DFT Study on C–F Bond Activation by Group 14 Dialkylamino Metalylenes: A Competition between Oxidative Additions versus Substitution Reactions

The C–F bond activation of pentafluoropyridine (<b>PFP</b>) by group 14 dialkylamino metalylenes has been studied employing DFT calculations. Emphasis is placed on the group 14 central atom (M = Si^II, Ge^II, and Sn^II) and substituents (−NMe₂, −N^<i>i</i>Pr₂, −Cl, −NH₂, and −PH₂) dependent switching of oxidative addition to the metathesis/substitution reaction route, using state-of-the-art theoretical methods (M062X/def2-QZVP­(SMD)//M062X/def2-TZVP) to provide a systematic classification of the individual mode of reactions. Moreover, an energy decomposition analysis (EDA) is implemented to get a brief insight into the physical factors that control the activation barriers originating via the different mode of reactions, viz., oxidative addition and metathesis routes. The key finding is that the distortion of <b>PFP</b> is the principal guiding factor in the oxidative addition reaction, while distortions imposed on both the <b>PFP</b> and metalylenes are inevitable toward the origin of the metathesis reaction barrier. The preferable oxidative addition reaction over metathesis of substituted silylenes can be explained on the basis of electron concentration and the HOMO–LUMO gap between the reacting substrates. However, the dramatic switch between oxidative addition and metathesis reaction in substituted germylenes depends on both the electronic and steric nature of the substituents. Similar observations are also noted for the reactivity of substituted stannylenes

Influence of the coordination environment of zinc(II) complexes of designed mannich ligands on phosphatase activity: A combined experimental and theoretical study

A mononucleating (HL1) and a dinucleating (HL2) \u201cendoff\u201d compartmental ligand have been designed and synthesized by controlled Mannich reaction using p-cresol and bis(2-methoxyethyl)amine, and their formation has been rationalized. Six complexes have been prepared on treating HL1 and HL2 with ZnIIX2 (X = Cl 12, Br 12, I 12) with the aim to investigate their hydrolytic activity on phosphoester bond cleavage. Interestingly, the mononucleating ligand was observed to yield dinuclear complexes, [Zn2(L1)2X2] (1 123), while the potential dinucleating ligand generated mononuclear complexes, [Zn(HL2)X2] (4 126). Four (1 124), out of six complexes studied, were characterized by single-crystal X-ray diffraction (XRD): the Zn ion exhibits trigonal bipyramidal and tetrahedral coordination spheres in the di- and mononuclear complex, respectively. The hydrolytic kinetics, followed spectrophotometrically with 4-nitrophenylphosphate (4-NPP) in buffered dimethylformamide (DMF) (97.5% DMF, v/v) because of solubility reasons, under excess substrate conditions (substrate:complex = 20:1), indicated that the complexes enormously accelerate the rate of phosphomonoester hydrolysis with first order rate constants (kcat) in the range 2 1210 s 121 at 25 \ub0C. In each case kinetic data analyses have been run by Michaelis 12Menten treatment. The efficacy in the order of conversion of substrate to product (pnitrophenolate ion) follows the trend 1 > 2 > 3 > 4 > 5 > 6, and the ratio of kcat of an analogous dinuclear to mononuclear complex is 432. An electrospray ionization-mass spectrometry (ESI-MS) study has revealed the dissociation of the centrosymmetric dinuclear complex to two mononuclear species instead of a syn-cooperative catalysis. Density functional theory (DFT) calculations have been performed to rationalize our proposed mechanistic pathway for phosphatase activity. The comparative analysis concludes the following facts under experimental conditions: (1) the halide bound to the active site affects the overall rate in the order: Cl 12 > Br 12 > I 12 regardless of nuclearity; (2) dinuclear complexes prevail over the mononuclear ones

A radical pathway in catecholase activity with nickel(ii) complexes of phenol based \u201cend-off\u201d compartmental ligands

Seven dinuclear and one dinuclear based dicyanamide bridged polymeric NiII complexes of phenol based compartmental ligands (HL1\u2013HL4) have been synthesized with the aim to investigate their catecholaselike activity and to evaluate the most probable mechanistic pathway involved in this process. The complexes have been characterized by routine physicochemical studies as well as by X-ray single crystal structure analyses namely [Ni2(L2)(SCN)3(H2O)(CH3OH)] (1), [Ni2(L4)(SCN)3(CH3OH)2] (2), [Ni2(L2)(SCN)2(AcO)- (H2O)] (3), [Ni2(L4)(SCN)(AcO)2] (4), [Ni2(L2)(N3)3(H2O)2] (5), [Ni2(L4)(N3)3(H2O)2] (6), [Ni2(L1)(AcO)2- (N(CN)2)]n (7) and [Ni2(L3)(AcO)2(N(CN)2)] (8), [SCN = isothiocyanate, AcO = acetate, N3 = azide, and N(CN)2 = dicyanamide anion; L1\u20134 = 2,6-bis(R2-iminomethyl)-4-R1-phenolato, where R1 = methyl and tert-butyl, R2 = N,N-dimethyl ethylene for L1\u20132 and R1 = methyl and tert-butyl, R2 = 2-(N-ethyl) pyridine for L3\u20134]. A UV-vis spectrophotometric study using 3,5-di-tert butylcatechol (3,5-DTBC) reveals that all the complexes are highly active in catalyzing the aerobic oxidation of (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) in methanol medium with the formation of hydrogen peroxide

Ligand-Controlled Palladium-Catalyzed Decarboxylative Heck Coupling for Regioselective Access to Branched Olefins

A highly chemo- and regioselective decarboxylative Heck-type coupling of carboxylic acids and terminal olefins has been developed using a catalytic system composed of Pd(OAc)2 in the presence of phosphine-sulfonamido ligands. Using the bulky ligand L1 leads to high selectivity for 1,1-disubstituted (branched; b) olefins that are generally difficult to obtain. The influence of all relevant reaction parameters was evaluated using a combination of design of experiments and one factor at a time optimization. The coupling of dimethoxy-benzoic acid with various olefinic substrates gave the corresponding branched olefins with excellent regioselectivity (b/l up to 42:1) in up to 80% isolated yields. In contrast, using the less bulky ligand L2 results in the inverse regioselectivity leading to the 1,2-disubstituted (linear; l) product again in high yield of 86% (b/l = 1:26). Detailed investigation of the mechanistic pathways by DFT calculations reveals that the sterically demanding aryl substituent at the sulfonamide group of ligand L1 favors the pathway via 1,2-insertion with an energy preference of 4.4 kcal/mol, thus furnishing the 1,1-disubstituted branched olefins. In contrast, the 2,1-insertion reaction is advantageous by 1.3 kcal/mol for the analogous less bulky ligand L2 leading to the linear products

Influence of the Coordination Environment of Zinc(II) Complexes of Designed Mannich Ligands on Phosphatase Activity: A Combined Experimental and Theoretical Study

A mononucleating (HL¹) and a dinucleating (HL²) “end-off” compartmental ligand have been designed and synthesized by controlled Mannich reaction using <i>p</i>-cresol and bis­(2-methoxyethyl)­amine, and their formation has been rationalized. Six complexes have been prepared on treating HL¹ and HL² with Zn^IIX₂ (X = Cl^–, Br^–, I^–) with the aim to investigate their hydrolytic activity on phosphoester bond cleavage. Interestingly, the mononucleating ligand was observed to yield dinuclear complexes, [Zn₂(L¹)₂X₂] (<b>1</b>–<b>3</b>), while the potential dinucleating ligand generated mononuclear complexes, [Zn­(HL²)­X₂] (<b>4</b>–<b>6</b>). Four (<b>1</b>–<b>4</b>), out of six complexes studied, were characterized by single-crystal X-ray diffraction (XRD): the Zn ion exhibits trigonal bipyramidal and tetrahedral coordination spheres in the di- and mononuclear complex, respectively. The hydrolytic kinetics, followed spectrophotometrically with 4-nitrophenylphosphate (4-NPP) in buffered dimethylformamide (DMF) (97.5% DMF, v/v) because of solubility reasons, under excess substrate conditions (substrate:complex = 20:1), indicated that the complexes enormously accelerate the rate of phosphomonoester hydrolysis with first order rate constants (<i>k</i>_cat) in the range 2–10 s^–1 at 25 °C. In each case kinetic data analyses have been run by Michaelis–Menten treatment. The efficacy in the order of conversion of substrate to product (<i>p</i>-nitrophenolate ion) follows the trend <b>1</b> > <b>2</b> > <b>3</b> > <b>4</b> > <b>5</b> > <b>6</b>, and the ratio of <i>k</i>_cat of an analogous dinuclear to mononuclear complex is ≃2. An electrospray ionization-mass spectrometry (ESI-MS) study has revealed the dissociation of the centrosymmetric dinuclear complex to two mononuclear species instead of a syn-cooperative catalysis. Density functional theory (DFT) calculations have been performed to rationalize our proposed mechanistic pathway for phosphatase activity. The comparative analysis concludes the following facts under experimental conditions: (1) the halide bound to the active site affects the overall rate in the order: Cl^– > Br^– > I^– regardless of nuclearity; (2) dinuclear complexes prevail over the mononuclear ones

Influence of the Coordination Environment of Zinc(II) Complexes of Designed Mannich Ligands on Phosphatase Activity: A Combined Experimental and Theoretical Study

A mononucleating (HL¹) and a dinucleating (HL²) “end-off” compartmental ligand have been designed and synthesized by controlled Mannich reaction using <i>p</i>-cresol and bis­(2-methoxyethyl)­amine, and their formation has been rationalized. Six complexes have been prepared on treating HL¹ and HL² with Zn^IIX₂ (X = Cl^–, Br^–, I^–) with the aim to investigate their hydrolytic activity on phosphoester bond cleavage. Interestingly, the mononucleating ligand was observed to yield dinuclear complexes, [Zn₂(L¹)₂X₂] (<b>1</b>–<b>3</b>), while the potential dinucleating ligand generated mononuclear complexes, [Zn­(HL²)­X₂] (<b>4</b>–<b>6</b>). Four (<b>1</b>–<b>4</b>), out of six complexes studied, were characterized by single-crystal X-ray diffraction (XRD): the Zn ion exhibits trigonal bipyramidal and tetrahedral coordination spheres in the di- and mononuclear complex, respectively. The hydrolytic kinetics, followed spectrophotometrically with 4-nitrophenylphosphate (4-NPP) in buffered dimethylformamide (DMF) (97.5% DMF, v/v) because of solubility reasons, under excess substrate conditions (substrate:complex = 20:1), indicated that the complexes enormously accelerate the rate of phosphomonoester hydrolysis with first order rate constants (<i>k</i>_cat) in the range 2–10 s^–1 at 25 °C. In each case kinetic data analyses have been run by Michaelis–Menten treatment. The efficacy in the order of conversion of substrate to product (<i>p</i>-nitrophenolate ion) follows the trend <b>1</b> > <b>2</b> > <b>3</b> > <b>4</b> > <b>5</b> > <b>6</b>, and the ratio of <i>k</i>_cat of an analogous dinuclear to mononuclear complex is ≃2. An electrospray ionization-mass spectrometry (ESI-MS) study has revealed the dissociation of the centrosymmetric dinuclear complex to two mononuclear species instead of a syn-cooperative catalysis. Density functional theory (DFT) calculations have been performed to rationalize our proposed mechanistic pathway for phosphatase activity. The comparative analysis concludes the following facts under experimental conditions: (1) the halide bound to the active site affects the overall rate in the order: Cl^– > Br^– > I^– regardless of nuclearity; (2) dinuclear complexes prevail over the mononuclear ones

Diverse Bonding Activations in the Reactivity of a Pentaphenylborole toward Sodium Phosphaethynolate: Heterocycle Synthesis and Mechanistic Studies

The reaction of the pentaphenylborole [(PhC)₄BPh] (<b>1</b>) with sodium phosphaethynolate·1,4-dioxane (NaOCP­(1,4-dioxane)_1.7) afforded the novel sodium salt of phosphaboraheterocycle <b>2</b>. It comprises anionic fused tetracyclic P/B-heterocycles that arise from multiple bond activation between the borole backbone and [OCP]⁻anion. Density functional theory calculations indicate that the [OCP]⁻ anion prefers the form of phosphaethynolate ^–O–CP over phosphaketenide OCP^– to interact with two molecules of <b>1</b>, along with various B–C, C–P, and C–C bond activations to form <b>2</b>. The calculations were verified by experimental studies: (i) the reaction of <b>1</b> with NaOCP­(1,4-dioxane)_1.7 and a Lewis base such as the N-heterocyclic carbene I_Ar [:C­{N­(Ar)­CH}₂] (Ar = 2,6-<i>i</i>Pr₂C₆H₃) and amidinato amidosilylene [{PhC­(N<i>t</i>Bu)₂}­(Me₂N)­Si:] afforded the Lewis base-pentaphenylborole adducts [(PhC)₄B­(Ph)­(LB)] (LB = I_Ar (<b>3</b>), :Si­(NMe₂)­{(N<i>t</i>Bu)₂CPh} (<b>4</b>)), respectively; (ii) the reaction of <b>1</b> with the carbodiimide ArNCNAr afforded the seven-membered B/N heterocycle [B­(Ph) (CPh)₄C­(NAr)­N­(Ar)] (<b>5</b>). Compounds <b>2</b>–<b>5</b> were fully characterized by NMR spectroscopy and X-ray crystallography

Influence of the Coordination Environment of Zinc(II) Complexes of Designed Mannich Ligands on Phosphatase Activity: A Combined Experimental and Theoretical Study

A mononucleating (HL¹) and a dinucleating (HL²) “end-off” compartmental ligand have been designed and synthesized by controlled Mannich reaction using <i>p</i>-cresol and bis­(2-methoxyethyl)­amine, and their formation has been rationalized. Six complexes have been prepared on treating HL¹ and HL² with Zn^IIX₂ (X = Cl^–, Br^–, I^–) with the aim to investigate their hydrolytic activity on phosphoester bond cleavage. Interestingly, the mononucleating ligand was observed to yield dinuclear complexes, [Zn₂(L¹)₂X₂] (<b>1</b>–<b>3</b>), while the potential dinucleating ligand generated mononuclear complexes, [Zn­(HL²)­X₂] (<b>4</b>–<b>6</b>). Four (<b>1</b>–<b>4</b>), out of six complexes studied, were characterized by single-crystal X-ray diffraction (XRD): the Zn ion exhibits trigonal bipyramidal and tetrahedral coordination spheres in the di- and mononuclear complex, respectively. The hydrolytic kinetics, followed spectrophotometrically with 4-nitrophenylphosphate (4-NPP) in buffered dimethylformamide (DMF) (97.5% DMF, v/v) because of solubility reasons, under excess substrate conditions (substrate:complex = 20:1), indicated that the complexes enormously accelerate the rate of phosphomonoester hydrolysis with first order rate constants (<i>k</i>_cat) in the range 2–10 s^–1 at 25 °C. In each case kinetic data analyses have been run by Michaelis–Menten treatment. The efficacy in the order of conversion of substrate to product (<i>p</i>-nitrophenolate ion) follows the trend <b>1</b> > <b>2</b> > <b>3</b> > <b>4</b> > <b>5</b> > <b>6</b>, and the ratio of <i>k</i>_cat of an analogous dinuclear to mononuclear complex is ≃2. An electrospray ionization-mass spectrometry (ESI-MS) study has revealed the dissociation of the centrosymmetric dinuclear complex to two mononuclear species instead of a syn-cooperative catalysis. Density functional theory (DFT) calculations have been performed to rationalize our proposed mechanistic pathway for phosphatase activity. The comparative analysis concludes the following facts under experimental conditions: (1) the halide bound to the active site affects the overall rate in the order: Cl^– > Br^– > I^– regardless of nuclearity; (2) dinuclear complexes prevail over the mononuclear ones