A New P,S-Chiral Auxiliary Derived from Thioglucose. X-ray Structure of a Palladium 1,3-Diphenylallyl Complex with a Strongly Rotated Allyl Ligand

The new ferrocene-based P,S-chiral auxiliary 1, derived from thioglucose, has been prepared and used in the palladium-catalyzed enantioselective allylic alkylation reaction. The X-ray structure of the allyl cationic complex [Pd(η3-PhCHCHCHPh)(1)]CF3SO3 (2) reveals a markedly rotated 1,3-diphenylallyl ligand such that the terminal allyl carbon C(3), trans to the phosphorus donor, is ca. 0.85(3) Å below the coordination plane. This distortion is pertinent to the Pd(0) transition state complex expected in the allylic alkylation reaction

Chemistry of Ruthenium(II) Alkyl Binap Complexes: Novel Bonding, Cyclometalation, and P−C Bond Splitting

Reactions of the bis-isopropyl and bis-cyclohexyl alkyl Binap ligands, 8 and 9, respectively, with [RuCl2(η6-p-cymene)]2 afford new dinuclear chloro-bridged Ru compounds which contain the Binap ligands as six- rather than four-electron donors. A backbone double bond proximate to one of the P-donors complexes the metal atom. NMR details of the olefin bonding plus isomerization reactions involving loss of the olefin complexation are reported. Reactions of 8 or 9 with [Ru(OAc)2(η6-p-cymene)] result in slow P−C bond cleavage and cyclometalation, instead of affording the anticipated [Ru(OAc)2(Binap)] complex. The new cyclometalated complexes, 15 and 16, contain the complexed R2P−O(CO)CH3 ligand and arise (presumably) via acetate attack at phosphorus with the electrons in the P−C bond moving to the ruthenium atom. The solid-state structure of one of these, the cyclohexyl analogue, 16, is reported and represents a rare structural example of a molecule with three different chelate ligands. The complexed R2P−O(CO)CH3 ligand is readily hydrolyzed in wet triflic acid to afford the R2P(OH) donor and an η6-arene ligand (via Ru−C protonation)

Contributions to the Enantioselective Heck Reaction Using MeO−Biphep Ligands. The Case Against Dibenzylidene Acetone

It is shown that the Pd-catalyzed enantioselective Heck reaction of p-XC6H4OTf, X = OMe, H, CO2Me, with dihydrofuran gives higher enantioselectivities when the chelating diphosphine MeO−Biphep, 1a, is replaced with its disubstituted analogue 3,5-di-tert-butyl MeO−Biphep, 1b. The phenylation of 5-methyl-2,3-dihydrofuran produces a new dihydrofuran containing a quaternary stereogenic center (ee, >98% with 1b, ca. 20% with 1a). Catalytic results for the reaction of phenyl triflate with dhf, together with stoichiometric oxidative addition reactions of aryl halides on Pd complexes of 1, show that the use of Pd(dba)(1), dba = dibenzylidene acetone, slows the oxidative addition relative to the reaction in which the Pd(0) precursor is generated from PdCl2(1) + NaBH4. The solid-state structures for two PdI(aryl)(1a), 3, derivatives, aryl = p-MeOOC−C6H4(3a) and C6F5 (3b) are reported

CO-Induced Reductive Elimination of P(<i>t</i>-Bu)₂H from the Platinum(II) Dinuclear Derivative Pt₂[μ-P(<i>t</i>-Bu)₂]₂(H)₂[P(<i>t</i>-Bu)₂H]₂, Affording Mononuclear Platinum(0) or Triangulo Triplatinum(I,I,II) Derivatives

Carbon monoxide (1 atm) quantitatively converts the Pt(II) dinuclear derivative Pt2[μ-P(t-Bu)2]2(H)2[P(t-Bu)2H]2 (1) into the new PtI2PtII triangulo cluster Pt3[μ-P(t-Bu)2]3(H)(CO)2 (2). The 44e- species 2 was characterized by IR and multinuclear NMR spectroscopy and by a single-crystal X-ray diffraction study. Complex 2 is formed through the slow CO-induced reductive elimination of P(t-Bu)2H from 1, affording the intermediate mononuclear Pt(0) carbonyl derivative Pt[P(t-Bu)2H]2(CO)2 (4), which equilibrates with the carbonyl-bridged triangulo derivative Pt3[P(t-Bu)2H]3(μ-CO)3 (5); these are the main products under high pressures of CO. Two alternative mechanisms were examined for the subsequent formation of complex 2, the first being the rapid condensation of complex 4 with unreacted 1 while the second assumes 5 as the direct precursor of 2. Although the first mechanism cannot be conclusively rejected, the second seems the most appropriate, since under high pressures of CO/H2 complex 2 was shown to equilibrate with 5. In the presence of an excess of other phosphines, the carbonylation of 1 yields quantitatively the mononuclear monocarbonyl derivatives Pt(PR3)3(CO) (R3 = Ph3, Et3, t-Bu2H)

New Chiral Complexes of Palladium(0) Containing P,S- and P,P-Bidentate Ligands

New chiral complexes of Pd(0) containing either the bis(phosphine) (6,6‘-dimethoxybiphenyl-2,2‘-diyl)bis(3,5-di-tert-butylphenylphosphine) (MeO-BIPHEP, 1) or the phosphine−sulfur chelate (2,3,4,6-tetra-O-acetyl-1-{(2-diphenylphosphino)benzyl)thio}-β-d-glucopyranose ((2-Ph2PC6H4CH2)−S−CHCH(OAc)CH(OAc)CH(OAc)CH(CH2OAc)O, 2) have been prepared, and the solid-state structure of one of these, Pd(benzoquinone)(2), has been determined. These Pd(0) complexes reveal interesting solution dynamics, as shown by 2-dimensional exchange spectroscopy. For the MeO-BIPHEP derivatives, one can obtain useful structural insights based on the observed restricted rotation around the aryl(3,5-di-tert-butylphenyl) P−C bonds

Synthesis, X-ray, and NMR Studies on Palladium BINAP Complexes Containing Oxazolidinone and Acetylacetonate Anions

A series of monocationic palladium BINAP complexes, [Pd(rac-BINAP)(an oxazolidinone anion)][X] and [Pd(rac-BINAP)(an acetylacetonate anion)][X] (X = a, CF3SO3-; b, BF4-) (9−13), have been synthesized and characterized. A dicationic intermediate, pertinent to the Pd-catalyzed hydroamination reaction, arising from the reaction of the bis-aquo complex [Pd(H2O)2(rac-BINAP)]2(CF3SO3)2 and 1 equiv of an oxazolidinone, has been characterized via low-temperature NMR studies. The structures of the complexes [Pd(rac-BINAP)(CH3−C(O)−C(CH3)−C(O)−CH3)](BF4), 12b, and [Pd(μ-OH)(rac-BINAP)]2(CF3SO3)2 have been determined by X-ray diffraction. The solid-state structures of two separate forms of the BF4- salt 12b were obtained. One form of the salt can be thought of as a tight ion pair, whereas the second form contains a dichloromethane solvent molecule, packed in approximately a fifth coordination position together with a relatively remote BF4- anion. These structures represent a rare example where both ion pairing and strong solvation could be individually characterized. PGSE diffusion coefficients (D values) were measured for both the CF3SO3- and BF4- salts of 9−13 in CD2Cl2. In addition, D values were obtained for the CF3SO3- salts in THF and CDCl3 solutions. The amount of ion pairing decreases in the sequence CDCl3 > THF > CD2Cl2. The 1H,19F-HOESY spectra for the salts in CDCl3 suggest that the CF3SO3- is approaching the positive metal and phosphorus centers via a pathway that brings it closest to the P-phenyl groups but remote from the chelating anion

Chiral Phosphito−Thioether Complexes of Palladium(0). Comments on the Pd, Rh, and Ir Regio- and-Enantioselective Allylic Alkylations of PhCHCHCH(OAc)R, R = H, Me, Et

The new chiral auxiliary (R)-2-ethylthio-1-(phenylethyl)-(R)-binaphthyl phosphite, 1, and three stable Pd(0) olefin complexes containing this chelate, 2−4, have been synthesized. The structure of the maleic anhydride complex 3 has been determined by X-ray diffraction methods. Solution details for 2−4 and aspects of their dynamics have been elucidated via 2-D NMR spectroscopy. The fumaronitrile complex 2 exchanges intramolecularly, whereas the maleic anhydride and pentenedione derivatives, 3 and 4, respectively, exchange intermolecularly. Ligand 1 has been used as auxiliary in the Pd, Rh, and Ir regio- and enantioselective allylic alkylation reactions of PhCHCHCH(OAc)R, R = H, Me, Et, with the anion of dimethyl malonate. Modest to good selectivities are reported

Hydrotris(pyrazolyl)borato Cycloocta-1,5-diene Complexes of Iridium(I): Synthetic Studies and Equilibria in Solution. X-ray Crystal Structures of a Four- and a Five-Coordinate Iridium(I) Hydrotris(pyrazolyl)borato Complex

The compounds [Tp3R,4R,5RIr(COD)] (COD = cycloocta-1,5-diene; Tp3R,4R,5R = hydrotris(pyrazolyl)borate (1), hydrotris(3-methylpyrazolyl)borate (2), hydrotris(3-isopropylpyrazolyl)borate (3), hydrotris(3,5-dimethylpyrazolyl)borate, hydrotris(3-(trifluoromethyl)-5-methylpyrazolyl)borate, hydrotris(3-phenyl-5-methylpyrazolyl)borate, hydrotris(3,5-diisopropylpyrazolyl)borate, hydrotris(3,4,5-trimethylpyrazolyl)borate, hydrotris(4-chloro-3,5-dimethylpyrazolyl)borate (9), hydrotris(4-bromo-3,5-dimethylpyrazolyl)borate) were prepared and characterized by IR and NMR spectroscopy. The X-ray crystal structure of 9·2MeOH (triclinic, space group P1̄ (No. 2); a = 10.044(1) Å, b = 11.186(2) Å, c = 15.499(3) Å; α = 77.90(1)°, β = 73.23(1)°, γ = 66.89(1)°; Z = 2; R = 0.0276 for 2469 observed reflections) shows that iridium is four-coordinate with an η2-hydrotris(pyrazolyl)borate. The X-ray crystal structure of 1 (triclinic, space group P1̄ (No. 2); a = 7.345(1) Å, b = 7.645(1) Å, c = 15.893(5) Å; α = 103.17(4)°, β = 90.30(2)°, γ = 93.50(3)°; Z = 2; R = 0.0433 for 2606 observed reflections) shows that iridium is five-coordinate with an η3-bonded tris(pyrazolyl)borate. Equilibria between corresponding four- (η2-Tp3R,4R,5R) and five-coordinate (η3-Tp3R,4R,5R) species of all the complexes are established in solution. The complex containing the ligand HB(Pz3Me)3 (Pz = pyrazolyl group) (2) rearranged first to the corresponding complex with HB(Pz3Me)2(Pz5Me) and then into that with HB(Pz3Me)(Pz5Me)2. However, 3, which contains HB(Pz3iPr)3, gave only the complex with coordinated HB(Pz3iPr)2(Pz5iPr)

Multinuclear NMR, X-ray, and DFT Studies on RhCl(diene)(phosphoramidite) Complexes

NMR, X-ray, and DFT studies on several [RhCl(diene)(phosphoramidite)] complexes suggest that both electronic and steric effects affect the nature of the olefin, chloride, and P-donor bonding. The X-ray study of [RhCl(1,5-COD)(phosphoramidite)] (phosphoramidite = (Binol)PN(CH(CH3)Ph)2) reveals an intramolecular selectivity in the back-bonding in which the C−C bond of the olefin trans to the Cl ligand is preferentially elongated. Two types of dynamic processes have been detected at ambient temperature in CD2Cl2 solution using 2-D NOESY methods: presumed phosphoramidite dissociation and diolefin rotation. The former is observed with both 1,5-COD and NBD. The latter is more selective in that the intramolecular dynamics for the NBD analogues are relatively fast, but those for the 1,5-COD compounds, barely detectable. DFT calculations suggest that the diolefin rotation proceeds over a tetrahedral transition state and that there is a smaller energy barrier for the NBD complexes relative to the analogous 1,5-COD species. Two bis phosphoramidite salts of the form [Rh(1,5-COD)(phosphoramidite)2]BF4 are reported

Multinuclear NMR, X-ray, and DFT Studies on RhCl(diene)(phosphoramidite) Complexes

NMR, X-ray, and DFT studies on several [RhCl(diene)(phosphoramidite)] complexes suggest that both electronic and steric effects affect the nature of the olefin, chloride, and P-donor bonding. The X-ray study of [RhCl(1,5-COD)(phosphoramidite)] (phosphoramidite = (Binol)PN(CH(CH3)Ph)2) reveals an intramolecular selectivity in the back-bonding in which the C−C bond of the olefin trans to the Cl ligand is preferentially elongated. Two types of dynamic processes have been detected at ambient temperature in CD2Cl2 solution using 2-D NOESY methods: presumed phosphoramidite dissociation and diolefin rotation. The former is observed with both 1,5-COD and NBD. The latter is more selective in that the intramolecular dynamics for the NBD analogues are relatively fast, but those for the 1,5-COD compounds, barely detectable. DFT calculations suggest that the diolefin rotation proceeds over a tetrahedral transition state and that there is a smaller energy barrier for the NBD complexes relative to the analogous 1,5-COD species. Two bis phosphoramidite salts of the form [Rh(1,5-COD)(phosphoramidite)2]BF4 are reported