C−H•••F−C Interactions: A Guide for Designing Fluorous Monodentate Ligands for the Highly Linear-Selective Hydroformylation at Near-Ambient Pressure

Organofluorine compounds often exhibit unique catalytic capabilities with novel structural scaffold, reactivity and mechanisms. Herein, we report a Rh-catalyzed hydroformylation under mild conditions using monodentate phosphite ligands P(OCH2CF3)3 (TTFP) and P(OCH2CF2CH3)3 (TDFP). The ligand were designed with the principle that the inclusion of fluorine-rich group can significantly change the physical and chemical properties of the complex through H•••F hydrogen bonds, the existence of which has been confirmed by crystal-packing studies. These monodentate phosphite ligands self-assemble to form bidentate ligands through C–H•••F–C interactions, and catalysts based on these ligands deliver extremely high regioselectivities in hydroformylation. Aldehydes were formed with up to 92% chemoselectivity, with linear aldehydes formed in high regioselectivity (n:iso=28/1) under a syngas pressure of only 2 atm.

Aerobically Stable and Substitutionally Labile α-Diimine Rhenium Dicarbonyl Complexes

New synthetic routes to aerobically stable and substitutionally labile a-diimine rhenium(I) dicarbonyl complexes are described. The molecules are prepared in high yield from the <i>cis-cis-trans-</i>[Re(CO)₂(<i>^t</i>Bu₂bpy)Br₂]^- anion (<b>2</b>, where<b> </b><i>^t</i>Bu₂bpy is 4,4'-di-<i>tert</i>-butyl-2,2'-bipyridine), which can be isolated from the one electron reduction of the corresponding 17-electron complex (<b>1</b>). Compound <b>2 </b>is stable in the solid state, but in solution it is oxidized by molecular oxygen back to <b>1</b>. Replacement of a single bromide of <b>2</b> by s-donor monodentate ligands (Ls) yields stable neutral 18-electron <i>cis-cis-trans-</i>[Re(CO)₂(<i>^t</i>Bu₂bpy)Br(L)] species. In coordinating solvents like methanol the halide is replaced giving the corresponding solvated cations. [Re(CO)₂(<i>^t</i>Bu₂bpy)Br(L)] species can be further reacted with Ls to prepare stable <i>cis-cis-trans-</i>[Re(CO)₂(<i>^t</i>Bu₂bpy)(L)₂]⁺ complexes in good yield. Ligand substitution of Re(I) complexes proceeds via pentacoordinate intermediates capable of Berry pseudorotation. In addition to the <i>cis-cis-trans-</i>complexes, <i>cis-cis-cis-</i> (all cis) enantiomers are also formed. In particular, <i>cis-cis-trans-</i>[Re(CO)₂(<i>^t</i>Bu₂bpy)(L)₂]⁺ complexes establish an equilibrium with all cis enantiomers in solution. The solid state crystal structure of nearly all molecules presented could be elucidated. The molecules adopt a slightly distorted octahedral geometry. In comparison to similar <i>fac</i>-[Re(CO)₃]⁺complexes, Re(I) diacarbonyl species are characterized by a bend (ca. 7°) of the axial ligands towards the a-diimine unit. [Re(CO)₂(<i>^t</i>Bu₂bpy)Br₂]^- and [Re(CO)₂(<i>^t</i>Bu₂bpy)Br(L)] complexes may be considered as synthons for the preparation of a variety of new stable diamagnetic dicarbonyl rhenium <i>cis-</i>[Re(CO)₂]⁺ complexes, offering a convenient entry in the chemistry of the core.

Aerobically Stable and Substitutionally Labile α-Diimine Rhenium Dicarbonyl Complexes

New synthetic routes to aerobically stable and substitutionally labile a-diimine rhenium(I) dicarbonyl complexes are described. The molecules are prepared in high yield from the <i>cis-cis-trans-</i>[Re(CO)₂(<i>^t</i>Bu₂bpy)Br₂]^- anion (<b>2</b>, where<b> </b><i>^t</i>Bu₂bpy is 4,4'-di-<i>tert</i>-butyl-2,2'-bipyridine), which can be isolated from the one electron reduction of the corresponding 17-electron complex (<b>1</b>). Compound <b>2 </b>is stable in the solid state, but in solution it is oxidized by molecular oxygen back to <b>1</b>. Replacement of a single bromide of <b>2</b> by s-donor monodentate ligands (Ls) yields stable neutral 18-electron <i>cis-cis-trans-</i>[Re(CO)₂(<i>^t</i>Bu₂bpy)Br(L)] species. In coordinating solvents like methanol the halide is replaced giving the corresponding solvated cations. [Re(CO)₂(<i>^t</i>Bu₂bpy)Br(L)] species can be further reacted with Ls to prepare stable <i>cis-cis-trans-</i>[Re(CO)₂(<i>^t</i>Bu₂bpy)(L)₂]⁺ complexes in good yield. Ligand substitution of Re(I) complexes proceeds via pentacoordinate intermediates capable of Berry pseudorotation. In addition to the <i>cis-cis-trans-</i>complexes, <i>cis-cis-cis-</i> (all cis) enantiomers are also formed. In particular, <i>cis-cis-trans-</i>[Re(CO)₂(<i>^t</i>Bu₂bpy)(L)₂]⁺ complexes establish an equilibrium with all cis enantiomers in solution. The solid state crystal structure of nearly all molecules presented could be elucidated. The molecules adopt a slightly distorted octahedral geometry. In comparison to similar <i>fac</i>-[Re(CO)₃]⁺complexes, Re(I) diacarbonyl species are characterized by a bend (ca. 7°) of the axial ligands towards the a-diimine unit. [Re(CO)₂(<i>^t</i>Bu₂bpy)Br₂]^- and [Re(CO)₂(<i>^t</i>Bu₂bpy)Br(L)] complexes may be considered as synthons for the preparation of a variety of new stable diamagnetic dicarbonyl rhenium <i>cis-</i>[Re(CO)₂]⁺ complexes, offering a convenient entry in the chemistry of the core.

Manganese(II) bromo- and iodo-complexes with phosphoramidate and phosphonate ligands: synthesis, characterization and photoluminescence

Tetrahedral Mn(II) bromo- and iodo-complexes with phosphoramidate and phosphonate ligands were synthesized and characterized. Mononuclear complexes with general formula [MnX2L2] were isolated by using the monodentate ligands O=P(OPh)2(NMe2) and O=P(OPh)2Ph....

Polycentric binding in complexes of trimethylamine-N-oxide with dihalogens

Dihalogens readily interact with trimethylamine-N-oxide under ambient conditions. Stable 1 : 1 adducts were obtained in a case of iodine chloride and iodine bromide. Formally monodentate ligands are bound in a polycentric manner.

Hydrogen and Halogen Bond Mediated Coordination Polymers of Chloro-Substituted Pyrazin-2-Amine Copper(I) Bromide Complexes

A new class of six mono- (1; 3-Cl-, 2; 5-Cl-, 3; 6-Cl-) and di-(4; 3,6-Cl, 5; 5,6-Cl-, 6; 3,5-Cl-) chloro-substituted pyrazin-2-amine ligands (1–6) form complexes with copper (I) bromide, to give 1D and 2D coordination polymers through a combination of halogen and hydrogen bonding that were characterized by X-ray diffraction analysis. These Cu(I) complexes were prepared indirectly from the ligands and CuBr2 via an in situ redox process in moderate to high yields. Four of the pyrazine ligands, 1, 4–6 were found to favor a monodentate mode of coordination to one CuI ion. The absence of a C6-chloro substituent in ligands 1, 2 and 6 supported N1–Cu coordination over the alternative N4–Cu coordination mode evidenced for ligands 4 and 5. These monodentate systems afforded predominantly hydrogen bond (HB) networks containing a catenated (μ3-bromo)-CuI ‘staircase’ motif, with a network of ‘cooperative’ halogen bonds (XB), leading to infinite polymeric structures. Alternatively, ligands 2 and 3 preferred a μ2-N,N’ bridging mode leading to three different polymeric structures. These adopt the (μ3-bromo)-CuI ‘staircase’ motif observed in the monodentate ligands, a unique single (μ2-bromo)-CuI chain, or a discrete Cu2Br2 rhomboid (μ2-bromo)-CuI dimer. Two main HB patterns afforded by self-complimentary dimerization of the amino pyrazines described by the graph set notation R22(8) and non-cyclic intermolecular N–H∙∙∙N’ or N–H∙∙∙Br–Cu leading to infinite polymeric structures are discussed. The cooperative halogen bonding between C–Cl∙∙∙Cl–C and the C–Cl∙∙∙Br–Cu XB contacts are less than the sum of the van der Waals radii of participating atoms, with the latter ranging from 3.4178(14) to 3.582(15) Å. In all cases, the mode of coordination and pyrazine ring substituents affect the pattern of HBs and XBs in these supramolecular structures.