Dimeric Rh Complexes Supported by a Bridging Phosphido/Bis(Phosphine) PPP Ligand.

Rh complexes of a tridentate PPP ligand bearing 1,2-pyrrolediyl linkers have been prepared, including examples with the central P donor being either a phosphine or a phosphide. Three bimetallic Rh complexes containing the diamandoid Rh2P2 core (P = phosphido) have been structurally and spectroscopically characterized. The Rh-Rh interaction in these three dimers was examined by way of structural comparisons and DFT investigations.

Rapid Polyolefin Hydrogenolysis by a Single-Site Organo-Tantalum Catalyst on a Super-Acidic Support: Structure and Mechanism.

The novel electrophilic organo-tantalum catalyst AlS/TaNpx (1) (Np=neopentyl) is prepared by chemisorption of the alkylidene Np3 Ta=CHt Bu onto highly Brønsted acidic sulfated alumina (AlS). The proposed catalyst structure is supported by EXAFS, XANES, ICP, DRIFTS, elemental analysis, and SSNMR measurements and is in good agreement with DFT analysis. Catalyst 1 is highly effective for the hydrogenolysis of diverse linear and branched hydrocarbons, ranging from C2 to polyolefins. To the best of our knowledge, 1 exhibits one of the highest polyolefin hydrogenolysis activities (9,800 (CH2 units) ⋅ mol(Ta)-1 ⋅ h-1 at 200 °C/17 atm H2 ) reported to date in the peer-reviewed literature. Unlike the AlS/ZrNp2 analog, the Ta catalyst is more thermally stable and offers multiple potential C-C bond activation pathways. For hydrogenolysis, AlS/TaNpx is effective for a wide variety of pre- and post-consumer polyolefin plastics and is not significantly deactivated by standard polyolefin additives at typical industrial concentrations.

Migration of Hydride, Methyl, and Chloride Ligands between Al and M in (PAlP)M Pincer Complexes (M = Rh or Ir).

Protolysis of AlMe3 or AlBui3 with 2-diisopropylphosphinopyrrole (1) yields molecules containing two flanking phosphines and a central Al-Me (2-Me), Al-iBu (2-iBu), or Al-H (2-H) unit. The reactions of 2-Me with [L2MCl]2 (L = cyclooctene or 1/2 1,5-cyclooctadiene and M = Rh or Ir) in the presence of pyridine produces PAlClP pincer complexes (3-Rh and 3-Ir) with Al-Cl and M-Me bonds. The analogous reaction of a mixture of 2-iBu and 2-H with [L2MCl]2 and pyridine resulted in the formation of analogous Rh-H (4-Rh) and Ir-H (4-Ir) complexes. Treatment of 3-Rh with NaBEt3H produced compound 5-Rh with an Al-Me and a Rh-H bond; the analogous reaction of 3-Ir did not result in a clean product. 4-Ir accepted an equivalent of H2 to produce 6-Ir with two terminal Ir-H bonds and one bridging Al-H-Ir moiety, whereas 4-Rh did not react with H2. The density functional theoretical treatment is in accord with this finding, highlights the likely mechanism for the H2 addition, and supports the bonding picture in 6-Ir arising from NMR and X-ray diffraction (XRD) observations. Spectroscopic data and XRD studies are consistent with distorted square-pyramidal structures (about Rh or Ir) for compounds 3-5, with an alane occupying the apical position. Complexes 3 and 4 possess some of the shortest known Rh-Al or Ir-Al distances.

Formation of an Ag→Al dative bond is avoided in reactions of an alane/tris(phosphine) ligand with monovalent silver.

An alane/tris(phospine) ligand reacts with AgOTf by coordination of three phosphines to the Ag center and transfer of triflate to the tris(pyrrolyl) Al site. Reaction with Ag[HCB11Cl11] results in the coordination of two phosphines to Ag and one to Al, with no significant Ag-Al bonding in either structure.

Unexpected B/Al Transelementation within a Rh Pincer Complex.

We report the synthesis of PAlP and PBP pincer complexes of Rh with a central bis(N-pyrrolyl)aluminyl or -boryl unit. Complex (PAlpyP)Rh(CO)2 possesses an aluminyl site stabilized by coordination of pyridine, resulting in a four-coordinate Al. Attempts to access the three-coordinate aluminyl by abstraction of pyridine with BF3·Et2O unexpectedly led to a B/Al metathesis with the preservation of the pincer structure in the product (PBP)Rh(CO)2. Abstraction of pyridine was carried out using B(C6F5)3, but the desired (PAlP)Rh(CO)2 underwent dimerization via isocarbonyl bridging.

Ni complexes of an alane/tris(phosphine) ligand built around a strongly Lewis acidic tris(N-pyrrolyl)aluminum.

Syntheses of a new tripodal alane/tris(phosphine) ligand (AlP3) based on 2-(diisopropylphosphino)pyrrole, and AlP3-supported Ni complexes are reported. The central tris(pyrrolyl)aluminum moiety acts as a stronger Lewis acid towards Ni than other related group 13 element-centered tripodal ligands, as demonstrated by the binding of H2 to Ni and the ease of reduction.

Redox Communication between Two Diarylamido/Bis(phosphine) (PNP)M Moieties Bridged by Ynediyl Linkers (M = Ni, Pd, Pt).

A series of binuclear homo- and heterobimetallic complexes of the general type (PNP)M-[linker]-M(PNP) have been prepared (M = Ni, Pd, Pt; PNP = a diarylamido/bis(phosphine) pincer ligand; -[linker]- = -C≡C-, -C≡CC≡C-, -C≡CC6H4C≡C-). Each (PNP)M site can be oxidized by one electron, and this work reports the investigation of the mixed-valence behavior in terms of the communication between the two redox sites and the degree of the delocalization in the monooxidized cation. The compounds were evaluated using cyclic voltammetry, UV-vis-NIR and EPR spectroscopy, X-ray crystallography, and DFT calculations. The complex with the longest examined linker, (PNP)Ni-C≡CC6H4C≡C-Ni(PNP) (9Ni), exhibited no discernible communication between the redox sites. The homobimetallic complexes (PNP)M-C≡CC≡C-M(PNP) (6M) displayed a lower degree of communication in comparison to the -C≡C- linker analogues (PNP)M-C≡C-M(PNP) (3M). Within each of these two subsets, the relative degree of communication and delocalization was determined to be Pd < Ni ≤ Pt. On the Robin-Day scale, compounds 6M can be assigned class I for M = Pd and class II for M = Ni, Pt. Complex 3Pd also falls into class II, while 3Ni and 3Pt may be viewed as borderline class II/III cases. It is likely that the communication in the Ni systems has the advantage of the smaller size of Ni, resulting in a greater physical proximity of the redox sites, while the 5d metal Pt possesses the greatest ability for orbital interaction with the -C≡C- linker.

Two- and Three-Dimensional Heterometallic Ln[Ru2-α-Ammonium Diphosphonate] Nets: Structures, Porosity, Magnetism, and Proton Conductivity.

By virtue of its magnetic moment and variable valencies, the D4h paddlewheel ruthenium dimer is a desirable molecular building block for the construction of functional networks. If in addition to the Ru open axial site the organic ligand is designed to allow transversal connections, a wider range of structural possibilities is expected. The organic ligand can also be modified to introduce other functionalities. In the present study we employed a diphosphonate containing a protonated amine, 1-ammoniummethylenediphosphonate [NH3CH(PO3)23-; (Hamdp)], as the ligand to construct paddlewheel Ru2(Hamdp)2 building block. Three networks of different structural dimensionalities were obtained. (H3O)2[RuII2(Hamdp)2] (1) forms one-dimensional chain of S = 1 RuII2 bridged at axial positions through Ru-O bonds. From 1 as a starting material, its reaction with lanthanide ions results in the bimetallic Dy(H2O)3[Ru2(Hamdp)2][Ru2(Hamdp)2(H2O)2][Ru2(Hamdp)(amdp)]0.5·12H2O (2), which has a pillared-bilayer structure and Yb[Ru2(Hamdp)2]2[Ru2(Hamdp)2(H2O)2]·15H2O (3), which is a three-dimensional open framework, both contain mixed-valent RuII/III2 units and show new connection topologies of the Ru2 dimers. After activation 2 does not adsorb N2 and CO2 but takes up 12 H2O. In contrast, 3 take up all three gases. The optimum proton conductivities were moderate reaching 1.44 × 10-6 for 2 and 0.93 × 10-5 S cm-1 for 3 at 95% relative humidity and 55 °C.