Formation of 18e− and 16e− Acyl(η3-cyclooctenyl)rhodium(III) Complexes in the Reaction of Cationic (Cycloocta-1,5-diene)rhodium(I) Compounds with 2-(Diphenylphosphino)benzaldehyde

Abstract

The reaction of cationic diolefinic rhodium(I) complexes with 2-(diphenylphosphino)benzaldehyde (pCHO) was studied. [Rh(cod) 2 ]ClO 4 (cod cycloocta-1,5-diene) reacted with pCHO to undergo the oxidative addition of one pCHO with (1,2,3-h)cyclooct-2-en-1-yl (h 3 -C 8 H 13 ) formation, and the coordination of a second pCHO molecule as (phosphino-kP)aldehyde-kO(s-coordination) chelate to give the 18e À acyl(allyl)rhodium(III) species [Rh(h 3 -C 8 H 13 )(pCO)(pCHO)]ClO 4 (see 1). Complex 1 reacted with [Rh(cod)(PR 3 ) 2 ]ClO 4 (R aryl) derivatives 3 ± 6 to give stable pentacoordinated 16e À acyl[(1,2,3-h)-cyclooct-2-en-1-yl]rhodium(III) species [Rh(h 3 -C 8 H 13 )(pCO)(PR 3 )]ClO 4 7 ± 10. The (1,2,3-h)-cyclooct-2-en-1-yl complexes contain cis-positioned P-atoms and were fully characterized by NMR, and the molecular structure of 1 was determined by X-ray crystal diffraction. The rhodium(III) complex 1 catalyzed the hydroformylation of hex-1-ene and produced 98% of aldehydes (n/iso 2.6).Introduction. ± The activation of CÀH bonds promoted by transition-metal complexes is an active area of research [1]. Cleavage of CÀH bonds of aldehydes and promoted by Rh may lead to acylhydrido species [2]. When the aldehyde is close to a donor atom and chelates can be formed, the corresponding acylhydrido complexes are easily obtained [3 ± 4], and some of them are active catalysts in the hydroacylation of olefins [4]. The 2-(diphenylphosphino)benzaldehyde (pCHO) has been used to add oxidatively to several late transition metals in low oxidation states [3] [5 ± 6], yielding cis-acylhydrido complexes that contain (phosphino-kP)acyl-kC chelates (pCO). Hydrido complexes containing cycloocta-1,5-diene may undergo insertion of the olefin into the MÀH bond to afford (1,4,5-h)-cyclooct-4-en-1-yl ((1-s-4,5-h 2 )-C 8 H 13 ) [7] or the corresponding p-allylic type (1,2,3-h 3 )-C 8 H 13 ) derivatives [8]. Also, [RhCl(penta-1,4-diene)] 2 has been reported to react with quinoline-8-carboxaldehyde (nCHO) to give an 18e À acylallyl compound [RhCl(h 3 -1-ethylallyl)(nCO)] 2 via an acyl(hydrido)-diolefin intermediate [9]. In contrast, the diolefinic complex [IrCl(cod)] 2 reacts with pCHO to give the thermally unstable [IrH(pCO)Cl(cod)] that has been proposed as model intermediate in the hydroacylation of olefins [5a], and we have recently reported that [RhCl(cod)] 2 and [Rh(cod)(bdh)Cl] (cod cycloocta-1,5-diene, bdh biacetyldihydrazone) react with pCHO (Rh/pCHO 1 : 2) to give acylhydrido derivatives with displacement of cycloocta-1,5-diene [10].We report now on the reaction of [Rh(cod) 2 ClO 4 with pCHO (Rh/pCHO 1 : 2), which adds oxidatively to form a fully characterized 18e À acyl[(1,2,3-h)-cyclooct-2-en-

Silyl–Thioether Multidentate Ligands – Synthesis of RhIII Complexes via RhI/RhIII Mixed‐Valent and Cyclooctenyl Intermediates

“…The 29 Si NMR spectrum [doublet at δ = 44.2 ppm, 1 J (RhSi) = 28 Hz] indicates the formation of a silyl–Rh bond. In the NMR spectra including 2D experiments of 3 , signals at δ = 5.14 and 3.78 ppm in the 1 H NMR spectrum, with 1 H and 2 H relative integrals, respectively, which correlate with two resonances at δ = 96.7 and 66.8 ppm in the 13 C NMR spectrum, suggest the presence of a η 3 ‐cyclooctenyl group with two equivalent C–H groups on the allyl fragment 25,35,38. The formation of 3 is supported by ESI‐MS spectroscopy that shows a molecular ion at m / z = 501.06 (calcd.…”

“…After 8 hours, 1 H NMR spectroscopy shows the presence of free cyclooctene (coe) and the formation of several intermediate complexes. Three relative integral 1 H multiplets at δ = 4.77, 4.61, and 3.68 ppm, which are characteristic of (η 3 ‐cyclooctenyl)‐Rh III compounds,35 are observed (for details, see Figure S18). This observation suggests the formation of (η 3 ‐cyclooctenyl) intermediates that could afterwards afford coe.…”

Aldehyde C–H activation with late transition metal organometallic compounds. Formation and reactivity of acyl hydrido complexes

“…The amino groups favour the cis diphosphine disposition and isomerisation reactions were observed, which were proposed to be assisted by ion pairing formation via hydrogen bonding. 33 Cationic rhodium(I) complexes [Rh(Cod 35 The activation of the C-H bond was followed by hydrogen transfer to the 1,5-cyclooctadiene and rearrangement to form the h 3 -allyl complex [Rh(h 3 -cyclooctenyl)(PPh 2 (o-C 6 H 4 CO))(k 2 -PPh 2 (o-C 6 H 4 CHO))]ClO 4 (49). The reaction of 49 with [Rh(Cod)(PR 3 ) 2 ]ClO 4 afforded only the stable unsaturated 16e rhodium(III) complexes 50 (eq.…”

o-(Diphenylphosphino)benzaldehyde: a versatile ligand and a useful hemilabile ligand precursor

“…(1)). The formation of 10 requires the opening of the P,raldehyde chelate in 9, followed by the oxidative addition of aldehyde to the rhodium(I) complex prior to phosphine exchange [19].…”