An Unprecedented Type of Migratory Insertion Reactions of Unsaturated C3 Units into Rh−O and Rh−C Bonds

Abstract

A series of iodo- and hydroxorhodium(I) complexes of the general composition trans-[RhX(=C=C=CRR')(PiPr3)2] (X = I: 5-7; X = OH: 8-11) was prepared from the related chlororhodium(I) precursors. The hydroxo compounds behave as organometallic Brønsted bases and react with acids like MeCO2H, PhCO2H, PhOH, or TsOH by elimination of water to give the substitution products trans-[RhX'(=C=C=CRR')(PiPr3)2] (X' = MeCO2: 12, 13; X' = PhCO2: 14; X' = PhO: 15, 16; X' = TsO: 17, 18) in good to excellent yields. In contrast to the tosylates 17, 18, which react with CO by cleavage of the allenylidene-metal bond to give trans-[Rh(OTs)(CO)(PiPr3)2] (19), treatment of the acetato and phenolato derivatives 12, 13 and 15, 16 with CO affords by migratory insertion of the allenylidene unit into the Rh-O bond the alkynyl complexes trans-[Rh[C(triple bond)CCR(R')X'](CO)(PiPr3)2] (X' = MeCO2: 20, 21; X' = OPh: 22, 23). Similarly, the reactions of the hydroxo compounds 8, 10, and 11 with CH2(CN)2 and either CO or CNMe yield the carbonyl and the isocyanide complexes trans-[Rh[C(triple bond)CCR(R')CH(CN)2](L')(PiPr3)2] (L' = CO: 25-27; L' = CNMe: 28-30), respectively. By protolytic cleavage of the Rh-C sigma bond the gamma-functionalized alkynes HC(triple bond)CCR(R')CH(CN)2 (31, 32) are generated from 25, 26 and HCl in benzene. The molecular structure of 22 was determined by X-ray crystallography.

20 Organometallic chemistry of monometallic species

“…210 A series of trans-Rh(allenylidene) 2 complexes 43 show an unprecedented type of migratory insertion reaction where the unsaturated C 3 unit migrates into the Rh-O and Rh-C bonds of cis ligands. 211 The first high-spin cobalt organometallic complex, (η 5 -cyclopentadienyl)(κ 3 -hydrotris(pyrazolyl)borate)cobalt() 44 has been isolated and characterised by SQUID magnetometry and X-ray diffraction. 212 The co-condensation reaction between Co vapour and tert-butylphosphaalkyne affords Co organometallics supported by the oligomer phosphacyclobutadiene including 45, and an unusual protonated tetraphospha-barrelene complex [Co(η 4 -P 4 C 4 Bu t 4 H)(η 4 -P 2 C 2 Bu t 2 )] 46 (which is structurally characterised as its [W(CO) 5 ] adduct).…”

Hexa-Fe(III) Carboxylate Complexes Facilitate Aerobic Hydrocarbon Oxidative Functionalization: Rh Catalyzed Oxidative Coupling of Benzene and Ethylene to Form Styrene

“…In one potential mechanism (Scheme ), a Fe III –OH–Fe III functionality performs one-electron oxidation of an Rh–H intermediate, abstracting a hydrogen atom to form one Fe II , water, and Rh•, which could undergo reaction with a μ–OH functionality in a second equiv of Fe 6 III (μ–OH) 2 (μ 3 –O) 2 (μ–OPiv) 12 (HOPiv) 2 to form an Rh–OH intermediate. This Rh–OH intermediate could subsequently be protonated by an equiv of HOPiv to regenerate the starting Rh–OPiv intermediate and release water . If Rh–OH protonation is occurring, this could rationalize improved catalysis when more acidic carboxylic acids are present (see the Supporting Information), in addition to the observed k H / k D of 1.19(2) when using HOPiv versus DOPiv (see below), although other explanations for the positive role of carboxylic acid are possible.…”

“…This Rh–OH intermediate could subsequently be protonated by an equiv of HOPiv to regenerate the starting Rh–OPiv intermediate and release water. 86 If Rh–OH protonation is occurring, this could rationalize improved catalysis when more acidic carboxylic acids are present (see the Supporting Information ), in addition to the observed k H / k D of 1.19(2) when using HOPiv versus DOPiv (see below), although other explanations for the positive role of carboxylic acid are possible.…”