Reduction of Carbon Monoxide by [(TMTAA)Rh]₂ To Form a Dimetal Ketone Complex

Abstract

Benzene solutions of [(TMTAA)Rh](2) (1) react with CO (P(CO) = 0.8-20 atm; T = 298 K) by cleaving the Rh(II)-Rh(II) bond to form dirhodium(III) ketone (TMTAA)Rh-C(O)-Rh(TMTAA) [2; ν(CO) = 1726 cm(-1); (1)J(103)Rh(13)C(O)(103)Rh = 45 Hz]. Thermodynamic values for the reaction of 1 with CO to form 2 were evaluated from equilibrium constant measurements [K(1)(298 K) = 5.0(0.6) × 10(3), ΔG(1)°(298 K) = -5.0(0.1) kcal mol(-1), ΔH(1)° = -14(1) kcal mol(-1), and ΔS(1)° = -30(3) cal K(-1) mol(-1)].

Electrochemical Reduction Mechanism of [(η5-C5H5)Fe(dppf)(CO)]+ (dppf = 1,1′-Bis(diphenylphosphino)ferrocene)

“…Two types of dimers were considered on the basis of the IR SEC spectrum. The reduced [ 1 ] 0 can dimerize, where the CO ligands can form a new C–C bond similar to the Rh II –CO bond described by Wayland et al, where [(por)­Rh­(μ-(OC) 2 )­Rh­(por)] showed two bands at 1780 and 1769 cm –1 . − The IR spectra of metal α-diketones have been described for complexes with the form [(OC) 5 M­(μ-(OC) 2 )­M­(CO) 5 ] (M = Re, Mn), and the spectra of such species contained two IR bands for the dionyl μ-(OC) 2 ligand that were in the range of 1700–1550 cm –1 . While such a dimer, [CpFe­(dppf)] 2 (μ-(CO) 2 ) (Scheme ), could be calculated, a vibrational analysis was deemed impractical due to the large number of atoms in this complex and the SEC IR spectrum (Figure ) did not fit with that of the reported (μ-M­(OC) 2 )­M.…”

Synthesis, functionalization and coordination chemistry of dibenzotetraaza[14]annulenes

“…Hence, DBTAA ligands offer a variety of geometric and coordination modes toward numerous metal ions [1]. Interestingly, porphyrins are classified as aromatic systems (4n+2) due to their rigid planar structure and full π-conjugation, whereas DBTAAs are not considered as part of the Hückel aromatic system (4n) [1,25]. As such, porphyrin molecules are usually found in a planar arrangement.…”

“…The dimeric rhodium(II) complex 14 was synthesized by refluxing rhodium(II) acetate with 2a in toluene (Scheme 6) [47]. The pressurized reaction of 14 with CO in benzene afforded the highly light-sensitive product 15, a bridged di-rhodium(III) carbonyl complex [25]. It was discovered that the reaction of 14 pressurized with a mixture of gaseous H2 and CO gave the complete conversion into 16 in 24 hours [48].…”

Heterobimetallic Complexes of Rhodium Dibenzotetramethylaza[14]annulene [(tmtaa)Rh-M]: Formation, Structures, and Bond Dissociation Energetics

“…1–3 A rhodium(II) tmtaa dimer ([(tmtaa)Rh] 2 , 1 ) has recently been reported to react with synthesis gas (H 2 /CO) in toluene and pyridine to form large equilibrium concentrations of a metallo-formyl complex ((tmtaa)Rh-C(O)H) (Figure 1). 3 Rhodium(II) porphyrins and related chelates and macrocycles provide precedents for reactions of H 2 /CO that produce η 1 -carbon-bonded formyl complexes.…”

“…The easily prepared, low cost N 4 2– macrocyclic ligand dibenzotetramethylaza[14]­annulene dianion (tmtaa) has been suggested as a substitute for porphyrins. − A rhodium­(II) tmtaa dimer ([(tmtaa)­Rh] 2 , 1 ) has recently been reported to react with synthesis gas (H 2 /CO) in toluene and pyridine to form large equilibrium concentrations of a metallo-formyl complex ((tmtaa)­Rh-C­(O)­H) (Figure ) . Rhodium­(II) porphyrins and related chelates and macrocycles provide precedents for reactions of H 2 /CO that produce η 1 -carbon-bonded formyl complexes. − Several approaches attempting to advance the utilization of this type of metal-formyl fragment in the production of organic oxygenates invoke reactions that occur at the formyl group, such as hydrogenation using a second catalyst. , Bimetal catalyst systems for alkene hydroformylation that involve intermolecular processes illustrate the efficacy of this type of strategy. − Heterobimetallic complexes can be anticipated to occur in bimetal catalyst systems as nonproductive traps for active metal catalyst species.…”