Two-Step Mechanochemical Synthesis of Carbene Complexes of Palladium(II) and Platinum(II)

A mechanochemical strategy for the synthesis of <i>N</i>-heterocyclic carbene complexes is described, in which 1,3-dibenzylimidazole complexes of palladium and platinum are produced in a two-step process by grinding together the reactants with a mortar and pestle. Crystallographic characterization reveals that unlike the solution syntheses, which produce a mixture of products, the solid-state reactions occur under topochemical conditions affording isomerically and polymorphically pure products

Insight into the Hydrogen Migration Processes Involved in the Formation of Metal–Borane Complexes: Importance of the Third Arm of the Scorpionate Ligand

The reactions of [Ir­(κ³<i>N</i>,<i>N</i>,<i>H</i>-<b>Tai</b>)­(COD)] and [Ir­(κ³<i>N</i>,<i>N</i>,<i>H</i>-^<b>Ph</b><b>Bai</b>)­(COD)] (where <b>Tai</b> = HB­(azaindolyl)₃ and ^<b>Ph</b><b>Bai</b> = Ph­(H)­B­(azaindolyl)₂) with carbon monoxide result in the formation of Z-type iridium–borane complexes supported by 7-azaindole units. Analysis of the reaction mixtures involving the former complex revealed the formation of a single species in solution, [Ir­(η¹-C₈H₁₃)­{κ³<i>N</i>,<i>N</i>,<i>B</i>-B­(azaindolyl)₃}­(CO)₂], as confirmed by NMR spectroscopy. In the case of the ^<b>Ph</b><b>Bai</b> complex, a mixture of species was observed. A postulated mechanism for the formation of the new complexes has been provided, supported by computational studies. Computational studies have also focused on the reaction step involving the migration of hydrogen from boron (in the borohydride group) to the iridium center. These investigations have demonstrated a small energy barrier for the hydrogen migration step (Δ<i>G</i>₂₉₈ = 10.3 kcal mol^–1). Additionally, deuterium labeling of the borohydride units in <b>Tai</b> and ^<b>Ph</b><b>Bai</b> confirmed the final position of the former borohydride hydrogen atom in the resulting complexes. The importance of the “third azaindolyl” unit within these transformations and the difference in reactivity between the two ligands are discussed. The selective coordination properties of this family of metallaboratrane complexes have also been investigated and are discussed herein

Insight into the Hydrogen Migration Processes Involved in the Formation of Metal–Borane Complexes: Importance of the Third Arm of the Scorpionate Ligand

The reactions of [Ir­(κ³<i>N</i>,<i>N</i>,<i>H</i>-<b>Tai</b>)­(COD)] and [Ir­(κ³<i>N</i>,<i>N</i>,<i>H</i>-^<b>Ph</b><b>Bai</b>)­(COD)] (where <b>Tai</b> = HB­(azaindolyl)₃ and ^<b>Ph</b><b>Bai</b> = Ph­(H)­B­(azaindolyl)₂) with carbon monoxide result in the formation of Z-type iridium–borane complexes supported by 7-azaindole units. Analysis of the reaction mixtures involving the former complex revealed the formation of a single species in solution, [Ir­(η¹-C₈H₁₃)­{κ³<i>N</i>,<i>N</i>,<i>B</i>-B­(azaindolyl)₃}­(CO)₂], as confirmed by NMR spectroscopy. In the case of the ^<b>Ph</b><b>Bai</b> complex, a mixture of species was observed. A postulated mechanism for the formation of the new complexes has been provided, supported by computational studies. Computational studies have also focused on the reaction step involving the migration of hydrogen from boron (in the borohydride group) to the iridium center. These investigations have demonstrated a small energy barrier for the hydrogen migration step (Δ<i>G</i>₂₉₈ = 10.3 kcal mol^–1). Additionally, deuterium labeling of the borohydride units in <b>Tai</b> and ^<b>Ph</b><b>Bai</b> confirmed the final position of the former borohydride hydrogen atom in the resulting complexes. The importance of the “third azaindolyl” unit within these transformations and the difference in reactivity between the two ligands are discussed. The selective coordination properties of this family of metallaboratrane complexes have also been investigated and are discussed herein

Regioselective B-Cyclometalation of a Bulky <i>o-</i>Carboranyl Phosphine and the Unexpected Formation of a Dirhodium(II) Complex

The bulky carboranyl monophosphine <i>closo-</i>1,2-B₁₀H₁₀C­(H)­C­(P^tBu₂) (<b>L</b>) has been prepared in a one-pot procedure from <i>o</i>-carborane. The reaction of [PdCl₂(NCPh)₂] with <b>L</b> rapidly gave the binuclear B-cyclopalladate [Pd₂(μ-Cl)₂(κ²-<b>L</b>′)₂] (<b>L</b>′ = <b>L</b> deprotonated at B3) as a mixture of two diastereoisomers, assigned structures <b>1a</b> and <b>1a</b>′. The Cl bridges of <b>1a</b>/<b>1a</b>′ are cleaved by the addition of PEt₃ to give the mononuclear [PdCl­(κ²-<b>L</b>′)­(PEt₃)] (<b>2</b>) as a single isomer, with the P atoms mutually trans. The metalation occurs at boron positions 3 and 6 in the carborane cluster, and DFT calculations show that the 3,6-borometalate is lower in energy than the isomeric 4,5-borometalate and 2-carbometalate. Treatment of [Rh₂Cl₂(CO)₄] with <b>L</b> led to the slow precipitation of the dirhodium­(II) species [Rh₂(μ-Cl)₂(CO)₂(κ²-<b>L</b>′)₂] (<b>3</b>). The crystal structures of ligand <b>L</b> and complexes <b>1a</b>, <b>2</b>, and <b>3</b> have been determined

Unexpectedly High Barriers to M–P Rotation in Tertiary Phobane Complexes: PhobPR Behavior That Is Commensurate with ^tBu₂PR

The four isomers of 9-butylphosphabicyclo[3.3.1]­nonane, <i>s-</i>PhobPBu, where Bu = <i>n</i>-butyl, <i>sec</i>-butyl, isobutyl, <i>tert</i>-butyl, have been prepared. Seven isomers of 9-butylphosphabicyclo[4.2.1]­nonane (<i>a</i>₅<i>-</i>PhobPBu, where Bu = <i>n</i>-butyl, <i>sec</i>-butyl, isobutyl, <i>tert</i>-butyl; <i>a</i>₇<i>-</i>PhobPBu, where Bu = <i>n-</i>butyl, isobutyl, <i>tert</i>-butyl) have been identified in solution; isomerically pure <i>a</i>₅<i>-</i>PhobPBu and <i>a</i>₇<i>-</i>PhobPBu, where Bu = <i>n</i>-butyl, isobutyl, have been isolated. The σ-donor properties of the PhobPBu ligands have been compared using the <i>J</i>_PSe values for the PhobP­(Se)­Bu derivatives. The following complexes have been prepared: <i>trans-</i>[PtCl₂(<i>s-</i>PhobPR)₂] (R = ⁿBu (<b>1a</b>), ⁱBu (<b>1b</b>), ^sBu (<b>1c</b>), ^tBu (<b>1d</b>)); <i>trans-</i>[PtCl₂(<i>a</i>₅<i>-</i>PhobPR)₂] (R = ⁿBu (<b>2a</b>), ⁱBu (<b>2b</b>)); <i>trans-</i>[PtCl₂(<i>a</i>₇<i>-</i>PhobPR)₂] (R = ⁿBu (<b>3a</b>), ⁱBu (<b>3b</b>)); <i>trans-</i>[PdCl₂(<i>s-</i>PhobPR)₂] (R = ⁿBu (<b>4a</b>), ⁱBu (<b>4b</b>)); <i>trans-</i>[PdCl₂(<i>a</i>₅<i>-</i>PhobPR)₂] (R = ⁿBu (<b>5a</b>), ⁱBu (<b>5b</b>)); <i>trans-</i>[PdCl₂(<i>a</i>₇<i>-</i>PhobPR)₂] (R = ⁿBu (<b>6a</b>), ⁱBu (<b>6b</b>)). The crystal structures of <b>1a</b>–<b>4a</b> and <b>1b</b>–<b>6b</b> have been determined, and of the ten structures, eight show an anti conformation with respect to the position of the ligand R groups and two show a syn conformation. Solution variable-temperature ³¹P NMR studies reveal that all of the Pt and Pd complexes are fluxional on the NMR time scale. In each case, two species are present (assigned to be the syn and anti conformers) which interconvert with kinetic barriers in the range 9 to >19 kcal mol^–1. The observed trend is that, the greater the bulk, the higher the barrier. The magnitudes of the barriers to M–P bond rotation for the PhobPR complexes are of the same order as those previously reported for ^tBu₂PR complexes. Rotational profiles have been calculated for the model anionic complexes [PhobPR-PdCl₃]⁻ using DFT, and these faithfully reproduce the trends seen in the NMR studies of <i>trans-</i>[MCl₂(PhobPR)₂]. Rotational profiles have also been calculated for [^tBu₂PR-PdCl₃]⁻, and these show that the greater the bulk of the R group, the lower the rotational barrier: i.e., the opposite of the trend for [PhobPR-PdCl₃]⁻. Calculated structures for the species at the maxima and minima in the M–P rotation energy curves indicate the origin of the restricted rotation. In the case of the PhobPR complexes, it is the rigidity of the bicycle that enforces unfavorable H···Cl clashes involving the Pd–Cl groups with H atoms on the α- or β-carbon in the R substituent and H atoms in 1,3-axial sites within the phosphabicycle

Expansion of the Ligand Knowledge Base for Chelating P,P-Donor Ligands (LKB-PP)

We have expanded the ligand knowledge base for bidentate P,P- and P,N-donor ligands (LKB-PP, Organometallics 2008, 27, 1372–1383) by 208 ligands and introduced an additional steric descriptor (nHe₈). This expanded knowledge base now captures information on 334 bidentate ligands and has been processed with principal component analysis (PCA) of the descriptors to produce a detailed map of bidentate ligand space, which better captures ligand variation and has been used for the analysis of ligand properties

Tunable Porous Organic Crystals: Structural Scope and Adsorption Properties of Nanoporous Steroidal Ureas

Previous work has shown that certain steroidal bis-(<i>N</i>-phenyl)­ureas, derived from cholic acid, form crystals in the <i>P</i>6₁ space group with unusually wide unidimensional pores. A key feature of the nanoporous steroidal urea (NPSU) structure is that groups at either end of the steroid are directed into the channels and may in principle be altered without disturbing the crystal packing. Herein we report an expanded study of this system, which increases the structural variety of NPSUs and also examines their inclusion properties. Nineteen new NPSU crystal structures are described, to add to the six which were previously reported. The materials show wide variations in channel size, shape, and chemical nature. Minimum pore diameters vary from ∼0 up to 13.1 Å, while some of the interior surfaces are markedly corrugated. Several variants possess functional groups positioned in the channels with potential to interact with guest molecules. Inclusion studies were performed using a relatively accessible tris-(<i>N</i>-phenyl)­urea. Solvent removal was possible without crystal degradation, and gas adsorption could be demonstrated. Organic molecules ranging from simple aromatics (e.g., aniline and chlorobenzene) to the much larger squalene (<i>M</i>_w = 411) could be adsorbed from the liquid state, while several dyes were taken up from solutions in ether. Some dyes gave dichroic complexes, implying alignment of the chromophores in the NPSU channels. Notably, these complexes were formed by direct adsorption rather than cocrystallization, emphasizing the unusually robust nature of these organic molecular hosts