A highly active alkane dehydrogenation catalyst: stabilization of dihydrido rhodium and iridium complexes by a P–C–P pincer ligand

Gupta, Monika; Hagen, C.; Flesher, Robert J.; Kaska, William C.; Jensen, Craig M.

doi:10.1039/cc9960002083

Cited by 341 publications

(286 citation statements)

References 22 publications

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“…by hydride and formation of 258 has been accomplished originally by using KH, 408 later also with LiBEt 3 H, 409 or simply with a non-nucleophilic base in the presence of an alkane like cyclooctane (coa). 410 The latter procedure affords an equilibrium between 258 and an iridium(I) complex comprising the PCP pincer ligand and coe.…”

Section: Scheme 101mentioning

confidence: 99%

Cyclometalation Using d-Block Transition Metals: Fundamental Aspects and Recent Trends

2009

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Section: Scheme 101mentioning

confidence: 99%

Cyclometalation Using d-Block Transition Metals: Fundamental Aspects and Recent Trends

2009

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“…A number of early reactivity studies showed that the chemistry of square-planar late-transition-metal pincer complexes of this type is particularly rich ([2] and references therein). Subsequent studies have demonstrated the utility of such complexes in Lewis acid catalysis [2a] [3], Heck reactions [4], Kharasch additions [5], catalytic dehydrogenation [6], transfer hydrogenation [7], and investigations of CÀH and CÀC oxidative addition reactions ( [8] and references in [8a]).…”

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Development of the First P-Stereogenic PCP Pincer Ligands, Their Metallation by Palladium and Platinum, and Preliminary Catalysis

Williams¹,

Dani²,

Lutz³

et al. 2001

HCA

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In memoriam Professor Luigi M. Venanzi for his pioneering work in organometallic chemistry, and in PCPpincer chemistry in particularThe potentially tridentate P-stereogenic [P*CP*] ligands 1,3-{bis[(tert-butyl)(phenyl)phosphino]methyl}-benzene and 1,3-{bis[(tert-butyl)(phenyl) phosphino]methyl}-2-bromobenzene have been synthesized as the protected phosphine-borane adducts. Deprotection with a secondary amine affords the free phosphine ligand which can be metallated by Pd and Pt with standard metal synthons. Two of the resultant [P*CP*] metal complexes have been characterized by X-ray crystallography. The complexes exhibit a C 2 symmetric environment about the remaining binding site of the square-planar center, with t-Bu groups filling two quadrants of the open site. The Pd complexes can be converted by use of a Ag salt to the analogous aquo complex, which is catalytically active in the aldol condensation of methyl 2-isocyanoacetate and benzaldehyde. Preliminary results and comparisons with previously reported catalysts with more distal C-stereogenicity are presented. [12], and solid supports [13]. Because of these advances in attachment of pincer ligands to recoverable supports, any new modification of the pincer framework or discovery of new patterns of reactivity can be applied in a straightforward manner to a practical catalytic process, in which the catalyst can be easily separated from the reaction medium, and thus the Introduction

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“…1 With the recent development of effective catalysts for dehydrogenation that involve Rh, or more especially Ir, complexes related to compound 1, interest in their application has been heightened. 2 Among the factors that contribute to their reactivity in the critical C-H activation step will be the chelate bite angle and the electronic character of both the s-and n-bonding entities. Synthesis and complexation chemistry of a higher homologue 2 based on cycloheptatriene has already been reported.…”

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Synthesis and reactivity of a ferrocene-derived PCP-pincer ligand

et al. 2002

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The 1,3-bis(diphosphinomethyl)ferrocene 3 readily reacts with [(C 2 H 4 ) 2 RhCl] 2 to form an equilibrating pair of diastereomers 8a and 8b by C-H insertion into the ferrocene.Pincer-type ligands have played a significant role in homogeneous catalysis. 1 With the recent development of effective catalysts for dehydrogenation that involve Rh, or more especially Ir, complexes related to compound 1, interest in their application has been heightened. 2 Among the factors that contribute to their reactivity in the critical C-H activation step will be the chelate bite angle and the electronic character of both the s-and n-bonding entities. Synthesis and complexation chemistry of a higher homologue 2 based on cycloheptatriene has already been reported. 3 For these reasons we are interested in the synthesis of the ferrocene analogue 3, and report its successful completion together with some preliminary reactions that demonstrate the access to pincer-type ligation.General methods for the preparation of 1,3-disubstituted ferrocenes are severely lacking. 4 In order to synthesise a suitable precursor, we prepared compound 4 according to published procedures, involving the photochemical displacement of p-xylene from CpFe[p-xylene] + BF 4 2 in the presence of 3-methoxycarbonyl-6-dimethylaminofulvene. 5,6 This was cleanly reduced by LiAlH 4 in refluxing THF to the primary diol 5a in 89% yield. 7 Attempts to form the diacetate 5b by conventional means (Ac 2 O, py, DMAP) were unsuccessful, but it was demonstrated that direct S N 1 reaction in AcOH at 80 °C proceeded cleanly, according to precedent. 8 Rather than isolate the diacetate according to conventional phosphination procedures, 9 diol 5a was converted directly into the desired diphosphine 3 by heating with HPBu t 2 (2 equiv.) in AcOH (80°C , 1 h), isolating the product † in 62% yield by precipitation from MeOH.The new ligand was surveyed for its reactivity towards simple unsaturated metal complexes under mild conditions. A model reaction was first established, using ligand 1b. By NMR (C 6 D 6 , 65 °C, 30 min), displacement of the pincer diamine ligand 10 in 6 by the diphosphine was observed. The formation of complex 7 was inferred, ‡ although it was not isolated. Repeating this reaction with ligand 3 gave no evidence of complexation, however. Reaction of the ferrocene-derived ligand 3 with (PPh 3 ) 3 RuCl 2 or (MeCN) 2 PdCl 2 likewise failed to give characterisable products.When ligand 3 was reacted with [(C 2 H 4 ) 2 RhCl] 2 in CD 2 Cl 2 at ambient temperature a clean transformation occurred within minutes, the product being characterised by NMR and MS. † Initially, two sets of resonances were observed in the 1 H NMR spectrum, in particular two distinct Rh-H signals at ca. 227 ppm. Equilibration occurred over 4 h so that the lower field signal, initially the minor component, became strongly predominant. The equilibration could also be followed by 31 P NMR, it being observed that the signal at 87.5 ppm, decreases monotonically over 3 h as the signal at 93.5 ppm increases. ...

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A highly active alkane dehydrogenation catalyst: stabilization of dihydrido rhodium and iridium complexes by a P–C–P pincer ligand

Abstract: The novel P-C-P pincer complex, [IrH2{C6H3(CH2PBuf2)2-2,6}] has long-term stability at 200 "C and catalyses the transfer dehydrogenation of cyclooctane to cyclooctene at the rate of 12 turnovers min-'.

Cited by 341 publications

References 22 publications

Cyclometalation Using d-Block Transition Metals: Fundamental Aspects and Recent Trends

Cyclometalation Using d-Block Transition Metals: Fundamental Aspects and Recent Trends

Development of the First P-Stereogenic PCP Pincer Ligands, Their Metallation by Palladium and Platinum, and Preliminary Catalysis

Synthesis and reactivity of a ferrocene-derived PCP-pincer ligand

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