Oxidative Dimerization of Arylalkynyl–Ruthenium Complexes

Abstract

Chemical oxidation of Ru(CCPh)(PPh3)2Cp with [FeCp2]PF6 affords the binuclear cationic complexes [Cp(PPh3)2Ru{CCHC6H4CPhC}Ru(PPh3)2Cp](PF6)2 (2) and [Cp(PPh3)2Ru{CC(C6H4)CPhC}Ru(PPh3)2Cp]PF6 (3) by radical coupling at sites shown to be electron-rich by DFT studies, particularly involving the acetylide Cβ and Ph Cpara atoms and, to a lesser extent, the Cp carbon atoms. Complexes 2 and 3 are related by facile deprotonation/protonation reactions. When the 4-position of the Ph group is blocked, attack by Cβ upon the Cp group occurs to give the bis(vinylidene) [Ru{CC(C6H4Me-4)-η-C5H4[Ru(PPh3)2{CCH(C6H4Me-4)}(PPh3)2Cp]}](PF6)2 (4), which can be deprotonated to give [Ru{CC(C6H4Me-4)-η-C5H4[Ru(PPh3)2{CC(C6H4Me-4)}(PPh3)2Cp]}]PF6 (5). Complex 4 is rapidly oxidized during workup to form [Ru{CC(C6H4Me)-η-C5H4[Ru(CO)(PPh3)2]}(PPh3)2Cp](PF6)2 (6). Single-crystal X-ray structure determinations of the salts 2, 3, and 6 are reported.

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

“…[127] However, very recent results suggest that the coupled products derived from phenylethynylene radicals may have an alternative structure. [128] the usual C β -C β fashion, presumably on steric grounds, coupled through C β of one radical and the para-phenyl carbon of the alkynyl substituent in another. The proton liberated on re-aromatisation of the phenylene ring is transferred to the basic acetylide moiety to give an unusual bis(vinylidene) product (25; Scheme 16).…”

“…Electronic structure calculations have been used to rationalise some of the more recent observations concerning the redox non-innocent character of σ-alkynyl and polyynyl ligands, particularly for complexes based on piano-stool fragments [M(L 2 )CpЈ] [M = Fe, L 2 = (dppe), CpЈ = Cp*; [13,14,17] M = Ru, L 2 = (PPh 3 ) 2 , dppe, CpЈ = Cp, Cp*], [10,18,32,128,153] [Mo(CO)L 2 CpЈ] [L 2 = (PMe 3 ) 2 , dppe; CpЈ = Cp, Cp*], [198] [M(dppe)(η 7 -C 7 H 7 )] [M = Mo, [20,21] W [19] ] and the octahedral moiety trans-[RuCl(dppe) 2 ]. [12,32] Many aspects of the computational rationalisation of ligand non-innocence have recently been reviewed by Costuas and Rigaut, [34] and so only key points will be emphasised here.…”

Some Ruthenium Derivatives of Penta-1,4-diyn-3-one

“…The significant weighting of the carbon-rich fragment in the HOMO is common in ruthenium complexes of this type. 15,44,49,50 There is a re-ordering of the HOMO-1 and HOMO-2 orbitals relative to those of the computational model system {trans-Fe(Me)(dHpe) 2 } 2 (-DEE) studied by Cao and Ren, 26b but neither of these orbitals feature any appreciable contribution from the ethenyl -system. The ligand * system lies well above the unoccupied orbitals of the Ru(dppe)Cp* fragments and comprises the LUMO+18.…”

The synthesis, molecular and electronic structure of cyanovinylidene complexes

“…However, the different combinations of solvent, supporting electrolyte, temperature and reference electrode employed in collecting the range of available data can make direct comparisons of the results collated from many different research groups difficult, especially in the absence of a reported potential for an internal reference compound [105]. Table 2 summarises the redox behaviour of a number of acetylide complexes pertinent to the present study in The cyclic voltammogram ( = 100 mV / s) of the parent compound Ru(CCPh)(PPh 3 ) 2 Cp (1) exhibits an oxidation wave at +0.54 V, which is only partially chemically reversible, even at -40C [40], as a result of the redox noninnocent nature of the phenylethynyl ligand and rapid dimerisation of the largely ligand-based radical cation in solution [106]. A completely irreversible wave is also observed at higher potentials (+1.34 V Table 2).…”