An Operationally Unsaturated Iridium-Pincer Complex That C-H Activates Methane and Ethane in the Crystalline Solid-State.

The known complex [Ir(Bu-PONOP)MeH][BAr], [Bu-PONOP κ-2,6-(BuPO)CHN); Ar = 3,5-(CF)(CH); 131, 8603], is a robust precursor for single-crystal to single-crystal (SC-SC) C-H activation of methane and ethane at 80 °C. This contrasts with the reported solution (CDCl) behavior, where decomposes by methane loss. Crystalline is accessed as a single polymorph on a gram scale.

Room Temperature Ethene to Propene (ETP) Tandem Catalysis using Single Crystalline Solid-State Molecular Pre-Catalysts.

A tandem catalytic ensemble of solid-state molecular organometallic (SMOM) crystalline pre-catalysts are deployed under batch or flow conditions for the ethene to propene process (ETP). These catalysts operate at ambient temperature and low pressure, via sequential ethene dimerization, butenes isomerization and cross-metathesis. Under flow conditions the on-stream ethene conversion (55 %), initial propene selectivity (92 %), stability (71 % selectivity after 7 h) and low temperature/pressures are competitive with the best-in-class heterogeneous systems, marking a new, in crystallo, approach to ETP.

Solid/Gas Reactivity of an Ir(I) Methylidene Complex.

stabilization of known, but solution unstable, methylidene complex [Ir(Bu-PONOP)(=CH)][BAr ] allows single-crystal to single-crystal solid/gas reactivity associated with the {Ir=CH} group to be studied. Addition of H results in [Ir(Bu-PONOP)(H)][BAr ]; exposure to CO forms iridium(I) carbonyl [Ir(Bu-PONOP)(CO)][BAr ], and reaction with NH gas results in the formation of methylamine complex [(Bu-PONOP)Ir(NHMe)][BAr ] via an aminocarbene intermediate. Periodic density functional theory and electronic structure analyses confirm the Ir=CH bond character but with a very low barrier to rotation around the Ir=CH bond.

A Gold(I)-Acetylene Complex Synthesised using Single-Crystal Reactivity.

Using single-crystal to single-crystal solid/gas reactivity the gold(I) acetylene complex [Au(L1)(η-HC≡CH)][BAr ] is cleanly synthesized by addition of acetylene gas to single crystals of [Au(L1)(CO)][BAr ] [L1=tris-2-(4,4'-di-tert-butylbiphenyl)phosphine, Ar=3,5-(CF)CH]. This simplest gold-alkyne complex has been characterized by single crystal X-ray diffraction, solution and solid-state NMR spectroscopy and periodic DFT. Bonding of HC≡CH with [Au(L1)] comprises both σ-donation and π-backdonation with additional dispersion interactions within the cavity-shaped phosphine.

T-Shaped Palladium and Platinum {MNO} Nitrosyl Complexes.

The synthesis and characterization of a homologous series of T-shaped {MNO} nitrosyl complexes of the form [M(PR)(NO)] (M = Pd, Pt; R = Bu, Ad) are reported. These diamagnetic nitrosyls are obtained from monovalent or zerovalent precursors by treatment with NO and NO, respectively, and are notable for distinctly bent M-NO angles of ∼123° in the solid state. Adoption of this coordination mode in solution is also supported by the analysis of isotopically enriched samples by N NMR spectroscopy.

Stability and C-H Bond Activation Reactions of Palladium(I) and Platinum(I) Metalloradicals: Carbon-to-Metal H-Atom Transfer and an Organometallic Radical Rebound Mechanism.

One-electron oxidation of palladium(0) and platinum(0) bis(phosphine) complexes enables isolation of a homologous series of linear d metalloradicals of the form [M(PR)] (M = Pd, Pt; R = Bu, Ad), which are stable in 1,2-difluorobenzene (DFB) solution for >1 day at room temperature when partnered with the weakly coordinating [BAr] (Ar = 3,5-(CF)CH) counterion. The metalloradicals exhibit reduced stability in THF, decreasing in the order palladium(I) > platinum(I) and PAd > PBu, especially in the case of [Pt(PBu)], which is converted into a 1:1 mixture of the platinum(II) complexes [Pt(PBuCMeCH)(PBu)] and [Pt(PBu)H] upon dissolution at room temperature. Cyclometalation of [Pt(PBu)] can also be induced by reaction with the 2,4,6-tri-butylphenoxyl radical in DFB, and a common radical rebound mechanism involving carbon-to-metal H-atom transfer and formation of an intermediate platinum(III) hydride complex, [Pt(PBuCMeCH)H(PBu)], has been substantiated by computational analysis.

Synthesis of a rhodium(III) dinitrogen complex using a calix[4]arene-based diphosphine ligand.

The synthesis and characterisation of the rhodium(III) dinitrogen complex [Rh(2,2'-biphenyl)(CxP)(N)] are described, where CxP is a -spanning calix[4]arene-based diphosphine and the dinitrogen ligand is projected into the cavity of the macrocycle.

Oxidative Addition of a Mechanically Entrapped C(sp)-C(sp) Bond to a Rhodium(I) Pincer Complex.

By use of a macrocyclic phosphinite pincer ligand and bulky substrate substituents, we demonstrate how the mechanical bond can be leveraged to promote the oxidative addition of an interlocked 1,3-diyne to a rhodium(I) center. The resulting rhodium(III) bis(alkynyl) product can be trapped out by reaction with carbon monoxide or intercepted through irreversible reaction with dihydrogen, resulting in selective hydrogenolysis of the C-C σ-bond.

Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity.

Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC-based pincer ligands-which feature dodecamethylene, tetradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNC-n)(C H )][BAr ] (n=12, 14, 16; Ar =3,5-(CF ) C H )-have been investigated, using the bulky alkynes HC≡CtBu and HC≡CAr' (Ar'=3,5-tBu C H ) as substrates. These stoichiometric reactions proceed with formation of rhodium(III) alkynyl alkenyl derivatives and produce rhodium(I) complexes of conjugated 1,3-enynes by C-C bond reductive elimination through the annulus of the ancillary ligand.

Isolation and structural characterisation of rhodium(iii) η-fluoroarene complexes: experimental verification of predicted regioselectivity.

The isolation and solid-state characterisation of complexes featuring partially coordinated benzene, fluorobenzene and all three isomers of difluorobenzene are described. Supported by a DFT analysis, this well-defined homologous series demonstrates the preference for η-coordination of fluoroarenes via the HC[double bond, length as m-dash]CH sites adjacent to a fluorine substituent.

Bulky bis(aryl)triazenides: just aspiring amidinates? A structural and spectroscopic study.

The synthesis and molecular structures (by single crystal X-ray diffraction) of s-, p- and d-metal complexes of the sterically demanding N,N'-bis(2,6-diisopropylphenyl)triazenide are reported and the spectroscopic (NMR spectroscopy and infrared spectroscopy) and physical properties of these complexes compared to related formamidinate complexes. Through the use of infrared spectroscopy the σ-donor capacity of this ligand is demonstrated to be reduced relative to the structurally isomorphous formamidinate congener, which supports previously advanced theoretical calcluations and DFT results reported herein. These electronic differences are highlighted by the stark contrast in reaction outcomes at rhodium; where [(DippN)Rh(CO)] (1) is an isolable, stable complex and the formamidinate complex is not.

A shape changing tandem Rh(CNC) catalyst: preparation of bicyclo[4.2.0]octa-1,5,7-trienes from terminal aryl alkynes.

The preparation of a range of tetraaryl-substituted bicyclo[4.2.0]octa-1,5,7-trienes using a one-pot procedure starting from terminal aryl alkynes and catalysed by a rhodium(i) complex is reported.

Synthesis and group 9 complexes of macrocyclic PCP and POCOP pincer ligands.

The synthesis of macrocyclic variants of commonly employed phosphine-based pincer (pro)ligands derived from meta-xylene (PCP-14) and resorcinol (POCOP-14) is described, where the P-donors are trans-substituted with a tetradecamethylene linker. The former was accomplished using a seven-step asymmetric procedure involving (-)-cis-1-amino-2-indanol as a chiral auxiliary and ring-closing olefin metathesis. A related, but non-diastereoselective route was employed for the latter, which consequently necessitated chromatographic separation from the cis-substituted by-product.

Synthesis and rhodium complexes of macrocyclic PNP and PONOP pincer ligands.

The synthesis of macrocyclic variants of commonly employed phosphine-based pincer ligands derived from lutidine (PNP-14) and 2,6-dihydroxypyridine (PONOP-14) is described, where the P-donors are trans-substituted with a tetradecamethylene linker. This was accomplished using an eight-step procedure involving borane protection, ring-closing olefin metathesis, chromatographic separation from the cis-substituted diastereomers, and borane deprotection. The rhodium coordination chemistry of these ligands has been explored, aided by the facile synthesis of 2,2'-biphenyl (biph) adducts [Rh(PNP-14)(biph)][BAr] and [Rh(PONOP-14)(biph)][BAr] (Ar = 3,5-(CF)CH).

Rhodium(I) Pincer Complexes of Nitrous Oxide.

The synthesis of two well-defined rhodium(I) complexes of nitrous oxide (N O) is reported. These normally elusive adducts are stable in the solid state and persist in solution at ambient temperature, enabling comprehensive structural interrogation by N NMR and IR spectroscopy, and single-crystal X-ray diffraction. These methods evidence coordination of N O through the terminal nitrogen atom in a linear fashion and are supplemented by a computational energy decomposition analysis, which provides further insights into the nature of the Rh-N O interaction.

Synthesis and Structural Dynamics of Five-Coordinate Rh(III) and Ir(III) PNP and PONOP Pincer Complexes.

The synthesis and characterization of a homologous series of five-coordinate rhodium(III) and iridium(III) complexes of PNP (2,6-( tBuPCH)CHN) and PONOP (2,6-( tBuPO)CHN) pincer ligands are described: [M(PNP)(biph)][BAr] (M = Rh, 1a; Ir, 1b; biph = 2,2'-biphenyl; Ar = 3,5-(CF)CH) and [M(PONOP)(biph)][BAr] (M = Rh, 2a; Ir, 2b). These complexes are structurally dynamic in solution, exhibiting pseudorotation of the biph ligand on the H NMR time scale (Δ G ca. 60 kJ mol) and, in the case of the flexible PNP complexes, undergoing interconversion between helical and puckered pincer ligand conformations (Δ G ca.

A convenient method for the generation of {Rh(PNP)} and {Rh(PONOP)} fragments: reversible formation of vinylidene derivatives.

The substitution reactions of [Rh(COD)2][BArF4] with PNP and PONOP pincer ligands 2,6-bis(di-tert-butylphosphinomethyl)pyridine and 2,6-bis(di-tert-butylphosphinito)pyridine in the weakly coordinating solvent 1,2-F2C6H4 are shown to be an operationally simple method for the generation of reactive formally 14 VE rhodium(i) adducts in solution. Application of this methodology enables synthesis of known adducts of CO, N2, H2, previously unknown water complexes, and novel vinylidene derivatives [Rh(pincer)(CCHR)][BArF4] (R = tBu, 3,5-tBu2C6H3), through reversible reactions with terminal alkynes.

Rhodium(III) and Iridium(III) Complexes of a NHC-Based Macrocycle: Persistent Weak Agostic Interactions and Reactions with Dihydrogen.

The synthesis and characterization of five-coordinate rhodium(III) and iridium(III) 2,2'-biphenyl complexes [M(CNC-12)(biph)][BAr ] (M = Rh (), Ir ()), featuring the macrocyclic lutidine- and NHC-based pincer ligand CNC-12 are reported. In the solid state these complexes are notable for the adoption of weak ε-agostic interactions that are characterized by ···H- contacts of ca. 3.

Terminal Alkyne Coupling Reactions through a Ring: Mechanistic Insights and Regiochemical Switching.

The mechanism and selectivity of terminal alkyne coupling reactions promoted by rhodium(I) complexes of NHC-based CNC pincer ligands have been investigated. Synthetic and kinetic experiments support E- and gem-enyne formation through a common reaction sequence involving hydrometallation and rate-determining C-C bond reductive elimination. The latter is significantly affected by the ligand topology: Employment of a macrocyclic variant enforced exclusive head-to-head coupling, contrasting the high selectivity for head-to-tail coupling observed for the corresponding acyclic pincer ligand.

Air stable NHCs: a study of stereoelectronics and metallorganic catalytic activity.

The air stable NHC IPrBr is reported. A stereoelectronic study of IPrBr and its similarly stable relative IMesBr demonstrates metal complex specific changes in NHC donicity versus the ubiquitous IPr and IMes. Application to a Suzuki coupling and an iridium transfer hydrogenation gives superior outcomes using IPrBr and IMesBr.

Ionic liquid effects on Mizoroki-Heck reactions: more than just carbene complex formation.

Reaction profiles for a Mizoroki-Heck reaction in either an ionic liquid or a molecular solvent with different palladium sources demonstrate that the rate enhancements observed in ionic liquids cannot be solely attributed to Pd-carbene complex formation.