrared, TRIR spectroscopy to complexes of the form M 2 L 4 , M 2 L 3 L 1 and M 2 L 2 L 2 1 where M = Mo or W and L or L 1 = a carboxylate or amidinate has allowed the nature of 1 MLCT S 1 states to be probed with respect to the location of charge on the ligands. The 3 MLCT states, which are formed by intersystem crossing, have similarly been probed in a few instances where M = W but for M = Mo the T 1 states are typically 3 MoMoδδ*. Examples of localized, valence trapped and delocalized ligand excited states have been found with the latter being favored by strong ligand–ligand coupling via the M 2 δ orbital.

The compounds M(2)(O(2)C(t)Bu)(4) and M(2)(O(2)CC(6)H(5))(4), where M = Mo or W, have been examined by femtosecond time-resolved IR (fs-TRIR) spectroscopy in tetrahydrofuran with excitation into the singlet metal-to-ligand charge-transfer ((1)MLCT) band. In the region from 1500 to 1600 cm(-1), a long-lived excited state (2 ns) has been detected for the compounds M(2)(O(2)C(t)Bu)(4) and Mo(2)(O(2)C-C(6)H(5))(4) with an IR absorption at ~1540 cm(-1) assignable to the asymmetric CO(2) stretch, ν(as)(CO(2)), of the triplet metal-metal δ-δ star ((3)MM δδ*) state. The fs-TRIR spectra of W(2)(O(2)C-C(6)H(5))(4) are notably different and are assigned to decay of the MLCT states. In (3)MM δδ*, the removal of an electron from the δ orbital reduces MM δ to CO(2) π* back-bonding and causes a shift of ν(as)(CO(2)) to higher energy by ~30-60 cm(-1), depending on the metal. TRIR spectroscopy also provides evidence for M(2)(O(2)C(t)Bu)(4), where M = Mo or W, having MM δδ* S(1) states with ν(as)(CO(2)) distinct from those of the (3)MM δδ* states.

The singlet S 1 and triplet T 1 photoexcited states of the compounds containing MM quadruple bonds trans -M 2 (T i PB) 2 (O 2 CC 6 H 4 -4-CN) 2 , where T i PB = 2,4,6-triisopropylbenzoate and M = Mo ( I ) or M = W ( I ′ ), and trans -M 2 (O 2 CMe) 2 ((N[ i Pr ]) 2 CC ≡ CC 6 H 5 ) 2 , where M = Mo ( II ) and M = W ( II ′ ), have been investigated by a variety of spectroscopic techniques including femtosecond time-resolved infrared spectroscopy. The singlet states are shown to be delocalized metal-to-ligand charge transfer (MLCT) states for I and I ′ but localized for II and II ′ involving the cyanobenzoate or amidinate ligands, respectively. The triplet states are MoMo δδ * for both I and II but delocalized 3 MLCT for I ′ and localized 3 MLCT for II ′ . These differences arise from consideration of the relative orbital energies of the M 2 δ or M 2 δ * and the ligand π ∗ as well as the magnitudes of orbital overlap.

The reactivities of aluminum(III) complexes LAlX, where L = 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TFPP), and 2,3,7,8,12,13,17,18-octaethylporphyirn (OEP) and X = Cl or OEt, have been studied with respect to their ability to homopolymerize propylene oxide (PO) and copolymerize PO and CO(2) to yield polypropylene oxide (PPO) and polypropylene carbonate (PPC), respectively, with and without the presence of a cocatalyst, namely, 4-dimethylaminopyridine (DMAP) or a PPN(+) salt where the anion is Cl(-) or N(3)(-). In the presence of a cocatalyst (0.5 equiv), the TFPP complex is the most active in copolymerization to yield PPC, with the latter being effective even at 10 bar CO(2). An increase in the PPN(+)X(-)/[Al] ratio decreases the rate of PPC formation and favors the formation of propylene carbonate, (PC). Studies of the polymers formed in reactions involving Al-alkoxide initiators and PPN(+) salts by mass spectrometry indicate that one chain is grown per Al center. These results are compared with earlier studies where the reactions display first order kinetics in the metal complex.

The reaction between W(2)(T(i)PB)(4), where T(i)PB = 2,4,6-triisopropylbenzoate, and 2 equiv of 4-isonicotinic acid (nicH) yields the compound W(2)(T(i)PB)(2)(nic)(2), 2, and T(i)PBH. Compound 2 is related to the previously reported molybdenum analog, Mo(2)(T(i)PB)(2)(nic)(2), 1. Compounds 1 and 2 react with 2 equiv of B(C(6)F(5))(3) in THF to form the adducts M(2)(T(i)PB)(2)(nic-B(C(6)F(5))(3))(2), 1B (M = Mo) and 2B (M = W), which have been crystallographically characterized as solvates M(2)(T(i)PB)(2)(nic-B(C(6)F(5))(3))(2)·2THF n-hexane. Compounds 1 and 2 are intensely colored due to M(2) δ to π* MLCT transitions, and upon complexation with B(C(5)F(5))(3) to give 1B and 2B, these bands shift to lower energy and gain in intensity. Each compound shows two one-electron ligand-based reductions with a ΔE(1/2) = 120 (1), 300 (1B), 440 (2), and 650 mV (2B). The larger ΔE(1/2) values for the tungsten compounds reflect the greater orbital mixing of the metal 5d-based M(2) δ and the nic π* LUMO. Reduction of solutions of 1B and 2B with (C(5)Me(5))(2)Co leads to the anions 1B(-) and 2B(-), which have been characterized spectroscopically by electron paramagnetic resonance (EPR) and UV-vis-NIR absorption. The EPR spectra of 1B(-) and 2B(-) are consistent with ligand-based (i.e., organic) radicals. The electronic spectra contain low-energy narrow charge resonance (IVCT) bands at 3800 (1B(-)) and 4500 cm(-1) (2B(-)), consistent with fully delocalized mixed valence radical anions. The results are compared with electronic structure calculations and with the spectral features of the metal-centered delocalized mixed valence radical cations [(Bu(t)CO(2))(3)M(2)](2)-μ(2)-(O(2)C-CO(2))(+), to which they are remarkably similar, as well as with other organic-based mixed valence systems.

La química organometálica trata con productos no naturales y, como tal, refleja nuestra evolución como químicos. Así, mientras la primera preparación del complejo metálico-olefínico K+[PtCl3(C2H4)]-- es atribuida a Zeise, no fue sino hasta el advenimiento de la instrumentación moderna (RMN, IR), la aplicación rutinaria de la difracción de rayos-X...

A summary of the reactions involved in the ring-opening polymerization (ROP) of lactide (LA) to give polylactides (PLAs) is presented along with competing reactions. Particular attention is given to the stereoselective polymerization of rac-LA to give heterotactic PLA and meso-LA to give syndiotactic PLA by aluminum Schiff-based catalysts and to the development of highly active group 2 metal single-site catalysts. Melt or solvent-free polymerization is also described along with reactions that lead exclusively to cyclic-polylactides.

The electroabsorption spectra for the metal-to-ligand charge transfer transition in complexes containing oxalate and terephthalate bridged MM quadruply bonded units, [(MM)(pivalate)(3)](2)-mu(2)-BR, where M = Mo or W and BR = oxalate or terephthalate, are reported. The measured magnitude of the change in dipole moment (|Deltamu|) and the change in polarizability (Deltaalpha) that accompany this electronic transition are found to be small and not to follow the behavior expected on the basis of the two-state model. In addition, the trend in the value of Deltaalpha for the neutral states is mirrored by the trend in the degree of electronic coupling (H(AB)) for the strongly coupled mixed valence states formed by the same complexes in their singly oxidized states.

The original "chop-chop" reaction reported by Schrock [J. Am. Chem. Soc. 1982, 104, 4291] involving W(2)(O(t)Bu)(6) and organic nitriles, RC[triple bond]N to give the metal alkylidyne and nitride products ((t)BuO)(3)WC[triple bond]R and ((t)BuO)(3)WC[triple bond]N, has been examined by a density functional theory based calculation where the bulky (t)BuO ligands have been substituted by MeO. The reaction between W(2)(OMe)(6) and MeCN proceeds via a ditungstaazacyclobutadiene intermediate having a planar W(2)CN core, I, with a structure related to that seen for Mo(2)(OCH(2)(t)Bu)(6)(mu-NCNMe(2)). Another possible intermediate having a pseudo tetrahedral W(2)CN core, II, a ditungstaazatetrahedrane was examined and shown to have a higher energy. The interconversion of I and II was found to be energetically unfavorable with respect to their formation of metathesis products. The highest energy transition state involving the conversion of I to products was comparable to that for the conversion of II to products but the initial formation of I from the reaction between W(2)(OMe)(6) and MeCN was favored over the formation of II. The related reaction between Mo(2)(OMe)(6) and MeCN was shown to be thermodynamically unfavorable with respect to either adduct formation or metathesis products. However the reaction between Mo(2)(OMe)(6) and Me(2)NCN did yield a thermodynamically favored 1:1 adduct with a structure related to I.

The development of a new class of single-site metal alkoxide catalysts employing trispyrazolyl ligands is described where the metal ions are Mg(2+), Zn(2+) and Ca(2+). A particularly promising ligand for the kinetically labile Ca(2+) ion is tris[3(-2-methoxy-1,1-dimethylpyrazolyl)] hydroborate, Tp C∗ . This ligand is capable of being extremely flexible in its coordination modes and its coordination with various group 1 and 2 metal ions is described. The complexes Tp C∗ MI exist as salts [Tp C∗ M] + I − , where M = Mg and Ca, but Tp C∗ ZnI contains a four coordinate Zn(2+) center. The complexes Tp C ∗CaN(SiMe 3 ) 2 and Tp C∗ CaOC 6 H 4 -p-Me contain 5 and 7 coordinate Ca(2+) ions and serve as initiators for the ring-opening polymerization of lactide and e-caprolactone. The compounds [Tp C∗ M] + [Tp C∗ ] − , where M = Mg and Ca, exist as salts in the solid-state and in solution show exchange between coordinated and free Tp C∗ ligands as determined by NMR spectroscopy.

The photophysical properties of the title compound have been studied by fs and ns transient absorption spectroscopy. The electronic absorption spectrum consists of three principle absorptions assigned to terpy 1LLCT at ~300 nm, ruthenium (II) t 2g 6 to terpy 1MLCT at ~470 nm and Mo2 δ to terpycarboxylate at ~670 nm. The compound shows weak room temperature emission in THF solution at ~1,100 nm when excited into each of the aforementioned bands. This emission is assigned to the T1 state, 3MMδδ*. Transient absorption spectroscopy indicates a lifetime for T1 of 9.6 μs.

The heteronuclear MM quadruply bonded oxalate bridged compound [(t-BuCO2)3MoW]2(µ-C2O4) (I) has been prepared from the reaction between MoW(O2Ct-Bu)4 and oxalic acid and characterized by elemental analysis, 1H NMR and UV-vis spectroscopy, and electrochemical studies. Single electron oxidation of I by reaction with Ag+PF6– leads to the formation of the kinetically labile radical cation I+, which has been characterized by UV-vis, NIR, and EPR spectroscopy. The latter results are compared with the properties of their related homonuclear Mo4- and W4-oxalate bridged compounds and their respective radical cations. The spectroscopic features of the related radical cations [(t-BuCO2)6MoxWy(µ-C2O4)]+, where x = 1, 2, 3 and y = 4 – x, are also described with the conclusion that the [(t-BuCO2)3Mo2(µ-C2O4)W2(O2Ct-Bu)3]+ and [(t-BuCO2)3Mo2(µ-C2O4)MoW (O2Ct-Bu)3]+ cations are valence trapped on the Robin and Day scheme for the classification of mixed valence compounds.Key words: molybdenum, tungsten, mixed valence.

Reactions involving MI2 where M = Mg, Ca, Sr, Ba or Zn and M′TpC* where M′ = Na or Tl and TpC* = tris[3-methoxy-1,1-dimethyl)pyrazolyl]hydroborate in tetrahydrofuran are described leading to the isolation and characterization of the complexes TpC*MgI, I, TpC*CaI, II, TpC*SrI, III, TpC*SrI(THF), IV, TpC*BaI, V, TpC*BaI(pz*H), VI, where pz*H = 3-(2-methoxyl-1,1-dimethyl)pyrazole, TpC*BaI·½toluene, VII and TpC*ZnI, VIII. The compounds I, II, IV, VI, VII and VIII have been characterized by single-crystal X-ray crystallography. Compounds I and II are isostructural and are salt-like containing κ6-TpM+ cations and I− anions. In all other structures, the iodide is bound to the metal and TpC* is κ6 bonded to the group 2 M(2+) ions. Reactions involving TpC*CaI, II, and sodium or lithium alkoxides or amides failed to yield the amide or alkoxide calcium TpC* derivative, though related reactions involving TpC*ZnI, VIII, and KOSiMe3 proceeded quantitatively to yield κ3TpC*ZnOSiMe3, IX, which was also structurally characterized and shown to have the κ3-TpC* bound ligand.

The electronic structures of the molecules (tBuO)3M≡N (M = Cr, Mo, W) have been investigated with gas phase photoelectron spectroscopy and density functional calculations. It is found that the alkoxide orbitals mix strongly with the M≡N triple bond orbitals and contribute substantially to the valence electronic structure. The first ionization of (tBuO)3Cr≡N is from an orbital of a2(C3v) symmetry that is oxygen based and contains no metal or nitrogen character by symmetry. In contrast, the first ionizations of the molybdenum and tungsten analogues are from orbitals of a1 and e symmetry that derive from the highest occupied M≡N σ and π orbitals mixed with the appropriate symmetry combinations of the oxygen p orbitals. In this a1 orbital, the oxygen p orbitals mix with the highest occupied M≡N orbital of σ symmetry. This mixing reduces the metal character, consequently reducing the metal−nitrogen overlap interaction in this orbital. From computational modeling, the polarity of the M≡N bond increases down the...