Synthesis, Structure, and Photophysical Properties of Mo2(NN)4 and Mo2(NN)2(T(i)PB)2, Where NN = N,N'-Diphenylphenylpropiolamidinate and T(i)PB = 2,4,6-Triisopropylbenzoate.

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).

MM Quadruply Bonded Complexes Supported by Vinylbenzoate Ligands: Synthesis, Characterization, Photophysical Properties and Application as Synthons.

From the reactions between M(T PB) compounds and and - vinylbenzoic acids (2 equiv) in toluene at room temperature the compounds -M(T PB)L, where L = -vinylbenzoate (M = Mo) and (M = W) and T PB = 2,4,6-triisopropylbenzoate, and where L = -vinylbenzoate (M = Mo) and (M = W) have been isolated. Compounds and have been shown to undergo Heck carbon-carbon coupling reactions with phenyliodide to produce -Mo(T PB)(OCCH--CH=CH-CH) and -Mo(T PB)(OCCH--CH=CH-CH), . The molybdenum compounds and have been structurally characterized by single crystal X-ray crystallography.

Electronic and spectroscopic properties of avobenzone derivatives attached to ditungsten quadruple bonds.

From the reactions between W2(T(i)PB)4, where T(i)PB is 2,4,6-triisopropylbenzoate, and 2 equiv of acid, 4-formylbenzoic acid, HBzald, 4-(3-oxo-3-phenylpropanoyl)benzoic acid, HAvo, or 4-(2,2-difluoro-6-phenyl-2H-1λ(3),3,2λ(4)-dioxaborinin-4-yl)benzoic acid, HAvoBF2, three new compounds W2(T(i)PB)2(Bzald)2, I, W2(T(i)PB)2(Avo)2, II, and W2(T(i)PB)2(AvoBF2)2, III, have been prepared. As solid compounds I and II are blue while compound III is green. Characterization of these compounds has been carried out by means of (1)H NMR, MALDI-TOF MS, steady-state absorption and emission spectroscopies, and femtosecond and nanosecond transient absorption and time-resolved infrared spectroscopies.

Electronic and Spectroscopic Properties of Avobenzone Derivatives Attached to Mo₂ Quadruple Bonds: Suppression of the Photochemical Enol-to-Keto Transformation.

From the reactions between Mo2(T(i)PB)4, where T(i)PB 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-1λ(3),3,2λ(4)-dioxaborinin-4-yl)benzoic acid, HAvoBF2, the compounds Mo2(T(i)PB)2(Bzald)2, I; Mo2(T(i)PB)2(Avo)2, II; and Mo2(T(i)PB)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 (1)H NMR, MALDI-TOF MS, steady-state absorption and emission spectroscopies, and femtosecond and nanosecond time-resolved transient absorption and infrared spectroscopies.

Photophysical studies of metal to ligand charge transfer involving quadruply bonded complexes of molybdenum and tungsten.

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.

Photophysical properties of cis-Mo2 quadruply bonded complexes and observation of photoinduced electron transfer to titanium dioxide.

The compounds cis-Mo2(DAniF)2(L)2 have been prepared, where DAniF = (N,N')-p-dianisyl formamidinate and L = thienyl-2-carboxylate (Th), 2,2'-bithienyl-5-carboxylate (BTh), and 2,2':5',5″-terthienyl-5-carboxylate (TTh). The compounds have been characterized by proton nuclear magnetic resonance ((1)H NMR), ultraviolet-visible (UV-vis) absorption and emission, differential pulse voltammetry, and time-resolved transient absorption and infrared (IR) spectroscopy. An X-ray crystal structure was obtained for the thienyl complex.

4-Nitrophenyl- and 4'-nitro-1,1'-biphenyl-4-carboxylates attached to Mo2 quadruple bonds: ground versus excited state M2δ-ligand conjugation.

From the reactions between Mo2(T(i)PB)4, where T(i)PB = 2,4,6-triisopropylbenzoate and two equivalents of the carboxylic acid LH (LH = 4-nitrobenzoic acid and 4'-nitro[1,1'-biphenyl]-4-carboxylic acid) the compounds trans-M2(T(i)PB)2L2 have been prepared: I (L = 4-nitrobenzoate and M = Mo), II (L = 4'-nitro-1,1'-biphenylcarboxylate and M = Mo) and III (L = 4-nitrobenzoate and M2 = MoW). The compounds have been characterized by (1)H NMR, UV-Vis and steady state emission spectroscopy, ns and fs transient absorption spectroscopy and cyclic voltammetry. These data are compared with predictions based on electronic structure calculations on model compounds where T(i)PB is substituted for formate.

Mo2 paddlewheel complexes functionalized with a single MLCT, S1 infrared-active carboxylate reporter ligand: preparation and studies of ground and photoexcited states.

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.

Concerning the ground state and S1 and T1 photoexcited states of the homoleptic quadruply bonded complexes Mo2(O2CC6H4-p-X)4, where X = C≡C-H or C≡N.

The preparation of the homoleptic MM quadruply bonded complexes Mo2(O2CC6H4-p-X)4, where X = C≡C-H (I) or C≡N (II), is reported along with the solution characterization data and electronic structure calculations employing density functional theory. The compounds are colored orange (I) and red (II) due to the metal-to-ligand charge transfer involving the HOMO, Mo2δ, and LUMO, which is a ligand-based π* combination. Studies of the S1 state, (1)MLCT, by femtosecond time-resolved infrared spectroscopy indicate that the negative charge is distributed principally over two trans ligands.

Modulating the M2δ-to-ligand charge transfer transition by the use of diarylboron substituents.

From the reactions between the quadruply bonded complexes M2(T(i)PB)4, where M = Mo or W and T(i)PB = 2,4,6-triisopropylbenzoate, and the carboxylic acids HOOC-C6H4-4-B(mesityl)2, LH (2 equivalents) the complexes trans-M2(T(i)PB)2L2 have been prepared. The new compounds have been characterized by (1)H NMR, MALDI-TOF MS, UV-Vis-NIR and steady-state emission spectroscopy, time-resolved transient absorption spectroscopy and cyclic voltammetry. These results are compared with the related properties of the benzoates, M2(T(i)PB)2(O2CPh)2 (prepared similarly) and with DFT calculations on model compounds where formate substitutes for T(i)PB.

Metal-metal quadruple bonds supported by 5-ethynylthiophene-2-carboxylato ligands: preparation, molecular and electronic structures, photoexcited state dynamics, and application as molecular synthons.

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.

Coordination of N,N-chelated Re(CO)3Cl units across a Mo2 quadruple bond: synthesis, characterization, and photophysical properties of a Re-Mo2-Re triad and its component pieces.

2-(2-Pyridyl)-4-methylthiazole carboxylic acid (PMT-H) and rhenium tricarbonyl chloride react to form the red crystalline compound fac-Re(PMT-H)(CO)3Cl, I, which is an analog of the well-known Re(bpy)(CO)3Cl molecule, where bpy is 2,2'-bipyridine. The acids PMT-H (2 equiv) and Re(PMT-H)(CO)3Cl (2 equiv) also react with Mo2(T(i)PB)4 (T(i)PB = 2,4,6-triisopropylbenzoate) in toluene to give the red compound trans-Mo2(T(i)PB)2(PMT)2, II, and the royal blue compound trans-Mo2(T(i)PB)2[(PMT)Re(CO)3Cl]2, III, respectively. The X-ray and spectroscopic characterization of I confirms its close relationship with Re(bpy)(CO)3Cl, as does the spectroscopic characterization of compounds II and III as analogs of other compounds of the form trans-M2(TiPB)2L2, where L is a π-acceptor ligand.

Electronic structure and excited-state dynamics of the molecular triads: trans-M2(T(i)PB)2[O2CC6H5-η6-Cr(CO)3]2, where M = Mo or W, and T(i)PB = 2,4,6-triisopropylbenzoate.

From the reactions between M(2)(T(i)PB)(4) and HO(2)CC(6)H(5)-η(6)-Cr(CO)(3) (2 equiv), the title compounds trans-M(2)(T(i)PB)(2)[O(2)CC(6)H(5)-η(6)-Cr(CO)(3)](2), where M = Mo or W, and T(i)PB = 2,4,6-triisopropylbenzoate have been prepared and characterized. Compound I (M = Mo) was characterized by a single crystal X-ray structural determination which revealed a centrosymmetric MoMo quadruply bonded molecule. Compound I is red and the tungsten complex II is blue as a result of intense metal-to-ligand charge transfer (MLCT), which is principally M(2)δ to benzoate π* with some chromium t(2g) participation, according to calculations employing density functional theory.