Intramolecular C–C Bond Coupling of Nitriles to a Diimine Ligand in Group 7 Metal Tricarbonyl Complexes

Dissolution of M­(CO)₃(Br)­(L^Ar) [L^Ar = (2,6-Cl₂-C₆H₃-NCMe)₂CH₂] in either acetonitrile [M = Mn, Re] or benzonitrile (M = Re) results in C–C coupling of the nitrile to the diimine ligand. When reacted with acetonitrile, the intermediate adduct [M­(CO)₃­(NCCH₃)­(L^Ar)]Br forms and undergoes an intramolecular C–C coupling reaction between the nitrile carbon and the methylene carbon of the β-diimine ligand

Pendant Alkyl and Aryl Groups on Tin Control Complex Geometry and Reactivity with H₂/D₂ in Pt(SnR₃)₂(CNBu^t)₂ (R = Bu^t, Prⁱ, Ph, Mesityl)

The complex Pt­(SnBu^t₃)₂­(CNBu^t)₂­(H)₂, <b>1</b>, was obtained from the reaction of Pt­(COD)₂ and Bu^t₃SnH, followed by addition of CNBu^t. The two hydride ligands in <b>1</b> can be eliminated, both in solution and in the solid state, to yield Pt­(SnBu^t₃)₂­(CNBu^t)₂, <b>2</b>. Addition of hydrogen to <b>2</b> at room temperature in solution and in the solid state regenerates <b>1</b>. Complex <b>2</b> catalyzes H₂−D₂ exchange in solution to give HD. The proposed mechanism of exchange involves reductive elimination of Bu^t₃SnH from <b>1</b> to afford vacant sites on the Pt center, thus facilitating the exchange process. This is supported by isolation and characterization of Pt­(SnMes₃)­(SnBu^t₃)­(CNBu^t)₂, <b>3</b>, when the addition of H₂ to <b>2</b> was carried out in the presence of free ligand Mes₃SnH (Mes = 2,4,6-Me₃C₆H₂). Complex Pt­(SnMes₃)₂­(CNBu^t)₂, <b>5</b>, can be prepared from the reaction of Pt­(COD)₂ with Mes₃SnH and CNBu^t. The exchange reaction of <b>2</b> with Ph₃SnH gave Pt­(SnPh₃)₃(CNBu^t)₂­(H), <b>6</b>, wherein both SnBu^t₃ ligands are replaced by SnPh₃. Complex <b>6</b> decomposes in air to form square planar Pt­(SnPh₃)₂­(CNBu^t)₂, <b>7</b>. The complex Pt­(SnPrⁱ₃)₂­(CNBu^t)₂, <b>8</b>, was also prepared. Out of the four analogous complexes Pt­(SnR₃)₂­(CNBu^t)₂ (R = Bu^t, Mes, Ph, or Prⁱ), only the Bu^t analogue does both H₂ activation and H₂−D₂ exchange. This is due to steric effects imparted by the bulky Bu^t groups that distort the geometry of the complex considerably from planarity. The reaction of Pt­(COD)₂ with Bu^t₃SnH and CO gas afforded <i>trans</i>-Pt­(SnBu^t₃)₂­(CO)₂, <b>9</b>. Compound <b>9</b> can be converted to <b>2</b> by replacement of the CO ligands with CNBu^t via the intermediate Pt­(SnBu^t₃)₂­(CNBu^t)₂­(CO), <b>10</b>

A Nickel-Based, Tandem Catalytic Approach to Isoindolinones from Imines, Aryl Iodides, and CO

We describe herein a modular nickel-catalyzed synthesis of isoindolinones from imines, aryl iodides, and CO. This reaction is catalyzed by Ni­(1,5-cyclooctadiene)₂ in concert with chloride salts and postulated to proceed via a tandem nickel-catalyzed carbonylation to form <i>N</i>-acyl iminium chloride salts, followed by a spontaneous nickel-catalyzed cyclization. A range of aryl iodides and imines have been found to be viable substrates in this reaction, providing a modular route to generate substituted isoindolinones with high atom economy

Ancillary Ligand Effects upon the Photochemistry of Mn(bpy)(CO)₃X Complexes (X = Br^–, PhCC^–)

The photochemistry of two Mn­(bpy)­(CO)₃X complexes (X = PhCC^–, Br^–) has been studied in the coordinating solvents THF (terahydrofuran) and MeCN (acetonitrile) employing time-resolved infrared spectroscopy. The two complexes are found to exhibit strikingly different photoreactivities and solvent dependencies. In MeCN, photolysis of <b>1</b>-(CO)­(Br) [<b>1</b> = Mn­(bpy)­(CO)₂] affords the ionic complex [<b>1</b>-(MeCN)₂]­Br as a final product. In contrast, photolysis of <b>1</b>-(CO)­(CCPh) in MeCN results in facial to meridional isomerization of the parent complex. When THF is used as solvent, photolysis results in facial to meridional isomerization in both complexes, though the isomerization rate is larger for X = Br^–. Pronounced differences are also observed in the photosubstitution chemistry of the two complexes where both the rate of MeCN exchange from <b>1</b>-(MeCN)­(X) by THFA (tetrahydrofurfurylamine) and the nature of the intermediates generated in the reaction are dependent upon X. DFT calculations are used to support analysis of some of the experiments

Oxidative Addition of Haloalkanes to Metal Centers: A Mechanistic Investigation

Photolysis of CpRe­(CO)₃ in the presence of dichloromethane results in the initial formation of the CpRe­(CO)₂(ClCH₂Cl) complex followed by insertion of the metal into the C–Cl bond. The activation enthalpy is determined to be 20.4 kcal/mol, and with the assistance of DFT calculations, a radical mechanism is proposed for the oxidative addition reaction. Photolysis of Ni­(CO)₂(PPh₃)₂ with dihalomethanes also results in oxidative addition, but the intermediacy of a halogen-bound adduct has not been established

Oxidative Addition of Haloalkanes to Metal Centers: A Mechanistic Investigation

Photolysis of CpRe­(CO)₃ in the presence of dichloromethane results in the initial formation of the CpRe­(CO)₂(ClCH₂Cl) complex followed by insertion of the metal into the C–Cl bond. The activation enthalpy is determined to be 20.4 kcal/mol, and with the assistance of DFT calculations, a radical mechanism is proposed for the oxidative addition reaction. Photolysis of Ni­(CO)₂(PPh₃)₂ with dihalomethanes also results in oxidative addition, but the intermediacy of a halogen-bound adduct has not been established

Synthesis of [Pt(SnBu^t₃)(IBu^t)(μ-H)]₂, a Coordinatively Unsaturated Dinuclear Compound which Fragments upon Addition of Small Molecules to Form Mononuclear Pt–Sn Complexes

The reaction of Pt­(COD)₂ with one equivalent of tri-<i>tert</i>-butylstannane, Bu^t₃SnH, at room temperature yields Pt­(SnBu^t₃)­(COD)­(H)­(<b>3</b>) in quantitative yield. In the presence of excess Bu^t₃SnH, the reaction goes further, yielding the dinuclear bridging stannylene complex [Pt­(SnBu^t₃)­(μ-SnBu^t₂)­(H)₂]₂ (<b>4</b>). The dinuclear complex <b>4</b> reacts rapidly and reversibly with CO to furnish [Pt­(SnBu^t₃)­(μ-SnBu^t₂)­(CO)­(H)₂]₂ (<b>5</b>). Complex <b>3</b> reacts with <i>N</i>,<i>N</i>′-di-<i>tert</i>-butylimidazol-2-ylidene, IBu^t, at room temperature to give the dinuclear bridging hydride complex [Pt­(SnBu^t₃)­(IBu^t)­(μ-H)]₂ (<b>6</b>). Complex <b>6</b> reacts with CO, C₂H₄, and H₂ to give the corresponding mononuclear Pt complexes Pt­(SnBu^t₃)­(IBu^t)­(CO)­(H)­(<b>7</b>), Pt­(SnBu^t₃)­(IBu^t)­(C₂H₄)­(H)­(<b>8</b>), and Pt­(SnBu^t₃)­(IBu^t)­(H)₃ (<b>9</b>), respectively. The reaction of IBu^t with the complex Pt­(SnBu^t₃)₂(CO)₂ (<b>10</b>) yielded an abnormal Pt-carbene complex Pt­(SnBu^t₃)₂(<i>a</i>IBu^t)­(CO) (<b>11</b>). DFT computational studies of the dimeric complexes [Pt­(SnR₃)­(NHC)­(μ-H)]₂, the potentially more reactive monomeric complexes Pt­(SnR₃)­(NHC)­(H) and the trihydride species Pt­(SnBu^t₃)­(IBu^t)­(H)₃ have been performed, for NHC = IMe and R = Me and for NHC = IBu^t and R = Bu^t. The structures of complexes <b>3</b>–<b>8</b> and <b>11</b> have been determined by X-ray crystallography and are reported

Thermal and Photochemical Reactivity of Manganese Tricarbonyl and Tetracarbonyl Complexes with a Bulky Diazabutadiene Ligand

The manganese tricarbonyl complex <i>fac</i>-Mn­(Br)­(CO)₃(ⁱPr₂Ph-DAB) (<b>1</b>) [ⁱPr₂Ph-DAB = (<i>N,N</i>′-bis­(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene)] was synthesized from the reaction of Mn­(CO)₅Br with the sterically encumbered DAB ligand. Compound <b>1</b> exhibits rapid CO release under low power visible light irradiation (560 nm) suggesting its possible use as a photoCORM. The reaction of compound <b>1</b> with TlPF₆ in the dark afforded the manganese­(I) tetracarbonyl complex, [Mn­(CO)₄(ⁱPr₂Ph-DAB)]­[PF₆] (<b>2</b>). While <b>2</b> is comparatively more stable than <b>1</b> in light, it demonstrates high thermal reactivity such that dissolution in CH₃CN or THF at room temperature results in rapid CO loss and formation of the respective solvate complexes. This unusual reactivity is due to the large steric profile of the DAB ligand which results in a weak Mn–CO binding interaction

Acrostichum indet.

The displacement of a CO ligand from an unusually labile rhenium carbonyl complex containing a bidentate carboxyaldehyde pyrrolyl ligand by PPh₃ and pyridine has been investigated. The reaction is found to proceed by an associative, preequilibrium mechanism. Theoretical calculations support the experimental data and provide a complete energetic profile for the reaction. While the Re–CO bond is found to be intrinsically weak in these complexes, it is postulated that the unusual lability of this species is due to the presence of a weak aldehyde Re–O link that can easily dissociate to open a coordination site on the metal center and accommodate an incoming ligand prior to CO loss. The resulting intermediate complex has been identified by IR spectroscopy. The presence of the hemilabile pyrrolyl ligand provides a lower-energy reaction channel for the release of CO and may be of relevance in the design of CO-releasing molecules