Reactions of Tris(oxazolinyl)phenylborato Rhodium(I) with C−X (X = Cl, Br, OTf) Bonds: Stereoselective Intermolecular Oxidative Addition

Abstract

The achiral and enantiopure chiral compounds To M Rh(CO) 2 (3) and To P Rh(CO) 2 (4) (To M = tris(4,4-dimethyl-2-oxazolinyl)phenylborate; To P = tris(4S-isopropyl-2-oxazolinyl)phenylborate) were prepared to investigate stereoselective oxidative addition reactions and develop new catalytic enantioselective bond functionalization and cross-coupling chemistry. Reactivity at the rhodium center is first shown by the substitution of the carbonyl ligands in 3 and 4 in the presence of the appropriate ligand; thus treatment of To M Rh(CO) 2 with P(OMe) 3 provides To M Rh(CO)[P(OMe) 3 ] (5). However, reaction of To M Rh(CO) 2 and MeOTf (Tf = SO 2 CF 3 ) affords the complex [{N-Me-κ 2 -To M }Rh(CO) 2 ]OTf (6), resulting from N-oxazoline methylation rather than oxidative addition to rhodium(I). In contrast, To M Rh(CO) 2 reacts with allyl bromide and chloroform, forming the rhodium(III) species (κ 3 -To M )Rh(η 1 -C 3 H 5 )Br(CO) (7) and (κ 3 -To M )Rh(CHCl 2 )Cl(CO) (8), respectively. Interestingly, the chiral To P Rh(CO) 2 and CHCl 3 react to give one diastereomer of (κ 3 -To P )-Rh(CHCl 2 )Cl(CO) (9; 100:3 dr) almost exclusively. To evaluate the reactivity of these rhodium(I) compounds, the carbonyl stretching frequencies have been examined. The data for the mono-and trivalent rhodium oxazolinylborate compounds indicate that the electron-donating ability of [To M ] -is slightly greater than that of [To P ] -, and both ligands provide electronic environments that can be compared to the tris(pyrazolyl)borate ligand family.

Optically active, bulky tris(oxazolinyl)borato magnesium and calcium compounds for asymmetric hydroamination/cyclization

“…These tridentate monoanionic ligands are electronically similar to the well-known tris(pyrazolyl)borate ligands [11,12]. The tridentate monoanionic oxazolinylborate ligands also may be compared to Gade's neutral tridentate tris(oxazolinyl)ethane ligands (trisox) [13] whereas the anionic borate center in the tris(oxazolinyl)borates provides an additional electrostatic component to their interaction with metal centers.…”

Acceptorless Photocatalytic Dehydrogenation for Alcohol Decarbonylation and Imine Synthesis

“…[Cp*M(CO) 2 ] and [Tp*M(CO) 2 ] (Cp* = h 5 -C 5 Me 5 , M= metal, Tp* = tris(3,5-dimethylpyrazolyl)borate) react with C À H bonds under mild irradiation. Furthermore, a compound prepared in our group, [To M Rh(CO) 2 ] (To M = tris(4,4-dimethyl-2-oxazolinyl)phenylborate), [13] is an order of magnitude more effective than [Tp*Rh(CO) 2 ]. For example, [Cp*-(PMe 3 )IrCl 2 ] reacts with primary alcohols at 135 8C to afford [Cp*(PMe 3 )IrR(CO)]Cl (R = Me, Et, Ph), [10] while photolysis of [Tp*Rh (1,3-C 8 H 12 )] in methanol gives [Tp*Rh(H) 2 CO], H 2 , and 1,3-C 8 H 12 .…”

“…[9] These compounds were chosen because related systems mediate stoichiometric decarbonylations. The related optically active [To P Rh(CO) 2 ] (2; To P = tris(4S-isopropyl-2-oxazolinyl)phenylborate) [13] is less active. [11] Also, a few iridium pincer compounds react with alcohols to give decarbonylation products.…”

Stoichiometric and catalytic reactivity of tris(oxazolinyl)borate main group metal compounds

“…All of the work contained in this chapter was performed by James Dunne, though the pulse program for the selective 3 ] analogs are readily available, and the ability of these ligands to donate 4 and 6 electrons, respectively, to metal centers has led to comparisons with -diketonates and cyclopentadienyl ligands. Tris(pyrazolyl)borate (Tp) and its bulkier derivatives have proven to be excellent ancillary ligands, and scorpionate complexes of most of the metals in the ‡Parts of the paper are reprinted with permission of Organometallics 2008, 27,[2399][2400][2401]. †Primary researcher and author §Contributed X-ray structure of HTo M periodic table have been preapred.…”

“…All calculations were performed with the NWChem software suite. 27 Density functional theory (DFT) was employed using the B3LYP hybrid functional to obtain optimized geometries, frequencies, and energies, including zero point energy correction. 28 The recently revised, uncontracted effective core potential (LANL08) developed at Los Alamos National Lab was used for magnesium, and the 6-311++G** basis set was used for all other heavy atoms.…”