Syntheses, Molecular Structures, and Reactivities of (π-Allyl)rhodium(I) Complexes Containing Bulky Bis(phosphino)methanes R‘₂PCH₂PiPr₂as Ligands

Abstract

The π-allyl complexes [Rh(η3-2-RC3H4)(κ2-R‘2PCH2PiPr2)] (R = H, Me; R‘ = iPr, Cy, Ph) (2−7) were prepared from [RhCl(η4-C8H12)]2, 2-RC3H4MgX, and R‘2PCH2PiPr2 via [Rh(η3-2-RC3H4)(η4-C8H12)] as the intermediate. Reaction of 2−4 (R = H) with Broensted acids HX (X = Cl, CF3CO2, CF3SO3) led to cleavage of the allyl−metal bond and to the formation of the monohydridorhodium(III) compounds [RhHX2(κ2-R‘2PCH2PiPr2)] (8−12). Variable-temperature NMR measurements of 8−12 confirm that these compounds are fluctional in solution. The reaction of 2−4 with CO gave in the initial step the 1:1 adducts [Rh(η3-C3H5)(CO)(κ2-R‘2PCH2PiPr2)] (16−18), of which that with R‘ = iPr was characterized by X-ray structure analysis. Compounds 16 (R‘ = iPr) and 18 (R‘ = Ph) reacted with excess carbon monoxide via migratory insertion of CO into the allyl−metal bond to yield the five-coordinate acylrhodium(I) complexes [Rh{C(O)CH2CHCH2}(CO)2(κ2-R‘2PCH2PiPr2)] (19, 20). This insertion reaction is reversible. The analogous acyl compound [Rh{C(O)CH2Ph}(CO)2(κ2-iPr2PCH2PiPr2)] (22) was obtained from [Rh(η3-CH2Ph)(κ2-iPr2PCH2PiPr2)] and CO. Acid cleavage of the acyl−metal bond of 19 (R‘ = iPr) afforded the aldehyde CH2CHCH2CHO (26) and a mixture of 8 and [RhHCl2(CO)(κ2-iPr2PCH2PiPr2)] (25).

Solid-state molecular organometallic chemistry. Single-crystal to single-crystal reactivity and catalysis with light hydrocarbon substrates

“…Such a chemical shift is characteristic of the methine proton in an η 3 -allyl ligand. 98 , 102 The hydride region was featureless. These data suggest a fluxional process is also occurring in solution at 298 K. Cooling to 193 K in CD 2 Cl 2 slows both decomposition and the fluxional process.…”

Rh-catalyzed C–C bond cleavage by transfer hydroformylation

“…The neutral Rh-complex 8a activates the aldehyde C–H bond to generate acyl-Rh III -hydride 8b . The 3-methoxybenzoate counterion can then undergo reductive elimination with the hydride ligand to generate acyl-Rh I 8c and 3-methoxybenzoic acid (35). In contrast, most hydroacylations and decarbonylations typically employ innocent counterions such as Cl − and BF 4 − .…”

A new route to achiral and chiral 1,2-bis(phosphino)ethanes, 1-arsino-2-phosphinoethanes, and 1,3-bis(phosphino)propanes and the molecular structure and catalytic activity of some rhodium(i) complexes derived thereof Dedicated to Professor Wolfdieter A. Schenk, a respected colleague and creative scientist, on the occasion of his 60th birthday.

“…The bite angle As(1)-Rh(1)-P(1) of 73.80(4)° is relatively small but comparable to the bite angle Sb-Rh-P of [Rh( 4 -C 8 H 12 )( 2 -iPr 2 PCH 2 SbtBu 2 )] + and to that of neutral and cationic rhodium complexes with bulky bis(phosphino)methanes as ligands. 3,21,22 While the Rh(1)-P(1) bond length lies in the expected range, 3,21 the distance Rh(1)-As(1) of 2.4533(8) Å is significantly ther, we also prepared the racemic mixtures of 7 and 8 (see Scheme 3) as well as the chiral unsymmetrical 1,3-bis(phosphino)propane (R)-8. These compounds are high-boiling, air-sensitive liquids which have been characterized by elemental analysis and mass spectra.…”

“…Results for the hydrogenation of -acetamidocinnamic acid methylester (ACM) at 1 bar pressure of H 2 in iPrOH (entry[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and in THF (entry[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] with complexes 12a-h as catalyst precursors a…”