Single-Crystal to Single-Crystal Addition of H2 to [Ir(iPr-PONOP)(propene)][BArF 4] and Comparison Between Solid-State and Solution Reactivity.

The reactivity of the Ir(I) PONOP pincer complex [Ir(iPr-PONOP)(η2-propene)][BArF 4], 6, [iPr-PONOP = 2,6-(iPr2PO)2C6H3N, ArF = 3,5-(CF3)2C6H3] was studied in solution and the solid state, both experimentally, using molecular density functional theory (DFT) and periodic-DFT computational methods, as well as in situ single-crystal to single-crystal (SC-SC) techniques. Complex 6 is synthesized in solution from sequential addition of H2 and propene, and then the application of vacuum, to [Ir(iPr-PONOP)(η2-COD)][BArF 4], 1, a reaction manifold that proceeds via the Ir(III) dihydrogen/dihydride complex [Ir(iPr-PONOP)(H2)H2][BArF 4], 2, and the Ir(III) dihydride propene complex [Ir(iPr-PONOP)(η2-propene)H2][BArF 4], 7, respectively. In solution (CD2Cl2) 6 undergoes rapid reaction with H2 to form dihydride 7 and then a slow (3 d) onward reaction to give dihydrogen/dihydride 2 and propane. DFT calculations on the molecular cation in solution support this slow, but productive, reaction, with a calculated barrier to rate-limiting propene migratory insertion of 24.8 kcal/mol. In the solid state single-crystals of 6 also form complex 7 on addition of H2 in an SC-SC reaction, but unlike in solution the onward reaction (i.e., insertion) does not occur, as confirmed by labeling studies using D2. The solid-state structure of 7 reveals that, on addition of H2 to 6, the PONOP ligand moves by 90° within a cavity of [BArF 4]- anions rather than the alkene moving. Periodic DFT calculations support the higher barrier to insertion in the solid state (ΔG ‡ = 26.0 kcal/mol), demonstrating that the single-crystal environment gates onward reactivity compared to solution. H2 addition to 6 to form 7 is reversible in both solution and the solid state, but in the latter crystallinity is lost. A rare example of a sigma amine-borane pincer complex, [Ir(iPr-PONOP)H2(η1-H3B·NMe3)][BArF 4], 5, is also reported as part of these studies.

Inverse Isotope Effects in Single-Crystal to Single-Crystal Reactivity and the Isolation of a Rhodium Cyclooctane σ-Alkane Complex.

The sequential solid/gas single-crystal to single-crystal reaction of [Rh(Cy2P(CH2)3PCy2)(COD)][BArF 4] (COD = cyclooctadiene) with H2 or D2 was followed in situ by solid-state 31P{1H} NMR spectroscopy (SSNMR) and ex situ by solution quenching and GC-MS. This was quantified using a two-step Johnson-Mehl-Avrami-Kologoromov (JMAK) model that revealed an inverse isotope effect for the second addition of H2, that forms a σ-alkane complex [Rh(Cy2P(CH2)3PCy2)(COA)][BArF 4]. Using D2, a temporal window is determined in which a structural solution for this σ-alkane complex is possible, which reveals an η2,η2-binding mode to the Rh(I) center, as supported by periodic density functional theory (DFT) calculations. Extensive H/D exchange occurs during the addition of D2, as promoted by the solid-state microenvironment.

Selectivity of Rh⋠⋠⋠H-C Binding in a σ-Alkane Complex Controlled by the Secondary Microenvironment in the Solid State.

Single-crystal to single-crystal solid-state molecular organometallic (SMOM) techniques are used for the synthesis and structural characterization of the σ-alkane complex [Rh(tBu2 PCH2 CH2 CH2 PtBu2 )(η2 ,η2 -C7 H12 )][BArF 4 ] (ArF =3,5-(CF3 )2 C6 H3 ), in which the alkane (norbornane) binds through two exo-C-H⋅⋅⋅Rh interactions. In contrast, the bis-cyclohexyl phosphine analogue shows endo-alkane binding. A comparison of the two systems, supported by periodic DFT calculations, NCI plots and Hirshfeld surface analyses, traces this different regioselectivity to subtle changes in the local microenvironment surrounding the alkane ligand. A tertiary periodic structure supporting a secondary microenvironment that controls binding at the metal site has parallels with enzymes. The new σ-alkane complex is also a catalyst for solid/gas 1-butene isomerization, and catalyst resting states are identified for this.

Solid-State Molecular Organometallic Catalysis in Gas/Solid Flow (Flow-SMOM) as Demonstrated by Efficient Room Temperature and Pressure 1-Butene Isomerization.

The use of solid-state molecular organometallic chemistry (SMOM-chem) to promote the efficient double bond isomerization of 1-butene to 2-butenes under flow-reactor conditions is reported. Single crystalline catalysts based upon the σ-alkane complexes [Rh(R2PCH2CH2PR2)(η2η2-NBA)][BArF 4] (R = Cy, tBu; NBA = norbornane; ArF = 3,5-(CF3)2C6H3) are prepared by hydrogenation of a norbornadiene precursor. For the tBu-substituted system this results in the loss of long-range order, which can be re-established by addition of 1-butene to the material to form a mixture of [Rh(tBu2PCH2CH2PtBu2)(cis-2-butene)][BArF 4] and [Rh(tBu2PCH2CH2PtBu2)(1-butene)][BArF 4], in an order/disorder/order phase change. Deployment under flow-reactor conditions results in very different on-stream stabilities. With R = Cy rapid deactivation (3 h) to the butadiene complex occurs, [Rh(Cy2PCH2CH2PCy2)(butadiene)][BArF 4], which can be reactivated by simple addition of H2. While the equivalent butadiene complex does not form with R = tBu at 298 K and on-stream conversion is retained up to 90 h, deactivation is suggested to occur via loss of crystallinity of the SMOM catalyst. Both systems operate under the industrially relevant conditions of an isobutene co-feed. cis:trans selectivites for 2-butene are biased in favor of cis for the tBu system and are more leveled for Cy.

Correction: Cyaphide-alkynyl complexes: metal-ligand conjugation and the influence of remote substituents.

Correction for 'Cyaphide-alkynyl complexes: metal-ligand conjugation and the influence of remote substituents' by Samantha K. Furfari, et al., Dalton Trans., 2019, 48, 8131-8143.

Cyaphide-alkynyl complexes: metal-ligand conjugation and the influence of remote substituents.

A homologous series of novel trans-cyaphide-alkynyl complexes, viz. trans-[Ru(dppe)2(C[triple bond, length as m-dash]P)(C[triple bond, length as m-dash]CC6H4R-p)] (R = Me, H, F, CO2Me, NO2) is prepared and comprehensively characterised, alongside their parent phosphaalkyne-complex cations trans-[Ru(dppe)2(η1-P[triple bond, length as m-dash]CSiMe3)(C[triple bond, length as m-dash]CC6H4R-p)]+. Structural data for trans-[Ru(dppe)2(C[triple bond, length as m-dash]P)(C[triple bond, length as m-dash]CC6H4R-p)] (R = Me, F) and trans-[Ru(dppe)2(η1-P[triple bond, length as m-dash]CSiMe3)(C[triple bond, length as m-dash]CC6H4R-p)]+ (R = F, CO2Me) are described, along with that for the previously reported trans-[Ru(dppe)2(C[triple bond, length as m-dash]P)(C[triple bond, length as m-dash]CCO2Me)]. NMR spectroscopic data indicate significant influence of the remote aromatic substituent over the properties of the cyaphide ligand, in line with the Hammett parameter (σp), suggesting appreciable 'communication' along the through-conjugate chain. Cyclic voltammety shows irreversible oxidative behaviour, at more anodic Epa than in the respective alkynyl-chloride complexes, though apparently moderated by the remote substituent.

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.

Hydride-bromide exchange at an NHC-a new route to brominated alanes and gallanes.

The reaction of [MH(3)(Quinuclidine)] (M = Al or Ga) with an air stable dibrominated N-heterocyclic carbene (NHC) affords the hydride-bromide exchange product [MBr(2)H(NHC)].

Bulky triazenide complexes of alumino- and gallohydrides.

The sterically bulky triazenes DitopN(3)(H)pTol, DitopN(3)(H)Mes, DmpN(3)(H)pTol and DmpN(3)(H)Mes, where Ditop = 2,6-di-p-tolylphenyl, Dmp = 2,6-dimesitylphenyl, pTol = p-MeC(6)H(4) and Mes = 2,4,6-Me(3)C(6)H(2), have been prepared. The reactivity of these triazenide precursors with LiAlH(4) and, in the cases of DmpN(3)(H)pTol and DmpN(3)(H)Mes, LiGaH(4), with diethyl ether as the solvent, has been examined. All reactions were undertaken in a 1:1 ratio giving rise to a variety of aluminium and gallium complexes that either incorporate LiH with a metal to triazenide ratio of 1:1 or generate 'LiH-free' aluminohydrides with aluminium to triazenide ratios of 1:1 or 1:2 dependant on triazenide bulk. Increasing triazenide bulk from DitopN(3)pTol through to DmpN(3)Mes results in a transition from complexes of structure [{Li(OEt(2))(mu-H)(mu-L)AlH (mu-H)}(n)] (L = triazenide ligand; n = 2 DitopN(3)pTol, n = 1 DitopN(3)Mes, DmpN(3)pTol), to bis(triazenide) monohydride complexes [AlH(L)(2)], through to monotriazenide dihydride complexes [AlH(2)(L)]. By contrast, both DmpN(3)(H)Ar (Ar = pTol or Mes) triazenides react with LiGaH(4) to afford the monomeric, lithium hydride containing, complexes [Li(ether)(mu-H)(mu-L)GaH(2)] (L = triazenide, ether = OEt(2) or THF). The molecular structures of [AlH(DitopN(3)Mes)(2)], [AlH(DmpN(3)pTol)(2)], [AlH(2)(DmpN(3)Mes)(THF)] and [Li(THF)(mu-H)(mu-DmpN(3)Mes)GaH(2)] are reported, as well as the structure of the triazene DmpN(3)(H)Mes which exists in the E-syn isomeric form in the solid-state.