Site-Selective Alkyl Dehydrogenation of a Coordinated Acylphosphine Ligand

Abstract

Regio- and stereoselective alkane dehydrogenation is a difficult challenge in organometallic chemistry. Intermolecular reactions of this type typically produce numerous olefin stereo- and regioisomers. Herein, we report our initial investigations into the intramolecular dehydrogenation of a datively bound alkyl ligand, demonstrating the first example of a site-selective dehydrogenation of an unactivated acyclic alkyl group. The alkyl group is located on an acylphosphine ligand that is coordinated to a Cp*IrCl2 monomer. A mechanistic proposal, guided by the isolation of a dimeric iridium complex and supported by computational results, is also described.

Organometallic Gas‐phase Ion Chemistry and Catalysis: Insights Into the Use of Metal Catalysts to Promote Selectivity in the Reactions of Carboxylic Acids and Their Derivatives

“…The dashed arrows represent ester fragmentation where the neutral product(s) are unknown. Scheme 15: Remote dehydrogenation of carboxylic acids, 32, via acylphosphine 33 derivatization followed by coordination to an iridium centre, 34, and organometallic formation, 35 (Whittemore et al, 2012). In one of the earliest studies of a model system for cytochrome P-450, Groves et al highlighted that the regioselectivity of hydroxylation in iron oxo porphyrin systems is influenced by proximity effects (Groves et al, 1979).…”

“…In a landmark review on C-H bond activation in the gas phase (Roithová & Schröder, 2010), Roithová and Schröder had the following comments to make regarding the transfer of concepts from gas-phase studies on remote functionalization to the condensed phase: The recent publication by Whittemore et al (Scheme 15) is an important breakthrough (Whittemore et al, 2012). It demonstrates that even for metal complexes in "realistic" oxidation states and decorated with ligands, reactivity is not quenched.…”

“…Whittemore et al have described the site-selective alkyl dehydrogenation of a coordinated acylphosphine ligand (Scheme 15)(Whittemore et al, 2012). While carboxylic acids, 32, were not directly activated, they can be transformed to acylphosphines, 33, which are now suitable ligands to bind to an iridium centre, to provide the iridium complexes, 34.…”

Aroylphosphanes: Base‐Free Synthesis and Their Coordination Chemistry with Platinum‐Group Metals

“…The coordination chemistry of such “phosphomide” ligands is, nonetheless, scant and largely restricted to groups 6–8 (Cr, Mo,, W, Mn, Re, Fe, Ru) with an emphasis on the first‐row metals. A limited range of group 9 complexes has been described with “Cp′RhCl 2 ” (Cp′ = Cp, Cp*) and “Cp*IrCl 2 ” fragments; however, trans ‐Rh(CO)(L) 2 Cl (L = PH 2 {C(O)Me}, PPh 2 {C(O)C 7 F 15 }, PPh 2 {C(O) p ‐An}) and [Rh{κ 2 ‐ P , P ‐C 6 H 3 N{PC(O)PPh 2 } 2 ‐2,6}Cl][13a] are the only low‐valent group 9 complexes known. Similarly, until recently only [Ni(CO) 3 (PAd{C(O) t Bu} 2 )],[12h] cis ‐[Pt(PPh 2 {C(O)C 6 H 5 }) 2 Cl 2 ] and cis ‐[Pd(PPh 2 ){C(O)C 6 H 5 } 2 ‐(SnCl 3 )Cl] were known from group 10, though complexes of the bis(phosphomides) C 6 H 4 {PC(O)PPh 2 } 2 ‐1,3 (Ni, Pd)[13b] and C 6 H 3 N{PC(O)PPh 2 } 2 ‐2,6 (Ni, Pd, Pt)[13a] have since been described.…”

A Primary Acyl Phosphine Stabilized by a Phosphonium Ylide

“…Acylphosphines and their corresponding oxides are important synthons, ligands [1] and UV initiators in the hardening of photopolymerizable materials, [2] respectively. The direct synthesis of primary acylphosphines has traditionally involved the acylation of phosphines or metal phosphides, [1c, 3] the hydrophosphination of ketenes, [4] or the desulfurization of acyl phosphine sulfides.…”