Search for: All records

Syntheses of Rh complexes of the phosphine-amido-silane SiNP ligand are reported. The reaction of the parent (SiNP)H ligand (4) with 0.5 equiv. [(COE)RhCl] 2 (COE = cis -cyclooctene) in the presence of NaN(SiME 3 ) 2 resulted in the formation of (SiNP)Rh(COE) (5). Compound 5 was converted to a series of (SiNP)Rh(P(OR) 3 ) complexes 6–10 (R = Ph, i Pr, n Bu, Et, or Me) by treatment with the corresponding phosphite. NMR and XRD structural data, as well as the DFT computational analysis indicate that compounds 5–10 are divided into two structural Types ( A and B ), differing in the nature of the interaction of the Si–H bond of the SiNP ligand with Rh.

The synthesis and coordination chemistry of a new class of silyl pincer ligand featuring pyrrole-based linkers is reported. The steric and electronic properties of these bis(phosphinopyrrole)methylsilane ligands were interrogated using their palladium, rhodium, and platinum complexes. The pyrrole-based linker attenuates the donor ability of the ligand relative to its reported 1,2-phenylene congener while maintaining a similar steric profile. Additionally, the silyl donor connected to the N -pyrrolyl groups exhibits a weaker trans influence than the analogous ligand featuring 1,2-phenylene linkers.

Pyridine and quinoline undergo selective C–H activation in the 2-position with Rh and Ir complexes of a boryl/bis(phosphine) PBP pincer ligand, resulting in a 2-pyridyl bridging the transition metal and the boron center. Examination of this reactivity with Rh and Ir complexes carrying different non-pincer ligands on the transition metal led to the realization of the possible isomerism derived from the 2-pyridyl fragment connecting either via B–N/C–M bonds or via B–C/N–M bonds. This M–C/M–N isomerism was systematically examined for four structural types. Each of these types has a defined set of ligands on Rh/Ir besides 2-pyridyl and PBP. A pair of M–C/M–N isomers for each type was computationally examined for Rh and for Ir, totaling 16 compounds. Several of these compounds were isolated or observed in solution by experimental methods, in addition to a few 2-quinolyl variants. The DFT predictions concerning the thermodynamic preference within each M–C/M–N isomeric match the experimental findings very well. In two cases where DFT predicts <2 kcal mol −1 difference in free energy, both isomers were experimentally observed in solution. Analysis of the structural data, of the relevant Wiberg bond indices, and of the ETS-NOCV partitioning of the interaction of the 2-pyridyl fragment with themore »rest of the molecule points to the strength of the M–C(pyridyl) bond as the dominant parameter determining the relative M–C/M–N isomer favorability. This M–C bond is always stronger for the analogous Ir vs. Rh compounds, but the nature of the ligand trans to it has a significant influence, as well. DFT calculations were used to evaluate the mechanism of isomerization for one of the molecule types.« less

We report a series of redox-active bis(pincer) Pd( ii ) complexes in which the redox active units are based on either a diarylamido or a carbazolide framework. Compounds 1 and 2 contain two full diarylamido/bis(pincer) PNP units connected either via an Ar–O–Ar linker ( 1 ) or an Ar–Ar bond ( 2 ). Compound 3 is a fused bis(pincer) where the two PNP units share an aromatic ring. Compound 4 is built around an indolo[3,2- b ]carbazole core in which two NNN pincers share an aromatic ring similarly to 3 . These metal complexes all display two reversible oxidation waves with the Δ E values increasing in the order of 1 < 2 < 4 < 3 . The same trend in increasing electronic coupling emerges from the analysis of the IV-CT bands in the NIR portion of the optical spectra. The analysis of these compounds was further advanced by data from EPR spectroscopy, X-ray diffractometry, and DFT calculations. It is concluded that the monooxidized cations 2+–4+ belong to Class III on the Robin-Day classification of mixed-valence compounds. Compound 4 possesses enforced near-planarity that enables delocalization of the unpaired electron in 4+ across a broader conjugated system compared to 3+more ».« less

Silver halide complexes of a borane/bis(phosphine) ligand have been prepared and characterized. With AgF, the borane abstracts fluoride, resulting in a zwitterionic complex. With AgCl, AgBr, and AgI, the halide stays coordinated to Ag, with little to no Ag–B interaction.

A new diarylmido-based pincer proto ligand ( iPrPNHSbPh ) with one –PPr i 2 and one –SbPh 2 side donor has been synthesized. Three complexes of its amido form were prepared using standard metalation techniques: ( iPrPNSbPh ) PdCl , ( iPrPNSbPh ) RhCO , and ( iPrPNSbPh ) Ir(COE) , where COE = cis -cyclooctene. These complexes were compared with their previously reported analogs incorporating a –PPh 2 side donor in place of –SbPh 2 . The –SbPh 2 donor arm is less donating towards the metal and is less strongly trans -influencing, based on the structural and IR spectroscopic analysis of the Rh complexes. The redox potential of the Pd complexes is only marginally affected by the change from –PPh 2 to –SbPh 2 . (iPrPNSbPh)Ir(COE) proved to be a slower and less selective catalyst in the dehydrogenative borylation of terminal alkynes (DHBTA) than its –PPh 2 analog.