“…An X-ray diffraction study of a single crystal of 3 reveals its structure as a monomeric Ru(II) N -pyrrolyl complex (Table and Figure ). The Ru−N pyrrolyl bond distance of 2.083(4) Å is shorter than the corresponding bond distance (2.153(6) Å) of Ru(1,5-η 5 -C 8 H 11 )( N -pyrrolyl)(PEt 3 ) 2 3 ORTEP of 3 (30% probability).…”
Section: Resultsmentioning
confidence: 82%
“…The Ru-N pyrrolyl bond distance of 2.083(4) Å is shorter than the corresponding bond distance (2.153(6) Å) of Ru(1,5-η 5 -C 8 H 11 )(N-pyrrolyl)(PEt 3 ) 2 . 44 Reports of 2-pyrrolyl complexes are rare, 45,46 and efforts to produce the 2-pyrrolyl complex TpRu(CO)-(NCMe)(2-pyrrolyl) did not yield clean, isolable products. For example, heating solutions of TpRu(CO)(NCMe)(Cl) or TpRu(CO)(NCMe)(OTf) (4) with Hg(2-pyrrolyl)Cl did not yield new products.…”
Section: Resultsmentioning
confidence: 99%
“…Initial activation of the 2-position C-H bond would be consistent with previously reported regioselective C-H activation at the 2-position of furan and thiophene by TpRu(CO)(NCMe)-(Me); 40 however, the majority of well-defined examples (i.e., products isolated and fully characterized) of metalmediated activation of pyrrole indicate selectivity for activation of the N-H bond in preference to C-H bond cleavage. 44,[47][48][49][50][51][52][53][54][55] A possible exception is the reported photolysis of [Cp 2 Re(NCMe)] + (Cp ) cyclopentadienyl) in pyrrole to produce [Cp 2 Re(2-pyrrolyl)(H)] + . 56 The source of the commonly observed selectivity for the pyrrole N-H bond over C-H bond activation could be the lower N-H bond dissociation enthalpy (BDE) of pyrrole (∼97 kcal/mol) versus the C-H BDEs at the 2-position or 3-position (∼118 kcal/mol).…”
The reaction of TpRu(CO)(NCMe)(Me) (1) and pyrrole forms TpRu(CO){κ2-N,N-(H)NC(Me)(NC4H3)} (2). The formation of complex 2 involves the cleavage of the N−H bond and
2-position C−H bonds of pyrrole as well as a C−C bond forming step between pyrrole and
the acetonitrile ligand of 1. Mechanistic studies indicate that the most likely reaction pathway
involves initial metal-mediated N−H activation of pyrrole to produce TpRu(CO)(N-pyrrolyl)(NCMe) (3) followed by C−C bond formation and proton transfer. Complex 3 has been
independently prepared and demonstrated to convert to 2. Computational studies support
the suggested selectivity for initial N−H bond cleavage in preference to C−H bond activation.
“…An X-ray diffraction study of a single crystal of 3 reveals its structure as a monomeric Ru(II) N -pyrrolyl complex (Table and Figure ). The Ru−N pyrrolyl bond distance of 2.083(4) Å is shorter than the corresponding bond distance (2.153(6) Å) of Ru(1,5-η 5 -C 8 H 11 )( N -pyrrolyl)(PEt 3 ) 2 3 ORTEP of 3 (30% probability).…”
Section: Resultsmentioning
confidence: 82%
“…The Ru-N pyrrolyl bond distance of 2.083(4) Å is shorter than the corresponding bond distance (2.153(6) Å) of Ru(1,5-η 5 -C 8 H 11 )(N-pyrrolyl)(PEt 3 ) 2 . 44 Reports of 2-pyrrolyl complexes are rare, 45,46 and efforts to produce the 2-pyrrolyl complex TpRu(CO)-(NCMe)(2-pyrrolyl) did not yield clean, isolable products. For example, heating solutions of TpRu(CO)(NCMe)(Cl) or TpRu(CO)(NCMe)(OTf) (4) with Hg(2-pyrrolyl)Cl did not yield new products.…”
Section: Resultsmentioning
confidence: 99%
“…Initial activation of the 2-position C-H bond would be consistent with previously reported regioselective C-H activation at the 2-position of furan and thiophene by TpRu(CO)(NCMe)-(Me); 40 however, the majority of well-defined examples (i.e., products isolated and fully characterized) of metalmediated activation of pyrrole indicate selectivity for activation of the N-H bond in preference to C-H bond cleavage. 44,[47][48][49][50][51][52][53][54][55] A possible exception is the reported photolysis of [Cp 2 Re(NCMe)] + (Cp ) cyclopentadienyl) in pyrrole to produce [Cp 2 Re(2-pyrrolyl)(H)] + . 56 The source of the commonly observed selectivity for the pyrrole N-H bond over C-H bond activation could be the lower N-H bond dissociation enthalpy (BDE) of pyrrole (∼97 kcal/mol) versus the C-H BDEs at the 2-position or 3-position (∼118 kcal/mol).…”
The reaction of TpRu(CO)(NCMe)(Me) (1) and pyrrole forms TpRu(CO){κ2-N,N-(H)NC(Me)(NC4H3)} (2). The formation of complex 2 involves the cleavage of the N−H bond and
2-position C−H bonds of pyrrole as well as a C−C bond forming step between pyrrole and
the acetonitrile ligand of 1. Mechanistic studies indicate that the most likely reaction pathway
involves initial metal-mediated N−H activation of pyrrole to produce TpRu(CO)(N-pyrrolyl)(NCMe) (3) followed by C−C bond formation and proton transfer. Complex 3 has been
independently prepared and demonstrated to convert to 2. Computational studies support
the suggested selectivity for initial N−H bond cleavage in preference to C−H bond activation.
“…Proton transfer to a bound ligand is well-known with lanthanide metals, being a key step in hydroamination catalysis; however, these involve highly basic metal alkyls or amides . Previous studies of activation of pyrrole have generally shown that N−H activation is favored over C−H activation, at least for low-oxidation-state complexes . In contrast, Sames has recently reported the rhodium(III)-catalyzed arylation of pyrrole and indoles in which C−H activation is preferred over N−H activation .…”
Reaction of a pyrrole imine with [IrCl 2 Cp*] 2 /NaOAc leads to N-H actiVation in preference to C-H actiVation at the pyrrole; howeVer, with the N-methylated ligand C-H actiVation occurs. Density functional calculations show that N-H bond actiVation is both kinetically and thermodynamically preferred to C-H actiVation. Both reactions occur with relatiVely low energy barriers by an electrophilic agostic interaction with the metal with simultaneous intramolecular hydrogen bonding with acetate leading to deprotonation Via a six-membered transition state.
“…While pyrrole is widely used in coordination complexes incorporating virtually all metals of the transition block, most of these show pyrrole to be bound in an η 1 fashion, directly forming a nitrogen–metal bond. − Interestingly, there are still many examples of η 5 -bound pyrrole in transition metal chemistry; however, it is often seen that such ligation is vulnerable to substitution reaction or haptotropic shifts. − The selected examples in which these side reactions are absent are mainly seen in early transition metal chemistry, and studies of such complexes elucidate the highly electrophilic nature of the metal and steric environment that are required to yield the pentahapto pyrrolyl-metal moiety. , Although studies of actinide-pyrrolyl complexes date as far back as 1974 with Marks’ preparation of tetrakis(2,5-dimethylpyrrolyl)uranium(IV), it is only in the past decade that pyrrolyl ligands have been reintroduced into actinide chemistry and the focus of continued investigation . In the first of these studies, Boncella et al revealed a U VI center coordinated to a bridged dipyrrolylmethane (dpm) ligand.…”
The synthesis of new actinide complexes utilizing bridged α-alkyl-pyrrolyl ligands is presented. Lithiation of the ligands followed by treatment with 1 equiv of actinide tetrachloride (uranium or thorium) produces the desired complex in good yield. X-ray diffraction studies reveal unique η(5):η(5) coordination of the pyrrolyl moieties; when the nonsterically demanding methylated ligand is used, rapid addition of the lithiated ligand solution to the metal precursor forms a bis-ligated complex that reveals η(5):η(1) coordination as determined by crystallographic analysis.
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