(η¹‐tpMn, η⁵‐tpCr) → (η¹‐tpCr, η⁵‐tpMn) Thiophene (tp) Conversion due to Bimetallic Activation: A Novel Metal‐Exchange Reaction

Abstract

The irreversible formal exchange of the metal atoms in dinuclear complexes has been observed for the first time. In polar solvents complex 1 rearranges to give the thermodynamically more stable complex 2.

Two different types of 2-thienyl bridge in dinuclear manganese and rhenium compounds

“…) [1.949(13) Å] (trans to phosphorus) is longer than Re(2)-C(22) [1.894(12) Å] (trans to sulfur), consistent with a higher trans influence of the phosphine, although, as might be expected, the longest Mn-CO distances are those associated with the mutually trans-CO ligands. The Re(1)-P(1) distance [2.435(2) Å] is slightly shorter than Re(2)-S(1) [2.473(3) Å] and indicates a stronger phosphorus than sulfur co-ordination.Diphenyl-2-thienylphosphine does not react thermally with [Re 2 (CO) 10 ] to give compound 4.…”

“…Terminal thienyl A is known in a number of systems. 13,17 There are three distinct types of doubly bridging thienyl, B to D. All known examples of µ-η 2 -thienyl 18 involve M-M bonded systems where the metal-metal distance is below 3 Å. Where there is no metal-metal bond or when the distance is above 3 Å for whatever reason, it becomes increasingly difficult for the thienyl to bridge in this way and instead the S-bonded mode C occurs.…”

“…13 C-{ 1 H} NMR: phenyl, δ 142.4 (d, J = 27.5, ipso), 137.8 (d, J = 54.3, ipso), 133.5 (d, J = 10.3, meta), 131.2 (d, J = 12.0, ortho), 130.5 (d, J = 2.3, para), 128.5 (d, J = 2.6, para), 128.5 (d, J = 10.7, ortho) and 128.1 (d, J = 9.1, meta); thienyl, 197.9 (d, J = 5.5), 167.5 (s), 135.2 (s) and 130.4 (s); CO (at Ϫ50 ЊC), 193.2 (m, two overlapping), 190.8 (d, J = 7.8), 188.6 (d, J = 38.6, trans to PPh 2 ), 188.4 (d, J = 7.2), 187.7 (d, J = 6.4), 186.3 (d, J = 6.4) and 185.3 (d, J = 32.9 Hz, trans PPh 2 ). The parent molecular ion was observed at low intensity in the EI MS.…”

Preferred Coordination Sites for Metal Fragments in σ,π-Bimetallic Complexes. Detailed Mechanistic Insight from Heteroatom, Bridging Ligand, Solvent, Temperature, and Pressure Effects on the Irreversible Exchange of Coordination Sites1

“…Substitution processes represented by the irreversible changing of σ- and π-coordination positions in bimetallic complexes with bridging acetylide ligands were described as acetylide migrations 8 or alkynyl transfer processes . By comparison, we described the multiple substitution processes whereby two metal fragments exchange σ and π coordination sites around a thiophene ring as a metal exchange process. , In both cases the terminology was determined by the number of coordination positions involved during the conversion. As more examples are reported, irreversible metal exchange processes or irreversible acetylide migrations seems to be both the result of the same driving force, i.e.…”

Metal–metal bond cleavage of carbene complexes by halogens: The crystal and molecular structures of ax-[Mn2(CO)9{C(OEt)2-thienyl}], [Mn(CO)4(I){C(OEt)2-thienyl}] and eq-[Mn2(CO)9{C(NH2)2-thienyl}]

“…Largely unnoticed in later work, the cleavage of the metal-metal bond of the dioxy carbene complexes by bromine, was also reported [9]. Reaction of the lithiated [(g 5 -thiophene)Cr(CO) 3 ] or the analogous lithiated [(g 6 -benzene)Cr(CO) 3 with [Mn(CO) 5 Br] involved attack either on the metal centre or on a carbonyl ligand with elimination of bromide and yielded for the thiophene precursor the binuclear complexes [{g 1 ,g 5 -thienyl-Mn(CO) 5 }Cr(CO) 3 ] and [{g 1 ,g 5 -thienyl-C(O)Mn(CO) 5 }Cr(CO) 3 ] (Scheme 1) [11,12]. By contrast, the corresponding reaction with [Re(CO) 5 Br] involved attack on a carbonyl ligand without the elimination of bromide.…”